# Patent

## Title
Instruction and logic for non-blocking register reclamation

## Abstract

A processor includes a logic to execute a first instruction and a second instruction. The first instruction is ordered before the second instruction. Each instruction references a respective logical register assigned to a respective physical register. The processor also includes logic to reassign a physical register of the second instruction to another logical register before retirement of the first instruction.

## Background
FIELD OF THE INVENTION
The present disclosure pertains to the field of processing logic, microprocessors, and associated instruction set architecture that, when executed by the processor or other processing logic, perform logical, mathematical, or other functional operations.
DESCRIPTION OF RELATED ART
Multiprocessor systems are becoming more and more common. Applications of multiprocessor systems include dynamic domain partitioning all the way down to desktop computing. In order to take advantage of multiprocessor systems, code to be executed may be separated into multiple threads for execution by various processing entities. Each thread may be executed in parallel with one another. Furthermore, in order to increase the utility of a processing entity, out-of-order execution may be employed. Out-of-order execution may execute instructions as input to such instructions is made available. Thus, an instruction that appears later in a code sequence may be executed before an instruction appearing earlier in a code sequence.



DESCRIPTION OF THE FIGURES
Embodiments are illustrated by way of example and not limitation in the Figures of the accompanying drawings:
FIG. 1A is a block diagram of an exemplary computer system formed with a processor that may include execution units to execute an instruction, in accordance with embodiments of the present disclosure;
FIG. 1B illustrates a data processing system, in accordance with embodiments of the present disclosure;
FIG. 1C illustrates other embodiments of a data processing system for performing text string comparison operations;
FIG. 2 is a block diagram of the micro-architecture for a processor that may include logic circuits to perform instructions, in accordance with embodiments of the present disclosure;
FIG. 3A illustrates various packed data type representations in multimedia registers, in accordance with embodiments of the present disclosure;
FIG. 3B illustrates possible in-register data storage formats, in accordance with embodiments of the present disclosure;
FIG. 3C illustrates various signed and unsigned packed data type representations in multimedia registers, in accordance with embodiments of the present disclosure;
FIG. 3D illustrates an embodiment of an operation encoding format;
FIG. 3E illustrates another possible operation encoding format having forty or more bits, in accordance with embodiments of the present disclosure;
FIG. 3F illustrates yet another possible operation encoding format, in accordance with embodiments of the present disclosure;
FIG. 4A is a block diagram illustrating an in-order pipeline and a register renaming stage, out-of-order issue/execution pipeline, in accordance with embodiments of the present disclosure;
FIG. 4B is a block diagram illustrating an in-order architecture core and a register renaming logic, out-of-order issue/execution logic to be included in a processor, in accordance with embodiments of the present disclosure;
FIG. 5A is a block diagram of a processor, in accordance with embodiments of the present disclosure;
FIG. 5B is a block diagram of an example implementation of a core, in accordance with embodiments of the present disclosure;
FIG. 6 is a block diagram of a system, in accordance with embodiments of the present disclosure;
FIG. 7 is a block diagram of a second system, in accordance with embodiments of the present disclosure;
FIG. 8 is a block diagram of a third system in accordance with embodiments of the present disclosure;
FIG. 9 is a block diagram of a system-on-a-chip, in accordance with embodiments of the present disclosure;
FIG. 10 illustrates a processor containing a central processing unit and a graphics processing unit which may perform at least one instruction, in accordance with embodiments of the present disclosure;
FIG. 11 is a block diagram illustrating the development of IP cores, in accordance with embodiments of the present disclosure;
FIG. 12 illustrates how an instruction of a first type may be emulated by a processor of a different type, in accordance with embodiments of the present disclosure;
FIG. 13 illustrates 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, in accordance with embodiments of the present disclosure;
FIG. 14 is a block diagram of an instruction set architecture of a processor, in accordance with embodiments of the present disclosure;
FIG. 15 is a more detailed block diagram of an instruction set architecture of a processor, in accordance with embodiments of the present disclosure;
FIG. 16 is a block diagram of an execution pipeline for an instruction set architecture of a processor, in accordance with embodiments of the present disclosure;
FIG. 17 is a block diagram of an electronic device for utilizing a processor, in accordance with embodiments of the present disclosure;
FIG. 18 illustrates an example of a system for implementing an instruction and logic for reclamation of non-blocking registers, in accordance with embodiments of the present disclosure;
FIGS. 19A and 19B illustrate example operation of a system to perform non-blocking register reclamation, in accordance with embodiments of the present disclosure; and
FIG. 20 is an illustration of an example method for reclaiming non-blocking registers, in accordance with embodiments of the present disclosure.



