# Patent

## Title
Instruction and logic for scheduling instructions

## Abstract

A processor includes a front end and a scheduler. The front end includes logic to determine whether to apply an acyclical or cyclical thread assignment scheme to code received at the processor, and to, based upon a determined thread assignment scheme, assign code to a static logical thread and to a rotating logical thread. The scheduler includes logic to assign the static logical thread to the same physical thread upon a subsequent control flow execution of the static logical thread, and to assign the rotating logical thread to different physical threads upon different executions of instructions in the rotating logical thread.

## 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 is a block diagram of a system 1800 for implementing an instruction and logic for scheduling instructions for execution, in accordance with embodiments of the present disclosure;
FIGS. 19A-19E are illustrations of the operation of scheduler 1820 to implement acyclic thread assignment schemes, in accordance with embodiments of the present disclosure;
FIGS. 20A-20C are illustrations of loop operations, in accordance with embodiments of the present disclosure;
FIG. 21 is an illustration of example operation of a system to perform loop rescheduling, according to embodiments of the present disclosure; and
FIG. 22 is an illustration of a method for implementing scheduling instructions for execution, in accordance with embodiments of the present disclosure.



DETAILED DESCRIPTION
The following description describes an instruction and processing logic for scheduling instructions with a processor, virtual processor, package, computer system, or other processing apparatus. Such scheduling may be performed with algorithms implemented by hardware, software, or a combination of hardware and software. Furthermore, such scheduling may be performed in a group of processors, such as clustered microprocessors. 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 Disc, 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 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 an0064 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, digital signal 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 static random access memory (SRAM) unit 930; a direct memory access (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 3rd 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 is a block diagram contrasting the use of a software instruction converter to convert binary instructions in a source instruction set to binary instructions in a target instruction set according to embodiments of the invention. In the illustrated embodiment, the instruction converter is a software instruction converter, although alternatively the instruction converter may be implemented in software, firmware, hardware, or various combinations thereof. FIG. 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 can perform substantially the same functions as an Intel processor with at least one x86 instruction set core by compatibly executing or otherwise processing (1) a substantial portion of the instruction set of the Intel x86 instruction set core or (2) object code versions of applications or other software targeted to run on an Intel processor with at least one x86 instruction set core, in order to achieve substantially the same result as an Intel processor with at least one x86 instruction set core. The x86 compiler 1304 represents a compiler that is operable to generate x86 binary code 1306 (e.g., object code) that can, with or without additional linkage processing, be executed on the processor with at least one x86 instruction set core 1316. Similarly, FIG. 13 shows the program in the 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.).
The instruction converter 1312 is used to convert the x86 binary code 1306 into alternative instruction set binary code 1311 that may be natively executed by the processor without an x86 instruction set core 1314. This converted code may or may not be the same as the alternative instruction set binary code 1310 resulting from an alternative instruction set compiler 1308; however, the converted code will accomplish the same general operation and be made up of instructions from the alternative instruction set. Thus, the 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 the 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 a liquid crystal display (LCD) video interface 1425, a subscriber interface module (SIM) interface 1430, a boot ROM interface 1435, a synchronous dynamic random access memory (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 another embodiment, memory system 1540 may include a retirement pointer 1582. Retirement pointer 1582 may store a value identifying the program order (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, 1M, or 2M 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 digital signal processor 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 scheduling instructions. Such scheduling may be performed with algorithms implemented by hardware, software, or a combination of hardware and software. Furthermore, such scheduling may be performed in a group of processors, such as clustered microprocessors. In one embodiment, such an instruction and logic may be a logical move in an out-of-order processor. FIG. 18 is a block diagram of a system 1800 for implementing an instruction and logic for scheduling instructions for execution, in accordance with embodiments of the present disclosure. In one embodiment, instructions may be assigned to logical threads. In another embodiment, the resulting logical threads may be mapped to physical threads in hardware for execution. The assignment of instructions to logical threads may be performed in any suitable way, such as by execution of software commands in a code stream specifying the assignment, by analysis of instructions in a code stream during interpretation or compilation, or in any other suitable manner. The assignment of logical threads may be performed by a compiler, just-in-time compiler, instructions included by a programmer, a dynamic binary translator. The mapping of logical threads to physical threads may be performed dynamically and in hardware. The mapping of logical threads to physical threads may constitute scheduling the underlying instructions for execution.
System 1800 may include any suitable number and kind of elements to perform the operations described herein. Furthermore, although specific elements of system 1800 may be described herein as performing a specific function, any suitable portion of system 1800 may perform the functionality described herein. System 1800 may fetch, dispatch, execute, and retire instructions out-of-order.
System 1800 may include a processor 1804 to perform processing of logical move instructions as well as other instructions. Processor 1804 may be implemented in part by any processor core, logical processor, processor, or other processing entity such as those illustrated in FIGS. 1-17. In various embodiments, processor 1804 may include a front end 1812 to fetch instructions to be executed; a scheduler 1820 to allocate assign instructions for execution to execution units or cores; and one or more execution units or cores 1822 to execute the instructions. Processor 1804 may include other suitable components that are not shown, such as allocation units to reserve alias resources or retirement units to recover resources used by the instructions.
