Patent Publication Number: US-2022237123-A1

Title: Apparatuses and methods for a processor architecture

Description:
FIELD OF THE INVENTION 
     The field of invention relates generally to computers, and, more specifically, to processor architectures. 
     BACKGROUND 
     Processors include many interconnected circuits and structures that function together to execute instructions and process information. These circuits and structures and the features they provide may be included in a processor in many different configurations and combinations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
         FIG. 1A  is a block diagram illustrating both an exemplary in-order pipeline and an exemplary register renaming, out-of-order issue/execution pipeline according to embodiments of the invention; 
         FIG. 1B  is a block diagram illustrating both an exemplary embodiment of an in-order architecture core and an exemplary register renaming, out-of-order issue/execution architecture core to be included in a processor according to embodiments of the invention; 
         FIGS. 2A-B  illustrate a block diagram of a more specific exemplary core architecture, which core would be one of several logic blocks (including other cores of the same type and/or different types) in a chip; 
         FIG. 2A  is a block diagram of a single processor core, along with its connection to the on-die interconnect network  202  and with its local subset of the Level 2 (L2) cache  204 , according to embodiments of the invention; 
         FIG. 2B  is an expanded view of part of the processor core in  FIG. 2A  according to embodiments of the invention; 
         FIG. 3  is a block diagram of an illustrative out-of-order issue/execution processor core that may be included in a processor according to embodiments of the invention; 
         FIG. 4  is a block diagram of an illustrative fetch unit that may be included in a processor core, such as that of  FIG. 3 , and/or a processor according to embodiments of the invention; 
         FIG. 5  is a block diagram of an illustrative decode unit that may be included in a processor core, such as that of  FIG. 3 , and/or a processor according to embodiments of the invention; 
         FIG. 6  is a block diagram of an illustrative integer execution unit that may be included in a processor core, such as that of  FIG. 3  and/or a processor according to embodiments of the invention; 
         FIG. 7  is a block diagram of an illustrative floating-point (FP) execution unit that may be included in a processor core, such as that of  FIG. 3 , or a processor according to embodiments of the invention; 
         FIG. 8  is a block diagram of an illustrative load/store unit that may be included in a processor core, such as that of  FIG. 3 , or a processor according to embodiments of the invention; 
         FIG. 9  is a block diagram of an illustrative out-of-order issue/execution processor core, such as that of  FIG. 3 , supporting simultaneous multi-threading (SMT) in a processor according to embodiments of the invention; 
         FIG. 10  is a block diagram illustrating an SMT static partitioning feature that may be included in a processor according to some embodiments; 
         FIG. 11  is a flow diagram illustrating a method for an SMT static partitioning feature that may be performed by a processor according to some embodiments; 
         FIG. 12  is a block diagram illustrating a resource allocator that may be included in a processor according to some embodiments; 
         FIG. 13  is a block diagram illustrating an algorithmic SMT feature that may be included in a processor  1300  according to embodiments; 
         FIG. 14  is a flow diagram illustrating a method for an algorithmic SMT feature that may be performed by a processor according to embodiments; 
         FIG. 15  is a block diagram illustrating an algorithmic SMT feature that may be included in a processor according to embodiments; 
         FIG. 16  shows a block diagram implementing a branch predictor priority algorithm in accordance with an exemplary embodiment; 
         FIG. 17  is a block diagram illustrating an arbitration circuit for an SMT thread switching feature that may be included in a processor according to embodiments; 
         FIG. 18  is a block diagram illustrating a deadlock avoidance hardware  1800  that may be included in a processor according to embodiments o; 
         FIG. 19  is a diagram showing a 256-bit load to a 256-bit register file using a pair of 128-bit μops, according to some embodiments; 
         FIG. 20  is a diagram illustrating a process for loading a 256-bit to a 256-bit register file using a pair of 128-bit μops, according to some embodiments; 
         FIG. 21  is a diagram showing a 256-bit store from a 256-bit register file using 128-bit μops, according to some embodiments. 
         FIG. 22  is a diagram illustrating a process for storing a 256-bit from a 256-bit register file using a pair of 128-bit μops, according to some embodiments 
         FIG. 23  is a block diagram illustrating a feature for allowing 256-bit arithmetic operations using 128-bit micro-operations according to some embodiments; 
         FIG. 24  is a block diagram illustrating cross-lane operations using a temporary storage area to store partial results according to some embodiments; 
         FIG. 25  is a block diagram illustrating a micro-op cache feature that may be included in a processor according to embodiments; 
         FIG. 26  is a flow diagram illustrating a method for a micro-op cache feature that may be performed by a processor according to embodiments; 
         FIG. 27  is a block diagram illustrating a micro-op cache feature that may be included in a processor according to embodiment; 
         FIG. 28  is a block diagram illustrating a micro-op cache feature that may be included in a processor according to embodiments; 
         FIG. 29  is a block diagram illustrating a register renaming and dependency tracking scheme involving a register alias table (RAT) according to embodiments; 
         FIG. 30  is a block diagram illustrating a RAT extended to include zero idioms, sign extension, and zero extension according to embodiments; 
         FIG. 31  is a block diagram illustrating reading extended RAT bits during register renaming and passing them down the pipeline with the micro-op that read the register according to embodiments; 
         FIG. 32  is a block diagram illustrating a virtual register renaming feature that may be included in a processor according to embodiments; 
         FIG. 33  is a flow diagram illustrating a method for a virtual register renaming feature that may be performed by a processor according to embodiments; 
         FIG. 34  is a block diagram illustrating an issue/execution pipeline that may be implemented in a processor core supporting a fused multiply-add (FMA) fission/fusion feature according to embodiments of the invention; 
         FIG. 35  is a flow diagram illustrating a method for FMA fission/fusion that may be performed by a processor according to embodiments of the invention; 
         FIG. 36  is a block diagram of a processor that may have more than one core, may have an integrated memory controller, and may have integrated graphics according to embodiments of the invention; 
         FIG. 37  is a block diagram of an illustrative central processing unit (CPU) complex that may be included in a processor according to embodiments of the invention; 
         FIG. 38  is a block diagram of an illustrative cache hierarchy that may be included in a processor according to embodiments of the invention; 
         FIG. 39  is a block diagram illustrating a memory hierarchy within which a cache line zeroing instruction may be implemented according to embodiments; 
         FIG. 40  is a block diagram illustrating a cache in a processor that implements a cache line zeroing instruction according to embodiments; 
         FIG. 41  is a flow diagram illustrating embodiments of the invention that first attempt to write to a cache of the issuing agent before using snoops; 
         FIG. 42  is a flow diagram illustrating embodiments of the invention that rely on snoops of the coherent caches; 
         FIG. 43  is a flow diagram illustrating embodiments of the invention that use write-update snoops to implement the snoop process; 
         FIG. 44  is a flow diagram illustrating embodiments of the invention that use write-invalidate snoops to implement the snoop process. 
         FIG. 45  is a flow diagram illustrating embodiments of the invention that use snoops that invalidate and write back to implement the snoop process; 
         FIG. 46  is a flow diagram illustrating embodiments of the invention that use snoops that write out any cache line that hits but does not send the data back to the first agent and does not result in the data being read from the downstream memory to implement the snoop process; 
         FIG. 47  is a diagram illustrating a page coalescing feature that may be included in a processor according to some embodiments; 
         FIG. 48  is a flow diagram that illustrates a method for coalescing page table entries into a single effective page according to some embodiments; 
         FIGS. 49-52  are block diagrams of exemplary computer architectures; 
         FIG. 49  shows a block diagram of a system in accordance with one embodiment of the present invention; 
         FIG. 50  is a block diagram of a first more specific exemplary system in accordance with an embodiment of the present invention; 
         FIG. 51  is a block diagram of a second more specific exemplary system in accordance with an embodiment of the present invention; 
         FIG. 52  is a block diagram of a system-on-chip (SoC) in accordance with an embodiment of the present invention; 
         FIGS. 53A-53B  are block diagrams illustrating a generic vector friendly instruction format and instruction templates thereof according to embodiments of the invention; 
         FIG. 53A  is a block diagram illustrating a generic vector friendly instruction format and class A instruction templates thereof according to embodiments of the invention; 
         FIG. 53B  is a block diagram illustrating the generic vector friendly instruction format and class B instruction templates thereof according to embodiments of the invention; 
         FIG. 54A  is a block diagram illustrating an exemplary specific vector friendly instruction format according to embodiments of the invention; 
         FIG. 54B  is a block diagram illustrating the fields of a specific vector friendly instruction format that make up the full opcode field according to one embodiment of the invention; 
         FIG. 54C  is a block diagram illustrating the fields of a specific vector friendly instruction format that make up the register index field according to one embodiment of the invention; 
         FIG. 54D  is a block diagram illustrating the fields of a specific vector friendly instruction format that make up the augmentation operation field according to one embodiment of the invention; 
         FIG. 55  is a block diagram of a register architecture according to one embodiment of the invention; and 
         FIG. 56  is a block diagram contrasting the use of a software instruction converter to convert binary instructions in a source instruction set to binary instructions in a target instruction set according to embodiments of the invention. 
         FIGS. 57-66  are illustrations of embodiments of the invention in systems. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. 
     References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     An apparatus, such as a computer, to process information may include one or more processor cores. Each processor core may include a variety of circuitry, hardware, structures, and other features, where each alone, or any number together in combination, may be referred to as a feature. Features may be implemented and/or arranged in various ways, employ various techniques, and be involved in performing various methods to attempt to achieve desired levels, in various combinations, of performance, power consumption, and/or other characteristics (e.g., increasing performance, decreasing power consumption and implementing power-saving features, and improving fairness, minimum performance guarantees, throughput, instructions per clock (IPC), instructions per unit time, quality of service, time and/or memory efficiency, to list just a few of the applicable criteria). Embodiments of the invention may include one or more of the features described in this specification. Some examples of architectures and systems in which the invention may be embodied are provided in the figures and description in this specification. 
     Processor cores in which the invention may be embodied may be implemented in different ways, for different purposes, and in different processors. For instance, implementations of such cores may include: 1) a general purpose in-order core intended for general-purpose computing; 2) a high performance general purpose out-of-order core intended for general-purpose computing; 3) a special purpose core intended primarily for graphics and/or scientific (throughput) computing. Implementations of different processors may include: 1) a central processing unit (CPU) including one or more general purpose in-order cores intended for general-purpose computing and/or one or more general purpose out-of-order cores intended for general-purpose computing; and 2) a coprocessor including one or more special purpose cores intended primarily for graphics and/or scientific (throughput) computing. Such different processors lead to different computer system architectures, which may include: 1) the coprocessor on a separate chip from the CPU; 2) the coprocessor on a separate die in the same package as a CPU; 3) the coprocessor on the same die as a CPU (in which case, such a coprocessor is sometimes referred to as special purpose logic, such as integrated graphics and/or scientific (throughput) logic, or as special purpose cores); and 4) a system on a chip (SoC) that may include on the same die the described CPU (sometimes referred to as the application core(s) or application processor(s)), the above described coprocessor, and additional functionality. 
     Exemplary core architectures are described next, followed by descriptions of exemplary processors and computer architectures. Each processor may include one or more cores, where each core and/or combination of cores may be architected and designed to execute one or more threads, processes, or other sequences of instructions at various times. Core architectures and design techniques may provide for and/or support the concurrent execution of multiple threads, according to any of a type of approaches known as simultaneous (or symmetric) multi-threading (SMT) or any other approach. Accordingly, processor cores in which the invention may be embodied, including those described as examples below, may include various novel features architected and designed to support SMT and/or various known features modified in various novel ways to support SMT, as may be described below. For ease of description, the meaning of the term SMT in this specification may include SMT in combination with any other approach to multi-threading (e.g., time-slicing). 
     As mentioned above and explained in more detail below, embodiments of the present disclosure may be desirable for a variety of reasons, including, e.g., increasing performance, decreasing power consumption and implementing power-saving features, and improving fairness, minimum performance guarantees, throughput, instructions per clock (IPC), instructions per unit time, quality of service, time and/or memory efficiency, to list just a few of the applicable criteria. The desirable criteria listed above and described herein are exemplary; as explained herein, the present disclosure is may be desirable for any of the reasons listed above, individually or in combination, and may further be desirable for additional reasons not specifically enumerated above. 
     Further, as mentioned above and explained in more detail below, embodiments of the present disclosure may apply to any type of processor or processing element, including general-purpose processors, server processors or processing elements for use in a server-environment, coprocessors (e.g., security coprocessors) high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device. The processor or processors may be implemented on one or more chips. The processor or processors  3600  may be a part of and/or may be implemented on one or more substrates using any of a number of process technologies, such as, for example, BiCMOS, CMOS, or NMOS. The processors and processing devices listed above and described herein are exemplary; as explained herein, the present disclosure is applicable to any processor or processing device. 
     Further, as mentioned above and explained in more detail below, embodiment of the present disclosure may apply to processors or processing elements using a wide variety of instruction sets and instruction set architectures, including for example, the x86 instruction set (optionally including extensions that have been added with newer versions); the MIPS instruction set of MIPS Technologies of Sunnyvale, Calif.; the ARM instruction set (with optional additional extensions such as NEON) of ARM Holdings of Sunnyvale, Calif.; IBM&#39;s “Power” instruction set, or any other instruction set, including both RISC and CISC instruction sets. The instruction sets and instruction set architectures listed above and described herein are exemplary; as explained herein, the present disclosure is applicable to any instruction set or instruction set architecture. 
     Exemplary Core Architectures 
     In-Order and Out-of-Order Core Block Diagram 
       FIG. 1A  is a block diagram illustrating both an exemplary in-order pipeline and an exemplary register renaming, out-of-order issue/execution pipeline according to embodiments of the invention.  FIG. 1B  is a block diagram illustrating both an exemplary embodiment of an in-order architecture core and an exemplary register renaming, out-of-order issue/execution architecture core to be included in a processor according to embodiments of the invention. The solid lined boxes in  FIGS. 1A-B  illustrate the in-order pipeline and in-order core, while the optional addition of the dashed lined boxes illustrates the register renaming, out-of-order issue/execution pipeline and core. Given that the in-order aspect is a subset of the out-of-order aspect, the out-of-order aspect will be described. 
     In  FIG. 1A , a processor pipeline  100  includes a fetch stage  102 , a length decode stage  104 , a decode stage  106 , an allocation stage  108 , a renaming stage  110 , a scheduling (also known as a dispatch or issue) stage  112 , a register read/memory read stage  114 , an execute stage  116 , a write back/memory write stage  118 , an exception handling stage  122 , and a commit stage  124 . 
       FIG. 1B  shows processor core  190  including a front end unit  130  coupled to an execution engine unit  150 , and both are coupled to a memory unit  170 . The core  190  may be a reduced instruction set computing (RISC) core, a complex instruction set computing (CISC) core, a very long instruction word (VLIW) core, or a hybrid or alternative core type. As yet another option, the core  190  may be a special-purpose core, such as, for example, a network or communication core, compression engine, coprocessor core, general purpose computing graphics processing unit (GPGPU) core, graphics core, or the like. For example, as explained above, core  190  may be any member of a set containing: general-purpose processors, server processors or processing elements for use in a server-environment, coprocessors (e.g., security coprocessors) high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device. 
     The front end unit  130  includes a branch prediction unit  132  coupled to a micro-op cache  133  and an instruction cache unit  134 , which is coupled to an instruction translation lookaside buffer (TLB)  136 , which is coupled to an instruction fetch unit  138 , which is coupled to a decode unit  140 . The decode unit  140  (or decoder) may decode instructions, and generate as an output one or more micro-operations, micro-code entry points, microinstructions, other instructions, or other control signals, which are decoded from, or which otherwise reflect, or are derived from, the original instructions. The micro-operations, micro-code entry points, microinstructions, etc. may be stored in at least the micro-op cache  133 . The decode unit  140  may be implemented using various different mechanisms. Examples of suitable mechanisms include, but are not limited to, look-up tables, hardware implementations, programmable logic arrays (PLAs), microcode read only memories (ROMs), etc. In one embodiment, the core  190  includes a microcode ROM or other medium that stores microcode for certain macroinstructions (e.g., in decode unit  140  or otherwise within the front end unit  130 ). The micro-op cache  133  and the decode unit  140  are coupled to a rename/allocator unit  152  in the execution engine unit  150 . In various embodiments, a micro-op cache such as  133  may also or instead be referred to as an op-cache, u-op cache, uop-cache, or μop-cache; and micro-operations may be referred to as micro-ops, u-ops, uops, and μops. 
     The execution engine unit  150  includes the rename/allocator unit  152  coupled to a retirement unit  154  and a set of one or more scheduler unit(s)  156 . The scheduler unit(s)  156  represents any number of different schedulers, including reservations stations, central instruction window, etc. The scheduler unit(s)  156  is coupled to the physical register file(s) unit(s)  158 . Each of the physical register file(s) units  158  represents one or more physical register files, different ones of which store one or more different data types, such as scalar integer, scalar floating point, packed integer, packed floating point, vector integer, vector floating point, status (e.g., an instruction pointer that is the address of the next instruction to be executed), etc. In one embodiment, the physical register file(s) unit  158  comprises a vector registers unit, a write mask registers unit, and a scalar registers unit. These register units may provide architectural vector registers, vector mask registers, and general purpose registers. The physical register file(s) unit(s)  158  is overlapped by the retirement unit  154  to illustrate various ways in which register renaming and out-of-order execution may be implemented (e.g., using a reorder buffer(s) and a retirement register file(s); using a future file(s), a history buffer(s), and a retirement register file(s); using a register maps and a pool of registers; etc.). The retirement unit  154  and the physical register file(s) unit(s)  158  are coupled to the execution cluster(s)  160 . The execution cluster(s)  160  includes a set of one or more execution units  162  and a set of one or more memory access units  164 . The execution units  162  may perform various operations (e.g., shifts, addition, subtraction, multiplication) and on various types of data (e.g., scalar floating point, packed integer, packed floating point, vector integer, vector floating point). While some embodiments may include a number of execution units dedicated to specific functions or sets of functions, other embodiments may include only one execution unit or multiple execution units that all perform all functions. The scheduler unit(s)  156 , physical register file(s) unit(s)  158 , and execution cluster(s)  160  are shown as being possibly plural because certain embodiments create separate pipelines for certain types of data/operations (e.g., a scalar integer pipeline, a scalar floating point/packed integer/packed floating point/vector integer/vector floating point pipeline, and/or a memory access pipeline that each have their own scheduler unit, physical register file(s) unit, and/or execution cluster—and in the case of a separate memory access pipeline, certain embodiments are implemented in which only the execution cluster of this pipeline has the memory access unit(s)  164 ). It should also be understood that where separate pipelines are used, one or more of these pipelines may be out-of-order issue/execution and the rest in-order. 
     The set of memory access units  164  is coupled to the memory unit  170 , which includes a data TLB unit  172  coupled to a data cache unit  174  coupled to a level 2 (L2) cache unit  176 . In one exemplary embodiment, the memory access units  164  may include a load unit, a store address unit, and a store data unit, each of which is coupled to the data TLB unit  172  in the memory unit  170 . The instruction cache unit  134  is further coupled to a level 2 (L2) cache unit  176  in the memory unit  170 . The L2 cache unit  176  is coupled to one or more other levels of cache and eventually to a main memory. 
     By way of example, the exemplary register renaming, out-of-order issue/execution core architecture may implement the pipeline  100  as follows: 1) the instruction fetch  138  performs the fetch and length decoding stages  102  and  104 ; 2) the decode unit  140  performs the decode stage  106 ; 3) the rename/allocator unit  152  performs the allocation stage  108  and renaming stage  110 ; 4) the scheduler unit(s)  156  performs the schedule stage  112 ; 5) the physical register file(s) unit(s)  158  and the memory unit  170  perform the register read/memory read stage  114 ; the execution cluster  160  perform the execute stage  116 ; 6) the memory unit  170  and the physical register file(s) unit(s)  158  perform the write back/memory write stage  118 ; 7) various units may be involved in the exception handling stage  122 ; and 8) the retirement unit  154  and the physical register file(s) unit(s)  158  perform the commit stage  124 . 
     The core  190  may support one or more instructions sets (e.g., the x86 instruction set (with some extensions that have been added with newer versions); the MIPS instruction set of MIPS Technologies of Sunnyvale, Calif.; the ARM instruction set (with optional additional extensions such as NEON) of ARM Holdings of Sunnyvale, Calif., IBM&#39;s “Power” instruction set, or any other instruction set, including both RISC and CISC instruction sets), including the instruction(s) described herein. In one embodiment, the core  190  includes logic to support a packed data instruction set extension (e.g., AVX, AVX2, AVX-512), thereby allowing the operations used by many multimedia applications to be performed using packed data. 
     It should be understood that the core may support multithreading (executing two or more parallel sets of operations or threads), and may do so in a variety of ways including time sliced multithreading, SMT (e.g., a single physical core provides a logical core for each of the threads that physical core is simultaneously multithreading), or a combination thereof (e.g., time sliced fetching and decoding, and SMT thereafter such as in the Intel® Hyperthreading technology). 
     While register renaming is described in the context of out-of-order execution, it should be understood that register renaming may be used in an in-order architecture. While the illustrated embodiment of the processor also includes separate instruction and data cache units  134 / 174  and a shared L2 cache unit  176 , alternative embodiments may have a single internal cache for both instructions and data, such as, for example, a Level 1 (L1) internal cache, or multiple levels of internal cache. In some embodiments, the system may include a combination of an internal cache and an external cache that is external to the core and/or the processor. Alternatively, all of the cache(s) may be external to the core and/or the processor. 
     Specific Exemplary Core Architecture 
       FIGS. 2A-B  illustrate a block diagram of a more specific exemplary core architecture, which core would be one of several logic blocks (including other cores of the same type and/or different types) in a chip. The logic blocks communicate through a high-bandwidth interconnect network (e.g., a ring network) with some fixed function logic, memory I/O interfaces, and other necessary I/O logic, depending on the application. 
       FIG. 2A  is a block diagram of a single processor core, along with its connection to the on-die interconnect network  202  and with its local subset of the Level 2 (L2) cache  204 , according to embodiments of the invention. In one embodiment, an instruction decoder  200  supports the x86 instruction set with a packed data instruction set extension. An L1 cache  206  allows low-latency accesses to cache memory into the scalar and vector units. While in one embodiment (to simplify the design), a scalar unit  208  and a vector unit  210  use separate register sets (respectively, scalar registers  212  and vector registers  214 ) and data transferred between them is written to memory and then read back in from a level 1 (L1) cache  206 , alternative embodiments of the invention may use a different approach (e.g., use a single register set or include a communication path that allow data to be transferred between the two register files without being written and read back). 
     The local subset of the L2 cache  204  is part of a global L2 cache that is divided into separate local subsets, one per processor core. Each processor core has a direct access path to its own local subset of the L2 cache  204 . Data read by a processor core is stored in its L2 cache subset  204  and can be accessed quickly, in parallel with other processor cores accessing their own local L2 cache subsets. Data written by a processor core is stored in its own L2 cache subset  204  and is flushed from other subsets, if necessary. The ring network ensures coherency for shared data. The ring network is bi-directional to allow agents such as processor cores, L2 caches and other logic blocks to communicate with each other within the chip. Each ring datapath is 1012-bits wide per direction. 
       FIG. 2B  is an expanded view of part of the processor core in  FIG. 2A  according to embodiments of the invention.  FIG. 2B  includes an L1 data cache  206 A part of the L1 cache  204 , as well as more detail regarding the vector unit  210  and the vector registers  214 . Specifically, the vector unit  210  is a 16-wide vector processing unit (VPU) (see the 16-wide ALU  228 ), which executes one or more of integer, single-precision float, and double-precision float instructions. The VPU supports swizzling the register inputs with swizzle unit  220 , numeric conversion with numeric convert units  222 A-B, and replication with replication unit  224  on the memory input. Write mask registers  226  allow predicating resulting vector writes. 
     Specific Exemplary Out-of-Order Core Architecture 
       FIG. 3  is a block diagram of an illustrative out-of-order issue/execution processor core that may be included in a processor according to embodiments of the invention. In  FIG. 3 , processor core  300  includes front-end unit  310 , integer unit  320 , FP unit  330 , load-store unit  340 , and level 2 (L2) cache unit  350 .  FIG. 3  is provided for illustrative purposes, and as such, shows various units arranged and named according to one of many approaches that are possible according to embodiments of the present invention. Any one or more embodiments may be illustrated in one or more ways. Each unit shown in  FIG. 3  may include circuitry and/or structures that may be included in other units in other representations of embodiments. For example, front-end unit  310  may additionally or alternatively be illustrated and described as including a fetch unit, such as fetch unit  400  in  FIG. 4 , and a decode unit, such as decode unit  500  in  FIG. 5 ; any or all of integer unit  320 , FP unit  330 , and load-store unit  340  may additionally or alternatively be illustrated and described, separately or collectively, as one or more execution units; and so on. Furthermore, various units within core  300  may be coupled in various ways; therefore, for convenience, different figures may show units within different larger units; for example, a particular unit may be shown within a first larger unit in a first figure and within a second larger unit in a second figure. 
     In  FIG. 3 , front-end unit  310  includes branch prediction unit  311 , micro-operation-cache (op-cache) unit  312 , instruction cache (i-cache) unit  313 , decode unit  314 , and micro-operation (micro-op) queue unit  315 . Branch prediction unit  311  includes branch prediction circuitry, such as a branch-target buffer (BTB), to reduce average branch delay and is coupled to op-cache unit  312  and i-cache unit  313 . Op-cache unit  312  includes an op-cache in which to cache micro-ops associated with instructions. I-cache  313  unit includes an i-cache, which in an embodiment may be a 64K, four-way i-cache, in which to cache instructions. I-cache unit  313  is coupled to decode unit  314  to provide cached instructions to be decoded. Decode unit  314  includes decoding circuitry, such as an instruction decoder, to decode instructions. In an embodiment, front-end unit  310  may fetch and decode unit  314  may decode up to four instructions per clock cycle. Op-cache unit  312  and decode unit  314  are each coupled to micro-op queue unit  315  to provide two paths for loading micro-ops into micro-op queue unit  315 . Micro-op queue unit  315  includes a micro-op queue, which in an embodiment may dispatch six micro-ops per cycle to one or more execution units. 
     Also in  FIG. 3 , integer unit  320  includes integer rename unit  321 ; integer scheduler units  322 A,  322 B,  322 C,  322 D,  322 E, and  322 F (collectively, integer scheduler units  322 ); integer physical register file  323 ; arithmetic-logic units (ALUs)  324 A,  324 B,  324 C, and  324 D (collectively, ALUs  324 ); and address generation units (AGUs)  325 A and  325 B (collectively, AGUs  325 ). Integer rename unit  321  is coupled to micro-op queue unit  315  to receive one or more micro-ops to be executed, in whole or in part, by one or more of ALUs  324  and/or AGUs  325 . Integer rename unit  321  includes register renaming circuitry and is also coupled to integer scheduler units  322 , which in turn are coupled to integer physical register file  323 , to provide for integer-register renaming. Integer scheduler units  322  include scheduling circuitry for scheduling micro-ops to be executed, in whole or in part, by one or more of ALUs  324  and/or AGUs  325 . Integer physical register file  323  includes a file of physical integer registers, which in an embodiment may include 168 physical integer registers. Each of ALUs  324  and AGUs  325  are coupled to physical register file  323  to receive values to be used as inputs in the execution of micro-ops and/or to provide values as outputs of the execution of micro-ops. 
     Also in  FIG. 3 , FP unit  330  includes FP rename unit  331 , FP scheduler unit  332 , FP register file  333 , FP multipliers  334 A and  334 B (collectively, FP multipliers  334 ), and FP adders  335 A and  335 B (collectively, FP adders  335 ). FP rename unit  331  is coupled to micro-op queue unit  315  to receive one or more micro-ops to be executed, in whole or in part, by one or more of FP multipliers  334  and/or FP adders  335 . FP rename unit  331  includes register renaming circuitry and is also coupled to FP scheduler unit  332 , which in turn are coupled to FP register file  333 , to provide for FP-register renaming. FP scheduler unit  332  includes scheduling circuitry for scheduling micro-ops to be executed, in whole or in part, by one or more of FP multipliers  334  and/or FP adders  335 . Each of FP multipliers  334  and FP adders  335  are coupled to FP register file  333  to receive values to be used as inputs in the execution of micro-ops and/or to provide values as outputs of the execution of micro-ops. 
     Also in  FIG. 3 , load-store unit  340  includes load-store queue unit  341  and data cache (d-cache) unit  342 . Load-store queue unit  341  may include any number of load and/or store queues, in an embodiment providing for two loads and one store per clock cycle, coupled to AGUs  325  to receive memory addresses for load and/or store operations. D-cache unit  342  includes a d-cache, which in an embodiment may be a 32K, eight-way level 1 (L1) d-cache, in which to cache data, coupled to integer physical register file  323 , FP register file  333 , and load-store queue unit  341  to receive and provide data generated by and to be used in the execution of micro-ops. 
     Also in  FIG. 3 , L2 cache unit  350  includes an L2 cache, which in an embodiment may be a 512K, eight-way cache, in which to cache instructions and data. 
       FIG. 4  is a block diagram of an illustrative fetch unit that may be included in a processor core, such as core  300  of  FIG. 3 , and/or a processor according to embodiments of the invention. In  FIG. 4 , fetch unit  400  includes next-program-count (PC) unit  410 , translation lookaside buffer (TLB) unit  420 , hash perceptron unit  430 , BTB return stack indirect target array (ITA) unit  440 , physical request queue unit  450 , micro-tag unit  460 , and i-cache unit  470 . 
       FIG. 5  is a block diagram of an illustrative decode unit that may be included in a processor core, such as core  300  of  FIG. 3 , and/or a processor according to embodiments of the invention. In  FIG. 5 , decode unit  500  includes instruction byte buffer unit  510 , pick unit  520 , decode unit  530 , op-cache unit  540 , micro-op queue unit  550 , microcode read-only memory (ROM) unit  560 , stack engine memory file (memfile) unit  570 , and dispatch unit  580 . 
       FIG. 6  is a block diagram of an illustrative integer execution unit that may be included in a processor core, such as core  300  of  FIG. 3 , and/or a processor according to embodiments of the invention. In  FIG. 6 , integer execution unit  600  includes map unit  610 ; retire queue unit  620 ; arithmetic-logic queue (ALQ) units  630 A,  630 B,  630 C, and  630 D (collectively, ALQs  630 ); address generation queue (AGQ) units  640 A and  640 B (collectively, AGQs  640 ); physical register file unit  650 , forwarding multiplexer (mux) unit  660 ; ALUs  670 A,  670 B,  670 C, and  670 D (collectively, ALUs  670 ); AGUs  680 A and  680 B (collectively, AGUs  680 ); and load-store unit  690 . 
       FIG. 7  is a block diagram of an illustrative FP execution unit that may be included in a processor core, such as core  300  of  FIG. 3 , or a processor according to embodiments of the invention. In  FIG. 7 , FP execution unit  700  includes non-schedulable micro-op queue unit  710 , schedulable micro-op queue unit  720 , retire queue unit  730 , FP convert unit  740 , FP physical register file  750 , forwarding mux unit  760 , FP multipliers  770 A and  770 B (collectively, FP multipliers  770 ), and FP adders  780 A and  780 B (collectively, FP adders  780 ). 
       FIG. 8  is a block diagram of an illustrative load/store unit that may be included in a processor core, such as core  300  of  FIG. 3 , or a processor according to embodiments of the invention. In  FIG. 8 , load/store unit  800  includes load queue unit  810 , load-pipe pick units  811 A and  811 B (collectively, load pick units  811 ), TLB units  812 A and  812 B, (collectively, TLB units  812 ), data pipe units  813 A and  813 B (collectively, data pipe units  813 ), store queue unit  820 , pre-fetch unit  821 , store-pipe pick units  822 ), store pipe unit  823 , store commit unit  824 , L1/L2 TLB and data cache tag array  830 , L1 data cache  840 , memory-address buffer  850 , and write-combining buffer  860 . 
       FIG. 9  is a block diagram of an illustrative out-of-order issue/execution processor core, such as core  300  of  FIG. 3 , supporting SMT in a processor according to embodiments of the invention. In  FIG. 9 , processor core  900  includes front-end unit  910 , integer unit  920 , FP unit  930 , load-store unit  940 , L2 cache unit  950 , and retire unit  960 . Front-end unit  910  includes branch prediction unit  911 , op-cache unit  912 , i-cache unit  913 , decode unit  914 , micro-op queue unit  915 , and instruction TLB unit  916 . Integer unit  920  includes integer rename unit  921 , integer scheduler unit  922 , integer physical register file  923 , ALUs  924 , and AGUs  925 . FP unit  930  includes FP rename unit  931 , FP scheduler unit  932 , FP register file  933 , FP multipliers  934 A and  934 B (collectively, FP multipliers  934 ), and FP adders  935 A and  935 B (collectively, FP adders  935 ). Load-store unit  940  includes load queue unit  941 A and store queue unit  941 B (collectively, load-store queue unit  941 ), data cache (d-cache) unit  942 , and TLB unit  943 . Retire unit  960  includes a retire queue. 
     SMT Features 
     Processor cores according to embodiments of the invention may include various features to support SMT. A number of such features are described separately using non-limiting examples below, but embodiments may include any combination of such features. 
     Static Partitioning of Resources 
     A processor core may support an SMT static partitioning feature according to some exemplary embodiments. Threads may be assigned to available resources which are statically shared in a simultaneous multithreading pipeline. In some embodiments, threads may be assigned to available resources using techniques such as a patterned based algorithm to improve performance and efficiency. In some embodiments, this feature may improve computer systems by providing a more efficient resource sharing between threads for statically shared resources. It may also use available resources that would otherwise have remained unused due to SMT static partitioning. 
     For example, resources in a pipeline may be statically shared, e.g., 50%-50%, between two threads to provide equal resources to both threads. In some embodiments, different percentages of available resources may be assigned to each thread, e.g., based on workload patterns. For example, if one thread is stalling for longer time than the other thread and there are empty entries available for the other thread, the available entries can be assigned to the stalled thread rather than keeping them empty in a statically shared resource. 
     In some embodiments, more than one thread could have a similar pattern. In such cases, a priority scheme may be used to assign resources in the case of a tie between threads. Tie-breaking may, for example, be performed by random selection, selecting the lower numbered thread, selecting the higher numbered thread, and/or selecting alternating threads. 
       FIG. 10  is a block diagram illustrating an SMT static partitioning feature that may be included in a processor according to some embodiments. SMT static partitioning feature may include a Pattern Detection Block  1001  according to an exemplary embodiment. First and second resources may be statically assigned to threads T0 and T1. A lookup pattern base table may determine that thread T1 has a long stall time. Pattern Detection Block can then adjust the statically assigned resources based on the pattern input. For example, the second resource, which was statically assigned to T1, can be assigned to T0. 
     In some embodiments, dynamic partitioning may be applied to other statically partitioned resources such as an instruction translation lookaside buffer (ITLB). 
       FIG. 11  is a flow diagram illustrating a method for an SMT static partitioning feature that may be performed by a processor according to some embodiments. In some embodiments, the method may comprise detecting patterns such as thread stalls for a statically shared resource in the pipeline, as illustrated in box CQB01. The method may further comprise adjusting the sharing (e.g., 50-50 sharing), as illustrated in box CQB02. The method adjusting may, for example, be based on length of stalls or some other similar events. 
     Summary of Some Embodiments 
     An embodiment may include a processor configured to detect a pattern for at least one of a first and second statically partitioned resource; and adjust an allocation of at least one of the first and second statically partitioned resource. 
     In some embodiments, one or more of the following apply. The first and second statically partitioned resource of pipeline may be resources of a simultaneous multithreading pipeline. The first and second statically partitioned resources may be allocated between a first and a second thread. The processor may be further configured to assign the first and second resources based on a patterned based algorithm. The processor may be further configured to assign at least one of the first and second resources based on one or more workload patterns. The processor may be further configured to assign at least one of the first and second resources based on a determination of whether at least one of the first and second threads has stalled for a longer period of time than the other. The processor may be further configured to assign at least one of the first and second resources based on a determination of whether there are empty entries associated with at least one of the first and the second resources that are available and assign at least one of the first and the second threads to the at least one of the first and the second resources that are available. The processor may be further configured to assign at least one of the first and second resources based on a priority scheme. The processor may be further configured to determine whether a stall has occurred based on a look up pattern base table. The first and second statically partitioned resources may be resources of an instruction translation lookaside buffer (ITLB). 
     An embodiment may include a method comprising detecting at least one of a pattern for a first and second statically partitioned resource; and adjusting an allocation of at least one of the first and second statically partitioned resource. 
     In some embodiments, one or more of the following apply. The first and second statically partitioned resource may be resources of a simultaneous multithreading pipeline. The first and second statically partitioned resources may be allocated between a first and a second thread. The method may further comprise assigning the first and second resources based on a patterned based algorithm. The method may further comprise assigning at least one of the first and second resources based on one or more workload patterns. The method may further comprise assigning at least one of the first and second resources based on a determination of whether at least one of the first and second threads has stalled for a longer period of time than the other. The method may further comprise assigning at least one of the first and second resources based on a determination of whether there are empty entries associated with at least one of the first and the second resources that are available and assigning at least one of the first and the second threads to the at least one of the first and the second resources that are available. The method may further comprise assigning at least one of the first and second resources based on a priority scheme. The method may further comprise determining whether a stall has occurred based on a look up pattern base table. The first and second statically partitioned resources may be resources of an instruction translation lookaside buffer (ITLB). 
     An embodiment may include a non-transitory machine-readable medium storing at least one instruction which when executed by a processor causes the processor to perform a method, the method comprising detecting at least one of a pattern for a first and second statically partitioned resource; and adjusting an allocation of at least one of the first and second statically partitioned resource. 
     In some embodiments, one or more of the following apply. The first and second statically partitioned resource may be resources of a simultaneous multithreading pipeline. The first and second statically partitioned resources may be allocated between a first and a second thread. The method may further comprise assigning the first and second resources based on a patterned based algorithm. The method may further comprise assigning at least one of the first and second resources based on one or more workload patterns. The method may further comprise assigning at least one of the first and second resources based on a determination of whether at least one of the first and second threads has stalled for a longer period of time than the other. The method may further comprise assigning at least one of the first and second resources based on a determination of whether there are empty entries associated with at least one of the first and the second resources that are available and assigning at least one of the first and the second threads to the at least one of the first and the second resources that are available. The method may further comprise assigning at least one of the first and second resources based on a priority scheme. The method may further comprise determining whether a stall has occurred based on a look up pattern base table. The first and second statically partitioned resources may be resources of an instruction translation lookaside buffer (ITLB). 
     An embodiment may include a system including a memory and a processor, the processor configured to detect a pattern for at least one of a first and second statically partitioned resource; and adjust an allocation of at least one of the first and second statically partitioned resource. 
     In some embodiments, one or more of the following apply. The first and second statically partitioned resource may be resources of a simultaneous multithreading pipeline. The first and second statically partitioned resources may be allocated between a first and a second thread. The processor may be further configured to assign the first and second resources based on a patterned based algorithm. The processor may be further configured to assign at least one of the first and second resources based on one or more workload patterns. The processor may be further configured to assign at least one of the first and second resources based on a determination of whether at least one of the first and second threads has stalled for a longer period of time than the other. The processor may be further configured to assign at least one of the first and second resources based on a determination of whether there are empty entries associated with at least one of the first and the second resources that are available and assign at least one of the first and the second threads to the at least one of the first and the second resources that are available. The processor may be further configured to assign at least one of the first and second resources based on a priority scheme. The processor may be further configured to determine whether a stall has occurred based on a look up pattern base table. The first and second statically partitioned resources may be resources of an instruction translation lookaside buffer (ITLB). 
     Competitive Sharing of Resources 
     A processor core may support SMT with competitive sharing of resources according to embodiments of the invention. A circuit, structure, or other resource in the core may be shared by multiple threads based on a policy in which threads compete for priority. In the embodiment of  FIG. 9 , each of the following resources may be shared between or among threads accord based on a competitive policy: branch prediction unit  911 , op-cache unit  912 , i-cache unit  913 , decode unit  914 , instruction TLB unit  916 , integer rename unit  921 , integer scheduler unit  922 , integer physical register file  923 , ALUs  924 , AGUs  925 , FP rename unit  931 , FP scheduler unit  932 , FP register file  933 , FP multipliers  934 A and  934 B, FP adders  935 A and  935 B, load queue unit  941 A, d-cache unit  942 , and TLB unit  943 . 
     Some of these resources, such as a buffer in integer rename unit  921 , integer scheduler unit  922 , FP rename unit  931 , FP scheduler unit  932 , or load queue unit  941 A, may have entries, subunits, or other parts that may be separately allocated to a thread. For convenience, this type of resource may be referred to as a divisible resource, and this type of allocation may be referred to as allocation-in-part. Others, such as each individual ALU of ALUs  924 , each individual AGU of AGUs  925 , FP multiplier  934 A, FP multiplier  934 B, FP adder  935 A, or FP adder  935 B, may only be allocated in full for a particular clock cycle, set of consecutive clock cycles to complete an operation, or other period of time or duration of operation. For convenience, this type of resource may be referred to as an indivisible resource, and this type of allocation may be referred to as allocation-in-full. 
       FIG. 12  is a block diagram illustrating a resource allocator  1200  that may be included in a processor according to embodiments of the invention. Resource allocator  1200  may include circuitry, structures, and/or hardware to allocate a core circuit, structure, unit, or resource, or any portion thereof, to a particular thread. In embodiments, resource allocator  1200  may be implemented to allocate a single resource and/or multiple resources. In either case, a processor or processor core may include multiple instances of one or more embodiments of resource allocator  1200 , each to allocate any one or more resources, each including any one or more of the blocks shown in  FIG. 12 , and each to implement any one or more resource allocation policies or combinations of resource allocation policies. 
     Resource allocator  1200  may include tracker circuit  1210 , policy circuit  1220 , decision circuit  1230 , and allocator circuit  1240 . Tracker circuit may include one or more of performance history circuit  1212 , usage history circuit  1214 , and thread state circuit  1216 . Policy circuit  1220  may include one or more of power policy circuit  1222 , fairness policy circuit  1224 , performance guarantee policy circuit  1226 , and throughput policy circuit  1228 . Embodiments may include, combine, and/or implement each of these circuits in various ways according to the types and number of resources to be allocated and the policies desired. 
     Performance history circuit  1212  may include circuitry, structures, and/or hardware to monitor, track, record, and/or report the performance of threads in one or more ways. In an embodiment, performance history circuit  1212  may include one or more hardware counters  1212 A per thread to count one or more measures of performance per thread, such as instructions retired per some measure of time or duration. For example, the measure of time or duration may be a window of clock cycles, where the size of the window (e.g., represented by the letter ‘N’) may be fixed (e.g., hardwired), configurable (e.g., by hardware or firmware), and/or programmable (e.g., by software). In an embodiment, N may be 1024. 
     Performance history circuit  1212  may also include one or more hardware comparators  1212 B to compare the performance, as measured by counters  1212 A, of a thread to one or more other threads. For example, at the end of each window of N clock cycles, hardware comparators  1212 B may compare the number of instructions retired during the window by a first thread to that of a second thread, and counters  1212 A may be reset for the next window. During that next window, the result of the comparison from the previous window may be used by policy circuit  1220  and/or decision circuit  1230  as described below. In embodiments, the comparison result may be a ranking of threads (e.g., which thread retired more instructions), the comparison result may be a ratio (e.g., a calculation or approximated calculation of the ratio of the number of instructions retired by a first thread to the number of instructions retired by the second thread), and/or any other measurement or calculation. 
     Embodiments may include more than one counter per thread. For example, two separate counters may be provided per thread: a first counter to track instructions identified as “power-hungry” (e.g., the execution of which typically consumes more power than other instructions) and a second counter to count other (i.e., non-power-hungry) instructions. For example, AVX-512 FMA instructions (as defined below) may be identified as power-hungry and tracked (possibly along with other power-hungry instructions) using a separate counter, 
     Usage history circuit  1214  may include circuitry, structures, and/or hardware to monitor, track, record, and/or report the usage of resources by threads. In an embodiment, usage history circuit  1214  may include one or more hardware counters  1214 A to count usage of a resource per thread, and one or more hardware comparators  1214 B to compare usage of a resource between threads. One or more results from counters  1214 A and/or comparators  1214 B may be used by policy circuit  1220  and/or decision circuit  1230  as described below. 
     For example, for a divisible resource such as a buffer, a counter may count the number of entries occupied by a thread. The count to be used for further calculations and/or allocation decisions may be a current count, reported or used directly at any point in time, and/or may be an average count, averaged over a window (e.g., a window of size N as described above). For an indivisible resource, the count to be used for further calculations and/or allocation decisions may be a time-averaged or time-weighted counted (e.g., the number of times a thread has used a resource within a time window, where the count is reset at the end of each time window, or where the count is right-shifted (to divide by a power of two) at the end of each time window). Results based on any of these counts may be the counts themselves, per-thread rankings of counts, and/or thread-to-thread ratios of counts. 
     Thread state circuit  1216  may include circuitry, structures, and/or hardware to monitor, track, record, and/or report state of a thread. For example, thread state circuit  1216  may report whether a thread is currently stalled, such as due to a long latency L2/L3 or other cache miss. 
     Historical and current information reported by tracker circuit  1210  may be used in resource allocation calculations and decisions according to policies specified by policy circuit  1220 . These policies may include any types of policies, with any priorities, in any combinations, including considerations of power consumption, fairness, minimum performance guarantees, and throughput. 
     Power policy circuit  1222  may include circuitry, structures, and/or hardware to implement one or more power policies and/or favor or select a thread based on the policy or policies. These policies may include any types of power policies, with any priorities, in any combinations. For example, a thread that is using fewer power-hungry instructions or a thread that is making slower progress may be favored or selected. 
     Fairness policy circuit  1224  may include circuitry, structures, and/or hardware to implement one or more fairness policies and/or favor or select a thread based on the policy or policies. For example, a thread that has lower recent performance, lower occupancy of a divisible resource, and/or lower recent usage of an indivisible resource may be favored or selected. 
     Performance guarantee policy circuit  1226  may include circuitry, structures, and/or hardware to implement one or more minimum performance guarantee policies and/or favor or select a thread based on the policy or policies. For example, a thread that is making progress below a certain minimum threshold may be favored or selected based on a performance guarantee policy. 
     Throughput policy circuit  1228  may include circuitry, structures, and/or hardware to implement one or more throughput policies and/or favor or select a thread based on the policy or policies. For example, a thread that is making relatively more or faster progress than other threads may be favored or selected. 
     Any or all of power policy circuit  1222 , fairness policy circuit  1224 , performance guarantee policy circuit  1226 , throughput policy circuit  1228 , and/or any other policy circuit may include individual storage locations or registers in which to store information and/or criteria to enable, modify (e.g., strengthen or weaken the importance of a policy or one or more criteria or measured used by a policy), or otherwise dynamically affect a policy. Embodiments may also or instead include a central or shared storage location or register for this information. Any one or more of individual or group storage locations are represented as policy register  1220 A. In embodiments, any such storage location or register may be configurable (e.g., by hardware or firmware) or programmable (e.g., by software). 
     Decision circuit  1230  may include circuitry, structures, and/or hardware to receive information, results, and/or signals from tracker circuit  1210  and information, criteria, and/or signals from policy circuit  1220  to use, weight, prioritize, filter, compare, combine, override, or otherwise process to generate information that may result in choosing a thread to which to allocate a resource and/or one or more indications or signals regarding that decision. For example, in an embodiment including a throughput policy and a minimum performance guarantee, the throughput policy may favor a first thread, but decision circuit  1230  may override that preference and choose a second thread to help meet a minimum performance guarantee for the second thread. In embodiments, resource allocator  1200  may include multiple instances of one or more embodiments of decision circuit  1230 , each for any resource or group of resources, and each to implement any one or more resource allocation policies or combinations of resource allocation policies, and each to implement any one or more approaches or combinations of approaches described below, where each may be configured or programmed to choose a thread according to any approach or combination of approaches (e.g., each may assign a different weight to information received from each separate policy circuit in policy circuit  1220 ). 
     In embodiments including an indivisible resource, decision circuit  1230  may determine which thread has priority for the dynamic allocation-in-full of the indivisible resource. In embodiments including a divisible resource, decision circuit  1230  may determine which thread has priority for the dynamic allocation-in-part of the divisible resource and/or part of the divisible resource, and/or how much (e.g., how many buffer entries) of the divisible resource to allocate to a thread. 
     In an embodiment, decision circuit  1230  may generate or provide one or more information, decision results, indicators, and/or signals, for example by storing them in one or more storage locations accessible by allocator circuit  1240  and/or sending them directly to allocator circuit  1240 , which may identify a single thread that has priority over any number of other threads or may specify a priority ranking of two or more threads. 
     Allocator circuit  1240  may include circuitry, structures, and/or hardware to receive information, decision results, indicators, and/or signals from decision circuit  1230  to act on, finalize, and/or implement resource allocation decisions, for example, by responding to a decision, from decision circuit  1230 , that a first thread has priority over a second thread, to send one or more signals to direct the allocation of a resource (e.g., resource  1250 ), in full or in part, to that thread. To do so, allocator circuit  1240  may send one or more signals (e.g., a “go” signal  1240 C) to a dispatch or other circuit that allow(s) a particular thread to use an indivisible resource or to use one or more parts of a divisible resource. 
     In embodiments, allocator circuit  1240  may also receive one or more requests (e.g., requests  1240 A and  1240 B) to use a resource. The requests may be signals and/or any other type of indicates from threads, from the resource, and/or from any type of dispatch circuitry associated with a thread or a resource. In embodiments, allocator circuit  1240  may choose or arbitrate between or among thread requests, e.g., using information, decision results, indicators, and/or signals from decision circuit  1230 , to determine which thread is to be allocated the resource. 
     In embodiments, allocator circuit  1240  may include circuitry, structures, and/or hardware to act on allocation decisions from decision circuit  1230  subject to or based on additional information or constraints. For example, allocator circuit  1240  may include a set of fixed, configurable, or programmable storage locations or registers  1242 , with one register per thread, that indicates how many parts of a divisible resource (e.g., how many entries of a buffer) are dedicated to each thread, a set of counters  1244 , one per thread, to track how many of each part are currently in use by each thread, and a set of comparators  1246 , one per thread, to check if a thread is using its full allocation. Allocator circuit  1240  may use results from comparators  1246  to accept or reject allocation decisions from decision circuit  1230 . Instead or additionally, an embodiment may include storage for an indicator for each part of a divisible resource (e.g., a bit or field of each entry in a buffer), to indicate which thread (or threads) is allowed to use that part of that resource, and allocator circuit  1240  may use the stored indicator to accept or reject allocation decisions from decision circuit  1230 . 
     Summary of Some Embodiments 
     An embodiment of the invention may include a processor comprising a resource allocator and a resource. including a tracker circuit, a policy circuit, a decision circuit, and an allocator circuit. The tracker circuit may be to track at least one of performance history of the resource, usage history of the resource, and a thread state, The policy circuit may be to provide policy information for implementing a resource allocation policy. The decision circuit may be to choose a thread based on an output of the tracker circuit and the policy information. The allocator circuit may be to use an output of the decision circuit to allocate the resource to the thread. 
     Algorithmic Competitive Sharing of Resources 
     A processor core may support an algorithmic SMT feature according to embodiments. In some embodiments, this feature solves the problem of thread assignment to available resources which are competitively shared in the pipeline. In some embodiments, this problem is solved using a priority algorithm. In some embodiments, a branch predictor block in a pipeline may be competitively shared and can use a priority algorithm for efficient entry allocation. In some embodiments, a priority algorithm may be implemented in hardware and/or software. In some embodiments, the thread assignment may be performed with two or more threads. In some embodiments, the thread assignment may assign a most efficient thread to an available resource in the pipeline to achieve a highest instructions per clock (IPC) and/or pipeline throughput. In some embodiments, this feature may provide a best known algorithm to prioritize a thread allocation to an available resource. As the number of thread increases and/or context switches between threads increase, the feature may provide further benefits by efficiently allocating resources. 
       FIG. 13  is a block diagram illustrating an algorithmic SMT feature that may be included in a processor  1300  according to embodiments. Priority algorithm hardware may, for example, include management based on dynamic behavior. The priority hardware may comprise at least one of an event detection block  1301 , a performance counter flag block  1302 , a deadlock prevention block  1303 , and an instruction type/class block  1304 . The event detection block  1301  may, for example, detect one or more events, such as a nuke, frequency of clear (e.g., JEClear and CRClear), frequency of BR, interrupt, and cache misses. The performance counter flag block  1302  may, for example, count one or more of the following: instructions retired, code misses, L2/L3 misses. The deadlock prevention block  1303  may prevent deadlock states. The instruction type/class block  1304  may, for example, allow a floating point instruction to retire. In some embodiments, one or more of the forgoing may be implemented in software and/or firmware. Additionally, in some embodiments, software may allow an operating system (OS) and/or a virtual machine manager (VMM) to set priorities. 
     In some embodiments, a priority algorithm may have learning capabilities such as machine learning. Learning capability may provide more intelligent thread selection and may be adaptive based, for example, on historical data and/or patterns being collected. 
     In some embodiments, there may be more than one thread with a similar event. In some embodiments, a priority scheme can be used in cases where there is tie between threads. Tie-breaking may, for example, be performed by random selection, selecting the lower numbered thread, selecting the higher numbered thread, and/or selecting alternating threads. 
       FIG. 14  is a flow diagram illustrating a method for an algorithmic SMT feature that may be performed by a processor according to embodiments. The method may comprise determining whether competitive shared resource in the pipeline is available, as illustrated in  1401 . The method may further comprise prioritizing threads, as illustrated in  1402 . For example, threads may be prioritized if there is more than one event. The method may further comprising picking the highest priority event or flag, as illustrated in  1403 . For example, the highest priority event or flag may be selected based on an assigned algorithm. The method may further comprise assigning resources to a thread, as illustrated in  1404 . For example, resources may be assigned to the most desirable thread based on the priority algorithm. 
