Patent Publication Number: US-10762877-B2

Title: System, apparatus and method for reducing voltage swing on an interconnect

Description:
TECHNICAL FIELD 
     Embodiments relate generally to data processing and more particularly to data processing via a general-purpose graphics processing unit. 
     BACKGROUND 
     Current parallel graphics data processing includes systems and methods developed to perform specific operations on graphics data such as, for example, linear interpolation, tessellation, rasterization, texture mapping, depth testing, etc. Traditionally, graphics processors used fixed function computational units to process graphics data; however, more recently, portions of graphics processors have been made programmable, enabling such processors to support a wider variety of operations for processing vertex and fragment data. 
     To further increase performance, graphics processors typically implement processing techniques such as pipelining that attempt to process, in parallel, as much graphics data as possible throughout the different parts of the graphics pipeline. Parallel graphics processors with single instruction, multiple thread (SIMT) architectures are designed to maximize the amount of parallel processing in the graphics pipeline. In an SIMT architecture, groups of parallel threads attempt to execute program instructions synchronously together as often as possible to increase processing efficiency. A general overview of software and hardware for SIMT architectures can be found in Shane Cook,  CUDA Programming , Chapter 3, pages 37-51 (2013) and/or Nicholas Wilt, CUDA Handbook,  A Comprehensive Guide to GPU Programming , Sections 2.6.2 to 3.1.2 (June 2013). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a computer system configured to implement one or more aspects of the embodiments described herein. 
         FIG. 2A-2D  illustrate a parallel processor components, according to an embodiment. 
         FIGS. 3A-3B  are block diagrams of graphics multiprocessors, according to embodiments. 
         FIG. 4A-4F  illustrate an exemplary architecture in which a plurality of GPUs are communicatively coupled to a plurality of multi-core processors. 
         FIG. 5  illustrates a graphics processing pipeline, according to an embodiment. 
         FIG. 6  is a schematic diagram of an interconnect in accordance with an embodiment of the present invention. 
         FIG. 7  is a schematic diagram of an interconnect in accordance with another embodiment of the present invention. 
         FIG. 8  is a schematic diagram of an interconnect driver in accordance with another embodiment of the present invention. 
         FIG. 9  is a timing diagram illustrating operation of a driver circuit in accordance with one embodiment of the present invention. 
         FIG. 10  is a schematic diagram of an interconnect driver in accordance with a still further embodiment of the present invention. 
         FIG. 11  is a schematic diagram of an interconnect driver in accordance with yet another embodiment of the present invention. 
         FIG. 12  is a schematic diagram of an interconnect driver in accordance with an additional embodiment of the present invention. 
         FIG. 13  is a flow diagram of a method in accordance with an embodiment of the present invention. 
         FIG. 14  is a block diagram of a processor in accordance with an embodiment of the present invention. 
         FIG. 15  illustrates a block diagram of a switching regulator according to an embodiment. 
         FIG. 16  is a block diagram of a system including a streaming multiprocessor in accordance with one or more embodiments. 
         FIG. 17  illustrates a block diagram of a parallel processing system according to one embodiment. 
         FIG. 18  is a block diagram of a processing system according to an embodiment. 
         FIG. 19  is a block diagram of an embodiment of a processor having one or more processor cores, an integrated memory controller, and an integrated graphics processor. 
         FIG. 20  is a block diagram of a graphics processor, which may be a discrete graphics processing unit, or may be a graphics processor integrated with a plurality of processing cores. 
         FIG. 21  is a block diagram of a graphics processing engine of a graphics processor in accordance with some embodiments. 
         FIG. 22  is a block diagram of another embodiment of a graphics processor. 
         FIG. 23  illustrates thread execution logic including an array of processing elements employed in some embodiments of a GPE. 
         FIG. 24  is a block diagram illustrating a graphics processor instruction formats according to some embodiments. 
         FIG. 25  is a block diagram of another embodiment of a graphics processor. 
         FIG. 26A  is a block diagram illustrating a graphics processor command format according to some embodiments. 
         FIG. 26B  is a block diagram illustrating a graphics processor command sequence according to an embodiment. 
         FIG. 27  illustrates exemplary graphics software architecture for a data processing system according to some embodiments. 
         FIG. 28  is a block diagram illustrating an IP core development system that may be used to manufacture an integrated circuit to perform operations according to an embodiment. 
         FIG. 29  is a block diagram illustrating an exemplary system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. 
         FIG. 30  is a block diagram illustrating an exemplary graphics processor of a system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. 
         FIG. 31  is a block diagram illustrating an additional exemplary graphics processor of a system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In some embodiments, a graphics processing unit (GPU) is communicatively coupled to host/processor cores to accelerate graphics operations, machine-learning operations, pattern analysis operations, and various general purpose GPU (GPGPU) functions. The GPU may be communicatively coupled to the host processor/cores over a bus or another interconnect (e.g., a high-speed interconnect such as PCIe or NVLink). In other embodiments, the GPU may be integrated on the same package or chip as the cores and communicatively coupled to the cores over an internal processor bus/interconnect (i.e., internal to the package or chip). Regardless of the manner in which the GPU is connected, the processor cores may allocate work to the GPU in the form of sequences of commands/instructions contained in a work descriptor. The GPU then uses dedicated circuitry/logic for efficiently processing these commands/instructions. 
     In the following description, numerous specific details are set forth to provide a more thorough understanding. However, it will be apparent to one of skill in the art that the embodiments described herein may be practiced without one or more of these specific details. In other instances, well-known features have not been described to avoid obscuring the details of the present embodiments. 
     System Overview 
       FIG. 1  is a block diagram illustrating a computing system  100  configured to implement one or more aspects of the embodiments described herein. The computing system  100  includes a processing subsystem  101  having one or more processor(s)  102  and a system memory  104  communicating via an interconnection path that may include a memory hub  105 . The memory hub  105  may be a separate component within a chipset component or may be integrated within the one or more processor(s)  102 . The memory hub  105  couples with an I/O subsystem  111  via a communication link  106 . The I/O subsystem  111  includes an I/O hub  107  that can enable the computing system  100  to receive input from one or more input device(s)  108 . Additionally, the I/O hub  107  can enable a display controller, which may be included in the one or more processor(s)  102 , to provide outputs to one or more display device(s)  110 A. In one embodiment the one or more display device(s)  110 A coupled with the I/O hub  107  can include a local, internal, or embedded display device. 
     In one embodiment the processing subsystem  101  includes one or more parallel processor(s)  112  coupled to memory hub  105  via a bus or other communication link  113 . The communication link  113  may be one of any number of standards based communication link technologies or protocols, such as, but not limited to PCI Express, or may be a vendor specific communications interface or communications fabric. In one embodiment the one or more parallel processor(s)  112  form a computationally focused parallel or vector processing system that an include a large number of processing cores and/or processing clusters, such as a many integrated core (MIC) processor. In one embodiment the one or more parallel processor(s)  112  form a graphics processing subsystem that can output pixels to one of the one or more display device(s)  110 A coupled via the I/O Hub  107 . The one or more parallel processor(s)  112  can also include a display controller and display interface (not shown) to enable a direct connection to one or more display device(s)  110 B. 
     Within the I/O subsystem  111 , a system storage unit  114  can connect to the I/O hub  107  to provide a storage mechanism for the computing system  100 . An I/O switch  116  can be used to provide an interface mechanism to enable connections between the I/O hub  107  and other components, such as a network adapter  118  and/or wireless network adapter  119  that may be integrated into the platform, and various other devices that can be added via one or more add-in device(s)  120 . The network adapter  118  can be an Ethernet adapter or another wired network adapter. The wireless network adapter  119  can include one or more of a Wi-Fi, Bluetooth, near field communication (NFC), or other network device that includes one or more wireless radios. 
     The computing system  100  can include other components not explicitly shown, including USB or other port connections, optical storage drives, video capture devices, and the like, may also be connected to the I/O hub  107 . Communication paths interconnecting the various components in  FIG. 1  may be implemented using any suitable protocols, such as PCI (Peripheral Component Interconnect) based protocols (e.g., PCI-Express), or any other bus or point-to-point communication interfaces and/or protocol(s), such as the NV-Link high-speed interconnect, or interconnect protocols known in the art. 
     In one embodiment, the one or more parallel processor(s)  112  incorporate circuitry optimized for graphics and video processing, including, for example, video output circuitry, and constitutes a graphics processing unit (GPU). In another embodiment, the one or more parallel processor(s)  112  incorporate circuitry optimized for general purpose processing, while preserving the underlying computational architecture, described in greater detail herein. In yet another embodiment, components of the computing system  100  may be integrated with one or more other system elements on a single integrated circuit. For example, the one or more parallel processor(s),  112  memory hub  105 , processor(s)  102 , and I/O hub  107  can be integrated into a system on chip (SoC) integrated circuit. Alternatively, the components of the computing system  100  can be integrated into a single package to form a system in package (SIP) configuration. In one embodiment at least a portion of the components of the computing system  100  can be integrated into a multi-chip module (MCM), which can be interconnected with other multi-chip modules into a modular computing system. 
     It will be appreciated that the computing system  100  shown herein is illustrative and that variations and modifications are possible. The connection topology, including the number and arrangement of bridges, the number of processor(s)  102 , and the number of parallel processor(s)  112 , may be modified as desired. For instance, in some embodiments, system memory  104  is connected to the processor(s)  102  directly rather than through a bridge, while other devices communicate with system memory  104  via the memory hub  105  and the processor(s)  102 . In other alternative topologies, the parallel processor(s)  112  are connected to the I/O hub  107  or directly to one of the one or more processor(s)  102 , rather than to the memory hub  105 . In other embodiments, the I/O hub  107  and memory hub  105  may be integrated into a single chip. Some embodiments may include two or more sets of processor(s)  102  attached via multiple sockets, which can couple with two or more instances of the parallel processor(s)  112 . 
     Some of the particular components shown herein are optional and may not be included in all implementations of the computing system  100 . For example, any number of add-in cards or peripherals may be supported, or some components may be eliminated. Furthermore, some architectures may use different terminology for components similar to those illustrated in  FIG. 1 . For example, the memory hub  105  may be referred to as a Northbridge in some architectures, while the I/O hub  107  may be referred to as a Southbridge. 
       FIG. 2A  illustrates a parallel processor  200 , according to an embodiment. The various components of the parallel processor  200  may be implemented using one or more integrated circuit devices, such as programmable processors, application specific integrated circuits (ASICs), or field programmable gate arrays (FPGA). The illustrated parallel processor  200  is a variant of the one or more parallel processor(s)  112  shown in  FIG. 1 , according to an embodiment. 
     In one embodiment the parallel processor  200  includes a parallel processing unit  202 . The parallel processing unit includes an I/O unit  204  that enables communication with other devices, including other instances of the parallel processing unit  202 . The I/O unit  204  may be directly connected to other devices. In one embodiment the I/O unit  204  connects with other devices via the use of a hub or switch interface, such as memory hub  105 . The connections between the memory hub  105  and the I/O unit  204  form a communication link  113 . Within the parallel processing unit  202 , the I/O unit  204  connects with a host interface  206  and a memory crossbar  216 , where the host interface  206  receives commands directed to performing processing operations and the memory crossbar  216  receives commands directed to performing memory operations. 
     When the host interface  206  receives a command buffer via the I/O unit  204 , the host interface  206  can direct work operations to perform those commands to a front end  208 . In one embodiment the front end  208  couples with a scheduler  210 , which is configured to distribute commands or other work items to a processing cluster array  212 . In one embodiment the scheduler  210  ensures that the processing cluster array  212  is properly configured and in a valid state before tasks are distributed to the processing clusters of the processing cluster array  212 . In one embodiment the scheduler  210  is implemented via firmware logic executing on a microcontroller. The microcontroller implemented scheduler  210  is configurable to perform complex scheduling and work distribution operations at coarse and fine granularity, enabling rapid preemption and context switching of threads executing on the processing array  212 . In one embodiment, the host software can prove workloads for scheduling on the processing array  212  via one of multiple graphics processing doorbells. The workloads can then be automatically distributed across the processing array  212  by the scheduler  210  logic within the scheduler microcontroller. 
     The processing cluster array  212  can include up to “N” processing clusters (e.g., cluster  214 A, cluster  214 B, through cluster  214 N). Each cluster  214 A- 214 N of the processing cluster array  212  can execute a large number of concurrent threads. The scheduler  210  can allocate work to the clusters  214 A- 214 N of the processing cluster array  212  using various scheduling and/or work distribution algorithms, which may vary depending on the workload arising for each type of program or computation. The scheduling can be handled dynamically by the scheduler  210 , or can be assisted in part by compiler logic during compilation of program logic configured for execution by the processing cluster array  212 . In one embodiment, different clusters  214 A- 214 N of the processing cluster array  212  can be allocated for processing different types of programs or for performing different types of computations. 
     The processing cluster array  212  can be configured to perform various types of parallel processing operations. In one embodiment the processing cluster array  212  is configured to perform general-purpose parallel compute operations. For example, the processing cluster array  212  can include logic to execute processing tasks including filtering of video and/or audio data, performing modeling operations, including physics operations, and performing data transformations. 
     In one embodiment the processing cluster array  212  is configured to perform parallel graphics processing operations. In embodiments in which the parallel processor  200  is configured to perform graphics processing operations, the processing cluster array  212  can include additional logic to support the execution of such graphics processing operations, including, but not limited to texture sampling logic to perform texture operations, as well as tessellation logic and other vertex processing logic. Additionally, the processing cluster array  212  can be configured to execute graphics processing related shader programs such as, but not limited to vertex shaders, tessellation shaders, geometry shaders, and pixel shaders. The parallel processing unit  202  can transfer data from system memory via the I/O unit  204  for processing. During processing the transferred data can be stored to on-chip memory (e.g., parallel processor memory  222 ) during processing, then written back to system memory. 
     In one embodiment, when the parallel processing unit  202  is used to perform graphics processing, the scheduler  210  can be configured to divide the processing workload into approximately equal sized tasks, to better enable distribution of the graphics processing operations to multiple clusters  214 A- 214 N of the processing cluster array  212 . In some embodiments, portions of the processing cluster array  212  can be configured to perform different types of processing. For example a first portion may be configured to perform vertex shading and topology generation, a second portion may be configured to perform tessellation and geometry shading, and a third portion may be configured to perform pixel shading or other screen space operations, to produce a rendered image for display. Intermediate data produced by one or more of the clusters  214 A- 214 N may be stored in buffers to allow the intermediate data to be transmitted between clusters  214 A- 214 N for further processing. 
     During operation, the processing cluster array  212  can receive processing tasks to be executed via the scheduler  210 , which receives commands defining processing tasks from front end  208 . For graphics processing operations, processing tasks can include indices of data to be processed, e.g., surface (patch) data, primitive data, vertex data, and/or pixel data, as well as state parameters and commands defining how the data is to be processed (e.g., what program is to be executed). The scheduler  210  may be configured to fetch the indices corresponding to the tasks or may receive the indices from the front end  208 . The front end  208  can be configured to ensure the processing cluster array  212  is configured to a valid state before the workload specified by incoming command buffers (e.g., batch-buffers, push buffers, etc.) is initiated. 
     Each of the one or more instances of the parallel processing unit  202  can couple with parallel processor memory  222 . The parallel processor memory  222  can be accessed via the memory crossbar  216 , which can receive memory requests from the processing cluster array  212  as well as the I/O unit  204 . The memory crossbar  216  can access the parallel processor memory  222  via a memory interface  218 . The memory interface  218  can include multiple partition units (e.g., partition unit  220 A, partition unit  220 B, through partition unit  220 N) that can each couple to a portion (e.g., memory unit) of parallel processor memory  222 . In one implementation the number of partition units  220 A- 220 N is configured to be equal to the number of memory units, such that a first partition unit  220 A has a corresponding first memory unit  224 A, a second partition unit  220 B has a corresponding memory unit  224 B, and an Nth partition unit  220 N has a corresponding Nth memory unit  224 N. In other embodiments, the number of partition units  220 A- 220 N may not be equal to the number of memory devices. 
     In various embodiments, the memory units  224 A- 224 N can include various types of memory devices, including dynamic random access memory (DRAM) or graphics random access memory, such as synchronous graphics random access memory (SGRAM), including graphics double data rate (GDDR) memory. In one embodiment, the memory units  224 A- 224 N may also include 3D stacked memory, including but not limited to high bandwidth memory (HBM). Persons skilled in the art will appreciate that the specific implementation of the memory units  224 A- 224 N can vary, and can be selected from one of various conventional designs. Render targets, such as frame buffers or texture maps may be stored across the memory units  224 A- 224 N, allowing partition units  220 A- 220 N to write portions of each render target in parallel to efficiently use the available bandwidth of parallel processor memory  222 . In some embodiments, a local instance of the parallel processor memory  222  may be excluded in favor of a unified memory design that utilizes system memory in conjunction with local cache memory. 
     In one embodiment, any one of the clusters  214 A- 214 N of the processing cluster array  212  can process data that will be written to any of the memory units  224 A- 224 N within parallel processor memory  222 . The memory crossbar  216  can be configured to transfer the output of each cluster  214 A- 214 N to any partition unit  220 A- 220 N or to another cluster  214 A- 214 N, which can perform additional processing operations on the output. Each cluster  214 A- 214 N can communicate with the memory interface  218  through the memory crossbar  216  to read from or write to various external memory devices. In one embodiment the memory crossbar  216  has a connection to the memory interface  218  to communicate with the I/O unit  204 , as well as a connection to a local instance of the parallel processor memory  222 , enabling the processing units within the different processing clusters  214 A- 214 N to communicate with system memory or other memory that is not local to the parallel processing unit  202 . In one embodiment the memory crossbar  216  can use virtual channels to separate traffic streams between the clusters  214 A- 214 N and the partition units  220 A- 220 N. 
     While a single instance of the parallel processing unit  202  is illustrated within the parallel processor  200 , any number of instances of the parallel processing unit  202  can be included. For example, multiple instances of the parallel processing unit  202  can be provided on a single add-in card, or multiple add-in cards can be interconnected. The different instances of the parallel processing unit  202  can be configured to inter-operate even if the different instances have different numbers of processing cores, different amounts of local parallel processor memory, and/or other configuration differences. For example and in one embodiment, some instances of the parallel processing unit  202  can include higher precision floating point units relative to other instances. Systems incorporating one or more instances of the parallel processing unit  202  or the parallel processor  200  can be implemented in a variety of configurations and form factors, including but not limited to desktop, laptop, or handheld personal computers, servers, workstations, game consoles, and/or embedded systems. 
       FIG. 2B  is a block diagram of a partition unit  220 , according to an embodiment. In one embodiment the partition unit  220  is an instance of one of the partition units  220 A- 220 N of  FIG. 2A . As illustrated, the partition unit  220  includes an L2 cache  221 , a frame buffer interface  225 , and a ROP  226  (raster operations unit). The L2 cache  221  is a read/write cache that is configured to perform load and store operations received from the memory crossbar  216  and ROP  226 . Read misses and urgent write-back requests are output by L2 cache  221  to frame buffer interface  225  for processing. Updates can also be sent to the frame buffer via the frame buffer interface  225  for processing. In one embodiment the frame buffer interface  225  interfaces with one of the memory units in parallel processor memory, such as the memory units  224 A- 224 N of  FIG. 2  (e.g., within parallel processor memory  222 ). 
     In graphics applications, the ROP  226  is a processing unit that performs raster operations such as stencil, z test, blending, and the like. The ROP  226  then outputs processed graphics data that is stored in graphics memory. In some embodiments the ROP  226  includes compression logic to compress depth or color data that is written to memory and decompress depth or color data that is read from memory. The compression logic can be lossless compression logic that makes use of one or more of multiple compression algorithms. The type of compression that is performed by the ROP  226  can vary based on the statistical characteristics of the data to be compressed. For example, in one embodiment, delta color compression is performed on depth and color data on a per-tile basis. 
     In some embodiments, the ROP  226  is included within each processing cluster (e.g., cluster  214 A- 214 N of  FIG. 2 ) instead of within the partition unit  220 . In such embodiment, read and write requests for pixel data are transmitted over the memory crossbar  216  instead of pixel fragment data. The processed graphics data may be displayed on a display device, such as one of the one or more display device(s)  110  of  FIG. 1 , routed for further processing by the processor(s)  102 , or routed for further processing by one of the processing entities within the parallel processor  200  of  FIG. 2A . 
       FIG. 2C  is a block diagram of a processing cluster  214  within a parallel processing unit, according to an embodiment. In one embodiment the processing cluster is an instance of one of the processing clusters  214 A- 214 N of  FIG. 2 . The processing cluster  214  can be configured to execute many threads in parallel, where the term “thread” refers to an instance of a particular program executing on a particular set of input data. In some embodiments, single-instruction, multiple-data (SIMD) instruction issue techniques are used to support parallel execution of a large number of threads without providing multiple independent instruction units. In other embodiments, single-instruction, multiple-thread (SIMT) techniques are used to support parallel execution of a large number of generally synchronized threads, using a common instruction unit configured to issue instructions to a set of processing engines within each one of the processing clusters. Unlike a SIMD execution regime, where all processing engines typically execute identical instructions, SIMT execution allows different threads to more readily follow divergent execution paths through a given thread program. Persons skilled in the art will understand that a SIMD processing regime represents a functional subset of a SIMT processing regime. 
     Operation of the processing cluster  214  can be controlled via a pipeline manager  232  that distributes processing tasks to SIMT parallel processors. The pipeline manager  232  receives instructions from the scheduler  210  of  FIG. 2  and manages execution of those instructions via a graphics multiprocessor  234  and/or a texture unit  236 . The illustrated graphics multiprocessor  234  is an exemplary instance of a SIMT parallel processor. However, various types of SIMT parallel processors of differing architectures may be included within the processing cluster  214 . One or more instances of the graphics multiprocessor  234  can be included within a processing cluster  214 . The graphics multiprocessor  234  can process data and a data crossbar  240  can be used to distribute the processed data to one of multiple possible destinations, including other shader units. The pipeline manager  232  can facilitate the distribution of processed data by specifying destinations for processed data to be distributed via the data crossbar  240 . 
     Each graphics multiprocessor  234  within the processing cluster  214  can include an identical set of functional execution logic (e.g., arithmetic logic units, load-store units, etc.). The functional execution logic can be configured in a pipelined manner in which new instructions can be issued before previous instructions are complete. The functional execution logic supports a variety of operations including integer and floating point arithmetic, comparison operations, Boolean operations, bit-shifting, and computation of various algebraic functions. In one embodiment the same functional-unit hardware can be leveraged to perform different operations and any combination of functional units may be present. 
     The instructions transmitted to the processing cluster  214  constitutes a thread. A set of threads executing across the set of parallel processing engines is a thread group. A thread group executes the same program on different input data. Each thread within a thread group can be assigned to a different processing engine within a graphics multiprocessor  234 . A thread group may include fewer threads than the number of processing engines within the graphics multiprocessor  234 . When a thread group includes fewer threads than the number of processing engines, one or more of the processing engines may be idle during cycles in which that thread group is being processed. A thread group may also include more threads than the number of processing engines within the graphics multiprocessor  234 . When the thread group includes more threads than the number of processing engines within the graphics multiprocessor  234 , processing can be performed over consecutive clock cycles. In one embodiment multiple thread groups can be executed concurrently on a graphics multiprocessor  234 . 