Front end 1812 may fetch and prepare instructions to be used by other elements of processor 1804, and may include any suitable number or kind of components. For example, front end 1812 may include a decoder 1814 to translate instructions into microcode commands. Furthermore, front end 1812 may arrange instructions into parallel groups or other mechanisms of out-of-order processing. Processor 1804 may include any suitable kind of compiler, translator, or interpreter. For example, processor 1804 may include a just-in-time translator, compiler, or a dynamic binary translator (DBT) 1816. Instructions may be processed for in-order or out-of-order execution. Front end 1812 and its components may include any suitable
Scheduler 1820 may schedule instructions to be executed on any suitable execution unit or core 1822. In one embodiment, a logical grouping of execution units or cores 1822 may constitute a physical thread. Instructions may be scheduled for in-order or out-of-order execution. In one embodiment, scheduler 1820 may dynamically map instructions arranged in logical threads to physical threads for execution. Scheduler 1820 may perform such mapping with any suitable mapping algorithm and may take into account information associated with the logical thread and load information from cores 1822.
Cores 1822 may be implemented in any suitable manner. A given core 1822 may include any suitable number, kind, and combination of execution units.
Instructions may be assigned to logical threads in any suitable manner. In one embodiment, instructions may be assigned to logical threads through designations associated with the instruction. The designations may be implemented by bits stored with the instruction, instructions modified to further designate logical threads, parameters passed with the instructions, or in another suitable manner. The bits implementing the assignment of the instruction to a logical thread may specify a logical thread that is unique within a window of execution.
In one embodiment, assignment of instructions to logical threads may be performed outside of processor 1804. For example, code 1808 as written by a developer may specify the assignment of instructions to logical threads through use of specific instructions that identify logical threads of other instructions, instructions that identify logical threads of itself in addition to performing other functions, or by making assignments to instruction ranges. In another example, compiler 1806 may add assignment of instructions to logical threads to existing code 1808. Such assignments may be made after analyzing the expected execution flow of code 1808. In such examples, code may be sent to processor 1804 in instruction stream 1802, in which logical thread designations 1810A are present.
In one embodiment, assignment of instructions to logical threads may be performed inside of processor 1804. For example, instruction stream 1802, which might not yet include logical thread designations, may be received by a compiler, interpreter, translator, or other mechanism such as DBT 1816 in processor 1804. DBT 1816 may add assignment of instructions to logical threads to the instruction stream. Such assignments may be made after analyzing the expected execution flow of the instruction stream. In such examples, code may be produce in decoded instruction stream 1818, in which logical thread designations 1810B are present.
Furthermore, in such embodiments, designations of instructions to logical threads may reduce the effort of dynamically scheduling instructions. The use of logical threads may include designating instructions to execute in logical first-in-first-out queues. Instructions in a given logical thread may execute in-order. Assignment of instructions to logical threads may be based upon grouping instructions into slices or graphs based upon, for example, register dependence (RDG), data dependence (DDG), memory dependencies (load-store slices), or control flow (CFG). Individual instructions may be grouped as atoms, and may execute together in groups or molecules. In some cases, out-of-order scheduling might be used only for scheduling across threads, rather than within a thread. Static techniques to assign instructions to logical threads may avoid run-time overhead by performing thread assignment only once. However, static techniques alone might result in poorer run-time schedules compared to dynamic techniques. On the other hand, dynamic techniques alone might result in higher dynamic schedule quality but at a cost of greater run-time overhead. By allowing assignment of instructions to logical threads in software such as compiler 1806 or DBT 1816 and mapping logical threads to physical threads dynamically by schedulers 1820, system 1800 may achieve both low dynamic overhead of static thread assignment schemes with the higher schedule quality of dynamic thread assignment solutions.
Scheduler 1820 may assign logical threads to physical threads in any suitable manner. In one embodiment, scheduler 1820 may identify logical threads that are to be scheduled as static logical threads. In such an embodiment, each instance of the logical thread may be assigned to the same physical thread in any iteration of execution. Upon a first execution of the logical thread, scheduler 1820 may assign the logical thread to a physical thread. Upon subsequent executions of the same logical thread, scheduler 1820 may assign the logical thread to the same physical thread that was originally assigned. In another embodiment, scheduler 1820 may identify logical threads that are to be scheduled as rotating logical threads. In such an embodiment, each instance of the logical thread may be assigned to any suitable physical thread in a given iteration. Scheduler 1820 may optimize scheduling of the logical thread to a physical thread considering workloads of hardware in processor 1804 such that overall execution is optimized.
Compiler 1806 or DBT 1816 may implement any suitable scheduling algorithm to map instructions to logical threads. In one embodiment, scheduler 1820 may implement acyclic thread assignment schemes to map instructions to logical threads. Acyclic thread assignment schemes may target acyclic code with few loops or loops with low trip counts. Furthermore, acyclic thread assignment schemes may be used for very large loops that are too big to benefit from cross iteration threading. In addition, acyclic thread assignment schemes may be applied as a default. In another embodiment, compiler 1806 or DBT 1816 may implement cyclic thread assignment schemes to map instructions to logical threads. Cyclic thread assignment schemes may include algorithms targeting cyclic control flow and data dependence patterns. Cyclic thread assignment schemes may be applied to code in which control structures or loops have a high average trip count. The decision of whether to apply cyclic or acyclic thread assignment schemes, and the decision of which specific cyclic or acyclic schemes to apply, may be based upon the structure of instruction stream and the loads being executed.
Compiler 1806 or DBT 1816 may implement any suitable acyclic thread assignment scheme. FIGS. 19A-19E are illustrations of the operation of scheduler 1820 to implement acyclic thread assignment schemes, in accordance with embodiments of the present disclosure. FIG. 19A illustrates an in-order schedule of two snippets or blocks of code from the same source that are sequentially ordered but data-independent, B1 and B2. In FIG. 19A, data dependence edges between instructions are represented as arrows and dashed arrows represent the critical path. Instructions are illustrated as they would otherwise be assigned to elements such as arithmetic logic units (ALU), memory execution units (MEM), or control execution units (CTRL). Gaps in rows of instructions include empty molecules or bubbles.