       FIG. 15  is a block diagram illustrating an algorithmic SMT feature that may be included in a processor according to embodiments.  FIG. 15  shows an allocation of a thread, e.g., thread T0, to a competitively shared resource based on an algorithmic priority block. For example, the feature may determine that a competitively shared resource  1501  is available, e.g., in accordance with box  1401  in  FIG. 14 . The algorithmic priority block  1502  may prioritize if there are more than one event, e.g., events Evt1 and Evt2, e.g., in accordance with box  1402  in  FIG. 14 . The algorithmic priority block  1502  may also pick the highest priority event or flag based on assigned algorithm, e.g., in accordance with box  1403  in  FIG. 14 . The algorithmic priority block  1502  may also assign a resource, e.g.,  1501  to a most disable thread, e.g., T0 based on the priority algorithm. 
     In some embodiments, a priority algorithm may comprise an integer rename and/or a floating point rename algorithm. The priority algorithm may comprise event based determinations based on events such as Nuke, Clear, and interrupt. The priority algorithm may comprise a performance counter, which may count occurrences such as instructions retired and code misses. The priority algorithm may comprise limiting physical registers, using deadlock prevention, and/or determining cache misses. The priority algorithm may comprise determining instruction types and classes. The priority algorithm may comprise allocating registers, for example, allocating a floating point wordline more of the floating point registers. The priority algorithm may comprise managing priority through software. For example, the priority algorithm may allow an operating system and/or a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority, e.g., based on dynamic behavior. 
     In some embodiments, a priority algorithm may comprise a branch predictor algorithm. In some embodiments the branch predictor algorithm may control action of branch target buffers (BTB) based on one or more of the following: frequency of clears (e.g., JEClears and CRClears), frequencies of branches (e.g., all, taken, not taken), properties other than branches (e.g., instructions retired, L2/L3 misses). The priority algorithm may comprise managing priority through software. For example, the priority algorithm may allow an operating system and/or a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority, e.g., based on dynamic behavior.  FIG. 16  shows a block diagram implementing a branch predictor priority algorithm in accordance with an exemplary embodiment. The partitioning logic  1602  may receive inputs  1603  such as frequency of clears (e.g., JEClears and CRClears), frequencies of branches (e.g., all, taken, not taken), properties other than branches (e.g., instructions retired, L2/L3 misses). The partitioning logic  1602  may allocate entries of the branch target buffers (BTB)  1601  based the inputs  1603 . 
     Summary of Some Embodiments 
     An embodiment may include a processor configured to identify an available competitively shared resource; select a thread based at least in part on a priority algorithm; and assign the selected thread to the available competitively shared resource. 
     In some embodiments, one or more of the following apply. In some embodiments, the processor may be further configured to competitively share branch prediction and to use the priority algorithm for entry allocation. In some embodiments, the processor may be further configured to assign a second thread based on the priority algorithm. In some embodiments, the processor may be further configured to assign a most efficient thread to the available resource in the pipeline to increase at least one of instructions per clock (IPC) and pipeline throughput. In some embodiments, the processor may be further configured to provide a best known algorithm to prioritize a thread allocation to the available resource. In some embodiments, the processor may be further configured to prioritize when two or more events are detected. In some embodiments, the processor may be further configured to select at least one of a highest priority event and flag based on an assigned algorithm. 
     In some embodiments, the processor may comprise an event detection block, a performance counter flag block, a deadlock prevention block, and an instruction type/class block. In some embodiments, the event detection block may detect at least one of a nuke, frequency of clear, frequency of BR, an interrupt, and a cache miss. In some embodiments, the performance counter flag block may count at least one of instructions retired, code misses, and L2/L3 misses. In some embodiments, the deadlock prevention block may prevent deadlock states. In some embodiments, the instruction type/class block may allow a floating point instruction to retire. In some embodiments, the processor may be further configured to allow at least one of an operating system (OS) and a virtual machine manager (VMM) to set priorities. In some embodiments, the priority algorithm may have at least one learning capability. In some embodiments, the at least one learning capability may be adaptive based on at least one of historical data and workload patterns. 
     In some embodiments, the priority algorithm may comprise at least one of an integer rename and a floating point rename algorithm. The priority algorithm may comprise event based determinations. The event based determination may comprise one or more of a nuke, a clear, and an interrupt. The priority algorithm may comprise a performance counter. The performance counter may count occurrences. The occurrences may be one or more of instructions retired and code misses. The priority algorithm may comprise one or more of limiting physical registers, using deadlock prevention, and determining cache misses. The priority algorithm may comprise determining instruction types and classes. The priority algorithm may comprise allocating registers. Allocating registers may comprise allocating a floating point wordline more of the floating point registers. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based on dynamic behavior. 
     In some embodiments, a priority algorithm may comprise a branch predictor algorithm. In some embodiments, the branch predictor algorithm may control action of branch target buffers (BTB) based at least in part on one or more of the following: frequency of clears, frequencies of branches, properties other than branches. The clears may comprise one or more of JEClears and CRClears. The frequencies of branches may comprise one or more of all, taken, not taken. The properties other than branches may comprise one or more of instructions retired, L2/L3 misses. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based at least on part on dynamic behavior. The priority algorithm may comprise using partitioning logic to receive inputs. The inputs may comprise one or more of frequency of clears, frequencies of branches, properties other than branches. The partitioning logic may allocate entries of the branch target buffers (BTB) based the inputs. 
     An embodiment may include a method comprising identifying an available competitively shared resource; selecting a thread based at least in part on a priority algorithm; and assigning the selected thread to the available competitively shared resource. 
     In some embodiments, one or more of the following apply. In some embodiments, the method may further comprise competitively sharing branch prediction and using the priority algorithm for entry allocation. In some embodiments, the method may further comprise assigning a second thread based on the priority algorithm. In some embodiments, the method may further comprise assigning a most efficient thread to the available resource in the pipeline to increase at least one of instructions per clock (IPC) and pipeline throughput. In some embodiments, the method may further comprise providing a best known algorithm to prioritize a thread allocation to the available resource. In some embodiments, the method may further comprise prioritizing when two or more events are detected. In some embodiments, the method may further comprise selecting at least one of a highest priority event and flag based on an assigned algorithm. 
     In some embodiments, the method may further comprise using an event detection block, a performance counter flag block, a deadlock prevention block, and an instruction type/class block. In some embodiments, the method may further comprise using the event detection block to detect at least one of a nuke, frequency of clear, frequency of BR, an interrupt, and a cache miss. In some embodiments, the method may further comprise using the performance counter flag block to count at least one of instructions retired, code misses, and L2/L3 misses. In some embodiments, the method may further comprise using the deadlock prevention block prevent deadlock states. In some embodiments, the method may further comprise using the instruction type/class block to allow a floating point instruction to retire. In some embodiments, the method may further comprise allowing at least one of an operating system (OS) and a virtual machine manager (VMM) to set priorities. In some embodiments, the priority algorithm may have at least one learning capability. In some embodiments, the at least one learning capability may be adaptive based on at least one of historical data and workload patterns. 
     In some embodiments, the priority algorithm may comprise at least one of an integer rename and a floating point rename algorithm. The priority algorithm may comprise event based determinations. The event based determination may comprise one or more of a nuke, a clear, and an interrupt. The priority algorithm may comprise a performance counter. The performance counter may count occurrences. The occurrences may be one or more of instructions retired and code misses. The priority algorithm may comprise one or more of limiting physical registers, using deadlock prevention, and determining cache misses. The priority algorithm may comprise determining instruction types and classes. The priority algorithm may comprise allocating registers. Allocating registers may comprise allocating a floating point wordline more of the floating point registers. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based on dynamic behavior. 
     In some embodiments, a priority algorithm may comprise a branch predictor algorithm. In some embodiments, the branch predictor algorithm may control action of branch target buffers (BTB) based at least in part on one or more of the following: frequency of clears, frequencies of branches, properties other than branches. The clears may comprise JEClears. The frequencies of branches may comprise one or more of all, taken, not taken. The properties other than branches may comprise one or more of instructions retired, L2/L3 misses. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based at least on part on dynamic behavior. The priority algorithm may comprise using partitioning logic to receive inputs. The inputs may comprise one or more of frequency of clears, frequencies of branches, properties other than branches. The partitioning logic may allocate entries of the branch target buffers (BTB) based the inputs. 
     An embodiment may include a non-transitory machine-readable medium storing at least one instruction which when executed by a processor causes the processor to perform a method, the method comprising identifying an available competitively shared resource; selecting a thread based at least in part on a priority algorithm; and assigning the selected thread to the available competitively shared resource. 
     In some embodiments, one or more of the following apply. In some embodiments, the method may further comprise competitively sharing branch prediction and using the priority algorithm for entry allocation. In some embodiments, the method may further comprise assigning a second thread based on the priority algorithm. In some embodiments, the method may further comprise assigning a most efficient thread to the available resource in the pipeline to increase at least one of instructions per clock (IPC) and pipeline throughput. In some embodiments, the method may further comprise providing a best known algorithm to prioritize a thread allocation to the available resource. In some embodiments, the method may further comprise prioritizing when two or more events are detected. In some embodiments, the method may further comprise selecting at least one of a highest priority event and flag based on an assigned algorithm. 
     In some embodiments, the method may further comprise using an event detection block, a performance counter flag block, a deadlock prevention block, and an instruction type/class block. In some embodiments, the method may further comprise using the event detection block to detect at least one of a nuke, frequency of clear, frequency of BR, an interrupt, and a cache miss. In some embodiments, the method may further comprise using the performance counter flag block to count at least one of instructions retired, code misses, and L2/L3 misses. In some embodiments, the method may further comprise using the deadlock prevention block prevent deadlock states. In some embodiments, the method may further comprise using the instruction type/class block to allow a floating point instruction to retire. In some embodiments, the method may further comprise allowing at least one of an operating system (OS) and a virtual machine manager (VMM) to set priorities. In some embodiments, the priority algorithm may have at least one learning capability. In some embodiments, the at least one learning capability may be adaptive based on at least one of historical data and workload patterns. 
     In some embodiments, the priority algorithm may comprise at least one of an integer rename and a floating point rename algorithm. The priority algorithm may comprise event based determinations. The event based determination may comprise one or more of a nuke, a clear, and an interrupt. The priority algorithm may comprise a performance counter. The performance counter may count occurrences. The occurrences may be one or more of instructions retired and code misses. The priority algorithm may comprise one or more of limiting physical registers, using deadlock prevention, and determining cache misses. The priority algorithm may comprise determining instruction types and classes. The priority algorithm may comprise allocating registers. Allocating registers may comprise allocating a floating point wordline more of the floating point registers. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based on dynamic behavior. 
     In some embodiments, a priority algorithm may comprise a branch predictor algorithm. In some embodiments, the branch predictor algorithm may control action of branch target buffers (BTB) based at least in part on one or more of the following: frequency of clears, frequencies of branches, properties other than branches. The clears may comprise one or more of JEClears and CRClears. The frequencies of branches may comprise one or more of all, taken, not taken. The properties other than branches may comprise one or more of instructions retired, L2/L3 misses. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based at least on part on dynamic behavior. The priority algorithm may comprise using partitioning logic to receive inputs. The inputs may comprise one or more of frequency of clears, frequencies of branches, properties other than branches. The partitioning logic may allocate entries of the branch target buffers (BTB) based the inputs. 
     An embodiment may include a system including a memory and a processor, the processor configured to identify an available competitively shared resource; select a thread based at least in part on a priority algorithm; and assign the selected thread to the available competitively shared resource. 
     In some embodiments, the priority algorithm may comprise at least one of an integer rename and a floating point rename algorithm. The priority algorithm may comprise event based determinations. The event based determination may comprise one or more of a nuke, a clear, and an interrupt. The priority algorithm may comprise a performance counter. The performance counter may count occurrences. The occurrences may be one or more of instructions retired and code misses. The priority algorithm may comprise one or more of limiting physical registers, using deadlock prevention, and determining cache misses. The priority algorithm may comprise determining instruction types and classes. The priority algorithm may comprise allocating registers. Allocating registers may comprise allocating a floating point wordline more of the floating point registers. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based on dynamic behavior. 
     In some embodiments, a priority algorithm may comprise a branch predictor algorithm. In some embodiments, the branch predictor algorithm may control action of branch target buffers (BTB) based at least in part on one or more of the following: frequency of clears, frequencies of branches, properties other than branches. The clears may comprise one or more of JEClears and CRClears. The frequencies of branches may comprise one or more of all, taken, not taken. The properties other than branches may comprise one or more of instructions retired, L2/L3 misses. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based at least on part on dynamic behavior. The priority algorithm may comprise using partitioning logic to receive inputs. The inputs may comprise one or more of frequency of clears, frequencies of branches, properties other than branches. The partitioning logic may allocate entries of the branch target buffers (BTB) based the inputs. 
     In some embodiments, one or more of the following apply. In some embodiments, the processor may be further configured to competitively share branch prediction and to use the priority algorithm for entry allocation. In some embodiments, the processor may be further configured to assign a second thread based on the priority algorithm. In some embodiments, the processor may be further configured to assign a most efficient thread to the available resource in the pipeline to increase at least one of instructions per clock (IPC) and pipeline throughput. In some embodiments, the processor may be further configured to provide a best known algorithm to prioritize a thread allocation to the available resource. In some embodiments, the processor may be further configured to prioritize when two or more events are detected. In some embodiments, the processor may be further configured to select at least one of a highest priority event and flag based on an assigned algorithm. 
     In some embodiments, the processor may comprise an event detection block, a performance counter flag block, a deadlock prevention block, and an instruction type/class block. In some embodiments, the event detection block may detect at least one of a nuke, frequency of clear, frequency of BR, an interrupt, and a cache miss. In some embodiments, the performance counter flag block may count at least one of instructions retired, code misses, and L2/L3 misses. In some embodiments, the deadlock prevention block may prevent deadlock states. In some embodiments, the instruction type/class block may allow a floating point instruction to retire. In some embodiments, the processor may be further configured to allow at least one of an operating system (OS) and a virtual machine manager (VMM) to set priorities. In some embodiments, the priority algorithm may have at least one learning capability. In some embodiments, the at least one learning capability may be adaptive based on at least one of historical data and workload patterns. 
     In some embodiments, the priority algorithm may comprise at least one of an integer rename and a floating point rename algorithm. The priority algorithm may comprise event based determinations. The event based determination may comprise one or more of a nuke, a clear, and an interrupt. The priority algorithm may comprise a performance counter. The performance counter may count occurrences. The occurrences may be one or more of instructions retired and code misses. The priority algorithm may comprise one or more of limiting physical registers, using deadlock prevention, and determining cache misses. The priority algorithm may comprise determining instruction types and classes. The priority algorithm may comprise allocating registers. Allocating registers may comprise allocating a floating point wordline more of the floating point registers. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based on dynamic behavior. 
     In some embodiments, a priority algorithm may comprise a branch predictor algorithm. In some embodiments, the branch predictor algorithm may control action of branch target buffers (BTB) based at least in part on one or more of the following: frequency of clears, frequencies of branches, properties other than branches. The clears may comprise one or more of JEClears and CRClears. The frequencies of branches may comprise one or more of all, taken, not taken. The properties other than branches may comprise one or more of instructions retired, L2/L3 misses. The priority algorithm may comprise managing priority through software. The priority algorithm may allow one or more of an operating system and a virtual machine manager to provide priority. The priority algorithm may comprise hardware managed priority. The hardware managed priority may be based at least on part on dynamic behavior. The priority algorithm may comprise using partitioning logic to receive inputs. The inputs may comprise one or more of frequency of clears, frequencies of branches, properties other than branches. The partitioning logic may allocate entries of the branch target buffers (BTB) based the inputs. 
     Thread Switching 
     A processor core may support an SMT thread switching feature according to embodiments of the invention. In a processor core implementing SMT with shared resources, SMT may involve choosing which of two or more threads to select at various stages in the processor issue/execution pipeline. Embodiments of the invention including an SMT thread switching feature may be desired to provide for this selection to be influenced by priorities among performance, fairness, and other factors (e.g., increasing performance, decreasing power consumption and implementing power-saving features, and improving fairness, minimum performance guarantees, throughput, instructions per clock (IPC), instructions per unit time, quality of service, time and/or memory efficiency, to list just a few of the applicable criteria). For example, in an issue/execution pipeline of processor core  900 , arbitration may be used to select a thread on which branch predictor  911  is to begin prediction, a thread for which to look up a prediction in i-TLB  916 , a thread for which to look up an i-TLB translation in i-cache  913 , a thread for which to decode bytes from i-cache  913  in decoder  914 , a thread for which to read from op-cache  912 , a thread for which to read from micro-op queue  915 , etc. 
       FIG. 17  is a block diagram illustrating an arbitration circuit  1700  for an SMT thread switching feature that may be included in a processor according to embodiments of the invention. Arbitration circuit  1700  may include circuitry, structures, and/or hardware to choose which of two or more threads to select for advancement at any of various stages in a processor issue/execution pipeline. A processor or processor core may include multiple instances of one or more embodiments of arbitration circuit  1700 , each for any one or more pipeline stages or resources, each including any one or more of the blocks shown in  FIG. 17 , and each to implement any one or more approaches or combinations of approaches described below. Furthermore, all or part of any instance of arbitration circuit  1700  may be included, integrated, or incorporated in other circuitry, structures, and/or hardware of a processor or processor core, such as resource allocation, scheduling, or sharing circuitry. 
     Arbitration circuit  1700  may include simple round-robin circuit  1710 , high-throughput round-robin circuit  1720 , dynamic round-robin circuit  1730 , and software-controllable round-robin circuit  1740 , along with any other circuitry desired to implement any other round-robin or other scheme(s). 
     Simple round-robin circuit  1710  may include circuitry, structures, and/or hardware to perform a simple round-robin scheme to select a thread. For example, it may implement a scheme in which the selection constantly alternates between choices; i.e., thread 0, then thread 1, then thread 0, then thread 1, and so on; or thread 0, thread 1, thread 2, thread 0, thread 1, thread 2, and so on; etc. 
     High-throughput round-robin circuit  1720  may include circuitry, structures, and/or hardware to perform a modified round-robin scheme to select a thread based on a desire to prioritize throughput over other possible factors (such as fairness). For example, it may implement a simple round-robin scheme (e.g., as described above) as long as each thread has work available at the thread-switching point, otherwise, it may choose the thread that has work available. In an embodiment with more than two threads from which to choose, it may drop from the simple round-robin scheme any thread without work available. 
     Dynamic round-robin circuit  1730  may include circuitry, structures, and/or hardware to perform a dynamically modifiable round-robin scheme to select a thread based on the dynamic behavior of threads. Dynamic round-robin circuit  1730  may include and/or use performance counters, other hardware counters, or other structures (any of which are represented as  1732 ) to provide information upon which to base a decision (e.g., heuristic). A ratio or other criteria upon which to base thread selection to favor a thread, as well as an indication of which measures of dynamic behavior are to be used, may be fixed (e.g., hardwired), configurable (e.g., by hardware or firmware), or programmable (e.g., by software). For example, a first thread may be favored or selected over a second thread by a 2:1 ratio (e.g., thread 0, thread 0, thread 1, thread 0, thread 0, thread 1, and so on). Examples of factors or criteria to determine that one thread is favored over another thread are: mispredict rate, instructions per cycle, cache miss rate, etc.) 
     Software-controllable round-robin circuit  1740  may include circuitry, structures, and/or hardware to perform a modified round-robin scheme to select a thread based on a priority provided by software (e.g., and operating system or virtual machine monitor), which may have more information about desired system behavior than is otherwise available to software. The indication, along with a ratio at which to favor and/or any other information regarding which scheme to use or how to implement it (e.g., whether and how to combine software-controllable round-robin with dynamic and/or modifiable round-robin) may be provided in a programmable storage location or register  1742  within or accessible to arbitration circuit  1700 . 
     In embodiments, combinations of approaches are possible. For example, software may provide (e.g., using the circuitry and/or techniques for software-controllable round-robin), a hint as to which thread to favor, and hardware (e.g., the circuitry or techniques of dynamic round-robin), may determine, based on thread behavior and/or heuristics, may determine a ratio according to which to favor that thread. 
     Summary of Some Embodiments 
     An embodiment of the invention may include a processor comprising an arbitration circuit. The arbitration circuit may include a first round-robin circuit and a second round-robin circuit. The first round-robin circuit may be to implement a simple round-robin thread switching scheme. The second round-robin circuit may be to implement a dynamically modified round-robin thread switching scheme. 
     Deadlock Avoidance 
     A processor core may support an SMT deadlock avoidance feature according to embodiments of the invention. Sharing of resources might, in some circumstances, lead to a thread making slow progress due to being starved of one or more resources, making no progress due to being unable to advance (e.g., retire an instruction), and/or any other deadlock-type situation. As a result, the user experience might include noticeably slower performance or an error, failure, or crash. Embodiments of the invention including a deadlock avoidance feature may be desired to reduce deadlock-type situations and improve user experience. Other benefits of these embodiments may include, e.g., increasing performance, decreasing power consumption and implementing power-saving features, and improving fairness, minimum performance guarantees, throughput, instructions per clock (IPC), instructions per unit time, quality of service, time and/or memory efficiency, to list just a few of the applicable criteria. 
       FIG. 18  is a block diagram illustrating a deadlock avoidance hardware  1800  that may be included in a processor according to embodiments of the invention. Deadlock avoidance hardware  1800  may include circuitry, structures, and/or hardware to affect the allocation and usage of core circuits, structures, units, and resources, and portions thereof, to reduce the incidence of deadlock-type situations. In embodiments, deadlock avoidance hardware  1800  may be implemented to avoid a deadlock involving a single resource and/or multiple resources. In either case, a processor or processor core may include multiple instances of one or more embodiments of deadlock avoidance hardware  1800 , each for any one or more resources, each including any one or more of the blocks shown in  FIG. 18 , and each to implement any one or more approaches or combinations of approaches described below. Furthermore, all or part of any instance of deadlock avoidance hardware  1800  may be included, integrated, or incorporated in other circuitry, structures, and/or hardware of a processor or processor core, such as resource allocation, scheduling, or sharing circuitry. 
     Deadlock avoidance hardware  1800  may include allocator circuit  1810 , which may include circuitry, structures, and/or hardware to allocate resources to threads. An embodiment or instance of an embodiment of allocator circuit  1810  may represent or correspond to an embodiment or instance of an embodiment of allocator circuit  1240  in  FIG. 12 . 
     Deadlock avoidance hardware  1800 , allocator circuit CGA10, and/or any other part of a processor or processor core may include circuitry, structure, and/or hardware to dynamically disable, block, or otherwise prevent allocator circuit CGA10 from allocating a resource, or a part of a divisible resource, to any one or more particular threads. For example, in an embodiment including any type of round-robin scheme, such as those described above, to choose or arbitrate between or among thread requests, blocking a particular thread from using a resource may be accomplished by temporarily dropping that thread from the round-robin scheme. Embodiments may include an AND gate having a thread request signal (e.g.,  1240 A,  1240 B) as one input and the complement of a thread block signal (e.g., generated by circuitry based on resource usage counters  1820 , as described below, or any other information, state, or signals), such that the output of the AND gate may indicate whether a thread is to be allocated a resource or to be considered as a candidate for which a resource is to be allocated. 
     Deadlock avoidance hardware  1800  may also include resource usage counter  1820 . In an embodiment, resource usage counter  1820  may be a per-thread hardware counter to count the number of parts (e.g., entries) of a divisible resource (e.g., buffer, queue, scheduler, reservation station) that are being occupied or used by a particular thread. For a particular resource, an instance of resource usage counter  1820  for a particular thread may be incremented in response to allocator circuit  1810  allocating an entry to that thread, decremented in response to the entry being deallocated or removed, and cleared in response to the resource being flushed. Allocator circuit  1810  may be dynamically disabled or blocked (e.g., as described above) from allocating an entry to a thread in response to the count for that thread reaching or exceeding a threshold. 
     The threshold may be chosen to be less than the total number of entries in the resource to prevent any single thread from using all entries at the same time, which might result in a deadlock-type situation. The threshold may also be chosen or adjusted based on other factors or criteria, including those related to tolerance for approaching deadlock-type situations and/or desire to prioritize throughput or other measures or factors of performance. The threshold may be fixed (e.g., hardwired), configurable (e.g., by hardware or firmware), or programmable (e.g., by software). 
     In an embodiment, a divisible resource may be logically partitioned for particular threads and groups of threads. For example, in a divisible resource having a set of N entries, a subset of N1 entries (where N1 is less than N) may be reserved for use only by a first thread, a subset of N2 entries (where N2 is less than N) may be reserved for use only by a second, and the remaining subset of N−(N1+N2) entries may be allocated to either thread. In embodiments, this approach may be enforced by one or more instances of allocator circuit  1810 . 
     In an embodiment in which completion of a load depends on reading data out of a cache, each cache entry may include a bit to indicate that the entry is locked by a thread that includes a load from that entry. Replacement of entries with that indicator bit set may be prevented until the bit is cleared in connection with completion of the load or the thread experiences a pipeline flush event (e.g., a mispredicted branch). In embodiments, this approach may be enforced by one or more instances of allocator circuit  1810 . 
     In an embodiment, resource usage counter  1820  may be a per-thread hardware counter to count the number of clock cycles that, for the oldest entry in a retire queue for a particular thread, that thread (the stalled thread) has been waiting for a corresponding dispatch to an indivisible resource (the condition involves the retire queue because the thread needs a dispatch slot and a writeback slot). Allocator circuit  1810 , in response to the count for the stalled thread reaching or exceeding a threshold, may be dynamically disabled or blocked (e.g., as described above) from allocating an operation from a different thread to the scheduler for the indivisible resource. Alternatively, dispatch of any operations to the indivisible resource may be disabled or blocked for a given number of clock cycles. 
     These approaches may prevent a deadlock-type situation over the use of an indivisible resource, such as an execution unit, that may perform different operations consuming a range of clock cycles. For example, it may allow an operation that may complete in a single cycle to use a resource that might otherwise be kept busy completing a succession of multiple-cycle operations. 
     The threshold may be fixed (e.g., hardwired), configurable (e.g., by hardware or firmware), or programmable (e.g., by software). It may be chosen and/or dynamically adjusted based on various factors or criteria, including those related to throughput and those related to fairness. For example, if fairness is a priority, then the threshold may be gradually reduced to more aggressively allow each thread to make progress; if throughput is a priority, it may be gradually increased to more aggressively allow threads that are making progress to continue without interruption. 
     Summary of Some Embodiments 
     An embodiment of the invention may include a processor comprising deadlock avoidance hardware and a resource. The deadlock avoidance hardware may include an allocator circuit and a resource usage counter. The allocator circuit may be to determine whether to allocate the resource to a thread based on an output from the resource usage counter. 
     Datapath Features 
     Processor cores according to embodiments of the invention may include various features to support an instruction set architecture (ISA) with a datapath that is narrower than that provided for by the ISA. A number of such features are described separately using non-limiting examples below, but embodiments may include any combination of such features. 
     A processor core may support a feature allowing operations on operands of a larger size (e.g., loads/stores/arithmetic operations on operands that are 256 bits in side) by breaking these operations up into multiple micro-operations (μops) that operate on smaller operands (e.g., multiple μops that operate on values that are 128 bits in size). Such a feature may be desirable for a variety of reasons: for example, a processor may support an instruction set architecture that involves larger operand sizes, but may use a microarchitecture based on smaller operand sizes. Additionally or alternatively, a processor may support an instruction set architecture that involves larger operand sizes and have a register file including registers of this larger size, but may include execution units that can only handle data in smaller chunks. Additionally or alternatively, a processor may have a larger-size register file, execution units, and load/store ports, but performing μops using operands of a smaller size may be desirable for, e.g., power-saving or scheduling purposes. Other potential benefits of a processor including the features described below include, but are not limited to, increasing performance, decreasing power consumption and implementing power-saving features, and improving fairness, minimum performance guarantees, throughput, instructions per clock (IPC), instructions per unit time, quality of service, and time and/or memory efficiency, to list just a few of the applicable criteria. 
     256 to 128 Bit Datapath Loads and Stores 
     A processor core may support a feature allowing 256-bit loads and stores using 128-bit micro-operations (μops), according to embodiments of the invention. In some embodiments, a processor may support a 256-bit instruction set architecture, but may use a 128-bit microarchitecture, including a 128-bit register file. In other embodiments, a processor may have a 256-bit instruction set architecture and a 256-bit register file, but may include load and/or store ports that can only handle data in 128-bit chunks. 
       FIG. 19  is a diagram showing a 256-bit load to a 256-bit register file using a pair of 128-bit μops, according to some embodiments. Memory  1901  includes a series of 256-bit values, such as the value stored in memory location  1902 . A first μop  1903  retrieves the lower half of the value stored in memory location  1902 , and a second μop  1904  retrieves the upper half of the value stored in memory location  1902 . The two halves of the value stored in memory location  1902  are blended together (1905) and the result of the blend operation is placed in 256-bit register file  1906 . 
       FIG. 20  is a flow diagram representing the process described above with reference to  FIG. 19 , according to some embodiments. During the process of decoding an instruction ( 2001 ) if a 256-bit load is detected, 3 μops are generated (box  2002 ), including a first load μop, a second load μop, and a blend μop. The μops are scheduled to be executed, and for each μop, the processor may wait until the data to be loaded/blended is ready ( 2003 ). When the first load μop is executed, the processor may retrieve the lower half of the value stored in memory location  1902 , as shown in box  2004 . When the second load μop is executed, the processor may retrieve the upper half of the value stored in memory location  1902 , as shown in box  2004 . When the blend μop is executed, the two retrieved halves of the value stored in memory location  1902  are combined and placed in a 256-bit register file, as shown in box  2004 . Finally, the decoded instructions are retired upon completion, as shown in box  2005 . 
     In some embodiments, a value may be stored from a 256-bit register file into memory using 128-bit μops.  FIG. 21  is a diagram illustrating this process. A 256-bit register file  2101  includes registers that are 256-bits wide, such as register  2102 . A first store μop,  2103 , retrieves the lower half of the value stored in register  2102  and stores it in the lower half of memory location  2104 . A second store μop,  2105 , retrieves the upper half of the value stored in register  2102  and stores it in the upper half of memory location  2104 . 
       FIG. 22  is a flow diagram representing the process described above with reference to  FIG. 21 , according to some embodiments. During the process of decoding an instruction ( 2201 ) if a 256-bit store is detected, 2 μops are generated (box  2202 ), including a first store μop and a second store μop. The μops are scheduled to be executed, and for each μop, the processor may wait until the data to be stored is ready ( 2203 ). When the first store μop is executed, the processor may retrieve the lower half of the value stored in register  2102 , as shown in box  2204 , and write it into the lower half of the memory location  2104 . When the second store μop is executed, the processor may retrieve the upper half of the value stored in register  2102 , as shown in box  2204 , and write it into the upper half of the memory location  2104 . Finally, the decoded instructions are retired upon completion, as shown in box  2205 . 
     In some embodiments, a 256-bit load instruction may load a 256-bit value into two 128-bit registers by executing two μops, a first μop to load the lower half of the 256-bit value into a first 128-bit register, and a second μop to load the upper half of the 256-bit value into a second 128-bit register. 
     In some embodiments a load is accomplished using a single μop that is “double-pumped”—i.e., that is executed twice, once to load the lower half of a value from memory, and a second time to load the upper half of a value from memory. In some embodiments, a store is accomplished using a single μop that is “double-pumped”—i.e., executed once to store the lower half of a register to memory, and once to store the upper half of a register to memory. In some embodiments, the μops used to implement a 256-bit load and/or store may be scheduled according to vector scheduling algorithms. In some embodiments, gang scheduling techniques may be used to schedule the multiple μops involved in a load and/or a store for execution on separate execution units. 
     The load/store features described above are not limited to performing loads and/or stores using memory, load ports, or register files of any particular size. For example, the techniques described above may be used to perform 512-bit loads and/or stores using underlying hardware that operates on 256 bits at a time] 
     256 to 128 Bit Datapath In-Lane Execution 
     A processor core may support a feature allowing 256-bit arithmetic operations using 128-bit micro-operations (μops), according to embodiments of the invention. In some embodiments, a processor may support a 256-bit instruction set architecture, but may use a 128-bit microarchitecture, including a 128-bit register file. In other embodiments, a processor may have a 256-bit instruction set architecture and a 256-bit register file, but may include execution units that can only handle data in 128-bit chunks. In some embodiments, a processor may have a 256-bit register file, execution units, and load/store ports, but it may be desirable for, e.g., power-saving or scheduling purposes, to implement 256-bit arithmetic operations using multiple 128-bit μops. 
       FIG. 23  illustrates this process according to some embodiments. A 256-bit instruction  2301  is decoded by splitting it into 2 128-bit μops  2302  and  2303 , which are then scheduled independently for execution on one or more 128-bit execution units  2304 ,  2305 . According to the embodiment shown in  FIG. 23 , the first 128-bit μop  2302  may execute an instruction using the lower halves of the 256-bit operands provided to the 256-bit arithmetic instruction and the processor may then store the result in the lower half of a 256-bit destination register. The second 128-bit μop  2303  may execute an instruction using the upper halves of the 256-bit operands provided to the 256-bit arithmetic instruction and the processor may then store the result in the upper half of a 256-bit destination register. 
     According to some embodiments, partitioning the 256-bit instruction into a pair of 128-bit μops bases the lower half of the result solely on the lower halves of the 256-bit instruction&#39;s operands, and the upper half of the result is based solely on the upper halves of the 256-bit instruction&#39;s operands (i.e., “in-lane” operations). In these in-lane scenarios, the two 128-bit μops may be scheduled independently of each other, because the result of the 256-bit instruction can be expressed as two independent results of two separate 128-bit μops. 
     In some embodiments, each of the 128-bit μops represent the same instruction (e.g., an ADD instruction), and the 256-bit instruction can be implemented using a single 128-bit μop that is “double-pumped,”—i.e., executed twice, once to calculate the lower half of the result, and once to calculate the upper half of the result. In some embodiments, the 256-bit instruction can be “split” into two distinct μops, which are independently scheduled and executed on one or more execution units. In some embodiments, the 256-bit instruction can be executed using two execution units simultaneously, each executing a 128-bit μop (this procedure is sometimes known in the art as “gang scheduling”). 
     The in-lane execution features described above are not limited to executing instructions using memory values, load ports, execution units or register files of any particular size. For example, the techniques described above may be used to perform 512-bit operations using underlying hardware that operates on 256 bits at a time, or to perform 1024-bit operations using underlying hardware that operates on 512 bits at a time. 
     256 to 128 Bit Datapath Cross-Lane Execution 
     In some embodiments, the 256-bit instruction to be executed cannot be partitioned into two completely independent 128-bit μops, because the lower half of the result depends on values stored the upper halves of the operands, and/or the upper half of the result depends on values stored in the lower halves of the operands (i.e., “cross-lane” operations). 
     Cross-lane operations may be implemented using a temporary storage area to store partial results, which are then combined into a final result and stored in a destination register.  FIG. 24  illustrates this process according to some embodiments of this feature. A cross-lane 256-bit instruction QJA01 is decoded by splitting it into 2 128-bit μops QJA02 and QJA03, which are then scheduled independently for execution on one or more 128-bit execution units QJA06, QJA07. A temporary storage area QJA04 is used to store partial results produced by μops QJA02 and QJA03. These temporary results are used by a third μop, QJA05, to produce a final result. 
     In some embodiments, each of the 128-bit μops QJA02 and QJA03 represent the same instruction, and may be implemented using a single 128-bit μop that is “double-pumped,”—i.e., executed twice, once to calculate a first partial result which is stored in the temporary storage area QJA04, and once to calculate a second partial result, which is stored in the temporary storage area QJA04. In some embodiments, the 256-bit instruction can be “split” into two distinct μops, which are independently scheduled and executed on one or more execution units, the partial results of which are stored in a temporary storage area. In some embodiments, the 256-bit instruction can be executed using two execution units simultaneously, each executing a 128-bit μop (this procedure is sometimes known in the art as “gang scheduling”). In some embodiments, a 256-bit μop may be executed using a “special” execution unit with 256-bit capabilities, eliminating the need for a temporary storage area (e.g., temporary storage area QJA04). 
     The cross-lane execution features described above are not limited to executing instructions using memory values, load ports, execution units or register files of any particular size. For example, the techniques described above may be used to perform 512-bit operations using underlying hardware that operates on 256 bits at a time, or to perform 1024-bit operations using underlying hardware that operates on 512 bits at a time. 
     Additional Independent and Combinable Features 
     Processor cores according to embodiments of the invention may include various additional features to support increased performance and/or decreased power consumption. A number of such features are described separately using non-limiting examples below, but embodiments may include any combination of such features. 
     Micro-Op Cache 
     A processor core may support a micro-op cache feature according to embodiments. In some embodiments, the micro-op cache feature may include allocation, replacement policy and different structure types (e.g., physical, virtual, etc.). The intelligent allocation in the micro-op cache feature may detect a type of instructions, such as loop stream or complex instructions with microcode sequencer (MS) flow, vs simple instructions and allocate accordingly. The micro-op cache feature may also cover adding a victim cache for future potential re-use and/or for determining how many micro-ops to assign per cache line. In some embodiments, the micro-op cache may be used to save decoded instructions (micro-ops) in a micro-op buffer for later reuse of the decoded instructions. In some embodiments, use of the micro-op buffer may shorten the pipeline by avoiding multiple (e.g., at least two) cycles of an instruction cache lookup and decode stage. It may also save power by using micro-ops already available and decoded in the micro-op buffer. In some embodiments, there could be more than one thread with a similar event (e.g., micro-of type, micro-op decode difficulty, micro-op use patterns), and a priority scheme may be used in cases where there is tie between threads to allocate resources to the micro-op cache. In some embodiments, the micro-op cache feature may provide intelligent allocation, replacement policy, and/or configuration for micro-op cache to achieve the highest IPC and/or instruction throughput in the pipeline. 
       FIG. 25  is a block diagram illustrating a micro-op cache feature that may be included in a processor according to embodiments. A micro-op cache feature may comprise one or more of the following: an instruction decoder  2501 , an intelligent allocation and replacement block  2502 , and a micro-op cache  2503 . An intelligent allocation and replacement block  2502  may receive instruction from the instruction decoder  2501 . The instruction decoder  2501  may also be omitted and the intelligent allocation and replacement block  2502  may receive an already decoded instruction. The intelligent allocation and replacement block  2502  may algorithmically determine what types of instructions to allocate, such as complex instruction (e.g., with MS flow), loop stream, etc. The intelligent allocation and replacement block  2502  may determine where to allocate an instruction in the micro-op cache KQA03 and may allocate the instruction in the determined location. In some embodiments, the intelligent allocation and replacement block  2502  may, for example, algorithmically determine what types of instructions to allocate based on one or more of the following: historical use patterns for instructions, frequency of use, decode difficulty, and decode time. Intelligent allocation and replacement block may, for example determine where to store instructions in the micro-op cache based on one or more of the following parameters: least recently used instructions information, historical use patterns for instructions, frequency of use, decode difficulty, whether instruction is part of a loop and whether other instructions from the loop are stored, and decode time of instructions stored in the micro op cache. These parameters may, for example, be stored in the intelligent allocation and replacement block, in the micro-op cache, and/or elsewhere (e.g., in a separate table). 
       FIG. 26  is a flow diagram illustrating a method for a micro-op cache feature that may be performed by a processor according to embodiments. The method may comprise receiving instructions as shown in box  2601 . The method may further comprise algorithmically determining what types of instructions to allocate, such as complex instruction, loop stream, etc., as shown in box  2602 . The method may further comprise determining where to allocate an instruction in a micro-op cache as shown in box  2603 . The method may further comprise allocating the instruction in the determined location of the micro-op cache as shown in box  2604 . 
       FIG. 27  is a block diagram illustrating a micro-op cache feature that may be included in a processor according to embodiments. The micro-op cache feature may comprise one or more of a branch prediction unit (BPU)  2701 , an instruction cache tag  2702 , a micro op tag  2703 , an instruction cache  2704 , a micro op cache  2705 , a decoder  2706 , and a micro op queue  2707 . BPU  2701  may perform branch prediction (e.g., to determine whether to perform conditional operations). As illustrated on the left side of  FIG. 27 , instruction cache tag  2702  may, for example, receive an instruction tag from the BPU  2701  and determine an instruction associated with the instruction tag. The instruction may be retrieved from the instruction cache  2704  and decoded by the decoder  2706 . The micro op queue  2707  may then receive the decoded instruction from the decoder  2706 . As illustrated on the right side of  FIG. 28 , the micro op tag  2703  may receive an instruction tag from the BPU  2701  and determine an associated micro op tag. The micro op cache  2705  can then be checked to determine whether the micro-op associated with the micro op tag is stored in the micro op cache  2705  and to retrieve the micro op from the micro op cache  2705 . Micro ops may be decoded and stored in the micro op cache  2705 , for example, as described above in connection with  FIGS. 25 and 26 . The micro-op cache feature may be physical and/or virtual. The micro-op cache feature may comprise shortening the pipeline. For example, as illustrated in  FIG. 27 , in the case where micro-ops have been previously decoded and stored in the micro-op cache, the pipeline on the right side is shorter than the pipeline on the left side because a decode operation may not need to be performed when the micro op is already stored in the micro op cache. The micro-op cache feature may comprise next line prediction within the micro op cache  2705 . The micro-op cache feature may store MS flows in the micro op cache  2705 . The micro-op cache feature may use replacement policies to determine which micro-ops to store in the cache and which micro-ops to replace with new micro-ops. The micro-op cache feature may determine the types of instructions to allocate into the micro-op cache  2705 , e.g., loop stream and/or complex instructions. The micro-op cache feature may prioritize micro-operations. The micro-op cache feature may comprise a victim cache (not shown). The victim cache may store instructions for potential re-use, such as instructions that were difficult to decode. 
       FIG. 28  is a block diagram illustrating a micro-op cache feature that may be included in a processor according to embodiments. The micro-op cache feature may comprise one or more of a physical micro op cache  2801  and a virtual micro op cache  2802 . The physical micro op cache  2801  may, for example, store micro-ops in physical memory using a physical address space. The virtual micro op cache may, for example, store micro ops in virtual memory using a virtual address space. The physical micro op cache  2801  and/or the virtual micro op cache  2802  may be flushed, e.g., on context and/or mode switch. The physical micro op cache  2801  and/or the virtual micro op cache  2802  may be shared competitively. 
     Summary of Some Embodiments 
     An embodiment may include a processor configured to algorithmically determine a type of instruction to allocate to a micro op cache; determine a location to allocate an instruction of the determined type to the micro op cache; and allocate the instruction to the determined location. 
     In some embodiments, one or more of the following apply. In some embodiments, the processor is further configured to cause an intelligent allocation and replacement block to receive an instruction from an instruction decoder. In some embodiments, the determined instruction type is at least one of a complex instruction and a loop stream. In some embodiments, the processor may comprise one or more of a branch prediction unit (BPU), an instruction cache tag, a micro op tag, an instruction cache, a micro op cache, and a decoder, and a micro op queue. In some embodiments, the micro op cache may comprise next line prediction. In some embodiments, the processor is configured to store MS flows in the micro op cache. In some embodiments, the processor is configured to prioritize micro operations. In some embodiments, the processor comprises a victim cache. In some embodiments, the micro op cache comprises at least one of a physical micro op cache and a virtual micro op cache. In some embodiments, the at least one of the physical micro op cache and the virtual micro op cache may be shared competitively. In some embodiments, the determination of what type of instruction to allocate to a micro op cache may be based at least in part on one or more of the following: historical use patterns, frequency of use, decode difficulty, and decode time. In some embodiments, the determination of the location to allocate the instruction of the determined type to the micro op cache may be based on one or more of the following: least recently used instructions information, historical use patterns for instructions, frequency of use, decode difficulty, loop status information, and decode time of instructions stored in the micro op cache. 
     An embodiment may include a method comprising algorithmically determining a type of instruction to allocate to a micro op cache; determining a location to allocate an instruction of the determined type to the micro op cache; and allocating the instruction to the determined location. 
     In some embodiments, one or more of the following apply. In some embodiments, the method may further comprise causing an intelligent allocation and replacement block to receive an instruction from an instruction decoder. In some embodiments, the determined instruction type is at least one of a complex instruction and a loop stream. In some embodiments, the method may further comprise using one or more of a branch prediction unit (BPU), an instruction cache tag, a micro op tag, an instruction cache, a micro op cache, and a decoder, and a micro op queue. In some embodiments, the micro op cache may comprise next line prediction. In some embodiments, the method may further comprise storing MS flows in the micro op cache. In some embodiments, the method may further comprise prioritizing micro operations. In some embodiments, the method may further comprise using a victim cache. In some embodiments, using the micro op cache comprises using at least one of a physical micro op cache and a virtual micro op cache. In some embodiments, the method may further comprise competitively sharing at least one of the physical micro op cache and the virtual micro op cache. In some embodiments, the determination of what type of instruction to allocate to a micro op cache may be based at least in part on one or more of the following: historical use patterns, frequency of use, decode difficulty, and decode time. In some embodiments, the determination of the location to allocate the instruction of the determined type to the micro op cache may be based on one or more of the following: least recently used instructions information, historical use patterns for instructions, frequency of use, decode difficulty, loop status information, and decode time of instructions stored in the micro op cache. 
     An embodiment may include a non-transitory machine-readable medium storing at least one instruction which when executed by a processor causes the processor to perform a method, the method comprising algorithmically determining a type of instruction to allocate to a micro op cache; determining a location to allocate an instruction of the determined type to the micro op cache; and allocating the instruction to the determined location. 
     In some embodiments, one or more of the following apply. In some embodiments, the method may further comprise causing an intelligent allocation and replacement block to receive an instruction from an instruction decoder. In some embodiments, the determined instruction type is at least one of a complex instruction and a loop stream. In some embodiments, the method may further comprise using one or more of a branch prediction unit (BPU), an instruction cache tag, a micro op tag, an instruction cache, a micro op cache, and a decoder, and a micro op queue. In some embodiments, the micro op cache may comprise next line prediction. In some embodiments, the method may further comprise storing MS flows in the micro op cache. In some embodiments, the method may further comprise prioritizing micro operations. In some embodiments, the method may further comprise using a victim cache. In some embodiments, using the micro op cache comprises using at least one of a physical micro op cache and a virtual micro op cache. In some embodiments, the method may further comprise competitively sharing at least one of the physical micro op cache and the virtual micro op cache. In some embodiments, the determination of what type of instruction to allocate to a micro op cache may be based at least in part on one or more of the following: historical use patterns, frequency of use, decode difficulty, and decode time. In some embodiments, the determination of the location to allocate the instruction of the determined type to the micro op cache may be based on one or more of the following: least recently used instructions information, historical use patterns for instructions, frequency of use, decode difficulty, loop status information, and decode time of instructions stored in the micro op cache. 
     An embodiment may include a system including a memory and a processor, the processor configured to algorithmically determine a type of instruction to allocate to a micro op cache; determine a location to allocate an instruction of the determined type to the micro op cache; and allocate the instruction to the determined location. 
     In some embodiments, one or more of the following apply. In some embodiments, the processor is further configured to cause an intelligent allocation and replacement block to receive an instruction from an instruction decoder. In some embodiments, the determined instruction type is at least one of a complex instruction and a loop stream. In some embodiments, the processor may comprise one or more of a branch prediction unit (BPU), an instruction cache tag, a micro op tag, an instruction cache, a micro op cache, and a decoder, and a micro op queue. In some embodiments, the micro op cache may comprise next line prediction. In some embodiments, the processor is configured to store MS flows in the micro op cache. In some embodiments, the processor is configured to prioritize micro operations. In some embodiments, the processor comprises a victim cache. In some embodiments, the micro op cache comprises at least one of a physical micro op cache and a virtual micro op cache. In some embodiments, the at least one of the physical micro op cache and the virtual micro op cache may be shared competitively. In some embodiments, the determination of what type of instruction to allocate to a micro op cache may be based at least in part on one or more of the following: historical use patterns, frequency of use, decode difficulty, and decode time. In some embodiments, the determination of the location to allocate the instruction of the determined type to the micro op cache may be based on one or more of the following: least recently used instructions information, historical use patterns for instructions, frequency of use, decode difficulty, loop status information, and decode time of instructions stored in the micro op cache. 
     Move Elimination 
     A processor core may support a move elimination feature according to embodiments of the invention. For many processors, executing a move instruction usually involves moving a value from one register to another register, or moving an immediate to a register. Because of the frequency of such move instructions, processor performance may be increased if move instructions are efficiently processed. 
     Most instructions operate on several source operands and generate results. They name, either explicitly or through an indirection, the source and destination locations where values are read from or written to. A name may be either a logical (architectural) register or a location in memory. 
     Usually, the number of physical registers available for a processor exceeds the number of logical registers, so that register renaming may be utilized to increase performance. In particular, for out-of-order processors, register renaming allows instructions to be executed out of their original program order. Thus, for many out-of-order processors, a move instruction is renamed so that logical register named in the original move instruction are renamed to physical registers. 
     Renaming a logical register involves mapping a logical register to a physical register. These mappings may be stored in a Register Alias Table (RAT). A RAT maintains the latest mapping for each logical register. A RAT is indexed by logical registers, and provides mappings to corresponding physical registers. 
     Illustrated in  FIG. 29  is a register renaming and dependency tracking scheme involving three structures RAT  2900 , active list (AL)  2902 , and free list (FL)  2904 . For each logical register specified by a renamed instruction, an unused physical register from FL  2904  is allocated and RAT  2900  is updated with this new mapping. Physical registers are free to be used again (i.e., reclaimed) once they are not referenced any more by instructions in the current instruction window. 
     Based on the data structures depicted in  FIG. 29 , one method for register reclaiming is to reclaim a physical register only when the instruction that evicted it from RAT  110 , i.e., the instruction that created a new mapping to the physical register, retires. As a result, whenever a new mapping updates RAT  2900 , the evicted old mapping is pushed into AL  2902 . (An AL entry is associated with each instruction in the instruction window.) When an instruction retires, the physical register of the old mapping recorded in AL  2902 , if any, is reclaimed and pushed into FL  2904 . This cycle is depicted in  FIG. 29 . 
     For many instructions, one of the source registers is also used as a destination register. If the value stored in this source register is needed by subsequent (in program order) instructions, a register-move instruction may be inserted prior to the subsequent instruction to copy the source operand in the source register to another logical location so that it can be accessed by the subsequent instruction. 
     Another reason for the insertion of register-move instructions is to set the parameter values in the appropriate registers prior to a procedure call. 
     As a result, the number of register-move instructions may be quite significant. Therefore, it may be desirable to provide for the efficient execution of register-move instructions with efficient register renaming and reclaiming schemes. 
     In  FIG. 1B , the register renaming functional unit is indicated as rename/allocator unit  152 , and the physical registers are indicated as physical register files unit  158 . In  FIG. 3 , the register renaming functional units are indicated as integer rename unit  321  and FP rename unit  331 , and the physical registers are indicated by integer physical register file  323  and FP register file  333 . Every logical register has a mapping to a physical register, where the mapping is stored in RAT  2900  as an entry. An entry in RAT  2900  is indexed by a logical register and contains a pointer to a physical register. 
     During renaming of an instruction, current entries in the RAT provide the required mapping for renaming the source logical register(s) of the instruction, and a new mapping is created for the destination logical register of the instruction. This new mapping evicts the old mapping in the RAT, and the RAT is updated with the new mapping. 
     Table 1 illustrates an example of register renaming. In Table 1, four instructions in original program order are provided in the first column. Renamed instructions are indicated in the second column. Next to each renamed instruction are the current entries in the RAT after the instruction renaming. The final column provides the mapping evicted by instruction renaming. For simplicity, only three logical registers, LRa, LRb, and LRb, are considered. A physical register is denoted by PRi where i is an integer. The first entry in Table 1 provides the current state of the RAT before the first listed instruction is renamed. 
     For example, in Table 1 the first instruction LRa+2→LRa (indicating that the immediate 2 is added to the value in logical register LRa and the result is stored in logical register LRa) is renamed to PR1+2→PR2, where physical register PR2 was assumed to be available. For this instruction, a new mapping LRa  4  PR2 was created and the old mapping LRa→PR1 was evicted from the RAT. 
     Note that there is a true dependence of the second and fourth instructions upon the first instruction, and a true dependence of the third instruction upon the second instruction. However, register renaming has removed the output dependency between the second and fourth instructions, as well as the anti-dependency between the third and fourth instructions, so that the second, third, and fourth instructions may be executed out of order, provided the execution order follows the various true dependencies. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Renamed 
                   