     In one embodiment the graphics multiprocessor  234  includes an internal cache memory to perform load and store operations. In one embodiment, the graphics multiprocessor  234  can forego an internal cache and use a cache memory (e.g., L1 cache  308 ) within the processing cluster  214 . Each graphics multiprocessor  234  also has access to L2 caches within the partition units (e.g., partition units  220 A- 220 N of  FIG. 2 ) that are shared among all processing clusters  214  and may be used to transfer data between threads. The graphics multiprocessor  234  may also access off-chip global memory, which can include one or more of local parallel processor memory and/or system memory. Any memory external to the parallel processing unit  202  may be used as global memory. Embodiments in which the processing cluster  214  includes multiple instances of the graphics multiprocessor  234  can share common instructions and data, which may be stored in the L1 cache  308 . 
     Each processing cluster  214  may include an MMU  245  (memory management unit) that is configured to map virtual addresses into physical addresses. In other embodiments, one or more instances of the MMU  245  may reside within the memory interface  218  of  FIG. 2 . The MMU  245  includes a set of page table entries (PTEs) used to map a virtual address to a physical address of a tile (talk more about tiling) and optionally a cache line index. The MMU  245  may include address translation lookaside buffers (TLB) or caches that may reside within the graphics multiprocessor  234  or the L1 cache or processing cluster  214 . The physical address is processed to distribute surface data access locality to allow efficient request interleaving among partition units. The cache line index may be used to determine whether a request for a cache line is a hit or miss. 
     In graphics and computing applications, a processing cluster  214  may be configured such that each graphics multiprocessor  234  is coupled to a texture unit  236  for performing texture mapping operations, e.g., determining texture sample positions, reading texture data, and filtering the texture data. Texture data is read from an internal texture L1 cache (not shown) or in some embodiments from the L1 cache within graphics multiprocessor  234  and is fetched from an L2 cache, local parallel processor memory, or system memory, as needed. Each graphics multiprocessor  234  outputs processed tasks to the data crossbar  240  to provide the processed task to another processing cluster  214  for further processing or to store the processed task in an L2 cache, local parallel processor memory, or system memory via the memory crossbar  216 . A preROP  242  (pre-raster operations unit) is configured to receive data from graphics multiprocessor  234 , direct data to ROP units, which may be located with partition units as described herein (e.g., partition units  220 A- 220 N of  FIG. 2 ). The preROP  242  unit can perform optimizations for color blending, organize pixel color data, and perform address translations. 
     It will be appreciated that the core architecture described herein is illustrative and that variations and modifications are possible. Any number of processing units, e.g., graphics multiprocessor  234 , texture units  236 , preROPs  242 , etc., may be included within a processing cluster  214 . Further, while only one processing cluster  214  is shown, a parallel processing unit as described herein may include any number of instances of the processing cluster  214 . In one embodiment, each processing cluster  214  can be configured to operate independently of other processing clusters  214  using separate and distinct processing units, L1 caches, etc. 
       FIG. 2D  shows a graphics multiprocessor  234 , according to one embodiment. In such embodiment the graphics multiprocessor  234  couples with the pipeline manager  232  of the processing cluster  214 . The graphics multiprocessor  234  has an execution pipeline including but not limited to an instruction cache  252 , an instruction unit  254 , an address mapping unit  256 , a register file  258 , one or more general purpose graphics processing unit (GPGPU) cores  262 , and one or more load/store units  266 . The GPGPU cores  262  and load/store units  266  are coupled with cache memory  272  and shared memory  270  via a memory and cache interconnect  268 . 
     In one embodiment, the instruction cache  252  receives a stream of instructions to execute from the pipeline manager  232 . The instructions are cached in the instruction cache  252  and dispatched for execution by the instruction unit  254 . The instruction unit  254  can dispatch instructions as thread groups (e.g., warps), with each thread of the thread group assigned to a different execution unit within GPGPU core  262 . An instruction can access any of a local, shared, or global address space by specifying an address within a unified address space. The address mapping unit  256  can be used to translate addresses in the unified address space into a distinct memory address that can be accessed by the load/store units  266 . 
     The register file  258  provides a set of registers for the functional units of the graphics multiprocessor  324 . The register file  258  provides temporary storage for operands connected to the data paths of the functional units (e.g., GPGPU cores  262 , load/store units  266 ) of the graphics multiprocessor  324 . In one embodiment, the register file  258  is divided between each of the functional units such that each functional unit is allocated a dedicated portion of the register file  258 . In one embodiment, the register file  258  is divided between the different warps being executed by the graphics multiprocessor  324 . 
     The GPGPU cores  262  can each include floating point units (FPUs) and/or integer arithmetic logic units (ALUs) that are used to execute instructions of the graphics multiprocessor  324 . The GPGPU cores  262  can be similar in architecture or can differ in architecture, according to embodiments. For example and in one embodiment, a first portion of the GPGPU cores  262  include a single precision FPU and an integer ALU while a second portion of the GPGPU cores include a double precision FPU. In one embodiment the FPUs can implement the IEEE 754-2008 standard for floating point arithmetic or enable variable precision floating point arithmetic. The graphics multiprocessor  324  can additionally include one or more fixed function or special function units to perform specific functions such as copy rectangle or pixel blending operations. In one embodiment one or more of the GPGPU cores can also include fixed or special function logic. 
     In one embodiment the GPGPU cores  262  include SIMD logic capable of performing a single instruction on multiple sets of data. In one embodiment GPGPU cores  262  can physically execute SIMD4, SIMD8, and SIMD16 instructions and logically execute SIMD1, SIMD2, and SIMD32 instructions. The SIMD instructions for the GPGPU cores can be generated at compile time by a shader compiler or automatically generated when executing programs written and compiled for single program multiple data (SPMD) or SIMT architectures. Multiple threads of a program configured for the SIMT execution model can executed via a single SIMD instruction. For example and in one embodiment, eight SIMT threads that perform the same or similar operations can be executed in parallel via a single SIMD8 logic unit. 
     The memory and cache interconnect  268  is an interconnect network that connects each of the functional units of the graphics multiprocessor  324  to the register file  258  and to the shared memory  270 . In one embodiment, the memory and cache interconnect  268  is a crossbar interconnect that allows the load/store unit  266  to implement load and store operations between the shared memory  270  and the register file  258 . The register file  258  can operate at the same frequency as the GPGPU cores  262 , thus data transfer between the GPGPU cores  262  and the register file  258  is very low latency. The shared memory  270  can be used to enable communication between threads that execute on the functional units within the graphics multiprocessor  234 . The cache memory  272  can be used as a data cache for example, to cache texture data communicated between the functional units and the texture unit  236 . The shared memory  270  can also be used as a program managed cached. Threads executing on the GPGPU cores  262  can programmatically store data within the shared memory in addition to the automatically cached data that is stored within the cache memory  272 . 
       FIGS. 3A-3B  illustrate additional graphics multiprocessors, according to embodiments. The illustrated graphics multiprocessors  325 ,  350  are variants of the graphics multiprocessor  234  of  FIG. 2C . The illustrated graphics multiprocessors  325 ,  350  can be configured as a streaming multiprocessor (SM) capable of simultaneous execution of a large number of execution threads. 
       FIG. 3A  shows a graphics multiprocessor  325  according to an additional embodiment. The graphics multiprocessor  325  includes multiple additional instances of execution resource units relative to the graphics multiprocessor  234  of  FIG. 2D . For example, the graphics multiprocessor  325  can include multiple instances of the instruction unit  332 A- 332 B, register file  334 A- 334 B, and texture unit(s)  344 A- 344 B. The graphics multiprocessor  325  also includes multiple sets of graphics or compute execution units (e.g., GPGPU core  336 A- 336 B, GPGPU core  337 A- 337 B, GPGPU core  338 A- 338 B) and multiple sets of load/store units  340 A- 340 B. In one embodiment the execution resource units have a common instruction cache  330 , texture and/or data cache memory  342 , and shared memory  346 . 
     The various components can communicate via an interconnect fabric  327 . In one embodiment the interconnect fabric  327  includes one or more crossbar switches to enable communication between the various components of the graphics multiprocessor  325 . In one embodiment the interconnect fabric  327  is a separate, high-speed network fabric layer upon which each component of the graphics multiprocessor  325  is stacked. The components of the graphics multiprocessor  325  communicate with remote components via the interconnect fabric  327 . For example, the GPGPU cores  336 A- 336 B,  337 A- 337 B, and  3378 A- 338 B can each communicate with shared memory  346  via the interconnect fabric  327 . The interconnect fabric  327  can arbitrate communication within the graphics multiprocessor  325  to ensure a fair bandwidth allocation between components. 
       FIG. 3B  shows a graphics multiprocessor  350  according to an additional embodiment. The graphics processor includes multiple sets of execution resources  356 A- 356 D, where each set of execution resource includes multiple instruction units, register files, GPGPU cores, and load store units, as illustrated in  FIG. 2D  and  FIG. 3A . The execution resources  356 A- 356 D can work in concert with texture unit(s)  360 A- 360 D for texture operations, while sharing an instruction cache  354 , and shared memory  362 . In one embodiment the execution resources  356 A- 356 D can share an instruction cache  354  and shared memory  362 , as well as multiple instances of a texture and/or data cache memory  358 A- 358 B. The various components can communicate via an interconnect fabric  352  similar to the interconnect fabric  327  of  FIG. 3A . 
     Persons skilled in the art will understand that the architecture described in  FIGS. 1, 2A-2D, and 3A-3B  are descriptive and not limiting as to the scope of the present embodiments. Thus, the techniques described herein may be implemented on any properly configured processing unit, including, without limitation, one or more mobile application processors, one or more desktop or server central processing units (CPUs) including multi-core CPUs, one or more parallel processing units, such as the parallel processing unit  202  of  FIG. 2 , as well as one or more graphics processors or special purpose processing units, without departure from the scope of the embodiments described herein. 
     In some embodiments a parallel processor or GPGPU as described herein is communicatively coupled to host/processor cores to accelerate graphics operations, machine-learning operations, pattern analysis operations, and various general purpose GPU (GPGPU) functions. The GPU may be communicatively coupled to the host processor/cores over a bus or other interconnect (e.g., a high speed interconnect such as PCIe or NVLink). In other embodiments, the GPU may be integrated on the same package or chip as the cores and communicatively coupled to the cores over an internal processor bus/interconnect (i.e., internal to the package or chip). Regardless of the manner in which the GPU is connected, the processor cores may allocate work to the GPU in the form of sequences of commands/instructions contained in a work descriptor. The GPU then uses dedicated circuitry/logic for efficiently processing these commands/instructions. 
     Techniques for GPU to Host Processor Interconnection 
       FIG. 4A  illustrates an exemplary architecture in which a plurality of GPUs  410 - 413  are communicatively coupled to a plurality of multi-core processors  405 - 406  over high-speed links  440 - 443  (e.g., buses, point-to-point interconnects, etc.). In one embodiment, the high-speed links  440 - 443  support a communication throughput of 4 GB/s, 30 GB/s, 80 GB/s or higher, depending on the implementation. Various interconnect protocols may be used including, but not limited to, PCIe 4.0 or 5.0 and NVLink 2.0. However, the underlying principles of the invention are not limited to any particular communication protocol or throughput. 
     In addition, in one embodiment, two or more of the GPUs  410 - 413  are interconnected over high-speed links  444 - 445 , which may be implemented using the same or different protocols/links than those used for high-speed links  440 - 443 . Similarly, two or more of the multi-core processors  405 - 406  may be connected over high speed link  433  which may be symmetric multi-processor (SMP) buses operating at 20 GB/s, 30 GB/s, 120 GB/s or higher. Alternatively, all communication between the various system components shown in  FIG. 4A  may be accomplished using the same protocols/links (e.g., over a common interconnection fabric). As mentioned, however, the underlying principles of the invention are not limited to any particular type of interconnect technology. 
     In one embodiment, each multi-core processor  405 - 406  is communicatively coupled to a processor memory  401 - 402 , via memory interconnects  430 - 431 , respectively, and each GPU  410 - 413  is communicatively coupled to GPU memory  420 - 423  over GPU memory interconnects  450 - 453 , respectively. The memory interconnects  430 - 431  and  450 - 453  may utilize the same or different memory access technologies. By way of example, and not limitation, the processor memories  401 - 402  and GPU memories  420 - 423  may be volatile memories such as dynamic random access memories (DRAMs) (including stacked DRAMs), Graphics DDR SDRAM (GDDR) (e.g., GDDR5, GDDR6), or High Bandwidth Memory (HBM) and/or may be non-volatile memories such as 3D XPoint or Nano-Ram. In one embodiment, some portion of the memories may be volatile memory and another portion may be non-volatile memory (e.g., using a two-level memory (2LM) hierarchy). 
     As described below, although the various processors  405 - 406  and GPUs  410 - 413  may be physically coupled to a particular memory  401 - 402 ,  420 - 423 , respectively, a unified memory architecture may be implemented in which the same virtual system address space (also referred to as the “effective address” space) is distributed among all of the various physical memories. For example, processor memories  401 - 402  may each comprise 64 GB of the system memory address space and GPU memories  420 - 423  may each comprise 32 GB of the system memory address space (resulting in a total of 256 GB addressable memory in this example). 
       FIG. 4B  illustrates additional details for an interconnection between a multi-core processor  407  and a graphics acceleration module  446  in accordance with one embodiment. The graphics acceleration module  446  may include one or more GPU chips integrated on a line card which is coupled to the processor  407  via the high-speed link  440 . Alternatively, the graphics acceleration module  446  may be integrated on the same package or chip as the processor  407 . 
     The illustrated processor  407  includes a plurality of cores  460 A- 460 D, each with a translation lookaside buffer  461 A- 461 D and one or more caches  462 A- 462 D. The cores may include various other components for executing instructions and processing data which are not illustrated to avoid obscuring the underlying principles of the invention (e.g., instruction fetch units, branch prediction units, decoders, execution units, reorder buffers, etc.). The caches  462 A- 462 D may comprise level 1 (L1) and level 2 (L2) caches. In addition, one or more shared caches  426  may be included in the caching hierarchy and shared by sets of the cores  460 A- 460 D. For example, one embodiment of the processor  407  includes 24 cores, each with its own L1 cache, twelve shared L2 caches, and twelve shared L3 caches. In this embodiment, one of the L2 and L3 caches are shared by two adjacent cores. The processor  407  and the graphics accelerator integration module  446  connect with system memory  441 , which may include processor memories  401 - 402   
     Coherency is maintained for data and instructions stored in the various caches  462 A- 462 D,  456  and system memory  441  via inter-core communication over a coherence bus  464 . For example, each cache may have cache coherency logic/circuitry associated therewith to communicate to over the coherence bus  464  in response to detected reads or writes to particular cache lines. In one implementation, a cache snooping protocol is implemented over the coherence bus  464  to snoop cache accesses. Cache snooping/coherency techniques are well understood by those of skill in the art and will not be described in detail here to avoid obscuring the underlying principles of the invention. 
     In one embodiment, a proxy circuit  425  communicatively couples the graphics acceleration module  446  to the coherence bus  464 , allowing the graphics acceleration module  446  to participate in the cache coherence protocol as a peer of the cores. In particular, an interface  435  provides connectivity to the proxy circuit  425  over high-speed link  440  (e.g., a PCIe bus, NVLink, etc.) and an interface  437  connects the graphics acceleration module  446  to the link  440 . 
     In one implementation, an accelerator integration circuit  436  provides cache management, memory access, context management, and interrupt management services on behalf of a plurality of graphics processing engines  431 ,  432 , N of the graphics acceleration module  446 . The graphics processing engines  431 ,  432 , N may each comprise a separate graphics processing unit (GPU). Alternatively, the graphics processing engines  431 ,  432 , N may comprise different types of graphics processing engines within a GPU such as graphics execution units, media processing engines (e.g., video encoders/decoders), samplers, and blit engines. In other words, the graphics acceleration module may be a GPU with a plurality of graphics processing engines  431 - 432 , N or the graphics processing engines  431 - 432 , N may be individual GPUs integrated on a common package, line card, or chip. 
     In one embodiment, the accelerator integration circuit  436  includes a memory management unit (MMU)  439  for performing various memory management functions such as virtual-to-physical memory translations (also referred to as effective-to-real memory translations) and memory access protocols for accessing system memory  441 . The MMU  439  may also include a translation lookaside buffer (TLB) (not shown) for caching the virtual/effective to physical/real address translations. In one implementation, a cache  438  stores commands and data for efficient access by the graphics processing engines  431 - 432 , N. In one embodiment, the data stored in cache  438  and graphics memories  433 - 434 , N is kept coherent with the core caches  462 A- 462 D,  456  and system memory  411 . As mentioned, this may be accomplished via proxy circuit  425  which takes part in the cache coherency mechanism on behalf of cache  438  and memories  433 - 434 , N (e.g., sending updates to the cache  438  related to modifications/accesses of cache lines on processor caches  462 A- 462 D,  456  and receiving updates from the cache  438 ). 
     A set of registers  445  store context data for threads executed by the graphics processing engines  431 - 432 , N and a context management circuit  448  manages the thread contexts. For example, the context management circuit  448  may perform save and restore operations to save and restore contexts of the various threads during contexts switches (e.g., where a first thread is saved and a second thread is stored so that the second thread can be execute by a graphics processing engine). For example, on a context switch, the context management circuit  448  may store current register values to a designated region in memory (e.g., identified by a context pointer). It may then restore the register values when returning to the context. In one embodiment, an interrupt management circuit  447  receives and processes interrupts received from system devices. 
     In one implementation, virtual/effective addresses from a graphics processing engine  431  are translated to real/physical addresses in system memory  411  by the MMU  439 . One embodiment of the accelerator integration circuit  436  supports multiple (e.g., 4, 8, 16) graphics accelerator modules  446  and/or other accelerator devices. The graphics accelerator module  446  may be dedicated to a single application executed on the processor  407  or may be shared between multiple applications. In one embodiment, a virtualized graphics execution environment is presented in which the resources of the graphics processing engines  431 - 432 , N are shared with multiple applications or virtual machines (VMs). The resources may be subdivided into “slices” which are allocated to different VMs and/or applications based on the processing requirements and priorities associated with the VMs and/or applications. 
     Thus, the accelerator integration circuit acts as a bridge to the system for the graphics acceleration module  446  and provides address translation and system memory cache services. In addition, the accelerator integration circuit  436  may provide virtualization facilities for the host processor to manage virtualization of the graphics processing engines, interrupts, and memory management. 
     Because hardware resources of the graphics processing engines  431 - 432 , N are mapped explicitly to the real address space seen by the host processor  407 , any host processor can address these resources directly using an effective address value. One function of the accelerator integration circuit  436 , in one embodiment, is the physical separation of the graphics processing engines  431 - 432 , N so that they appear to the system as independent units. 
     As mentioned, in the illustrated embodiment, one or more graphics memories  433 - 434 , M are coupled to each of the graphics processing engines  431 - 432 , N, respectively. The graphics memories  433 - 434 , M store instructions and data being processed by each of the graphics processing engines  431 - 432 , N. The graphics memories  433 - 434 , M may be volatile memories such as DRAMs (including stacked DRAMs), GDDR memory (e.g., GDDR5, GDDR6), or HBM, and/or may be non-volatile memories such as 3D XPoint or Nano-Ram. 
     In one embodiment, to reduce data traffic over link  440 , biasing techniques are used to ensure that the data stored in graphics memories  433 - 434 , M is data which will be used most frequently by the graphics processing engines  431 - 432 , N and preferably not used by the cores  460 A- 460 D (at least not frequently). Similarly, the biasing mechanism attempts to keep data needed by the cores (and preferably not the graphics processing engines  431 - 432 , N) within the caches  462 A- 462 D,  456  of the cores and system memory  411 . 
       FIG. 4C  illustrates another embodiment in which the accelerator integration circuit  436  is integrated within the processor  407 . In this embodiment, the graphics processing engines  431 - 432 , N communicate directly over the high-speed link  440  to the accelerator integration circuit  436  via interface  437  and interface  435  (which, again, may be utilize any form of bus or interface protocol). The accelerator integration circuit  436  may perform the same operations as those described with respect to  FIG. 4B , but potentially at a higher throughput given its close proximity to the coherency bus  462  and caches  462 A- 462 D,  426 . 
     One embodiment supports different programming models including a dedicated-process programming model (no graphics acceleration module virtualization) and shared programming models (with virtualization). The latter may include programming models which are controlled by the accelerator integration circuit  436  and programming models which are controlled by the graphics acceleration module  446 . 
     In one embodiment of the dedicated process model, graphics processing engines  431 - 432 , N are dedicated to a single application or process under a single operating system. The single application can funnel other application requests to the graphics engines  431 - 432 , N, providing virtualization within a VM/partition. 
     In the dedicated-process programming models, the graphics processing engines  431 - 432 , N, may be shared by multiple VM/application partitions. The shared models require a system hypervisor to virtualize the graphics processing engines  431 - 432 , N to allow access by each operating system. For single-partition systems without a hypervisor, the graphics processing engines  431 - 432 , N are owned by the operating system. In both cases, the operating system can virtualize the graphics processing engines  431 - 432 , N to provide access to each process or application. 
     For the shared programming model, the graphics acceleration module  446  or an individual graphics processing engine  431 - 432 , N selects a process element using a process handle. In one embodiment, process elements are stored in system memory  411  and are addressable using the effective address to real address translation techniques described herein. The process handle may be an implementation-specific value provided to the host process when registering its context with the graphics processing engine  431 - 432 , N (that is, calling system software to add the process element to the process element linked list). The lower 16-bits of the process handle may be the offset of the process element within the process element linked list. 
       FIG. 4D  illustrates an exemplary accelerator integration slice  490 . As used herein, a “slice” comprises a specified portion of the processing resources of the accelerator integration circuit  436 . Application effective address space  482  within system memory  411  stores process elements  483 . In one embodiment, the process elements  483  are stored in response to GPU invocations  481  from applications  480  executed on the processor  407 . A process element  483  contains the process state for the corresponding application  480 . A work descriptor (WD)  484  contained in the process element  483  can be a single job requested by an application or may contain a pointer to a queue of jobs. In the latter case, the WD  484  is a pointer to the job request queue in the application&#39;s address space  482 . 
     The graphics acceleration module  446  and/or the individual graphics processing engines  431 - 432 , N can be shared by all or a subset of the processes in the system. Embodiments of the invention include an infrastructure for setting up the process state and sending a WD  484  to a graphics acceleration module  446  to start a job in a virtualized environment. 
     In one implementation, the dedicated-process programming model is implementation-specific. In this model, a single process owns the graphics acceleration module  446  or an individual graphics processing engine  431 . Because the graphics acceleration module  446  is owned by a single process, the hypervisor initializes the accelerator integration circuit  436  for the owning partition and the operating system initializes the accelerator integration circuit  436  for the owning process at the time when the graphics acceleration module  446  is assigned. 
     In operation, a WD fetch unit  491  in the accelerator integration slice  490  fetches the next WD  484  which includes an indication of the work to be done by one of the graphics processing engines of the graphics acceleration module  446 . Data from the WD  484  may be stored in registers  445  and used by the MMU  439 , interrupt management circuit  447  and/or context management circuit  446  as illustrated. For example, one embodiment of the MMU  439  includes segment/page walk circuitry for accessing segment/page tables  486  within the OS virtual address space  485 . The interrupt management circuit  447  may process interrupt events  492  received from the graphics acceleration module  446 . When performing graphics operations, an effective address  493  generated by a graphics processing engine  431 - 432 , N is translated to a real address by the MMU  439 . 
     In one embodiment, the same set of registers  445  are duplicated for each graphics processing engine  431 - 432 , N and/or graphics acceleration module  446  and may be initialized by the hypervisor or operating system. Each of these duplicated registers may be included in an accelerator integration slice  490 . Exemplary registers that may be initialized by the hypervisor are shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Hypervisor Initialized Registers 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 Slice Control Register 
               