In one embodiment, compiler 1806 or DBT 1816 may implement basic block thread assignment. In such an embodiment, compiler 1806 or DBT 1816 may simply put different basic blocks of instructions in different logical threads. Basic block schedules may be sufficiently efficient and instruction-level-parallelism is to be exploited across basic blocks. All atoms of a block may be assigned to the same logical thread, but different blocks may be assigned to different logical threads. In another embodiment, certain atoms may be assigned to a logical thread designated as a fixed or static logical thread, while all other atoms may be assigned to one or more rotating logical threads. In yet another embodiment, thread mapping may be rotated on each branch operation. Accordingly, scheduler 1820 may assign each block, other than those instructions in the static logical thread, for execution on different physical threads than its predecessor block.
For example, FIG. 19A illustrates that the elements of B1, forming a block, might be assigned as a first logical thread, while the elements of B2, forming a block, are assigned to a second logical thread. The data dependence edges show that there are no data dependencies between B1 and B2.
By application of a basic block assignment, elements from B2 may be reassigned to B1 as shown in FIG. 19B. As space exists within B1 within its ALUs for ADD4, ADD7, and ADD6, these may be assigned to B1 from B2. As space exists within B1 within its MEMs for LD6, LD5, LD7, LD9, LD10, and LD11, these may be assigned to B1 from B2. Additional space exists within the ALUs and MEMs of physical thread 1902 for ADD7 and LD12. However, such space might only be available in an order that would violate the data dependencies illustrated in FIG. 19A. Accordingly, these may remain in B2. Furthermore, additional space exists within the ALUs of MEMs of B1 for some of the B2 instructions to be moved even earlier for execution, such as ADD6 to ALU1 or LD11 to MEM1. However, such space might represent a change in execution order that would violate the data dependencies illustrated in FIG. 19A. In FIG. 19B, instructions associated with B2 may be represented in bold print and instructions from B2 reassigned to B1 may be represented in shaded boxes.
FIG. 19C illustrates a conventional out-of-order scheduling that might be performed by system 1900. Out-of-order scheduling may provide for more efficient run-time execution compared to the scheme applied in FIG. 19C. However, system 1900 may apply other acyclic schemes that may have performance enhancements over the conventional out-of-order scheduling.
In one embodiment, compiler 1806 or DBT 1816 may implement simulation guided threat assignment. In such an embodiment, compiler 1806 or DBT 1816 may target finer-grained instruction-level parallelism and may be useful for code undergoing high levels of optimization where the increased overhead is acceptable in view of the performance gains. Simulation guided thread assignment may include dynamically selecting the specific instructions in a basic block that could be potentially hoisted into prior blocks. In one embodiment, simulation guided thread assignment may further include prioritizing these instructions through logical thread assignment, static rescheduling, or both. For example, an order of instructions within B1 may present a restriction on where instructions from B2 may be hoisted into B1. However, the order of instructions within B1 might be moved to open a slot within B1 to make room for an instruction from B2 while still preserving the order requirements as originally presented in FIG. 19A. In another example, an order of instructions within B1 might be amended using thread assignment, including placing non-critical instructions in separate logical threads that are then assigned to different physical threads. In the example of FIG. 19D, an empty slot may have been created by moving OR1 to ALU0, creating an empty slot for ADD4. In another example of FIG. 19D, non-critical instructions such as LD5 may have been placed in a separate physical thread.
In one embodiment, simulation guided threat assignment may include converting the control flow graph of code into a set of straight-line paths. Straight-line paths may be generated by traversing the CFG, starting at the entry point, and adding each visited block to the path until all blocks are added into at least one straight-line path. Branch probability information, which may be maintained in DBT 1816, may be used to guide the traversal of the CFG such that the various branch targets are traversed in the order of the branch probabilities. Furthermore, the branch probability information may be used such that one straight-line path is created for each of the options. A code block may be present in more than one straight-line path.
In another embodiment, for each path, a greedy schedule may be identified. Instructions may be evaluated and scheduled as early as possible. Each instruction is moved as early as possible within the existing schedule. Instructions are moved down in the schedule as long as the overall schedule length is not increased. In a further embodiment, this may provide empty slots for critical path instructions. Then each instruction may be hoisted, starting from the top of the straight-line path, as high as possible while ensuring that all data dependencies, hardware resource constraints, and operation latencies are satisfied. In the example of FIG. 19, wherein there are no data dependencies between B1 and B2, in the simulated schedule resulting in FIG. 19D, nearly all the instructions have been hoisted into B1.
In yet another embodiment, the instructions in the greedy schedule may be assigned to threads. In a further embodiment, multiple threads may be used. A non-rotating (or static) base thread, a non-rotating serial thread, and a rotating active thread may be used. All instructions may originally be assigned to a base thread, and subsequently certain instructions may be assigned to serial and rotating active threads. The separation may remove false ordering constraints imposed by static scheduling while not increasing static schedule length.
All branch instructions and their flag producers may be assigned to a non-rotating serial thread to help resolve branches as soon as possible. The non-rotating thread may be executed with higher priority. Stores or other instructions, for which speculative or out-of-order execution are not supported, may also be assigned to the non-rotating serial thread to force them to execute after branch resolution. Furthermore, instructions that benefit from earlier execution, as defined to the greedy schedule, may be assigned to the rotating active thread. These instructions may be identified as instructions that originated in a prior basic block and have moved past another instruction from the base thread. In addition, instructions that remain, which cannot execute earlier than their static location or do not benefit from earlier execution, may be assigned to the base thread.
In the example of FIG. 19D, BRC1 may be assigned to the serial thread as it is a branch operation. CMP may also be assigned to the serial thread since it a producer for BRC1. LD6 from B2 moved up past ADD2, which is in the base thread and from B1 and is therefore assigned to the active thread. LD12 is not added to the active thread since it only moved past the CMP and BRC from B1, both of which are in the serial thread. Given this assignment, it can be seen that the active thread instructions are all completed after ADD7. This contrasts with FIG. 19B, wherein active thread instructions are all completed after ADD8.
Furthermore, entire dependence chains may be assigned to a separate, rotating helper thread. For example, assignment to a helper thread of the dependence chain leading to a branch known to have high misprediction rates or a load known to have a high miss rate may prioritize these instructions. The helper thread may also be used to break false ordering constraints among the active thread instructions.