                 EVICTED 
               
               
                 INSTRUCTION 
                 Instruction 
                 RAT 
                 MAPPING 
               
               
                   
               
             
            
               
                 . . . 
                 . . . 
                 LRa → PR1 
                 . . . 
               
               
                   
                   
                 LRb → PR11 
               
               
                   
                   
                 LRc → PR10 
               
               
                 LRa + 2 → LRa 
                 PR1 + 2 → PR2 
                 LRa → PR2 
                 LRa → PR1 
               
               
                   
                   
                 LRb → PR11 
               
               
                   
                   
                 LRc → PR10 
               
               
                 LRa + 3 → LRb 
                 PR2 + 3 → PR12 
                 LRa → PR2 
                 LRb → PR11 
               
               
                   
                   
                 LRb → PR12 
               
               
                   
                   
                 LRc → PR10 
               
               
                 LRb + 2 → LRc 
                 PR12 + 2 → PR13 
                 LRa → PR2 
                 LRc → PR10 
               
               
                   
                   
                 LRb → PR12 
               
               
                   
                   
                 LRc → PR13 
               
               
                 LRa + 5 → LRb 
                 PR2 + 5 → PR14 
                 LRa → PR2 
                 LRb → PR12 
               
               
                   
                   
                 LRb → PR14 
               
               
                   
                   
                 LRc → PR13 
               
               
                   
               
            
           
         
       
     