DETAILED DESCRIPTION
The following description describes an instruction and processing logic for non-blocking register reclamation within or in association with a processor, virtual processor, package, computer system, or other processing apparatus. Such a processing apparatus may include an out-of-order processor. In the following description, numerous specific details such as processing logic, processor types, micro-architectural conditions, events, enablement mechanisms, and the like are set forth in order to provide a more thorough understanding of embodiments of the present disclosure. It will be appreciated, however, by one skilled in the art that the embodiments may be practiced without such specific details. Additionally, some well-known structures, circuits, and the like have not been shown in detail to avoid unnecessarily obscuring embodiments of the present disclosure.
Although the following embodiments are described with reference to a processor, other embodiments are applicable to other types of integrated circuits and logic devices. Similar techniques and teachings of embodiments of the present disclosure may be applied to other types of circuits or semiconductor devices that may benefit from higher pipeline throughput and improved performance. The teachings of embodiments of the present disclosure are applicable to any processor or machine that performs data manipulations. However, the embodiments are not limited to processors or machines that perform 512-bit, 256-bit, 128-bit, 64-bit, 32-bit, or 16-bit data operations and may be applied to any processor and machine in which manipulation or management of data may be performed. In addition, the following description provides examples, and the accompanying drawings show various examples for the purposes of illustration. However, these examples should not be construed in a limiting sense as they are merely intended to provide examples of embodiments of the present disclosure rather than to provide an exhaustive list of all possible implementations of embodiments of the present disclosure.
Although the below examples describe instruction handling and distribution in the context of execution units and logic circuits, other embodiments of the present disclosure may be accomplished by way of a data or instructions stored on a machine-readable, tangible medium, which when performed by a machine cause the machine to perform functions consistent with at least one embodiment of the disclosure. In one embodiment, functions associated with embodiments of the present disclosure are embodied in machine-executable instructions. The instructions may be used to cause a general-purpose or special-purpose processor that may be programmed with the instructions to perform the steps of the present disclosure. Embodiments of the present disclosure may be provided as a computer program product or software which may include a machine or computer-readable medium having stored thereon instructions which may be used to program a computer (or other electronic devices) to perform one or more operations according to embodiments of the present disclosure. Furthermore, steps of embodiments of the present disclosure might be performed by specific hardware components that contain fixed-function logic for performing the steps, or by any combination of programmed computer components and fixed-function hardware components.
Instructions used to program logic to perform embodiments of the present disclosure may be stored within a memory in the system, such as DRAM, cache, flash memory, or other storage. Furthermore, the instructions may be distributed via a network or by way of other computer-readable media. Thus a machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer), but is not limited to, floppy diskettes, optical disks, Compact Discs, Read-Only Memory (CD-ROMs), and magneto-optical disks, Read-Only Memory (ROMs), Random Access Memory (RAM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), magnetic or optical cards, flash memory, or a tangible, machine-readable storage used in the transmission of information over the Internet via electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Accordingly, the computer-readable medium may include any type of tangible machine-readable medium suitable for storing or transmitting electronic instructions or information in a form readable by a machine (e.g., a computer).
A design may go through various stages, from creation to simulation to fabrication. Data representing a design may represent the design in a number of manners. First, as may be useful in simulations, the hardware may be represented using a hardware description language or another functional description language. Additionally, a circuit level model with logic and/or transistor gates may be produced at some stages of the design process. Furthermore, designs, at some stage, may reach a level of data representing the physical placement of various devices in the hardware model. In cases wherein some semiconductor fabrication techniques are used, the data representing the hardware model may be the data specifying the presence or absence of various features on different mask layers for masks used to produce the integrated circuit. In any representation of the design, the data may be stored in any form of a machine-readable medium. A memory or a magnetic or optical storage such as a disc may be the machine-readable medium to store information transmitted via optical or electrical wave modulated or otherwise generated to transmit such information. When an electrical carrier wave indicating or carrying the code or design is transmitted, to the extent that copying, buffering, or retransmission of the electrical signal is performed, a new copy may be made. Thus, a communication provider or a network provider may store on a tangible, machine-readable medium, at least temporarily, an article, such as information encoded into a carrier wave, embodying techniques of embodiments of the present disclosure.
In modern processors, a number of different execution units may be used to process and execute a variety of code and instructions. Some instructions may be quicker to complete while others may take a number of clock cycles to complete. The faster the throughput of instructions, the better the overall performance of the processor. Thus it would be advantageous to have as many instructions execute as fast as possible. However, there may be certain instructions that have greater complexity and require more in terms of execution time and processor resources, such as floating point instructions, load/store operations, data moves, etc.
As more computer systems are used in internet, text, and multimedia applications, additional processor support has been introduced over time. In one embodiment, an instruction set may be associated with one or more computer architectures, including data types, instructions, register architecture, addressing modes, memory architecture, interrupt and exception handling, and external input and output (I/O).
In one embodiment, the instruction set architecture (ISA) may be implemented by one or more micro-architectures, which may include processor logic and circuits used to implement one or more instruction sets. Accordingly, processors with different micro-architectures may share at least a portion of a common instruction set. For example, Intel® Pentium 4 processors, Intel® CoreTM processors, and processors from Advanced Micro Devices, Inc. of Sunnyvale Calif. implement nearly identical versions of the x86 instruction set (with some extensions that have been added with newer versions), but have different internal designs. Similarly, processors designed by other processor development companies, such as ARM Holdings, Ltd., MIPS, or their licensees or adopters, may share at least a portion a common instruction set, but may include different processor designs. For example, the same register architecture of the ISA may be implemented in different ways in different micro-architectures using new or well-known techniques, including dedicated physical registers, one or more dynamically allocated physical registers using a register renaming mechanism (e.g., the use of a Register Alias Table (RAT), a Reorder Buffer (ROB) and a retirement register file. In one embodiment, registers may include one or more registers, register architectures, register files, or other register sets that may or may not be addressable by a software programmer.
An instruction may include one or more instruction formats. In one embodiment, an instruction format may indicate various fields (number of bits, location of bits, etc.) to specify, among other things, the operation to be performed and the operands on which that operation will be performed. In a further embodiment, some instruction formats may be further defined by instruction templates (or sub-formats). For example, the instruction templates of a given instruction format may be defined to have different subsets of the instruction format's fields and/or defined to have a given field interpreted differently. In one embodiment, an instruction may be expressed using an instruction format (and, if defined, in a given one of the instruction templates of that instruction format) and specifies or indicates the operation and the operands upon which the operation will operate.
Scientific, financial, auto-vectorized general purpose, RMS (recognition, mining, and synthesis), and visual and multimedia applications (e.g., 2D/3D graphics, image processing, video compression/decompression, voice recognition algorithms and audio manipulation) may require the same operation to be performed on a large number of data items. In one embodiment, Single Instruction Multiple Data (SIMD) refers to a type of instruction that causes a processor to perform an operation on multiple data elements. SIMD technology may be used in processors that may logically divide the bits in a register into a number of fixed-sized or variable-sized data elements, each of which represents a separate value. For example, in one embodiment, the bits in a 64-bit register may be organized as a source operand containing four separate 16-bit data elements, each of which represents a separate 16-bit value. This type of data may be referred to as ‘packed’ data type or ‘vector’ data type, and operands of this data type may be referred to as packed data operands or vector operands. In one embodiment, a packed data item or vector may be a sequence of packed data elements stored within a single register, and a packed data operand or a vector operand may a source or destination operand of a SIMD instruction (or ‘packed data instruction’ or a ‘vector instruction’). In one embodiment, a SIMD instruction specifies a single vector operation to be performed on two source vector operands to generate a destination vector operand (also referred to as a result vector operand) of the same or different size, with the same or different number of data elements, and in the same or different data element order.
SIMD technology, such as that employed by the Intel® CoreTM processors having an instruction set including x86, MMXTM, Streaming SIMD Extensions (SSE), SSE2, SSE3, SSE4.1, and SSE4.2 instructions, ARM processors, such as the ARM Cortex® family of processors having an instruction set including the Vector Floating Point (VFP) and/or NEON instructions, and MIPS processors, such as the Loongson family of processors developed by the Institute of Computing Technology (ICT) of the Chinese Academy of Sciences, has enabled a significant improvement in application performance (CoreTM and MMXTM are registered trademarks or trademarks of Intel Corporation of Santa Clara, Calif.).
In one embodiment, destination and source registers/data may be generic terms to represent the source and destination of the corresponding data or operation. In some embodiments, they may be implemented by registers, memory, or other storage areas having other names or functions than those depicted. For example, in one embodiment, “DEST1” may be a temporary storage register or other storage area, whereas “SRC1” and “SRC2” may be a first and second source storage register or other storage area, and so forth. In other embodiments, two or more of the SRC and DEST storage areas may correspond to different data storage elements within the same storage area (e.g., a SIMD register). In one embodiment, one of the source registers may also act as a destination register by, for example, writing back the result of an operation performed on the first and second source data to one of the two source registers serving as a destination registers.
FIG. 1A is a block diagram of an exemplary computer system formed with a processor that may include execution units to execute an instruction, in accordance with embodiments of the present disclosure. System 100 may include a component, such as a processor 102 to employ execution units including logic to perform algorithms for process data, in accordance with the present disclosure, such as in the embodiment described herein. System 100 may be representative of processing systems based on the PENTIUM® III, PENTIUM® 4, XeonTM, Itanium®, XScaleTM and/or StrongARMTM microprocessors available from Intel Corporation of Santa Clara, Calif., although other systems (including PCs having other microprocessors, engineering workstations, set-top boxes and the like) may also be used. In one embodiment, sample system 100 may execute a version of the WINDOWSTM operating system available from Microsoft Corporation of Redmond, Wash., although other operating systems (UNIX and Linux for example), embedded software, and/or graphical user interfaces, may also be used. Thus, embodiments of the present disclosure are not limited to any specific combination of hardware circuitry and software.
Embodiments are not limited to computer systems. Embodiments of the present disclosure may be used in other devices such as handheld devices and embedded applications. Some examples of handheld devices include cellular phones, Internet Protocol devices, digital cameras, personal digital assistants (PDAs), and handheld PCs. Embedded applications may include a micro controller, a digital signal processor (DSP), system on a chip, network computers (NetPC), set-top boxes, network hubs, wide area network (WAN) switches, or any other system that may perform one or more instructions in accordance with at least one embodiment.
Computer system 100 may include a processor 102 that may include one or more execution units 108 to perform an algorithm to perform at least one instruction in accordance with one embodiment of the present disclosure. One embodiment may be described in the context of a single processor desktop or server system, but other embodiments may be included in a multiprocessor system. System 100 may be an example of a ‘hub’ system architecture. System 100 may include a processor 102 for processing data signals. Processor 102 may include a complex instruction set computer (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing a combination of instruction sets, or any other processor device, such as a digital signal processor, for example. In one embodiment, processor 102 may be coupled to a processor bus 110 that may transmit data signals between processor 102 and other components in system 100. The elements of system 100 may perform conventional functions that are well known to those familiar with the art.
In one embodiment, processor 102 may include a Level 1 (L1) internal cache memory 104. Depending on the architecture, the processor 102 may have a single internal cache or multiple levels of internal cache. In another embodiment, the cache memory may reside external to processor 102. Other embodiments may also include a combination of both internal and external caches depending on the particular implementation and needs. Register file 106 may store different types of data in various registers including integer registers, floating point registers, status registers, and instruction pointer register.
Execution unit 108, including logic to perform integer and floating point operations, also resides in processor 102. Processor 102 may also include a microcode (ucode) ROM that stores microcode for certain macroinstructions. In one embodiment, execution unit 108 may include logic to handle a packed instruction set 109. By including the packed instruction set 109 in the instruction set of a general-purpose processor 102, along with associated circuitry to execute the instructions, the operations used by many multimedia applications may be performed using packed data in a general-purpose processor 102. Thus, many multimedia applications may be accelerated and executed more efficiently by using the full width of a processor's data bus for performing operations on packed data. This may eliminate the need to transfer smaller units of data across the processor's data bus to perform one or more operations one data element at a time.
Embodiments of an execution unit 108 may also be used in micro controllers, embedded processors, graphics devices, DSPs, and other types of logic circuits. System 100 may include a memory 120. Memory 120 may be implemented as a Dynamic Random Access Memory (DRAM) device, a Static Random Access Memory (SRAM) device, flash memory device, or other memory device. Memory 120 may store instructions and/or data represented by data signals that may be executed by processor 102.
A system logic chip 116 may be coupled to processor bus 110 and memory 120. System logic chip 116 may include a memory controller hub (MCH). Processor 102 may communicate with MCH 116 via a processor bus 110. MCH 116 may provide a high bandwidth memory path 118 to memory 120 for instruction and data storage and for storage of graphics commands, data and textures. MCH 116 may direct data signals between processor 102, memory 120, and other components in system 100 and to bridge the data signals between processor bus 110, memory 120, and system I/O 122. In some embodiments, the system logic chip 116 may provide a graphics port for coupling to a graphics controller 112. MCH 116 may be coupled to memory 120 through a memory interface 118. Graphics card 112 may be coupled to MCH 116 through an Accelerated Graphics Port (AGP) interconnect 114.
System 100 may use a proprietary hub interface bus 122 to couple MCH 116 to I/O controller hub (ICH) 130. In one embodiment, ICH 130 may provide direct connections to some I/O devices via a local I/O bus. The local I/O bus may include a high-speed I/O bus for connecting peripherals to memory 120, chipset, and processor 102. Examples may include the audio controller, firmware hub (flash BIOS) 128, wireless transceiver 126, data storage 124, legacy I/O controller containing user input and keyboard interfaces, a serial expansion port such as Universal Serial Bus (USB), and a network controller 134. Data storage device 124 may comprise a hard disk drive, a floppy disk drive, a CD-ROM device, a flash memory device, or other mass storage device.
For another embodiment of a system, an instruction in accordance with one embodiment may be used with a system on a chip. One embodiment of a system on a chip comprises of a processor and a memory. The memory for one such system may include a flash memory. The flash memory may be located on the same die as the processor and other system components. Additionally, other logic blocks such as a memory controller or graphics controller may also be located on a system on a chip.
FIG. 1B illustrates a data processing system 140 which implements the principles of embodiments of the present disclosure. It will be readily appreciated by one of skill in the art that the embodiments described herein may operate with alternative processing systems without departure from the scope of embodiments of the disclosure.
Computer system 140 comprises a processing core 159 for performing at least one instruction in accordance with one embodiment. In one embodiment, processing core 159 represents a processing unit of any type of architecture, including but not limited to a CISC, a RISC or a VLIW-type architecture. Processing core 159 may also be suitable for manufacture in one or more process technologies and by being represented on a machine-readable media in sufficient detail, may be suitable to facilitate said manufacture.
Processing core 159 comprises an execution unit 142, a set of register files 145, and a decoder 144. Processing core 159 may also include additional circuitry (not shown) which may be unnecessary to the understanding of embodiments of the present disclosure. Execution unit 142 may execute instructions received by processing core 159. In addition to performing typical processor instructions, execution unit 142 may perform instructions in packed instruction set 143 for performing operations on packed data formats. Packed instruction set 143 may include instructions for performing embodiments of the disclosure and other packed instructions. Execution unit 142 may be coupled to register file 145 by an internal bus. Register file 145 may represent a storage area on processing core 159 for storing information, including data. As previously mentioned, it is understood that the storage area may store the packed data might not be critical. Execution unit 142 may be coupled to decoder 144. Decoder 144 may decode instructions received by processing core 159 into control signals and/or microcode entry points. In response to these control signals and/or microcode entry points, execution unit 142 performs the appropriate operations. In one embodiment, the decoder may interpret the opcode of the instruction, which will indicate what operation should be performed on the corresponding data indicated within the instruction.
Processing core 159 may be coupled with bus 141 for communicating with various other system devices, which may include but are not limited to, for example, Synchronous Dynamic Random Access Memory (SDRAM) control 146, Static Random Access Memory (SRAM) control 147, burst flash memory interface 148, Personal Computer Memory Card International Association (PCMCIA)/Compact Flash (CF) card control 149, Liquid Crystal Display (LCD) control 150, Direct Memory Access (DMA) controller 151, and alternative bus master interface 152. In one embodiment, data processing system 140 may also comprise an I/O bridge 154 for communicating with various I/O devices via an I/O bus 153. Such I/O devices may include but are not limited to, for example, Universal Asynchronous Receiver/Transmitter (UART) 155, Universal Serial Bus (USB) 156, Bluetooth wireless UART 157 and I/O expansion interface 158.
One embodiment of data processing system 140 provides for mobile, network and/or wireless communications and a processing core 159 that may perform SIMD operations including a text string comparison operation. Processing core 159 may be programmed with various audio, video, imaging and communications algorithms including discrete transformations such as a Walsh-Hadamard transform, a fast Fourier transform (FFT), a discrete cosine transform (DCT), and their respective inverse transforms; compression/decompression techniques such as color space transformation, video encode motion estimation or video decode motion compensation; and modulation/demodulation (MODEM) functions such as pulse coded modulation (PCM).
FIG. 1C illustrates other embodiments of a data processing system that performs SIMD text string comparison operations. In one embodiment, data processing system 160 may include a main processor 166, a SIMD coprocessor 161, a cache memory 167, and an input/output system 168. Input/output system 168 may optionally be coupled to a wireless interface 169. SIMD coprocessor 161 may perform operations including instructions in accordance with one embodiment. In one embodiment, processing core 170 may be suitable for manufacture in one or more process technologies and by being represented on a machine-readable media in sufficient detail, may be suitable to facilitate the manufacture of all or part of data processing system 160 including processing core 170.
In one embodiment, SIMD coprocessor 161 comprises an execution unit 162 and a set of register files 164. One embodiment of main processor 165 comprises a decoder 165 to recognize instructions of instruction set 163 including instructions in accordance with one embodiment for execution by execution unit 162. In other embodiments, SIMD coprocessor 161 also comprises at least part of decoder 165 to decode instructions of instruction set 163. Processing core 170 may also include additional circuitry (not shown) which may be unnecessary to the understanding of embodiments of the present disclosure.