In yet another embodiment, compiler 1806 or DBT 1816 may reconcile different thread assignments that are made for repeated code blocks from different straight-line paths. Reconciliation may be made by creating a consistent assignment by selecting the most common thread assignment and using it for all the straight-line paths. Furthermore, weights may be assigned to the paths based upon branch probabilities. The thread assignment for the path with the maximum weight may be chose as the common thread assignment.
In another embodiment, compiler 1806 or DBT 1816 may correct false ordering constraints. As instructions within a thread execute in-order, the scheduled order might reflect a false ordering constraint. Compiler 1806 or DBT 1816 may, based upon the greedy simulated schedule, remove such dependencies. As a result, out-of-order operation and execution may be more suitable for reducing front-end bandwidth requirements.
For example, in FIG. 19E, false ordering constraints may be eliminated by moving LD5 and LD7 to the MEM1 slot. Accordingly, these may be scheduled earlier, which may help the critical instruction LD7 to be scheduled earlier. In another example, the non-critical OR1 may be scheduled later, which allows the critical path instruction ADD4 to be executed earlier. Molecule packing, which impacts front-end bandwidth, may be improved by moving LD4 into the following molecule. This rescheduling might not delay LD4 and increasing the packing density of the modules.
In yet another embodiment, compiler 1806 or DBT 1816 may merge schedules. Merging the schedules may be performed by merging the statically rescheduled straight-line paths. If a static basic block only exists on a single straight-line path, then the new schedule of the block is the same as the schedule of the straight-line path. In cases where CFG straightening resulted in a static basic block being part of more than one straight-line path, multiple schedules from the straight-line paths may be merged. Merging may be performed in any suitable manner, such as by using heuristic rules. Such rules may consider the thread assignment as well as the average rescheduling position of an instruction relative to other instructions.
For example, instructions which are assigned to rotating threads may have a higher priority than instructions assigned to static threads. For a given instruction, dependencies and operation latencies may be covered for other intra-thread instructions before the instruction is scheduled. Furthermore, for a given instruction, latencies across threads might not need to be covered before the instruction is scheduled. As an example, a load operation might be assigned to a different thread than the consumer of the load. Accordingly, the consumer may be statically scheduled immediately after the load even though the load may take multiple cycles to execute. An instruction with a lower average rescheduling position assigned to a particular thread may be scheduled ahead of an instruction from the same thread with a higher average rescheduling position.
Returning to FIG. 18, compiler 1806 or DBT 1816 may, as previously discussed, implement cyclic thread assignment schemes to map instructions to logical threads. Cyclic thread assignment may include thread assignment techniques that specifically target loop bodies. Thread assignment may be made upon loop iterations, upon branch instructions (which may include a backward branch in the case of a loop iteration), upon control flow instructions (which may include branches as well as backward branches in loop iterations). Although loop iterations may be referred to herein as triggering mechanisms for thread assignments, branch instructions and control flow instructions may also be considered to fulfill the role of such triggering mechanisms. While in some simply cases, wherein a loop iteration is completely independent of previous iterations, a new physical thread may be assigned to a logical thread of each iteration resulting, in effect, as many parallel threads as allowed by the number of available physical threads. However, loop iterations commonly have dependencies upon previous iterations. Specifically, loop iterations have dependencies upon the instructions of previous iterations of the same code.
Example loop dependencies may include loop carried dependence (LCD), wherein the value of variable x produced in the nth iteration of the loop is consumed in computing the value of another variable y in the (n+1) iteration of the loop. Another example loop dependency may be recurrence, wherein the value of one variable x computed in the nth iteration is used in computing the value of the same variable x in the (n+1) iteration of the loop. In these examples, although the (n+1) iteration is referenced, any iteration subsequent to n may trigger the example dependency.
For example, consider the loop presented in FIG. 21 at (A). The boxes represent instructions and the edges between the boxes represent the data dependence between the instructions. R1 and R2 may represent a cross-iteration dependence of recurrence type, whereas P2, P1, C1, and C2 may represent a LCD. As seen from unrolling two successive iterations of the loop, virtually no speedup can be obtained by attempting to execute the iterations in parallel since the R1-R2 cross-iteration dependence serializes the successive iteration execution. Thus, cross-iteration dependencies limit may the amount of parallelism that can be exposed simply by overlapping iterations. Compiler 1806 or DBT 1816 may perform cyclic thread assignment algorithms that assign threads to successive iterations taking the cross-iteration dependencies into account. This may increase the amount of instruction-level parallelism across successive iterations.
In one embodiment, compiler 1806 or DBT 1816 may statically move the atoms involved in the recurrence and LCD chains closer to each other. Furthermore, the top of the iteration may be closed. This may allow the remaining atoms to be overlapped with the top of the next loop iteration.
For example, at (B), graph 2000 may be rescheduled such that graph 2002 is produced. Using static rescheduling, R2 can be rescheduled immediately following R1, thereby allowing R1 of the next iteration to be scheduled immediately following R2 of the previous iteration. Furthermore R2 and R1 may be moved close to each other. At (C), multiple iterations are illustrated. Graph 2002 illustrates only one possible rescheduling, among many, as well as the resultant overlap of the loop iterations.
To achieve rescheduling, compiler 1806 or DBT 1816 may perform any suitable steps. In one embodiment, compiler 1806 or DBT 1816 may build the DFG of the loop. In another embodiment, compiler 1806 or DBT 1816 may identify the cross-iteration recurrence dependences. In yet another embodiment, compiler 1806 or DBT 1816 may, for every recurrence and LCD, identify the producer atom (such as R2 in the above example), follow the dependence chain of the producer to identify the slice instructions, and put the producer and its slice in a high priority list. Furthermore, compiler 1806 or DBT 1816 may list schedule the atoms in the high priority list first, followed by the low priority list.
In one embodiment, compiler 1806 or DBT 1816 may perform recurrence thread assignment. Such assignment may be performed when static rescheduling is not possible or is accompanied by increased overhead in the form of compensation code or static bubbles. Recurrence thread assignment may be used to simulate the effect of hoisting recurrence atoms to the top of the loop by assigning all recurrence atoms to a single dedicated logical thread. Such a thread may correspond to the reoccurrence thread.