     Renamed instructions are place in the instruction window buffer. Entries in the instruction window buffer contain the opcode of the renamed instruction, as well as other fields to be described later. For this embodiment, the results of instructions are not stored in the instruction window buffer but reside in the physical register file. 
     The instruction window buffer allows for instruction retirement in original program order. For complex instruction set computer (CISC) architectures, a complex instruction is retired when all micro-instructions making up the complex instruction are retired together. The instruction window buffer is operated as a circular buffer, where a first pointer points to the next instruction to be retired and a second pointer points to the next available entry for a newly decoded instruction. Incrementing of the pointers in done in modulo-N arithmetic, where N is the number of available entries in the buffer. When an instruction retires, the first pointer is incremented. The pointers are incremented by one for each decoded instruction in reduced instruction set computer (RISC) architectures, and may be incremented by more than one for CISC architectures. 
     For a store instruction that writes its result to a memory location, the data cache is updated upon instruction retirement. For an instruction that writes its result to a logical register, no write need be done on retirement because there are no registers dedicated as logical registers. For such an instruction, the physical register file has the result of the retiring instruction in the physical register to which the destination logical register was mapped when the instruction was renamed. 
     The scheduler schedules instructions to execution units for execution. The scheduling function may, for example, be realized by reservation stations implementing Tomasulo&#39;s algorithm (or variations thereof). Execution units may retrieve data from or send data to the data cache or the physical register file, depending on the instruction (or micro-instruction) to be executed. 
     In other embodiments of the invention, the information content contained in the data structures of the physical register file and the instruction window buffer may be realized by different functional units. For example, a re-order buffer may replace the instruction window buffer and the physical register file, so that results are stored in the re-order buffer, and in addition, registers in a register file are dedicated as logical registers. For this type of embodiment, the result of an instruction specifying a write to a logical register is written to a logical register upon instruction retirement. 
     We now distinguish two types of move instructions: register-to-register moves and immediate-to-register moves. In a register-to-register move, a value is moved from one register, the source logical register, to another register, the destination logical register. In an immediate-to-register move, an immediate value is moved to a logical register. 
     In embodiments of the invention, move instructions are executed by mapping more than one logical register to the same physical register. The execution of a register-to-register move instruction is performed by mapping the destination logical register of the move instruction to the physical register mapped by the source logical register of the move instruction. 
     The execution of an immediate-to-register move instruction may be performed by accessing a value-matching cache. Entries in a value-matching cache are indexed by values, where a cache entry associates a value with a physical register storing that value. The value matching cache may have fewer entries than the number of physical registers. If there is a hit in the value matching cache, then the destination logical register of the move instruction is mapped to the physical register indicated by the value-matching cache. If there isn&#39;t a hit, then the move execution is performed as in prior art architectures, and the value-matching cache is updated. 
     The physical register file may itself serve the function of a value-matching cache, such that the value-matching cache is not needed. In this case, the register file would need an extra port to perform parallel tag matching, where the tag is the value stored in a physical register. 
     As discussed above, register-to-register move instructions and immediate-to-register move instructions (provided there is a hit in the value-matching cache for the latter type of move) are executed by creating multiple mappings in which more than one logical register is mapped to the same physical register. Effectively, such move instructions are “eliminated” in the sense that they no longer are performed by execution units. Instead move eliminations are performed during the renaming stage. These instructions remain in the instruction buffer window ready to be retired. Dependency graphs are collapsed since instructions dependent on such move instructions are made directly dependent on the real producer (dependencies are redirected). There may also be a reduction in the requirement for physical registers, and there may be fewer writes into the register file. 
     Idiom elimination mechanisms similarly effect instruction operations without passing them down a traditional out-of-order pipeline. Idioms are instances of general purpose instructions coded to achieve a specific effect, often in a more optimized way compared to explicit instructions. Move idioms include any instruction constructed to place the contents of a source register into a destination register with no other effects, such as R1=ADD R0, #0. Zero idioms similarly are general purpose instructions coded to set a register to zero, such as R0=XOR R0, R0. No-ops (NOPs) are instructions defined to have no effect on architectural state, including explicit NOP opcode and NOP idioms such as R0=ADD R0, #0. 
     Embodiments of the invention may be desired to improve on existing move elimination and idiom elimination techniques by saving micro-op renaming/allocation bandwidth, increasing performance, decreasing power consumption and implementing power-saving features, and improving fairness, minimum performance guarantees, throughput, instructions per clock (IPC), instructions per unit time, quality of service, time and/or memory efficiency, and expanding coverage of move eliminations to more instruction types. 
     In embodiments, the results of on-the-fly move elimination and idiom elimination operations on an instruction stream may be cached into a decoded micro-op cache, such as micro-op cache  133  or  312 . Therefore, rediscovery of the necessary conditions and repeat of the operations that eliminate the original instructions from the pipeline may be avoided. 
     The eliminated instructions may be replaced with metadata stored in the micro-op cache that achieves the same effect as the eliminated instructions. When the micro-op cache is written, the results of the move elimination or idiom elimination are converted to metadata so that the micro-ops may be removed from the micro-op cache and thus optimized out of the delivered micro-op stream. Since the on-the-fly instruction elimination mechanism have already done the work to identify the opportunities, the micro-op cache build may be modified to scan and remove the affected micro-ops. The metadata includes information needed to perform the renaming operations, plus relevant architectural information, such as the existence of event boundaries and effects of performance monitoring counters. For example, the metadata may indicate how many instructions were eliminated, and/or, for a CISC architecture, how many micro-ops were eliminated for each instruction, and/or that an end-of-macro-instruction happened after an instruction that was eliminated. Metadata may be stored in a field in an entry for a micro-op before and/or after eliminated micro-ops. 
     In an embodiment, move elimination may be expanded to include zero-extend and sign-extend operations. For example, R0=MOV.ZE R1 may be move eliminated, even though it is not a simple move. 
     In an embodiment, RAT  3000  may be extended as shown in  FIG. 30  to include zero idioms, sign extension, and zero extension. The RAT is extended with following three bits: Z, when set, the rest of the RAT entry is ignored and the logical register is treated as zero; SE, when set, the value of the logical register is the sign-extended version of the physical register file identifier (PRF ID) stored in the entry; and ZE, when set, the value of the logical register is the zero-extended version of the PRF ID stored in the entry. 
     Then, as illustrated in  FIG. 31 , the Z, SE, and ZE bits may be read during register renaming and passed down the pipeline with the micro-op that read the register. The bits are interpreted prior to operation of ALU  3120  to create the correct result. In  FIG. 31 , the left source path is conceptually augmented to include interpretation of the Z, SE, and ZE bits by multiplexer  3110 . Based on these bits, the source is used unmodified from the bypass network or physical register file, replaced with a zero, used after sign-extension, or used after zero-extension. 
     Summary of Some Embodiments 
     An embodiment of the invention may include a processor comprising a micro-operation cache including a plurality of entry locations. At least one entry location may include a first field and a second field. The first field may be to store a first micro-operation. The second field may be to store metadata to indicate the elimination of a second micro-operation from a stream of micro-operations to be decoded from a stream of instructions, where the second micro-operation is to result from a decode of a move instruction. 
     An embodiment of the invention may include a processor comprising a register alias table including a plurality of entries. At least one entry may include a field in which to store one of a zero indicator, a sign-extend indicator, and a zero-extend indicator. The zero indicator is to indicate that a source operand is to be replaced with a zero. The sign-extend indicator is to indicate that the source operand is to be used after sign-extension. The zero-extend indicator is to indicate that the source operand is to be used after zero-extension. 
     Virtual Register Renaming 
     A processor core may support a virtual register renaming feature according to embodiments. In some embodiments, a 256 bit operand ymmi may be stored in a 128 bit register file. The upper half of the 256 bit operand may be stored in the 128 bit register file as 128 bit operand ymmihigh. The lower half of the 256 bit operand may be stored in the 128 bit register file as the 128 bit operand xmmi (ymmilow) by virtually renaming the lower half of the 256 bit operand. In some embodiments, this feature advantageously allows for implementing a wider ISA on a smaller physical register by renaming halves of the instruction. In some embodiments, use of smaller physical registers improves the computer system by providing more flexibility, power savings, and better performance because, for example, portions of the instructions can be accessed individually. In some embodiments, other sizes of instructions and registers may be used (e.g., 512 bit operands with 256 bit registers). In some embodiments, operands may be divided into smaller pieces, e.g., thirds, quarters, eighths, sixteenths. For example, the virtual register renaming feature could, for example, be used to remain a 512 bit operand as eight parts to be stored in a 64 bit register file. 
       FIG. 32  is a block diagram illustrating a virtual register renaming feature that may be included in a processor according to embodiments. The virtual register renaming feature may comprise an operand  3201  such as a 256 bit operand ymmi. The virtual register renaming feature may further comprise a 128 bit register file  3201 . The 256 bit operand ymmi  3201  may be stored in a 128 bit register file  3202 . The upper half of the 256-bit operand  3201  may be stored in the 128 bit register file  3202  as 128 bit operand ymmihigh. The lower half of the 256 bit operand  3201  may be stored in the 128 bit register file  3202  as the 128 bit operand xmmi (ymmilow) by virtually renaming the lower half of the 256 bit operand. 
       FIG. 33  is a flow diagram illustrating a method for a virtual register renaming feature that may be performed by a processor according to embodiments. The method comprises storing a lower half of an operand in a register file as shown in  3301 . The method further comprises virtually rename an upper half of the operand as shown in  3302 . The method further comprises storing the virtually renamed upper half of the operand in the register file. In further embodiments, other modifications are possible. For example, the lower have of the operand may be virtually renamed instead of or in addition to virtually renaming the upper half. Additionally, the operations may be performed in different orders. For example, the storing of the non-virtually renamed half may be performed before or after the virtual renaming and/or storing of the virtually renamed half. Additionally, the virtually renamed half may be virtually renamed and then stored or vice-versa. 
     Summary of Some Embodiments 
     An embodiment may include a processor configured to store a first half of an operand in a register file; virtually rename a second half of the operand; and store the virtually renamed second half of the operand in the register file. In some embodiments, one or more of the following apply. The operand may be a 256 bit operand. The register file may be a 128 bit register file. 
     An embodiment may include a method comprising storing a first half of an operand in a register file; virtually renaming a second half of the operand; storing the virtually renamed second half of the operand in the register file. In some embodiments, one or more of the following apply. The operand may be a 256 bit operand. The register file may be a 128 bit register file. 
     An embodiment may include a non-transitory machine-readable medium storing at least one instruction which when executed by a processor causes the processor to perform a method, the method comprising storing a first half of an operand in a register file; virtually renaming a second half of the operand; storing the virtually renamed second half of the operand in the register file. In some embodiments, one or more of the following apply. The operand may be a 256 bit operand. The register file may be a 128 bit register file. 
     An embodiment may include a system including a memory and a processor, the processor configured to store a first half of an operand in a register file; virtually rename a second half of the operand; and store the virtually renamed second half of the operand in the register file. In some embodiments, one or more of the following apply. The operand may be a 256 bit operand. The register file may be a 128 bit register file. 
     FMA Fission and Fusion 
     A processor core may support fission and fusion of multiply-add instructions and operations according to embodiments of the invention. In various embodiments, a processor core may support an instruction set having any one or more add, multiply, fused multiply-add (FMAD), and/or fused multiply-accumulate (FMAC) instructions (where FMAD and/or FMAC may be referred to as FMA) to operate on FP values. Such a core may include any one or more of an adder circuit, a multiplier circuit, and/or an FMA circuit to perform FP add, multiply, and/or FMA operations in response to these instructions. Separate instructions and/or circuitry may be provided to operate on integer values (e.g., FMAC) and FP values (e.g., FMAD), and embodiments may be described with reference to one or the other (integer or FP); however, various embodiments of the invention may include either or both. 
     Embodiments of the invention provide for converting FMA instructions/operations into pairs of add and multiply instructions/operations (fission) and/or converting pairs of add and multiply instructions/operations into FMA instructions/operations (fusion) between and/or within various stages in an instruction issue/execution pipeline. This feature may be generally referred to as FMA fission/fusion or dynamic FMA fission/fusion. 
     Embodiments of the invention including FMA fission/fusion may be desired for many reasons, including: providing the capability to execute FMA instructions and/or perform FMA operations in a core having an adder circuit and a multiplier circuit, but no FMA circuit; providing the capability to execute a multiply instruction and an add instruction using an FMA operation to increase throughput through one or more core resources; providing the capability to dynamically split FMA instructions or operations into multiply operations and add operations to reduce the critical path in a loop and increase the instructions per cycle; and providing the possibility of optimizing, on a stage-by-stage basis, an FMA-capable pipeline for a desired combination of performance, complexity, and power (e.g., increasing performance, decreasing power consumption and implementing power-saving features, and improving fairness, minimum performance guarantees, throughput, instructions per clock (IPC), instructions per unit time, quality of service, time and/or memory efficiency, to list just a few of the applicable criteria). 
       FIG. 34  is a block diagram illustrating an issue/execution pipeline  3400  that may be implemented in a processor core supporting an FMA fission/fusion feature according to embodiments of the invention. In  FIG. 34 , pipeline  3400  includes instruction fetch stage  3401 , instruction decode stage  3402 , rename/allocate stage  3403 , schedule stage  3404 , execute stage  3405 , and retire/commit stage  3406 . Pipeline  3400  is provided for illustrative purposes, and may be implemented and/or modified in a variety of ways in various embodiments of the invention. Therefore, the following description of pipeline  3400  may refer to various blocks shown in other figures described in this specification. 
     For example, instruction fetch stage  3401  may include using an instruction fetch circuit (e.g.,  138 ,  400 ) to identify (e.g., using next-PC register  410 ) an instruction or the memory location of an instruction to be fetched and to fetch the instruction from an i-cache (e.g.,  134 ,  313 ,  470 ,  913 ) or other memory location; instruction decode stage  3402  may include using an instruction decode circuit (e.g.,  140 ,  314 ,  500 ,  914 ) to decode (e.g., using decoder  530 ) the instruction; rename/allocate stage  3403  may include using a rename/allocator circuit (e.g.,  152 ,  331 ,  931 ) to rename register operands and/or to allocate storage locations and/or tags for register renaming; schedule stage  3404  may include using a scheduler circuit (e.g.,  156 ,  332 ,  932 ) to schedule operations and/or micro-ops (e.g., from decoder  140 ,  314 ,  530 , or  614  or micro-op cache  133 ,  312 ,  540 , or  912 ) associated with the instruction for execution; execute stage  3405  may include using an execute circuit (e.g.,  162 ,  334 ,  335 ,  770 ,  780 ,  934 ,  935 ) to execute operations and/or micro-ops (e.g., from decoder  140 ,  314 ,  530 , or  614  or micro-op cache  133 ,  312 ,  540 , or  912 ) associated with the instruction; and retire/commit stage  3406  may include using a retirement circuit (e.g.,  154 ,  730 ,  960 ) to retire the instruction and/or commit its result to a physical register file (e.g.,  158 ,  333 ,  750 ,  933 ) or memory. Each stage shown in  FIG. 34  may represent one or more stages and/or clock cycles in various embodiments. 
       FIG. 34  also shows fused path  3410  and split path  3420 , each representing an embodiment of a path through pipeline  3400 . Fused path  3410  may include circuits, structures, and/or hardware to process, perform, and/or execute an FMA instruction, operation, and/or micro-op as a fused instruction, operation, and/or micro-op, as described using illustrative embodiments below. Split path  3420  may include circuits, structures, and/or hardware to process, perform, and/or execute a multiply and an add instruction, operation, and/or micro-op as separate instructions, operations, and/or micro-ops, as described using illustrative embodiments below. Furthermore, split path  3420  may include circuits, structures, and/or hardware to process, perform, and/or execute an FMA instruction, operation, and/or micro-op as a multiply and an add instruction, operation, and/or micro-op; and fused path  3410  may include circuits, structures, and/or hardware to process, perform, and/or execute a multiply and an add instruction, operation, and/or micro-op as a fused instruction, operation, and/or micro-op. 
     Therefore,  FIG. 34  conceptually illustrates a set of core resources that may be used to process, perform, and/or execute fused and/or separate multiply and add instructions, operations, and micro-operations. Various embodiments may include various subsets of these resources to support various capabilities, as will be further described below. Also, implementations may include various additional resources not shown in  FIG. 34  that may be provided and/or configured to practice various embodiments of the invention. 
       FIG. 34  also shows FMA fission/fusion controller  3430 , which may represent a programmable, configurable, or hardwired controller or control structure, including one or more control circuits and/or software programmable or hardware configuration registers to generate control signals to direct the flow of instructions, operations, micro-ops, operands, values, and/or other data through and/or between fused path  3410  and/or split path  3420 . These control signals may provide for one or more paths through pipeline  3400  that include a combination of resources in fused path  3410  and split path  3420 . These control signals may provide for dynamic FMA fission/fusion by causing an FMA instruction, operation, and/or micro-op to be processed, performed, and/or executed as a fused instruction, operation, and/or micro-op in response to a first condition and as separate multiply and add instructions, operations, and/or micro-ops in response to a second condition and/or by causing separate multiply and add instructions, operations, and/or micro-ops to be processed, performed, and/or executed as a fused instruction, operation, and/or micro-op in response to a third condition and as separate multiply and add instructions, operations, and/or micro-ops in response to a fourth condition. 
     For example, an FMA instruction may be fetched by hardware in fused path  3410 , and controller  3430  may generate one or more control signals to route the instruction to hardware in split path  3420  to decode the instruction into two separate micro-ops, a multiply micro-op and an add micro-op. Although shown as an independent block in  FIG. 34 , in various embodiments controller  3430  may be integrated or included within another control structure in a processor core or may be omitted entirely (e.g., in an embodiment in which the core provides only one possible path, examples of which are described below). 
     In  FIG. 34 , fused path  3410  includes fetcher  3411 , decoder  3412 , renamer  3413 , scheduler  3414 , fused multiply-adder  3415 , and re-order buffer/retire queue (ROB/RQ)  3416 ; and split path  3420  includes fetcher  3421 , decoder  3422 , renamer  3423 , scheduler  3424 , multiplier  3425 A and adder  3425 B, and re-order buffer/retire queue (ROB/RQ)  3426 . 
     Fetcher  3411  may include circuitry and/or structures to fetch an FMA instruction (e.g., an AVX (as defined below) instruction such as VFMADD132PS, VFMADD213PS, VFMADD231PS, VFMADD132PD, VFMADD213PD, VFMADD231PD, VFMADD132SS, VFMADD213SS, VFMADD231SS, VFMADD132SD, VFMADD213SD, VFMADD231SD, VFMSUB132PS, VFMSUB213PS, VFMSUB231PS, VFMSUB132PD, VFMSUB213PD, VFMSUB231PD, VFMSUB132SS, VFMSUB213SS, VFMSUB231SS, VFMSUB132SD, VFMSUB213SD, VFMSUB231SD, VFNMADD132PS, VFNMADD213PS, VFNMADD231PS, VFNMADD132PD, VFNMADD213PD, VFNMADD231PD, VFNMADD132SS, VFNMADD213SS, VFNMADD231SS, VFNMADD132SD, VFNMADD213SD, VFNMADD231SD, VFNMSUB132PS, VFNMSUB213PS, VFNMSUB231PS, VFNMSUB132PD, VFNMSUB213PD, VFNMSUB231PD, VFNMSUB 132SS, VFNMSUB213SS, VFNMSUB231SS, VFNMSUB132SD, VFNMSUB213SD, VFNMSUB231SD, VFMADDSUB132PS, VFMADDSUB213PS, VFMADDSUB231PS, VFMADDSUB132PD, VFMADDSUB213PD, VFMADDSUB231PD, VFMSUBADD132PS, VFMSUBADD213PS, VFMSUBADD231PS, VFMSUBADD132PD, VFMSUBADD213PD, or VFMSUBADD231PD). 
     An FMA instruction fetched by fetcher  3411  may have three operands. For example, a VFMADD231PS instruction may have a first operand (xmm1 or ymm1), a second operand (xmm2 or ymm2), and a third operand (xmm3 or ymm3), where xmm and ymm registers that may be specified by these operands are described below. These registers may hold scalar or packed values, and for a convenient description of an embodiment, the letter ‘d’ may be used to refer to the source/destination register or a portion of the register specified by the xmm1 operand and/or a value stored or to be stored in this register or a portion of this register; the letter ‘a’ may be used to refer to the source register or a portion of the register specified by the xmm2 operand and/or a value stored or to be stored in this register or a portion of this register; and the letter ‘b’ may be used to refer to the source register or a portion of the specified by the xmm3 operand and/or a value stored or to be stored in this register or a portion of this register. Therefore, a conceptual representation of an operation to be performed in response to a VFMADD231PS instruction, where a, b, and d may also be referred to as operands, is d=a*b+d. Furthermore, although this description refers to operands as registers, embodiments may use memory locations instead of registers for any or all operands. 
     Fetcher  3421  may include circuitry, structures, and/or hardware to fetch a multiply instruction (e.g., an SSE (streaming single-instruction-multiple-data extension) instruction such as MULPS, MULPD, MULSS, or MULSD) and an add instruction (e.g., an SSE instruction such as ADDPS, ADDPD, ADDSS, or ADDSD), each having two operands For example, a MULPS instruction may have a first operand (xmm1) and a second operand (xmm2), and an ADDPS instruction may have a first operand (xmm1) and a second operand (xmm2), where, in general, each of the MULPS xmm1, MULPS xmm2, ADDPS xmm1, and ADDPS xmm2 operands may be different registers. However, in an embodiment of the invention, fetcher  3421  may pair a MULPS instruction with an ADDPS instruction when it is determined that the ADDPS instruction depends on the MULPS instruction (i.e., the MULPS result is an input to the ADDPS). For example, with ‘a’ as the MULPS xmm1 operand and ‘b’ as the MULPS xmm2 operand, the corresponding multiply operation a=a*b, and if a is next used as an ADDPS xmm2 operand, with ‘d’ as the ADDPS xmm1 operand, the corresponding add operation is d=d+a, and fetcher  3421  may pair the MULPS and ADDPS instructions. In embodiments, the pairing and/or determining whether the condition for pairing is satisfied may be performed in response to a control signal from controller  3430 . 
     Fetcher  3411  may be coupled or connected, as represented by arrow  3432 A, to decoder  3412  and/or, as represented by arrow  3432 B, to decoder  3422 . Fetcher  3421  may be coupled or connected, as represented by arrow  3432 C, to decoder  3412  and/or, as represented by arrow  3432 D, to decoder  3422 . The coupling or connecting and/or the decoder operation may be static (e.g., hardwired) or dynamic (e.g., depending on control signals from  3430 ) in various embodiments. 
     Decoder  3412  may include circuitry, structures, and/or hardware to decode an FMA instruction, received from fetcher  3411 , into an FMA micro-op having three operands (e.g., d, a, and b). Instead or additionally, decoder  3412  may include circuitry, structures, and/or hardware to decode a paired multiply and add instruction, received from fetcher  3421 , into an FMA micro-op having three operands (e.g., d, a, and b). 
     Decoder  3422  may include circuitry, structures, and/or hardware to decode an FMA instruction, received from fetcher  3411 , into a multiply micro-op having two operands and an add micro-op having two operands. Instead or additionally, decoder  3422  may include circuitry, structures, and/or hardware to decode a paired multiply and add instruction from fetcher  3421  into a multiply micro-op having two operands and an add micro-op having two operands. For example, the multiply micro-op may be represented as t=a*b and the add micro-op as d=d+t, where a new operand ‘t’ may be introduced to serve as the destination of the multiply operation and a source for the add operation. 
     Decoder  3412  may be coupled or connected, as represented by arrow  3433 A, to renamer  3413  and/or, as represented by arrow  3433 B, to renamer  3423 . Decoder  3422  may be coupled or connected, as represented by arrow  3433 C, to renamer  3413  and/or, as represented by arrow  3433 D, to renamer  3423 . The coupling or connecting and/or the renamer operation may be static (e.g., hardwired) or dynamic (e.g., depending on control signals from  3430 ) in various embodiments. 
     Renamers  3413  and/or  3423  may include circuitry, structures, and/or hardware, such as a re-order buffer, to rename register operands and/or to allocate storage locations and/or tags for register renaming, for example to accommodate out-of-order processing. In embodiments, to eliminate register conflicts (e.g., for a, b, t, and/or d), renamer  3413  may rename operands for the FMA operation (e.g., as a′, b′, and/or d′); and/or renamer  3423  may rename operands for the multiply operation (e.g., as a′ and/or b′) and for the add operation (e.g., as t′ and/or d′). 
     Renamer  3413  may be coupled or connected, as represented by arrow  3434 A, to scheduler  3414 , and/or, as represented by arrow  3434 B, to scheduler  3424 . Renamer  3423  may be coupled or connected, as represented by arrow  3434 C, to scheduler  3414  and/or, as represented by arrow  3434 D, to scheduler  3424 . The coupling or connecting and/or the scheduler operation may be static (e.g., hardwired) or dynamic (e.g., depending on control signals from  3430 ) in various embodiments. 
     Schedulers  3414  and/or  3424  may include circuitry, structures, and/or hardware, such as a reservation station, to schedule operations and/or micro-ops for execution. In embodiments, scheduler  3414  may schedule, in a reservation station for an FP execution circuit, an FMA operation to be executed with the operands a, b, and d, and/or scheduler  3424  may schedule, in a reservation station for an FP execution circuit, a multiply operation to be executed with the operands a and b and an add operation to be executed with the operands t and d. 
     Scheduler  3414  may be coupled or connected, as represented by arrow  3435 A, to fused multiply/adder  3415 , and/or, as represented by arrow  3435 B, to multiplier  3425 A or both multiplier  3425 A and adder  3425 B. Scheduler  3424  may be coupled or connected, as represented by arrow  3434 C, to fused multiply/adder  3415 , and/or, as represented by arrow  3434 D, to multiplier  3425 A or both multiplier  3425 A and adder  3425 B. The coupling or connecting and/or the scheduler operation may be static (e.g., hardwired) or dynamic (e.g., depending on control signals from  3430 ) in various embodiments. 
     Fused multiply/adder  3415 , multiplier  3425 A, and adder  3425 B may include circuitry, structures, and/or hardware to perform a fused-multiply-add operation, a multiply operation, and an add operation, respectively. In an embodiment, multiplier  3425 A may be coupled to a reservation station to receive two inputs (e.g., a and b) for a multiply operation and coupled to adder  3425 B to provide its output (e.g., t) to be used as one of two inputs (e.g., t and d) for an add operation. In this embodiment, the precision of a dedicated fused multiply-adder (e.g., according to IEEE standard 754) may be obtained by sending the unrounded multiply result to the adder. In another embodiment, multiplier  3425 A may be coupled to a reservation station to receive two inputs (e.g., a and b) for a multiply operation that generates an output (e.g., t), and adder  3425 A may be coupled to the reservation station to receive two inputs for an add operation (e.g., t and d). In this embodiment, the precision of a dedicated fused multiply-adder may be obtained by increasing the width of the internal storage locations for the intermediate result (e.g., t) or by using a microcode assist or trap to provide special handling. 
     Fused multiply-adder  3415  may be coupled or connected, as represented by arrow  3436 A, to ROB/RQ  3416 , and/or, as represented by arrow  3436 B, to ROB/RQ  3426 . Adder  3425 B may be coupled or connected, as represented by arrow  3436 C, to ROB/RQ  3416 , and/or, adder  3425 B or both multiplier  3425 A and adder  3425 B may be coupled or connected, as represented by arrow  3436 D, to ROB/RQ  3426 . The coupling or connecting and/or the scheduler operation may be static (e.g., hardwired) or dynamic (e.g., depending on control signals from  3430 ) in various embodiments. 
     ROB/RQ  3416  and/or ROB/RQ  3426  may include circuitry, structures, and/or hardware, such as a re-order buffer and/or a retirement queue, to retire instructions and/or commit results. In an embodiment, ROB/RQ  3416  may retire an FMA instruction and commit its result (e.g., xmm1). In an embodiment, ROB/RQ  3426  may retire a multiply instruction and an add instruction and commit their results (e.g., MULPS xmm1, ADDPS xmm1, respectively). In an embodiment, ROB/RQ  3416  may commit the result of an FMA operation that has been created by fusion of a separate multiply and a separate add instruction, so long as the result of the separate multiply operation is not desired (e.g., expected according to the instruction set architecture). In an embodiment, ROB/RQ  3426  may commit, as the result of an FMA instruction, the result of an add operation that has been created by fission of the FMA instruction. In a processor core according to embodiments of the invention, the result of the add instruction will be the same as the result of a corresponding FMA instruction. 
     As illustrated in  FIG. 34 , embodiments may provide for FMA fission or fusion at various stages of an issue/execution pipeline. In an embodiment, fission at decode stage  3402  may provide for fused multiply-add instructions to be executed in a core without a dedicated fused multiply-adder. In an embodiment, fusion at decode stage  3402 , rename/allocate stage  3403 , schedule stage  3404 , execute stage  3405 , and/or retire stage  3406  may provide for greater throughput through hardware resources (one instruction/operation/micro-op instead of two instructions/operations/micro-ops). In an embodiment, fission at rename/allocate stage  3403  may provide for reduced complexity in the renaming hardware by restricting the number of operands to two instead of three. In an embodiment, fusion at rename/allocate stage  3403  and/or schedule stage  3404  may provide for the use of fewer entries in renaming, re-ordering, and/or scheduling storage to allow deeper out-of-order execution windows and/or the discovery of greater instruction level parallelism. In an embodiment, fission at schedule stage  3404  nay provide for reduced hardware complexity by limiting the number of out-of-order wake-up sources to two per entry instead of three. In an embodiment, fission at schedule stage  3404  and/or execution stage  3405  may provide for reduced latency by allowing separate parts of an FMA operation to execute at different times to limit the critical path to that of the slowest part instead of the sum of the two parts. In an embodiment, fusion at execution stage  3405  may provide for increased performance, increased precision, and/or reduced power by using a dedicated fused multiply-adder. 
       FIG. 35  is a flow diagram illustrating a method for FMA fission/fusion that may be performed by a processor according to embodiments of the invention. In block  3510  of method  3500  of  FIG. 35 , an instruction fetch circuit (e.g.,  138 ,  400 ) may fetch an instruction from an i-cache (e.g.,  134 ,  313 ,  470 ,  913 ) or other memory location. For example, the instruction may be an instance of an FMA instruction such as VFMADD231PS, having a first operand (‘d’), a second operand (a′), and a third operand (‘b’), to which a processor is to respond by performing an FMA operation (e.g., d=a*b+d). 
     In block  3520 , an instruction decode circuit or decoder (e.g.,  140 ,  314 ,  500 ,  914 ) that is hardwired, configured, or programmed to perform fission of FMA instructions may decode the instruction into multiple separate micro-ops, a multiply micro-op and an add micro-op. The decoder may select particular operands from the FMA instruction and/or from another micro-op, assign one or more of them to one or more of the separate micro-ops, and/or create new operands for one or more of the separate micro-ops. For example, the decoder may select the FMA instruction&#39;s ‘a’ and ‘b’ operands as source operands for a multiply micro-op and create a ‘t’ operand as the destination operand for the multiply micro-op, to which the processor is to respond by performing the multiply operation t=a*b; and the decoder may select the FMA instruction&#39;s ‘d’ operands and the multiply micro-op&#39;s ‘t’ operand as source operands for an add micro-op and select the FMA instruction&#39;s ‘d’ operand as the destination operand for the add micro-op, to which the processor is to respond by performing the add operation d=d*t. 
     In block  3530 , a register renaming circuit (e.g.,  152 ,  331 ,  931 ) may rename any of the operands, allocate storage locations and/or tags for register renaming (e.g., in a re-order buffer) and/or implement the assignment of the output of the multiply micro-op (e.g., ‘t’) as an input to the add micro-op. 
     In block  3540 , a scheduler circuit (e.g.,  156 ,  332 ,  932 ) may schedule the separate micro-ops for execution, e.g., in a reservation station for an FP unit. In an embodiment, multiple separate micro-ops decoded from the same instance of an instruction (e.g., a multiply and an add micro-op decoded from an FMA instruction) may be scheduled in a reservation station for dispatch in a specified order (e.g., the add micro-op may be scheduled for dispatch only after dispatch and/or completion of the multiple micro-op). 
     In block  3550 , an execute circuit (e.g.,  162 ,  334 ,  770 ,  934 ) may execute one of the separate micro-ops. For example, FP multiplier  334 A,  334 B,  770 A,  770 B,  934 A, or  934 B may execute the multiply micro-op. 
     In block  3552 , an execute circuit (e.g.,  162 ,  335 ,  780 ,  935 ) may execute the other of the separate micro-ops. For example, FP adder  335 A,  335 B,  780 A,  780 B,  935 A, or  935 B may execute the add micro-op. 
     In block  3560 , a retirement circuit (e.g.,  154 ,  730 ,  960 ) may retire the instruction and/or commit its result to a physical register file (e.g.,  158 ,  333 ,  750 ,  933 ) or memory. In an embodiment, block  3560  may include retirement of only one of the separate micro-ops decoded from an instruction. For example, an FMA instruction may be retired and/or its result committed by retiring a corresponding add micro-op from a re-order buffer and committing its result (e.g., d). 
     Summary of Some Embodiments 
     An embodiment of the invention may include a processor comprising a plurality of circuits arranged in a pipeline. The plurality of circuits may include a decoder to decode a fused multiply-add instruction into at least two separate micro-operations. The plurality of circuits may also include a multiplier to operate on a first of the two separate micro-operations and an adder to operate on a second of the two separate micro-operations. 
     Specific Processor Architectures 
       FIG. 36  is a block diagram of a processor  3600  that may have more than one core, may have an integrated memory controller, and may have integrated graphics according to embodiments of the invention. The solid lined boxes in  FIG. 36  illustrate a processor  3600  with a single core  3602 A, a system agent  3610 , a set of one or more bus controller units  3616 , while the optional addition of the dashed lined boxes illustrates an alternative processor  3600  with multiple cores  3602 A-N, a set of one or more integrated memory controller unit(s)  3614  in the system agent unit  3610 , and special purpose logic  3608 . 
     Thus, different implementations of the processor  3600  may include: 1) a CPU with the special purpose logic  3608  being integrated graphics and/or scientific (throughput) logic (which may include one or more cores), and the cores  3602 A-N being one or more general purpose cores (e.g., general purpose in-order cores, general purpose out-of-order cores, a combination of the two); 2) a coprocessor with the cores  3602 A-N being a large number of special purpose cores intended primarily for graphics and/or scientific (throughput); and 3) a coprocessor with the cores  3602 A-N being a large number of general purpose in-order cores. Thus, the processor  3600  may be a general-purpose processors, server processors or processing elements for use in a server-environment, coprocessors (e.g., security coprocessors) high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device. The processor may be implemented on one or more chips. The processor  3600  may be a part of and/or may be implemented on one or more substrates using any of a number of process technologies, such as, for example, BiCMOS, CMOS, or NMOS. 
     The memory hierarchy includes one or more levels of cache within the cores, a set or one or more shared cache units  3606 , and external memory (not shown) coupled to the set of integrated memory controller units  3614 . The set of shared cache units  3606  may include one or more mid-level caches, such as level 2 (L2), level 3 (L3), level 4 (L4), or other levels of cache, a last level cache (LLC), and/or combinations thereof. While in one embodiment a ring based interconnect unit  3612  interconnects the integrated graphics logic  3608  (integrated graphics logic  3608  is an example of and is also referred to herein as special purpose logic), the set of shared cache units  3606 , and the system agent unit  3610 /integrated memory controller unit(s)  3614 , alternative embodiments may use any number of well-known techniques for interconnecting such units. In one embodiment, coherency is maintained between one or more cache units  3606  and cores  3602 -A-N. 
     In some embodiments, one or more of the cores  3602 A-N are capable of multi-threading. The system agent  3610  includes those components coordinating and operating cores  3602 A-N. The system agent unit  3610  may include for example a power control unit (PCU) and a display unit. The PCU may be or include logic and components needed for regulating the power state of the cores  3602 A-N and the integrated graphics logic  3608 . The display unit is for driving one or more externally connected displays. 
     The cores  3602 A-N may be homogenous or heterogeneous in terms of architecture instruction set; that is, two or more of the cores  3602 A-N may be capable of execution the same instruction set, while others may be capable of executing only a subset of that instruction set or a different instruction set. 
       FIG. 37  is a block diagram of an illustrative central processing unit (CPU) complex that may be included in a processor according to embodiments of the invention. In an embodiment, the L3 cache is an 8 MB 16-way cache split over a four-core module (referred to as a CPU complex or CCX), affording a 2 MB “slice” of L3 cache per core. However, the L3 cache slices in a CCX are implemented such that the L3 cache is a shared cache. Multiple CCXs may be included in a single processor (e.g., two CCXs form a 16 MB L3 cache). The 8 MB caches on each CCX are separate, so they act as a last level cache per four-core module with the appropriate hooks into the other L3 cache to determine if data is needed (the protocols involved in the L3 cache design allow each core to access the L3 cache of each other core). Thus, these L1, L2, and L3 caches are coherent caches, with the L3 cache slices within a CCX and between CCXs being connected by a cache coherent interconnect (also referred to as a cache coherent fabric). 
       FIG. 38  is a block diagram of an illustrative cache hierarchy that may be included in a processor according to embodiments of the invention. In  FIG. 38 , cache hierarchy  3800  includes L1 i-cache  3810 A and L1 d-cache  3810 B (collectively, L1 cache  3810 ), L2 instruction and date cache  3820 , and level 3 (L3) instruction and data cache  3830 . In an embodiment, both L1 cache  3810  and L2 cache  3820  are private/local writeback caches, while L3 cache  3830  is a victim cache. In an embodiment, L1 i-cache  3810 A is a 64 KB 4-way cache, L1 d-cache  3810 B is a 32 KB 8-way cache, L2 cache  3820  is a 512 KB 8-way cache, and level 3 (L3) cache  3830  is an 8 MB 16-way cache. 
     Memory Organization Features 
     Processor cores, processors, and systems according to embodiments of the invention may include various features related to the organization and use of memory. A number of such features are described separately using non-limiting examples below, but embodiments may include any combination of such features. 
     Cache Line Zeroing 
     Some embodiments include an instruction whose execution causes a cache line sized write of zeros at a memory address. Such an instruction may be referred to as a cache line zeroing instruction, CLZERO instruction, CLZEROING instruction, cache line initialization instruction, CLINIT instruction, etc. In one embodiment, the cache line zeroing instruction is a macro-instruction executed by a core, such as core  190  and/or core  5300 . Specifically, the decoder  140  and/or the decoder  5314  would be implemented to decode such a macro-instruction into one or more relatively lower-level instructions or control signals (e.g., one or more microinstructions, micro-operations (micro-ops), micro-code entry points, decoded instructions or control signals) that cause the memory access unit(s)  164  and/or the address generation unit(s)  325 /load-store unit  340 , respectively, to perform the operation. 
     A cache line zeroing instruction has the advantage of being a faster and more deterministic way to zero a cache line because it does not need to use a request for ownership (RFO) operation or at least does not need the data back or returned. An RFO operation is an operation in cache coherency protocols that combines a read and an invalidate broadcast (a read operation with intent to write to that memory address), and thus causes all other coherent caches to set the state of such a cache line to the cache coherency protocol state of “invalid.” For example, an RFO operation is typically issued by a processor trying to write into a cache line that is in the shared (S) or invalid (I) states of the MESI protocol. The MESI protocol uses the cache coherency protocol states of “modified,” “exclusive,” “shared,” and “invalid.” In contrast, an implementation of a cache line zeroing instruction does not require that a line be read and returned to the issuing agent because it is zeroing the data; in fact, in some embodiments, the issuing agent does not have to have ownership of the data. 