In operation, main processor 166 executes a stream of data processing instructions that control data processing operations of a general type including interactions with cache memory 167, and input/output system 168. Embedded within the stream of data processing instructions may be SIMD coprocessor instructions. Decoder 165 of main processor 166 recognizes these SIMD coprocessor instructions as being of a type that should be executed by an attached SIMD coprocessor 161. Accordingly, main processor 166 issues these SIMD coprocessor instructions (or control signals representing SIMD coprocessor instructions) on the coprocessor bus 166. From coprocessor bus 166, these instructions may be received by any attached SIMD coprocessors. In this case, SIMD coprocessor 161 may accept and execute any received SIMD coprocessor instructions intended for it.
Data may be received via wireless interface 169 for processing by the SIMD coprocessor instructions. For one example, voice communication may be received in the form of a digital signal, which may be processed by the SIMD coprocessor instructions to regenerate digital audio samples representative of the voice communications. For another example, compressed audio and/or video may be received in the form of a digital bit stream, which may be processed by the SIMD coprocessor instructions to regenerate digital audio samples and/or motion video frames. In one embodiment of processing core 170, main processor 166, and a SIMD coprocessor 161 may be integrated into a single processing core 170 comprising an execution unit 162, a set of register files 164, and a decoder 165 to recognize instructions of instruction set 163 including instructions in accordance with one embodiment.
FIG. 2 is a block diagram of the micro-architecture for a processor 200 that may include logic circuits to perform instructions, in accordance with embodiments of the present disclosure. In some embodiments, an instruction in accordance with one embodiment may be implemented to operate on data elements having sizes of byte, word, doubleword, quadword, etc., as well as datatypes, such as single and double precision integer and floating point datatypes. In one embodiment, in-order front end 201 may implement a part of processor 200 that may fetch instructions to be executed and prepares the instructions to be used later in the processor pipeline. Front end 201 may include several units. In one embodiment, instruction prefetcher 226 fetches instructions from memory and feeds the instructions to an instruction decoder 228 which in turn decodes or interprets the instructions. For example, in one embodiment, the decoder decodes a received instruction into one or more operations called “micro-instructions” or “micro-operations” (also called micro op or uops) that the machine may execute. In other embodiments, the decoder parses the instruction into an opcode and corresponding data and control fields that may be used by the micro-architecture to perform operations in accordance with one embodiment. In one embodiment, trace cache 230 may assemble decoded uops into program ordered sequences or traces in uop queue 234 for execution. When trace cache 230 encounters a complex instruction, microcode ROM 232 provides the uops needed to complete the operation.
Some instructions may be converted into a single micro-op, whereas others need several micro-ops to complete the full operation. In one embodiment, if more than four micro-ops are needed to complete an instruction, decoder 228 may access microcode ROM 232 to perform the instruction. In one embodiment, an instruction may be decoded into a small number of micro-ops for processing at instruction decoder 228. In another embodiment, an instruction may be stored within microcode ROM 232 should a number of micro-ops be needed to accomplish the operation. Trace cache 230 refers to an entry point programmable logic array (PLA) to determine a correct micro-instruction pointer for reading the micro-code sequences to complete one or more instructions in accordance with one embodiment from micro-code ROM 232. After microcode ROM 232 finishes sequencing micro-ops for an instruction, front end 201 of the machine may resume fetching micro-ops from trace cache 230.
Out-of-order execution engine 203 may prepare instructions for execution. The out-of-order execution logic has a number of buffers to smooth out and re-order the flow of instructions to optimize performance as they go down the pipeline and get scheduled for execution. The allocator logic allocates the machine buffers and resources that each uop needs in order to execute. The register renaming logic renames logic registers onto entries in a register file. The allocator also allocates an entry for each uop in one of the two uop queues, one for memory operations and one for non-memory operations, in front of the instruction schedulers: memory scheduler, fast scheduler 202, slow/general floating point scheduler 204, and simple floating point scheduler 206. Uop schedulers 202, 204, 206, determine when a uop is ready to execute based on the readiness of their dependent input register operand sources and the availability of the execution resources the uops need to complete their operation. Fast scheduler 202 of one embodiment may schedule on each half of the main clock cycle while the other schedulers may only schedule once per main processor clock cycle. The schedulers arbitrate for the dispatch ports to schedule uops for execution.
Register files 208, 210 may be arranged between schedulers 202, 204, 206, and execution units 212, 214, 216, 218, 220, 222, 224 in execution block 211. Each of register files 208, 210 perform integer and floating point operations, respectively. Each register file 208, 210, may include a bypass network that may bypass or forward just completed results that have not yet been written into the register file to new dependent uops. Integer register file 208 and floating point register file 210 may communicate data with the other. In one embodiment, integer register file 208 may be split into two separate register files, one register file for low-order thirty-two bits of data and a second register file for high order thirty-two bits of data. Floating point register file 210 may include 128-bit wide entries because floating point instructions typically have operands from 64 to 128 bits in width.
Execution block 211 may contain execution units 212, 214, 216, 218, 220, 222, 224. Execution units 212, 214, 216, 218, 220, 222, 224 may execute the instructions. Execution block 211 may include register files 208, 210 that store the integer and floating point data operand values that the micro-instructions need to execute. In one embodiment, processor 200 may comprise a number of execution units: address generation unit (AGU) 212, AGU 214, fast Arithmetic Logic Unit (ALU) 216, fast ALU 218, slow ALU 220, floating point ALU 222, floating point move unit 224. In another embodiment, floating point execution blocks 222, 224, may execute floating point, MMX, SIMD, and SSE, or other operations. In yet another embodiment, floating point ALU 222 may include a 64-bit by 64-bit floating point divider to execute divide, square root, and remainder micro-ops. In various embodiments, instructions involving a floating point value may be handled with the floating point hardware. In one embodiment, ALU operations may be passed to high-speed ALU execution units 216, 218. High-speed ALUs 216, 218 may execute fast operations with an effective latency of half a clock cycle. In one embodiment, most complex integer operations go to slow ALU 220 as slow ALU 220 may include integer execution hardware for long-latency type of operations, such as a multiplier, shifts, flag logic, and branch processing. Memory load/store operations may be executed by AGUs 212, 214. In one embodiment, integer ALUs 216, 218, 220 may perform integer operations on 64-bit data operands. In other embodiments, ALUs 216, 218, 220 may be implemented to support a variety of data bit sizes including sixteen, thirty-two, 128, 256, etc. Similarly, floating point units 222, 224 may be implemented to support a range of operands having bits of various widths. In one embodiment, floating point units 222, 224, may operate on 128-bit wide packed data operands in conjunction with SIMD and multimedia instructions.
In one embodiment, uops schedulers 202, 204, 206, dispatch dependent operations before the parent load has finished executing. As uops may be speculatively scheduled and executed in processor 200, processor 200 may also include logic to handle memory misses. If a data load misses in the data cache, there may be dependent operations in flight in the pipeline that have left the scheduler with temporarily incorrect data. A replay mechanism tracks and re-executes instructions that use incorrect data. Only the dependent operations might need to be replayed and the independent ones may be allowed to complete. The schedulers and replay mechanism of one embodiment of a processor may also be designed to catch instruction sequences for text string comparison operations.
The term “registers” may refer to the on-board processor storage locations that may be used as part of instructions to identify operands. In other words, registers may be those that may be usable from the outside of the processor (from a programmer's perspective). However, in some embodiments registers might not be limited to a particular type of circuit. Rather, a register may store data, provide data, and perform the functions described herein. The registers described herein may be implemented by circuitry within a processor using any number of different techniques, such as dedicated physical registers, dynamically allocated physical registers using register renaming, combinations of dedicated and dynamically allocated physical registers, etc. In one embodiment, integer registers store 32-bit integer data. A register file of one embodiment also contains eight multimedia SIMD registers for packed data. For the discussions below, the registers may be understood to be data registers designed to hold packed data, such as 64-bit wide MMXTM registers (also referred to as ‘mm’ registers in some instances) in microprocessors enabled with MMX technology from Intel Corporation of Santa Clara, Calif. These MMX registers, available in both integer and floating point forms, may operate with packed data elements that accompany SIMD and SSE instructions. Similarly, 128-bit wide XMM registers relating to SSE2, SSE3, SSE4, or beyond (referred to generically as “SSEx”) technology may hold such packed data operands. In one embodiment, in storing packed data and integer data, the registers do not need to differentiate between the two data types. In one embodiment, integer and floating point may be contained in the same register file or different register files. Furthermore, in one embodiment, floating point and integer data may be stored in different registers or the same registers.
In the examples of the following figures, a number of data operands may be described. FIG. 3A illustrates various packed data type representations in multimedia registers, in accordance with embodiments of the present disclosure. FIG. 3A illustrates data types for a packed byte 310, a packed word 320, and a packed doubleword (dword) 330 for 128-bit wide operands. Packed byte format 310 of this example may be 128 bits long and contains sixteen packed byte data elements. A byte may be defined, for example, as eight bits of data. Information for each byte data element may be stored in bit 7 through bit 0 for byte 0, bit 15 through bit 8 for byte 1, bit 23 through bit 16 for byte 2, and finally bit 120 through bit 127 for byte 15. Thus, all available bits may be used in the register. This storage arrangement increases the storage efficiency of the processor. As well, with sixteen data elements accessed, one operation may now be performed on sixteen data elements in parallel.
Generally, a data element may include an individual piece of data that is stored in a single register or memory location with other data elements of the same length. In packed data sequences relating to SSEx technology, the number of data elements stored in a XMM register may be 128 bits divided by the length in bits of an individual data element. Similarly, in packed data sequences relating to MMX and SSE technology, the number of data elements stored in an MMX register may be 64 bits divided by the length in bits of an individual data element. Although the data types illustrated in FIG. 3A may be 128 bits long, embodiments of the present disclosure may also operate with 64-bit wide or other sized operands. Packed word format 320 of this example may be 128 bits long and contains eight packed word data elements. Each packed word contains sixteen bits of information. Packed doubleword format 330 of FIG. 3A may be 128 bits long and contains four packed doubleword data elements. Each packed doubleword data element contains thirty-two bits of information. A packed quadword may be 128 bits long and contain two packed quad-word data elements.
FIG. 3B illustrates possible in-register data storage formats, in accordance with embodiments of the present disclosure. Each packed data may include more than one independent data element. Three packed data formats are illustrated; packed half 341, packed single 342, and packed double 343. One embodiment of packed half 341, packed single 342, and packed double 343 contain fixed-point data elements. For another embodiment one or more of packed half 341, packed single 342, and packed double 343 may contain floating-point data elements. One embodiment of packed half 341 may be 128 bits long containing eight 16-bit data elements. One embodiment of packed single 342 may be 128 bits long and contains four 32-bit data elements. One embodiment of packed double 343 may be 128 bits long and contains two 64-bit data elements. It will be appreciated that such packed data formats may be further extended to other register lengths, for example, to 96-bits, 160-bits, 192-bits, 224-bits, 256-bits or more.
FIG. 3C illustrates various signed and unsigned packed data type representations in multimedia registers, in accordance with embodiments of the present disclosure. Unsigned packed byte representation 344 illustrates the storage of an unsigned packed byte in a SIMD register. Information for each byte data element may be stored in bit 7 through bit 0 for byte 0, bit 15 through bit 8 for byte 1, bit 23 through bit 16 for byte 2, and finally bit 120 through bit 127 for byte 15. Thus, all available bits may be used in the register. This storage arrangement may increase the storage efficiency of the processor. As well, with sixteen data elements accessed, one operation may now be performed on sixteen data elements in a parallel fashion. Signed packed byte representation 345 illustrates the storage of a signed packed byte. Note that the eighth bit of every byte data element may be the sign indicator. Unsigned packed word representation 346 illustrates how word seven through word zero may be stored in a SIMD register. Signed packed word representation 347 may be similar to the unsigned packed word in-register representation 346. Note that the sixteenth bit of each word data element may be the sign indicator. Unsigned packed doubleword representation 348 shows how doubleword data elements are stored. Signed packed doubleword representation 349 may be similar to unsigned packed doubleword in-register representation 348. Note that the necessary sign bit may be the thirty-second bit of each doubleword data element.
FIG. 3D illustrates an embodiment of an operation encoding (opcode). Furthermore, format 360 may include register/memory operand addressing modes corresponding with a type of opcode format described in the “IA-32 Intel Architecture Software Developer's Manual Volume 2: Instruction Set Reference,” which is available from Intel Corporation, Santa Clara, Calif. on the world-wide-web (www) at intel.com/design/litcentr. In one embodiment, and instruction may be encoded by one or more of fields 361 and 362. Up to two operand locations per instruction may be identified, including up to two source operand identifiers 364 and 365. In one embodiment, destination operand identifier 366 may be the same as source operand identifier 364, whereas in other embodiments they may be different. In another embodiment, destination operand identifier 366 may be the same as source operand identifier 365, whereas in other embodiments they may be different. In one embodiment, one of the source operands identified by source operand identifiers 364 and 365 may be overwritten by the results of the text string comparison operations, whereas in other embodiments identifier 364 corresponds to a source register element and identifier 365 corresponds to a destination register element. In one embodiment, operand identifiers 364 and 365 may identify 32-bit or 64-bit source and destination operands.
FIG. 3E illustrates another possible operation encoding (opcode) format 370, having forty or more bits, in accordance with embodiments of the present disclosure. Opcode format 370 corresponds with opcode format 360 and comprises an optional prefix byte 378. An instruction according to one embodiment may be encoded by one or more of fields 378, 371, and 372. Up to two operand locations per instruction may be identified by source operand identifiers 374 and 375 and by prefix byte 378. In one embodiment, prefix byte 378 may be used to identify 32-bit or 64-bit source and destination operands. In one embodiment, destination operand identifier 376 may be the same as source operand identifier 374, whereas in other embodiments they may be different. For another embodiment, destination operand identifier 376 may be the same as source operand identifier 375, whereas in other embodiments they may be different. In one embodiment, an instruction operates on one or more of the operands identified by operand identifiers 374 and 375 and one or more operands identified by operand identifiers 374 and 375 may be overwritten by the results of the instruction, whereas in other embodiments, operands identified by identifiers 374 and 375 may be written to another data element in another register. Opcode formats 360 and 370 allow register to register, memory to register, register by memory, register by register, register by immediate, register to memory addressing specified in part by MOD fields 363 and 373 and by optional scale-index-base and displacement bytes.
FIG. 3F illustrates yet another possible operation encoding (opcode) format, in accordance with embodiments of the present disclosure. 64-bit single instruction multiple data (SIMD) arithmetic operations may be performed through a coprocessor data processing (CDP) instruction. Operation encoding (opcode) format 380 depicts one such CDP instruction having CDP opcode fields 382 an 0064 389. The type of CDP instruction, for another embodiment, operations may be encoded by one or more of fields 383, 384, 387, and 388. Up to three operand locations per instruction may be identified, including up to two source operand identifiers 385 and 390 and one destination operand identifier 386. One embodiment of the coprocessor may operate on eight, sixteen, thirty-two, and 64-bit values. In one embodiment, an instruction may be performed on integer data elements. In some embodiments, an instruction may be executed conditionally, using condition field 381. For some embodiments, source data sizes may be encoded by field 383. In some embodiments, Zero (Z), negative (N), carry (C), and overflow (V) detection may be done on SIMD fields. For some instructions, the type of saturation may be encoded by field 384.
FIG. 4A is a block diagram illustrating an in-order pipeline and a register renaming stage, out-of-order issue/execution pipeline, in accordance with embodiments of the present disclosure. FIG. 4B is a block diagram illustrating an in-order architecture core and a register renaming logic, out-of-order issue/execution logic to be included in a processor, in accordance with embodiments of the present disclosure. The solid lined boxes in FIG. 4A illustrate the in-order pipeline, while the dashed lined boxes illustrates the register renaming, out-of-order issue/execution pipeline. Similarly, the solid lined boxes in FIG. 4B illustrate the in-order architecture logic, while the dashed lined boxes illustrates the register renaming logic and out-of-order issue/execution logic.
In FIG. 4A, a processor pipeline 400 may include a fetch stage 402, a length decode stage 404, a decode stage 406, an allocation stage 408, a renaming stage 410, a scheduling (also known as a dispatch or issue) stage 412, a register read/memory read stage 414, an execute stage 416, a write-back/memory-write stage 418, an exception handling stage 422, and a commit stage 424.
In FIG. 4B, arrows denote a coupling between two or more units and the direction of the arrow indicates a direction of data flow between those units. FIG. 4B shows processor core 490 including a front end unit 430 coupled to an execution engine unit 450, and both may be coupled to a memory unit 470.
Core 490 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. In one embodiment, core 490 may be a special-purpose core, such as, for example, a network or communication core, compression engine, graphics core, or the like.
Front end unit 430 may include a branch prediction unit 432 coupled to an instruction cache unit 434. Instruction cache unit 434 may be coupled to an instruction Translation Lookaside Buffer (TLB) 436. TLB 436 may be coupled to an instruction fetch unit 438, which is coupled to a decode unit 440. Decode unit 440 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 may be decoded from, or which otherwise reflect, or may be derived from, the original instructions. The decoder 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, instruction cache unit 434 may be further coupled to a level 2 (L2) cache unit 476 in memory unit 470. Decode unit 440 may be coupled to a rename/allocator unit 452 in execution engine unit 450.
Execution engine unit 450 may include rename/allocator unit 452 coupled to a retirement unit 454 and a set of one or more scheduler units 456. Scheduler units 456 represent any number of different schedulers, including reservations stations, central instruction window, etc. Scheduler units 456 may be coupled to physical register file units 458. Each of physical register file units 458 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, etc., status (e.g., an instruction pointer that is the address of the next instruction to be executed), etc. Physical register file units 458 may be overlapped by retirement unit 154 to illustrate various ways in which register renaming and out-of-order execution may be implemented (e.g., using one or more reorder buffers and one or more retirement register files, using one or more future files, one or more history buffers, and one or more retirement register files; using register maps and a pool of registers; etc.). Generally, the architectural registers may be visible from the outside of the processor or from a programmer's perspective. The registers might not be limited to any known particular type of circuit. Various different types of registers may be suitable as long as they store and provide data as described herein. Examples of suitable registers include, but might not be limited to, dedicated physical registers, dynamically allocated physical registers using register renaming, combinations of dedicated and dynamically allocated physical registers, etc. Retirement unit 454 and physical register file units 458 may be coupled to execution clusters 460. Execution clusters 460 may include a set of one or more execution units 162 and a set of one or more memory access units 464. Execution units 462 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. Scheduler units 456, physical register file units 458, and execution clusters 460 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 unit, and/or execution cluster—and in the case of a separate memory access pipeline, certain embodiments may be implemented in which only the execution cluster of this pipeline has memory access units 464). 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 464 may be coupled to memory unit 470, which may include a data TLB unit 472 coupled to a data cache unit 474 coupled to a level 2 (L2) cache unit 476. In one exemplary embodiment, memory access units 464 may include a load unit, a store address unit, and a store data unit, each of which may be coupled to data TLB unit 472 in memory unit 470. L2 cache unit 476 may be 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 pipeline 400 as follows: 1) instruction fetch 438 may perform fetch and length decoding stages 402 and 404; 2) decode unit 440 may perform decode stage 406; 3) rename/allocator unit 452 may perform allocation stage 408 and renaming stage 410; 4) scheduler units 456 may perform schedule stage 412; 5) physical register file units 458 and memory unit 470 may perform register read/memory read stage 414; execution cluster 460 may perform execute stage 416; 6) memory unit 470 and physical register file units 458 may perform write-back/memory-write stage 418; 7) various units may be involved in the performance of exception handling stage 422; and 8) retirement unit 454 and physical register file units 458 may perform commit stage 424.