Compiler 1806 or DBT 1816 may perform recurrence thread assignment in any suitable manner. In one embodiment, compiler 1806 or DBT 1816 may build the DFG for the loop body, identify the cross-iteration recurrence dependences, and schedule all the atoms involved in the recurrence in a fixed or static “recurrence thread.” In another embodiment, compiler 1806 or DBT 1816 may further schedule the remaining atoms in a rotating thread. The assignment of the rotating thread to the physical thread may be shifted for every iteration of the loop at the execution of the back edge.
FIG. 21 illustrates example operation of system 1800 to perform loop rescheduling, according to embodiments of the present disclosure. An example of one potential thread assignment using these steps is shown by schedule 2104. R1 and R2 are illustrated as in Thread0, in order, and repeating according to their first and second iterations. Next, in Thread1, the first iterations of the other elements are scheduled in a single rotating thread. Next, in Thread2, the second iterations of the other elements are scheduled in a rotating thread. If a third iteration were added, the R1 and R2 of the third iteration would be added to Thread0 and the third iteration of the other components would receive their own Thread3.
In another embodiment, compiler 1806 and DBT 1816 may perform a combination of recurrence and LCD thread assignment. Compiler 1806 and DBT 1816 may implement recurrence thread assignment simply and with low scheduling overhead, but such benefits may be limited due to unbalanced thread utilization. For example, when the entire recurrence chain consists of only one atom (that is, incrementing the loop index), the utilization of the recurrence thread becomes low and the entirety of the loop body is assigned to the rotating thread (i.e., Thread1 of schedule 2104). This may limit the overlap that can be achieved between successive iterations. By performing a combination of recurrence and LDC thread assignment, the recurrence thread assignment may be extended by utilizing separate rotating logical threads for LCD chains in addition to assigning the recurrence chain to the recurrence thread.
Compiler 1806 or DBT 1816 may perform recurrence thread assignment in any suitable manner. In one embodiment, compiler 1806 or DBT 1816 may build the DFG for the loop body, identify the cross-iteration recurrence and LCD dependences, and schedule all the atoms involved in the recurrence in a fixed or static “recurrence thread.” In another embodiment, compiler 1806 or DBT 1816 may schedule each LCD to a different rotating thread. The virtual to physical thread assignment for these threads may rotate on the first producer (in program order) of the LCD to which it is assigned. In yet another embodiment, the virtual to physical thread assignment for this thread rotates on the back edge.
For example, compiler 1806 or DBT 1816 may produce schedule 2106, wherein R1 and R2 are illustrated as in Thread0, in order, and repeating according to their first and second iterations. Next, in Thread1, the first iterations of A1 and A2 are scheduled in a single rotating thread, offset from the first iteration of R1. Similarly, in Thread2, the first iterations of C1 and C2 are scheduled in a single rotating thread, offset from the first iteration of R1. Next, in Thread3, the first iterations of P2 and P1, in addition to the second iterations of C1 and C2, are included in a rotating thread. Second iterations of the other elements are scheduled in a rotating thread. Thread4 includes the second iterations of A1 and A2 and Thread5 includes the second iterations of P2 and P1. Accordingly, schedule 2106 may result in more instruction-level parallelism, but at a cost of more threads.
The pair A1 and A2 in their first iteration are illustrated as in Thread1, while C1 and C2 in their first iteration are illustrated as being placed in Thread2. The first iterations of P2 and P1, followed by the second iterations of C1 and C2, may be placed in Thread3.
FIG. 22 is a flowchart of an example embodiment of a method 2200 for scheduling instructions, in accordance with embodiments of the present disclosure. Method 2200 may illustrate operations performed by, for example, processor 1804, compiler 1806, DBT 1816, or scheduler 1820. Method 2200 may begin at any suitable point and may execute in any suitable order. In one embodiment, method 2200 may begin at 2205.
At 2205, instructions to be executed on a processor such as processor 1804 may be received. Within such instructions, one or more blocks of instructions may be identified. Instructions may be moved between such blocks of instructions.
At 2210, it may be determined, based upon the code, whether to use acyclical, cyclical, or both kinds of thread assignment. Although FIG. 22 illustrates method 2200 as choosing between the two categories of thread assignment, each may be applied in turn in various embodiments. Any suitable criteria may be used to determine what type of thread assignment to use. For example, if a control structure or loop within the code is longer than a threshold, or have an average trip-count lower than a threshold, acyclical assignments may be made and method 2200 may proceed to 2215. Otherwise, cyclical assignments may be made and method 2200 may proceed to 2230.
At 2215, any suitable acyclical assignment of threads may be made. In one embodiment, it may be determined whether a basic block thread assignment or a simulated, guided thread assignment is to be made. Such a determination may be made based upon whether the expected efficiency increases of a simulated, guided thread assignment outweigh the increased overhead when compared to basic block assignments. If basic block thread assignment is to be used, method 2200 may proceed to 2220. Otherwise, method 2200 may proceed to 2225.
At 2220, any suitable manner of implementing basic block thread assignment may be used. In one embodiment, atoms may be moved to an earlier block if room is available. Remaining atoms may be assigned to the same rotating thread. The earlier block may be assigned to the same rotating thread. Different blocks may be assigned to different threads. Some special instructions may be placed in different logical threads. The thread mapping may be rotated on every branch operation. A block may thus use a different physical thread than its predecessor. Method 2200 may proceed to 2270.
At 2225, the specific instructions that could be hoisted into a prior block (which is originally scheduled to execute earlier in time) may be identified. In one embodiment, these may be further prioritized through dynamic scheduling through thread assignment. In another embodiment, these hoisted instructions may be further prioritized through static rescheduling. Any suitable implementation of simulated, guided thread assignment may be used.
In one embodiment, the CFG may be converted to a set of straight-path lines. Straight-line paths may be made by traversing the CFG and adding each visited block to the path until all blocks are added to at least one path. A code block may be present in more than one path.
In another embodiment, the instructions in each path are greedily scheduled, wherein an instructions moves as early as possible without increasing the schedule length. Next, each instruction, starting from the top of a path, is hoisted as much as possible while preserving dependencies and constraints.