               
                 2 
                 Real Address (RA) Scheduled Processes Area Pointer 
               
               
                 3 
                 Authority Mask Override Register 
               
               
                 4 
                 Interrupt Vector Table Entry Offset 
               
               
                 5 
                 Interrupt Vector Table Entry Limit 
               
               
                 6 
                 State Register 
               
               
                 7 
                 Logical Partition ID 
               
               
                 8 
                 Real address (RA) Hypervisor Accelerator Utilization Record Pointer 
               
               
                 9 
                 Storage Description Register 
               
               
                   
               
            
           
         
       
     
     Exemplary registers that may be initialized by the operating system are shown in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Operating System Initialized Registers 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 Process and Thread Identification 
               
               
                 2 
                 Effective Address (EA) Context Save/Restore Pointer 
               
               
                 3 
                 Virtual Address (VA) Accelerator Utilization Record Pointer 
               
               
                 4 
                 Virtual Address (VA) Storage Segment Table Pointer 
               
               
                 5 
                 Authority Mask 
               
               
                 6 
                 Work descriptor 
               
               
                   
               
            
           
         
       
     
     In one embodiment, each WD  484  is specific to a particular graphics acceleration module  446  and/or graphics processing engine  431 - 432 , N. It contains all the information a graphics processing engine  431 - 432 , N requires to do its work or it can be a pointer to a memory location where the application has set up a command queue of work to be completed. 
       FIG. 4E  illustrates additional details for one embodiment of a shared model. This embodiment includes a hypervisor real address space  498  in which a process element list  499  is stored. The hypervisor real address space  498  is accessible via a hypervisor  496  which virtualizes the graphics acceleration module engines for the operating system  495 . 
     The shared programming models allow for all or a subset of processes from all or a subset of partitions in the system to use a graphics acceleration module  446 . There are two programming models where the graphics acceleration module  446  is shared by multiple processes and partitions: time-sliced shared and graphics directed shared. 
     In this model, the system hypervisor  496  owns the graphics acceleration module  446  and makes its function available to all operating systems  495 . For a graphics acceleration module  446  to support virtualization by the system hypervisor  496 , the graphics acceleration module  446  may adhere to the following requirements: 1) An application&#39;s job request must be autonomous (that is, the state does not need to be maintained between jobs), or the graphics acceleration module  446  must provide a context save and restore mechanism. 2) An application&#39;s job request is guaranteed by the graphics acceleration module  446  to complete in a specified amount of time, including any translation faults, or the graphics acceleration module  446  provides the ability to preempt the processing of the job. 3) The graphics acceleration module  446  must be guaranteed fairness between processes when operating in the directed shared programming model. 
     In one embodiment, for the shared model, the application  480  is required to make an operating system  495  system call with a graphics acceleration module  446  type, a work descriptor (WD), an authority mask register (AMR) value, and a context save/restore area pointer (CSRP). The graphics acceleration module  446  type describes the targeted acceleration function for the system call. The graphics acceleration module  446  type may be a system-specific value. The WD is formatted specifically for the graphics acceleration module  446  and can be in the form of a graphics acceleration module  446  command, an effective address pointer to a user-defined structure, an effective address pointer to a queue of commands, or any other data structure to describe the work to be done by the graphics acceleration module  446 . In one embodiment, the AMR value is the AMR state to use for the current process. The value passed to the operating system is similar to an application setting the AMR. If the accelerator integration circuit  436  and graphics acceleration module  446  implementations do not support a User Authority Mask Override Register (UAMOR), the operating system may apply the current UAMOR value to the AMR value before passing the AMR in the hypervisor call. The hypervisor  496  may optionally apply the current Authority Mask Override Register (AMOR) value before placing the AMR into the process element  483 . In one embodiment, the CSRP is one of the registers  445  containing the effective address of an area in the application&#39;s address space  482  for the graphics acceleration module  446  to save and restore the context state. This pointer is optional if no state is required to be saved between jobs or when a job is preempted. The context save/restore area may be pinned system memory. 
     Upon receiving the system call, the operating system  495  may verify that the application  480  has registered and been given the authority to use the graphics acceleration module  446 . The operating system  495  then calls the hypervisor  496  with the information shown in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 OS to Hypervisor Call Parameters 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 A work descriptor (WD) 
               
               
                 2 
                 An Authority Mask Register (AMR) value (potentially masked). 
               
               
                 3 
                 An effective address (EA) Context Save/Restore Area Pointer (CSRP) 
               
               
                 4 
                 A process ID (PID) and optional thread ID (TID) 
               
               
                 5 
                 A virtual address (VA) accelerator utilization record pointer (AURP) 
               
               
                 6 
                 The virtual address of the storage segment table pointer (SSTP) 
               
               
                 7 
                 A logical interrupt service number (LISN) 
               
               
                   
               
            
           
         
       
     
     Upon receiving the hypervisor call, the hypervisor  496  verifies that the operating system  495  has registered and been given the authority to use the graphics acceleration module  446 . The hypervisor  496  then puts the process element  483  into the process element linked list for the corresponding graphics acceleration module  446  type. The process element may include the information shown in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Process Element Information 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 A work descriptor (WD) 
               
               
                 2 
                 An Authority Mask Register (AMR) value (potentially masked). 
               
               
                 3 
                 An effective address (EA) Context Save/Restore Area Pointer (CSRP) 
               
               
                 4 
                 A process ID (PID) and optional thread ID (TID) 
               
               
                 5 
                 A virtual address (VA) accelerator utilization record pointer (AURP) 
               
               
                 6 
                 The virtual address of the storage segment table pointer (SSTP) 
               
               
                 7 
                 A logical interrupt service number (LISN) 
               
               
                 8 
                 Interrupt vector table, derived from the hypervisor call parameters. 
               
               
                 9 
                 A state register (SR) value 
               
               
                 10 
                 A logical partition ID (LPID) 
               
               
                 11 
                 A real address (RA) hypervisor accelerator utilization record pointer 
               
               
                 12 
                 The Storage Descriptor Register (SDR) 
               
               
                   
               
            
           
         
       
     
     In one embodiment, the hypervisor initializes a plurality of accelerator integration slice  490  registers  445 . 
     As illustrated in  FIG. 4F , one embodiment of the invention employs a unified memory addressable via a common virtual memory address space used to access the physical processor memories  401 - 402  and GPU memories  420 - 423 . In this implementation, operations executed on the GPUs  410 - 413  utilize the same virtual/effective memory address space to access the processors memories  401 - 402  and vice versa, thereby simplifying programmability. In one embodiment, a first portion of the virtual/effective address space is allocated to the processor memory  401 , a second portion to the second processor memory  402 , a third portion to the GPU memory  420 , and so on. The entire virtual/effective memory space (sometimes referred to as the effective address space) is thereby distributed across each of the processor memories  401 - 402  and GPU memories  420 - 423 , allowing any processor or GPU to access any physical memory with a virtual address mapped to that memory. 
     In one embodiment, bias/coherence management circuitry  494 A- 494 E within one or more of the MMUs  439 A- 439 E ensures cache coherence between the caches of the host processors (e.g.,  405 ) and the GPUs  410 - 413  and implements biasing techniques indicating the physical memories in which certain types of data should be stored. While multiple instances of bias/coherence management circuitry  494 A- 494 E are illustrated in  FIG. 4F , the bias/coherence circuitry may be implemented within the MMU of one or more host processors  405  and/or within the accelerator integration circuit  436 . 
     One embodiment allows GPU-attached memory  420 - 423  to be mapped as part of system memory, and accessed using shared virtual memory (SVM) technology, but without suffering the typical performance drawbacks associated with full system cache coherence. The ability to GPU-attached memory  420 - 423  to be accessed as system memory without onerous cache coherence overhead provides a beneficial operating environment for GPU offload. This arrangement allows the host processor  405  software to setup operands and access computation results, without the overhead of tradition I/O DMA data copies. Such traditional copies involve driver calls, interrupts and memory mapped I/O (MMIO) accesses that are all inefficient relative to simple memory accesses. At the same time, the ability to access GPU attached memory  420 - 423  without cache coherence overheads can be critical to the execution time of an offloaded computation. In cases with substantial streaming write memory traffic, for example, cache coherence overhead can significantly reduce the effective write bandwidth seen by a GPU  410 - 413 . The efficiency of operand setup, the efficiency of results access, and the efficiency of GPU computation all play a role in determining the effectiveness of GPU offload. 
     In one implementation, the selection of between GPU bias and host processor bias is driven by a bias tracker data structure. A bias table may be used, for example, which may be a page-granular structure (i.e., controlled at the granularity of a memory page) that includes 1 or 2 bits per GPU-attached memory page. The bias table may be implemented in a stolen memory range of one or more GPU-attached memories  420 - 423 , with or without a bias cache in the GPU  410 - 413  (e.g., to cache frequently/recently used entries of the bias table). Alternatively, the entire bias table may be maintained within the GPU. 
     In one implementation, the bias table entry associated with each access to the GPU-attached memory  420 - 423  is accessed prior the actual access to the GPU memory, causing the following operations. First, local requests from the GPU  410 - 413  that find their page in GPU bias are forwarded directly to a corresponding GPU memory  420 - 423 . Local requests from the GPU that find their page in host bias are forwarded to the processor  405  (e.g., over a high-speed link as discussed above). In one embodiment, requests from the processor  405  that find the requested page in host processor bias complete the request like a normal memory read. Alternatively, requests directed to a GPU-biased page may be forwarded to the GPU  410 - 413 . The GPU may then transition the page to a host processor bias if it is not currently using the page. 
     The bias state of a page can be changed either by a software-based mechanism, a hardware-assisted software-based mechanism, or, for a limited set of cases, a purely hardware-based mechanism. 
     One mechanism for changing the bias state employs an API call (e.g. OpenCL), which, in turn, calls the GPU&#39;s device driver which, in turn, sends a message (or enqueues a command descriptor) to the GPU directing it to change the bias state and, for some transitions, perform a cache flushing operation in the host. The cache flushing operation is required for a transition from host processor  405  bias to GPU bias, but is not required for the opposite transition. 
     In one embodiment, cache coherency is maintained by temporarily rendering GPU-biased pages uncacheable by the host processor  405 . To access these pages, the processor  405  may request access from the GPU  410  which may or may not grant access right away, depending on the implementation. Thus, to reduce communication between the processor  405  and GPU  410  it is beneficial to ensure that GPU-biased pages are those which are required by the GPU but not the host processor  405  and vice versa. 
     Graphics Processing Pipeline 
       FIG. 5  illustrates a graphics processing pipeline  500 , according to an embodiment. In one embodiment a graphics processor can implement the illustrated graphics processing pipeline  500 . The graphics processor can be included within the parallel processing subsystems as described herein, such as the parallel processor  200  of  FIG. 2 , which, in one embodiment, is a variant of the parallel processor(s)  112  of  FIG. 1 . The various parallel processing systems can implement the graphics processing pipeline  500  via one or more instances of the parallel processing unit (e.g., parallel processing unit  202  of  FIG. 2 ) as described herein. For example, a shader unit (e.g., graphics multiprocessor  234  of  FIG. 3 ) may be configured to perform the functions of one or more of a vertex processing unit  504 , a tessellation control processing unit  508 , a tessellation evaluation processing unit  512 , a geometry processing unit  516 , and a fragment/pixel processing unit  524 . The functions of data assembler  502 , primitive assemblers  506 ,  514 ,  518 , tessellation unit  510 , rasterizer  522 , and raster operations unit  526  may also be performed by other processing engines within a processing cluster (e.g., processing cluster  214  of  FIG. 3 ) and a corresponding partition unit (e.g., partition unit  220 A- 220 N of  FIG. 2 ). The graphics processing pipeline  500  may also be implemented using dedicated processing units for one or more functions. In one embodiment, one or more portions of the graphics processing pipeline  500  can be performed by parallel processing logic within a general purpose processor (e.g., CPU). In one embodiment, one or more portions of the graphics processing pipeline  500  can access on-chip memory (e.g., parallel processor memory  222  as in  FIG. 2 ) via a memory interface  528 , which may be an instance of the memory interface  218  of  FIG. 2 . 
     In one embodiment the data assembler  502  is a processing unit that collects vertex data for surfaces and primitives. The data assembler  502  then outputs the vertex data, including the vertex attributes, to the vertex processing unit  504 . The vertex processing unit  504  is a programmable execution unit that executes vertex shader programs, lighting and transforming vertex data as specified by the vertex shader programs. The vertex processing unit  504  reads data that is stored in cache, local or system memory for use in processing the vertex data and may be programmed to transform the vertex data from an object-based coordinate representation to a world space coordinate space or a normalized device coordinate space. 
     A first instance of a primitive assembler  506  receives vertex attributes from the vertex processing unit  50 . The primitive assembler  506  readings stored vertex attributes as needed and constructs graphics primitives for processing by tessellation control processing unit  508 . The graphics primitives include triangles, line segments, points, patches, and so forth, as supported by various graphics processing application programming interfaces (APIs). 
     The tessellation control processing unit  508  treats the input vertices as control points for a geometric patch. The control points are transformed from an input representation from the patch (e.g., the patch&#39;s bases) to a representation that is suitable for use in surface evaluation by the tessellation evaluation processing unit  512 . The tessellation control processing unit  508  can also compute tessellation factors for edges of geometric patches. A tessellation factor applies to a single edge and quantifies a view-dependent level of detail associated with the edge. A tessellation unit  510  is configured to receive the tessellation factors for edges of a patch and to tessellate the patch into multiple geometric primitives such as line, triangle, or quadrilateral primitives, which are transmitted to a tessellation evaluation processing unit  512 . The tessellation evaluation processing unit  512  operates on parameterized coordinates of the subdivided patch to generate a surface representation and vertex attributes for each vertex associated with the geometric primitives. 
     A second instance of a primitive assembler  514  receives vertex attributes from the tessellation evaluation processing unit  512 , reading stored vertex attributes as needed, and constructs graphics primitives for processing by the geometry processing unit  516 . The geometry processing unit  516  is a programmable execution unit that executes geometry shader programs to transform graphics primitives received from primitive assembler  514  as specified by the geometry shader programs. In one embodiment the geometry processing unit  516  is programmed to subdivide the graphics primitives into one or more new graphics primitives and calculate parameters used to rasterize the new graphics primitives. 
     In some embodiments the geometry processing unit  516  can add or delete elements in the geometry stream. The geometry processing unit  516  outputs the parameters and vertices specifying new graphics primitives to primitive assembler  518 . The primitive assembler  518  receives the parameters and vertices from the geometry processing unit  516  and constructs graphics primitives for processing by a viewport scale, cull, and clip unit  520 . The geometry processing unit  516  reads data that is stored in parallel processor memory or system memory for use in processing the geometry data. The viewport scale, cull, and clip unit  520  performs clipping, culling, and viewport scaling and outputs processed graphics primitives to a rasterizer  522 . 
     The rasterizer  522  can perform depth culling and other depth-based optimizations. The rasterizer  522  also performs scan conversion on the new graphics primitives to generate fragments and output those fragments and associated coverage data to the fragment/pixel processing unit  524 . The fragment/pixel processing unit  524  is a programmable execution unit that is configured to execute fragment shader programs or pixel shader programs. The fragment/pixel processing unit  524  transforming fragments or pixels received from rasterizer  522 , as specified by the fragment or pixel shader programs. For example, the fragment/pixel processing unit  524  may be programmed to perform operations included but not limited to texture mapping, shading, blending, texture correction and perspective correction to produce shaded fragments or pixels that are output to a raster operations unit  526 . The fragment/pixel processing unit  524  can read data that is stored in either the parallel processor memory or the system memory for use when processing the fragment data. Fragment or pixel shader programs may be configured to shade at sample, pixel, tile, or other granularities depending on the sampling rate configured for the processing units. 
     The raster operations unit  526  is a processing unit that performs raster operations including, but not limited to stencil, z test, blending, and the like, and outputs pixel data as processed graphics data to be stored in graphics memory (e.g., parallel processor memory  222  as in  FIG. 2 , and/or system memory  104  as in  FIG. 1 , to be displayed on the one or more display device(s)  110  or for further processing by one of the one or more processor(s)  102  or parallel processor(s)  112 . In some embodiments the raster operations unit  526  is configured to compress z or color data that is written to memory and decompress z or color data that is read from memory. 
     System, Apparatus and Method for Reducing Voltage Swing on an Interconnect 
     In various embodiments, interconnect structures as adapted on an integrated circuit may be provided with interconnect drivers that seek to reduce dynamic power dissipation by enabling low swing clock and data interconnect lines. While such drivers can be used in many different locations, some embodiments described herein may be used in connection with one or more graphics processors, e.g., as implemented into a processor or other system on chip (SoC). The power consumed during a signal transition is defined by the discharged capacitance (C), activity factor (a), frequency (f), supply voltage (Vcc) and the voltage swing (Vswing) according to Equation [1]:
 