Core 490 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.).
It should be understood that the core may support multithreading (executing two or more parallel sets of operations or threads) in a variety of manners. Multithreading support may be performed by, for example, including time sliced multithreading, simultaneous multithreading (where a single physical core provides a logical core for each of the threads that physical core is simultaneously multithreading), or a combination thereof. Such a combination may include, for example, time sliced fetching and decoding and simultaneous multithreading thereafter such as in the Intel® Hyperthreading technology.
While register renaming may be 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 may also include a separate instruction and data cache units 434/474 and a shared L2 cache unit 476, other 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 may be external to the core and/or the processor. In other embodiments, all of the cache may be external to the core and/or the processor.
FIG. 5A is a block diagram of a processor 500, in accordance with embodiments of the present disclosure. In one embodiment, processor 500 may include a multicore processor. Processor 500 may include a system agent 510 communicatively coupled to one or more cores 502. Furthermore, cores 502 and system agent 510 may be communicatively coupled to one or more caches 506. Cores 502, system agent 510, and caches 506 may be communicatively coupled via one or more memory control units 552. Furthermore, cores 502, system agent 510, and caches 506 may be communicatively coupled to a graphics module 560 via memory control units 552.
Processor 500 may include any suitable mechanism for interconnecting cores 502, system agent 510, and caches 506, and graphics module 560. In one embodiment, processor 500 may include a ring-based interconnect unit 508 to interconnect cores 502, system agent 510, and caches 506, and graphics module 560. In other embodiments, processor 500 may include any number of well-known techniques for interconnecting such units. Ring-based interconnect unit 508 may utilize memory control units 552 to facilitate interconnections.
Processor 500 may include a memory hierarchy comprising one or more levels of caches within the cores, one or more shared cache units such as caches 506, or external memory (not shown) coupled to the set of integrated memory controller units 552. Caches 506 may include any suitable cache. In one embodiment, caches 506 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.
In various embodiments, one or more of cores 502 may perform multithreading. System agent 510 may include components for coordinating and operating cores 502. System agent unit 510 may include for example a Power Control Unit (PCU). The PCU may be or include logic and components needed for regulating the power state of cores 502. System agent 510 may include a display engine 512 for driving one or more externally connected displays or graphics module 560. System agent 510 may include an interface 1214 for communications busses for graphics. In one embodiment, interface 1214 may be implemented by PCI Express (PCIe). In a further embodiment, interface 1214 may be implemented by PCI Express Graphics (PEG). System agent 510 may include a direct media interface (DMI) 516. DMI 516 may provide links between different bridges on a motherboard or other portion of a computer system. System agent 510 may include a PCIe bridge 1218 for providing PCIe links to other elements of a computing system. PCIe bridge 1218 may be implemented using a memory controller 1220 and coherence logic 1222.
Cores 502 may be implemented in any suitable manner. Cores 502 may be homogenous or heterogeneous in terms of architecture and/or instruction set. In one embodiment, some of cores 502 may be in-order while others may be out-of-order. In another embodiment, two or more of cores 502 may execute the same instruction set, while others may execute only a subset of that instruction set or a different instruction set.
Processor 500 may include a general-purpose processor, such as a CoreTM i3, i5, i7, 2 Duo and Quad, XeonTM, ItaniumTM, XScaleTM or StrongARMTM processor, which may be available from Intel Corporation, of Santa Clara, Calif. Processor 500 may be provided from another company, such as ARM Holdings, Ltd, MIPS, etc. Processor 500 may be a special-purpose processor, such as, for example, a network or communication processor, compression engine, graphics processor, co-processor, embedded processor, or the like. Processor 500 may be implemented on one or more chips. Processor 500 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.
In one embodiment, a given one of caches 506 may be shared by multiple ones of cores 502. In another embodiment, a given one of caches 506 may be dedicated to one of cores 502. The assignment of caches 506 to cores 502 may be handled by a cache controller or other suitable mechanism. A given one of caches 506 may be shared by two or more cores 502 by implementing time-slices of a given cache 506.
Graphics module 560 may implement an integrated graphics processing subsystem. In one embodiment, graphics module 560 may include a graphics processor. Furthermore, graphics module 560 may include a media engine 565. Media engine 565 may provide media encoding and video decoding.
FIG. 5B is a block diagram of an example implementation of a core 502, in accordance with embodiments of the present disclosure. Core 502 may include a front end 570 communicatively coupled to an out-of-order engine 580. Core 502 may be communicatively coupled to other portions of processor 500 through cache hierarchy 503.
Front end 570 may be implemented in any suitable manner, such as fully or in part by front end 201 as described above. In one embodiment, front end 570 may communicate with other portions of processor 500 through cache hierarchy 503. In a further embodiment, front end 570 may fetch instructions from portions of processor 500 and prepare the instructions to be used later in the processor pipeline as they are passed to out-of-order execution engine 580.
Out-of-order execution engine 580 may be implemented in any suitable manner, such as fully or in part by out-of-order execution engine 203 as described above. Out-of-order execution engine 580 may prepare instructions received from front end 570 for execution. Out-of-order execution engine 580 may include an allocate module 1282. In one embodiment, allocate module 1282 may allocate resources of processor 500 or other resources, such as registers or buffers, to execute a given instruction. Allocate module 1282 may make allocations in schedulers, such as a memory scheduler, fast scheduler, or floating point scheduler. Such schedulers may be represented in FIG. 5B by resource schedulers 584. Allocate module 1282 may be implemented fully or in part by the allocation logic described in conjunction with FIG. 2. Resource schedulers 584 may determine when an instruction is ready to execute based on the readiness of a given resource's sources and the availability of execution resources needed to execute an instruction. Resource schedulers 584 may be implemented by, for example, schedulers 202, 204, 206 as discussed above. Resource schedulers 584 may schedule the execution of instructions upon one or more resources. In one embodiment, such resources may be internal to core 502, and may be illustrated, for example, as resources 586. In another embodiment, such resources may be external to core 502 and may be accessible by, for example, cache hierarchy 503. Resources may include, for example, memory, caches, register files, or registers. Resources internal to core 502 may be represented by resources 586 in FIG. 5B. As necessary, values written to or read from resources 586 may be coordinated with other portions of processor 500 through, for example, cache hierarchy 503. As instructions are assigned resources, they may be placed into a reorder buffer 588. Reorder buffer 588 may track instructions as they are executed and may selectively reorder their execution based upon any suitable criteria of processor 500. In one embodiment, reorder buffer 588 may identify instructions or a series of instructions that may be executed independently. Such instructions or a series of instructions may be executed in parallel from other such instructions. Parallel execution in core 502 may be performed by any suitable number of separate execution blocks or virtual processors. In one embodiment, shared resources—such as memory, registers, and caches—may be accessible to multiple virtual processors within a given core 502. In other embodiments, shared resources may be accessible to multiple processing entities within processor 500.
Cache hierarchy 503 may be implemented in any suitable manner. For example, cache hierarchy 503 may include one or more lower or mid-level caches, such as caches 572, 574. In one embodiment, cache hierarchy 503 may include an LLC 595 communicatively coupled to caches 572, 574. In another embodiment, LLC 595 may be implemented in a module 590 accessible to all processing entities of processor 500. In a further embodiment, module 590 may be implemented in an uncore module of processors from Intel, Inc. Module 590 may include portions or subsystems of processor 500 necessary for the execution of core 502 but might not be implemented within core 502. Besides LLC 595, Module 590 may include, for example, hardware interfaces, memory coherency coordinators, interprocessor interconnects, instruction pipelines, or memory controllers. Access to RAM 599 available to processor 500 may be made through module 590 and, more specifically, LLC 595. Furthermore, other instances of core 502 may similarly access module 590. Coordination of the instances of core 502 may be facilitated in part through module 590.
FIGS. 6-8 may illustrate exemplary systems suitable for including processor 500, while FIG. 9 may illustrate an exemplary System on a Chip (SoC) that may include one or more of cores 502. Other system designs and implementations known in the arts for laptops, desktops, handheld PCs, personal digital assistants, engineering workstations, servers, network devices, network hubs, switches, embedded processors, DSPs, graphics devices, video game devices, set-top boxes, micro controllers, cell phones, portable media players, hand held devices, and various other electronic devices, may also be suitable. In general, a huge variety of systems or electronic devices that incorporate a processor and/or other execution logic as disclosed herein may be generally suitable.
FIG. 6 illustrates a block diagram of a system 600, in accordance with embodiments of the present disclosure. System 600 may include one or more processors 610, 615, which may be coupled to Graphics Memory Controller Hub (GMCH) 620. The optional nature of additional processors 615 is denoted in FIG. 6 with broken lines.
Each processor 610,615 may be some version of processor 500. However, it should be noted that integrated graphics logic and integrated memory control units might not exist in processors 610,615. FIG. 6 illustrates that GMCH 620 may be coupled to a memory 640 that may be, for example, a dynamic random access memory (DRAM). The DRAM may, for at least one embodiment, be associated with a non-volatile cache.
GMCH 620 may be a chipset, or a portion of a chipset. GMCH 620 may communicate with processors 610, 615 and control interaction between processors 610, 615 and memory 640. GMCH 620 may also act as an accelerated bus interface between the processors 610, 615 and other elements of system 600. In one embodiment, GMCH 620 communicates with processors 610, 615 via a multi-drop bus, such as a frontside bus (FSB) 695.
Furthermore, GMCH 620 may be coupled to a display 645 (such as a flat panel display). In one embodiment, GMCH 620 may include an integrated graphics accelerator. GMCH 620 may be further coupled to an input/output (I/O) controller hub (ICH) 650, which may be used to couple various peripheral devices to system 600. External graphics device 660 may include be a discrete graphics device coupled to ICH 650 along with another peripheral device 670.
In other embodiments, additional or different processors may also be present in system 600. For example, additional processors 610, 615 may include additional processors that may be the same as processor 610, additional processors that may be heterogeneous or asymmetric to processor 610, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units), field programmable gate arrays, or any other processor. There may be a variety of differences between the physical resources 610, 615 in terms of a spectrum of metrics of merit including architectural, micro-architectural, thermal, power consumption characteristics, and the like. These differences may effectively manifest themselves as asymmetry and heterogeneity amongst processors 610, 615. For at least one embodiment, various processors 610, 615 may reside in the same die package.
FIG. 7 illustrates a block diagram of a second system 700, in accordance with embodiments of the present disclosure. As shown in FIG. 7, multiprocessor system 700 may include a point-to-point interconnect system, and may include a first processor 770 and a second processor 780 coupled via a point-to-point interconnect 750. Each of processors 770 and 780 may be some version of processor 500 as one or more of processors 610,615.
While FIG. 7 may illustrate two processors 770, 780, it is to be understood that the scope of the present disclosure is not so limited. In other embodiments, one or more additional processors may be present in a given processor.
Processors 770 and 780 are shown including integrated memory controller units 772 and 782, respectively. Processor 770 may also include as part of its bus controller units point-to-point (P-P) interfaces 776 and 778; similarly, second processor 780 may include P-P interfaces 786 and 788. Processors 770, 780 may exchange information via a point-to-point (P-P) interface 750 using P-P interface circuits 778, 788. As shown in FIG. 7, IMCs 772 and 782 may couple the processors to respective memories, namely a memory 732 and a memory 734, which in one embodiment may be portions of main memory locally attached to the respective processors.
Processors 770, 780 may each exchange information with a chipset 790 via individual P-P interfaces 752, 754 using point to point interface circuits 776, 794, 786, 798. In one embodiment, chipset 790 may also exchange information with a high-performance graphics circuit 738 via a high-performance graphics interface 739.
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' local cache information may be stored in the shared cache if a processor is placed into a low power mode.
Chipset 790 may be coupled to a first bus 716 via an interface 796. In one embodiment, first bus 716 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 disclosure is not so limited.
As shown in FIG. 7, various I/O devices 714 may be coupled to first bus 716, along with a bus bridge 718 which couples first bus 716 to a second bus 720. In one embodiment, second bus 720 may be a Low Pin Count (LPC) bus. Various devices may be coupled to second bus 720 including, for example, a keyboard and/or mouse 722, communication devices 727 and a storage unit 728 such as a disk drive or other mass storage device which may include instructions/code and data 730, in one embodiment. Further, an audio I/O 724 may be coupled to second bus 720. Note that other architectures may be possible. For example, instead of the point-to-point architecture of FIG. 7, a system may implement a multi-drop bus or other such architecture.
FIG. 8 illustrates a block diagram of a third system 800 in accordance with embodiments of the present disclosure. Like elements in FIGS. 7 and 8 bear like reference numerals, and certain aspects of FIG. 7 have been omitted from FIG. 8 in order to avoid obscuring other aspects of FIG. 8.
FIG. 8 illustrates that processors 870, 880 may include integrated memory and I/O Control Logic (“CL”) 872 and 882, respectively. For at least one embodiment, CL 872, 882 may include integrated memory controller units such as that described above in connection with FIGS. 5 and 7. In addition. CL 872, 882 may also include I/O control logic. FIG. 8 illustrates that not only memories 832, 834 may be coupled to CL 872, 882, but also that I/O devices 814 may also be coupled to control logic 872, 882. Legacy I/O devices 815 may be coupled to chipset 890.
FIG. 9 illustrates a block diagram of a SoC 900, in accordance with embodiments of the present disclosure. Similar elements in FIG. 5 bear like reference numerals. Also, dashed lined boxes may represent optional features on more advanced SoCs. An interconnect units 902 may be coupled to: an application processor 910 which may include a set of one or more cores 902A-N and shared cache units 906; a system agent unit 910; a bus controller units 916; an integrated memory controller units 914; a set or one or more media processors 920 which may include integrated graphics logic 908, an image processor 924 for providing still and/or video camera functionality, an audio processor 926 for providing hardware audio acceleration, and a video processor 928 for providing video encode/decode acceleration; an SRAM unit 930; a DMA unit 932; and a display unit 940 for coupling to one or more external displays.
FIG. 10 illustrates a processor containing a Central Processing Unit (CPU) and a graphics processing unit (GPU), which may perform at least one instruction, in accordance with embodiments of the present disclosure. In one embodiment, an instruction to perform operations according to at least one embodiment could be performed by the CPU. In another embodiment, the instruction could be performed by the GPU. In still another embodiment, the instruction may be performed through a combination of operations performed by the GPU and the CPU. For example, in one embodiment, an instruction in accordance with one embodiment may be received and decoded for execution on the GPU. However, one or more operations within the decoded instruction may be performed by a CPU and the result returned to the GPU for final retirement of the instruction. Conversely, in some embodiments, the CPU may act as the primary processor and the GPU as the co-processor.
In some embodiments, instructions that benefit from highly parallel, throughput processors may be performed by the GPU, while instructions that benefit from the performance of processors that benefit from deeply pipelined architectures may be performed by the CPU. For example, graphics, scientific applications, financial applications and other parallel workloads may benefit from the performance of the GPU and be executed accordingly, whereas more sequential applications, such as operating system kernel or application code may be better suited for the CPU.
In FIG. 10, processor 1000 includes a CPU 1005, GPU 1010, image processor 1015, video processor 1020, USB controller 1025, UART controller 1030, SPI/SDIO controller 1035, display device 1040, memory interface controller 1045, MIPI controller 1050, flash memory controller 1055, Dual Data Rate (DDR) controller 1060, security engine 1065, and I2S/I2C controller 1070. Other logic and circuits may be included in the processor of FIG. 10, including more CPUs or GPUs and other peripheral interface controllers.
One or more aspects of at least one embodiment may be implemented by representative data 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 (“tape”) and supplied to various customers or manufacturing facilities to load into the fabrication machines that actually make the logic or processor. For example, IP cores, such as the CortexTM family of processors developed by ARM Holdings, Ltd. and Loongson IP cores developed the Institute of Computing Technology (ICT) of the Chinese Academy of Sciences may be licensed or sold to various customers or licensees, such as Texas Instruments, Qualcomm, Apple, or Samsung and implemented in processors produced by these customers or licensees.
FIG. 11 illustrates a block diagram illustrating the development of IP cores, in accordance with embodiments of the present disclosure. Storage 1130 may include simulation software 1120 and/or hardware or software model 1110. In one embodiment, the data representing the IP core design may be provided to storage 1130 via memory 1140 (e.g., hard disk), wired connection (e.g., internet) 1150 or wireless connection 1160. The IP core information generated by the simulation tool and model may then be transmitted to a fabrication facility where it may be fabricated by a third party to perform at least one instruction in accordance with at least one embodiment.
In some embodiments, one or more instructions may correspond to a first type or architecture (e.g., x86) and be translated or emulated on a processor of a different type or architecture (e.g., ARM). An instruction, according to one embodiment, may therefore be performed on any processor or processor type, including ARM, x86, MIPS, a GPU, or other processor type or architecture.
FIG. 12 illustrates how an instruction of a first type may be emulated by a processor of a different type, in accordance with embodiments of the present disclosure. In FIG. 12, program 1205 contains some instructions that may perform the same or substantially the same function as an instruction according to one embodiment. However the instructions of program 1205 may be of a type and/or format that is different from or incompatible with processor 1215, meaning the instructions of the type in program 1205 may not be able to execute natively by the processor 1215. However, with the help of emulation logic, 1210, the instructions of program 1205 may be translated into instructions that may be natively be executed by the processor 1215. In one embodiment, the emulation logic may be embodied in hardware. In another embodiment, the emulation logic may be embodied in a tangible, machine-readable medium containing software to translate instructions of the type in program 1205 into the type natively executable by processor 1215. In other embodiments, emulation logic may be a combination of fixed-function or programmable hardware and a program stored on a tangible, machine-readable medium. In one embodiment, the processor contains the emulation logic, whereas in other embodiments, the emulation logic exists outside of the processor and may be provided by a third party. In one embodiment, the processor may load the emulation logic embodied in a tangible, machine-readable medium containing software by executing microcode or firmware contained in or associated with the processor.
FIG. 13 illustrates 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, in accordance with embodiments of the present disclosure. In the illustrated embodiment, the instruction converter may be a software instruction converter, although the instruction converter may be implemented in software, firmware, hardware, or various combinations thereof. FIG. 13 shows a program in a high level language 1302 may be compiled using an x86 compiler 1304 to generate x86 binary code 1306 that may be natively executed by a processor with at least one x86 instruction set core 1316. The processor with at least one x86 instruction set core 1316 represents any processor that may perform substantially the same functions as a 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. x86 compiler 1304 represents a compiler that may be operable to generate x86 binary code 1306 (e.g., object code) that may, with or without additional linkage processing, be executed on the processor with at least one x86 instruction set core 1316. Similarly, FIG. 13 shows the program in high level language 1302 may be compiled using an alternative instruction set compiler 1308 to generate alternative instruction set binary code 1310 that may be natively executed by a processor without at least one x86 instruction set core 1314 (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.). Instruction converter 1312 may be used to convert x86 binary code 1306 into code that may be natively executed by the processor without an x86 instruction set core 1314. This converted code might not be the same as alternative instruction set binary code 1310; however, the converted code will accomplish the general operation and be made up of instructions from the alternative instruction set. Thus, instruction converter 1312 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 x86 binary code 1306.