In yet another embodiment, instructions may be placed into two or more possible logical threads. Such threads may include a static base thread, a static serial thread, and a rotating active thread. All instructions may be assigned to the static base thread by default. All branch instructions and their producers may be assigned to the status serial thread. Furthermore, stores and other instructions which do not support speculative or out-of-order execution may be placed in the static serial thread. This may force them to execute after branch resolution. Any instruction that has been moved according to the greedy schedule may be assigned to the rotating active thread. These instructions may have moved past another instruction residing in the static base thread from a prior base block. Remaining instructions, which cannot execute earlier than their static location or otherwise benefit from earlier execution, may remain in the static base thread. In a further embodiment, an additional rotating thread may be used to store entire dependence chains. For example, the dependence chain leading to a branch or a load may be assigned to the additional rotational thread.
In another embodiment, potentially different thread assignments for a repeated code block from different straight-line paths may be reconciled to a consistent assignment. The different assignments may be merged using the most common thread assignment and applying it to all the paths. Furthermore, weights may be assigned to the paths based upon branch possibilities. The path with the maximum weight may be selected as the common thread assignment which will be applied to the other paths.
In yet another embodiment, static rescheduling may be performed to eliminate false ordering constraints. Based upon the greedy schedule, such dependency may be broken by moving an instruction. This may free up the schedule for out-of-order execution. Rescheduling may also be performed to increase the density of the code, reducing front-end bandwidth requirements.
In another embodiment, schedules may be merged. This may be performed in a manner similar to merging of logical thread assignments. If a static block only exists in one path, then the new schedule of that block is the same as the schedule of the path. If the static block is in more than one path, then the schedules for the paths may be merged with respect to the block. Instructions that are assigned to the rotating active thread or other rotating threads may be given a higher priority than instructions assigned to static threads. Dependences and latencies may be evaluated and handled with respect to other instructions within the same thread, but cross-thread dependencies may be ignored for the purposes of schedule merging. An instruction with a lower average rescheduling position assigned may be scheduled ahead of an instruction from the same thread with a higher average rescheduling position.
Method 2200 may proceed to 2270.
At 2230, recurrence and LCD chains in a loop may be determined. At 2235 it may be determined whether to employ static loop rescheduling or to employ any combination of recurrence-based thread assignment and LCD-based thread assignment. In one embodiment, such a determination may be based on, whether static rescheduling is not possible or is accompanied by increased overhead. Such overhead may be in the form of compensation code or static bubbles. If static rescheduling is to be used, method 2200 may proceed to 2240. Otherwise, method 2200 may proceed to 2245.
At 2240, the atoms involved in the recurrence and LCD chains may be statically rescheduled. In one embodiment, the atoms involved in the chains may be moved closer to each other. In another embodiment, the atoms may be moved close to the top of the iteration, allowing subsequent atoms to be overlapped with the top of the next loop iteration. To perform these steps, a DFG of the loop may be built and the cross-iteration recurrence and LCD dependencies may be identified. For each recurrence and LCD, the producer atom may be identified and the dependence chain may be followed to identify slices. The producer and its slice may be placed in a high-priority list. The schedule may list the high-priority atoms first, followed by the low-priority atoms. Method 2200 may proceed to 2270.
At 2245, a DFG may be built for the loop. Cross-iteration dependencies with respect to LCD and recurrence may be identified. In one embodiment, all atoms involved with the recurrence may be scheduled in a fixed recurrence logical thread.
At 2250, it may be determined whether LCD thread assignment, recurrence thread assignment, or both will be performed. Such a determination may be based upon whether recurrence thread assignment alone is limited in benefit because of unbalanced thread utilization. For example, if the entire recurrence chain is a single atom, utilization of the static recurrence thread may be load and thus limit the overlap that can be achieved between successive iterations. LCD thread assignment may be performed in addition to recurrence thread assignment. If LCD thread assignment is to be performed, method 2200 may proceed to 2260. If LCD thread assignment is not to be performed and only recurrence thread assignment is to be performed, method 2200 may proceed to 2255.
At 2255, all remaining atoms may be scheduled in a rotating thread. The assignment of the rotating thread to physical threads, in one embodiment, may be shifted at every iteration of the loop at the execution of the back edge of the graph. Method 2200 may proceed to 2270.
At 2260, in one embodiment each LCD may be scheduled to a different rotating thread. The assignment of the rotating thread to a physical thread may be made upon execution of the first producer (in program order) of the LCD to which it is assigned. The remaining atoms may be scheduled to another rotating thread. The virtual to physical thread assignment for such a thread may rotate on the back edge of the graph.
At 2270, for fixed logical threads, the thread may be assigned to the same physical thread for each iteration of the thread. At 2275, for rotating logical threads, the thread may be assigned to any suitable, available physical thread for each iteration. In one embodiment, the physical thread assigned may vary from iteration to iteration. The selection of the physical thread may be made using any suitable optimization or utilization scheme.
Method 2200 may terminate or repeat as necessary.
Method 2200 may be initiated by any suitable criteria. Furthermore, although method 2200 describes an operation of particular elements, method 2200 may be performed by any suitable combination or type of elements. For example, method 2200 may be implemented by the elements illustrated in FIGS. 1-20 or any other system operable to implement method 2200. As such, the preferred initialization point for method 2200 and the order of the elements comprising method 2200 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:
a front end, including:
a first logic to determine whether to apply an acyclical thread assignment scheme to code received at the processor;
a second logic to determine whether to apply a cyclical thread assignment scheme to code received at the processor;
a third logic to, based upon a determined thread assignment scheme, assign first code to a static logical thread; and
a fourth logic to, based upon the determined thread assignment scheme, assign second code to a rotating logical thread; and
a scheduler, including:
a fifth logic to assign the static logical thread to a first physical thread;
a sixth logic to assign the static logical thread to the first physical thread upon each subsequent control flow instruction of the static logical thread;
a seventh logic to assign the rotating logical thread to a second physical thread; and
an eighth logic to assign the rotating logical thread to a third physical thread upon a subsequent execution of the rotating logical thread.