 P=a*C*Vcc*V swing* f   [EQ. 1].
 
     Using embodiments, swing voltage transfer, Vswing, along an interconnect may be dynamically reduced, in turn reducing energy consumption during transitions. 
     While different implementations will be described herein, some embodiments provide a single supply, low voltage swing interconnect driver in which one or more pullup devices are controlled to transition from operation in a linear region into operation in a diode-connected saturation region when an input signal transitions between states (e.g., from a logic 0 to a logic 1). Such embodiments may thus balance power savings with delay. 
     Note that repeater transistor sizing in such interconnect drivers may be determined by optimizing gate delay, wire delay, repeater distance, repeater latency, maximum allowed signal slew rate, short circuit current in a first inverter of a repeater due to degraded slew rates and reliability. One manner of lowering voltage swing on a long capacitive interconnect is to provide fully differential small swing signaling. In this case, both data and data_bar line signals have small voltage/current differentials and full swing signals are regenerated using sense amplifiers at a receiver end. Although such design may result in lower power consumption, additional chip real estate resources are consumed, as twice the metal resources are used, which may not be suitable for implementation of wide buses. Also, differential coupling noise may increase a minimum voltage differential for successful data propagation. 
     Referring now to  FIG. 6 , shown is a schematic diagram of an interconnect  600  in accordance with an embodiment of the present invention. More specifically, interconnect  600  is a signal transmission device that may be implemented as a conductive trace or line on one or more layers of a semiconductor die. For ease of illustration a single interconnect  600  is shown. However in many cases a given interconnect such as a clock bus, memory bus or other bus, or another coupling between components within a processor pipeline or other component may include many parallel lines, each having similar structures and arrangements as shown with regard to interconnect  600 . 
     As illustrated, interconnect  600  includes a plurality of repeaters  610   1 - 610   3  adapted on interconnect  600  to maintain signal fidelity as a signal traverses along a relatively long interconnect length. As examples, repeaters  610  may be adapted at predetermined distances from each other along an interconnect, e.g., between approximately 100 and 200 microns, in some embodiments. 
     With particular reference to repeater  610   1 , a buffer is formed of a plurality of inverters, namely a first inverter including metal oxide semiconductor field effect transistors (MOSFETs), namely a first inverter formed of a p-channel MOSFET (PMOS) P 1,1  and an n-channel MOSFET (NMOS) N 1,1 . As seen, MOSFETs P 1,1  and N 1,1  have gate terminals coupled to receive an input signal, Input, which may be swing between 0 volts and a supply voltage (Vcc) level. MOSFETs P 1,1  and N 1,1  may have commonly coupled drain terminals and source terminals that couple to, respectively a supply voltage node (Vcc) and a reference voltage node (e.g., ground). 
     This first inverter operates to invert the value of the input signal that is output at an inter-inverter node I 1,1  that in turn is coupled to gate terminals of PMOS P 2,1  and NMOS N 2,1  of a second inverter. PMOS P 2,1  and NMOS N 2,1  may similarly have their drain terminals coupled together. The source terminal of NMOS N 2,1  is coupled to the reference voltage node. In turn, the source terminal of PMOS P 2,1  is coupled to another device, namely an additional pullup device, D 1 . Note that in embodiments, device D 1  may be a diode-connected NMOS/PMOS device coupled in the pullup path of the driver gate to limit the output voltage swing from the second inverter. With this arrangement, while the output of the second inverter is of substantially the same character as the input signal, it has a reduced voltage swing, to thereby reduce power consumption of data communication on interconnect  600 . 
     In the embodiment of  FIG. 6 , diode-connected device D 1  that is connected in the pullup path of the driver gate limits the voltage swing, namely a reduction by a threshold voltage (from 0 to Vcc−VtD 1 ), instead of a full voltage swing. Note that as the gate overdrive voltage for drivers of repeaters  610  (e.g., PMOSs P 2,x ) is reduced for the entire period, an increase in the rise delay may occur in certain implementations, which may not comply with certain device specifications. Note that a complementary topology with a diode-clamp in the pulldown path limits the voltage swing from Vcc to Vtn/Vtp. 
     Still with reference to  FIG. 6 , note that the routing line of interconnect  600 , which may be configured as a metal line on a semiconductor die, can be modeled by a RC network formed of a resistor R 1  and parallel coupled capacitors C 1  and C 2 . Repeater  610   2  has substantially the same arrangement as repeater  610   1  with an additional PMOS device D 2  with a diode connected arrangement coupled between PMOS P 2,1  and the supply voltage node. As repeater  610   3  is a last repeater on interconnect  600 , no additional diode-connected device is present, such that the output signal is output with original voltage swing. 
     In another embodiment, instead of providing additional diode-connected devices in the pullup path of a driver gate, repeaters can couple to a separate voltage supply at a lower level. And then at an end of an interconnect, a level shifting driver can be provided to re-buffer the signal to the original swing level. Referring now to  FIG. 7 , shown is a schematic diagram of an interconnect in accordance with another embodiment of the present invention. As shown in  FIG. 7 , an interconnect  700  includes repeaters  710   1 - 710   3  within circuit portion  750 , which is a low voltage repeater domain, coupled to a different supply voltage node, LVcc, which is at a lower voltage level than a primary supply voltage, Vcc. In embodiments, this primary supply voltage Vcc may range between approximately 0.8 volts and 1.1 volts, while in turn the lower supply voltage may range between 0.7 volts and 1.0 volts. 
     In other aspects, repeaters  710  in low voltage repeater domain  750  may be configured as pairs of inverters, with both first and second inverters coupled to this low voltage supply node (with the exception of the first inverter of first repeater  710   1 , which couples to the primary supply voltage node). To enable a return to a full voltage swing level, the output of a last repeater (namely repeater  710   3  in the embodiment of  FIG. 7 ) couples to a level shifting buffer  760 , which returns the output signal to its original voltage swing level (namely 0−Vcc). In the embodiment of  FIG. 7 , repeater domain  750  may operate using a separate low voltage supply. In such an embodiment, power savings may be realized by precisely controlling the low voltage supply. However, a circuit arrangement as in  FIG. 7  may result in higher rise and fall delays due to reduced gate voltages (e.g., on driver NMOS devices (N 2,x ). An embodiment as in  FIG. 7  also may complicate the physical design due to Lvcc grid routing over the interconnect repeaters. 
     While embodiments as in  FIGS. 6 and 7  may reduce interconnect power consumption, there may be concerns in certain implementations as to delay increases caused by the arrangements of these circuits. Accordingly, in other embodiments it is possible to provide a driver for an interconnect that operates on a single supply voltage (namely the primary supply voltage) and has a controllable or programmable additional pullup device that enables a reduced voltage swing on the interconnect to reduce power consumption, while avoiding or at least reducing adverse delay effects. 
     Referring now to  FIG. 8 , shown is a schematic diagram of an interconnect driver in accordance with another embodiment of the present invention. As shown in  FIG. 8 , an interconnect  800  includes a driver  810  that couples to the interconnect, which is represented by an RC network, namely resistor R 1  and parallel capacitors C 1  and C 2 . Note that while a single driver  810  is shown for ease of illustration, as with the embodiments discussed above, it is possible for an interconnect to include multiple ones of these drivers or repeaters to enable appropriate signal fidelity in cases where an interconnect is greater than a given length. 
     As illustrated, driver  810  includes a repeater formed of a first inverter  820  and a second inverter  830 . Note that second inverter  830  has an additional header device  840  coupled between PMOS P 2  and a supply voltage node Vcc. In the embodiment shown in  FIG. 8 , header device  840  is implemented as a PMOS transistor P 4 . More specifically, PMOS P 4  has a source terminal coupled to the supply voltage node Vcc and a drain terminal coupled to an inter-transistor node P_Inter (further to which the source terminal of PMOS P 2  also is coupled). 
     To provide programmable control of header device  840 , a feedback device  850  is coupled to a gate terminal of PMOS P 4 . In the embodiment shown in  FIG. 8 , feedback device  850  is implemented as a pair of transistors, namely NMOS N 3  and PMOS P 3  having corresponding source terminals coupled to an output node, Out, and drain terminals commonly coupled to provide a control signal, P_Control, to the gate terminal of PMOS P 4 . As further shown, PMOS P 3  has its gate terminal coupled to a reference voltage node (e.g., Vss) and NMOS N 3  has its gate terminal commonly coupled with the gate terminal of PMOS P 2  to an inter-inverter node, In_Bar. 
     In operation, header device  840 , under control of feedback device  850 , operates when in a diode-connected saturation region to reduce the output voltage output by inverter  830  by its threshold voltage, Vtp 4 . Dynamic header device  840  is driven from the output (Out) in a controlled fashion. Specifically header device  840  is controlled by a control signal, P_Control, that is governed by feedback device  850  (formed of NMOS N 3  and PMOS P 3 ). NMOS N 3  is driven from the inter-inverter node, In_Bar, while PMOS P 3  is always on, having a gate terminal connected to Vss. 
     When the input signal (In) is at a low voltage level (0), first inverter  820  outputs an inverted signal, In_Bar, having a high voltage level (1). And in turn, second inverter  830  outputs the output signal, Out, at a low voltage level (0). With these signal levels, the control signal, P_control, output by feedback device  850  is at 0, as NMOS N 3  is fully on. In turn, dynamic header device  840  is in operation in the linear region and drives P_Inter node to Vcc. There is no short circuit current in the pullup path as PMOS P 2  is off (In_Bar=1). 
     When the input signal transitions from 0 to 1, In_Bar transitions from 1 to 0. This transition turns off NMOS N 3  of feedback device  850 , and floats the P_Control node momentarily (as shown in the timing diagram of  FIG. 9 ). Note that P_Control is initialized to 0 before the input rising transition. Due to the falling transition on the gate terminal of NMOS N 3  of feedback device  850 , which couples to inter-inverter node, In_Bar, PMOS P 4  of header device  840  drives PMOS P 2  even stronger to have a fast rising transition. Also, there is no contention as NMOS N 3  of feedback device  850  only initializes the gate terminal of PMOS P 4  of header device  840  to 0 when the input signal goes high. As such, the output signal (at Out node) starts to rise due to a current conduction path through the pullup devices of PMOS P 2  and PMOS P 4 . Once the Out node rises above the threshold voltage of PMOS P 3  of feedback device  850 , P_Control is coupled to the Out node. As a result, P_Control follows the Out node and configures PMOS P 4  of dynamic header device  850  into the diode-connected saturation region. At this point, the P_Inter node also follows the Out node and reaches a voltage of Vcc-Vtp 4 . 
     Thus PMOS P 4  of dynamic header  840  initially operates in the linear region and is then configured into the diode-connected region dynamically as the Out node rising transition crosses a certain threshold (Vtp 3  in this case, namely the threshold voltage of PMOS P 3 ). This arrangement results in a significantly improved rise delay as compared to a statically connected diode clamp header as in the embodiment of  FIG. 6 . Also the gate voltage of NMOS N 2  is not reduced as in the case of a separate low voltage supply scenario as in  FIG. 7 . As a result, using an embodiment as in  FIG. 8  may lower voltage swing (e.g., to Vcc−Vt), without degrading rising delay significantly as compared to a full swing driver. 
     Referring now to  FIG. 9 , shown is a timing diagram illustrating operation of a driver circuit in accordance with one embodiment of the present invention. More specifically,  FIG. 9  shows the signals present in interconnect driver  810  of  FIG. 8 . As seen, the received input signal In (which itself may be received with a reduced voltage swing) causes driver circuit  810  to output an output signal, Out, also having a reduced voltage swing. Still further, with the arrangement of  FIG. 8 , reduced delay and improved signal fidelity is realized for this output signal. 
     Referring now to  FIG. 10 , shown is a schematic diagram of an interconnect driver in accordance with a still further embodiment of the present invention. As seen in  FIG. 10 , interconnect driver  1010  of an interconnect  1000  is configured substantially the same as interconnect driver  810  of  FIG. 8 . As shown, interconnect driver  1010  includes a first inverter  1020 , a second inverter  1030  and a dynamic header device  1040 . 
     Note that in the embodiment of  FIG. 10 , however a feedback device  1050  is implemented with stacked sets of MOSFETs. Specifically, a set of NMOSs N 3 , N 5  and N 6  are coupled between output node, Out, and the gate terminal of PMOS P 4  of dynamic header device  1040 . As illustrated, these NMOSs have gate terminals coupled to the inter-inverter node, In_Bar. Similarly, PMOSs P 3 , P 5  and P 6  also couple between the output node and the gate terminal of PMOS P 4 . 
     In the embodiment of  FIG. 10 , the header mode transition (from linear to diode-connected regions) may be optimized during rising output transitions using stacked feedback device  1050 . With this configuration, the transition point of configuring PMOS P 4  of dynamic header device  1040  from the linear region to the diode-connected region can be optimized by optimizing the feedback transistor (N 3 -N 5 -N 6  and P 3 -P 5 -P 6 ) threshold voltages, sizing and stack height. Note that increasing the feedback stack height increases dynamic capacitance (C DYN ) and thus may lower the power benefit. 
     Referring now to  FIG. 11 , shown is a schematic diagram of an interconnect driver in accordance with yet another embodiment of the present invention. As illustrated,  FIG. 11  interconnect driver  1110  of an interconnect  1100  is configured substantially the same as interconnect driver  810  of  FIG. 8 . As shown, interconnect driver  1110  includes a first inverter  1120 , a second inverter  1130 , a dynamic header device  1140 , and a feedback device  1150 . 
     Note that in the embodiment to  FIG. 11 , an additional NMOS N 7  has corresponding source and drain terminals that couple to the gate terminal of PMOS P 4  of feedback device  1140 . And the commonly coupled gate terminal of NMOS N 7  (with NMOS N 3 ) is driven by In_Bar, coupled to the inter-inverter node. 
     In the embodiment of  FIG. 11 , the output rising transition may be optimized by capacitively coupling the falling transition on In_Bar node to P_Control node and increasing the gate overdrive of PMOS P 4  of dynamic header device  1140 . Note that the output rise delay can be improved by driving PMOS P 4  with an increased gate overdrive voltage. As shown in  FIG. 11  additional transistor NMOS N 7  is connected between the In_Bar and P_Control nodes. When In_Bar transitions from 1 to 0, P_Control node is driven below 0 due to capacitive coupling which improves the rise delay, at the expense of increased Cdyn (e.g., NMOS N 7  gate capacitance), which may lower the power benefit. 
     Referring now to  FIG. 12 , shown is a schematic diagram of an interconnect driver in accordance with an additional embodiment of the present invention. As seen in  FIG. 12 , interconnect driver  1210  of an interconnect  1200  is configured substantially the same as interconnect driver  810  of  FIG. 8 . As shown, interconnect driver  1210  includes a first inverter  1220 , a second inverter  1230 , a dynamic header device  1240 , and a feedback device  1250 . To provide greater configurability and optimization with regard to rise time delays, an additional PMOS device P 7  is included in feedback device  1250 . As illustrated, PMOS P 7  has a source terminal coupled to the drain terminal of PMOS P 3 , a gate terminal that couples to a drain terminal of NMOS N 8  and a drain terminal that commonly couples with the drain terminal of NMOS N 3  to provide the control signal, P_Control, to the gate terminal of PMOS P 4  of dynamic header device  1240 . 
     To realize this dynamic configuration, interconnect driver  1210  receives a control signal, 2Vt_Enable, e.g., from a power controller, which is used to control a switch circuit  1260  formed of NMOS N 8  and PMOS P 8 . When this control signal is of a logic low level, PMOS P 8  is active to provide a diode-connected arrangement of PMOS P 7 . With this configuration, the header mode transition (from linear to diode-connected regions) during a rising output transition can be optimized by an additional threshold (namely from a Vtp 3  threshold to a Vtp 3 +Vtp 7  threshold) using diode-connected PMOS P 7  of feedback device  1250 . In this way, the transition of PMOS P 4  of dynamic header device  1240  from the linear region to the diode-connected region can be increased from one Vtp threshold to two Vtp thresholds to improve the rise delay. That is, when the control signal is 0, P_Control node starts to follow Out node when its value transitions above a voltage of Vtp 3 +Vtp 7 . This arrangement maintains PMOS P 4  in the linear region for a longer duration, improving the rise delay. 
     Instead, when the control signal is of a logic high level, PMOS P 7  is configured by control of switches  1260  to be stacked with PMOS P 3 . That is, when the control signal is 1, PMOS P 7  has its gate terminal coupled to ground, and thus the arrangement of feedback device  1250  is similar to the stacked arrangement of  FIG. 10 . 
     Referring now to  FIG. 13 , shown is a flow diagram of a method in accordance with an embodiment of the present invention. More specifically, method  1300 , which may be performed in different embodiments by hardware, software, firmware and/or combinations thereof, may be used to programmably control operation of a control signal that in turn is used to control a feedback device of one or more interconnect drivers as described herein. In one particular embodiment, method  1300  may be performed by a power controller of a processor, such as a power control unit (PCU) that is configured to perform power management operations on behalf of a processor. Such processor may be a multicore processor including a plurality of processing cores and an integrated graphics processing unit (GPU) itself including one or more graphics processing engines. Such PCU may be implemented as a dedicated microcontroller, other control logic or as a set of instructions executable on one or more general-purpose processing cores. 
     As illustrated, method  1300  begins by determining a power budget of the processor (block  1310 ). In many cases, a processor may be configured with a maximum power budget that it can withstand, given a particular cooling system for a given platform implementation. Next control passes to block  1320  where during normal operation requests may be received for performance states of one or more processing engines of the processor. These performance state requests may be received from an operating system (OS), processor cores themselves, or a graphics driver which may issue requests for performance states for graphics engines, as examples. Control next passes to diamond  1330  where it is determined whether sufficient power budget exists to operate at the requested performance state. To determine this sufficiency, access may be made to a lookup table that identifies corresponding power consumption levels for different performance states. If it is determined that there is insufficient power budget for a requested performance state, control passes to block  1340  where a reduced performance state can be determined based on the available power budget. For example, a given processing engine may be controlled to operate at a lower than requested performance state in the absence of a power budget sufficient to meet the requested performance state. 
     In any event, control next passes to block  1350  where the processing engine(s) may be caused to operate at the determined power state, which may be the requested power state (where sufficient power budget is available) or a lower performance state (in the absence of sufficient power budget). Control next passes to diamond  1360 . There it can be determined whether the operating voltage associated with the given performance state is above an operating voltage threshold level. Such threshold level may be a programmed value such as stored in a fuse storage that is a threshold at which interconnect drivers can be dynamically controlled as described herein. That is, with reference to, e.g., the interconnect driver of  FIG. 12 , a programmable control signal can be sent to the interconnect driver to more finely control a reduced voltage swing along an interconnect based on an operating voltage at which circuitry coupled to or otherwise associated with the interconnect is operating. 
     If it is determined at diamond  1360  that the operating voltage is greater than the threshold level, control passes to block  1370  where a control signal having a first value (e.g., logic low level) is sent to control a feedback device of the interconnect driver to be of a first configuration. More specifically, the feedback device is controlled in this case to cause the additional PMOS P 7  of feedback device  1250  to be in a diode-connected configuration in  FIG. 12  such that the voltage swing can be reduced by two Vt thresholds. With this additional diode-connected PMOS P 7 , an optimized header mode transition from the linear region to the diode-connected, saturation region occurs during rising output transitions. In this way, rise delay is improved, enabling the interconnect to operate at a higher frequency (corresponding to a higher operating voltage). 
     Instead, when it is determined that the operating voltage is less than this threshold level, control passes to block  1380 . There the control signal having a second value (e.g., a logic high level) is sent to control the feedback device of the interconnect driver to be of a second configuration. In this second configuration, the control signal operates to control switch  1260  ((NMOS N 8  and PMOS P 8 ) such that PMOS P 7  is stacked with PMOS P 3  as part of feedback circuit  1250 . Understand while shown at this high level in the embodiment of  FIG. 13 , many variations and alternatives are possible. 
     Referring now to  FIG. 14 , shown is a block diagram of a processor in accordance with an embodiment of the present invention. More specifically, processor  1400  is a multicore processor that further includes a graphics processor that can operate at a plurality of different performance states depending upon requests received from various entities, as well as available power budget, as described herein. In the particular embodiment of  FIG. 14 , processor  1400  includes a central processing unit (CPU) domain  1410  including a plurality of cores  1412   0 - 1412   n . In the embodiment of  FIG. 14 , these cores may be powered by way of corresponding integrated voltage regulators (IVRs)  1414   0 - 1414   n . Understand that such integrated voltage regulators are optional, and in other cases, cores  1412  may be directly powered by way of voltages received from off-chip voltage regulators. Furthermore, cores  1412  may receive clock signals having operating frequencies generated by corresponding clock generators  1416   0 - 1416   n . In embodiments, such clock generators  1416  may include PLLs that operate as described herein. As further shown, CPU domain  1410  further includes a local power controller  1418  that may be implemented as a microcontroller or other programmable controller to perform local power management operations, such as the local power control of one or more cores  1412 , such as by way of power gating, clock gating and so forth. 