     Different embodiments may implement the cache line zeroing instruction to indicate a memory address in different ways. For example, the cache line zeroing instruction may be implemented to indicate address information explicitly (e.g., via an immediate, one or more fields), indirectly (e.g., by specifying one or more registers in which address information is stored), and/or implicitly (e.g., one or more designated registers). The memory address information may be a memory address or be information used in combination with other information (e.g., information from a segment register, etc.) to generate a memory address. While in some embodiments the memory address is aligned on a cache line boundary, alternative embodiments may also support the memory address being between cache line boundaries and treated as indicating the cache line between those boundaries. The address information may either represent absolute memory address information or relative memory address information, which may indicate a memory location relative to a base memory address or other memory location. In addition, different indirect memory addressing modes may optionally be used. As one specific example, the instruction may implicitly indicate a register (e.g., a general-purpose register) that is used to store relative memory address information that may be combined with additional memory address information stored in another implicit register (e.g., a code, data, or extended segment register) to generate the final memory address used to identify the memory address. This is just one example. Other forms of the address information are also possible. 
     Different embodiments may implement different sized cache lines (e.g., 32 bytes, 64 bytes) and/or a given embodiment may implement more than one cache line size. For example, embodiments may support a cache line zeroing instruction that is: 1) implemented for a specific cache line size (and thus it does not need to designate a cache line size); 2) implemented to use a current cache size where different types of cores have different cache line sizes (e.g., the current cache size may be indicated via a value in a register); or 3) implemented to have a field to indicate a cache line size. In some embodiments, the instruction allows for the indication of a size parameter that indicates one or more cache lines (i.e., a multiple of a cache line size). In some embodiments, there is additionally or instead, a ZERO instruction that allows for the indication of a size parameter that is not be tied to a cache line size (e.g. just indicates a #of bytes) as this enables software to be unaware of the cache line size (if the size is not a multiple of a cache line size (e.g. specified in bytes and the #of bytes is 112 even though cache line size is 64 bytes), embodiments could either zero up to the cache line or issue an RFO for just the remaining data in that last line). 
     In some embodiments, the cache line zeroing instruction is atomic. Thus, either the entire cache line of zeros will be stored in its entirety, or none of it, not just a portion (i.e., a completion atomicity guaranty). The atomicity may also guarantee that the zeros written by a cache line zeroing instruction will not be interleaved with data stored by other stores. The atomicity may be with respect to other accesses so that any such accesses will either observe all of the data stored in its entirety, or none of the data stored, but not just a portion. The atomicity may also be with respect to a power failure, system crash, reboot, or other such event, so that even in the face of such events, either all the zeros are stored, or none of the zeros are stored, not just a portion. There are various possible uses of such an atomic operation. One example of such a use is to atomically update a piece of data in a database. Another example of such a use is to atomically update a piece of shared data in a multi-processing environment. Yet another example of such a use is to atomically store data to a location to replace a lock, a semaphore, to update a shared variable, to synchronize, to coordinate, or the like. Still other uses of such an atomic store operation are contemplated and will be apparent to those skilled in the art and having the benefit of the present disclosure. 
     Exemplary Memory Hierarchies 
       FIG. 39  is a block diagram illustrating a memory hierarchy within which a cache line zeroing instruction may be implemented according to embodiments of the invention. The illustrated memory hierarchy can be implemented in conjunction with various processor cores, core clusters, CCXs, processors, computer architectures, etc. By way of specific embodiments, an implementation of the cache zeroing instruction will be described with reference to the memory hierarchy of  FIG. 39  in conjunction with the core/CCX of  FIGS. 3, 8, 38, and 37 . This is for illustrative purposes, and the cache zeroing instruction may be implemented in different memory hierarchies and/or in conjunction with different cores, core clusters, etc. 
       FIG. 39  illustrates a coherent agent  3900  and a coherent agent  3901 , as well as the possibility of other coherent agents as represented by “ . . . ” and coherent agent  3902  using a dashed box. The memory hierarchy in  FIG. 39  includes coherent caches  3904 A, an interconnect  3920 , and downstream memory  3930 . Different embodiments may implement different numbers of caches and cache levels as part of coherent caches  3904 A. The coherent agents and the coherent caches are part of a cache coherence domain within which cache coherency is maintained using a cache coherency protocol (e.g., the MESI protocol which uses the cache coherency protocol states of “modified,” “exclusive,” “shared,” and “invalid”; the MESIF protocol which adds the cache coherency protocol state of “forward”; the MOESI protocol which instead adds the cache coherency protocol state of “Owned”; and other such cache coherency protocols). 
     The coherent agent  3900  is coupled to the interconnect  3920  through one or more caches at successively lower levels of a cache hierarchy. A cache hierarchy includes a cache that is at the highest level of the cache hierarchy and that is coupled to the coherent agent  3900 , a cache (e.g., an L3 cache  3915 ) that is at a lowest level of the cache hierarchy and that is coupled to the interconnect  3920  (and thus, this cache is referred to as the lowest level cache or last level cache (LLC)), and zero or more caches (e.g., an L2 cache  3910 ) that are at mid-level(s) of the cache hierarchy coupled to one of the caches at a higher level and one of the caches at a lower level (e.g.,  FIG. 39  illustrates the coherent agent  3900  coupled to L1 cache  3905 , which is coupled to L2 cache  3910 , which is coupled to L3 cache  3915 , which is coupled to the interconnect  3920 ). 
     The coherent agent  3901  is also coupled to the interconnect through one or more levels of caches.  FIG. 39  illustrates the coherent agent  3901  coupled to an optional L1 cache  3906 , which is coupled to an optional L2 cache  3911 , which is coupled to the L3 cache  3915 . In addition,  FIG. 3902  also illustrates that optional coherent agent  3902  may be coupled directly to the interconnect  3920  (i.e., no have any coherent caches). 
     In addition to or in lieu of the connectivity including the coherent agents being coupled to the interconnect  3920  through successive levels of caches, certain embodiments implement other connectivity to allow for direct or more direct communication (e.g., couple the coherent agent  3900  directly to the interconnect  3920 , couple the coherent agent  3900  directly to the L2 cache  3910 , couple the L1 cache  3905  directly to the interconnect  3920 , and/or couple the L2 cache  3910  directly to the interconnect  3920  as respectively illustrated by dashed lines  3935 ,  3936 ,  3937 , and  3938 ). 
     The interconnect  3920  is coupled to the downstream memory  3930  (e.g., through a set of one or more memory controllers (not shown)). The downstream memory  3930  is at a lower level of the memory hierarchy than the coherent caches  3904 , and may include one or more types of memory and/or a hierarchy of memories (e.g., volatile memory and/or non-volatile memory, main memory, memory mapped input/output (MMIO), memory-side cache(s), two level memory (2LM), DRAM, flash, phase change memory, 3D Xpoint™). 
     The interconnect  3920  (also referred to as a cache coherent interconnect, a fabric, an interconnect, part of an uncore, interconnect network, interconnect unit(s)) includes a snoop controller  3925  to issue snoops to the coherent caches  3904  and receive any responses therefrom. The snoop controller  3925  includes a snoop generator  3926  to issue snoops, and, in some embodiments, a snoop responder  3927  to receive any responses. In addition, the snoop controller  3925  in certain embodiments includes a write generator  3929  (to effectively generate a cache line sized write of all zeros) and/or a write converter QOS28 (to effectively convert a cache line of data received responsive to a snoop to all zeros). In addition, while in one embodiment the interconnect  3920  is illustrated as being between the L3 cache  3915  and the downstream memory  3930 , alternative embodiments may implement the interconnect  3920  at another location (e.g., between the L2 caches and the L3 cache, with either a set or one or more memory controllers to the downstream memory  3930  off the interconnect  3920  (e.g., as a home agent) or a set or one or more memory controllers between the L3 cache  3915  and the downstream memory  3930 ). The interconnect  3920  (e.g., as part of the snoop controller  3925 ) may include other items, such as a snoop filter (not shown). 
     Different embodiments may be implemented with different numbers of the coherent agents as general purpose cores (also known as central processing units (CPUs)). For example, in some embodiments, the coherent agent  3900  is a core, the coherent agent  391  is a core, there are zero or more additional coherent agents that are cores, and there are zero or more additional coherent agents that are other types of agents (e.g., general-purpose processors, server processors or processing elements for use in a server-environment, coprocessors (e.g., security coprocessors) high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device, to name just a few examples). 
     In some embodiments, the coherent agents and the coherent caches  3904  are implemented as in  FIGS. 38 and 37 . For example, in a CCX, there are 4 coherent agents that are cores, a private/local L1 cache per core, a private/local L2 cache per core, and a shared L3 cache; and there can be multiple CCXs coupled together in a single processor. The L1 and L2 caches are write back caches, the L2 caches are inclusive caches, and the L3 cache is a victim cache. In addition, the L3 cache  3915  is split into slices between multiple coherent agents (e.g., 2 MB per core over 4 cores, totaling 8 MB) within a module (a CCX), and optionally between one or more such modules (e.g., two CCXs, each with 8 MB, to form a 16 MB L3 cache).  FIG. 39  illustrates this with L3 cache slice  3916  of coherent agent  3900  and L3 cache slice  3917  of coherent agent  3901 . The interconnect  3920  may, for example, represent: 1) just an interconnect within a CCX; 2) an interconnect within and between CCXs; 3) separate interconnects within different CCXs, as well as an interconnect(s) between CCXs. Different embodiments may implement the interconnect  3920  differently, including one or more of a ring, multiple rings, point to point links, shared buss(es), etc. In embodiments that implement a home agent and caching agents, the interconnect  3920  is considered to include the caching agents. 
     One or more, or all, of the coherent agents in  FIG. 39  may be implemented to execute a cache line zeroing instruction (see the possible cache line zeroing instruction issuing agent  3903  being identified as any of coherent agent  3900 ,  3901 , and  3902 ). The coherent agent that is currently executing a cache line zeroing instruction is the “issuing agent,” “issuing coherent agent,” or “first agent”, and its caches are referred to as the Lx cache of the issuing agent (where x may be a 1, 2, or 3; and where the L3 cache is implemented with slices, it is the L3 cache slice of the issuing agent). In the discussion below, this will be coherent agent  3900 . A coherent agent that is not currently executing a cache line zeroing instruction is referred to as the “coherent but no issuing agent,” “non-issuing agent,” “non-issuing coherent agent,” or “second agent” (as discussed above, there may be multiple second agents, but one will be discussed below for simplicity), and its caches are referred to as the Lx cache of the second agent (where x may be a 1, 2, or 3; and where the L3 cache is implemented with slices, it is the L3 cache slice of the second agent). In the discussion below, this will be coherent agent  391 . 
     Exemplary Cache Architecture 
       FIG. 40  is a block diagram illustrating a cache in a processor that implements a cache line zeroing instruction according to embodiments of the invention.  FIG. 40  includes a Lx cache  4050 , where x indicates the level in the cache hierarchy (e.g., 1, 2, 3). Lx cache  4050  includes a cache controller  4051  to control the operation of the cache, including detecting hits/misses, causing writes/reads to cache lines, receiving snoops (and thus, in some embodiments the cache controller  4051  includes a snoop interface, and in some embodiments, a snoop controller  4043 ), etc. The cache controller includes a tag array  4055  with entries  4060  (which includes what is sometimes referred to as the “tag state”), and the Lx cache  4050  includes a data array  4056  with corresponding cache lines  4070 . Each of the entries  4060  includes a tag field  4061  to store a tag used to determine whether a given address hits or misses the data in the corresponding one of the cache lines  4070 . In addition, each of the entries  4060  includes a set of one or more attribute field(s)  4062  (sometimes referred to as “tag state”) to store attributes of the data stored in the corresponding one of the cache lines  4070 . The attribute field(s)  4062  include a cache coherency protocol state field  4065  to store a value indicating a current cache coherency protocol state of the data stored in the corresponding one of the cache lines  4070 . The attribute field(s)  4062  may optionally include other fields, such as a zero-line field  4066 , a poison field  4067 , an error correction code field (not shown). While  FIG. 40  illustrates the attribute field(s)  4062  being in the tag array, alternative embodiments may implement these field(s) in a separate state array (not shown). In one embodiment, a given cache line may have multiple poison indications (e.g., one for the two 32 byte chunks of a 64-byte cache line) in the poison field  4067 . While  FIG. 40  illustrates a separate poison field  4067 , alternative embodiments may encode the poison indications into another field (e.g. the error correction code (ECC) field or cache coherency protocol state field). 
     Responsive to a hit in the cache (e.g., based on a tag in the tag field  4061 ), the cache controller  4051  includes circuitry (e.g., cache coherency protocol state circuitry or other circuitry) to respond to the cache coherency protocol state in the cache coherency protocol state field  4056  for the hit (e.g., the cache coherency protocol state field  4056  corresponding to the tag field  4061  whose tag matched); which response differs between embodiments and based on various factors (e.g., whether the cache lookup was initiated responsive to a write command, a read command, a snoop (and possibly the type of snoop)). For example, in some embodiments, the response is to determine whether the cache coherency protocol state is one that grants the cache authority to modify the cache line (e.g., a “modified” or “exclusive” state) responsive to a write command and/or certain types of snoops as discussed in more detail below. In some embodiments, the cache controller  4051  includes: 1) hit-miss circuitry (not shown) to determine whether there is a hit or miss in the cache responsive to a command (e.g., a write command, a read command, a snoop command); 2) the snoop controller  4043  coupled to a snoop interface (not shown) to receive snoops and to transmit response messages to the snoops; and 3) cache line read circuitry (not shown) and cache line write circuitry (not shown). 
     Techniques to Configure a Cache Line to Indicate all Zeros 
     While some embodiments are implemented to configure a cache line to indicate all zeros by writing over the data in the cache line with zeros (first technique), alternative embodiments may configure a cache line to indicate all zeros using other techniques (the second-fourth techniques described below are examples). Such other techniques may be implemented for a variety of reasons, such as the size of a cache line is typically larger than the width of some busses/structures within a core (e.g., one or more of the intermediate buffers, such load queue  810 , store queue  820 , write combining buffer (WCB)  860 ) and/or writing over the data in a cache line with zeros consumes power and increases complexity of the cache. 
     The second technique is to invalidate the cache line in the way of the cache in which that cache line currently resides, and write a cache line of zeros into a different way of the cache. 
     The third and fourth techniques involve changing the tag state rather than the data in the data array  4056 , and these can be used in one or more of the cache levels and/or in the interconnect. The third technique is to implement a field (referred to as a zero-line field  4066 ) for each of the cache lines (e.g., in the attribute field(s)  4062 ), and the value in this field (which may be one bit) indicates whether: 1) the cache line should be treated as having the value of the data stored in that cache line; or 2) the cache line should be treated as being all zeros (regardless of the actual data stored in that cache line). In such embodiments, reads (including evictions) of that cache line will either pass the value of the zero-line field  4066  to another structure that supports such a zero-line field or convert the data to zeros. The data would also be converted before is it used by one of the coherent agents (e.g., coherent agent  3900 ) on a read. While in some such embodiments the data is also converted before being written to downstream memory QO30, alternative embodiments also implement a zero-line field in the downstream memory  3930  or an alternative memory structure managed by the memory controller. 
     The fourth technique is like the third, but rather than implementing a separate field, implements a new encoding in an existing one of the attribute field(s) (e.g., a new encoding in a cache coherency protocol state field or the error correct code (ECC) syndrome field). 
     Certain embodiments may implement a cache to, as part of configuring a cache line to indicate all zeros, modify the cache coherency protocol state of that cache line to “modified” or “owned” (or in the case of using a new encoding in the cache coherency state field to indicate zero line, then to the zero-line state) and cause any poison indication(s) to be ignored (data no longer poisoned) or cleared. Thus, another advantage of a cache line zeroing instruction is that it may be used to clear out poisoned lines consistently. 
     On a related note, a mechanism to force a cache line to zero may be implemented only in certain cache levels (e.g., a subset of the L1 caches, L2 caches and the L3 caches, such as only in the L1 cache and not in the L2 or L3 caches), and a given cache level that lacks such a mechanism may be implemented to configure a cache line to indicate all zeros by sending it to a different cache level that has the mechanism (e.g., a higher cache level (e.g., the L1 caches) is implemented to configure a cache line to indicate all zeros by evicting the data to a lower cache level (e.g., the L2 caches) that can do the zeroing; a lower cache level (e.g., the L2 caches) is implemented to configure a cache line to indicate all zeros by forwarding it to a higher level cache (e.g., the L1 caches) that can do the zeroing). As described in more detail below, different embodiments may implement the zeroing of a cache line responsive to a write and/or a snoop. In embodiments that implement zeroing of a cache line responsive to both a write and a snoop, a given cache level could be implemented to do the zeroing responsive to only one of a write or a snoop (but not both), and could push/evict or forward the data to a lower or higher level cache that can do the zeroing responsive to the other of a write and a snoop. 
     Triggering a Cache to Configure a Cache Line to Indicate all Zeros 
     Regardless of the technique implemented in a cache to configure a cache line to indicate all zeros (see above), triggering a cache to configure a cache line to indicate all zeros could be responsive to a message sent from the interconnect to one of the caches, by the issuing agent on its own, or by the issuing agent responsive to a message sent from the interconnect. 
     In the case of the issuing agent (on its own or responsive to a message from the interconnect) triggering a cache to configure a cache line to indicate all zeros, different embodiments may use different techniques, including techniques to implement the cache line zeroing instruction to be atomic in the case where a cache line is wider (e.g., 32 bytes, 64 bytes) than the natively supported data width of an issuing agent (e.g., 32 bits, 64 bits, 128 bits, 256 bits, 512 bits, 1024 bits). The natively supported data width may manifest itself in different ways in different embodiments. In some embodiments, the natively supported data width may represent the width in bits of the widest set of registers, and/or the width of the operand(s) that are to be operated on the by the instructions. In some embodiments, the natively supported data width may represent the width of the arithmetic and/or logical execution units (e.g., when it has the same width of the operands indicated by the instructions such that multiple portions of the operands are not sequentially pumped through it (double pumped or more)). In some embodiments, the natively supported data width may represent the width of a bus (e.g., a load pipe). The amount of data that can be atomically stored may be limited by the width of one or more internal structure of the issuing agent (e.g., busses, intermediate buffers). 
     Thus, in some embodiments in which the issuing agent (on its own or responsive to a message from the interconnect) does the triggering (of a cache to configure a cache line to indicate all zeros), the issuing agent either: 1) implements a zero-line field in other structures, such as one or more of the intermediate buffers (e.g., the store queue  820  and the write combining buffer (WCB)  860 ); or 2) implements a new command (e.g., a micro-op, control signal, micro-instruction), which does not carry the cache line of zeros but indicates a cache line sized write of zeros, that can pass through the intermediate buffers (e.g., the store queue  820  and write combining buffer (WCB)  860 ). As such, where the cache line size is wider (e.g., 32 bytes, 64 bytes) than the natively supported data width of an issuing agent, a cache line of zeros can be represented in these narrower structures. The conversion to a line of zeros is performed when the zero line (as indicated by the zero-line field or new command/micro-op) is being sent to a structure that is lower in the memory hierarchy and that does not support the zero-line field or the new command (e.g., the conversion to a line of zero may be performed when the zero line is sent to the data cache  840  (which may perform another of the above techniques), sent from the write combining buffer  8600 , sent by the L3 cache to the interconnect, or sent by the interconnect (e.g., via a memory controller) to the downstream memory). 
     As another example, in some embodiments in which the issuing agent (on its own or responsive to a message from the interconnect) does the triggering (of a cache to configure a cache line to indicate all zeros), the issuing agent sequentially writes smaller chucks (e.g., 16 bytes at a time, 32 bytes at a time) of zeros in an intermediate buffer (e.g., the store queue  820 , the write combining buffer (WCB)  860 , a separate staging buffer (not shown)) that does not respond to snoops (or does not respond to snoops while the chunks are being written) and that gets evicted responsive to enough chunks having been written to equal the size of a cache line (and not earlier) so that the chunks are written concurrently; thereby implementing the cache line zeroing instruction atomically. 
     Other Aspects 
     Different embodiments may implement a cache line zeroing instruction with different ordering (e.g., weakly ordered, strongly ordered, an ordering that is weaker the weakly ordered, an ordering that is stronger than strongly ordered). In the case of a cache line zeroing instruction that is weakly ordered, embodiments may implement the instruction such that it is auto-evicting. 
     The cache line zeroing instruction may be implemented such that it will not configure a cache line to indicate all zeros before retirement of that instruction. In such embodiments, there is a mechanism to ensure that the cache line zero instruction has completed and the cache line is configured to indicate all zeros for all readers (e.g., one or more of a fence instruction, a lock instruction, an architecturally serializing instruction, a younger store being GO (strongly ordered), younger load being GO (stricter than strongly ordered)). 
     The cache line zeroing instruction may be treated like a store for the purposes of page table walks (including virtualization tables (e.g., Extended Page Tables (EPT) (in which the A and D bits will be updated), shadow page tables) and will fault if not writeable. 
     Embodiments that First Attempt to Write to a Cache of the Issuing Agent Before Using Snoops 
       FIG. 41  is a flow diagram illustrating embodiments of the invention that first attempt to write to a cache of the issuing agent before using snoops. As discussed above, the first agent  3900  is to decode and execute an instruction whose execution is to cause a cache line sized write of zeros at a memory address (block  4110 ). Responsive to the decoding and executing of the instruction, the first agent is to issue, to one of the coherent caches coupled to the first agent (e.g., the L1 cache  3905 ), a write command to initiate the cache line sized write of zeros at the memory address (in which case, the first agent is also referred to as the issuing agent) (block  4112 ). In some embodiments, the first agent includes a decode unit (e.g., decoder  140 , decoder  314 ) to decode the instruction whose execution is to cause the cache line sized write of zeros at a memory address. The first agent also includes an execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ), responsive to the decode unit, to issue the command to initiate the cache line sized write of zeros at the memory address. 
     When there is a hit for a cache line of the cache (e.g., the L1 cache  3905 ) to which the command is issued (block  4114 ) and that cache line&#39;s cache coherency protocol state is one that grants the cache the authority to modify the cache line without broadcasting to other caches (e.g., “modified” or “exclusive”) (block  4116 ), then that cache is to configure the cache line to indicate all zeros and suppress snoops (block  4118 ). Different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros.” In some embodiments, if there is a hit for a cache line of the cache (e.g., the L1 cache  3905 ) to which the command is issued (block  4114 ), the cache line is still zeroed for one or more other cache coherency protocol states (e.g., one or more of “owned,” “forward,” or “shared”). For any state for which this is done, control passes to block  4119 ; for any state for which this is not done control, passes to block  4120 . Thus, in the embodiments in which control passes to block  4119  for any state that is not “modified,” “exclusive,” and “invalid,” then block  4120  is not implemented; and vice versa. However, embodiments may be implemented in which control passes to block  4119  or  4120  depending on the state. In block  4119 , that cache is to configure the cache line to indicate all zeros; from block  4119 , control passes to block  4122  (described in more detail later herein) in which the cache is to issue the write command toward the interconnect (depending on the embodiment, to the next cache level, or to the interconnect to issue snoops (e.g., a write-update snoop (also referred to as a write-zero snoop or a write-and-zero snoop), a write-invalidate snoop (also referred to as an invalidate-even-if-modified snoop), or a snoop that indicates to invalidate and write back (also referred to as a writeback-and-invalidate snoop)). It is possible that the write command passed to the next cache level or interconnect will indicate that a line with a state other than “modified” or “exclusive” was configured to indicate all zeros. One usage of this modified write command is so that if a “shared” line is configured to all zeros and its state is changed to either “modified” or “owned”, then a write-update snoop would not be sent out. In that situation, the interconnect could issue a different snoop type (e.g. a write-invalidate snoop or a writeback-and-invalidate snoop). In block  4120 , the cache is to change that cache line&#39;s cache coherency protocol state to “invalid” and control passes to block  4122 . If there is a cache miss (block  4114 ), then control passes to block  4122 . 
     By way of specific example regarding the forward or owned state, when a cache of the issuing agent has the cache line in the forward or owned state, that cache line may be in other caches in the shared state. As such, if the cache line is zeroed in block  4119 , then a snoop may be sent to either invalidate those other cache lines that are in the shared state or to configure to indicate all zeros those other cache lines that are in the shared state. Alternatively, the cache line in the forward or owned state could be invalidated (or clean evict and invalidate) (block  4120 ) and a new line created that is modified and zeroed or owned and zeroed. That new line that is zeroed could be inserted (filled) into the same cache as the cache line that was found in the forward or owned state (e.g., in a different set or way of that cache), or it could be inserted into a different cache (e.g., if the cache line was found in the forward or owned state in the L2 cache or L3 cache, the cache line may be invalidated and a new line of modified and zeroed or owned and zeroed created in the L1 cache). 
     In block  4122 , the cache is to issue the write command toward the interconnect. This write command may be issued directly to the interconnect  3920 , or may be sent to one or more lower levels of the caches of the first agent. By way of examples: 1) in some embodiments, the write command is issued directly to the interconnect (i.e., skipping any caches at lower levels of the cache hierarchy—e.g., from the L1 cache  3905  directly to the interconnect  3920 , skipping any lower level caches (e.g., the L2 cache OQA10, the L3 cache OQA15)—in which case, the write command is used for data L1 cache of the first agent, while snoops (described next) are used for the instruction L1 cache, the L2 cache and L3 cache (more specifically, the L3 cache slice  3916  if implemented) of the first agent, as well as for the caches of the second agent); 2) in some embodiments, the write command is issued to the L2 cache  3910  which repeats the above, and if it does not configure a cache line to indicate all zeros, issues the write command directly to the interconnect  3920 —in which case, the write command is used for L1 cache and L2 cache of the first agent, while snoops (described next) are used for the L3 cache (more specifically, the L3 cache slice  3916  if implemented) of the first agent and the caches of the second agent; 3) in some embodiments, the write command is issued to the L2 cache  3910  which repeats the above, and if it does not configure a cache line to indicate all zeros, issues the write command to the L3 cache  3915  (more specifically, the L3 cache slice  3916  if implemented), and if it does not configure a cache line to indicate all zeros, to the interconnect  3920 —in which case, the write command is used for the caches of the first agent, while snoops (described next) are used for the caches of the second agent. In certain embodiments, the cache(s) to which the write commands are issued includes a cache controller implemented to, responsive to the above discussed write commands, determine whether or not there are cache hits, configure cache lines to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”), and issue the write commands toward the interconnect on cache misses. In one specific example, responsive to a cache line hit, in the L2 cache  3910  (of the issuing agent), that is modified, exclusive, and/or owned, the L2 cache is implemented to configure a cache line to indicate all zeros by forwarding the task to the L1 cache. 
     The snoop controller  3925  of the interconnect  3920 , responsive to the write command, is implemented to initiate a snooping process (block  4190 ) to locate any caches that may be storing the cache line. To implement the snooping process  4190 , the snoop controller  3925  is implemented (e.g., via the snoop generator  3926 ) to issue a snoop to those of the coherent caches that may be storing the cache line (block  4126 ) (in other words, those of the coherent caches for which it must be determined if there is a hit). In some embodiments, the coherent caches that may be storing the cache line are those of the coherent caches: 1) to which the write command was not previously issued; and 2) in embodiments that implement a snoop filter (not shown) in the interconnect  3920 , which the snoop filter indicates the cache might contain the line (i.e., for which the snoop filter does not suppress the snoop). This may include the one or more levels of caches (e.g., the L1 cache  3906 , the L2 cache  3911 , the L3 cache  3915 ) coupling the second agent  3901  to the interconnect  3920 ; as well as any of the caches (e.g., the L2 cache  3910 , the L3 cache  3915 ) that couple the first agent  3900  (the issuing agent) to the interconnect  3920 , that did not receive the write command (i.e., caches that were skipped), and that, in embodiments that implement a snoop filter (not show) in the interconnect  3920 , the snoop filter indicates might contain the line (i.e., the snoop filter does not suppress the snoop). In embodiments where a snoop is issued to one or more of the caches coupling the first agent to the interconnect, each such snoop may also be referred to as a back snoop. As part of the snooping process  4190 , different embodiments may be implemented to issue different types of snoops depending on the situation, or issue just one type of snoop. There are a variety of possible snoops types that may be used (e.g., a write-update snoop (also referred to as a write-zero snoop or a write-and-zero snoop), a write-invalidate snoop (also referred to as an invalidate-even-if-modified snoop), a snoop that indicates to invalidate and write back (also referred to as a writeback-and-invalidate snoop), a snoop that writes out any cache line that hits but does not send the data back to the first agent and does not result in the data being read from the downstream memory, a prior art snoop (e.g., an RFO)) as discussed in more detail later herein. Specifically, where write-update snoops are used, the snoop controller  3925  is also implemented to determine whether the cache line sized write was performed by one of the caches responsive to one of the write-update snoops (shown as dashed block  4128 ) as part of the snooping process  4190 ; if so, the process is complete (block  4130 ); otherwise, control passes to block  4132 . Block  4128  is dashed as it is not used when the other types of snoops are used for the snooping process  4190 . 
     The write command and the snoops operate to handle cases where there is a cache line that contains the data to be zeroed in one or more of the caches. The cache line sized write of zeros may have been performed by one of the caches responsive to the write command (as described above), or, in embodiments that issue write-update snoops, by one of the caches responsive to one of the write-update snoops as described in more detail below. If the cache line sized write of zeros has not been performed by any of the caches, then in block  4132  the interconnect  3920  (e.g., via the write generator  3929  of the snoop controller  3925 ), or the first agent (the issuing agent) responsive to a message from the interconnect  3920 , causes a cache line in one or more of the coherent caches (e.g., the L1 cache  3905 , the L2 cache  3910 , the L3 cache  3915 ) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the memory address. As indicated above and in more detail below, in certain embodiments the snoop controller  3925  includes a snoop responder  3927  (and optionally a write converter  3928  and a write generator  3929 ) responsible for this action. In certain embodiments, the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) performs its roll (if any) in this action. In an alternative embodiment, the interconnect  3920  instructs a memory controller to cause the write of zeros to the downstream memory. 
     As described above in the section titled “Triggering a cache to configure a cache line to indicate all zeros,” different embodiments may implement the issuing agent differently to cause the triggering of a cache to configure a cache line to indicate all zeros (e.g., to ensure atomicity where a cache line is wider (e.g., 32 bytes, 64 bytes) than the natively supported data width of an issuing agent, implementing a zero-line field in other structures (e.g., the intermediate buffers), implementing a new command (which does not carry the cache line of zeros but indicates a cache line sized write of zeros) that can pass through the intermediate buffers, or implementing a sequential writes of smaller chucks (e.g., 16 bytes at a time, 32 bytes at a time) of zeros in an intermediate buffer (e.g., the store queue  8200 , the write combining buffer (WCB)  8600 , a separate staging buffer (not shown)) that does not respond to snoops (or does not respond to snoops while the chunks are being written) and that gets evicted responsive to enough chunks having been written to equal the size of a cache line (and not earlier) so that the chunks are written concurrently). 
     Embodiments that Rely on Snoops of the Coherent Caches 
       FIG. 42  is a flow diagram illustrating embodiments of the invention that rely on snoops of the coherent caches (they do not first attempt to write to a cache of the issuing agent). As discussed above, the first agent  3900  is to decode and execute an instruction whose execution is to cause a cache line sized write of zeros at a memory address (block  4210 ). Responsive to the decoding and executing of the instruction, the first agent is to issue, to the interconnect  3920 , a command to initiate the cache line sized write of zeros at the memory address (in which case, the first agent is also referred to as the issuing agent) (block  4212 ). In some embodiments, the first agent includes a decode unit (e.g., decoder  140 , decoder  314 ) to decode the instruction whose execution is to cause the cache line sized write of zeros at a memory address. The first agent also includes an execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ), responsive to the decode unit, to issue the command to initiate the cache line sized write of zeros at the memory address. 
     The command from the first agent/issuing agent  3900  is issued to the interconnect  3920  (block  4212 ), and the interconnect  3920 , responsive to the command, is implemented to initiate a snooping process (block  4290 ) to locate any caches that may be storing the cache line. To implement the snooping process  4290 , the interconnect  3920  (e.g., via the snoop controller  3925 ) is implemented (e.g., via the snoop generator  3926 ) to issue a snoop to those of the coherent caches that may be storing the cache line (block  4226 ) (in other words, those of the coherent caches for which it must be determined if there is a hit). In some embodiments, the coherent caches that may be storing the cache line are those of the coherent caches: 1) any of the coherent caches (e.g., the L1 cache  3905 , the L2 cache  3910 , the L1 cache  3906 , the L2 cache  3911 , the L3 cache  3915 ) in embodiments that do not implement a snoop filter (not shown) in the interconnect  3920 ; or 2) those of the coherent caches for which a snoop filter (not shown) in the interconnect  3920  indicates the cache might contain the line (i.e., the snoop filter does not suppress the snoop) in embodiments that implement such a snoop filter. In embodiments where a snoop is issued to one or more of the caches coupling the first agent to the interconnect, each such snoop may also be referred to as a back snoop. As before, as part of the snooping process  4290 , different embodiments may issue different types of snoops depending on the situation, or issue just one type of snoop. There are a variety of possible snoops types that may be used (e.g., a write-update snoop (also referred to as a write-zero snoop or a write-and-zero snoop), a write-invalidate snoop (also referred to as an invalidate-even-if-modified snoop), a snoop that indicates to invalidate and write back (also referred to as a writeback-and-invalidate snoop), a snoop that writes out any cache line that hits but does not send the data back to the first agent and does not result in the data being read from the downstream memory, a prior art snoop (e.g., an RFO) as discussed in more detail later herein. Specifically, where write-update snoops are used, the snoop controller  3925  is also implemented to determine whether the cache line sized write was performed by one of the caches responsive to one of the write-update snoops (shown as dashed block  4228 ) as part of the snooping process  4290 ; if so, the process is complete (block  4230 ); otherwise, control passes to block  4232 . Block  4228  is dashed as it is not used when the other types of snoops are used for the snooping process  4290 . 
     In an alternative embodiment, block  4212  is replaced with the first agent being implemented to issue a snoop command to those of the coherent caches that may be storing the cache line (in which case, block  4226  is not present, and flow passes to block  4228  in embodiments that use write-update snoops or to block  4232  otherwise). 
     The snoops operate to handle cases where there is a cache line that contains the data to be zeroed in one or more of the caches. In embodiments that issue write-update snoops, the cache line sized write of zeros may have been performed by one or more of the caches. If the cache line sized write of zeros has not been performed by any of the caches, then in block  4232  the first agent on its own, the interconnect  3920  (e.g., via the write generator  3929 ), or the first agent responsive to a message from the interconnect  3920 , causes a cache line in one or more of the caches (e.g., the L1 cache  3905 , the L2 cache  3910 , the L3 cache  3915 ) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the address. As indicated above and in more detail below, in certain embodiments the snoop controller  3925  includes a snoop responder  3927  (and optionally a write converter  3928  and a write generator  3929 ) to perform its role (if any) in this action. In certain embodiments, the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) performs its role (if any) in this action. In an alternative embodiment, the interconnect  3920  instructs a memory controller to cause the write of zeros to the downstream memory. 
     As described above in the section titled “Triggering a cache to configure a cache line to indicate all zeros,” different embodiments may implement the issuing agent differently to cause the triggering of a cache to configure a cache line to indicate all zeros (e.g., to ensure atomicity where a cache line is wider (e.g., 32 bytes, 64 bytes) than the natively supported data width of an issuing agent, implementing a zero-line field in other structures (e.g., the intermediate buffers), implementing a new command (which does not carry the cache line of zeros but indicates a cache line sized write of zeros) that can pass through the intermediate buffers, or implementing a sequential writes of smaller chucks (e.g., 16 bytes at a time, 32 bytes at a time) of zeros in an intermediate buffer (e.g., the store queue  8200 , the write combining buffer (WCB)  8600 , a separate staging buffer (not shown)) that does not respond to snoops (or does not respond to snoops while the chunks are being written) and that gets evicted responsive to enough chunks having been written to equal the size of a cache line (and not earlier) so that the chunks are written concurrently). 
     Different Types of Snoops 
     As previously indicated, as part of the snooping process  4190  or the snooping process  4290 , different embodiments may issue different types of snoops depending on the situation, or issue just one type of snoop. There are a variety of possible snoops types that may be used (e.g., a write-update snoop (also referred to as a write-zero snoop or a write-and-zero snoop), a write-invalidate snoop, a snoop that indicates to invalidate and write back (also referred to as an invalidate-even-if-modified snoop), a snoop that writes out any cache line that hits but does not send the data back to the first agent and does not result in the data being read from the downstream memory, a prior art snoop (e.g., an RFO)). As indicated previously, any one of these different types of snoops may be used in conjunction with any the above embodiments discussed with regard to  FIGS. 41 and 42 . More detail regarding the different types of snoops will now be described. 
     Write-update snoops:  FIG. 43  is a flow diagram illustrating embodiments of the invention that use write-update snoops (also referred to as write-zero snoops or write-and-zero snoops) to implement the snoop process  4190  or  4290 . In the context of  FIGS. 41 and 42 , flow respectively passes from block  4124  or block  4212  to block  4326 , which performs block  4126  or  4226  using a write-update snoop. The interconnect  3920  (e.g., via the snoop generator  3926  of the snoop controller  3925 ) is implemented to issue write-update snoops to those of the coherent caches that may be storing the cache line (block  4326 ) (in other words, those of the coherent caches for which it must be determined if there is a hit). When there is a hit for a cache line of a cache (e.g., the L1 cache, the L2 cache, and/or the L3 cache slice of the first agent, and the L1 cache, the L2 cache, and the L3 cache slice of the second agent) to which a write-update snoop is issued (block  4340 ), then that cache is to: 1) if the hitting cache line&#39;s cache coherency protocol state is “modified” (and in some embodiments, one or more of “forward”, “exclusive,” “owned,” and/or “shared”) (block  4342 ), configure the cache line to indicate all zeros (block  4344 ) (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) and issue to the interconnect  3920  a response message indicating zeroed (in some embodiments that support zeroing of a hitting cache line that is in the shared state, the response message also distinguishes the state of the cache line—such as modified-and-zero or owned-and-zero versus shared-and-zero (the latter indicating that the original state was “shared” and the cache has configured the cache line to indicate all zeros and its state is still “shared”); in an alternative embodiment that support zeroing of a cache line in the shared state, a response message indicating not zeroed (as in block  4350 ) is sent when the original state was “shared” and the cache has configured the cache line to indicate all zeros and its state is still “shared”)) ( 4346 ); and 2) otherwise, configure that cache line&#39;s cache coherency protocol state to “invalid” (block  4328 ) and issue a response message indicating not zeroed to the interconnect (block  4350 ). When there is not a hit for a cache line of the cache to which a write-update snoop is issued (block  4340 ), then the cache issues a response message indicating not zeroed to the interconnect (block  4350 ). Thus, in some embodiments, a coherent cache may be implemented such that a write command or write-and-zero snoop that hits a cache line in any of the modified, owned, exclusive, and forward states will cause the cache to configure the cache line to be zeroed (and change its state to modified (modified-and-zeroed) or owned (owned-and-zeroed)). In alternative embodiments, such a cache may do so for only a subset of the modified, owned, exclusive, and forward states; in which case, it would cause any hit cache line that is in the modified, owned, exclusive or forward states and that is not being changed to modified-and-zeroed or owned-and-zeroed, to be changed to the invalid state responsive to a write-and-zero snoop. As such, in some embodiments, all or a subset of the coherent caches are implemented to, for all or a subset of the modified, exclusive, owned, or forward states, cause a cache line to be zeroed (and its state change to modified (modified-and-zeroed) or owned (owned-and-zeroed)) responsive to a write command or write-and-update (aka write-and-zero) snoop that hits in that cache. Embodiments that support zeroing of a hitting cache line that is in the shared state and leaving it in the shared state will do so only when any Modified, Exclusive, Owned or Forward line that is hit in other caches are changed to Owned and Zeroed or invalidated instead of changed to Modified and Zeroed. In certain embodiments, a cache implemented to respond to a write-update snoop includes the cache controller  4051  (e.g., via the snoop controller  4053 ), responsive to the write-update snoops, to determine whether or not there are cache hits, configure cache lines that hit to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”), and issue the response messages to the interconnect  3920 . 