2. The processor of claim 1, wherein the front end further includes, as part of the acyclical thread assignment scheme:
a ninth logic to move atoms from within a second block of code to an earlier, first block of code; and
a tenth logic to assign atoms remaining in the second block of code to the rotating logical thread.

3. The processor of claim 1, wherein the front end further includes, as part of the acyclical thread assignment scheme:
a ninth logic to move atoms from within a second block of code to an earlier, first block of code;
a tenth logic to prioritize the moved atoms by assigning the moved atoms to the rotating logical thread; and
an eleventh logic to assign branch instructions to the static logical thread.

4. The processor of claim 3, wherein the front end further includes, as part of the acyclical thread assignment scheme, a twelfth logic to assign remaining instructions to another static logical thread.

5. The processor of claim 1, wherein the front end further includes, as part of the cyclical thread assignment scheme:
a ninth logic to determine any recurrence chains and loop carried dependence (LCD) chains in a loop;
a tenth logic to, for each recurrence chain and LCD chain, schedule atoms in the chain to execute closer to other atoms of the chain in a first iteration of the loop; and
an eleventh logic to schedule other atoms of the loop to overlap with a beginning of a second iteration of the loop.

6. The processor of claim 1, wherein the front end further includes, as part of the cyclical thread assignment scheme:
a ninth logic to determine a recurrence chain in a loop;
a tenth logic to schedule all atoms of the recurrence chain in the fixed logical thread; and
an eleventh logic to schedule remaining atoms in the rotating logical thread.