     As further illustrated, processor  1400  also includes a graphics domain  1420  including a plurality of graphics engines  1422   0 - 1422   n . In the embodiment of  FIG. 14 , these engines may be powered by way of corresponding integrated voltage regulators (IVRs)  1424   0 - 1424   n . Understand that such integrated voltage regulators are optional, and in other cases, engines  1422  may be directly powered by way of voltages received from off-chip voltage regulators. Furthermore, engines  1422  may receive clock signals having operating frequencies generated by corresponding clock generators  1426   0 - 1426   n . As further shown, graphics domain  1420  further includes a local power controller  1428  that may be implemented as a microcontroller or other programmable controller to perform local power management operations, such as the local power control of one or more engines  1422 , such as by way of power gating, clock gating and so forth. 
     Still with reference to  FIG. 14 , a shared cache memory  1430  couples to CPU domain  1410  and graphics domain  1420 . In different embodiments, shared cache memory  1430  may be implemented in a partitioned manner, with different portions allocated to the cores and graphics engine of domains  1410  and  1420 . 
     Processor  1400  further includes a power control unit (PCU)  1440 . In various embodiments, PCU  1440  may be implemented as a dedicated microcontroller to perform processor-wide power management operations. As illustrated, PCU  1440  may include constituent control circuitry, including a power budget controller  1442 , an interconnect driver control circuit  1444  and a performance state controller  1446 . Still further, PCU  1440  includes an P-state table  1445 . Power budget controller  1442  is configured to allocate portions of an overall processor power budget (which may be set based at least in part on a maximum power budget available to the processor, a cooling solution of a given platform and so forth) to CPU domain  1410  and graphics domain  1420 , e.g., based on requests for particular performance states, environmental conditions such as processor temperature, and so forth. 
     Interconnect driver control circuit  1444  is configured, in response to a request for a change in performance state of one or more of cores  1412  and/or graphics engines  1422 , to identify an operating voltage associated with a determined power state (e.g., with reference to information in P-State table  1445 ). Then based upon the identified operating voltage control circuit  1444  can determine whether this value is above or below a threshold level and generate a control signal for communication to one or more interconnect drivers associated with an interconnect associated with a domain having that operating voltage to cause a dynamic re-configuration of a feedback device of the interconnect driver so that output voltage swing can be optimized while enabling delay characteristics of the interconnect driver to meet specified tolerances for a given operating frequency at which the interconnect is to operate. PCU  1440  further includes performance state controller  1446  that is configured to receive incoming performance state request for the various cores  1412  and graphics engines  1422 , and to allow such performance state changes to occur, when power budget is available. 
     Processor  1400  further includes a memory controller  1450  that may act as an interface between processor  1400  and a system memory, such as a dynamic random access memory (DRAM) coupled to the processor (not shown for ease of illustration in  FIG. 14 ). Still further, processor  1400  includes one or more interfaces  1460  to act as an interface to other components of a platform. Understand while shown at this high level in the embodiment of  FIG. 14 , many variations and alternatives are possible. 
     Embodiments may be used in a variety of interconnect structures, such as always-ON interconnects (such as clocks) and data buses (with low activity factor) for varying repeater distances, metal tracks, and supply voltages. In embodiments for data buses, repeaters of interconnect drivers such as described herein may be placed at predetermined distances from each other along an interconnect. In some embodiments, such repeaters may be placed at a predetermined distance of between approximately 150 microns to 200 microns, although the scope of the present invention is not limited in this regard. Using embodiments as described herein in connection with such interconnect drivers, dynamic power savings may be realized with a small penalty in delay across an operating voltage range, as compared to a baseline interconnect driver design that operates at a full voltage swing. 
     For an always-on interconnect such as for clock signaling, interconnect drivers having reduced voltage swings as described herein may be placed with a smaller predetermined distance between drivers, e.g., between approximately 20-80 microns. With such smaller repeater distance, the contribution of device capacitance may be as significant as interconnect capacitance, and as such, interconnect drivers as described herein may incur higher power and penalty than a full swing design. However, as repeater distance becomes greater (e.g., greater than approximately 40 microns), embodiments may provide for lower dynamic power as compared to a full swing arrangement. Understand while these power savings and delays are described for purposes of illustration, embodiments are not limited in this aspect in any way. 
     Power Components 
       FIG. 15  illustrates a block diagram of a switching regulator according to an embodiment. One or more switching regulators shown in  FIG. 15  may be incorporated in various systems discussed herein to provide power to one or more Integrated Circuit (IC) chips. While a single phase of the current-parking switching regulator with a single inductor may be discussed with reference to  FIG. 15 , one or more of the multiple phases of the current-parking switching regulator may be implemented with a split inductor. Furthermore, a combination of one or more current-parking switching regulators (with or without a split inductor) may be used with one or more conventional electric power conversion devices to provide power to the load (e.g., logic circuitry  1514 ). 
     More particularly,  FIG. 15  illustrates a system  1500  that includes a switching regulator (sometimes referred to as a current-parking switching regulator). The current-parking switching regulator may be a multi-phase switching regulator in various embodiments. The multi-phase control unit  1502  is coupled to multiple phases, where each phase may include one or more upstream phases  1504  and one or more downstream phases  1506 . As shown, an electrical power source  1508  is coupled to upstream control logic  1510  (which provides a current control mechanisms in each upstream phase). More than one upstream control logic may be used in various implementations. Each upstream phase may include an inductor (not shown) that is coupled to a respective downstream phase. In an embodiment, the upstream phases may each include one or more inductors. The multi-phase control unit  1502  may configure any active upstream control logic  1510 , e.g., to generate a current through an inductor coupled between the upstream phases and the downstream phases. The downstream control logic  1512  may be configured by the multi-phase control unit  1502  to be ON, OFF, or switching to regulate the voltage level at the load (e.g., logic circuitry  1514 ). In turn, the downstream control logic  1512  may be configured by the multi-phase control unit  1502  to maintain the voltage level at the load within a range based at least in part on Vmin (minimum voltage) and Vmax (maximum voltage) values. 
     In one embodiment, an inductor (coupled between a downstream phase and a respective upstream phase) may be positioned outside of a semiconductor package  1516  that includes the load  1514 . Another inductor (not shown) may be positioned inside of the package  1516 , e.g., to reduce parasitic capacitance. In one embodiment, the inductor inside the package  1516  may be a planar air-core inductor that is coupled to the logic circuitry  1514  via one or more switching logic which include planar Metal-Oxide Semiconductor Field-Effect Transistors (MOSFETs). Furthermore, one or more of the components discussed herein (e.g., with reference to  FIGS. 15, 16 and 17 , including, for example, L3 cache, upstream control logic, and/or downstream control logic) may be provided in substrate layer(s) (e.g., between semiconductor packages), on an integrated circuit die, or outside of a semiconductor package (e.g., on a Printed Circuit Board (PCB)) in various embodiments. 
       FIG. 16  is a block diagram of a system  1600  including a streaming multiprocessor  1602 , in accordance with one or more embodiments. The streaming multiprocessor may include 32 Single-Instruction, Multiple Thread (SIMT) lanes  1604  that are capable of collectively issuing up to 32 instructions per clock cycle, e.g., one from each of 32 threads. More or less lanes may be present depending on the implementation such as 64, 128, 256, etc. The SIMT lanes 2x04 may in turn include one or more: Arithmetic Logic Units (ALUs)  1606 , Special Function Units (SFUs)  1608 , memory units (MEM)  1610 , and/or texture units (TEX)  1612 . 
     In some embodiments, one or more of ALU(s)  1606  and/or TEX unit(s)  1612  may be low energy or high capacity, e.g., such as discussed with reference to items  1620  and  1622 . For example, the system may map 100% of the register addresses for threads  0 - 30  to the low energy portion and 100% of the register addresses for threads  31 - 127  to the high capacity portion. As another example, the system may map 20% of each thread&#39;s registers to the low energy portion and to map 80% of each thread&#39;s registers to the high capacity portion. Moreover, the system may determine the number of entries allocated per thread based on runtime information. 
     As illustrated in  FIG. 16 , the streaming multiprocessor  1602  also include a register file  1614 , a scheduler logic  1616  (e.g., for scheduling threads or thread groups, or both), and shared memory  1618 , e.g., local scratch storage. As discussed herein, a “thread group” refers to a plurality of threads that are grouped with ordered (e.g., sequential or consecutive) thread indexes. Generally, a register file refers to an array of registers accessed by components of a processor (including a graphics processor) such as those discussed herein. The register file  1614  includes a low energy portion or structure  1620  and a high capacity portion or structure  1622 . The streaming multiprocessor  1602  may be configured to address the register file  1614  using a single logical namespace for both the low energy portion and the high capacity portion. 
     In some embodiments, the system may include a number of physical registers which can be shared by the simultaneously running threads on the system. This allows the system to use a single namespace to implement a flexible register mapping scheme. A compiler may then allocate register live ranges to register addresses, and the compiler may use a register allocation mechanism to minimize or reduce the number of registers used per thread. Multiple live ranges can be allocated to the same register address as long as the live ranges do not overlap in an embodiment. This allows for determination, e.g., at runtime and after instructions have been compiled, of how many entries per thread will be allocated in the low energy portion versus the high capacity portion. For example, the system may map 100% of the register addresses for threads  0 - 30  to the low energy portion and 100% of the register addresses for threads  31 - 127  to the high capacity portion. As another example, the system may map 20% of each thread&#39;s registers to the low energy portion and to map 80% of each thread&#39;s registers to the high capacity portion. The system may determine the number of entries allocated per thread based on runtime information, e.g., regarding the number of thread groups executing and the marginal benefit from launching more thread groups or allocating a smaller number of thread groups more space in the low energy portion. 
       FIG. 17  illustrates a block diagram of a parallel processing system  1700 , according to one embodiment. System  1700  includes a Parallel Processing (Previously Presented) subsystem  1702  which in turn includes one or more Parallel Processing Units (PPUs) PPU- 0  through PPU-P. Each PPU is coupled to a local Parallel Processing (PP) memory (e.g., Mem- 0  through MEM-P, respectively). In some embodiments, the PP subsystem system  1702  may include P number of PPUs. PPU- 0   1704  and parallel processing memories  1706  may be implemented using one or more integrated circuit devices, such as programmable processors, Application Specific Integrated Circuits (ASICs), or memory devices. 
     Referring to  FIG. 17 , several optional switch or connections  1707  are shown that may be used in system  1700  to manage power. While several switches  1707  are shown, embodiments are not limited to the specifically shown switches and more or less switches may be utilized depending on the implementation. These connections/switches  1707  may be utilized for clock gating or general power gating. Hence, items  1707  may include one or more of a power transistor, on-die switch, power plane connections, or the like. In an embodiment, prior to shutting power to a portion of system  1700  via switches/connections  1707 , logic (e.g., a microcontroller, digital signal processor, firmware, etc.) may ensure the results of operation are committed (e.g., to memory) or finalized to maintain correctness. 
     Further, in some embodiments, one or more of PPUs in parallel processing subsystem  1702  are graphics processors with rendering pipelines that may be configured to perform various tasks such as those discussed herein with respect to other figures. The graphics information/data may be communicated via memory bridge  1708  with other components of a computing system (including components of system  1700 ). The data may be communicated via a shared bus and/or one or more interconnect(s)  1710  (including, for example, one or more direct or point-to-point links). PPU- 0   1704  may access its local parallel processing memory  1714  (which may be used as graphics memory including, e.g., a frame buffer) to store and update pixel data, delivering pixel data to a display device (such as those discussed herein), etc. In some embodiments, the parallel processing subsystem  1702  may include one or more PPUs that operate as graphics processors and one or more other PPUs that operate to perform general-purpose computations. The PPUs may be identical or different, and each PPU may have access to its own dedicated parallel processing memory device(s), no dedicated parallel processing memory device(s), or a shared memory device or cache. 
     In an embodiment, operations performed by PPUs may be controlled by another processor (or one of the PPUs) generally referred to as a master processor or processor core. In one embodiment, the master processor/core may write a stream of commands for each PPU to a push buffer in various locations such as a main system memory, a cache, or other memory such as those discussed herein with reference to other figures. The written commands may then be read by each PPU and executed asynchronously relative to the operation of master processor/core. 
     Furthermore, as shown in  FIG. 17 , PPU- 0  includes a front end logic  1720  which may include an Input/Output (I/O or IO) unit (e.g., to communicate with other components of system  1700  through the memory bridge  1708 ) and/or a host interface (e.g., which receives commands related to processing tasks). The front end  1720  may receive commands read by the host interface (for example from the push buffer)). The front end  1720  in turn provides the commands to a work scheduling unit  1722  that schedules and allocates operation(s)/task(s) associated with the commands to a processing cluster array or arithmetic subsystem  1724  for execution. 
     As shown in  FIG. 17 , the processing cluster array  1724  may include one or more General Processing Cluster (GPC) units (e.g., GPC- 0   1726 , GPC- 1   1728 , through GPC-M  1730 ). Each GPC may be capable of executing a large number (e.g., hundreds or thousands) of threads concurrently, where each thread is an instance of a program. In various applications, different GPCs may be allocated for processing different types of programs or for performing different types of computations. For example, in a graphics application, a first set of GPCs (e.g., including one or more GPC units) may be allocated to perform tessellation operations and to produce primitive topologies for patches, and a second set of GPCs (e.g., including one or more GPC units) may be allocated to perform tessellation shading to evaluate patch parameters for the primitive topologies and to determine vertex positions and other per-vertex attributes. The allocation of GPCs may vary depending on the workload arising for each type of program or computation. 
     Additionally, processing tasks that are assigned by the work scheduling unit  1722  may include indices of data to be processed, such surface/patch data, primitive data, vertex data, pixel data, and/or state parameters and commands defining how the data is to be processed (e.g., what program is to be executed). The work scheduling unit  1722  may be configured to fetch the indices corresponding to the tasks, or may receive the indices from front end  1720 . Front end  1720  may also ensure that GPCs are configured to a valid state before the processing specified by the push buffers is initiated. 
     In one embodiment, the communication path  1712  is a Peripheral Component Interface (PCI) express (or PCI-e) link, in which dedicated lanes may be allocated to each PPU. Other communication paths may also be used. For example, commands related to processing tasks may be directed to the host interface  1718 , while commands related to memory operations (e.g., reading from or writing to parallel processing memory  1714 ) may be directed to a memory crossbar unit  1732 . 
     In some embodiments, parallel processing subsystem  1702  may be implemented as an add-in card that is inserted into an expansion slot of computer system or server (such as a blade server). In other embodiments, a PPU may be integrated on a single chip with a bus bridge, such as memory bridge  1708 , an I/O bridge, etc. In still other embodiments, some or all components of PPU may be integrated on a single integrated circuit chip with one or more other processor cores, memory devices, caches, etc. 
     Furthermore, one of the major problems with today&#39;s modern processors is they have hit a clock rate limit at around 4 GHz. At this point they just generate too much heat for the current technology and require special and expensive cooling solutions. This is because as we increase the clock rate, the power consumption rises. In fact, the power consumption of a CPU, if you fix the voltage, is approximately the cube of its clock rate. To make this worse, as you increase the heat generated by the CPU, for the same clock rate, the power consumption also increases due to the properties of the silicon. This conversion of power into heat is a complete waste of energy. This increasingly inefficient use of power eventually means you are unable to either power or cool the processor sufficiently and you reach the thermal limits of the device or its housing, the so-called power wall. 
     Faced with not being able to increase the clock rate, making forever-faster processors, the processor manufacturers had to come up with another game plan. They have been forced down the route of adding more cores to processors, rather than continuously trying to increase CPU clock rates and/or extract more instructions per clock through instruction-level parallelism. 
     Moreover, power usage is a big consideration when designing machines that constantly run. Often the operating costs of running a supercomputer over just a few years can equate to the cost of installing it in the first place. Certainly, the cost of running such a machine over its lifetime will easily exceed the original installation costs. Power usage comes from the components themselves, but also from the cooling necessary to allow such computers to operate. Even one high-end workstation with four GPUs requires some planning on how to keep it cool. Unless you live in a cold climate and can banish the computer to somewhere cold, it will do a nice job of heating up the office for you. Put a number of such machines into one room, and very rapidly the air temperature in that room will start to rise to quite unacceptable levels. 
     A significant amount of power is therefore expended on installing air conditioning systems to ensure computers remain cool and can operate without producing errors. This is especially so where summer temperatures can reach 85 F/30 C or higher. Air conditioning is expensive to run. Significant thought should be given to how best to cool such a system and if the heat energy can in some way be reused. Liquid-cooled systems are very efficient in this way in that the liquid can be circulated through a heat exchanger and into a conventional heating system without any chance of the two liquids ever mixing. With the ever-increasing costs of natural resources, and the increasing pressures on companies to be seen as green, simply pumping the heat out the window is no longer economically or socially acceptable. 
     Liquid-cooled systems provide an interesting option in terms of recycling the waste heat energy. While an air-cooled system can only be used to heat the immediate area it is located in, heat from liquid-based coolants can be pumped elsewhere. By using a heat exchanger, the coolant can be cooled using conventional water. This can then be pumped into a heating system or even used to heat an outdoor swimming pool or other large body of water. Where a number of such systems are installed, such as in a company or university computer center, it can really make sense to use this waste heat energy to reduce the heating bill elsewhere in the organization. 
     Many supercomputer installations site themselves next to a major river precisely because they need a ready supply of cold water. Others use large cooling towers to dissipate the waste heat energy. Neither solution is particularly green. Having paid for the energy already it makes little sense to simply throw it away when it could so easily be used for heating. When considering power usage, we must also remember that program design actually plays a very big role in power consumption. The most expensive operation, power wise, is moving data on and off chip. Thus, simply making efficient use of the registers and shared memory within the device vastly reduces power usage. If you also consider that the total execution time for well-written programs is much smaller than for poorly written ones, you can see that rewriting old programs to make use of new features such as larger shared memory can even reduce operating costs in a large data center. 
     Referring to  FIG. 17 , memory interface  1714  includes N partition units (e.g., Unit- 0   1734 , Unit- 1   1736 , through Unit-N  1738 ) that are each directly coupled to a corresponding portion of parallel processing memory  1706  (such as Mem- 0   1740 , Mem- 1   1742 , through Mem-N  1744 ). The number of partition units may generally be equal to the number of Previously Presented memory (or N as shown). The Previously Presented memory may be implemented with volatile memory such as Dynamic Random Access Memory (DRAM) or other types of volatile memory such as those discussed herein. In other embodiments, the number of partition units may not equal the number of memory devices. Graphics data (such as render targets, frame buffers, or texture maps) may be stored across Previously Presented memory devices, allowing partition units to write portions of graphics data in parallel to efficiently use the available bandwidth of the parallel processing memory  1706 . 
     Furthermore, any one of GPCs may process data to be written to any of the partition units within the parallel processing memory. Crossbar unit  1732  may be implemented as an interconnect that is configured to route the output of each GPC to the input of any partition unit or to another GPC for further processing. Hence, GPCs  1726  to  1730  may communicate with memory interface  1714  through crossbar unit  1732  to read from or write to various other (or external) memory devices. As shown, crossbar unit  1732  may directly communicate with the front end  1720 , as well as having a coupling (direct or indirect) to local memory  1706 , to allow the processing cores within the different GPCs to communicate with system memory and/or other memory that is not local to PPU. Furthermore, the crossbar unit  1732  may utilize virtual channels to organize traffic streams between the GPCs and partition units. 
     System Overview 