FIG. 14 is a block diagram of an instruction set architecture 1400 of a processor, in accordance with embodiments of the present disclosure. Instruction set architecture 1400 may include any suitable number or kind of components.
For example, instruction set architecture 1400 may include processing entities such as one or more cores 1406, 1407 and a graphics processing unit 1415. Cores 1406, 1407 may be communicatively coupled to the rest of instruction set architecture 1400 through any suitable mechanism, such as through a bus or cache. In one embodiment, cores 1406, 1407 may be communicatively coupled through an L2 cache control 1408, which may include a bus interface unit 1409 and an L2 cache 1410. Cores 1406, 1407 and graphics processing unit 1415 may be communicatively coupled to each other and to the remainder of instruction set architecture 1400 through interconnect 1410. In one embodiment, graphics processing unit 1415 may use a video code 1420 defining the manner in which particular video signals will be encoded and decoded for output.
Instruction set architecture 1400 may also include any number or kind of interfaces, controllers, or other mechanisms for interfacing or communicating with other portions of an electronic device or system. Such mechanisms may facilitate interaction with, for example, peripherals, communications devices, other processors, or memory. In the example of FIG. 14, instruction set architecture 1400 may include an LCD video interface 1425, a Subscriber Interface Module (SIM) interface 1430, a boot ROM interface 1435, an SDRAM controller 1440, a flash controller 1445, and a Serial Peripheral Interface (SPI) master unit 1450. LCD video interface 1425 may provide output of video signals from, for example, GPU 1415 and through, for example, a Mobile Industry Processor Interface (MIPI) 1490 or a High-Definition Multimedia Interface (HDMI) 1495 to a display. Such a display may include, for example, an LCD. SIM interface 1430 may provide access to or from a SIM card or device. SDRAM controller 1440 may provide access to or from memory such as an SDRAM chip or module. Flash controller 1445 may provide access to or from memory such as flash memory or other instances of RAM. SPI master unit 1450 may provide access to or from communications modules, such as a Bluetooth module 1470, high-speed 3G modem 1475, global positioning system module 1480, or wireless module 1485 implementing a communications standard such as 802.11.
FIG. 15 is a more detailed block diagram of an instruction set architecture 1500 of a processor, in accordance with embodiments of the present disclosure. Instruction architecture 1500 may implement one or more aspects of instruction set architecture 1400. Furthermore, instruction set architecture 1500 may illustrate modules and mechanisms for the execution of instructions within a processor.
Instruction architecture 1500 may include a memory system 1540 communicatively coupled to one or more execution entities 1565. Furthermore, instruction architecture 1500 may include a caching and bus interface unit such as unit 1510 communicatively coupled to execution entities 1565 and memory system 1540. In one embodiment, loading of instructions into execution entities 1564 may be performed by one or more stages of execution. Such stages may include, for example, instruction prefetch stage 1530, dual instruction decode stage 1550, register rename stage 155, issue stage 1560, and writeback stage 1570.
In one embodiment, memory system 1540 may include an executed instruction pointer 1580. Executed instruction pointer 1580 may store a value identifying the oldest, undispatched instruction within a batch of instructions. The oldest instruction may correspond to the lowest Program Order (PO) value. A PO may include a unique number of an instruction. Such an instruction may be a single instruction within a thread represented by multiple strands. A PO may be used in ordering instructions to ensure correct execution semantics of code. A PO may be reconstructed by mechanisms such as evaluating increments to PO encoded in the instruction rather than an absolute value. Such a reconstructed PO may be known as an “RPO.” Although a PO may be referenced herein, such a PO may be used interchangeably with an RPO. A strand may include a sequence of instructions that are data dependent upon each other. The strand may be arranged by a binary translator at compilation time. Hardware executing a strand may execute the instructions of a given strand in order according to PO of the various instructions. A thread may include multiple strands such that instructions of different strands may depend upon each other. A PO of a given strand may be the PO of the oldest instruction in the strand which has not yet been dispatched to execution from an issue stage. Accordingly, given a thread of multiple strands, each strand including instructions ordered by PO, executed instruction pointer 1580 may store the oldest—illustrated by the lowest number—PO in the thread.
In another embodiment, memory system 1540 may include a retirement pointer 1582. Retirement pointer 1582 may store a value identifying the PO of the last retired instruction. Retirement pointer 1582 may be set by, for example, retirement unit 454. If no instructions have yet been retired, retirement pointer 1582 may include a null value.
Execution entities 1565 may include any suitable number and kind of mechanisms by which a processor may execute instructions. In the example of FIG. 15, execution entities 1565 may include ALU/Multiplication Units (MUL) 1566, ALUs 1567, and Floating Point Units (FPU) 1568. In one embodiment, such entities may make use of information contained within a given address 1569. Execution entities 1565 in combination with stages 1530, 1550, 1555, 1560, 1570 may collectively form an execution unit.
Unit 1510 may be implemented in any suitable manner. In one embodiment, unit 1510 may perform cache control. In such an embodiment, unit 1510 may thus include a cache 1525. Cache 1525 may be implemented, in a further embodiment, as an L2 unified cache with any suitable size, such as zero, 128 k, 256 k, 512 k, 1 M, or 2 M bytes of memory. In another, further embodiment, cache 1525 may be implemented in error-correcting code memory. In another embodiment, unit 1510 may perform bus interfacing to other portions of a processor or electronic device. In such an embodiment, unit 1510 may thus include a bus interface unit 1520 for communicating over an interconnect, intraprocessor bus, interprocessor bus, or other communication bus, port, or line. Bus interface unit 1520 may provide interfacing in order to perform, for example, generation of the memory and input/output addresses for the transfer of data between execution entities 1565 and the portions of a system external to instruction architecture 1500.
To further facilitate its functions, bus interface unit 1520 may include an interrupt control and distribution unit 1511 for generating interrupts and other communications to other portions of a processor or electronic device. In one embodiment, bus interface unit 1520 may include a snoop control unit 1512 that handles cache access and coherency for multiple processing cores. In a further embodiment, to provide such functionality, snoop control unit 1512 may include a cache-to-cache transfer unit that handles information exchanges between different caches. In another, further embodiment, snoop control unit 1512 may include one or more snoop filters 1514 that monitors the coherency of other caches (not shown) so that a cache controller, such as unit 1510, does not have to perform such monitoring directly. Unit 1510 may include any suitable number of timers 1515 for synchronizing the actions of instruction architecture 1500. Also, unit 1510 may include an AC port 1516.
Memory system 1540 may include any suitable number and kind of mechanisms for storing information for the processing needs of instruction architecture 1500. In one embodiment, memory system 1504 may include a load store unit 1530 for storing information such as buffers written to or read back from memory or registers. In another embodiment, memory system 1504 may include a translation lookaside buffer (TLB) 1545 that provides look-up of address values between physical and virtual addresses. In yet another embodiment, bus interface unit 1520 may include a Memory Management Unit (MMU) 1544 for facilitating access to virtual memory. In still yet another embodiment, memory system 1504 may include a prefetcher 1543 for requesting instructions from memory before such instructions are actually needed to be executed, in order to reduce latency.
The operation of instruction architecture 1500 to execute an instruction may be performed through different stages. For example, using unit 1510 instruction prefetch stage 1530 may access an instruction through prefetcher 1543. Instructions retrieved may be stored in instruction cache 1532. Prefetch stage 1530 may enable an option 1531 for fast-loop mode, wherein a series of instructions forming a loop that is small enough to fit within a given cache are executed. In one embodiment, such an execution may be performed without needing to access additional instructions from, for example, instruction cache 1532. Determination of what instructions to prefetch may be made by, for example, branch prediction unit 1535, which may access indications of execution in global history 1536, indications of target addresses 1537, or contents of a return stack 1538 to determine which of branches 1557 of code will be executed next. Such branches may be possibly prefetched as a result. Branches 1557 may be produced through other stages of operation as described below. Instruction prefetch stage 1530 may provide instructions as well as any predictions about future instructions to dual instruction decode stage.
Dual instruction decode stage 1550 may translate a received instruction into microcode-based instructions that may be executed. Dual instruction decode stage 1550 may simultaneously decode two instructions per clock cycle. Furthermore, dual instruction decode stage 1550 may pass its results to register rename stage 1555. In addition, dual instruction decode stage 1550 may determine any resulting branches from its decoding and eventual execution of the microcode. Such results may be input into branches 1557.
Register rename stage 1555 may translate references to virtual registers or other resources into references to physical registers or resources. Register rename stage 1555 may include indications of such mapping in a register pool 1556. Register rename stage 1555 may alter the instructions as received and send the result to issue stage 1560.
Issue stage 1560 may issue or dispatch commands to execution entities 1565. Such issuance may be performed in an out-of-order fashion. In one embodiment, multiple instructions may be held at issue stage 1560 before being executed. Issue stage 1560 may include an instruction queue 1561 for holding such multiple commands. Instructions may be issued by issue stage 1560 to a particular processing entity 1565 based upon any acceptable criteria, such as availability or suitability of resources for execution of a given instruction. In one embodiment, issue stage 1560 may reorder the instructions within instruction queue 1561 such that the first instructions received might not be the first instructions executed. Based upon the ordering of instruction queue 1561, additional branching information may be provided to branches 1557. Issue stage 1560 may pass instructions to executing entities 1565 for execution.
Upon execution, writeback stage 1570 may write data into registers, queues, or other structures of instruction set architecture 1500 to communicate the completion of a given command. Depending upon the order of instructions arranged in issue stage 1560, the operation of writeback stage 1570 may enable additional instructions to be executed. Performance of instruction set architecture 1500 may be monitored or debugged by trace unit 1575.
FIG. 16 is a block diagram of an execution pipeline 1600 for an instruction set architecture of a processor, in accordance with embodiments of the present disclosure. Execution pipeline 1600 may illustrate operation of, for example, instruction architecture 1500 of FIG. 15.
Execution pipeline 1600 may include any suitable combination of steps or operations. In 1605, predictions of the branch that is to be executed next may be made. In one embodiment, such predictions may be based upon previous executions of instructions and the results thereof. In 1610, instructions corresponding to the predicted branch of execution may be loaded into an instruction cache. In 1615, one or more such instructions in the instruction cache may be fetched for execution. In 1620, the instructions that have been fetched may be decoded into microcode or more specific machine language. In one embodiment, multiple instructions may be simultaneously decoded. In 1625, references to registers or other resources within the decoded instructions may be reassigned. For example, references to virtual registers may be replaced with references to corresponding physical registers. In 1630, the instructions may be dispatched to queues for execution. In 1640, the instructions may be executed. Such execution may be performed in any suitable manner. In 1650, the instructions may be issued to a suitable execution entity. The manner in which the instruction is executed may depend upon the specific entity executing the instruction. For example, at 1655, an ALU may perform arithmetic functions. The ALU may utilize a single clock cycle for its operation, as well as two shifters. In one embodiment, two ALUs may be employed, and thus two instructions may be executed at 1655. At 1660, a determination of a resulting branch may be made. A program counter may be used to designate the destination to which the branch will be made. 1660 may be executed within a single clock cycle. At 1665, floating point arithmetic may be performed by one or more FPUs. The floating point operation may require multiple clock cycles to execute, such as two to ten cycles. At 1670, multiplication and division operations may be performed. Such operations may be performed in four clock cycles. At 1675, loading and storing operations to registers or other portions of pipeline 1600 may be performed. The operations may include loading and storing addresses. Such operations may be performed in four clock cycles. At 1680, write-back operations may be performed as required by the resulting operations of 1655-1675.
FIG. 17 is a block diagram of an electronic device 1700 for utilizing a processor 1710, in accordance with embodiments of the present disclosure. Electronic device 1700 may include, for example, a notebook, an ultrabook, a computer, a tower server, a rack server, a blade server, a laptop, a desktop, a tablet, a mobile device, a phone, an embedded computer, or any other suitable electronic device.
Electronic device 1700 may include processor 1710 communicatively coupled to any suitable number or kind of components, peripherals, modules, or devices. Such coupling may be accomplished by any suitable kind of bus or interface, such as I2C bus, System Management Bus (SMBus), Low Pin Count (LPC) bus, SPI, High Definition Audio (HDA) bus, Serial Advance Technology Attachment (SATA) bus, USB bus (versions 1, 2, 3), or Universal Asynchronous Receiver/Transmitter (UART) bus.
Such components may include, for example, a display 1724, a touch screen 1725, a touch pad 1730, a Near Field Communications (NFC) unit 1745, a sensor hub 1740, a thermal sensor 1746, an Express Chipset (EC) 1735, a Trusted Platform Module (TPM) 1738, BIOS/firmware/flash memory 1722, a DSP 1760, a drive 1720 such as a Solid State Disk (SSD) or a Hard Disk Drive (HDD), a wireless local area network (WLAN) unit 1750, a Bluetooth unit 1752, a Wireless Wide Area Network (WWAN) unit 1756, a Global Positioning System (GPS), a camera 1754 such as a USB 3.0 camera, or a Low Power Double Data Rate (LPDDR) memory unit 1715 implemented in, for example, the LPDDR3 standard. These components may each be implemented in any suitable manner.
Furthermore, in various embodiments other components may be communicatively coupled to processor 1710 through the components discussed above. For example, an accelerometer 1741, Ambient Light Sensor (ALS) 1742, compass 1743, and gyroscope 1744 may be communicatively coupled to sensor hub 1740. A thermal sensor 1739, fan 1737, keyboard 1746, and touch pad 1730 may be communicatively coupled to EC 1735. Speaker 1763, headphones 1764, and a microphone 1765 may be communicatively coupled to an audio unit 1764, which may in turn be communicatively coupled to DSP 1760. Audio unit 1764 may include, for example, an audio codec and a class D amplifier. A SIM card 1757 may be communicatively coupled to WWAN unit 1756. Components such as WLAN unit 1750 and Bluetooth unit 1752, as well as WWAN unit 1756 may be implemented in a Next Generation Form Factor (NGFF).
Embodiments of the present disclosure involve an instruction and logic for reclamation of non-blocking registers. FIG. 18 illustrates an example of a system 1800 for implementing an instruction and logic for reclamation of non-blocking registers, in accordance with embodiments of the present disclosure. In one embodiment, such registers may include logical registers. In another embodiment, such registers may include logical registers renamed to physical registers, and vice-versa. In yet another embodiment, such registers may include registers used in conjunction with out-of-order processing. In still yet another embodiment, such registers may be identified in a physical register file. In a further embodiment, reclamation of non-blocking registers may achieve the effect of a larger Physical Register File (PRF), as the registers identified by the PRF may be used more efficiently. By providing more efficient use of a PRF, a relatively smaller PRF may be used in a processor. Furthermore, by providing more efficient use of a PRF, increased usage of three-source operands by a processor may be facilitated.
System 1800 may fetch, dispatch, execute, and retire instructions, such as those in instruction stream 1822, out-of-order. System 1800 may utilize any suitable number or kind of out-of-order processors or processing entities. System 1800 may illustrate elements of such a processor, which may include any processor core, logical processor, processor, or other processing entity such as those illustrated in FIGS. 1-17.
System 1800 may be implemented in any suitable manner to perform non-blocking register reclamation while executing instruction stream 1822. System 1800 may include a front end 1830 communicatively coupled to an out-of-order execution engine 1834. Front end 1830 may process instructions so that they may be executed by out-of-order execution engine 1834. Front end 1830 may be implemented by, for example, front end 201, front end unit 430, or front end 570. Out-of-order execution engine 1834 may be implemented by, for example, out-of-order execution engine 203, execution engine unit 450, or out of order engine 580. Front end 1830 may include decoder 1828 to decode and interpret instructions from instruction stream 1822, which may indicate what operation should be performed on the corresponding data indicated within the instruction operands and data to be applied.
In one embodiment, out-of-order execution engine 1834 may include an allocator 1804 to allocate resources for out-of-order execution. In another embodiment, out-of-order execution engine 1834 may include a retirement unit 1802 to reclaim resources associated with out-of-order execution. In yet another embodiment, out-of-order execution engine 1834 may include a scheduler 1832 to assign the execution of particular instructions in a given execution unit. Out-of-order execution engine 1834 may include any suitable number or kind of elements to support the operation of scheduler 1832, allocator 1804, and retirement unit 1802. For example, in various embodiments out-of-order execution engine 1834 may include a scheduler 1832, execution units 1836, PRF 1820, Reorder Buffer (ROB) 1818, freelist 1816, Rename Alias Table (RAT) 1806, Register Reclamation Table (RRT) 1808, Retirement RAT (RRAT) 1810, a second RRT (RRT2) 1812, and a Checkpoint Table (CPT) 1814. Each such element may be accessible by one or both of allocator 1804 and retirement unit 1802. Furthermore, although a specific one of allocator 1804, scheduler 1832, or retirement unit 1802 may be described herein as performing a specific function with respect to these elements, any suitable portion of system 1800 may implement the functionality described herein.
Scheduler 1832 may be implemented by, for example, schedulers 202, 204, 206, scheduling stage 412, scheduler units 456, resource schedulers 584, or issue stage 1560. Execution units 1836 may be implemented by, for example, execution unit 108, execution unit 142, execution units 212, 214, 216, 218, 220, 222, 224, execution unit 162, or execution clusters 460.
PRF 1820 may include mappings of logical resources to physical resources. The resources may include registers, memory locations, or registers implemented as memory locations. By mapping logical resources to physical resources, PRF 1820 may facilitate out-of-order processing. Within instruction stream 1822, repeated references may be made to a given logical resource such as a register. However, different references to and operations of the same logical resource may not depend upon each other. In such circumstances, uses of the same logical resource may be performed out-of-order, in parallel, or in any other non-sequential manner. To allow multiple, perhaps simultaneous use of the same logical resource, different uses of the logical resource in instruction stream 1822 may actually be made to different physical resources. The mappings of multiple instances of a single logical resource to different physical resources may be stored in PRF 1820. As used herein, a logical resource may be described, for example, by an identifiable register name and an associated physical resource may be described with an address in brackets. For example, instances of EAX registers may include “EAX {10}” or “EAX {40}”, wherein certain references to EAX within instruction stream 1822 may be redirected to physical location “10” and other references to EAX may be redirected to physical location “40”.
PRF 1820 may be populated as necessary by, for example, an allocator 1804 based upon instant needs to process instruction stream 1822 out-of-order. Allocator 1804 may be implemented fully or in part by, for example, rename/allocator unit 452, allocation stage 408, allocate 582, out of order engine 580, register rename stage 1555, issue stage 1560, issue stage 1560, execution engine unit 450, or out of order engine 203.
Furthermore, system 1800 may reclaim entries in PRF 1820 when they are no longer needed. System 1800 may include retirement unit 1802 to perform such reclamation. Retirement unit 1802 may be implemented fully or in part by, for example by write back/memory write 418, execution engine unit 450, retirement unit 454, write back stage 1570, write back stage 1680, out of order engine 580, or out of order engine 203. For example, after no more references to “EAX {10}” are to be made, use of the mapping between “EAX” and “{10}” may be unnecessary.