7. The processor of claim 1, wherein the front end further includes, as part of the cyclical thread assignment scheme:
a ninth logic to determine a recurrence chain and a plurality of loop carried dependence (LCD) chains in a loop;
a tenth logic to schedule all atoms of the recurrence chain in the fixed logical thread; and
an eleventh logic to schedule each LCD chain in a respective LCD rotating logical thread; and
a twelfth logic to schedule remaining atoms in the rotating logical thread.

8. A method comprising, within a processor:
determining whether to apply an acyclical thread assignment scheme to code received at the processor;
determining whether to apply a cyclical thread assignment scheme to code received at the processor;
based upon a determined thread assignment scheme, assigning first code to a static logical thread; and
based upon the determined thread assignment scheme, assigning second code to a rotating logical thread;
assigning the static logical thread to a first physical thread;
assigning the static logical thread to the first physical thread upon each subsequent control flow execution of the static logical thread;
assigning the rotating logical thread to a second physical thread; and
assigning the rotating logical thread to a third physical thread upon a subsequent execution of the rotating logical thread.

9. The method of claim 8, further comprising applying the acyclical thread assignment scheme by:
moving atoms within a second block of code to an earlier, first block of code as part of the acyclical thread assignment scheme; and
assigning atoms remaining in the second block of code to the rotating logical thread as part of the acyclical thread assignment scheme.

10. The method of claim 8, further comprising applying the acyclical thread assignment scheme by:
moving atoms within a second block of code to an earlier, first block of code;
prioritizing the moved atoms by assigning the moved atoms to the rotating logical thread; and
assigning branch instructions to the static logical thread.

11. The method of claim 8, further comprising applying the cyclical thread assignment scheme by:
determining any recurrence chains and loop carried dependence (LCD) chains in a loop;
for each recurrence chain and LCD chain, scheduling atoms in the chain to execute closer to other atoms of the chain in a first iteration of the loop; and
scheduling other atoms of the loop to overlap with a beginning of a second iteration of the loop.

12. The method of claim 8, further comprising applying the cyclical thread assignment scheme by:
determining a recurrence chain in a loop;
scheduling all atoms of the recurrence chain in the fixed logical thread; and
scheduling remaining atoms in the rotating logical thread.

13. The method of claim 8, further comprising applying the cyclical thread assignment scheme by:
determining a recurrence chain and a plurality of loop carried dependence (LCD) chains in a loop;
scheduling all atoms of the recurrence chain in the fixed logical thread; and
scheduling each LCD chain in a respective LCD rotating logical thread; and
scheduling remaining atoms in the rotating logical thread.

14. A system for executing instructions, including:
a processor;
a front end, including:
a first logic to determine whether to apply an acyclical thread assignment scheme to code received at the processor;
a second logic to determine whether to apply a cyclical thread assignment scheme to code received at the processor;
a third logic to, based upon a determined thread assignment scheme, assign first code to a static logical thread; and
a fourth logic to, based upon the determined thread assignment scheme, assign second code to a rotating logical thread; and
a scheduler, including:
a fifth logic to assign the static logical thread to a first physical thread;
a sixth logic to assign the static logical thread to the first physical thread upon each subsequent control flow execution of the static logical thread;
a seventh logic to assign the rotating logical thread to a second physical thread; and
an eighth logic to assign the rotating logical thread to a third physical thread upon a subsequent execution of the rotating logical thread.

15. The system of claim 14, wherein the front end further includes, as part of the acyclical thread assignment scheme:
a ninth logic to move atoms from within a second block of code to an earlier, first block of code; and
a tenth logic to assign atoms remaining in the second block of code to the rotating logical thread.

16. The system of claim 14, wherein the front end further includes, as part of the acyclical thread assignment scheme:
a ninth logic to move atoms from within a second block of code to an earlier, first block of code;
a tenth logic to prioritize the moved atoms by assigning the moved atoms to the rotating logical thread; and
an eleventh logic to assign branch instructions to the static logical thread.

17. The system of claim 16, wherein the front end further includes, as part of the acyclical thread assignment scheme, a twelfth logic to assign remaining instructions to another static logical thread.

18. The system of claim 14, wherein the front end further includes, as part of the cyclical thread assignment scheme:
a ninth logic to determine any recurrence chains and loop carried dependence (LCD) chains in a loop;
a tenth logic to, for each recurrence chain and LCD chain, schedule atoms in the chain to execute closer to other atoms of the chain in a first iteration of the loop; and
an eleventh logic to schedule other atoms of the loop to overlap with a beginning of a second iteration of the loop.

19. The system of claim 14, wherein the front end further includes, as part of the cyclical thread assignment scheme:
a ninth logic to determine a recurrence chain in a loop;
a tenth logic to schedule all atoms of the recurrence chain in the fixed logical thread; and
an eleventh logic to schedule remaining atoms in the rotating logical thread.

20. The system of claim 14, wherein the front end further includes, as part of the cyclical thread assignment scheme:
a ninth logic to determine a recurrence chain and a plurality of loop carried dependence (LCD) chains in a loop;
a tenth logic to schedule all atoms of the recurrence chain in the fixed logical thread; and
an eleventh logic to schedule each LCD chain in a respective LCD rotating logical thread; and
a twelfth logic to schedule remaining atoms in the rotating logical thread.