     After issuing the write-update snoops, the interconnect  3920  (e.g., via the snoop responder  3927  of the snoop controller  3925 ) is implemented to track receipt of the respective response messages (block  4352 ) (e.g., in one embodiment the snoop generator  3926  indicates to the snoop responder  3927  information for it to track receipt of the respective response messages). From block  4352 , control passes to either block  4128  or block  4228  depending on whether an embodiment of  FIG. 41 or 42  is being implemented. The cache line sized write of zeros may have been performed by one of the caches responsive to one of the write-update snoops (however, in embodiments that implement zeroing of a cache line in the “shared” state and none of the response messages reflect one of the cache lines being owned-and-zero or modified-and-zero, then the cache line write of zeros is not considered to have been performed by one of the caches responsive to one of the write-update snoops). If the cache line sized write of zeros has not been performed by any of the caches (block  4128  and block  4228 ) (all the response messages indicate not zeroed; or in embodiments that implement zeroing of a cache line in the “shared” state and none of the response messages reflect one of the cache lines being owned-and-zero or modified-and-zero), then either block  4132  or block  4232  is performed—namely, the interconnect  3920  (e.g., via the write generator  3929  of the snoop controller QO25), or the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) responsive to a message from the interconnect  3920 , causes a cache line in one of the caches (e.g., the L1 cache, the L2 cache, the L3 cache) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the address. 
     As illustrated above, the use of a write-update snoop, as opposed to the use of an RFO operation, is advantageous in that it does not require that a line be read and returned to the issuing agent and does require ownership of the data be given to the issuing agent (when the conditions of  4340  and  4342  are met, the write-update snoop causes the cache line to be zeroed in the cache of another coherent agent). Thus, an advantage of embodiments that use write-update snoops is that they can directly update a local cache of another agent (e.g., the second agent/non-issuing agent). For example, this allow for relatively fast communication—such as updating a variable that another agent is spinning on. 
     As indicated previously, write-update snoops may be used in conjunction with the embodiments of  FIGS. 41 and 42 . By way of example, one specific embodiment will be described that implements write-update snoops in one of the embodiments from  FIG. 41 . In this specific embodiment, the issuing agent  3900  first attempts to write to the L1 cache  3905  of the issuing agent  3900 ; and if snoops are required, the interconnect  3920  issues write-update snoops to those of the coherent caches that may be storing the cache line as described above. Thus, the L1 caches are implemented to respond to write commands as described above; the L1 caches, L2 caches, and the L3 caches (more specifically, the L3 cache slices if implemented) are implemented to respond to write-update snoops as described above; the interconnect  3920  is implemented to issue the write-update snoops responsive to the write commands (e.g., via the snoop generator  3926  of the snoop controller  3925 ) and to respond to the response messages (e.g., via the snoop responder  3927  of the snoop controller  3925 ) as described above; and the interconnect  3920  (e.g., via the write generator  3929  of the snoop controller QO25), or the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) responsive to a message from the interconnect, is implemented to cause a cache line in one of the caches (e.g., the L1 cache  3905 , the L2 cache  3910 , or the L3 cache  3915  (more specifically, the L3 cache slice  3916  if implemented) of the first agent) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the memory address. 
     Write-invalidate snoops:  FIG. 44  is a flow diagram illustrating embodiments of the invention that use write-invalidate snoops (also referred to as “invalidate-even-if-modified snoops) to implement the snoop process  4190  or  4290 . In the context of  FIGS. 41 and 42 , flow respectively passes from block  4124  or block  4212  to block  4426 , which performs block  4126  or  4226  using write-invalidate snoops. The interconnect  3920  (e.g., via the snoop generator  3926  of the snoop controller  3925 ) is implemented to issue write-invalidate snoops to those of the coherent caches that may be storing the cache line (block  4426 ) (in other words, those of the coherent caches for which it must be determined if there is a hit). When there is a hit for a cache line of a cache (e.g., the L1 cache, the L2 cache, and/or the L3 cache slice of the first agent, and the L1 cache, the L2 cache, and the L3 cache slice of the second agent) to which a write-invalidate snoop is issued (block  4440 ), then that cache is to make the cache coherency protocol state indicate “invalid” (even if in the current state is “modified”) (block  4448 ); the cache need not configure the cache line to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or issue a response message to the interconnect if the invalidate completes in fixed time (if the invalidate does not complete in fixed time, then one embodiments has the snooped caches send response messages that indicate the snoop is complete). When there is not a hit for a cache line of the cache to which a write-invalidate snoop is issued ( 4440 ), then that cache in one embodiment does nothing (block  4430 ). 
     In addition, in the context of  FIGS. 41 and 42 , flow respectively passes from block  4124  or block  4212  to block  4132  or  4232  (blocks  4128  and  4228  are not implemented when write-invalidate snoops are used). In block  4132  or  4232 , the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) on its own, the interconnect  3920  (e.g., via the write generator  3929  of the snoop controller QO25), or the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) responsive to a message from the interconnect, causes a cache line in one of the caches (e.g., the L1 cache  3905 , the L2 cache  3910 , or the L3 cache  3915  (more specifically, the L3 cache slice  3916  if implemented) of the first agent) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the address. 
     As illustrated above, the use of a write-invalidate snoop, as opposed to the use of an RFO operation, is advantageous in that it does not require that a cache line be read and returned to the issuing agent because the issuing agent will be zeroing the data. 
     As indicated previously, write-invalidate snoops may be used in conjunction with the embodiments of  FIGS. 41 and 42 . By way of example, one specific embodiment will be described that implements write-invalidate snoops in one of the embodiments from  FIG. 41 . In this specific embodiment, the issuing agent  3900  first attempts to write to the L1 cache  3905  of the issuing agent  3900 ; and if snoops are required, the interconnect  3920  issues write-invalidate snoops to those of the coherent caches that may be storing the cache line as described above. Thus, the L1 caches are implemented to respond to write commands as described above; the L1 caches, L2 caches, and the L3 cache (more specifically, the L3 cache slices if implemented) are implemented to respond to write-invalidate snoops as described above; the interconnect  3920  is implemented to issue the write-invalidate snoops responsive to the write commands; and the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) on its own, the interconnect  3920  (e.g., via the write generator  3929  of the snoop controller QO25), or the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) responsive to a message from the interconnect, are implemented to cause a cache line in one of the caches (e.g., the L1 cache  3905 , the L2 cache  3910 , or the L3 cache  3915  (more specifically, the L3 cache slice  3916  if implemented) of the first agent) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the memory address. 
     Snoops that invalidate and write back:  FIG. 45  is a flow diagram illustrating embodiments of the invention that use snoops, which invalidate and write back (also referred to as “writeback-and-invalidate snoops”), to implement the snoop process  4190  or  4290 . In the context of  FIGS. 41 and 42 , flow respectively passes from block  4124  or block  4212  to block  4526 , which performs block  4126  or  4226  using a writeback-and-invalidate snoop (a snoop that invalidates and write backs). The interconnect  3920  (e.g., via the snoop generator  3926  of the snoop controller  3925 ) is implemented to issue writeback-and-invalidate snoops to those of the coherent caches that may be storing the cache line (block  4526 ) (in other words, those of the coherent caches for which it must be determined if there is a hit). When there is a hit for a cache line of a cache (e.g., the L1 cache, the L2 cache, and/or the L3 cache slice of the first agent, and the L1 cache, the L2 cache, and the L3 cache slice of the second agent) to which such a snoop is issued (block  4540 ), then that cache is to: 1) if the cache coherency protocol state of the cache line is “modified” (block  4542 ) (and in some embodiments, “clean-evict”), write back the cache line to the interconnect  3920  (block  4544 ); and regardless 2) make the cache coherency protocol state of the cache line indicate “invalid” (block  4548 ) (the cache need not configure the cache line to indicate all zeros). When there is not a hit for a cache line of the cache to which the snoop is issued (block  4540 ), then the cache in one embodiment does nothing (control passes to block  4552 ). In certain embodiments, a cache implemented to respond to such a snoop includes the cache controller  4051 , responsive to such snoops, to determine whether or not there are cache hits, write back modified cache lines (e.g., those that hit and have a cache coherency protocol state of “modified”) to the interconnect  3920 , and modify the cache coherency protocol states of cache lines to “invalid.” 
     After issuing the snoops, the interconnect  3920  (e.g., via the snoop responder  3927  of the snoop controller  3925 ) is implemented to track receipt of any respective response messages (block  4552 ) (e.g., in one embodiment the snoop generator  3926  indicates to the snoop responder  3927  information for it to track receipt of any respective response messages). If a response message is received with the data (block  4560 ) (i.e., the data from the modified cache line), then the interconnect  3920  is optionally implemented (e.g., via the write converter  3928  of the snoop controller  3925 ) to effectively convert the data to zeros (block  4562 ). Otherwise, the interconnect  3920  is optionally implemented (e.g., via the write generator  3929  of the snoop controller  3925 ) to effectively creates a zero line (block  4564 ). Control passes from blocks  4562  and  4564  to either block  4132  or block  4232  (blocks  4128  and  4228  are not implemented when snoops that invalidate and write back are used) depending on whether an embodiment of  FIG. 41 or 42  is being implemented. In block  4132  or  4232 , the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) on its own, the interconnect  3920  (e.g., the snoop controller QO25), or the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) responsive to a message from the interconnect  3920 , causes a cache line in one of the caches (e.g., the L1 cache, the L2 cache, the L3 cache) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the address. In one embodiment, blocks  4560  and  4562  are not implemented, and block  4564  is always performed. In another embodiment, block  4562  is not performed, written back data is sent to the first agent, and the first agent zeros the data. In another embodiment, blocks  4560 ,  4562 , and  4564  are not performed, and the first agent zeros the data. 
     As illustrated above, the use of a snoop that invalidates and write backs, as opposed to the use of an RFO operation, is advantageous in that it does not require that a cache line be read and returned to the issuing agent because the issuing agent will be zeroing the data. 
     As previously described, the above is begun responsive to the first agent issuing the command to initiate the cache line sized write of zeros at an address aligned on a cache line boundary (e.g., block  4112  or  4212 ). As previously described, this command may take the form of a write command (e.g., block  4112  or  4212 ). In other embodiments, this command may be a read command (e.g., block  4212 ); in which case, a cache line in one of the caches (e.g., the L1 cache, the L2 cache, the L3 cache) is caused to be configured to indicate all zeros by: 1) the interconnect  3920  (e.g., the snoop controller  3925 ) being implemented to respond to the read command from the first agent with a response to the first agent indicating a zero line (which line will have its cache coherency protocol state set to modified or exclusive); and 2) the first agent being implemented to put the result of its read command into a cache (cause a cache (e.g., the L1 cache  3905 ) to configure a cache line to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”), but not into an architectural register file of the first agent. 
     As indicated previously, the snoops that indicate to invalidate and write back may be used in conjunction with the embodiments of  FIGS. 41 and 42 . By way of example, one specific embodiment will be described that implements such snoops in one of the embodiments from  FIG. 41 . In this specific embodiment, the issuing agent  3900  first attempts to write to the L1 cache  3905  of the issuing agent  3900 ; and if snoops are required, the interconnect  3920  issues the snoops to those of the coherent caches that may be storing the cache line as described above. Thus, the L1 caches are implemented to respond to write commands as described above; the L1 caches, L2 caches, and the L3 cache (more specifically, the L3 cache slices if implemented) are implemented to respond to the snoops as described above; the interconnect  3920  is implemented to issue the snoops responsive to write commands, optionally implemented to effectively convert to zero any received data responsive to the snoops (e.g., via the write converter  3928  of the snoop controller  3925 ), and optionally implemented to effectively create a zero line if no data is received responsive to the snoops (e.g., write generator  3929  of the snoop controller  3925 ; and the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) on its own, the interconnect  3920  (e.g., via the snoop controller QO25), or the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) responsive to a message from the interconnect, is implemented to cause a cache line in one of the caches (e.g., the L1 cache  3905 , the L2 cache  3910 , or the L3 cache  3915  (more specifically, the L3 cache slice  3916  if implemented) of the first agent) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the memory address. 
     Snoops that write out any cache line that hits but does not send the data back to the first agent and does not result in the data being read from the downstream memory, or Prior art snoops that writes lines out normally (an RFO):  FIG. 46  is a flow diagram illustrating embodiments of the invention that use snoops, which write out any cache line that hits but does not send the data back to the first agent and does not result in the data being read from the downstream memory (or prior art snoops that writes lines out normally—e.g., an RFO operation), to implement the snoop process  4190  or  4290 . In the context of  FIGS. 41 and 42 , flow respectively passes from block  4124  or block  4212  to block  4526 , which performs block  4126  or  4226  using such a snoop. The interconnect  3920  (e.g., via the snoop generator  3926  of the snoop controller  3925 ) is implemented to issue such snoops to those of the coherent caches that may be storing the cache line (block  4626 ) (in other words, those of the coherent caches for which it must be determined if there is a hit). When there is a hit for a cache line of a cache (e.g., the L1 cache, the L2 cache, and/or the L3 cache slice of the first agent, and the L1 cache, the L2 cache, and the L3 cache slice of the second agent) to which such a snoop is issued (block  4640 ), then that cache is to respond to the snoop ( 4644 ). In some embodiments, the caches are implemented to respond to such snoops as a prior art cache would normally respond according to the implemented cache coherency protocol. While in some embodiments a new type of snoop is used, in other a prior art snoop (e.g., a RFO operation) is used—in which case, incorporating the cache line zeroing instruction into an existing processor design requires no modification or a small modification to the caches depending (see above section titled “Triggering a cache to configure a cache line to indicate all zeros”). When there is not a hit for a cache line of the cache to which the snoop is issued ( 4640 ), then the cache in one embodiment does nothing (control passes to block  4652 ). 
     After issuing the snoops, the interconnect  3920  (e.g., via the snoop responder  3927  of the snoop controller  3925 ) is implemented to track receipt of any respective response messages (e.g., in one embodiment the snoop generator  3926  indicates to the snoop responder  3927  information for it to track receipt of any respective response messages). If a response message is received with the data (block  4660 ) (e.g., the data from a modified cache line), then the interconnect  3920  (e.g., via the snoop responder  3927  of the snoop controller  3925 ) is implemented to not send the data to the issuing agent or any of the caches of the issuing agent (block  4662 ). If a response message with the data is not received ( 4660 ), the interconnect  3920  (e.g., via the snoop responder  3927  of the snoop controller  3925 ) is implemented to not read the data from the downstream memory since it is not needed (block  4664 ). 
     Control passes from blocks  4662  and  4664  to either block  4132  or  4232  (blocks  4128  and  4228  are not implemented when such snoops are used) depending on whether an embodiment of  FIG. 41 or 42  is being implemented. In block  4132  or  4232 , the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) on its own (block  4232  only), the interconnect  3920  (e.g., the snoop controller QO25), or the first agent (e.g., through the execution unit (e.g., memory access unit(s)  164 , load-store unit  340 ) or other hardware structure) responsive to a message from the interconnect  3920 , causes a cache line in one of the caches (e.g., the L1 cache, the L2 cache, the L3 cache) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the address. In an embodiment in which block  4662  is not implemented (the data is sent back to the first agent) and/or block  4664  is not implemented (downstream memory is accessed and the data returned to the first agent), then the first agent zeros the data. 
     As illustrated above, even if an RFO operation is used, the illustrated embodiments are advantageous in that they work with an existing cache design, which supports an RFO operation, with no or little modification. 
     As indicated previously, these types of snoops may be used in conjunction with the embodiments of  FIGS. 41 and 42 . By way of example, one specific embodiment will be described that implements such snoops in one of the embodiments from  FIG. 42 . In this specific embodiment, the issuing agent  3900  is to issue the command to initiate the cache line sized write of zeros at a memory address directly to the interconnect  3920  (skipping the caches of the issuing agent/first agent), the interconnect  3920  (e.g., via the snoop generator  3926  of the snoop controller  3925 ) is implemented to issue the snoops to those of the coherent caches that may be storing the cache line as described above; if a response message is received with the data (i.e., the data from the modified cache line), then the interconnect  3920  is optionally implemented (e.g., via the snoop responder  3927  of the snoop controller  3925 ) to not send the data to the issuing agent or any caches of the issuing agent; if a response message with the data is not received, the interconnect  3920  (e.g., via the snoop responder  3927  of the snoop controller  3925 ) is optionally implemented to not read the data from the downstream memory since it is not needed; and the issuing agent (the first agent) on its own, or the first agent responsive to a message from the interconnect, causes a cache line in one of the caches (e.g., the L1 cache, the L2 cache, the L3 cache) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the address. Thus, in certain embodiments, the L1 caches, L2 caches, and the L3 caches (more specifically, the L3 cache slices if implemented) are implemented to respond to the snoops as described above; the interconnect  3920  is implemented to issue the snoops responsive to the commands (e.g., via the snoop generator  3926  of the snoop controller  3925 ) and respond to responsive data from the caches (e.g., via the snoop responder  3927  of the snoop controller  3925 ) as described above; the issuing agent is implemented to send the command to initiate the cache line sized write of zeros at a memory address directly to the interconnect  3920 ; and the issuing agent (the first agent) on its own, or the first agent responsive to a message from the interconnect, causes a cache line in one of the caches (e.g., the L1 cache, the L2 cache, the L3 cache) to be configured to indicate all zeros (different embodiments may implement caches to configure the cache line to indicate all zeros as previously described in the section titled “Techniques to configure a cache line to indicate all zeros”) or causes a write of zeros of the cache line size to the downstream memory at the address. In one specific embodiment, the issuing agent (the first agent) on its own causes a cache line in one of the caches (e.g., the L1 cache, the L2 cache, the L3 cache) to be configured to indicate all zeros. 
     Multiple Sockets 
     As previously described, the interconnect  3920  may, for example, represent: 1) just an interconnect within a CCX; 2) an interconnect within and between CCXs; 3) separate interconnects within different CCXs, as well as an interconnect(s) between CCXs. As discussed herein, a system may be implemented with one or more of the above processors (each including one or more CCXs) (see below section titled “Exemplary Computer Architectures). Such a system may include one or more sockets (as known as a CPU socket or CPU slot) that each comprise one or more mechanical components providing mechanical and electrical connections. In systems with multiple sockets (e.g. a server), the sockets are connected by a set of one or more interconnects (also referred to as socket-to-socket interconnects). Different embodiments may implement the set of socket-to-socket interconnects differently, including one or more of a ring, multiple rings, point to point links (e.g., point-to-point links, such as QuickPath Interconnect (QPI), UltraPath Interconnect (UPI), HyperTransport (HP)), shared buss(es), etc. This set of socket-to-socket interconnects may be viewed as part of the interconnect  3920  or as separate depending on the embodiment. In some embodiments, this set of interconnects is implemented to support the same communications (write commands, snoops, response messages, etc.) discussed above with regard the interconnect  3920 ; where each of these communications may have the same or a different format when sent over a socket-to-socket interconnect. In other embodiments, one or more of these communications (e.g., one or more of the snoop types and/or response messages) is converted when sent socket-to-socket. For example, some embodiments may use a write-update snoop within a processor(s) in a single socket, but convert such a snoop to a write-invalidate or writeback-and-invalidate snoop when it is sent to another socket. An advantage of such embodiments is that the decision whether to generate a new zeroed cache line is only within a socket (as such, there is no need for a “zeroed” or “not zeroed” indication from the other sockets). 
     Summary of Some Embodiments 
     One embodiment of the invention may include a processor comprising a first coherent agent, a second coherent agent, and an interconnect. The first agent is coupled to the interconnect through a cache of the first agent. The second agent is coupled to the interconnect through a cache of the second agent. The first agent is to decode and execute an instruction whose execution is to cause a cache line sized write of zeros at a memory address. The first agent is to issue, to the cache of the first agent, a write command to initiate the cache line sized write of zeros at the memory address. The cache of the first agent, when there is a hit for a cache line responsive to receiving the write command and that cache line&#39;s cache coherency protocol state is a modified state or an exclusive state, to configure that cache line to indicate all zeros. The cache of the first agent, when there is a cache miss responsive receiving to the write command, to issue the write command toward the interconnect. The interconnect, responsive to receiving the write command, to issue a snoop to the cache of the second agent. The interconnect, or the first agent responsive to a message from the interconnect, to cause a cache line in the cache of the first agent to be configured to indicate all zeros when the write command and the snoop did not cause the cache line write of zeros to be performed. 
     In addition, the following may apply: In some embodiments, the cache of the first agent, when there is a hit for a cache line responsive to receiving the write command and that cache line&#39;s cache coherency protocol state is not the modified state or the exclusive state, to make that cache line&#39;s cache coherency protocol state be an invalid state and issue the write command toward the interconnect. 
     Another embodiment of the invention may include a processor comprising a decoder to decode an instruction to zero a cache line. The processor also comprising an execution unit, coupled to the decoder and responsive to the decode of the instruction, to issue a write command to initiate a cache line sized write of zeros at a memory address. The processor also comprising a coherent cache, coupled to the execution unit, to receive the write command, to determine whether there is a hit in the coherent cache responsive to the write command, to determine whether a cache coherency protocol state of the hit cache line is a modified state or an exclusive state, to configure a cache line to indicate all zeros when the cache coherency protocol state is the modified state or the exclusive state, and to issue the write command toward an interconnect when there is a miss responsive receiving to the write command. The interconnect, responsive to receipt of the write command, to issue a snoop to each of a plurality of other coherent caches for which it must be determined if there is a hit. The interconnect, or the execution unit responsive to a message from the interconnect, to cause a cache line in one of the coherent caches to be configured to indicate all zeros when the write command and the snoop did not cause the cache line write of zeros to be performed. 
     In addition, the following may apply: In some embodiments, the coherent cache also to make that cache line&#39;s cache coherency protocol state be an invalid state and issue the write command toward the interconnect when the cache coherency protocol state of the hit cache line is not the modified state or the exclusive state. In some embodiments, the decoder and the execution unit are part of a first core, and the plurality of coherent caches includes a coherent cache of a second core. 
     Another embodiment of the invention may include a processor comprising a first core to issue a write command responsive to execution of a cache line zeroing instruction. The first core also comprising a level 1 (L1) cache coupled to receive the write command, to determine whether there is a hit or a miss in the cache responsive to the write command, and to determine responsive to the hit whether a cache coherency protocol state of a cache line that hit is one that grants the cache authority to modify the cache line without a broadcast to other caches. The L1 cache is to configure the cache line to indicate all zeros responsive to the hit when a cache coherency protocol state of a cache line that hit is one that grants the cache authority to modify the cache line without a broadcast to other caches. The L1 cache to issue the write command toward the interconnect responsive to the miss. The interconnect, coupled to the first core and responsive to the write command, to issue a snoop to those of a plurality of other caches for which it must be determined if there is a hit. The first core, the interconnect, or the first core responsive to a message from the interconnect, to cause a cache line in the cache or one of the plurality of other caches to be configured to indicate all zeros when the write command and the snoop did not cause the cache line write of zeros to be performed. 
     In addition, the following may apply: In some embodiments, the L1 cache may also to make the cache coherency protocol state be invalid and issue the write command toward an interconnect responsive to the hit when the cache coherency protocol state of the cache line that hit is not one that grants the cache authority to modify the cache line without a broadcast to other caches. In some embodiments, each of the plurality of other caches, responsive to the snoop, may also be implemented to determine whether there is a hit or a miss in that other cache, and to determine responsive to the hit whether a cache coherency protocol state of a cache line that hit in that other cache is one that grants the cache authority to modify the cache line without a broadcast to other caches. Each of the plurality of other caches to: configure a cache line in that cache to indicate all zeros and issue a response message indicating zeroed responsive to the hit when a cache coherency protocol state of the cache line that hit in that cache is one that grants the cache authority to modify the cache line that hit in that cache without a broadcast to other caches; and issue a response message indicating not zeroed responsive to the miss or responsive to the hit when the cache coherency protocol state of the cache line that hit in that cache is not one that grants the cache authority to modify the cache line that hit in that cache. The interconnect to determine track receipt of the response messages to determine if the snoop caused one of the plurality of other caches to be configured to indicate all zeros. 
     Another embodiment of the invention may include a processor comprising a first coherent agent, a second coherent agent, and an interconnect. The first agent is coupled to the interconnect through a cache of the first agent. The second agent is coupled to the interconnect through a cache of the second agent. The first agent is to decode and execute an instruction whose execution is to cause a cache line sized write of zeros at a memory address. The first agent is to issue, to the interconnect, a command. The interconnect, responsive to receiving the command, is to issue a snoop to the cache of the first agent and the cache of the second agent. The first agent, the interconnect, or the first agent responsive to a message from the interconnect, to cause a cache line in the cache of the first agent to be configured to indicate all zeros when the snoop did not cause the cache line write of zeros to be performed. 
     Another embodiment of the invention may include a processor comprising a decoder to decode an instruction to zero a cache line. The processor also comprising an execution unit, coupled to the decoder, to issue a command responsive to the decode of the instruction. The interconnect, responsive to receipt of the command, to issue a snoop to each of a plurality of coherent caches for which it must be determined if there is a hit. The execution unit on its own, the interconnect, or the execution unit responsive to a message from the interconnect, to cause a cache line in one of the plurality of coherent caches coupled to the execution unit to be configured to indicate all zeros when the snoop did not cause the cache line write of zeros to be performed. 
     Another embodiment of the invention may include a processor comprising a first core to issue a command responsive to execution of a cache line zeroing instruction. The processor also comprising an interconnect, coupled to a level 3 (L3) cache that is shared, a level 2 (L2) cache of the first core, and a level 1 (L1) cache of the first core, to issue responsive to the command a snoop to those of a plurality of coherent caches for which it must be determined if there is a hit. In some embodiments, the plurality of coherent caches includes the L1 cache of the first core, the L2 cache of the first core, the L3 cache, an L1 cache of a second core, and an L2 of the second core. The first core on its own, the interconnect, or the first core responsive to a message from the interconnect, to cause a cache line in one of the plurality of coherent caches coupled to the first core to be configured to indicate all zeros. 
     PTE Coalescing 
     A processor core may support a page table coalescing feature according to some exemplary embodiments, allowing multiple smaller memory pages to be coalesced into a single, effective, larger memory page. In some embodiments, for example, eight 4 KB memory pages may be coalesced into a single 32 KB memory page. In other embodiments, 16 4 KB memory pages may be coalesced into a single 64 KB memory page. 
     Current computer architectures allow virtual memory pages of various sizes. For example, an x86 architecture may allow pages of 4 KB, 2 MB, and 1 GB. A processor implementing such an architecture may provide a translation lookaside buffer (TLB) for each of these page sizes, providing a mapping of virtual addresses to physical addresses. When attempting to translate a virtual address to a physical one, the processor may search each of the applicable TLBs to determine whether any of them contains an entry corresponding to the virtual address. If an entry is found (i.e., a “TLB hit”), the entry is retrieved from the TLB in which it is found, and the translation from a virtual to a physical address proceeds. 
     If no entry corresponding to the virtual address is found in any of the TLBs present on the processor (i.e., a “TLB miss”), the processor may attempt to locate an entry in the page table that corresponds to the virtual address. If an entry is found (i.e., a “page table hit”), the entry is retrieved from the page table and inserted into the appropriate TLB. The translation from a virtual to a physical address may then be retried, yielding a TLB hit. 
     If no entry corresponding to the virtual address is found in the page table (i.e., a “page table miss”) it may indicate that there is currently no physical address in memory that corresponds to the provided virtual address. In this event, the processor may cause the page corresponding to the virtual address to be loaded from other storage (e.g., a disk) into memory at a particular physical address, and may insert a mapping from the provided virtual address to this physical address into the page table. A subsequent attempt to translate the provided virtual address will result in a page table hit, which will cause a corresponding entry to be added to the appropriate TLB. 
     A difficulty with some current processor architectures is a lack of granularity in allowable page sizes. For example, as explained above, some processor architectures allow pages of 4 KB, 2 MB, and 1 GB, providing a relatively “coarse” spread between page sizes. 
     According to some embodiments, this difficulty may be addressed by coalescing multiple smaller pages, yielding an intermediate page size that is, e.g., larger than 4 KB, but smaller than 2 MB. In some embodiments, this may be achieved by opportunistically coalescing, e.g., eight 4 KB pages to create a single effective 32 KB page under certain conditions. In some embodiments, the eight 4 KB pages must be aligned to a 32 KB address boundary. 
     In some embodiments, the eight 4 KB pages must be contiguous in one or both of (a) virtual; and (b) physical address spaces. For example, some embodiments may require that bits  12 - 14  of virtual address VA and physical address PA are equal to each other. That is, in some embodiments, smaller pages are coalesced into a larger one only if, for each of the smaller pages, VA[14:12]==PA[14:12]. 
     In some embodiments, smaller pages are coalesced into a larger one only if each of the smaller pages has the same permission bits. In some embodiments, when smaller pages are coalesced into a larger one, the operating system may combine the accessed/dirty bits corresponding to each of the smaller pages into a single value, by, e.g., performing a logical OR operation on all of the smaller pages&#39; accessed/dirty bits. In some embodiments, when smaller pages are coalesced into a larger one, the operating system may set only the appropriate 4 KB page dirty/accessed bits, thereby tracking which portions of the larger page have been accessed and/or are dirty. 
       FIG. 47  is a diagram illustrating a page coalescing feature that may be included in a processor according to some embodiments. Block  4700  represents a portion of a page table containing eight entries  4701 - 4708 , each corresponding to pages that are 4 KB in size. As  FIG. 47  shows, the eight entries  4701 - 08  have contiguous addresses, with bits  12 - 14  of the eight Addresses taking the consecutive values 000, 001, 010, 011, 100, 101, 110, and 111. According to some embodiments, as shown in  FIG. 47 , these eight 4 KB pages may be combined into effective 32 KB page  4709 . 
     In some embodiments, effective 32 KB page  4709  may be denoted by including an additional bit in each page table entry (PTE), indicating that the eight 4 KB pages should be treated as an effective 32 KB page. In some embodiments, effective 32 KB page  4709  may be denoted by an additional bit in the page directory entry corresponding to the page table entries  4701 - 08 , indicating that the eight 4 KB pages should be treated as an effective 32 KB page. In some embodiments, upon each access to one of the eight 4 KB pages, the consecutive, aligned addresses of the eight 4 KB pages may be detected by the hardware and treated as an effective 32 KB page. 
     Detecting whether multiple smaller pages meet the criteria for coalescing into an effective larger page may be achieved using a variety of methods. For example,  FIG. 48  is a flow diagram that illustrates a method for coalescing page table entries into a single effective page. On a TLB miss in all TLBs (e.g., all 4 KB, 32 KB, 2 MB, and 1 GB TLBs) as shown in box  4801 , the processor may walk the page tables according to the hierarchical structure of the page directory (e.g., using the x86 page table definition), as shown in box  4802 . Upon determining the location of the appropriate page table entry, the processor may then retrieve a cache line containing multiple page table entries (box  4803 ). For example, in some embodiments, the processor may retrieve eight page table entries in a cache line. 
     Upon retrieval of the multiple page table entries in the cache line, the processor may test whether the page table entries correspond to pages that meet the requirements for coalescing, as shown in  4804 . For example, the processor may test whether the pages&#39; addresses are consecutive in virtual and/or physical memory. In some embodiments, the processor may further test whether the values of the pages&#39; permission bits are the same. In some embodiments, the processor may determine whether the pages&#39; addresses are aligned to a 32 KB boundary. 
     If the multiple page table entries in the cache line meet the criteria for coalescing into a single combined page (for example, an effective 32 KB page) an entry corresponding to the combined page may be placed into the appropriate TLB (for example, the 32 KB TLB), and the entries in the cache line that were combined into a single entry are invalidated, as shown in box  4805 . If the multiple page table entries do not meet the criteria for coalescing into a single combined page, then the virtual-to-physical address translation may continue per usual, by allocating an entry in the TLB corresponding to the smaller (e.g., 4 KB) TLB, as shown in box  4806 . 
     In some embodiments, the processor may determine whether to coalesce multiple smaller pages based on the contents of the relevant TLB. For example, after a 4 KB TLB miss, the processor may detect whether the corresponding 4 KB page may be coalesced with additional entries that are present in the TLB (e.g., seven other TLB entries corresponding to 4 KB pages). If the entry corresponding to the provided address can be combined with others to create an effective larger page (e.g., an effective 32 KB page), the existing TLB entries to be combined are invalidated, and an entry is created corresponding to the effective larger page in the appropriate TLB (e.g., in the TLB corresponding to 32 KB pages). In some embodiments, a separate TLB corresponding to the combined effective page size is not used, and instead information relating to the virtual-to-physical address translation for combined pages are stored in the TLB corresponding to the smaller page size (e.g., the 4 KB page TLB). In some embodiments, this information may be encoded in the TLB corresponding to the smaller page size using additional bits reserved for that purpose. 
     In some embodiments, the above features may be used in conjunction with an operating system that allocates pages using an algorithm optimized for page coalescing as described above. Existing operating systems have algorithms designed for allocating, e.g., 4 KB, 2 MB, and/or 1 GB pages. Operating systems that may be used in conjunction with some embodiments may use additional algorithms that are designed for allocating combined pages (e.g., effective pages of 32 KB). 
     The page coalescing features described above are not limited to combining a particular number of pages of a particular size, but may be used to coalesce varying numbers of pages of various sizes. For example, some embodiments may coalesce 16 4 KB pages, forming effective combined pages of 64 KB. Some embodiments may additionally support effective combined pages of multiple sizes (e.g., combined pages of 32 KB and 64 KB). In some embodiments, pages of multiple sizes (e.g., pages of 4 KB and 32 KB) may be combined into a single effective page (e.g., an effective 64 KB page). 
     Exemplary Computer Architectures 
       FIGS. 49-52  are block diagrams of exemplary computer architectures. Other system designs and configurations known in the arts for laptops, desktops, handheld PCs, personal digital assistants, engineering workstations, servers, network devices, network hubs, switches, embedded processors, digital signal processors (DSPs), general-purpose processors, server processors or processing elements for use in a server-environment, coprocessors (e.g., security coprocessors) high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device, graphics devices, video game devices, set-top boxes, micro controllers, cell phones, portable media players, hand held devices, and various other electronic devices, are also suitable. In general, a huge variety of systems or electronic devices capable of incorporating a processor and/or other execution logic as disclosed herein are generally suitable. 
     Referring now to  FIG. 49 , shown is a block diagram of a system  4900  in accordance with one embodiment of the present invention. The system  4900  may include one or more processors  4910 ,  4915 , which are coupled to a controller hub  4920 . In one embodiment, the controller hub  4920  includes a graphics memory controller hub (GMCH)  4990  and an Input/Output Hub (IOH)  4950  (which may be on separate chips); the GMCH  4990  includes memory and graphics controllers to which are coupled memory  4940  and a coprocessor  4945 ; the IOH  4950  couples input/output (I/O) devices  4960  to the GMCH  4990 . Alternatively, one or both of the memory and graphics controllers are integrated within the processor (as described herein), the memory  4940  and the coprocessor  4945  are coupled directly to the processor  4910 , and the controller hub  4920  in a single chip with the IOH  4950 . 
     The optional nature of additional processors  4915  is denoted in  FIG. 49  with broken lines. Each processor  4910 ,  4915  may include one or more of the processing cores described herein and may be some version of the processor  3600 . 
     The memory  4940  may be, for example, dynamic random access memory (DRAM), phase change memory (PCM), or a combination of the two. For at least one embodiment, the controller hub  4920  communicates with the processor(s)  4910 ,  4915  via a multi-drop bus, such as a front-side bus (FSB), point-to-point interface such as QuickPath Interconnect (QPI), or similar connection  4995 . 
     In one embodiment, the coprocessor  4945  is a special-purpose processor (including, e.g., general-purpose processors, server processors or processing elements for use in a server-environment, coprocessors such as security coprocessors, high-throughput MIC processors, GPGPU&#39;s, accelerators, such as, e.g., graphics accelerators or digital signal processing (DSP) units, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device). In one embodiment, controller hub  4920  may include an integrated graphics accelerator. 
     There can be a variety of differences between the physical resources  4910 ,  4915  in terms of a spectrum of metrics of merit including architectural, microarchitectural, thermal, power consumption characteristics, and the like. 