As system 1800 fetches, dispatches, and executes instruction stream 1822 out-of-order, allocator 1804 may rearrange the order of instructions in instruction stream 1822. ROB 1818 may track the order of instructions as they were originally fetched. ROB 1818 may be implemented in any suitable manner, such as by ROB 588. In one embodiment, ROB 1818 may be implemented by a doubly-linked queue. ROB 1818 may add entries for instructions as the instructions are dispatched. Furthermore, as results are returned from execution, ROB 1818 may store and track such results until they are committed and retired. As results of execution are determined, they may be written to ROB 1818. ROB 1818 may include various information for each entry, such as the instruction type (such as write to memory, write to register, JMP, read, load) the destination of the results (such as a given memory location or register), and the result of the instruction. Storing information in ROB 181 may facilitate restoration of execution if predictions are incorrect by, for example branch prediction unit 432. In such restoration, the executed results may be scrapped and code reexecuted according to updated predictions or operations. Furthermore, if execution of instruction stream 1822 has progressed such that execution results of ROB 1818 may be committed and the instructions retired, then the entries may be removed from ROB 1818. An element in ROB 1818 to be considered for retirement may be indicated by retirement pointer 1826.
In one embodiment, retirement of an instruction or a resource of an instruction may include commitment of the result of the instruction or the value of a resource by an execution engine to the rest of the architecture of the processor. Such a commitment may include, for example, writing a value to a register or putting the processor in a different state. An instruction or resource may have executed or been accessed, but may not yet have been retired. The delay between execution and retirement may be to account for an error in out-of-order processing, such as a data-dependency error or a misprediction of a branch that has not yet occurred but may affect the instruction or resource. Thus, retirement may be delayed until the opportunity for such an error has passed. In another embodiment, upon execution an instruction or resource may be placed in a list or queue of such entities awaiting retirement. Retirement may be delayed until a convenient or efficient time to perform retirement.
PRF 1820 may include a limited number of entries. Certain situations may cause a strain on the available number of entries in PRF 1820. For example, if an instruction at the head of ROB 1818, indicated by corresponding to retirement pointer 1826, has a long latency, PRF 1820 may begin to fill with assignments that cannot be removed because retirement has not been effected for various instructions following the long-latency operation in ROB 1820. Such long-latency operations may include, for example, a load from random access memory. In another example, long latency may be caused by a chain of smaller latency instructions that, when combined, have the same effect as a long-latency instruction. Long latency may include a length of time for an operation that exceeds a designated threshold. The threshold may be defined, for example, in terms of processor cycles to complete, or in comparison of the time or cycles to complete an example, benchmark, average, or median operation. Long latency operations may be identified in a suitable data structure or list for reference when evaluating whether a given operation includes long latency.
Efficient use of PRF 1820 may be increased by system 1800 taking steps to identify and reclaim register mappings in PRF 1820. In one embodiment, by identifying and reclaiming register mappings in PRF 1820, the effect of size constraints on PRF 1820 may be lessened. In a further embodiment, system 1800 may enable specific steps to determine whether register mappings in PRF 1820 that do not block retirement may be released, even though the associated instructions have not yet been retired. Such register mappings may be known as non-blocking registers, since they are virtual-physical resource mappings that do not block the retirement of other instructions. Thus, system 1800 may enable or disable non-blocking register reclamation.
In one embodiment, system 1800 may enable non-blocking register reclamation under certain situations. For example, non-blocking register reclamation may be enabled when a given instruction categorized as a long-latency instruction reaches retirement pointer of ROB 1818. In another example, non-blocking register reclamation may be enabled when a quantity of free physical resources in PRF 1820 goes below a minimum threshold. In yet another example, non-blocking register reclamation may be enabled based upon a long-latency instruction and a minimum number of physical resources available in PRF 1820.
Non-blocking register reclamation may include determining, for a set of instructions, whether any registers or other resources in PRF 1820 may be reclaimed despite that instructions associated with the resource have not yet been retired. During non-blocking register reclamation, data dependency between instructions in ROB 1818 may be analyzed. Any instructions or resources that depend upon a long-latency instruction may be determined to be unsuitable for non-blocking register reclamation, as such resources or instructions are blocking the execution of subsequent instructions. These instructions and registers may be deemed “poisoned” due to their dependency upon a long-latency instruction. In turn, any instructions or registers depending upon such “poisoned” instructions or registers may in turn be deemed as also dependent upon the same long-latency instruction. Thus, these may also be deemed “poisoned”.
Furthermore, any instruction or register that is a source to a register or instruction that in turn is dependent upon a long-latency instruction may be preserved. When the dependent instruction or register finally is able to execute after the long latency, the value of the source instruction or register will be needed. Thus, these source instructions or registers might not be reclaimed, as reclamation may cause their values to be unavailable when they are needed. These source instructions or registers may be deemed as “protected” from non-blocking register reclamation, even though the source instructions or registers do not block execution.
All other instructions or registers that have been dispatched and executed may be eligible for non-blocking register reclamation in PRF 1820. These may be considered for reclamation even though the associated instruction has not yet been retired.
RAT 1806 may be implemented in any suitable manner such as by a table, array, or other suitable data structure. RAT 1806 may implement some of the functionality of PRF 1820, such as the mapping or aliasing between physical and logical resources.
If an error occurs after non-blocking reclamation, such as an incorrect branch prediction or a fault on a long-latency operation, execution must be rolled back to a known point. Accordingly, allocator 1804 may take a snapshot or checkpoint of RAT 1806 before engaging in non-blocking register reclamation. Such a checkpoint may include a record of architectural registers of system 1800. The checkpoint may be taken as if the instruction at the top of ROB 1818 initiating the long-latency operation was the last renamed instruction. Thus, renaming operations subsequent to the checkpoint will not be affected. As these registers are preserved in the case of a necessary rollback, registers contained within the checkpoint might not be reclaimed during non-blocking register reclamation. The checkpoint may be stored in any suitable table or data structure such as, for example, CPT 1814. In one embodiment, CPT 1814 may be established upon enabling non-blocking register reclamation. In another embodiment, CPT 1814 may be populated after enabling non-blocking register reclamation when elements of the checkpoint are encountered during a process of pseudo-retirement. In various embodiments, CPT 1814 may be implemented by a bit field in RRAT 1810 or RRT2 1812.
After saving checkpoint registers in CPT 1814, non-blocking register reclamation may pseudo-retire instructions for the purposes of physical register reclamation in PRF 1820. The physical register reclamation may include reclaiming resources out-of-order, wherein a resource of a later instruction is reclaimed while an earlier instruction is executing or has not yet executed. The physical register reclamation may be made of resources that are not blocking the data flow of an earlier instruction that is, for example, waiting on a long latency operation.
In one embodiment, pseudo-retirement may include walking through a series of ordered instructions, determining whether each instruction is data-dependent upon a long-latency operation, and reclaiming resources of instructions that are data-independent of the long-latency operation. Data dependency may be evaluated within the context of data-flow analysis. For example, a later-ordered instruction may be said to be data-independent of an earlier instruction if the later-ordered instruction requires no data from the earlier instruction to execute. The need for data between two such instructions may include any number or kind of instructions in a dependency chain. In another embodiment, the resources may be reclaimed even if they are used in instructions ordered after previous instructions that have not retired. In yet another embodiment, resources may be reclaimed if its associated instruction has been executed. However, some exceptions may apply to these resources such that they are not reclaimed during non-blocking register reclamation, as discussed further below.
In another embodiment, pseudo-retirement may include walking through the series of ordered instructions, determining whether each instruction is data-dependent upon a long-latency operation or a source to an operation data-dependent upon long-latency operation, marking the resources with data-dependency upon long-latency operations (for example, as “poisoned”), and marking the sources to such data-dependent instructions and resources (for example, as “protected”). The marked resources may be identified as associated with the long-latency operation. Furthermore, the marked resources might not be reclaimed during non-blocking register reclamation. These marked resources may be considered to be pseudo-retired. However, some exceptions may apply to marked resources such that they are not marked as pseudo-retired, as discussed below. Such marked, pseudo-retired resources may be reclaimed after the long-latency operation has finished with specific handling after the long-term latency operation. The handling may be enabled by identifying marked, pseudo-retired resources in a specific structure (such as RRT2 1812, below).
As discussed above, some exceptions may apply to otherwise pseudo-retired resources. These exceptions may cancel or postpone a determination of “pseudo-retired”. A pseudo-retired resource may be reclaimed during non-blocking register reclamation or during reclamation of marked resources. In one embodiment, resources may be considered as pseudo-retired if, except for their sequential order, they are otherwise ready for retirement. A resource might not be ready for retirement, for example, through data dependency with elements outside the pseudo-retirement window of instructions. In another example, a resource might not be ready for retirement if the resource might be needed again. In such a case, it may be unknown whether or not the resource will be needed again, and as such is preserved to avoid errors. Accordingly, pseudo-retirement might not be applied to a resource if the resource might be needed later.
For example, consider the pseudo-retirement of an instruction “EAX {1}=EAX {2}+ECX {3}”. Each instruction may be analyzed within context to determine, if encountered in a typical retirement evaluation, the resource could be retired. Such an evaluation may be made on the basis of whether a given resource will be needed at a later time. For example, register EAX {2} may be eligible for retirement, as its results are read into another instance of the same logical register, EAX {1} (albeit to a different physical register). A subsequently-ordered instruction accessing register EAX might need the value of register EAX {1} rather than register EAX {2}, as register EAX {2} might include outdated information. The retirement eligibility of register EAX {1} and register ECX {3} may depend upon the context of additional instructions. As register EAX {1} has been loaded with a new value, it may be needed again. However, as there are no more uses of register EAX or register EAX {1} in the instructions under evaluation, register EAX {1} may nevertheless be retired. Similarly, if register ECX {3} is not used again in the instructions, or if register ECX is not used again in the instructions, then register ECX {3} may be retired. Nevertheless, in some embodiments this ability to evaluate subsequent use of a given register may be unavailable. In such embodiments, registers might not be determined as pseudo-retired until it can be determined definitely that they are no longer needed. Consequently, during pseudo-retirement, EAX {2} may be identified as pseudo-retired (and thus eligible for non-blocking register reclamation or for marked resource reclamation); ECX {3} and EAX {1} might not be identified as pseudo-retired unless visibility into subsequent instructions shows that they are no longer needed.
Pseudo-retirement may be implemented in any suitable manner. In one embodiment, ROB 1818 may include retirement pointer 1826 indicating the last uop or instruction that was retired. In another embodiment, ROB 1818 may include a pseudo-retirement pointer 1824 indicating the last uop or instruction that was pseudo-retired. Upon initialization of pseudo-retirement, pseudo-retirement pointer 1824 may be set to retirement pointer 1826. During pseudo-retirement, retirement unit 1802 may step through instructions as presented in ROB 1818 using pseudo-retirement pointer. Instructions and resources that are dependent upon long-latency operations, such as those deemed “poisoned” may be pseudo-retired. Instructions and resources that are sources of “poisoned” instructions and resources may wait for their execution completion to be pseudo-retired. Pseudo-retirement pointer 1824 may be advanced past these instructions. Subsequent instructions may be evaluated for pseudo-retirement.
Furthermore, during pseudo-retirement, retirement unit 1802 may determine whether an instruction or resource is eligible for retirement, despite being ordered after a still-executing instruction. In various embodiments, such a determination may include, for example, that an instruction or resource is not dependent upon a long-latency instruction, is not a source of another instruction or resource that is dependent upon a long-latency instruction, and is not part of the checkpoint. In addition, retirement unit may determine whether an instruction or resource will not be used again. For example, after a read from a logical register at a physical register, if the same combination of logical register and physical register is not used again in the code to be executed, the physical register may be retired. If necessary, retirement unit 1802 may wait for execution of such an instruction to complete in the execution pipeline. The eligibility for retirement, such as a denotation that the associated uop is valid, may be written upon completion of execution. In one embodiment, retirement unit 1802 may wait for such an instruction to be eligible for retirement before advancing pseudo-retirement pointer 1824 past such an instruction. In a further embodiment, such an instruction may be set as eligible for retirement but may not yet be retired, as older long-latency instructions in instruction stream 1822 have not yet been retired.
A given instruction may be pseudo-retired wherein pseudo-retirement pointer 1824 has passed the given instruction in ROB 1818. In one embodiment, reclamation of resources in PRF 1820 may be made upon pseudo-retired registers that are not part of the determined checkpoint, are not dependent upon a long-latency operation, nor are sources for a register dependent upon a long-latency operation. Furthermore, such pseudo-retired registers must be otherwise eligible for retirement. Reclamation of resources in PRF 1820 may include identifying physical resources as available in, for example, freelist 1816. Allocator 1804 may overwrite mappings in PRF 1820 when a so-identified physical resource is to be mapped to a new logical resource. Thus, in another embodiment, physical resources such as registers may be reclaimed even though they are referenced later in instruction stream 1822 than other registers still involved in execution.
Resources that have been determined to be part of a checkpoint, dependent upon a long-latency operation, or a source to an instruction or resource dependent upon a long-latency operation may be tracked. Such resources may be reclaimed at a later time that the reclamation for the resources determined to be eligible for retirement but were not part of a checkpoint, dependent upon a long-latency operation, or a source to an instruction or resource dependent upon a long-latency operation. To track resources that have been determined to be part of a checkpoint, dependent upon a long-latency operation, or a source to an instruction or resource dependent upon a long-latency operation may also be reclaimed, system 1800 may include RRAT 1810.
RRAT 1810 may be implemented in any suitable manner. In one embodiment, RRAT 1810 may mimic the operations of RAT 1806 continually, using logical and physical destination information passed from RRT 1808. Updates to RRAT 1810 may be made even when non-blocking register reclamation has not been enabled. In another embodiment, RRAT 1810 may include a field designating whether a given instruction's physical destination (such as a register) is dependent upon a long-latency operation and is thus “poisoned”. In yet another embodiment, RRAT 1810 may include a field designating whether a given resource is a source to another instruction or resource that is dependent upon a long-latency operation. Such a given instruction's physical destination may be known as “protected”. In still yet another embodiment, RRAT 1810 may include a field designating whether a given physical destination was part of the initial checkpoint. Such a field may be used in addition to or supplanting CPT 1814. Each of the fields may be implemented in any suitable manner such as, for example, a bit. In various embodiments, the fields described for RRAT 1810 may be included in RAT 1806, wherein RRAT 1810 is implemented fully or in part by RAT 1806.
RRAT 1810 may be populated by retirement unit 1802 upon enabling non-blocking register reclamation. For example, after determining that an instruction is a long-latency operation and at the top of ROB 1818, retirement unit 1802 may set a bit for a destination register of the long-latency operation indicating that it is dependent upon a long-latency operation and is thus “poisoned”. In another example, upon finding any subsequent instructions or resources that are dependent upon the register, retirement unit 1802 may also set the bit indicating that the subsequent instructions' registers are dependent upon a long-latency operation and are thus “poisoned”. In yet another example, upon finding registers that are sources to registers marked as dependent upon a long-latency operation, retirement unit 1802 may set the bit indicating that the instruction's destination register is “protected”. In various embodiments, a given resource may be marked by two or more such fields.
During pseudo-retirement, retirement unit 1802 may reference RRAT 1810 and the associated fields for each instruction encountered as pseudo-retirement pointer 1824 traverses ROB 1818. Furthermore, retirement unit 1802 may reference CPT 1814 for each instruction encountered as pseudo-retirement pointer 1824 traverses ROB 1818. If RRAT 1810 or CPT 1814 indicates that a given instruction or resource is dependent upon a long-latency instruction, a source to an instruction or resource dependent upon a long-latency instruction, or that a resource was included in an initial checkpoint, then during pseudo-retirement the destination resource might not be reclaimed and pseudo-retirement pointer 1824 may be advanced.
Instructions and resources that are pseudo-retired, but are still marked as dependent upon a long-latency instruction, a source to an instruction or resource dependent upon a long-latency instruction, or that a resource was included in an initial checkpoint in RRAT 1810 or CPT 1814 may be tracked. Furthermore, system 1800 may include RRT 1808 to track registers that are reclaimed. As described above, in one embodiment system 1800 may include a second register reclamation table (RRT2) 1812 to track instructions and resources that have been pseudo-retired but not yet actually retired. Such instructions and resources may have been pseudo-retired but are not yet retired because, for example, they are marked as dependent upon a long-latency instruction, a source to an instruction or resource dependent upon a long-latency instruction, or that a resource was included in an initial checkpoint in RRAT 1810 or CPT 1814. These may be specifically reclaimed after the long-latency instruction has terminated.
During retirement of resources, retirement unit 1802 may determine that instructions utilizing a given “poisoned” or “protected” resource have finished execution and are eligible for retirement. Such a determination may be made by, for example, advancement of retirement pointer 1826 to such an instruction. After determining that retirement pointer 1826 has advanced to a given point, retirement unit 1802 may evaluate whether the instruction immediately following retirement pointer 1826 is eligible for retirement. If the instruction is eligible for retirement, the instruction may be retired by retirement unit 1802 and retirement pointer 126 advanced. In one embodiment, once an instruction has been retired, retirement unit 1802 may reclaim resources identified in RRT2 1812 with the instruction. Such resources may be removed from RAT 1806, RRAT 1810, and PRF 1820, and identified in a freelist 1816 so that allocator 1804 may assign the resource to other virtual resources.
Resources that have been marked as associated with a checkpoint may be reclaimed only when all instructions associated with the same checkpoint are retired. In one embodiment, such a condition may be indicated when retirement pointer 1826 equals pseudo-retirement pointer 1824. In such a condition, retirement unit 1802 may reclaim all resources associated with the checkpoint and identify them in freelist 1816 for reuse by allocator 1804.
If an error, such as an incorrect prediction of a branch of execution that depended from a load, is detected during out-of-order execution, the state of execution may be rolled back to the determined checkpoint. Out-of-order execution engine 1834 may include any suitable mechanism for reclaiming resources assigned after the checkpoint was established and execution was attempted. In one example, out-of-order execution engine 1834 may include a history table of all sequential assignments of physical to logical resources, which may be stepped through for reclamation in case of an error. In one embodiment, out-of-order execution engine 1834 may utilize information already in RRAT 1810 rather than include such a table. In RRAT 1810, such resources may have been mapped to a logical register in RRAT 1810, but not correspond to entries in CPT 1814 or include bits indicating that they belong to the checkpoint. During a rollback, if a resource such as a physical register is mapped to a logical register in RRAT 1810 and has its checkpoint bit set (or corresponds to an entry in CPT 1814), retirement unit 1802 may reclaim the physical resource. Entries in RRAT 1810 or CPT 1814 that are part of the checkpoint may be reclaimed as previously described.
FIGS. 19A and 19B illustrate example operation of system 1800 to perform non-blocking register reclamation, in accordance with embodiments of the present disclosure. In FIG. 19A, four example instructions from instruction stream 1822 may be shown: I1, I2, I3, and I4. The four instructions may include, for example:
I1:LOAD(EAX,[mem_loc])
I2:EBX=ADD(EAX,EBX)
I3:EAX=SUB(EDX,ESI)
I4:EDX=XOR(EAX,ESI)
Allocator 1804 may assign physical-logical resource mappings to these four lines of instructions. Such mappings may facilitate out-of-order execution. The instructions with the mappings applied may be shown in the table below:







TABLE 1







Example Instructions
















Logical
Logical


Instruc-



Source
Source


tion
Physical
Logical

{Physical
{Physical


ID
Destination
Destination
Operation
Source}
Source}





I1
10
EAX =
Load
[memory







location]


I2
20
EBX =
Add
EAX {10}
EBX {8}


I3
30
EAX =
Sub
EDX {6}
ESI {4}


I4
40
EDX =
XOR
EAX {30}
ESI {4}









The data dependency of these instructions may be illustrated in FIG. 19A. I1 may include a load operation of the memory contents of a memory location into register EAX. Register EAX may be stored at physical register location 10. Instruction I2 may depend upon the result of instruction I1, since register EAX will be added to register EBX (at physical register location 8) and stored in physical register EBX (at physical register location 20). Instruction I3 may also reference register EAX. However, instruction I3 will load a new value into register EAX. As such, there is no data dependency between instruction I3 and the previous instructions I2 and I1, even though all three make reference to register EAX. Accordingly, register EAX within instruction I3 may be mapped to physical register location 30, allowing instruction I3 to be executed out-of-order with respect to instructions I2 and I1. Instruction I3 may cause register EDX (at physical register 6) to be subtracted from register ESI (at physical register 4) and stored in register EAX (at physical register 30). Furthermore, instruction I4 may depend upon the data of 13, as an exclusive-or operation may be performed on register EAX (at physical register 30) with register ESI (at physical register 4), wherein the result is stored in register EDX (at physical register 40).
Allocator 1804 may have allocated physical register resources for the logical registers in the instructions. Mappings of allocated and logical registers may be included in, for example, RAT 1806 or PRF 1820.
FIG. 19B may illustrate retirement unit 1802 performing non-blocking register reclamation for the example instructions. At (1), allocator 1804 may determine that I1 is at the head of ROB 1818. Retirement pointer 1826 may be pointing to an instruction before I1 such as I0 (not shown). Furthermore, allocator 1804 may determine that the instruction of I1, a load from random access memory, is a long-latency instruction. Such a determination may be made by reference to a list of instructions that are to be categorized as long-latency instructions. Furthermore, allocator 1804 may determine that less than a threshold number of free registers are available in PRF 1820. Based on one or more such conditions, allocator 1804 may enable non-blocking register reclamation.
Allocator 1804 may determine that I1 and I2 make up a first dependency chain, and that I3 and I4 make up a second dependency chain. Thus, resources of I3 and I4 may be isolated from operations of I1 and I2.
In one embodiment, at (2) allocator 1804 may set CPT 1814 with information about register values in existence upon consideration of I1. Such information may make up a checkpoint. For example, an instruction before I1 such as I0 may reference register ECX. I0 may specify, for example, “ECX {90}=ADD (1, ECX {91}). Thus, a checkpoint including I0 referencing adding a value to register ECX may be stored in CPT 1814. In another embodiment, at (2) allocator 1804 may set fields in RRAT 1810 indicating that the register values are associated with a checkpoint.
At (3), allocator 1804 may determine that the instruction responsible for the long-latency load, I1, has caused its target resource, EAX {10}, to be “poisoned” by its dependence on the long-latency operation. EAX {10} is blocking reclamation.
At (4), allocator 1804 may determine that any registers and instructions that depend upon the “poisoned” instruction and EAX {10}, such as 12's addition of EAX {10} and EBX {8}, is likewise “poisoned” because it too depends upon a long-latency operation. Thus, the destination of I1's operation, EBX {20}, may be determined as “poisoned” as it depends on a long-latency operation. EBX {20} is blocking reclamation. A resource or instruction determined to be “poisoned” as dependent upon a long-latency operation may be ineligible for register reclamation, as the register value is still needed.
At (5), allocator 1804 may determine that EBX {8} does not depend upon the data of a long-latency operation. However, EBX {8} is a source for other instructions or resources that otherwise do depend on the data of a long-latency operation. The value of EBX {8} may be needed when its dependents finally execute after conclusion of the long latency. EBX {8} is blocking reclamation. Thus, a resource or instruction determined to be a source to another instruction or resource that is dependent upon a long-latency operation may be ineligible for register reclamation, as the register value is still needed. Such sources may be deemed “protected”.
At (6), allocator 1804 may determine that none of EDX {6}, ESI {4}, EAX {30}, or EDX {40} depends upon a long-latency operation, or any other resources that in turn depend upon a long-latency operation. Furthermore, none of these are sources to instructions or resources that depend upon a long-latency operation. These can be said to neither be “poisoned” nor “protected”. Thus, these may be eligible for reclamation as they are not blocking the operation of any other resource. Furthermore, they are not a part of any checkpointed registers.
At (7), in one embodiment allocator 1804 may add indications to RRAT 1810 that register EAX {10} and register EBX {20} depend on long-latency operations, or upon other instructions that depend on long-latency operations, and are thus “poisoned”. The indications may signify that these registers will not be reclaimed during non-blocking register reclamation. The indications may include, for example, a bit in a field associated with a table entry for the register in RRAT 1810. In another embodiment, retirement unit 1802 may wait until register EAX {10} and register EBX {20} are pseudo-retired before adding indications to RRAT 1810.
At (8), in one embodiment allocator 1804 may add indications to RRAT 1810 that register EBX {8} is a source to instructions or resources that depend on long-latency operations, and are thus “protected”. The indications may signify that this register will not be reclaimed during non-blocking register reclamation. The indication may include, for example, a bit in a field associated with a table entry for the register in RRAT 1810. In another embodiment, retirement unit 1802 may wait until register EBX {8} is pseudo-retired before adding an indication to RRAT 1810.
At (9), pseudo-retirement may be initiated. Pseudo-retirement may be carried about any suitable portion of system 1800. In one embodiment, pseudo-retirement may be carried out by retirement unit 1802. Pseudo-retirement pointer 1824 may be originally set to instruction I0 in ROB 1818. In one embodiment, pseudo-retirement may be carried out for instructions in ROB 1818 until retirement unit 1802 determines that the long latency of instruction I1 has ended. Such a determination may be made, for example, by determining that retirement pointer 1826 has advanced, indicating that instruction I1 is itself retired. In another embodiment, pseudo-retirement may be carried out until all non-blocking registers identified in PRF 1820 or RAT 1806 are reclaimed.
Thus, upon initiation of pseudo-retirement, pseudo-retirement pointer 1824 may be advanced to instruction I1 and retirement unit 1802 may pseudo-retire instruction I1 and its resources. Retirement pointer 1826 may be maintained as pointing to instruction I0 as I1 is not yet ready for retirement.
At (10), RRAT 1810 and CPT 1814 may be read by retirement unit 1802 to determine whether any resources of instruction I1 are associated with a checkpoint, are dependent upon a long-latency operation and are thus “poisoned,” or are a source to a “poisoned” instruction or resource and thus are “protected”. In the example of FIG. 19B, it may be determined that instruction I1 includes the “poisoned” register EAX {10}.
At (11), retirement unit 1802 may determine whether any such determined resources from (10) are pseudo-retired. If they are pseudo-retired, they will be added to RRT2 1812 so that they may be tracked for later reclamation. If they are not pseudo-retired, then they may be held for later evaluation to determine if they are pseudo-retired, at which point they may be added to RRT2 1812. Furthermore, any such determined resources (pseudo-retired or otherwise) may be determined to be blocking, and thus not reclaimed during non-blocking. In the example of FIG. 19B, register EAX {10} may be identified in I1. Given only the context of I1, it may not be possible to determine whether register EAX {10} would otherwise be retired, as any subsequent use is unknown. Thus, in one embodiment register EAX {10} might not yet be determined as pseudo-retired, and might not be added to RRT2 1812. In another embodiment, wherein visibility into subsequent instructions is available, register EAX {10} still might be pseudo-retired, as register EAX {10} may be used in conjunction with subsequent instruction I2.
At (12), pseudo-retirement may continue as pseudo-retirement pointer 1824 is advanced to point to instruction I2 of ROB 1818 and instruction I2 may be pseudo-retired. At (13), RRAT 1810 and CPT 1814 may be read by retirement unit 1802 to determine whether any resources of instruction I2 are associated with a checkpoint, are dependent upon a long-latency operation and are thus “poisoned,” or are a source to a “poisoned” instruction or resource and thus are “protected”. In the example of FIG. 19B, it may be determined that instruction I2 includes the “poisoned” registers EAX {10} and EBX {20} and the “protected” register of EBX {8}.
At (14), retirement unit 1802 may determine whether registers EAX {10}, EBX {8}, and EBX {20} are pseudo-retired and, if so, add them to RRT2 1818. The determination of pseudo-retirement may include determining, for each of registers EAX {10}, EBX {8}, and EBX {20}, whether the resource might otherwise be retired. For example, it may be determined that EBX {8} is no longer needed because a newer logical resource instance (EBX {20}) has taken its place. Thus, EBX {8} may be added to RRT2 1818. Given only the context of I2 and its previous instructions, it may not be possible to determine whether registers EAX {10} and EBX {20} would otherwise be retired, as any subsequent use is unknown. Thus, in one embodiment register EAX {10} and EBX {20} might not yet be determined as pseudo-retired, and might not be added to RRT2 1812. In another embodiment, wherein visibility into subsequent instructions is available, registers EBX {20} and EAX {10} might be pseudo-retired, as no further uses of registers EBX {20} and EAX {10} are made in the illustrated instructions. In yet another embodiment, wherein visibility into subsequent instructions is available, registers EBX {20} and EAX {10} might be pseudo-retired, as other instances of logical registers EBX and EAX are subsequently made with different physical locations.
At (15), pseudo-retirement may continue as pseudo-retirement pointer 1824 is advanced to point to instruction I3 of ROB 1818 and instruction I3 may be pseudo-retired. At (16), RRAT 1810 and CPT 1814 may be read by retirement unit 1802 to determine whether any resources of instruction I3 are associated with a checkpoint, are dependent upon a long-latency operation and are thus “poisoned,” or are a source to a “poisoned” instruction or resource and thus are “protected”. In the example of FIG. 19B, it may be determined that instruction I3 does not include any such resources. The registers EAX {30}, EDX {6}, and ESI {4} may thus be not “poisoned,” “protected,” or associated with a checkpoint and are thus non-blocking. Based on these determinations, register reclamation may be performed for these resources if they are eligible for pseudo-retirement. Furthermore, registers EAX {10} and EBX {20} may still be pending for pseudo-retirement consideration.
At (17), retirement unit 1802 may determine whether registers EAX {10}, EBX {20}, EAX {30}, EDX {6}, and ESI {4} are pseudo-retired and, if so, add them to RRT2 1818 or reclaim them, as appropriate. The determination of pseudo-retirement may include determining, for each of the registers, whether the resource might otherwise be retired. For example, it may be determined that Register EAX {10} is no longer needed because a newer logical resource instance (EAX {30}) has taken its place. Register EAX {10} may be pseudo-retired. Given only the context of I3 and its previous instructions, it may not be possible to determine whether EBX {20}, EAX {30}, EDX {6}, and ESI {4} would otherwise be retired, as any subsequent use is unknown. Thus, in one embodiment register EBX {20} might not yet be determined as pseudo-retired, and might not be added to RRT2 1812. Furthermore, registers EAX {30}, EDX {6}, and ESI {4} might not yet be determined as pseudo-retired, and might not yet be reclaimed.
In another embodiment, wherein visibility into subsequent instructions is available, registers EBX {20} might already have been pseudo-retired. Furthermore, EDX {6} might be pseudo-retired, as no further uses of register EDX {6} is made in the illustrated instructions. In yet another embodiment, wherein visibility into subsequent instructions is available, register EDX {6} might be pseudo-retired, as other instances of logical register EDX are subsequently made with a different physical location.
At (18), retirement unit 1802 may add register EAX {10} to RRT2 1818 as it is “poisoned” and will not be reclaimed during non-blocking register reclamation register reclamation may be applied to the resources determined to be non-blocking.
At (19), pseudo-retirement may continue as pseudo-retirement pointer 1824 is advanced to point to instruction I4 of ROB 1818 and instruction I4 may be pseudo-retired. At (20), RRAT 1810 and CPT 1814 may be read to determine whether any resources of instruction I4 are associated with a checkpoint, are dependent upon a long-latency operation and are thus “poisoned,” or are a source to a “poisoned” instruction or resource and thus are “protected”. In the example of FIG. 19B, it may be determined that instruction I4 does not include any such resources. The registers EDX {40}, EAX {30}, and ESI {4} may thus be not “poisoned,” “protected,” or associated with a checkpoint and are thus non-blocking. It may be determined whether these registers can be pseudo-retired. Furthermore, registers EBX {20}, EAX {30}, EDX {6}, and ESI {4} may still be pending with respect to pseudo-retirement from previous iterations.
At (21), retirement unit 1802 may determine whether registers EDX {40}, EBX {20}, EAX {30}, EDX {6}, and ESI {4} are pseudo-retired and, if so, add them to RRT2 1818 or reclaim them, as appropriate. The determination of pseudo-retirement may include determining, for each of the registers, whether the resource might otherwise be retired. For example, it may be determined that Register EDX {6} is no longer needed because a newer logical resource instance (EDX {40}) has taken its place. Register EDX {6} may be pseudo-retired. Given only the context of I4 and its previous instructions, it may not be possible to determine whether registers EDX {40}, EBX {20}, EAX {30}, and ESI {4} would otherwise be retired, as any subsequent use is unknown. Thus, in one embodiment register EBX {20} might not yet be determined as pseudo-retired, and might not be added to RRT2 1812. Furthermore, registers EDX {40}, EAX {30}, and ESI {4} might not yet be determined as pseudo-retired, and might not yet be reclaimed. These registers might be used by instructions further below the window illustrated in FIG. 19. In another embodiment, wherein visibility into subsequent instructions is available, registers EBX {20} might already have been pseudo-retired. Furthermore, registers EDX {40}, EAX {30}, and ESI {4} might be pseudo-retired, as no further uses of registers EDX {40}, EAX {30}, and ESI {4} is made in the illustrated instructions.
Reclamation may be performed even though the associated instruction has only been pseudo-retired, rather than retired. Retirement pointer 1826 may not yet point to the associated instruction. In one embodiment, register reclamation may be applied to the resources of an instruction once the instruction has been determined to be eligible for retirement. An instruction might not yet be eligible for retirement if, for example, the instruction has not yet finished executing. Thus, it may be determined whether the instruction is eligible for retirement. If an instruction is not yet eligible for retirement, retirement unit 1802 may wait until the instruction becomes eligible for retirement. Any suitable indication or mechanism for showing or determining that an instruction is eligible for retirement may be used. In one embodiment, RRT 1808 may include a field, bit, or other indicator showing that a given instruction is “valid” and thus eligible for retirement. Such an indicator may be set upon completion of execution by any suitable portion of system 1800. In the example of FIG. 19B, instruction I4 may be valid and eligible for retirement according to RRT 1808.
At (22), retirement unit 1802 may apply register reclamation to EDX {6}, as it has been pseudo-retired and has been determined to be non-blocking Retirement unit 1802 may identify register EDX {6} in freelist 1816 and share freelist 1816 with allocator 1804. Allocator 1804 may reallocate the freed resources at a subsequent time and overwrite the mapping for address {6} in PRF 1820 or RAT 1806.
Pseudo-retirement may terminate based upon any suitable criteria. In one embodiment, pseudo-retirement may be terminated when retirement pointer 1826 has caught up with pseudo-retirement pointer 1824. In another embodiment, pseudo-retirement may be terminated when all non-blocking registers in, for example, PRF 1820 or RAT 1806 have been reclaimed. In yet another embodiment, pseudo-retirement may be terminated when the long latency of the operation identified in (1) ends. Retirement unit 1802, for example, may detect of termination of the long latency by determining, for example, that the instruction in question has retired or is eligible to be retired. Determination that the instruction has retired may be made by, for example, determining that retirement pointer 1826 has been advanced. In another example, determining that instruction is eligible to be retired may be made by referencing the “valid” bit of RRT 1808. In the example of FIG. 19B, all non-blocking registers in PRF 1820 may have been reclaimed, or the long-latency load operation in instruction I1 may have finished. Pseudo-retirement may be terminated.
Regardless of how pseudo-retirement ends, reclamation of the blocking pseudo-retired registers may be postponed until the long-latency load operation which triggered non-blocking register reclamation has finished.
At (23), reclamation of pseudo-retired blocking registers may be initiated by retirement unit 1802. The long-latency load of instruction I1 may have finished. Instruction I1 may be retired. Retirement pointer 1826 may be advanced to point to instruction I1. RRT 1808 may indicate that instruction I1 is “valid” and is eligible for retirement. Thus, the resources associated with instruction I1 may be reclaimed. Such resources may have previously been pseudo-retired but not reclaimed. Retirement unit 1802 may take any suitable action to determine whether such resources are still in need of reclamation. In one embodiment, retirement unit 1802 may identify the resources of pseudo-retired and blocking resources from RRT2 1812 and compare them against the resources of the instruction to be retired. In another embodiment, retirement unit 1802 may determine whether any mappings for the resources of the instruction exist in, for example, PRF 1820 or RAT 1806. Furthermore, retirement unit 1802 may take any suitable action to perform reclamation for the identified resources. In one embodiment, retirement unit 1802 may identify the resources to be reclaimed in freelist 1816 to allocator 1804. Allocator 1804 may reuse physical resources identified in freelist 1816 to create new mappings in PRF 1820 or RAT 1806. In the example of FIG. 19B, retirement unit 1812 may identify register EAX {10} and allocator 1804 may assign a new logical register to physical register {10}, if such a mapping is subsequently needed.
At (24), retirement unit 1802 may continue retirement of instructions. Instruction I2 may be retired. Retirement pointer 1826 may point to instruction I2. RRT 1808 may indicate that instruction I2 is “valid” and is eligible for retirement. Retirement unit 1802 may read the resources identified in RRT2 1812 and compare them against the resources of instruction I2 and the mappings of PRF 1820. Retirement unit 1802 may consequently reclaim register EBX {8}. For example, retirement unit 1802 may identify register EBX {8} in freelist 1816. Allocate module may assign new logical resources to physical register {8}, if such mappings are subsequently necessary.
At (25), retirement unit 1802 may continue retirement of instructions. Instruction I3 may be retired. Retirement pointer 1826 may point to instruction I3. RRT 1808 may indicate that instruction I3 is “valid” and is eligible for retirement. Retirement unit 1802 may read the resources identified in RRT2 1812 and compare them against the resources of instruction I3 and the mappings of PRF 1820. In the example of FIG. 19B, retirement unit 1802 may determine that no resources of instruction I3 are left to be reclaimed.
At (26), retirement unit 1802 may continue retirement of instructions. Instruction I4 may be retired. Retirement pointer 1826 may point to instruction I4. RRT 1808 may indicate that instruction I4 is “valid” and is eligible for retirement. Retirement unit 1802 may read the resources identified in RRT2 1812 and compare them against the resources of instruction I4 and the mappings of PRF 1820. In the example of FIG. 19B, retirement unit 1802 may determine that no resources of instruction I4 are left to be reclaimed.
At (27), retirement unit 1802 may determine that resources associated with the checkpoint determined in (2) are to be reclaimed. In one embodiment, such a determination may be made by determining that retirement pointer 1826 is equal to pseudo-retirement pointer 1824 after pseudo-retirement and reclamation has been performed. In the example of FIG. 19B, retirement pointer 1826 may have caught up to pseudo-retirement pointer 1824 and both may point to instruction I4. Reclamation of checkpointed resources may be made by determining all checkpointed resources not already reclaimed. For example, retirement unit 1802 may identify the resource contents of CPT 1814, or may determine what elements of RRAT 1810 are marked as associated with a checkpoint. Furthermore, retirement unit 1802 may identify these resources in freelist 1816 for reuse by allocator 1804. In the example of FIG. 19B, retirement unit 1802 may identify registers ECX {90} and ECX {91} of instruction I0 from CPT 1814. As register ECX {91} is a logical-physical register instance of register ECX with a later such instance of register ECX (that is, ECX {90}), register ECX {91} may be retired. Retirement unit 1802 may populate freelist 1816 with register ECX {91}.
Out-of-order engine 1834 may continue processing and executing instructions until another long-latency operation is encountered. Out-of-order engine 1834 may subsequently repeat the actions of FIGS. 19A and 19B upon encountering such an operation.
FIG. 20 is an illustration of an example method 2000 for reclaiming non-blocking registers, in accordance with embodiments of the present disclosure. Method 2000 may begin at any suitable point and may execute in any suitable order. In one embodiment, method 2000 may begin at 2002. In various embodiments, method 2000 may be performed during the execution of an out-of-order processor.
At 2002, an instruction stream may be loaded, fetched, and executed in out-of-order fashion. At 2004, it may be determined whether a long-latency operation has been encountered. Such a long-latency operation may be identified by, for example, reference to indicators of operators that have been pre-determined to experience long latency in a given system. Furthermore, it may be determined whether such a long-latency operation has been encountered at the top of a ROB. If no long-latency operation has been determined, method 2000 may return to 2002. If a long-latency operation has been determined, method 2000 may proceed to 2006.
At 2006, it may be determined whether the number of available physical resources, such as registers, is below a threshold number x. The physical resources may be unavailable as mapped to logical resources, and available as unmapped to any logical resource. The mapping may be included in, for example, a PRF or a RAT. The physical resources may be listed as unavailable in, for example, freelist 1816. The mappings may be made in order to facilitate out-of-order processing through data independence. If the number of available physical resources is below the threshold number, method 2000 may proceed to 2008. If the number of physical resources is not below the threshold number, method 2000 may return to 2002.
At 2008, a retirement pointer may be set to an instruction immediately before the determined long-latency operation. If the retirement pointer was not already set to such a location, method 2000 may wait for such a condition to occur. The retirement pointer may indicate the last instruction that was retired in the system.
At 2010, preexisting register assignments, such as mappings between physical registers and logical registers in a PRF, may be stored as a checkpoint. The mappings may exclude any mappings that would be created subsequent to execution of the long-latency operation. Identifications of the resource and the checkpoint may be stored in, for example, bits of an RRAT or in a separate table.
At 2012, for each subsequent instruction of the long-latency operation, it may be determined whether resources of the instruction are dependent upon the long-latency operation. If so, the resources and the instruction may be marked as “poisoned”. Such a marking may be stored in, for example, a bit in an RRAT. At 2014, for each subsequent instruction of the long-latency operation, it may be determined whether resources of the instruction are dependent upon any “poisoned” resource. If so, the resources and the instruction may be marked as “poisoned.” At 2016, for each subsequent instruction of the long-latency operation, it may be determined whether resources of the instruction are sources to any “poisoned” resource. If so, the resources may be marked as “protected.” Such a marking may be stored in, for example, a bit in an RRAT.
At 2018, pseudo-retirement may be initiated. A pseudo-retirement pointer in a ROB may be set to the long-latency operation. The pseudo-retirement pointer may track which instructions have been pseudo-retired.
At 2020, for any resources in the instruction corresponding to the pseudo-retirement pointer, as well as for any resources previously encountered during pseudo-retirement, it may be determined whether such a resource is in a condition for retirement. Such a condition may be made with respect to any factor other than the position of the retirement pointer or that the instruction has not yet retired. For example, it may be determined whether a logical-physical resource combination is no longer needed. This may occur, for example, when a reference to a logical resource paired with a physical resource has been followed by another reference to the same logical resource paired with a different physical resource. Thus, the resource might otherwise be eligible for retirement. For any resources otherwise eligible for retirement, method 2000 may proceed to 2022. Otherwise, method 2000 may proceed to 2028.
At 2022, the resource may be pseudo-retired. Such a designation may be made by marking the resource in a table or other data structure.
At 2024, for each pseudo-retired instruction, it may be determined whether the resource is marked as “poisoned”, “protected”, or part of checkpoint. If so, method 2000 may proceed to 2026 for each such resource. If not, method 2000 may proceed to 2028 for each such resource. A determination that a given resource is marked as “poisoned”, “protected”, or part of checkpoint may be a determination that the resource is blocking. A determination that a resource is none of these may be a determination that the resource is non-blocking.
At 2026, a given non-blocking resource may be reclaimed. Reclamation may be made through any suitable mechanism or process. For example, reclaimed resources may be identified to an allocation module that will reuse the physical resources for new logical resources. The available, reclaimed resources may be identified in a freelist. Furthermore, an allocator, upon need for a free physical resource to assign to a logical resource, may read physical resource entries in the freelist and remap the physical resource to a new logical resource, thus overwriting a mapping in, for example, a PRF or RAT. Meanwhile, blocking resources might not be reclaimed.
At 2028, it may be determined whether pseudo-retirement is to be terminated. Such a termination may be made upon, for example, the pseudo-retirement pointer catching up with the retirement pointer, retirement of the long-latency operation, or reclamation of all non-blocking resources in a PRF or RAT. If pseudo-retirement is to be continued, method 2000 may proceed to 2030. If pseudo-retirement is to be stopped, method 2000 may proceed to 2032.
At 2030, the pseudo-retirement pointer may be advanced to the next instruction. Thus, pseudo-retirement may be applied to subsequent instructions. Method 2000 may proceed to 2020.
At 2032, any resources associated with the checkpoint may be reclaimed. At 2034, normal retirement may occur. During such normal retirement, resources previously identified as poisoned or protected may be reclaimed as their instructions are retired. At 2036, it may be determined whether method 2000 will terminate. If so, method 2000 will end. If not method 2000 may repeat by, for example, returning to 2002.
Method 2000 may be initiated by any suitable criteria. Furthermore, although method 2000 describes an operation of particular elements, method 2000 may be performed by any suitable combination or type of elements. For example, method 2000 may be implemented by the elements illustrated in FIGS. 1-19 or any other system operable to implement method 2000. As such, the preferred initialization point for method 2000 and the order of the elements comprising method 2000 may depend on the implementation chosen. In some embodiments, some elements may be optionally omitted, reorganized, repeated, or combined.
Embodiments of the mechanisms disclosed herein may be implemented in hardware, software, firmware, or a combination of such implementation approaches. Embodiments of the disclosure may be implemented as computer programs or program code executing on programmable systems comprising at least one processor, 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 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 may include 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), magnetic or optical cards, or any other type of media suitable for storing electronic instructions.
Accordingly, embodiments of the disclosure may 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.
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.
Thus, techniques for performing one or more instructions according to at least one embodiment are disclosed. While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on other embodiments, and that such embodiments not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art upon studying this disclosure. In an area of technology such as this, where growth is fast and further advancements are not easily foreseen, the disclosed embodiments may be readily modifiable in arrangement and detail as facilitated by enabling technological advancements without departing from the principles of the present disclosure or the scope of the accompanying claims.