       FIG. 18  is a block diagram of a processing system  1800 , according to an embodiment. In various embodiments the system  1800  includes one or more processors  1802  and one or more graphics processors  1808 , and may be a single processor desktop system, a multiprocessor workstation system, or a server system having a large number of processors  1802  or processor cores  1807 . In one embodiment, the system  1800  is a processing platform incorporated within a system-on-a-chip (SoC) integrated circuit for use in mobile, handheld, or embedded devices. 
     An embodiment of system  1800  can include, or be incorporated within a server-based gaming platform, a game console, including a game and media console, a mobile gaming console, a handheld game console, or an online game console. In some embodiments system  1800  is a mobile phone, smart phone, tablet computing device or mobile Internet device. Data processing system  1800  can also include, couple with, or be integrated within a wearable device, such as a smart watch wearable device, smart eyewear device, augmented reality device, or virtual reality device. In some embodiments, data processing system  1800  is a television or set top box device having one or more processors  1802  and a graphical interface generated by one or more graphics processors  1808 . 
     In some embodiments, the one or more processors  1802  each include one or more processor cores  1807  to process instructions which, when executed, perform operations for system and user software. In some embodiments, each of the one or more processor cores  1807  is configured to process a specific instruction set  1809 . In some embodiments, instruction set  1809  may facilitate Complex Instruction Set Computing (CISC), Reduced Instruction Set Computing (RISC), or computing via a Very Long Instruction Word (VLIW). Multiple processor cores  1807  may each process a different instruction set  1809 , which may include instructions to facilitate the emulation of other instruction sets. Processor core  1807  may also include other processing devices, such a Digital Signal Processor (DSP). 
     In some embodiments, the processor  1802  includes cache memory  1804 . Depending on the architecture, the processor  1802  can have a single internal cache or multiple levels of internal cache. In some embodiments, the cache memory is shared among various components of the processor  1802 . In some embodiments, the processor  1802  also uses an external cache (e.g., a Level-3 (L3) cache or Last Level Cache (LLC)) (not shown), which may be shared among processor cores  1807  using known cache coherency techniques. A register file  1806  is additionally included in processor  1802  which may include different types of registers for storing different types of data (e.g., integer registers, floating point registers, status registers, and an instruction pointer register). Some registers may be general-purpose registers, while other registers may be specific to the design of the processor  1802 . 
     In some embodiments, processor  1802  is coupled with a processor bus  1810  to transmit communication signals such as address, data, or control signals between processor  1802  and other components in system  1800 . In one embodiment the system  1800  uses an exemplary ‘hub’ system architecture, including a memory controller hub  1816  and an Input Output (I/O) controller hub  1830 . A memory controller hub  1816  facilitates communication between a memory device and other components of system  1800 , while an I/O Controller Hub (ICH)  1830  provides connections to I/O devices via a local I/O bus. In one embodiment, the logic of the memory controller hub  1816  is integrated within the processor. 
     Memory device  1820  can be a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, flash memory device, phase-change memory device, or some other memory device having suitable performance to serve as process memory. In one embodiment the memory device  1820  can operate as system memory for the system  1800 , to store data  1822  and instructions  1821  for use when the one or more processors  1802  executes an application or process. Memory controller hub  1816  also couples with an optional external graphics processor  1812 , which may communicate with the one or more graphics processors  1808  in processors  1802  to perform graphics and media operations. 
     In some embodiments, ICH  1830  enables peripherals to connect to memory device  1820  and processor  1802  via a high-speed I/O bus. The I/O peripherals include, but are not limited to, an audio controller  1846 , a firmware interface  1828 , a wireless transceiver  1826  (e.g., Wi-Fi, Bluetooth), a data storage device  1824  (e.g., hard disk drive, flash memory, etc.), and a legacy I/O controller  1840  for coupling legacy (e.g., Personal System 2 (PS/2)) devices to the system. One or more Universal Serial Bus (USB) controllers  1842  connect input devices, such as keyboard and mouse  1844  combinations. A network controller  1834  may also couple with ICH  1830 . In some embodiments, a high-performance network controller (not shown) couples with processor bus  1810 . It will be appreciated that the system  1800  shown is exemplary and not limiting, as other types of data processing systems that are differently configured may also be used. For example, the I/O controller hub  1830  may be integrated within the one or more processor  1802 , or the memory controller hub  1816  and I/O controller hub  1830  may be integrated into a discreet external graphics processor, such as the external graphics processor  1812 . 
       FIG. 19  is a block diagram of an embodiment of a processor  1900  having one or more processor cores  1902 A- 1902 N, an integrated memory controller  1914 , and an integrated graphics processor  1908 . Those elements of  FIG. 19  having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such. Processor  1900  can include additional cores up to and including additional core  1902 N represented by the dashed lined boxes. Each of processor cores  1902 A- 1902 N includes one or more internal cache units  1904 A- 1904 N. In some embodiments each processor core also has access to one or more shared cached units  1906 . 
     The internal cache units  1904 A- 1904 N and shared cache units  1906  represent a cache memory hierarchy within the processor  1900 . The cache memory hierarchy may include at least one level of instruction and data cache within each processor core and one or more levels of shared mid-level cache, such as a Level 2 (L2), Level 3 (L3), Level 4 (L4), or other levels of cache, where the highest level of cache before external memory is classified as the LLC. In some embodiments, cache coherency logic maintains coherency between the various cache units  1906  and  1904 A- 1904 N. 
     In some embodiments, processor  1900  may also include a set of one or more bus controller units  1916  and a system agent core  1910 . The one or more bus controller units  1916  manage a set of peripheral buses, such as one or more Peripheral Component Interconnect buses (e.g., PCI, PCI Express). System agent core  1910  provides management functionality for the various processor components. In some embodiments, system agent core  1910  includes one or more integrated memory controllers  1914  to manage access to various external memory devices (not shown). 
     In some embodiments, one or more of the processor cores  1902 A- 1902 N include support for simultaneous multi-threading. In such embodiment, the system agent core  1910  includes components for coordinating and operating cores  1902 A- 1902 N during multi-threaded processing. System agent core  1910  may additionally include a power control unit (PCU), which includes logic and components to regulate the power state of processor cores  1902 A- 1902 N and graphics processor  1908 . 
     In some embodiments, processor  1900  additionally includes graphics processor  1908  to execute graphics processing operations. In some embodiments, the graphics processor  1908  couples with the set of shared cache units  1906 , and the system agent core  1910 , including the one or more integrated memory controllers  1914 . In some embodiments, a display controller  1911  is coupled with the graphics processor  1908  to drive graphics processor output to one or more coupled displays. In some embodiments, display controller  1911  may be a separate module coupled with the graphics processor via at least one interconnect, or may be integrated within the graphics processor  1908  or system agent core  1910 . 
     In some embodiments, a ring based interconnect unit  1912  is used to couple the internal components of the processor  1900 . However, an alternative interconnect unit may be used, such as a point-to-point interconnect, a switched interconnect, or other techniques, including techniques well known in the art. In some embodiments, graphics processor  1908  couples with the ring interconnect  1912  via an I/O link  1913 . 
     The exemplary I/O link  1913  represents at least one of multiple varieties of I/O interconnects, including an on package I/O interconnect which facilitates communication between various processor components and a high-performance embedded memory module  1918 , such as an eDRAM module. In some embodiments, each of the processor cores  1902 A- 1902 N and graphics processor  1908  use embedded memory modules  1918  as a shared Last Level Cache. 
     In some embodiments, processor cores  1902 A- 1902 N are homogenous cores executing the same instruction set architecture. In another embodiment, processor cores  1902 A- 1902 N are heterogeneous in terms of instruction set architecture (ISA), where one or more of processor cores  1902 A- 1902 N execute a first instruction set, while at least one of the other cores executes a subset of the first instruction set or a different instruction set. In one embodiment processor cores  1902 A- 1902 N are heterogeneous in terms of microarchitecture, where one or more cores having a relatively higher power consumption couple with one or more power cores having a lower power consumption. Additionally, processor  1900  can be implemented on one or more chips or as an SoC integrated circuit having the illustrated components, in addition to other components. 
       FIG. 20  is a block diagram of a graphics processor  2000 , which may be a discrete graphics processing unit, or may be a graphics processor integrated with a plurality of processing cores. In some embodiments, the graphics processor communicates via a memory mapped I/O interface to registers on the graphics processor and with commands placed into the processor memory. In some embodiments, graphics processor  2000  includes a memory interface  2014  to access memory. Memory interface  2014  can be an interface to local memory, one or more internal caches, one or more shared external caches, and/or to system memory. 
     In some embodiments, graphics processor  2000  also includes a display controller  2002  to drive display output data to a display device  2020 . Display controller  2002  includes hardware for one or more overlay planes for the display and composition of multiple layers of video or user interface elements. In some embodiments, graphics processor  2000  includes a video codec engine  2006  to encode, decode, or transcode media to, from, or between one or more media encoding formats, including, but not limited to Moving Picture Experts Group (MPEG) formats such as MPEG-2, Advanced Video Coding (AVC) formats such as H.264/MPEG-4 AVC, as well as the Society of Motion Picture &amp; Television Engineers (SMPTE) 421MIVC-1, and Joint Photographic Experts Group (JPEG) formats such as JPEG, and Motion JPEG (MJPEG) formats. 
     In some embodiments, graphics processor  2000  includes a block image transfer (BLIT) engine  2004  to perform two-dimensional (2D) rasterizer operations including, for example, bit-boundary block transfers. However, in one embodiment, 2D graphics operations are performed using one or more components of graphics processing engine (GPE)  2010 . In some embodiments, GPE  2010  is a compute engine for performing graphics operations, including three-dimensional (3D) graphics operations and media operations. 
     In some embodiments, GPE  2010  includes a 3D pipeline  2012  for performing 3D operations, such as rendering three-dimensional images and scenes using processing functions that act upon 3D primitive shapes (e.g., rectangle, triangle, etc.). The 3D pipeline  2012  includes programmable and fixed function elements that perform various tasks within the element and/or spawn execution threads to a 3D/Media sub-system  2015 . While 3D pipeline  2012  can be used to perform media operations, an embodiment of GPE  2010  also includes a media pipeline  2016  that is specifically used to perform media operations, such as video post-processing and image enhancement. 
     In some embodiments, media pipeline  2016  includes fixed function or programmable logic units to perform one or more specialized media operations, such as video decode acceleration, video de-interlacing, and video encode acceleration in place of, or on behalf of video codec engine  2006 . In some embodiments, media pipeline  2016  additionally includes a thread spawning unit to spawn threads for execution on 3D/Media sub-system  2015 . The spawned threads perform computations for the media operations on one or more graphics execution units included in 3D/Media sub-system  2015 . 
     In some embodiments, 3D/Media subsystem  2015  includes logic for executing threads spawned by 3D pipeline  2012  and media pipeline  2016 . In one embodiment, the pipelines send thread execution requests to 3D/Media subsystem  2015 , which includes thread dispatch logic for arbitrating and dispatching the various requests to available thread execution resources. The execution resources include an array of graphics execution units to process the 3D and media threads. In some embodiments, 3D/Media subsystem  2015  includes one or more internal caches for thread instructions and data. In some embodiments, the subsystem also includes shared memory, including registers and addressable memory, to share data between threads and to store output data. 
     Graphics Processing Engine 
       FIG. 21  is a block diagram of a graphics processing engine  2110  of a graphics processor in accordance with some embodiments. In one embodiment, the graphics processing engine (GPE)  2110  is a version of the GPE  2010  shown in  FIG. 20 . Elements of  FIG. 21  having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such. For example, the 3D pipeline  2012  and media pipeline  2016  of  FIG. 20  are illustrated. The media pipeline  2116  is optional in some embodiments of the GPE  2110  and may not be explicitly included within the GPE  2110 . For example and in at least one embodiment, a separate media and/or image processor is coupled to the GPE  2110 . 
     In some embodiments, GPE  2110  couples with or includes a command streamer  2103 , which provides a command stream to the 3D pipeline  2112  and/or media pipelines  2016 . In some embodiments, command streamer  2103  is coupled with memory, which can be system memory, or one or more of internal cache memory and shared cache memory. In some embodiments, command streamer  2103  receives commands from the memory and sends the commands to 3D pipeline  2112  and/or media pipeline  2116 . The commands are directives fetched from a ring buffer, which stores commands for the 3D pipeline  2112  and media pipeline  2116 . In one embodiment, the ring buffer can additionally include batch command buffers storing batches of multiple commands. The commands for the 3D pipeline  2112  can also include references to data stored in memory, such as but not limited to vertex and geometry data for the 3D pipeline  2112  and/or image data and memory objects for the media pipeline  2116 . The 3D pipeline  2112  and media pipeline  2116  process the commands and data by performing operations via logic within the respective pipelines or by dispatching one or more execution threads to a graphics core array  2114 . 
     In various embodiments the 3D pipeline  2112  can execute one or more shader programs, such as vertex shaders, geometry shaders, pixel shaders, fragment shaders, compute shaders, or other shader programs, by processing the instructions and dispatching execution threads to the graphics core array  2114 . The graphics core array  2114  provides a unified block of execution resources. Multi-purpose execution logic (e.g., execution units) within the graphic core array  2114  includes support for various 3D API shader languages and can execute multiple simultaneous execution threads associated with multiple shaders. 
     In some embodiments the graphics core array  2114  also includes execution logic to perform media functions, such as video and/or image processing. In one embodiment, the execution units additionally include general-purpose logic that is programmable to perform parallel general purpose computational operations, in addition to graphics processing operations. The general purpose logic can perform processing operations in parallel or in conjunction with general purpose logic within the processor core(s)  1807  of  FIG. 18  or core  1902 A- 1902 N as in  FIG. 19 . 
     Output data generated by threads executing on the graphics core array  2114  can output data to memory in a unified return buffer (URB)  2118 . The URB  2118  can store data for multiple threads. In some embodiments the URB  2118  may be used to send data between different threads executing on the graphics core array  2114 . In some embodiments the URB  2118  may additionally be used for synchronization between threads on the graphics core array and fixed function logic within the shared function logic  2120 . 
     In some embodiments, graphics core array  2114  is scalable, such that the array includes a variable number of graphics cores, each having a variable number of execution units based on the target power and performance level of GPE  2110 . In one embodiment the execution resources are dynamically scalable, such that execution resources may be enabled or disabled as needed. 
     The graphics core array  2114  couples with shared function logic  2120  that includes multiple resources that are shared between the graphics cores in the graphics core array. The shared functions within the shared function logic  2120  are hardware logic units that provide specialized supplemental functionality to the graphics core array  2114 . In various embodiments, shared function logic  2120  includes but is not limited to sampler  2121 , math  2122 , and inter-thread communication (ITC)  2123  logic. Additionally, some embodiments implement one or more cache(s)  2125  within the shared function logic  2120 . A shared function is implemented where the demand for a given specialized function is insufficient for inclusion within the graphics core array  2114 . Instead a single instantiation of that specialized function is implemented as a stand-alone entity in the shared function logic  2120  and shared among the execution resources within the graphics core array  2114 . The precise set of functions that are shared between the graphics core array  2114  and included within the graphics core array  2114  varies between embodiments. 
       FIG. 22  is a block diagram of another embodiment of a graphics processor  2200 . Elements of  FIG. 22  having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such. 
     In some embodiments, graphics processor  2200  includes a ring interconnect  2202 , a pipeline front-end  2204 , a media engine  2237 , and graphics cores  2280 A- 2280 N. In some embodiments, ring interconnect  2202  couples the graphics processor to other processing units, including other graphics processors or one or more general-purpose processor cores. In some embodiments, the graphics processor is one of many processors integrated within a multi-core processing system. 
     In some embodiments, graphics processor  2200  receives batches of commands via ring interconnect  2202 . The incoming commands are interpreted by a command streamer  2203  in the pipeline front-end  2204 . In some embodiments, graphics processor  2200  includes scalable execution logic to perform 3D geometry processing and media processing via the graphics core(s)  2280 A- 2280 N. For 3D geometry processing commands, command streamer  2203  supplies commands to geometry pipeline  2236 . For at least some media processing commands, command streamer  2203  supplies the commands to a video front end  2234 , which couples with a media engine  2237 . In some embodiments, media engine  2237  includes a Video Quality Engine (VQE)  2230  for video and image post-processing and a multi-format encode/decode (MFX)  2233  engine to provide hardware-accelerated media data encode and decode. In some embodiments, geometry pipeline  2236  and media engine  2237  each generate execution threads for the thread execution resources provided by at least one graphics core  2280 A. 
     In some embodiments, graphics processor  2200  includes scalable thread execution resources featuring modular cores  2280 A- 2280 N (sometimes referred to as core slices), each having multiple sub-cores  2250 A- 2250 N,  2260 A- 2260 N (sometimes referred to as core sub-slices). In some embodiments, graphics processor  2200  can have any number of graphics cores  2280 A through  2280 N. In some embodiments, graphics processor  2200  includes a graphics core  2280 A having at least a first sub-core  2250 A and a second sub-core  2260 A. In other embodiments, the graphics processor is a low power processor with a single sub-core (e.g.,  2250 A). In some embodiments, graphics processor  2200  includes multiple graphics cores  2280 A- 2280 N, each including a set of first sub-cores  2250 A- 2250 N and a set of second sub-cores  2260 A- 2260 N. Each sub-core in the set of first sub-cores  2250 A- 2250 N includes at least a first set of execution units  2252 A- 2252 N and media/texture samplers  2254 A- 2254 N. Each sub-core in the set of second sub-cores  2260 A- 2260 N includes at least a second set of execution units  2262 A- 2262 N and samplers  2264 A- 2264 N. In some embodiments, each sub-core  2250 A- 2250 N,  2260 A- 2260 N shares a set of shared resources  2270 A- 2270 N. In some embodiments, the shared resources include shared cache memory and pixel operation logic. Other shared resources may also be included in the various embodiments of the graphics processor. 
     Execution Units 
       FIG. 23  illustrates thread execution logic  2300  including an array of processing elements employed in some embodiments of a GPE. Elements of  FIG. 23  having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such. 
     In some embodiments, thread execution logic  2300  includes a shader processor  2302 , a thread dispatcher  2304 , instruction cache  2306 , a scalable execution unit array including a plurality of execution units  2308 A- 2308 N, a sampler  2310 , a data cache  2312 , and a data port  2314 . In one embodiment the scalable execution unit array can dynamically scale by enabling or disabling one or more execution units (e.g., any of execution unit  2308 A,  2308 B,  2308 C,  2308 D, through  2308 N- 1  and  2308 N) based on the computational requirements of a workload. In one embodiment the included components are interconnected via an interconnect fabric that links to each of the components. In some embodiments, thread execution logic  2300  includes one or more connections to memory, such as system memory or cache memory, through one or more of instruction cache  2306 , data port  2314 , sampler  2310 , and execution units  2308 A- 2308 N. In some embodiments, each execution unit (e.g.  2308 A) is a stand-alone programmable general purpose computational unit that is capable of executing multiple simultaneous hardware threads while processing multiple data elements in parallel for each thread. In various embodiments, the array of execution units  2308 A- 2308 N is scalable to include any number individual execution units. 
     In some embodiments, the execution units  2308 A- 2308 N are primarily used to execute shader programs. A shader processor  2302  can process the various shader programs and dispatch execution threads associated with the shader programs via a thread dispatcher  2304 . In one embodiment the thread dispatcher includes logic to arbitrate thread initiation requests from the graphics and media pipelines and instantiate the requested threads on one or more execution unit in the execution units  2308 A- 2308 N. For example, the geometry pipeline (e.g.,  2236  of  FIG. 22 ) can dispatch vertex, tessellation, or geometry shaders to the thread execution logic  2300  ( FIG. 23 ) for processing. In some embodiments, thread dispatcher  2304  can also process runtime thread spawning requests from the executing shader programs. 