     In one embodiment, the processor  4910  executes instructions that control data processing operations of a general type. Embedded within the instructions may be coprocessor instructions. The processor  4910  recognizes these coprocessor instructions as being of a type that should be executed by the attached coprocessor  4945 . Accordingly, the processor  4910  issues these coprocessor instructions (or control signals representing coprocessor instructions) on a coprocessor bus or other interconnect, to coprocessor  4945 . Coprocessor(s)  4945  accept and execute the received coprocessor instructions. 
     Referring now to  FIG. 50 , shown is a block diagram of a first more specific exemplary system  5000  in accordance with an embodiment of the present invention. As shown in  FIG. 50 , multiprocessor system  5000  is a point-to-point interconnect system, and includes a first processor  5070  and a second processor  5080  coupled via a point-to-point interconnect  5050 . Each of processors  5070  and  5080  may be some version of the processor  3600 . In one embodiment of the invention, processors  5070  and  5080  are respectively processors  4910  and  4915 , while coprocessor  5038  is coprocessor  4945 . In another embodiment, processors  5070  and  5080  are respectively processor  4910  coprocessor  4945 . 
     Processors  5070  and  5080  are shown including integrated memory controller (IMC) units  5072  and  5082 , respectively. Processor  5070  also includes as part of its bus controller unit&#39;s point-to-point (P-P) interfaces  5076  and  5078 ; similarly, second processor  5080  includes P-P interfaces  5086  and  5088 . Processors  5070 ,  5080  may exchange information via a point-to-point (P-P) interface  5050  using P-P interface circuits  5078 ,  5088 . As shown in  FIG. 50 , IMCs  5072  and  5082  couple the processors to respective memories, namely a memory  5032  and a memory  5034 , which may be portions of main memory locally attached to the respective processors. 
     Processors  5070 ,  5080  may each exchange information with a chipset  5090  via individual P-P interfaces  5052 ,  5054  using point to point interface circuits  5076 ,  5094 ,  5086 ,  5098 . Chipset  5090  may optionally exchange information with the coprocessor  5038  via a high-performance interface  5092 . In one embodiment, the coprocessor  5038  is a special-purpose processor, such as, for example, a high-throughput MIC processor, a network or communication processor, compression engine, graphics processor, GPGPU, embedded processor, or the like. 
     A shared cache (not shown) may be included in either processor or outside of both processors, yet connected with the processors via P-P interconnect, such that either or both processors&#39; local cache information may be stored in the shared cache if a processor is placed into a low power mode. 
     Chipset  5090  may be coupled to a first bus  5016  via an interface  5096 . In one embodiment, first bus  5016  may be a Peripheral Component Interconnect (PCI) bus, or a bus such as a PCI Express bus or another third generation I/O interconnect bus, although the scope of the present invention is not so limited. 
     As shown in  FIG. 50 , various I/O devices  5014  may be coupled to first bus  5016 , along with a bus bridge  5018  which couples first bus  5016  to a second bus  5020 . In one embodiment, one or more additional processor(s)  5015 , such as general-purpose processors, server processors or processing elements for use in a server-environment, coprocessors (e.g., security coprocessors) high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device, are coupled to first bus  5016 . In one embodiment, second bus  5020  may be a low pin count (LPC) bus. Various devices may be coupled to a second bus  5020  including, for example, a keyboard and/or mouse  5022 , communication devices  5027  and a storage unit  5028  such as a disk drive or other mass storage device which may include instructions/code and data  5030 , in one embodiment. Further, an audio I/O  5024  may be coupled to the second bus  5020 . Note that other architectures are possible. For example, instead of the point-to-point architecture of  FIG. 50 , a system may implement a multi-drop bus or other such architecture. 
     Referring now to  FIG. 51 , shown is a block diagram of a second more specific exemplary system  5100  in accordance with an embodiment of the present invention. Like elements in  FIGS. 50 and 51  bear like reference numerals, and certain aspects of  FIG. 50  have been omitted from  FIG. 51  in order to avoid obscuring other aspects of  FIG. 51 . 
       FIG. 51  illustrates that the processors  5070 ,  5080  may include integrated memory and I/O control logic (“CL”)  5072  and  5082 , respectively. Thus, the CL  5072 ,  5082  include integrated memory controller units and include I/O control logic.  FIG. 51  illustrates that not only are the memories  5032 ,  5034  coupled to the CL  5072 ,  5082 , but also that I/O devices  5114  are also coupled to the control logic  5072 ,  5082 . Legacy I/O devices  5115  are coupled to the chipset  5090 . 
     Referring now to  FIG. 52 , shown is a block diagram of a SoC  5200  in accordance with an embodiment of the present invention. Similar elements in  FIG. 36  bear like reference numerals. Also, dashed lined boxes are optional features on more advanced SoCs. In  FIG. 52 , an interconnect unit(s)  5202  is coupled to: an application processor  5210  which includes a set of one or more cores  3602 A-N, which include cache units  3604 A-N, and shared cache unit(s)  3606 ; a system agent unit  3610 ; a bus controller unit(s)  3616 ; an integrated memory controller unit(s)  3614 ; a set or one or more coprocessors  5220  which may include integrated graphics logic, an image processor, an audio processor, and a video processor, general-purpose processors, server processors or processing elements for use in a server-environment, security coprocessors, high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device; an static random access memory (SRAM) unit  5230 ; a direct memory access (DMA) unit  5232 ; and a display unit  5240  for coupling to one or more external displays. In one embodiment, the coprocessor(s)  5220  include a special-purpose processor, such as, for example, a network or communication processor, compression engine, GPGPU, a high-throughput MIC processor, embedded processor, or the like. 
     Embodiments of the mechanisms disclosed herein may be implemented in hardware, software, firmware, or a combination of such implementation approaches. Embodiments of the invention may be implemented as computer programs or program code executing on programmable systems comprising at least one processor, including, e.g., general-purpose processors, server processors or processing elements for use in a server-environment, coprocessors (e.g., security coprocessors) high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units, cryptographic accelerators, fixed function accelerators, machine learning accelerators, networking accelerators, or computer vision accelerators), field programmable gate arrays, or any other processor or processing device, a storage system (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device. 
     Program code, such as code  5030  illustrated in  FIG. 50 , may be applied to input instructions to perform the functions described herein and generate output information. The output information may be applied to one or more output devices, in known fashion. For purposes of this application, a processing system includes any system that has a processor, such as, for example; a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), or a microprocessor. 
     The program code may be implemented in a high level procedural or object oriented programming language to communicate with a processing system. The program code may also be implemented in assembly or machine language, if desired. In fact, the mechanisms described herein are not limited in scope to any particular programming language. In any case, the language may be a compiled or interpreted language. 
     One or more aspects of at least one embodiment may be implemented by representative instructions stored on a machine-readable medium which represents various logic within the processor, which when read by a machine causes the machine to fabricate logic to perform the techniques described herein. Such representations, known as “IP cores” may be stored on a tangible, machine readable medium and supplied to various customers or manufacturing facilities to load into the fabrication machines that actually make the logic or processor. 
     Such machine-readable storage media may include, without limitation, non-transitory, tangible arrangements of articles manufactured or formed by a machine or device, including storage media such as hard disks, any other type of disk including floppy disks, optical disks, compact disk read-only memories (CD-ROMs), compact disk rewritables (CD-RWs), and magneto-optical disks, semiconductor devices such as read-only memories (ROMs), random access memories (RAMs) such as dynamic random access memories (DRAMs), static random access memories (SRAMs), erasable programmable read-only memories (EPROMs), flash memories, electrically erasable programmable read-only memories (EEPROMs), phase change memory (PCM), magnetic or optical cards, or any other type of media suitable for storing electronic instructions. 
     Accordingly, embodiments of the invention also include non-transitory, tangible machine-readable media containing instructions or containing design data, such as Hardware Description Language (HDL), which defines structures, circuits, apparatuses, processors and/or system features described herein. Such embodiments may also be referred to as program products. 
     Instructions to be executed by a processor core according to embodiments of the invention may be embodied in a “generic vector friendly instruction format” which is detailed below. In other embodiments, such a format is not utilized and another instruction format is used, however, the description below of the write-mask registers, various data transformations (swizzle, broadcast, etc.), addressing, etc. is generally applicable to the description of the embodiments of the instruction(s) above. Additionally, exemplary systems, architectures, and pipelines are detailed below. Instructions may be executed on such systems, architectures, and pipelines, but are not limited to those detailed. 
     Instruction Sets 
     An instruction set may include one or more instruction formats. A given instruction format may define various fields (e.g., number of bits, location of bits) to specify, among other things, the operation to be performed (e.g., opcode) and the operand(s) on which that operation is to be performed and/or other data field(s) (e.g., mask). Some instruction formats are further broken down though the definition of instruction templates (or subformats). For example, the instruction templates of a given instruction format may be defined to have different subsets of the instruction format&#39;s fields (the included fields are typically in the same order, but at least some have different bit positions because there are less fields included) and/or defined to have a given field interpreted differently. Thus, each instruction of an ISA is expressed using a given instruction format (and, if defined, in a given one of the instruction templates of that instruction format) and includes fields for specifying the operation and the operands. For example, an exemplary ADD instruction has a specific opcode and an instruction format that includes an opcode field to specify that opcode and operand fields to select operands (source1/destination and source2); and an occurrence of this ADD instruction in an instruction stream will have specific contents in the operand fields that select specific operands. A set of SIMD extensions referred to as the Advanced Vector Extensions (AVX, AVX2, and AVX-512) and using the Vector Extensions (VEX) coding scheme has been released and/or published (e.g., see Intel® 64 and IA-32 Architectures Software Developer&#39;s Manual, September 2014; Intel® Advanced Vector Extensions Programming Reference, October 2014; and Intel® Architecture Instruction Set Extensions Programming Reference, October 2016). 
     Exemplary Instruction Formats 
     Embodiments of the instruction(s) described herein may be embodied in different formats. Additionally, exemplary systems, architectures, and pipelines are detailed below. Embodiments of the instruction(s) may be executed on such systems, architectures, and pipelines, but are not limited to those detailed. 
     Generic Vector Friendly Instruction Format 
     A vector friendly instruction format is an instruction format that is suited for vector instructions (e.g., there are certain fields specific to vector operations). While embodiments are described in which both vector and scalar operations are supported through the vector friendly instruction format, alternative embodiments use only vector operations the vector friendly instruction format. 
       FIGS. 53A-53B  are block diagrams illustrating a generic vector friendly instruction format and instruction templates thereof according to embodiments of the invention.  FIG. 53A  is a block diagram illustrating a generic vector friendly instruction format and class A instruction templates thereof according to embodiments of the invention; while  FIG. 53B  is a block diagram illustrating the generic vector friendly instruction format and class B instruction templates thereof according to embodiments of the invention. Specifically, a generic vector friendly instruction format  5300  for which are defined class A and class B instruction templates, both of which include no memory access  5305  instruction templates and memory access  5320  instruction templates. The term generic in the context of the vector friendly instruction format refers to the instruction format not being tied to any specific instruction set. 
     While embodiments of the invention will be described in which the vector friendly instruction format supports the following: a 64 byte vector operand length (or size) with 32 bit (4 byte) or 64 bit (8 byte) data element widths (or sizes) (and thus, a 64 byte vector consists of either 16 doubleword-size elements or alternatively, 8 quadword-size elements); a 64 byte vector operand length (or size) with 16 bit (2 byte) or 8 bit (1 byte) data element widths (or sizes); a 32 byte vector operand length (or size) with 32 bit (4 byte), 64 bit (8 byte), 16 bit (2 byte), or 8 bit (1 byte) data element widths (or sizes); and a 16 byte vector operand length (or size) with 32 bit (4 byte), 64 bit (8 byte), 16 bit (2 byte), or 8 bit (1 byte) data element widths (or sizes); alternative embodiments may support more, less and/or different vector operand sizes (e.g., 256 byte vector operands) with more, less, or different data element widths (e.g., 128 bit (16 byte) data element widths). 
     The class A instruction templates in  FIG. 53A  include: 1) within the no memory access  5305  instruction templates there is shown a no memory access, full round control type operation  5310  instruction template and a no memory access, data transform type operation  5315  instruction template; and 2) within the memory access  5320  instruction templates there is shown a memory access, temporal  5325  instruction template and a memory access, non-temporal  5330  instruction template. The class B instruction templates in  FIG. 53B  include: 1) within the no memory access  5305  instruction templates there is shown a no memory access, write mask control, partial round control type operation  5312  instruction template and a no memory access, write mask control, vsize type operation  5317  instruction template; and 2) within the memory access  5320  instruction templates there is shown a memory access, write mask control  5327  instruction template. 
     The generic vector friendly instruction format  5300  includes the following fields listed below in the order illustrated in  FIGS. 53A-53B . 
     Format field  5340 —a specific value (an instruction format identifier value) in this field uniquely identifies the vector friendly instruction format, and thus occurrences of instructions in the vector friendly instruction format in instruction streams. As such, this field is optional in the sense that it is not needed for an instruction set that has only the generic vector friendly instruction format. 
     Base operation field  5342 —its content distinguishes different base operations. 
     Register index field  5344 —its content, directly or through address generation, specifies the locations of the source and destination operands, be they in registers or in memory. These include a sufficient number of bits to select N registers from a P×Q (e.g. 32×512, 16×128, 32×1024, 64×1024) register file. While in one embodiment N may be up to three sources and one destination register, alternative embodiments may support more or less sources and destination registers (e.g., may support up to two sources where one of these sources also acts as the destination, may support up to three sources where one of these sources also acts as the destination, may support up to two sources and one destination). 
     Modifier field  5346 —its content distinguishes occurrences of instructions in the generic vector instruction format that specify memory access from those that do not; that is, between no memory access  5305  instruction templates and memory access  5320  instruction templates. Memory access operations read and/or write to the memory hierarchy (in some cases specifying the source and/or destination addresses using values in registers), while non-memory access operations do not (e.g., the source and destinations are registers). While in one embodiment this field also selects between three different ways to perform memory address calculations, alternative embodiments may support more, less, or different ways to perform memory address calculations. 
     Augmentation operation field  5350 —its content distinguishes which one of a variety of different operations to be performed in addition to the base operation. This field is context specific. In one embodiment of the invention, this field is divided into a class field  5368 , an alpha field  5352 , and a beta field  5354 . The augmentation operation field  5350  allows common groups of operations to be performed in a single instruction rather than 2, 3, or 4 instructions. 
     Scale field  5360 —its content allows for the scaling of the index field&#39;s content for memory address generation (e.g., for address generation that uses 2scale*index+base). 
     Displacement Field  5362 A—its content is used as part of memory address generation (e.g., for address generation that uses 2scale*index+base+displacement). 
     Displacement Factor Field  5362 B (note that the juxtaposition of displacement field  5362 A directly over displacement factor field  5362 B indicates one or the other is used)—its content is used as part of address generation; it specifies a displacement factor that is to be scaled by the size of a memory access (N)—where N is the number of bytes in the memory access (e.g., for address generation that uses 2scale*index+base+scaled displacement). Redundant low-order bits are ignored and hence, the displacement factor field&#39;s content is multiplied by the memory operands total size (N) in order to generate the final displacement to be used in calculating an effective address. The value of N is determined by the processor hardware at runtime based on the full opcode field  5374  (described later herein) and the data manipulation field  5354 C. The displacement field  5362 A and the displacement factor field  5362 B are optional in the sense that they are not used for the no memory access  5305  instruction templates and/or different embodiments may implement only one or none of the two. 
     Data element width field  5364 —its content distinguishes which one of a number of data element widths is to be used (in some embodiments for all instructions; in other embodiments for only some of the instructions). This field is optional in the sense that it is not needed if only one data element width is supported and/or data element widths are supported using some aspect of the opcodes. 
     Write mask field  5370 —its content controls, on a per data element position basis, whether that data element position in the destination vector operand reflects the result of the base operation and augmentation operation. Class A instruction templates support merging-writemasking, while class B instruction templates support both merging- and zeroing-writemasking. When merging, vector masks allow any set of elements in the destination to be protected from updates during the execution of any operation (specified by the base operation and the augmentation operation); in other one embodiment, preserving the old value of each element of the destination where the corresponding mask bit has a 0. In contrast, when zeroing vector masks allow any set of elements in the destination to be zeroed during the execution of any operation (specified by the base operation and the augmentation operation); in one embodiment, an element of the destination is set to 0 when the corresponding mask bit has a 0 value. A subset of this functionality is the ability to control the vector length of the operation being performed (that is, the span of elements being modified, from the first to the last one); however, it is not necessary that the elements that are modified be consecutive. Thus, the write mask field  5370  allows for partial vector operations, including loads, stores, arithmetic, logical, etc. While embodiments of the invention are described in which the write mask field&#39;s  5370  content selects one of a number of write mask registers that contains the write mask to be used (and thus the write mask field&#39;s  5370  content indirectly identifies that masking to be performed), alternative embodiments instead or additional allow the mask write field&#39;s  5370  content to directly specify the masking to be performed. 
     Immediate field  5372 —its content allows for the specification of an immediate. This field is optional in the sense that is it not present in an implementation of the generic vector friendly format that does not support immediate and it is not present in instructions that do not use an immediate. 
     Class field  5368 —its content distinguishes between different classes of instructions. With reference to  FIGS. 53A-B , the contents of this field select between class A and class B instructions. In  FIGS. 53A-B , rounded corner squares are used to indicate a specific value is present in a field (e.g., class A  5368 A and class B  5368 B for the class field  5368  respectively in  FIGS. 53A-B ). 
     Instruction Templates of Class A 
     In the case of the non-memory access  5305  instruction templates of class A, the alpha field  5352  is interpreted as an RS field  5352 A, whose content distinguishes which one of the different augmentation operation types are to be performed (e.g., round  5352 A. 1  and data transform  5352 A. 2  are respectively specified for the no memory access, round type operation  5310  and the no memory access, data transform type operation  5315  instruction templates), while the beta field  5354  distinguishes which of the operations of the specified type is to be performed. In the no memory access  5305  instruction templates, the scale field  5360 , the displacement field  5362 A, and the displacement scale filed  5362 B are not present. 
     No-Memory Access Instruction Templates—Full Round Control Type Operation 
     In the no memory access full round control type operation  5310  instruction template, the beta field  5354  is interpreted as a round control field  5354 A, whose content(s) provide static rounding. While in the described embodiments of the invention the round control field  5354 A includes a suppress all floating point exceptions (SAE) field  5356  and a round operation control field  5358 , alternative embodiments may support may encode both these concepts into the same field or only have one or the other of these concepts/fields (e.g., may have only the round operation control field  5358 ). 
     SAE field  5356 —its content distinguishes whether or not to disable the exception event reporting; when the SAE field&#39;s  5356  content indicates suppression is enabled, a given instruction does not report any kind of floating-point exception flag and does not raise any floating point exception handler. 
     Round operation control field  5358 —its content distinguishes which one of a group of rounding operations to perform (e.g., Round-up, Round-down, Round-towards-zero and Round-to-nearest). Thus, the round operation control field  5358  allows for the changing of the rounding mode on a per instruction basis. In one embodiment of the invention where a processor includes a control register for specifying rounding modes, the round operation control field&#39;s  5350  content overrides that register value. 
     No Memory Access Instruction Templates—Data Transform Type Operation 
     In the no memory access data transform type operation  5315  instruction template, the beta field  5354  is interpreted as a data transform field  5354 B, whose content distinguishes which one of a number of data transforms is to be performed (e.g., no data transform, swizzle, broadcast). 
     In the case of a memory access  5320  instruction template of class A, the alpha field  5352  is interpreted as an eviction hint field  5352 B, whose content distinguishes which one of the eviction hints is to be used (in  FIG. 53A , temporal  5352 B. 1  and non-temporal  5352 B. 2  are respectively specified for the memory access, temporal  5325  instruction template and the memory access, non-temporal  5330  instruction template), while the beta field  5354  is interpreted as a data manipulation field  5354 C, whose content distinguishes which one of a number of data manipulation operations (also known as primitives) is to be performed (e.g., no manipulation; broadcast; up conversion of a source; and down conversion of a destination). The memory access  5320  instruction templates include the scale field  5360 , and optionally the displacement field  5362 A or the displacement scale field  5362 B. 
     Vector memory instructions perform vector loads from and vector stores to memory, with conversion support. As with regular vector instructions, vector memory instructions transfer data from/to memory in a data element-wise fashion, with the elements that are actually transferred is dictated by the contents of the vector mask that is selected as the write mask. 
     Memory Access Instruction Templates—Temporal 
     Temporal data is data likely to be reused soon enough to benefit from caching. This is, however, a hint, and different processors may implement it in different ways, including ignoring the hint entirely. 
     Memory Access Instruction Templates—Non-Temporal 
     Non-temporal data is data unlikely to be reused soon enough to benefit from caching in the 1st-level cache and should be given priority for eviction. This is, however, a hint, and different processors may implement it in different ways, including ignoring the hint entirely. 
     Instruction Templates of Class B 
     In the case of the instruction templates of class B, the alpha field  5352  is interpreted as a write mask control (Z) field  5352 C, whose content distinguishes whether the write masking controlled by the write mask field  5370  should be a merging or a zeroing. 
     In the case of the non-memory access  5305  instruction templates of class B, part of the beta field  5354  is interpreted as an RL field  5357 A, whose content distinguishes which one of the different augmentation operation types are to be performed (e.g., round  5357 A. 1  and vector length (VSIZE)  5357 A. 2  are respectively specified for the no memory access, write mask control, partial round control type operation  5312  instruction template and the no memory access, write mask control, VSIZE type operation  5317  instruction template), while the rest of the beta field  5354  distinguishes which of the operations of the specified type is to be performed. In the no memory access  5305  instruction templates, the scale field  5360 , the displacement field  5362 A, and the displacement scale filed  5362 B are not present. 
     In the no memory access, write mask control, partial round control type operation  5310  instruction template, the rest of the beta field  5354  is interpreted as a round operation field  5359 A and exception event reporting is disabled (a given instruction does not report any kind of floating-point exception flag and does not raise any floating point exception handler). 
     Round operation control field  5359 A—just as round operation control field  5358 , its content distinguishes which one of a group of rounding operations to perform (e.g., Round-up, Round-down, Round-towards-zero and Round-to-nearest). Thus, the round operation control field  5359 A allows for the changing of the rounding mode on a per instruction basis. In one embodiment of the invention where a processor includes a control register for specifying rounding modes, the round operation control field&#39;s  5350  content overrides that register value. 
     In the no memory access, write mask control, VSIZE type operation  5317  instruction template, the rest of the beta field  5354  is interpreted as a vector length field  5359 B, whose content distinguishes which one of a number of data vector lengths is to be performed on (e.g., 128, 256, or 512 byte). 
     In the case of a memory access  5320  instruction template of class B, part of the beta field  5354  is interpreted as a broadcast field  5357 B, whose content distinguishes whether or not the broadcast type data manipulation operation is to be performed, while the rest of the beta field  5354  is interpreted the vector length field  5359 B. The memory access  5320  instruction templates include the scale field  5360 , and optionally the displacement field  5362 A or the displacement scale field  5362 B. 
     With regard to the generic vector friendly instruction format  5300 , a full opcode field  5374  is shown including the format field  5340 , the base operation field  5342 , and the data element width field  5364 . While one embodiment is shown where the full opcode field  5374  includes all of these fields, the full opcode field  5374  includes less than all of these fields in embodiments that do not support all of them. The full opcode field  5374  provides the operation code (opcode). 
     The augmentation operation field  5350 , the data element width field  5364 , and the write mask field  5370  allow these features to be specified on a per instruction basis in the generic vector friendly instruction format. 
     The combination of write mask field and data element width field create typed instructions in that they allow the mask to be applied based on different data element widths. 
     The various instruction templates found within class A and class B are beneficial in different situations. In some embodiments of the invention, different processors or different cores within a processor may support only class A, only class B, or both classes. For instance, a high performance general purpose out-of-order core intended for general-purpose computing may support only class B, a core intended primarily for graphics and/or scientific (throughput) computing may support only class A, and a core intended for both may support both (of course, a core that has some mix of templates and instructions from both classes but not all templates and instructions from both classes is within the purview of the invention). Also, a single processor may include multiple cores, all of which support the same class or in which different cores support different class. For instance, in a processor with separate graphics and general purpose cores, one of the graphics cores intended primarily for graphics and/or scientific computing may support only class A, while one or more of the general purpose cores may be high performance general purpose cores with out of order execution and register renaming intended for general-purpose computing that support only class B. Another processor that does not have a separate graphics core, may include one more general purpose in-order or out-of-order cores that support both class A and class B. Of course, features from one class may also be implement in the other class in different embodiments of the invention. Programs written in a high level language would be put (e.g., just in time compiled or statically compiled) into an variety of different executable forms, including: 1) a form having only instructions of the class(es) supported by the target processor for execution; or 2) a form having alternative routines written using different combinations of the instructions of all classes and having control flow code that selects the routines to execute based on the instructions supported by the processor which is currently executing the code. 
     Exemplary Specific Vector Friendly Instruction Format 
       FIG. 54A  is a block diagram illustrating an exemplary specific vector friendly instruction format according to embodiments of the invention.  FIG. 54A  shows a specific vector friendly instruction format  5400  that is specific in the sense that it specifies the location, size, interpretation, and order of the fields, as well as values for some of those fields. The specific vector friendly instruction format  5400  may be used to extend the x86 instruction set, and thus some of the fields are similar or the same as those used in the existing x86 instruction set and extension thereof (e.g., AVX). This format remains consistent with the prefix encoding field, real opcode byte field, MOD R/M field, SIB field, displacement field, and immediate fields of the existing x86 instruction set with extensions. The fields from  FIG. 53  into which the fields from  FIG. 54A  map are illustrated. 
     It should be understood that, although embodiments of the invention are described with reference to the specific vector friendly instruction format  5400  in the context of the generic vector friendly instruction format  5300  for illustrative purposes, the invention is not limited to the specific vector friendly instruction format  5400  except where claimed. For example, the generic vector friendly instruction format  5300  contemplates a variety of possible sizes for the various fields, while the specific vector friendly instruction format  5400  is shown as having fields of specific sizes. By way of specific example, while the data element width field  5364  is illustrated as a one bit field in the specific vector friendly instruction format  5400 , the invention is not so limited (that is, the generic vector friendly instruction format  5300  contemplates other sizes of the data element width field  5364 ). 
     The generic vector friendly instruction format  5300  includes the following fields listed below in the order illustrated in  FIG. 54A . 
     EVEX Prefix (Bytes 0-3)  5402 —is encoded in a four-byte form. 
     Format Field  5340  (EVEX Byte 0, bits [7:0])—the first byte (EVEX Byte 0) is the format field  5340  and it contains 0x62 (the unique value used for distinguishing the vector friendly instruction format in one embodiment of the invention). 
     The second-fourth bytes (EVEX Bytes 1-3) include a number of bit fields providing specific capability. 
     REX field  5405  (EVEX Byte 1, bits [7-5])—consists of a EVEX.R bit field (EVEX Byte 1, bit [7]-R), EVEX.X bit field (EVEX byte 1, bit [6]-X), and  5357 BEX byte 1, bit[5]-B). The EVEX.R, EVEX.X, and EVEX.B bit fields provide the same functionality as the corresponding VEX bit fields, and are encoded using is complement form, i.e. ZMM0 is encoded as 1111B, ZMM15 is encoded as 0000B. Other fields of the instructions encode the lower three bits of the register indexes as is known in the art (rrr, xxx, and bbb), so that Rrrr, Xxxx, and Bbbb may be formed by adding EVEX.R, EVEX.X, and EVEX.B. 
     REX′ field  5310 —this is the first part of the REX′ field  5310  and is the EVEX.R′ bit field (EVEX Byte 1, bit [4]-R′) that is used to encode either the upper 16 or lower 16 of the extended 32 register set. In one embodiment of the invention, this bit, along with others as indicated below, is stored in bit inverted format to distinguish (in the well-known x86 32-bit mode) from the BOUND instruction, whose real opcode byte is 62, but does not accept in the MOD R/M field (described below) the value of 11 in the MOD field; alternative embodiments of the invention do not store this and the other indicated bits below in the inverted format. A value of 1 is used to encode the lower 16 registers. In other words, R′Rrrr is formed by combining EVEX.R′, EVEX.R, and the other RRR from other fields. 
     Opcode map field  5415  (EVEX byte 1, bits [3:0]-mmmm)—its content encodes an implied leading opcode byte (0F, 0F 38, or 0F 3). 
     Data element width field  5364  (EVEX byte 2, bit [7]-W)—is represented by the notation EVEX.W. EVEX.W is used to define the granularity (size) of the datatype (either 32-bit data elements or 64-bit data elements). 
     EVEX.vvvv  5420  (EVEX Byte 2, bits [6:3]-vvvv)—the role of EVEX.vvvv may include the following: 1) EVEX.vvvv encodes the first source register operand, specified in inverted (1s complement) form and is valid for instructions with 2 or more source operands; 2) EVEX.vvvv encodes the destination register operand, specified in is complement form for certain vector shifts; or 3) EVEX.vvvv does not encode any operand, the field is reserved and should contain 1111b. Thus, EVEX.vvvv field  5420  encodes the 4 low-order bits of the first source register specifier stored in inverted (1s complement) form. Depending on the instruction, an extra different EVEX bit field is used to extend the specifier size to 32 registers. 
     EVEX.U  5368  Class field (EVEX byte 2, bit [2]-U)—If EVEX.0=0, it indicates class A or EVEX.U0; if EVEX.0=1, it indicates class B or EVEX.U1. 
     Prefix encoding field  5425  (EVEX byte 2, bits [1:0]-pp)—provides additional bits for the base operation field. In addition to providing support for the legacy SSE instructions in the EVEX prefix format, this also has the benefit of compacting the SIMD prefix (rather than requiring a byte to express the SIMD prefix, the EVEX prefix requires only 2 bits). In one embodiment, to support legacy SSE instructions that use a SIMD prefix (66H, F2H, F3H) in both the legacy format and in the EVEX prefix format, these legacy SIMD prefixes are encoded into the SIMD prefix encoding field; and at runtime are expanded into the legacy SIMD prefix prior to being provided to the decoder&#39;s PLA (so the PLA can execute both the legacy and EVEX format of these legacy instructions without modification). Although newer instructions could use the EVEX prefix encoding field&#39;s content directly as an opcode extension, certain embodiments expand in a similar fashion for consistency but allow for different meanings to be specified by these legacy SIMD prefixes. An alternative embodiment may redesign the PLA to support the 2 bit SIMD prefix encodings, and thus not require the expansion. 
     Alpha field  5352  (EVEX byte 3, bit [7]-EH; also known as EVEX.EH, EVEX.rs, EVEX.RL, EVEX.write mask control, and EVEX.N; also illustrated with α)—as previously described, this field is context specific. 
     Beta field  5354  (EVEX byte 3, bits [6:4]-SSS, also known as EVEX.s2-0, EVEX.r2-0, EVEX.rr1, EVEX.LL0, EVEX.LLB; also illustrated with βββ)—as previously described, this field is context specific. 
     REX′ field  5310 —this is the remainder of the REX′ field and is the EVEX.V′ bit field (EVEX Byte 3, bit [3]-V′) that may be used to encode either the upper 16 or lower 16 of the extended 32 register set. This bit is stored in bit inverted format. A value of 1 is used to encode the lower 16 registers. In other words, V′VVVV is formed by combining EVEX.V′, EVEX.vvvv. 
     Write mask field  5370  (EVEX byte 3, bits [2:0]-kkk)—its content specifies the index of a register in the write mask registers as previously described. In one embodiment of the invention, the specific value EVEX.kkk=000 has a special behavior implying no write mask is used for the particular instruction (this may be implemented in a variety of ways including the use of a write mask hardwired to all ones or hardware that bypasses the masking hardware). 
     Real Opcode Field  5430  (Byte 4) is also known as the opcode byte. Part of the opcode is specified in this field. 
     MOD R/M Field  5440  (Byte 5) includes MOD field  5442 , Reg field  5444 , and R/M field  5446 . As previously described, the MOD field&#39;s  5442  content distinguishes between memory access and non-memory access operations. The role of Reg field  5444  can be summarized to two situations: encoding either the destination register operand or a source register operand, or be treated as an opcode extension and not used to encode any instruction operand. The role of R/M field  5446  may include the following: encoding the instruction operand that references a memory address, or encoding either the destination register operand or a source register operand. 
     Scale, Index, Base (SIB) Byte (Byte 6)—As previously described, the scale field&#39;s  5350  content is used for memory address generation. SIB.xxx  5454  and SIB.bbb  5456 —the contents of these fields have been previously referred to with regard to the register indexes Xxxx and Bbbb. 
     Displacement field  5362 A (Bytes 7-10)—when MOD field  5442  contains 10, bytes 7-10 are the displacement field  5362 A, and it works the same as the legacy 32-bit displacement (disp32) and works at byte granularity. 
     Displacement factor field  5362 B (Byte 7)—when MOD field  5442  contains 01, byte 7 is the displacement factor field  5362 B. The location of this field is that same as that of the legacy x86 instruction set 8-bit displacement (disp8), which works at byte granularity. Since disp8 is sign extended, it can only address between −128 and 127 bytes offsets; in terms of 64 byte cache lines, disp8 uses 8 bits that can be set to only four really useful values −128, −64, 0, and 64; since a greater range is often needed, disp32 is used; however, disp32 requires 4 bytes. In contrast to disp8 and disp32, the displacement factor field  5362 B is a reinterpretation of disp8; when using displacement factor field  5362 B, the actual displacement is determined by the content of the displacement factor field multiplied by the size of the memory operand access (N). This type of displacement is referred to as disp8*N. This reduces the average instruction length (a single byte of used for the displacement but with a much greater range). Such compressed displacement is based on the assumption that the effective displacement is multiple of the granularity of the memory access, and hence, the redundant low-order bits of the address offset do not need to be encoded. In other words, the displacement factor field  5362 B substitutes the legacy x86 instruction set 8-bit displacement. Thus, the displacement factor field  5362 B is encoded the same way as an x86 instruction set 8-bit displacement (so no changes in the ModRM/SIB encoding rules) with the only exception that disp8 is overloaded to disp8*N. In other words, there are no changes in the encoding rules or encoding lengths but only in the interpretation of the displacement value by hardware (which needs to scale the displacement by the size of the memory operand to obtain a byte-wise address offset). Immediate field  5372  operates as previously described. 
     Full Opcode Field 
       FIG. 54B  is a block diagram illustrating the fields of the specific vector friendly instruction format  5400  that make up the full opcode field  5374  according to one embodiment of the invention. Specifically, the full opcode field  5374  includes the format field  5340 , the base operation field  5342 , and the data element width (W) field  5364 . The base operation field  5342  includes the prefix encoding field  5425 , the opcode map field  5415 , and the real opcode field  5430 . 
     Register Index Field 
       FIG. 54C  is a block diagram illustrating the fields of the specific vector friendly instruction format  5400  that make up the register index field  5344  according to one embodiment of the invention. Specifically, the register index field  5344  includes the REX field  5405 , the REX′ field  5410 , the MODR/M.reg field  5444 , the MODR/M.r/m field  5446 , the VVVV field  5420 , xxx field  5454 , and the bbb field  5456 . 
     Augmentation Operation Field 
       FIG. 54D  is a block diagram illustrating the fields of the specific vector friendly instruction format  5400  that make up the augmentation operation field  5350  according to one embodiment of the invention. When the class (U) field  5368  contains 0, it signifies EVEX.U0 (class A  5368 A); when it contains 1, it signifies EVEX.U1 (class B  5368 B). When U=0 and the MOD field  5442  contains 11 (signifying a no memory access operation), the alpha field  5352  (EVEX byte 3, bit [7]-EH) is interpreted as the rs field  5352 A. When the rs field  5352 A contains a 1 (round  5352 A. 1 ), the beta field  5354  (EVEX byte 3, bits [6:4]-SSS) is interpreted as the round control field  5354 A. The round control field  5354 A includes a one bit SAE field  5356  and a two bit round operation field  5358 . When the rs field  5352 A contains a 0 (data transform  5352 A. 2 ), the beta field  5354  (EVEX byte 3, bits [6:4]-SSS) is interpreted as a three bit data transform field  5354 B. When U=0 and the MOD field  5442  contains 00, 01, or 10 (signifying a memory access operation), the alpha field  5352  (EVEX byte 3, bit [7]-EH) is interpreted as the eviction hint (EH) field  5352 B and the beta field  5354  (EVEX byte 3, bits [6:4]-SSS) is interpreted as a three bit data manipulation field  5354 C. 
     When U=1, the alpha field  5352  (EVEX byte 3, bit [7]-EH) is interpreted as the write mask control (Z) field  5352 C. When U=1 and the MOD field  5442  contains 11 (signifying a no memory access operation), part of the beta field  5354  (EVEX byte 3, bit [4]-S0) is interpreted as the RL field  5357 A; when it contains a 1 (round  5357 A. 1 ) the rest of the beta field  5354  (EVEX byte 3, bit [6-5]-S2-1) is interpreted as the round operation field  5359 A, while when the RL field  5357 A contains a 0 (VSIZE  5357 .A 2 ) the rest of the beta field  5354  (EVEX byte 3, bit [6-5]-S2-1) is interpreted as the vector length field  5359 B (EVEX byte 3, bit [6-5]-L1-0). When U=1 and the MOD field  5442  contains 00, 01, or 10 (signifying a memory access operation), the beta field  5354  (EVEX byte 3, bits [6:4]-SSS) is interpreted as the vector length field  5359 B (EVEX byte 3, bit [6-5]-L1-0) and the broadcast field  5357 B (EVEX byte 3, bit [4]-B). 
     Exemplary Register Architecture 
       FIG. 55  is a block diagram of a register architecture  5500  according to one embodiment of the invention. In the embodiment illustrated, there are 32 vector registers  5510  that are 512 bits wide; these registers are referenced as zmm0 through zmm31 (the zmm register set). Other embodiments may include, instead of the zmm register set, a set of sixteen vector registers that are 256 bits wide; these registers are referenced as ymm0 through ymm15 (the ymm register set). Other embodiments may include, instead of the zmm register set or ymm register set, a set of sixteen vector registers that are 128 bits wide; these registers are references as xmm0 through xmm15 (the xmm register set). In  FIG. 55 , the lower order 256 bits of the lower 16 zmm registers are overlaid on registers ymm0-15, and the lower order 128 bits of the lower 16 zmm registers (the lower order 128 bits of the ymm registers) are overlaid on registers xmm0-15. 
     The specific vector friendly instruction format  5400  operates on these overlaid register file as illustrated in the below table. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Adjustable Vector 
                   