## Claims

1. A processor, comprising circuitry to:
execute a first instruction and a second instruction, the first instruction ordered before the second instruction, the first instruction including a reference to a first logical register assigned to a first physical register, the second instruction including a reference to a second logical register assigned to a second physical register;
determine whether the second instruction is data-independent of the first instruction;
reassign the second physical register to another logical register before retirement of the first instruction based upon the determination whether the second instruction is data-independent of the first instruction;
execute one or more checkpoint instructions including references to one or more checkpoint logical registers assigned to one or more checkpoint physical registers, the checkpoint instructions ordered before the first instruction; and
determine whether the second physical register is unequal to each of the checkpoint physical registers;
wherein reassigning the second physical register to another logical register before retirement of the first instruction is based upon the determination whether the second physical register is unequal to each of the checkpoint physical registers.

2. The processor of claim 1, further comprising circuitry to:
identify latent execution of the first instruction, wherein latent execution includes expected latency above a threshold;
wherein reassigning the second physical register to another logical register before retirement of the first instruction is based upon the identification of latent execution of the first instruction.

3. The processor of claim 1, further comprising circuitry to:
execute a third instruction, the third instruction:
ordered after the first instruction;
including a reference to a third logical register assigned to a third physical register; and
data-dependent upon the first register; and

reassign the third physical register to another logical register after retirement of the first instruction based upon data-dependence upon the first register.

4. The processor of claim 1, further comprising circuitry to:
determine whether the second physical register is a source of information to the first instruction;
wherein reassigning the second physical register to another logical register before retirement of the first instruction is based upon the determination whether the second physical register is a source of information to the first instruction.

5. The processor of claim 1, further comprising circuitry to:
determine an available number of physical registers below a threshold;
wherein reassigning the second physical register to another logical register before retirement of the first instruction is based upon the determination of the available number of physical registers below a threshold.

6. A method comprising, within a processor:
executing a first instruction and a second instruction, the first instruction ordered before the second instruction, the first instruction including a reference a first logical register assigned to a first physical register, the second instruction including a reference to a second logical register assigned to a second physical register;
determining whether the second instruction is data-independent of the first instruction;
reassigning the second physical register to another logical register before retirement of the first instruction based upon determining whether the second instruction is data-independent of the first instruction;
executing one or more checkpoint instructions including references to one or more checkpoint logical registers assigned to one or more checkpoint physical registers, the checkpoint instructions ordered before the first instruction; and
determining whether the second physical register is unequal to each of the checkpoint physical registers;
wherein reassigning the second physical register to another logical register before retirement of the first instruction is based upon determining whether the second physical register is unequal to each of the checkpoint physical registers.

7. The method of claim 6 further comprising:
identifying latent execution of the first instruction, wherein latent execution includes expected latency above a threshold;
wherein reassigning the second physical register to another logical register before retirement of the first instruction is based upon identifying latent execution of the first instruction.

8. The method of claim 6, further comprising:
executing a third instruction that is:
ordered after the first instruction;
includes a reference to a third logical register assigned to a third physical register; and
data-dependent upon the first register; and

reassigning the third physical register to another logical register after retirement of the first instruction based upon data-dependence upon the first register.

9. The method of claim 6, further comprising:
determining whether the second physical register is a source of information to the first instruction;
wherein reassigning the second physical register to another logical register before retirement of the first instruction is based upon the determining whether the second physical register is a source of information to the first instruction.

10. The method of claim 6, further comprising:
determining an available number of physical registers below a threshold;
wherein the reassigning the second physical register to another logical register before retirement of the first instruction is based upon determining an available number of physical registers below the threshold.

11. A system comprising:
an interface to receive a first instruction and a second instruction;
a processor, including circuitry to:
execute the first instruction and the second instruction, the first instruction ordered before the second instruction, the first instruction including a reference a first logical register assigned to a first physical register, the second instruction including a reference to a second logical register assigned to a second physical register;
determine whether the second instruction is data-independent of the first instruction; and
reassign the second physical register to another logical register before retirement of the first instruction based upon the determination whether the second instruction is data-independent of the first instruction;
execute one or more checkpoint instructions including references to one or more checkpoint logical registers assigned to one or more checkpoint physical registers, the checkpoint instructions ordered before the first instruction; and
determine whether the second physical register is unequal to each of the checkpoint physical registers;
wherein reassigning the second physical register to another logical register before retirement of the first instruction is based upon the determination whether the second physical register is unequal to each of the checkpoint physical registers.

12. The system of claim 11, wherein:
the processor further includes circuitry to identify latent execution of the first instruction, wherein latent execution includes expected latency above a threshold; and
reassigning the second physical register to another logical register before retirement of the first instruction is based upon the identification of latent execution of the first instruction.

13. The system of claim 11, wherein the processor further includes circuitry to:
execute a third instruction, the third instruction:
ordered after the first instruction;
including a reference to a third logical register assigned to a third physical register; and
data-dependent upon the first register; and

reassign the third physical register to another logical register after retirement of the first instruction based upon data-dependence upon the first register.

14. The system of claim 11, wherein:
the processor further includes circuitry to determine whether the second physical register is a source of information to the first instruction; and
reassigning the second physical register to another logical register before retirement of the first instruction is based upon the determination whether the second physical register is a source of information to the first instruction.

15. The system of claim 11, wherein:
the processor includes circuitry to determine an available number of physical registers below a threshold; and
reassigning the second physical register to another logical register before retirement of the first instruction is based upon the determination of the available number of physical registers below a threshold.