     In some embodiments, the execution units  2308 A- 2308 N support an instruction set that includes native support for many standard 3D graphics shader instructions, such that shader programs from graphics libraries (e.g., Direct 3D and OpenGL) are executed with a minimal translation. The execution units support vertex and geometry processing (e.g., vertex programs, geometry programs, vertex shaders), pixel processing (e.g., pixel shaders, fragment shaders) and general-purpose processing (e.g., compute and media shaders). Each of the execution units  2308 A- 2308 N is capable of multi-issue single instruction multiple data (SIMD) execution and multi-threaded operation enables an efficient execution environment in the face of higher latency memory accesses. Each hardware thread within each execution unit has a dedicated high-bandwidth register file and associated independent thread-state. Execution is multi-issue per clock to pipelines capable of integer, single and double precision floating point operations, SIMD branch capability, logical operations, transcendental operations, and other miscellaneous operations. While waiting for data from memory or one of the shared functions, dependency logic within the execution units  2308 A- 2308 N causes a waiting thread to sleep until the requested data has been returned. While the waiting thread is sleeping, hardware resources may be devoted to processing other threads. For example, during a delay associated with a vertex shader operation, an execution unit can perform operations for a pixel shader, fragment shader, or another type of shader program, including a different vertex shader. 
     Each execution unit in execution units  2308 A- 2308 N operates on arrays of data elements. The number of data elements is the “execution size,” or the number of channels for the instruction. An execution channel is a logical unit of execution for data element access, masking, and flow control within instructions. The number of channels may be independent of the number of physical Arithmetic Logic Units (ALUs) or Floating Point Units (FPUs) for a particular graphics processor. In some embodiments, execution units  2308 A- 2308 N support integer and floating-point data types. 
     The execution unit instruction set includes SIMD instructions. The various data elements can be stored as a packed data type in a register and the execution unit will process the various elements based on the data size of the elements. For example, when operating on a 256-bit wide vector, the 256 bits of the vector are stored in a register and the execution unit operates on the vector as four separate 64-bit packed data elements (Quad-Word (QW) size data elements), eight separate 32-bit packed data elements (Double Word (DW) size data elements), sixteen separate 16-bit packed data elements (Word (W) size data elements), or thirty-two separate 8-bit data elements (byte (B) size data elements). However, different vector widths and register sizes are possible. 
     One or more internal instruction caches (e.g.,  2306 ) are included in the thread execution logic  2300  to cache thread instructions for the execution units. In some embodiments, one or more data caches (e.g.,  2312 ) are included to cache thread data during thread execution. In some embodiments, a sampler  2310  is included to provide texture sampling for 3D operations and media sampling for media operations. In some embodiments, sampler  2310  includes specialized texture or media sampling functionality to process texture or media data during the sampling process before providing the sampled data to an execution unit. 
     During execution, the graphics and media pipelines send thread initiation requests to thread execution logic  2300  via thread spawning and dispatch logic. Once a group of geometric objects has been processed and rasterized into pixel data, pixel processor logic (e.g., pixel shader logic, fragment shader logic, etc.) within the shader processor  2302  is invoked to further compute output information and cause results to be written to output surfaces (e.g., color buffers, depth buffers, stencil buffers, etc.). In some embodiments, a pixel shader or fragment shader calculates the values of the various vertex attributes that are to be interpolated across the rasterized object. In some embodiments, pixel processor logic within the shader processor  2302  then executes an application programming interface (API)-supplied pixel or fragment shader program. To execute the shader program, the shader processor  2302  dispatches threads to an execution unit (e.g.,  2308 A) via thread dispatcher  2304 . In some embodiments, pixel shader  2302  uses texture sampling logic in the sampler  2310  to access texture data in texture maps stored in memory. Arithmetic operations on the texture data and the input geometry data compute pixel color data for each geometric fragment, or discards one or more pixels from further processing. 
     In some embodiments, the data port  2314  provides a memory access mechanism for the thread execution logic  2300  output processed data to memory for processing on a graphics processor output pipeline. In some embodiments, the data port  2314  includes or couples to one or more cache memories (e.g., data cache  2312 ) to cache data for memory access via the data port. 
       FIG. 24  is a block diagram illustrating a graphics processor instruction formats  2400  according to some embodiments. In one or more embodiment, the graphics processor execution units support an instruction set having instructions in multiple formats. The solid lined boxes illustrate the components that are generally included in an execution unit instruction, while the dashed lines include components that are optional or that are only included in a sub-set of the instructions. In some embodiments, instruction format  2400  described and illustrated are macro-instructions, in that they are instructions supplied to the execution unit, as opposed to micro-operations resulting from instruction decode once the instruction is processed. 
     In some embodiments, the graphics processor execution units natively support instructions in a 128-bit instruction format  2410 . A 64-bit compacted instruction format  2430  is available for some instructions based on the selected instruction, instruction options, and number of operands. The native 128-bit instruction format  2410  provides access to all instruction options, while some options and operations are restricted in the 64-bit format  2430 . The native instructions available in the 64-bit format  2430  vary by embodiment. In some embodiments, the instruction is compacted in part using a set of index values in an index field  2413 . The execution unit hardware references a set of compaction tables based on the index values and uses the compaction table outputs to reconstruct a native instruction in the 128-bit instruction format  2410 . 
     For each format, instruction opcode  2412  defines the operation that the execution unit is to perform. The execution units execute each instruction in parallel across the multiple data elements of each operand. For example, in response to an add instruction the execution unit performs a simultaneous add operation across each color channel representing a texture element or picture element. By default, the execution unit performs each instruction across all data channels of the operands. In some embodiments, instruction control field  2414  enables control over certain execution options, such as channels selection (e.g., predication) and data channel order (e.g., swizzle). For instructions in the 128-bit instruction format  2410  an exec-size field  2416  limits the number of data channels that will be executed in parallel. In some embodiments, exec-size field  2416  is not available for use in the 64-bit compact instruction format  2430 . 
     Some execution unit instructions have up to three operands including two source operands, src 0   2420 , src 1   2422 , and one destination  2418 . In some embodiments, the execution units support dual destination instructions, where one of the destinations is implied. Data manipulation instructions can have a third source operand (e.g., SRC 2   2424 ), where the instruction opcode  2412  determines the number of source operands. An instruction&#39;s last source operand can be an immediate (e.g., hard-coded) value passed with the instruction. 
     In some embodiments, the 128-bit instruction format  2410  includes an access/address mode field  2426  specifying, for example, whether direct register addressing mode or indirect register addressing mode is used. When direct register addressing mode is used, the register address of one or more operands is directly provided by bits in the instruction. 
     In some embodiments, the 128-bit instruction format  2410  includes an access/address mode field  2426 , which specifies an address mode and/or an access mode for the instruction. In one embodiment the access mode is used to define a data access alignment for the instruction. Some embodiments support access modes including a 16-byte aligned access mode and a 1-byte aligned access mode, where the byte alignment of the access mode determines the access alignment of the instruction operands. For example, when in a first mode, the instruction may use byte-aligned addressing for source and destination operands and when in a second mode, the instruction may use 16-byte-aligned addressing for all source and destination operands. 
     In one embodiment, the address mode portion of the access/address mode field  2426  determines whether the instruction is to use direct or indirect addressing. When direct register addressing mode is used bits in the instruction directly provide the register address of one or more operands. When indirect register addressing mode is used, the register address of one or more operands may be computed based on an address register value and an address immediate field in the instruction. 
     In some embodiments instructions are grouped based on opcode  2412  bit-fields to simplify Opcode decode  2440 . For an 8-bit opcode, bits  4 ,  5 , and  6  allow the execution unit to determine the type of opcode. The precise opcode grouping shown is merely an example. In some embodiments, a move and logic opcode group  2442  includes data movement and logic instructions (e.g., move (mov), compare (cmp)). In some embodiments, move and logic group  2442  shares the five most significant bits (MSB), where move (mov) instructions are in the form of 0000xxxxb and logic instructions are in the form of 0001xxxxb. A flow control instruction group  2444  (e.g., call, jump (jmp)) includes instructions in the form of 0010xxxxb (e.g., 0x20). A miscellaneous instruction group  2446  includes a mix of instructions, including synchronization instructions (e.g., wait, send) in the form of 0011xxxxb (e.g., 0x30). A parallel math instruction group  2448  includes component-wise arithmetic instructions (e.g., add, multiply (mul)) in the form of 0100xxxxb (e.g., 0x40). The parallel math group  2448  performs the arithmetic operations in parallel across data channels. The vector math group  2450  includes arithmetic instructions (e.g., dp4) in the form of 0101xxxxb (e.g., 0x50). The vector math group performs arithmetic such as dot product calculations on vector operands. 
     Graphics Pipeline 
       FIG. 25  is a block diagram of another embodiment of a graphics processor  2500 . Elements of  FIG. 25  having the same reference numbers (or names) as the elements of any other figure herein can operate or function in any manner similar to that described elsewhere herein, but are not limited to such. 
     In some embodiments, graphics processor  2500  includes a graphics pipeline  2520 , a media pipeline  2530 , a display engine  2540 , thread execution logic  2550 , and a render output pipeline  2570 . In some embodiments, graphics processor  2500  is a graphics processor within a multi-core processing system that includes one or more general purpose processing cores. The graphics processor is controlled by register writes to one or more control registers (not shown) or via commands issued to graphics processor  2500  via a ring interconnect  2502 . In some embodiments, ring interconnect  2502  couples graphics processor  2500  to other processing components, such as other graphics processors or general-purpose processors. Commands from ring interconnect  2502  are interpreted by a command streamer  2503 , which supplies instructions to individual components of graphics pipeline  2520  or media pipeline  2530 . 
     In some embodiments, command streamer  2503  directs the operation of a vertex fetcher  2505  that reads vertex data from memory and executes vertex-processing commands provided by command streamer  2503 . In some embodiments, vertex fetcher  2505  provides vertex data to a vertex shader  2507 , which performs coordinate space transformation and lighting operations to each vertex. In some embodiments, vertex fetcher  2505  and vertex shader  2507  execute vertex-processing instructions by dispatching execution threads to execution units  2552 A- 2552 B via a thread dispatcher  2531 . 
     In some embodiments, execution units  2552 A- 2552 B are an array of vector processors having an instruction set for performing graphics and media operations. In some embodiments, execution units  2552 A- 2552 B have an attached L1 cache  2551  that is specific for each array or shared between the arrays. The cache can be configured as a data cache, an instruction cache, or a single cache that is partitioned to contain data and instructions in different partitions. 
     In some embodiments, graphics pipeline  2520  includes tessellation components to perform hardware-accelerated tessellation of 3D objects. In some embodiments, a programmable hull shader  2511  configures the tessellation operations. A programmable domain shader  2517  provides back-end evaluation of tessellation output. A tessellator  2513  operates at the direction of hull shader  2511  and contains special purpose logic to generate a set of detailed geometric objects based on a coarse geometric model that is provided as input to graphics pipeline  2520 . In some embodiments, if tessellation is not used, tessellation components (e.g., hull shader  2511 , tessellator  2513 , and domain shader  2517 ) can be bypassed. 
     In some embodiments, complete geometric objects can be processed by a geometry shader  2519  via one or more threads dispatched to execution units  2552 A- 2552 B, or can proceed directly to the clipper  2529 . In some embodiments, the geometry shader operates on entire geometric objects, rather than vertices or patches of vertices as in previous stages of the graphics pipeline. If the tessellation is disabled the geometry shader  2519  receives input from the vertex shader  2507 . In some embodiments, geometry shader  2519  is programmable by a geometry shader program to perform geometry tessellation if the tessellation units are disabled. 
     Before rasterization, a clipper  2529  processes vertex data. The clipper  2529  may be a fixed function clipper or a programmable clipper having clipping and geometry shader functions. In some embodiments, a rasterizer and depth test component  2573  in the render output pipeline  2570  dispatches pixel shaders to convert the geometric objects into their per pixel representations. In some embodiments, pixel shader logic is included in thread execution logic  2550 . In some embodiments, an application can bypass the rasterizer and depth test component  2573  and access un-rasterized vertex data via a stream out unit  2523 . 
     The graphics processor  2500  has an interconnect bus, interconnect fabric, or some other interconnect mechanism that allows data and message passing amongst the major components of the processor. In some embodiments, execution units  2552 A- 2552 B and associated cache(s)  2551 , texture and media sampler  2554 , and texture/sampler cache  2558  interconnect via a data port  2556  to perform memory access and communicate with render output pipeline components of the processor. In some embodiments, sampler  2554 , caches  2551 ,  2558  and execution units  2552 A- 2552 B each have separate memory access paths. 
     In some embodiments, render output pipeline  2570  contains a rasterizer and depth test component  2573  that converts vertex-based objects into an associated pixel-based representation. In some embodiments, the rasterizer logic includes a windower/masker unit to perform fixed function triangle and line rasterization. An associated render cache  2578  and depth cache  2579  are also available in some embodiments. A pixel operations component  2577  performs pixel-based operations on the data, though in some instances, pixel operations associated with 2D operations (e.g. bit block image transfers with blending) are performed by the 2D engine  2541 , or substituted at display time by the display controller  2543  using overlay display planes. In some embodiments, a shared L3 cache  2575  is available to all graphics components, allowing the sharing of data without the use of main system memory. 
     In some embodiments, graphics processor media pipeline  2530  includes a media engine  2537  and a video front end  2534 . In some embodiments, video front end  2534  receives pipeline commands from the command streamer  2503 . In some embodiments, media pipeline  2530  includes a separate command streamer. In some embodiments, video front-end  2534  processes media commands before sending the command to the media engine  2537 . In some embodiments, media engine  2537  includes thread spawning functionality to spawn threads for dispatch to thread execution logic  2550  via thread dispatcher  2531 . 
     In some embodiments, graphics processor  2500  includes a display engine  2540 . In some embodiments, display engine  2540  is external to processor  2500  and couples with the graphics processor via the ring interconnect  2502 , or some other interconnect bus or fabric. In some embodiments, display engine  2540  includes a 2D engine  2541  and a display controller  2543 . In some embodiments, display engine  2540  contains special purpose logic capable of operating independently of the 3D pipeline. In some embodiments, display controller  2543  couples with a display device (not shown), which may be a system integrated display device, as in a laptop computer, or an external display device attached via a display device connector. 
     In some embodiments, graphics pipeline  2520  and media pipeline  2530  are configurable to perform operations based on multiple graphics and media programming interfaces and are not specific to any one application programming interface (API). In some embodiments, driver software for the graphics processor translates API calls that are specific to a particular graphics or media library into commands that can be processed by the graphics processor. In some embodiments, support is provided for the Open Graphics Library (OpenGL), Open Computing Language (OpenCL), and/or Vulkan graphics and compute API, all from the Khronos Group. In some embodiments, support may also be provided for the Direct3D library from the Microsoft Corporation. In some embodiments, a combination of these libraries may be supported. Support may also be provided for the Open Source Computer Vision Library (OpenCV). A future API with a compatible 3D pipeline would also be supported if a mapping can be made from the pipeline of the future API to the pipeline of the graphics processor. 
     Graphics Pipeline Programming 
       FIG. 26A  is a block diagram illustrating a graphics processor command format  2600  according to some embodiments.  FIG. 26B  is a block diagram illustrating a graphics processor command sequence  2610  according to an embodiment. The solid lined boxes in  FIG. 26A  illustrate the components that are generally included in a graphics command while the dashed lines include components that are optional or that are only included in a sub-set of the graphics commands. The exemplary graphics processor command format  2600  of  FIG. 26A  includes data fields to identify a target client  2602  of the command, a command operation code (opcode)  2604 , and the relevant data  2606  for the command. A sub-opcode  2605  and a command size  2608  are also included in some commands. 
     In some embodiments, client  2602  specifies the client unit of the graphics device that processes the command data. In some embodiments, a graphics processor command parser examines the client field of each command to condition the further processing of the command and route the command data to the appropriate client unit. In some embodiments, the graphics processor client units include a memory interface unit, a render unit, a 2D unit, a 3D unit, and a media unit. Each client unit has a corresponding processing pipeline that processes the commands. Once the command is received by the client unit, the client unit reads the opcode  2604  and, if present, sub-opcode  2605  to determine the operation to perform. The client unit performs the command using information in data field  2606 . For some commands an explicit command size  2608  is expected to specify the size of the command. In some embodiments, the command parser automatically determines the size of at least some of the commands based on the command opcode. In some embodiments commands are aligned via multiples of a double word. 
     The flow diagram in  FIG. 26B  shows an exemplary graphics processor command sequence  2610 . In some embodiments, software or firmware of a data processing system that features an embodiment of a graphics processor uses a version of the command sequence shown to set up, execute, and terminate a set of graphics operations. A sample command sequence is shown and described for purposes of example only as embodiments are not limited to these specific commands or to this command sequence. Moreover, the commands may be issued as batch of commands in a command sequence, such that the graphics processor will process the sequence of commands in at least partially concurrence. 
     In some embodiments, the graphics processor command sequence  2610  may begin with a pipeline flush command  2612  to cause any active graphics pipeline to complete the currently pending commands for the pipeline. In some embodiments, the 3D pipeline  2622  and the media pipeline  2624  do not operate concurrently. The pipeline flush is performed to cause the active graphics pipeline to complete any pending commands. In response to a pipeline flush, the command parser for the graphics processor will pause command processing until the active drawing engines complete pending operations and the relevant read caches are invalidated. Optionally, any data in the render cache that is marked ‘dirty’ can be flushed to memory. In some embodiments, pipeline flush command  2612  can be used for pipeline synchronization or before placing the graphics processor into a low power state. 
     In some embodiments, a pipeline select command  2613  is used when a command sequence requires the graphics processor to explicitly switch between pipelines. In some embodiments, a pipeline select command  2613  is required only once within an execution context before issuing pipeline commands unless the context is to issue commands for both pipelines. In some embodiments, a pipeline flush command  2612  is required immediately before a pipeline switch via the pipeline select command  2613 . 
     In some embodiments, a pipeline control command  2614  configures a graphics pipeline for operation and is used to program the 3D pipeline  2622  and the media pipeline  2624 . In some embodiments, pipeline control command  2614  configures the pipeline state for the active pipeline. In one embodiment, the pipeline control command  2614  is used for pipeline synchronization and to clear data from one or more cache memories within the active pipeline before processing a batch of commands. 
     In some embodiments, return buffer state commands  2616  are used to configure a set of return buffers for the respective pipelines to write data. Some pipeline operations require the allocation, selection, or configuration of one or more return buffers into which the operations write intermediate data during processing. In some embodiments, the graphics processor also uses one or more return buffers to store output data and to perform cross thread communication. In some embodiments, the return buffer state  2616  includes selecting the size and number of return buffers to use for a set of pipeline operations. 
     The remaining commands in the command sequence differ based on the active pipeline for operations. Based on a pipeline determination  2620 , the command sequence is tailored to the 3D pipeline  2622  beginning with the 3D pipeline state  2630  or the media pipeline  2624  beginning at the media pipeline state  2640 . 
     The commands to configure the 3D pipeline state  2630  include 3D state setting commands for vertex buffer state, vertex element state, constant color state, depth buffer state, and other state variables that are to be configured before 3D primitive commands are processed. The values of these commands are determined at least in part based on the particular 3D API in use. In some embodiments, 3D pipeline state  2630  commands are also able to selectively disable or bypass certain pipeline elements if those elements will not be used. 