                   
                   
               
               
                 Length 
                 Class 
                 Operations 
                 Registers 
               
               
                   
               
             
            
               
                 Instruction Templates 
                 A (FIG. 
                 5310, 5315, 
                 zmm registers (the vector 
               
               
                 that do not include the 
                 53A; 
                 5325, 5330 
                 length is 64 byte) 
               
               
                 vector length field 
                 U = 0) 
               
               
                 5359B 
                 B (FIG. 
                 5312 
                 zmm registers (the vector 
               
               
                   
                 53B; 
                   
                 length is 64 byte) 
               
               
                   
                 U = 1) 
               
               
                 Instruction templates 
                 B (FIG. 
                 5317, 5327 
                 zmm, ymm, or xmm 
               
               
                 that do include the 
                 53B; 
                   
                 registers (the vector 
               
               
                 vector length field 
                 U = 1) 
                   
                 length is 64 byte, 
               
               
                 5359B 
                   
                   
                 32 byte, or 16 byte) 
               
               
                   
                   
                   
                 depending on the 
               
               
                   
                   
                   
                 vector length field 
               
               
                   
                   
                   
                 5359B 
               
               
                   
               
            
           
         
       
     
     In other words, the vector length field  5359 B selects between a maximum length and one or more other shorter lengths, where each such shorter length is half the length of the preceding length; and instructions templates without the vector length field  5359 B operate on the maximum vector length. Further, in one embodiment, the class B instruction templates of the specific vector friendly instruction format  5400  operate on packed or scalar single/double-precision floating point data and packed or scalar integer data. Scalar operations are operations performed on the lowest order data element position in an zmm/ymm/xmm register; the higher order data element positions are either left the same as they were prior to the instruction or zeroed depending on the embodiment. 
     Write mask registers  5515 —in the embodiment illustrated, there are 8 write mask registers (k0 through k7), each 64 bits in size. In an alternate embodiment, the write mask registers  5515  are 16 bits in size. In one embodiment, the vector mask register k0 cannot be used as a write mask; when the encoding that would normally indicate k0 is used for a write mask, it selects a hardwired write mask of 0xFFFF, effectively disabling write masking for that instruction. 
     General-purpose registers  5525 —in the embodiment illustrated, there are sixteen 64-bit general-purpose registers that are used along with the existing x86 addressing modes to address memory operands. These registers are referenced by the names RAX, RBX, RCX, RDX, RBP, RSI, RDI, RSP, and R8 through R15. 
     Scalar floating point stack register file (x87 stack)  5545 , on which is aliased the MMX packed integer flat register file  5550 —in the embodiment illustrated, the x87 stack is an eight-element stack used to perform scalar floating-point operations on 32/64/80-bit floating point data using the x87 instruction set extension; while the MMX registers are used to perform operations on 64-bit packed integer data, as well as to hold operands for some operations performed between the MMX and XMM registers. 
     Alternative embodiments of the invention may use wider or narrower registers. Additionally, alternative embodiments of the invention may use more, less, or different register files and registers. 
     Emulation (Including Binary Translation, Code Morphing, Etc.) 
     In some cases, an instruction converter may be used to convert an instruction from a source instruction set to a target instruction set. For example, the instruction converter may translate (e.g., using static binary translation, dynamic binary translation including dynamic compilation), morph, emulate, or otherwise convert an instruction to one or more other instructions to be processed by the core. The instruction converter may be implemented in software, hardware, firmware, or a combination thereof. The instruction converter may be on processor, off processor, or part on and part off processor. 
       FIG. 56  is a block diagram contrasting the use of a software instruction converter to convert binary instructions in a source instruction set to binary instructions in a target instruction set according to embodiments of the invention. In the illustrated embodiment, the instruction converter is a software instruction converter, although alternatively the instruction converter may be implemented in software, firmware, hardware, or various combinations thereof.  FIG. 56  shows a program in a high level language  5602  may be compiled using an x86 compiler  5604  to generate x86 binary code  5606  that may be natively executed by a processor with at least one x86 instruction set core  5616 . The processor with at least one x86 instruction set core  5616  represents any processor that can perform substantially the same functions as an Intel processor with at least one x86 instruction set core by compatibly executing or otherwise processing (1) a substantial portion of the instruction set of the Intel x86 instruction set core or (2) object code versions of applications or other software targeted to run on an Intel processor with at least one x86 instruction set core, in order to achieve substantially the same result as an Intel processor with at least one x86 instruction set core. The x86 compiler  5604  represents a compiler that is operable to generate x86 binary code  5606  (e.g., object code) that can, with or without additional linkage processing, be executed on the processor with at least one x86 instruction set core  5616 . Similarly,  FIG. 56  shows the program in the high level language  5602  may be compiled using an alternative instruction set compiler  5608  to generate alternative instruction set binary code  5610  that may be natively executed by a processor without at least one x86 instruction set core  5614  (e.g., a processor with cores that execute the MIPS instruction set of MIPS Technologies of Sunnyvale, Calif. and/or that execute the ARM instruction set of ARM Holdings of Sunnyvale, Calif.). The instruction converter  5612  is used to convert the x86 binary code  5606  into code that may be natively executed by the processor without an x86 instruction set core  5614 . This converted code is not likely to be the same as the alternative instruction set binary code  5610  because an instruction converter capable of this is difficult to make; however, the converted code will accomplish the general operation and be made up of instructions from the alternative instruction set. Thus, the instruction converter  5612  represents software, firmware, hardware, or a combination thereof that, through emulation, simulation or any other process, allows a processor or other electronic device that does not have an x86 instruction set processor or core to execute the x86 binary code  5606 . 
       FIG. 57  illustrates a conceptual overview of a data center  5700  that may generally be representative of a data center or other type of computing network in/for which one or more techniques described herein may be implemented according to various embodiments. As shown in  FIG. 57 , data center  5700  may generally contain a plurality of racks, each of which may house computing equipment comprising a respective set of physical resources. In the particular non-limiting example depicted in  FIG. 57 , data center  5700  contains four racks  5702 A to  5702 D, which house computing equipment comprising respective sets of physical resources (PCRs)  5705 A to  5705 D. According to this example, a collective set of physical resources  5706  of data center  5700  includes the various sets of physical resources  5705 A to  5705 D that are distributed among racks  5702 A to  5702 D. Physical resources  5706  may include resources of multiple types, such as—for example—processors, co-processors, accelerators, field-programmable gate arrays (FPGAs), memory, and storage. The embodiments are not limited to these examples. 
     The illustrative data center  5700  differs from typical data centers in many ways. For example, in the illustrative embodiment, the circuit boards (“sleds”) on which components such as CPUs, memory, and other components are placed are designed for increased thermal performance. In particular, in the illustrative embodiment, the sleds are shallower than typical boards. In other words, the sleds are shorter from the front to the back, where cooling fans are located. This decreases the length of the path that air must to travel across the components on the board. Further, the components on the sled are spaced further apart than in typical circuit boards, and the components are arranged to reduce or eliminate shadowing (i.e., one component in the air flow path of another component). In the illustrative embodiment, processing components such as the processors are located on a top side of a sled while near memory, such as DIMMs, are located on a bottom side of the sled. As a result of the enhanced airflow provided by this design, the components may operate at higher frequencies and power levels than in typical systems, thereby increasing performance. Furthermore, the sleds are configured to blindly mate with power and data communication cables in each rack  5702 A,  5702 B,  5702 C,  5702 D, enhancing their ability to be quickly removed, upgraded, reinstalled, and/or replaced. Similarly, individual components located on the sleds, such as processors, accelerators, memory, and data storage drives, are configured to be easily upgraded due to their increased spacing from each other. In the illustrative embodiment, the components additionally include hardware attestation features to prove their authenticity. 
     Furthermore, in the illustrative embodiment, the data center  5700  utilizes a single network architecture (“fabric”) that supports multiple other network architectures including Ethernet and Omni-Path. The sleds, in the illustrative embodiment, are coupled to switches via optical fibers, which provide higher bandwidth and lower latency than typical twister pair cabling (e.g., Category 5, Category 5e, Category 6, etc.). Due to the high bandwidth, low latency interconnections and network architecture, the data center  5700  may, in use, pool resources, such as memory, accelerators (e.g., graphics accelerators, FPGAs, ASICs, etc.), and data storage drives that are physically disaggregated, and provide them to compute resources (e.g., processors) on an as needed basis, enabling the compute resources to access the pooled resources as if they were local. The illustrative data center  5700  additionally receives usage information for the various resources, predicts resource usage for different types of workloads based on past resource usage, and dynamically reallocates the resources based on this information. 
     The racks  5702 A,  5702 B,  5702 C,  5702 D of the data center  5700  may include physical design features that facilitate the automation of a variety of types of maintenance tasks. For example, data center  5700  may be implemented using racks that are designed to be robotically-accessed, and to accept and house robotically-manipulable resource sleds. Furthermore, in the illustrative embodiment, the racks  5702 A,  5702 B,  5702 C,  5702 D include integrated power sources that receive a greater voltage than is typical for power sources. The increased voltage enables the power sources to provide additional power to the components on each sled, enabling the components to operate at higher than typical frequencies.  FIG. 58  illustrates an exemplary logical configuration of a rack  202  of the data center  5700 . As shown in  FIG. 58 , rack  5802  may generally house a plurality of sleds, each of which may comprise a respective set of physical resources. In the particular non-limiting example depicted in  FIG. 58 , rack  5802  houses sleds  5804 - 1  to  5804 - 4  comprising respective sets of physical resources  5805 - 1  to  5805 - 4 , each of which constitutes a portion of the collective set of physical resources  5806  comprised in rack  5802 . With respect to  FIG. 1 , if rack  5802  is representative of—for example—rack  102 A, then physical resources  5806  may correspond to the physical resources  105 A comprised in rack  102 A. In the context of this example, physical resources  105 A may thus be made up of the respective sets of physical resources, including physical storage resources  5805 - 1 , physical accelerator resources  5805 - 2 , physical memory resources  5804 - 3 , and physical compute resources  5805 - 5  comprised in the sleds  5804 - 1  to  5804 - 4  of rack  5802 . The embodiments are not limited to this example. Each sled may contain a pool of each of the various types of physical resources (e.g., compute, memory, accelerator, storage). By having robotically accessible and robotically manipulable sleds comprising disaggregated resources, each type of resource can be upgraded independently of each other and at their own optimized refresh rate. 
       FIG. 59  illustrates an example of a data center  5900  that may generally be representative of one in/for which one or more techniques described herein may be implemented according to various embodiments. In the particular non-limiting example depicted in  FIG. 59 , data center  5900  comprises racks  5902 - 1  to  5902 - 32 . In various embodiments, the racks of data center  5900  may be arranged in such fashion as to define and/or accommodate various access pathways. For example, as shown in  FIG. 59 , the racks of data center  5900  may be arranged in such fashion as to define and/or accommodate access pathways  5911 A,  5911 B,  5911 C, and  5911 D. In some embodiments, the presence of such access pathways may generally enable automated maintenance equipment, such as robotic maintenance equipment, to physically access the computing equipment housed in the various racks of data center  5900  and perform automated maintenance tasks (e.g., replace a failed sled, upgrade a sled). In various embodiments, the dimensions of access pathways  5911 A,  5911 B,  5911 C, and  5911 D, the dimensions of racks  5902 - 1  to  5902 - 32 , and/or one or more other aspects of the physical layout of data center  5900  may be selected to facilitate such automated operations. The embodiments are not limited in this context. 
       FIG. 60  illustrates an example of a data center  6000  that may generally be representative of one in/for which one or more techniques described herein may be implemented according to various embodiments. As shown in  FIG. 60 , data center  6000  may feature an optical fabric  6012 . Optical fabric  6012  may generally comprise a combination of optical signaling media (such as optical cabling) and optical switching infrastructure via which any particular sled in data center  6000  can send signals to (and receive signals from) each of the other sleds in data center  6000 . The signaling connectivity that optical fabric  6012  provides to any given sled may include connectivity both to other sleds in a same rack and sleds in other racks. In the particular non-limiting example depicted in  FIG. 60 , data center  6000  includes four racks  6002 A to  6002 D. Racks  6002 A to  6002 D house respective pairs of sleds  6004 A- 1  and  6004 A- 2 ,  6004 B- 1  and  6004 B- 2 ,  6004 C- 1  and  6004 C- 2 , and  6004 D- 1  and  6004 D- 2 . Thus, in this example, data center  6000  comprises a total of eight sleds. Via optical fabric  6012 , each such sled may possess signaling connectivity with each of the seven other sleds in data center  6000 . For example, via optical fabric  6012 , sled  6004 A- 1  in rack  6002 A may possess signaling connectivity with sled  6004 A- 2  in rack  6002 A, as well as the six other sleds  6004 B- 1 ,  6004 B- 2 ,  6004 C- 1 ,  6004 C- 2 ,  6004 D- 1 , and  6004 D- 2  that are distributed among the other racks  6002 B,  6002 C, and  6002 D of data center  6000 . The embodiments are not limited to this example. 
       FIG. 5  illustrates an overview of a connectivity scheme  500  that may generally be representative of link-layer connectivity that may be established in some embodiments among the various sleds of a data center, such as any of example data centers  5700 ,  5900 , and  6000  of  FIGS. 57, 59, and 60 . Connectivity scheme  6100  may be implemented using an optical fabric that features a dual-mode optical switching infrastructure  6114 . Dual-mode optical switching infrastructure  6114  may generally comprise a switching infrastructure that is capable of receiving communications according to multiple link-layer protocols via a same unified set of optical signaling media, and properly switching such communications. In various embodiments, dual-mode optical switching infrastructure  6114  may be implemented using one or more dual-mode optical switches  6115 . In various embodiments, dual-mode optical switches  6115  may generally comprise high-radix switches. In some embodiments, dual-mode optical switches  6115  may comprise multi-ply switches, such as four-ply switches. In various embodiments, dual-mode optical switches  6115  may feature integrated silicon photonics that enable them to switch communications with significantly reduced latency in comparison to conventional switching devices. In some embodiments, dual-mode optical switches  6115  may constitute leaf switches  6130  in a leaf-spine architecture additionally including one or more dual-mode optical spine switches  6120 . 
     In various embodiments, dual-mode optical switches may be capable of receiving both Ethernet protocol communications carrying Internet Protocol (IP packets) and communications according to a second, high-performance computing (HPC) link-layer protocol (e.g., Intel&#39;s Omni-Path Architecture&#39;s, Infiniband) via optical signaling media of an optical fabric. As reflected in  FIG. 61A , with respect to any particular pair of sleds  6104 A and  6104 B possessing optical signaling connectivity to the optical fabric, connectivity scheme  6100  may thus provide support for link-layer connectivity via both Ethernet links and HPC links. Thus, both Ethernet and HPC communications can be supported by a single high-bandwidth, low-latency switch fabric. The embodiments are not limited to this example. 
       FIG. 61B  illustrates a general overview of a rack architecture  600  that may be representative of an architecture of any particular one of the racks depicted in  FIGS. 57 to 60  according to some embodiments. As reflected in  FIG. 61B , rack architecture  600  may generally feature a plurality of sled spaces into which sleds may be inserted, each of which may be robotically-accessible via a rack access region  601 . In the particular non-limiting example depicted in  FIG. 61B , rack architecture  6100  features five sled spaces  6103 - 1  to  6103 - 5 . Sled spaces  6103 - 1  to  6103 - 5  feature respective multi-purpose connector modules (MPCMs)  6116 - 1  to  6116 - 5 .  FIG. 61C  is a detailed diagram of a portion of the rack architecture  6100  of  FIG. 61B . As shown in  FIG. 61C , when a sled is inserted into any given one of sled spaces  6103 - 1  to  6103 - 5 , the corresponding MPCM (e.g., MPCM  6116 - 3 ) may couple with a counterpart MPCM  6120  of the inserted sled. This coupling may provide the inserted sled with connectivity to both signaling infrastructure and power infrastructure of the rack in which it is housed. 
     Included among the types of sleds to be accommodated by rack architecture  6100  may be one or more types of sleds that feature expansion capabilities.  FIG. 62  illustrates an example of a sled  6204  that may be representative of a sled of such a type. As shown in  FIG. 62 , sled  6204  may comprise a set of physical resources  6205 , as well as an MPCM  6216  designed to couple with a counterpart MPCM when sled  6204  is inserted into a sled space such as any of sled spaces  603 - 1  to  603 - 5  of  FIG. 61A . Sled  6204  may also feature an expansion connector  6217 . Expansion connector  6217  may generally comprise a socket, slot, or other type of connection element that is capable of accepting one or more types of expansion modules, such as an expansion sled  6218 . By coupling with a counterpart connector on expansion sled  6218 , expansion connector  6217  may provide physical resources  6205  with access to supplemental computing resources  6205 B residing on expansion sled  6218 . The embodiments are not limited in this context. 
       FIG. 63  illustrates an example of a rack architecture  800  that may be representative of a rack architecture that may be implemented in order to provide support for sleds featuring expansion capabilities, such as sled  6204  of  FIG. 62 . In the particular non-limiting example depicted in  FIG. 63 , rack architecture  6300  includes seven sled spaces  6303 - 1  to  6303 - 7 , which feature respective MPCMs  6316 - 1  to  6316 - 7 . Sled spaces  6303 - 1  to  6303 - 7  include respective primary regions  6303 - 1 A to  6303 - 7 A and respective expansion regions  6303 - 1 B to  6303 - 7 B. With respect to each such sled space, when the corresponding MPCM is coupled with a counterpart MPCM of an inserted sled, the primary region may generally constitute a region of the sled space that physically accommodates the inserted sled. The expansion region may generally constitute a region of the sled space that can physically accommodate an expansion module, such as expansion sled  6218  of  FIG. 62 , in the event that the inserted sled is configured with such a module. 
       FIG. 64  illustrates an example of a rack  902  that may be representative of a rack implemented according to rack architecture  800  of  FIG. 8  according to some embodiments. In the particular non-limiting example depicted in  FIG. 64 , rack  6402  features seven sled spaces  6403 - 1  to  6403 - 7 , which include respective primary regions  6403 - 1 A to  6403 - 7 A and respective expansion regions  6403 - 1 B to  6403 - 7 B. In various embodiments, temperature control in rack  6402  may be implemented using an air cooling system. For example, as reflected in  FIG. 64 , rack  6402  may feature a plurality of fans  6419  that are generally arranged to provide air cooling within the various sled spaces  6403 - 1  to  6403 - 7 . In some embodiments, the height of the sled space is greater than the conventional “1U” server height. In such embodiments, fans  6419  may generally comprise relatively slow, large diameter cooling fans as compared to fans used in conventional rack configurations. Running larger diameter cooling fans at lower speeds may increase fan lifetime relative to smaller diameter cooling fans running at higher speeds while still providing the same amount of cooling. The sleds are physically shallower than conventional rack dimensions. Further, components are arranged on each sled to reduce thermal shadowing (i.e., not arranged serially in the direction of air flow). As a result, the wider, shallower sleds allow for an increase in device performance because the devices can be operated at a higher thermal envelope (e.g., 250 W) due to improved cooling (i.e., no thermal shadowing, more space between devices, more room for larger heat sinks, etc.). 
     MPCMs  6416 - 1  to  6416 - 7  may be configured to provide inserted sleds with access to power sourced by respective power modules  6420 - 1  to  6420 - 7 , each of which may draw power from an external power source  6421 . In various embodiments, external power source  6421  may deliver alternating current (AC) power to rack  6402 , and power modules  6420 - 1  to  6420 - 7  may be configured to convert such AC power to direct current (DC) power to be sourced to inserted sleds. In some embodiments, for example, power modules  6420 - 1  to  6420 - 7  may be configured to convert 277-volt AC power into 12-volt DC power for provision to inserted sleds via respective MPCMs  6416 - 1  to  6416 - 7 . The embodiments are not limited to this example. 
     MPCMs  6416 - 1  to  6416 - 7  may also be arranged to provide inserted sleds with optical signaling connectivity to a dual-mode optical switching infrastructure  6414 , which may be the same as—or similar to—dual-mode optical switching infrastructure  514  of  FIG. 5 . In various embodiments, optical connectors contained in MPCMs  6416 - 1  to  6416 - 7  may be designed to couple with counterpart optical connectors contained in MPCMs of inserted sleds to provide such sleds with optical signaling connectivity to dual-mode optical switching infrastructure  6414  via respective lengths of optical cabling  6422 - 1  to  6422 - 7 . In some embodiments, each such length of optical cabling may extend from its corresponding MPCM to an optical interconnect loom  6423  that is external to the sled spaces of rack  6402 . In various embodiments, optical interconnect loom  6423  may be arranged to pass through a support post or other type of load-bearing element of rack  6402 . The embodiments are not limited in this context. Because inserted sleds connect to an optical switching infrastructure via MPCMs, the resources typically spent in manually configuring the rack cabling to accommodate a newly inserted sled can be saved. 
       FIG. 65  illustrates an example of a sled  6504  that may be representative of a sled designed for use in conjunction with rack  6402  of  FIG. 64  according to some embodiments. Sled  6504  may feature an MPCM  6516  that comprises an optical connector  6516 A and a power connector  6516 B, and that is designed to couple with a counterpart MPCM of a sled space in conjunction with insertion of MPCM  6516  into that sled space. Coupling MPCM  6516  with such a counterpart MPCM may cause power connector  6516  to couple with a power connector comprised in the counterpart MPCM. This may generally enable physical resources  6505  of sled  6504  to source power from an external source, via power connector  6516  and power transmission media  6524  that conductively couples power connector  6516  to physical resources  6505 . 
     Sled  6504  may also include dual-mode optical network interface circuitry  6526 . Dual-mode optical network interface circuitry  6526  may generally comprise circuitry that is capable of communicating over optical signaling media according to each of multiple link-layer protocols supported by dual-mode optical switching infrastructure  6414  of  FIG. 64 . In some embodiments, dual-mode optical network interface circuitry  6526  may be capable both of Ethernet protocol communications and of communications according to a second, high-performance protocol. In various embodiments, dual-mode optical network interface circuitry  6526  may include one or more optical transceiver modules  6527 , each of which may be capable of transmitting and receiving optical signals over each of one or more optical channels. The embodiments are not limited in this context. 
     Coupling MPCM  6516  with a counterpart MPCM of a sled space in a given rack may cause optical connector  6516 A to couple with an optical connector comprised in the counterpart MPCM. This may generally establish optical connectivity between optical cabling of the sled and dual-mode optical network interface circuitry  6526 , via each of a set of optical channels  6525 . Dual-mode optical network interface circuitry  6526  may communicate with the physical resources  6505  of sled  6504  via electrical signaling media  6528 . In addition to the dimensions of the sleds and arrangement of components on the sleds to provide improved cooling and enable operation at a relatively higher thermal envelope (e.g., 250 W), as described above with reference to  FIG. 64 , in some embodiments, a sled may include one or more additional features to facilitate air cooling, such as a heatpipe and/or heat sinks arranged to dissipate heat generated by physical resources  6505 . It is worthy of note that although the example sled  6504  depicted in  FIG. 65  does not feature an expansion connector, any given sled that features the design elements of sled  6504  may also feature an expansion connector according to some embodiments. The embodiments are not limited in this context. 
       FIG. 66  illustrates an example of a data center  6600  that may generally be representative of one in/for which one or more techniques described herein may be implemented according to various embodiments. As reflected in  FIG. 66 , a physical infrastructure management framework  6650 A may be implemented to facilitate management of a physical infrastructure  6600 A of data center  6600 . In various embodiments, one function of physical infrastructure management framework  6650 A may be to manage automated maintenance functions within data center  6600 , such as the use of robotic maintenance equipment to service computing equipment within physical infrastructure  6600 A. In some embodiments, physical infrastructure  6600 A may feature an advanced telemetry system that performs telemetry reporting that is sufficiently robust to support remote automated management of physical infrastructure  6600 A. In various embodiments, telemetry information provided by such an advanced telemetry system may support features such as failure prediction/prevention capabilities and capacity planning capabilities. In some embodiments, physical infrastructure management framework  6650 A may also be configured to manage authentication of physical infrastructure components using hardware attestation techniques. For example, robots may verify the authenticity of components before installation by analyzing information collected from a radio frequency identification (RFID) tag associated with each component to be installed. The embodiments are not limited in this context. 
     As shown in  FIG. 66 , the physical infrastructure  6600 A of data center  6600  may comprise an optical fabric  6612 , which may include a dual-mode optical switching infrastructure  6614 . Optical fabric  6612  and dual-mode optical switching infrastructure  6614  may be the same as—or similar to—optical fabric  412  of  FIG. 4  and dual-mode optical switching infrastructure  514  of  FIG. 5 , respectively, and may provide high-bandwidth, low-latency, multi-protocol connectivity among sleds of data center  6600 . As discussed above, with reference to  FIG. 1 , in various embodiments, the availability of such connectivity may make it feasible to disaggregate and dynamically pool resources such as accelerators, memory, and storage. In some embodiments, for example, one or more pooled accelerator sleds  6630  may be included among the physical infrastructure  6600 A of data center  6600 , each of which may comprise a pool of accelerator resources—such as co-processors and/or FPGAs, for example—that is available globally accessible to other sleds via optical fabric  6612  and dual-mode optical switching infrastructure  6614 . 
     In another example, in various embodiments, one or more pooled storage sleds  6632  may be included among the physical infrastructure  6600 A of data center  6600 , each of which may comprise a pool of storage resources that is available globally accessible to other sleds via optical fabric  6612  and dual-mode optical switching infrastructure  6614 . In some embodiments, such pooled storage sleds  6632  may comprise pools of solid-state storage devices such as solid-state drives (SSDs). In various embodiments, one or more high-performance processing sleds  6634  may be included among the physical infrastructure  6600 A of data center  6600 . In some embodiments, high-performance processing sleds  6634  may comprise pools of high-performance processors, as well as cooling features that enhance air cooling to yield a higher thermal envelope of up to 250 W or more. In various embodiments, any given high-performance processing sled  6634  may feature an expansion connector  6617  that can accept a far memory expansion sled, such that the far memory that is locally available to that high-performance processing sled  6634  is disaggregated from the processors and near memory comprised on that sled. In some embodiments, such a high-performance processing sled  6634  may be configured with far memory using an expansion sled that comprises low-latency SSD storage. The optical infrastructure allows for compute resources on one sled to utilize remote accelerator/FPGA, memory, and/or SSD resources that are disaggregated on a sled located on the same rack or any other rack in the data center. The remote resources can be located one switch jump away or two-switch jumps away in the spine-leaf network architecture described above with reference to  FIG. 61 . The embodiments are not limited in this context. 
     In various embodiments, one or more layers of abstraction may be applied to the physical resources of physical infrastructure  6600 A in order to define a virtual infrastructure, such as a software-defined infrastructure  6600 B. In some embodiments, virtual computing resources  6636  of software-defined infrastructure  6600 B may be allocated to support the provision of cloud services  6640 . In various embodiments, particular sets of virtual computing resources  6636  may be grouped for provision to cloud services  6640  in the form of SDI services  6638 . Examples of cloud services  6640  may include—without limitation—software as a service (SaaS) services  6642 , platform as a service (PaaS) services  6644 , and infrastructure as a service (IaaS) services  6646 . 
     In some embodiments, management of software-defined infrastructure  6600 B may be conducted using a virtual infrastructure management framework  6650 B. In various embodiments, virtual infrastructure management framework  6650 B may be designed to implement workload fingerprinting techniques and/or machine-learning techniques in conjunction with managing allocation of virtual computing resources  6636  and/or SDI services  6638  to cloud services  6640 . In some embodiments, virtual infrastructure management framework  6650 B may use/consult telemetry data in conjunction with performing such resource allocation. In various embodiments, an application/service management framework  6650 C may be implemented in order to provide QoS management capabilities for cloud services  6640 . The embodiments are not limited in this context. 
     Operations in flow diagrams may have been described with reference to exemplary embodiments of other figures. However, it should be understood that the operations of the flow diagrams may be performed by embodiments of the invention other than those discussed with reference to other figures, and the embodiments of the invention discussed with reference to other figures may perform operations different than those discussed with reference to flow diagrams. Furthermore, while the flow diagrams in the figures show a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). 
     One or more parts of embodiments of the invention may be implemented using different combinations of software, firmware, and/or hardware. Embodiments may be implemented using an electronic device that stores and transmits (internally and/or with other electronic devices over a network) code (which is composed of software instructions and which is sometimes referred to as computer program code or a computer program) and/or data using machine-readable media (also called computer-readable media), such as machine-readable storage media (e.g., magnetic disks, optical disks, read only memory (ROM), flash memory devices, phase change memory) and machine-readable transmission media (also called a carrier) (e.g., electrical, optical, radio, acoustical or other form of propagated signals—such as carrier waves, infrared signals). Thus, an electronic device (e.g., a computer) may include hardware and software, such as a set of one or more processors coupled to one or more machine-readable storage media to store code for execution on the set of processors and/or to store data. For instance, an electronic device may include non-volatile memory containing the code since the non-volatile memory may persist code/data even when the electronic device is turned off (when power is removed), and while the electronic device is turned on that part of the code that is to be executed by the processor(s) of that electronic device is typically copied from the slower non-volatile memory into volatile memory (e.g., dynamic random access memory (DRAM), static random access memory (SRAM)) of that electronic device. Typical electronic devices also include a set or one or more physical network interface(s) to establish network connections (to transmit and/or receive code and/or data using propagating signals) with other electronic devices. 
     While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.