     In some embodiments, 3D primitive  2632  command is used to submit 3D primitives to be processed by the 3D pipeline. Commands and associated parameters that are passed to the graphics processor via the 3D primitive  2632  command are forwarded to the vertex fetch function in the graphics pipeline. The vertex fetch function uses the 3D primitive  2632  command data to generate vertex data structures. The vertex data structures are stored in one or more return buffers. In some embodiments, 3D primitive  2632  command is used to perform vertex operations on 3D primitives via vertex shaders. To process vertex shaders, 3D pipeline  2622  dispatches shader execution threads to graphics processor execution units. 
     In some embodiments, 3D pipeline  2622  is triggered via an execute  2634  command or event. In some embodiments, a register write triggers command execution. In some embodiments execution is triggered via a ‘go’ or ‘kick’ command in the command sequence. In one embodiment, command execution is triggered using a pipeline synchronization command to flush the command sequence through the graphics pipeline. The 3D pipeline will perform geometry processing for the 3D primitives. Once operations are complete, the resulting geometric objects are rasterized and the pixel engine colors the resulting pixels. Additional commands to control pixel shading and pixel back end operations may also be included for those operations. 
     In some embodiments, the graphics processor command sequence  2610  follows the media pipeline  2624  path when performing media operations. In general, the specific use and manner of programming for the media pipeline  2624  depends on the media or compute operations to be performed. Specific media decode operations may be offloaded to the media pipeline during media decode. In some embodiments, the media pipeline can also be bypassed and media decode can be performed in whole or in part using resources provided by one or more general purpose processing cores. In one embodiment, the media pipeline also includes elements for general-purpose graphics processor unit (GPGPU) operations, where the graphics processor is used to perform SIMD vector operations using computational shader programs that are not explicitly related to the rendering of graphics primitives. 
     In some embodiments, media pipeline  2624  is configured in a similar manner as the 3D pipeline  2622 . A set of commands to configure the media pipeline state  2640  are dispatched or placed into a command queue before the media object commands  2642 . In some embodiments, media pipeline state commands  2640  include data to configure the media pipeline elements that will be used to process the media objects. This includes data to configure the video decode and video encode logic within the media pipeline, such as encode or decode format. In some embodiments, media pipeline state commands  2640  also support the use of one or more pointers to “indirect” state elements that contain a batch of state settings. 
     In some embodiments, media object commands  2642  supply pointers to media objects for processing by the media pipeline. The media objects include memory buffers containing video data to be processed. In some embodiments, all media pipeline states must be valid before issuing a media object command  2642 . Once the pipeline state is configured and media object commands  2642  are queued, the media pipeline  2624  is triggered via an execute command  2644  or an equivalent execute event (e.g., register write). Output from media pipeline  2624  may then be post processed by operations provided by the 3D pipeline  2622  or the media pipeline  2624 . In some embodiments, GPGPU operations are configured and executed in a similar manner as media operations. 
     Graphics Software Architecture 
       FIG. 27  illustrates exemplary graphics software architecture for a data processing system  2700  according to some embodiments. In some embodiments, software architecture includes a 3D graphics application  2710 , an operating system  2720 , and at least one processor  2730 . In some embodiments, processor  2730  includes a graphics processor  2732  and one or more general-purpose processor core(s)  2734 . The graphics application  2710  and operating system  2720  each execute in the system memory  2750  of the data processing system. 
     In some embodiments, 3D graphics application  2710  contains one or more shader programs including shader instructions  2712 . The shader language instructions may be in a high-level shader language, such as the High Level Shader Language (HLSL) or the OpenGL Shader Language (GLSL). The application also includes executable instructions  2714  in a machine language suitable for execution by the general-purpose processor core  2734 . The application also includes graphics objects  2716  defined by vertex data. 
     In some embodiments, operating system  2720  is a Microsoft® Windows® operating system from the Microsoft Corporation, a proprietary UNIX-like operating system, or an open source UNIX-like operating system using a variant of the Linux kernel. The operating system  2720  can support a graphics API  2722  such as the Direct3D API, the OpenGL API, or the Vulkan API. When the Direct3D API is in use, the operating system  2720  uses a front-end shader compiler  2724  to compile any shader instructions  2712  in HLSL into a lower-level shader language. The compilation may be a just-in-time (JIT) compilation or the application can perform shader pre-compilation. In some embodiments, high-level shaders are compiled into low-level shaders during the compilation of the 3D graphics application  2710 . In some embodiments, the shader instructions  2712  are provided in an intermediate form, such as a version of the Standard Portable Intermediate Representation (SPIR) used by the Vulkan API. 
     In some embodiments, user mode graphics driver  2726  contains a back-end shader compiler  2727  to convert the shader instructions  2712  into a hardware specific representation. When the OpenGL API is in use, shader instructions  2712  in the GLSL high-level language are passed to a user mode graphics driver  2726  for compilation. In some embodiments, user mode graphics driver  2726  uses operating system kernel mode functions  2728  to communicate with a kernel mode graphics driver  2729 . In some embodiments, kernel mode graphics driver  2729  communicates with graphics processor  2732  to dispatch commands and instructions. 
     IP Core Implementations 
     One or more aspects of at least one embodiment may be implemented by representative code stored on a machine-readable medium which represents and/or defines logic within an integrated circuit such as a processor. For example, the machine-readable medium may include instructions which represent various logic within the processor. When read by a machine, the instructions may cause the machine to fabricate the logic to perform the techniques described herein. Such representations, known as “IP cores,” are reusable units of logic for an integrated circuit that may be stored on a tangible, machine-readable medium as a hardware model that describes the structure of the integrated circuit. The hardware model may be supplied to various customers or manufacturing facilities, which load the hardware model on fabrication machines that manufacture the integrated circuit. The integrated circuit may be fabricated such that the circuit performs operations described in association with any of the embodiments described herein. 
       FIG. 28  is a block diagram illustrating an IP core development system  2800  that may be used to manufacture an integrated circuit to perform operations according to an embodiment. The IP core development system  2800  may be used to generate modular, reusable designs that can be incorporated into a larger design or used to construct an entire integrated circuit (e.g., an SOC integrated circuit). A design facility  2830  can generate a software simulation  2810  of an IP core design in a high level programming language (e.g., C/C++). The software simulation  2810  can be used to design, test, and verify the behavior of the IP core using a simulation model  2812 . The simulation model  2812  may include functional, behavioral, and/or timing simulations. A register transfer level (RTL) design  2815  can then be created or synthesized from the simulation model  2812 . The RTL design  2815  is an abstraction of the behavior of the integrated circuit that models the flow of digital signals between hardware registers, including the associated logic performed using the modeled digital signals. In addition to an RTL design  2815 , lower-level designs at the logic level or transistor level may also be created, designed, or synthesized. Thus, the particular details of the initial design and simulation may vary. 
     The RTL design  2815  or equivalent may be further synthesized by the design facility into a hardware model  2820 , which may be in a hardware description language (HDL), or some other representation of physical design data. The HDL may be further simulated or tested to verify the IP core design. The IP core design can be stored for delivery to a 3 rd  party fabrication facility  2865  using non-volatile memory  2840  (e.g., hard disk, flash memory, or any non-volatile storage medium). Alternatively, the IP core design may be transmitted (e.g., via the Internet) over a wired connection  2850  or wireless connection  2860 . The fabrication facility  2865  may then fabricate an integrated circuit that is based at least in part on the IP core design. The fabricated integrated circuit can be configured to perform operations in accordance with at least one embodiment described herein. 
     Exemplary System on a Chip Integrated Circuit 
       FIGS. 29-31  illustrated exemplary integrated circuits and associated graphics processors that may be fabricated using one or more IP cores, according to various embodiments described herein. In addition to what is illustrated, other logic and circuits may be included, including additional graphics processors/cores, peripheral interface controllers, or general purpose processor cores. 
       FIG. 29  is a block diagram illustrating an exemplary system on a chip integrated circuit  2900  that may be fabricated using one or more IP cores, according to an embodiment. Exemplary integrated circuit  2900  includes one or more application processor(s)  2905  (e.g., CPUs), at least one graphics processor  2910 , and may additionally include an image processor  2915  and/or a video processor  2920 , any of which may be a modular IP core from the same or multiple different design facilities. Integrated circuit  2900  includes peripheral or bus logic including a USB controller  2925 , UART controller  2930 , an SPI/SDIO controller  2935 , and an I 2 S/I 2 C controller  2940 . Additionally, the integrated circuit can include a display device  2945  coupled to one or more of a high-definition multimedia interface (HDMI) controller  2950  and a mobile industry processor interface (MIPI) display interface  2955 . Storage may be provided by a flash memory subsystem  2960  including flash memory and a flash memory controller. Memory interface may be provided via a memory controller  2965  for access to SDRAM or SRAM memory devices. Some integrated circuits additionally include an embedded security engine  2970 . 
       FIG. 30  is a block diagram illustrating an exemplary graphics processor  3010  of a system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. Graphics processor  3010  can be a variant of the graphics processor  2910  of  FIG. 29 . Graphics processor  3010  includes a vertex processor  3005  and one or more fragment processor(s)  3015 A- 3015 N (e.g.,  3015 A,  3015 B,  3015 C,  3015 D, through  3015 N- 1 , and  3015 N). Graphics processor  3010  can execute different shader programs via separate logic, such that the vertex processor  3005  is optimized to execute operations for vertex shader programs, while the one or more fragment processor(s)  3015 A- 3015 N execute fragment (e.g., pixel) shading operations for fragment or pixel shader programs. The vertex processor  3005  performs the vertex processing stage of the 3D graphics pipeline and generates primitives and vertex data. The fragment processor(s)  3015 A- 3015 N use the primitive and vertex data generated by the vertex processor  3005  to produce a framebuffer that is displayed on a display device. In one embodiment, the fragment processor(s)  3015 A- 3015 N are optimized to execute fragment shader programs as provided for in the OpenGL API, which may be used to perform similar operations as a pixel shader program as provided for in the Direct 3D API. 
     Graphics processor  3010  additionally includes one or more memory management units (MMUs)  3020 A- 3020 B, cache(s)  3025 A- 3025 B, and circuit interconnect(s)  3030 A- 3030 B. The one or more MMU(s)  3020 A- 3020 B provide for virtual to physical address mapping for integrated circuit  3010 , including for the vertex processor  3005  and/or fragment processor(s)  3015 A- 3015 N, which may reference vertex or image/texture data stored in memory, in addition to vertex or image/texture data stored in the one or more cache(s)  3025 A- 3025 B. In one embodiment the one or more MMU(s)  3025 A- 3025 B may be synchronized with other MMUs within the system, including one or more MMUs associated with the one or more application processor(s)  2905 , image processor  2915 , and/or video processor  2920  of  FIG. 29 , such that each processor  2905 - 2920  can participate in a shared or unified virtual memory system. The one or more circuit interconnect(s)  3030 A- 3030 B enable graphics processor  3010  to interface with other IP cores within the SoC, either via an internal bus of the SoC or via a direct connection, according to embodiments. 
       FIG. 31  is a block diagram illustrating an additional exemplary graphics processor  3110  of a system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. Graphics processor  3110  can be a variant of the graphics processor  2910  of  FIG. 29 . Graphics processor  3110  includes the one or more MMU(s)  3020 A- 3020 B, caches  3025 A- 3025 B, and circuit interconnects  3030 A- 3030 B of the integrated circuit  3000  of  FIG. 30 . 
     Graphics processor  3110  includes one or more shader core(s)  3115 A- 3115 N (e.g.,  3115 A,  3115 B,  3115 C,  3115 D,  3115 E,  3115 F, through  3015 N- 1 , and  3015 N), which provides for a unified shader core architecture in which a single core or type or core can execute all types of programmable shader code, including shader program code to implement vertex shaders, fragment shaders, and/or compute shaders. The exact number of shader cores present can vary among embodiments and implementations. Additionally, graphics processor  3110  includes an inter-core task manager  3105 , which acts as a thread dispatcher to dispatch execution threads to one or more shader cores  3115 A- 3115 N and a tiling unit  3118  to accelerate tiling operations for tile-based rendering, in which rendering operations for a scene are subdivided in image space, for example to exploit local spatial coherence within a scene or to optimize use of internal caches. 
     The following examples pertain to further embodiments. 
     In one example, an apparatus comprises: a repeater to receive an input signal at an input node and output an output signal at an output node; a dynamic header device coupled between the repeater and a supply voltage node, the dynamic header device to be dynamically controlled by a feedback device; and the feedback device coupled between the output node and the dynamic header device, the feedback device to dynamically control the dynamic header device based at least in part on the output signal. 
     In an example, the feedback device is to cause the dynamic header device to transition into a saturation region in response to a first transition in the output signal. 
     In an example, the repeater comprises a first inverter and a second inverter. The first inverter may include: a first transistor of a first polarity having a gate terminal to receive the input signal, a first terminal coupled to the supply voltage node and a second terminal coupled to an inter-inverter node; and a first transistor of a second polarity having a gate terminal to receive the input signal and a second terminal coupled to the inter-inverter node. The second inverter may include: a second transistor of the first polarity having a gate terminal coupled to the inter-inverter node and a second terminal coupled to an output node; and a second transistor of the second polarity having a gate terminal coupled to the inter-inverter node, a first terminal coupled to the reference voltage node, and a second terminal coupled to the output node. 
     In an example, the dynamic header device comprises a third transistor of the first polarity having a gate terminal coupled to the feedback device, a first terminal coupled to the supply voltage node and a second terminal coupled to an intermediate node. 
     In an example, the second transistor of the first polarity has a first terminal coupled to the intermediate node. 
     In an example, the feedback device comprises: a third transistor of the second polarity having a gate terminal coupled to the inter-inverter node, a first terminal coupled to the output node and a second terminal coupled to the dynamic header device; and a fourth transistor of the first polarity having a gate terminal coupled to a reference voltage node, a first terminal coupled to the output node and a second terminal coupled to the dynamic header device. 
     In an example, the feedback device further comprises a fourth transistor of the second polarity having a gate terminal coupled to the inter-inverter node and first and second terminals coupled to the dynamic header device. 
     In an example, the feedback device further comprises a fifth transistor of the first polarity coupled between the third transistor of the second polarity and the dynamic header device and to be dynamically configured with a diode connection based on a first value of a second control signal, the second control signal to be received from a power controller. 
     In an example, the feedback device comprises: a first plurality of transistors of the first polarity stacked between the output node and the dynamic header device; and a second plurality of transistors of the second polarity stacked between the output node and the dynamic header device. 
     In an example, the first plurality of transistors of the first polarity have gate terminals coupled to a reference voltage node and the second plurality of transistors of the second polarity have gate terminals coupled to the inter-inverter node. 
     In an example, the output signal has a lower voltage swing than the input signal. 
     In an example, the lower voltage swing comprises a threshold voltage of the dynamic header device. 
     In an example, the apparatus comprises an interconnect driver having a reduced voltage swing, where the interconnect driver is to couple to a single supply voltage via the supply voltage node. 
     In another example, a method comprises: determining, in a power controller of a processor, an operating voltage for at least one circuit portion of the processor; causing the at least one circuit portion to operate at a performance state associated with the operating voltage; comparing the operating voltage to a threshold level; and sending a control signal to a feedback device of an interconnect driver based at least in part on the comparison. 
     In an example, the feedback device is to control a dynamic header device coupled between a repeater of the interconnect driver and a supply voltage node. 
     In an example, the method further comprises sending the control signal with a first value in response to determining that the operating voltage exceeds the threshold level, where in response to the control signal with the first value, the feedback device is to have a first configuration. 
     In an example, the method further comprises sending the control signal with a second value in response to determining that the operating voltage is less than the threshold level, where in response to the control signal with the second value, the feedback device is to have a second configuration. 
     In another example, a computer readable medium including instructions is to perform the method of any of the above examples. 
     In another example, a computer readable medium including data is to be used by at least one machine to fabricate at least one integrated circuit to perform the method of any one of the above examples. 
     In another example, an apparatus comprises means for performing the method of any one of the above examples. 
     In yet another embodiment, a processor includes at least one core and at least one graphics processor having at least one interconnect driver to drive an output signal to an interconnect. In an example, the at least one interconnect driver comprises: a first repeater to receive an input signal at an input node and output an output signal at an output node, the repeater including a first inverter and a second inverter; a dynamic header device coupled between the second inverter and a supply voltage node; and a feedback device to dynamically control the dynamic header device based at least in part on the output signal, to enable the output signal to be communicated along at least a portion of the interconnect with a reduced output swing. The processor may further include a power controller to control power consumption of the processor. 
     In an example, the feedback device is to cause the dynamic header device to transition into a saturation region in response to a first transition in the output signal, where in the saturation region, the dynamic header device is to cause the output signal at the output node to have the reduced output swing corresponding to a threshold voltage of the dynamic header device. 
     In an example, the power controller is, when an operating voltage exceeds a threshold level, to send a control signal to the interconnect driver to cause the feedback device to have a first configuration, to enable the dynamic header device to enter into a saturation region when the output signal exceeds a plurality of threshold voltages. 
     In yet another example, an apparatus comprises: repeater means for receiving an input signal at an input node and output an output signal at an output node; dynamic header means coupled between the repeater means and a supply voltage node, the dynamic header means for being dynamically controlled by a feedback means; and the feedback means coupled between the output node and the dynamic header means, the feedback means for dynamically controlling the dynamic header means based at least in part on the output signal. 
     In an example, the feedback means for causing the dynamic header means for transitioning into a saturation region in response to a first transition in the output signal. 
     In an example, the output signal has a lower voltage swing than the input signal. 
     In an example, the lower voltage swing comprises a threshold voltage of the dynamic header means. 
     In an example, the apparatus comprises an interconnect driver means having a reduced voltage swing, where the interconnect driver means is to couple to a single supply voltage via the supply voltage node. 
     Understand that various combinations of the above examples are possible. 
     Note that the terms “circuit” and “circuitry” are used interchangeably herein. As used herein, these terms and the term “logic” are used to refer to alone or in any combination, analog circuitry, digital circuitry, hard wired circuitry, programmable circuitry, processor circuitry, microcontroller circuitry, hardware logic circuitry, state machine circuitry and/or any other type of physical hardware component. Embodiments may be used in many different types of systems. For example, in one embodiment a communication device can be arranged to perform the various methods and techniques described herein. Of course, the scope of the present invention is not limited to a communication device, and instead other embodiments can be directed to other types of apparatus for processing instructions, or one or more machine readable media including instructions that in response to being executed on a computing device, cause the device to carry out one or more of the methods and techniques described herein. 
     Embodiments may be implemented in code and may be stored on a non-transitory storage medium having stored thereon instructions which can be used to program a system to perform the instructions. Embodiments also may be implemented in data and may be stored on a non-transitory storage medium, which if used by at least one machine, causes the at least one machine to fabricate at least one integrated circuit to perform one or more operations. Still further embodiments may be implemented in a computer readable storage medium including information that, when manufactured into a SoC or other processor, is to configure the SoC or other processor to perform one or more operations. The storage medium may include, but is not limited to, any type of disk including floppy disks, optical disks, solid state drives (SSDs), 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. 
     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.