Patent Publication Number: US-2022222886-A1

Title: Apparatus and method for implementing bounding volume hierarchy (bvh) operations on tesselation hardware

Description:
BACKGROUND 
     Field of the Invention 
     This invention relates generally to the field of graphics processors. More particularly, the invention relates to an apparatus and method for implementing bounding volume hierarchy operations on tessellation hardware. 
     Description of the Related Art 
     Ray tracing is a graphics rendering technique that is becoming increasingly popular in a number of applications and contexts. For example, ray tracing may be used to compute a global illumination solution for a graphics scene. In general, ray tracing may be used in computer graphics to determine visibility by directing one or more rays from a vantage point described by the ray&#39;s position vector along a line of sight described by the ray&#39;s direction vector. To determine the nearest visible surface along that line of sight requires that the ray to be effectively tested for intersection against all of the geometry within the virtual scene and retain the nearest intersection. 
     However, determining the intersections of each ray with the geometries of a scene may be computationally complex and resource intensive, thereby limiting a real-time ray tracing solution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which: 
         FIG. 1  is a block diagram of an embodiment of a computer system with a processor having one or more processor cores and graphics processors; 
         FIG. 2  is a block diagram of one embodiment of a processor having one or more processor cores, an integrated memory controller, and an integrated graphics processor; 
         FIG. 3  is a block diagram of one embodiment of a graphics processor which may be a discreet graphics processing unit, or may be graphics processor integrated with a plurality of processing cores; 
         FIG. 4  is a block diagram of an embodiment of a graphics-processing engine for a graphics processor; 
         FIG. 5  is a block diagram of another embodiment of a graphics processor; 
         FIG. 6  is a block diagram of thread execution logic including an array of processing elements; 
         FIG. 7  illustrates a graphics processor execution unit instruction format according to an embodiment; 
         FIG. 8  is a block diagram of another embodiment of a graphics processor which includes a graphics pipeline, a media pipeline, a display engine, thread execution logic, and a render output pipeline; 
         FIG. 9A  is a block diagram illustrating a graphics processor command format according to an embodiment; 
         FIG. 9B  is a block diagram illustrating a graphics processor command sequence according to an embodiment; 
         FIG. 10  illustrates exemplary graphics software architecture for a data processing system according to an embodiment; 
         FIG. 11  illustrates an exemplary IP core development system that may be used to manufacture an integrated circuit to perform operations according to an embodiment; 
         FIG. 12  illustrates an exemplary system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment; 
         FIG. 13  illustrates an exemplary graphics processor of a system on a chip integrated circuit that may be fabricated using one or more IP cores; 
         FIG. 14  illustrates an additional exemplary graphics processor of a system on a chip integrated circuit that may be fabricated using one or more IP cores 
         FIG. 15  illustrates one embodiment in which a tessellation unit generates a bounding volume hierarchy (BVH); 
         FIG. 16  illustrates a mapping of an exemplary set of primitives and a concurrently-generated BVH; 
         FIG. 17  illustrates one embodiment which uses the BVH to test the input surface and its primitives for intersection with a set of N rays before tessellation; 
         FIG. 18  illustrates a method in accordance with one embodiment of the invention; 
         FIG. 19  is a block diagram illustrating a computer system configured to implement one or more aspects of the embodiments described herein; 
         FIG. 20A-20D  illustrate a parallel processor components, according to an embodiment; 
         FIGS. 21A-21B  are block diagrams of graphics multiprocessors, according to embodiments; 
         FIG. 22A-22F  illustrate an exemplary architecture in which a plurality of GPUs are communicatively coupled to a plurality of multi-core processors; and 
         FIG. 23  illustrates a graphics processing pipeline, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described below. It will be apparent, however, to one skilled in the art that the embodiments of the invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid obscuring the underlying principles of the embodiments of the invention. 
     Exemplary Graphics Processor Architectures and Data Types 
     System Overview 
       FIG. 1  is a block diagram of a processing system  100 , according to an embodiment. In various embodiments the system  100  includes one or more processors  102  and one or more graphics processors  108 , and may be a single processor desktop system, a multiprocessor workstation system, or a server system having a large number of processors  102  or processor cores  107 . In one embodiment, the system  100  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  100  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  100  is a mobile phone, smart phone, tablet computing device or mobile Internet device. Data processing system  100  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  100  is a television or set top box device having one or more processors  102  and a graphical interface generated by one or more graphics processors  108 . 
     In some embodiments, the one or more processors  102  each include one or more processor cores  107  to process instructions which, when executed, perform operations for system and user software. In some embodiments, each of the one or more processor cores  107  is configured to process a specific instruction set  109 . In some embodiments, instruction set  109  may facilitate Complex Instruction Set Computing (CISC), Reduced Instruction Set Computing (RISC), or computing via a Very Long Instruction Word (VLIW). Multiple processor cores  107  may each process a different instruction set  109 , which may include instructions to facilitate the emulation of other instruction sets. Processor core  107  may also include other processing devices, such a Digital Signal Processor (DSP). 
     In some embodiments, the processor  102  includes cache memory  104 . Depending on the architecture, the processor  102  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  102 . In some embodiments, the processor  102  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  107  using known cache coherency techniques. A register file  106  is additionally included in processor  102  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  102 . 
     In some embodiments, processor  102  is coupled with a processor bus  110  to transmit communication signals such as address, data, or control signals between processor  102  and other components in system  100 . In one embodiment the system  100  uses an exemplary ‘hub’ system architecture, including a memory controller hub  116  and an Input Output (I/O) controller hub  130 . A memory controller hub  116  facilitates communication between a memory device and other components of system  100 , while an I/O Controller Hub (ICH)  130  provides connections to I/O devices via a local I/O bus. In one embodiment, the logic of the memory controller hub  116  is integrated within the processor. 
     Memory device  120  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  120  can operate as system memory for the system  100 , to store data  122  and instructions  121  for use when the one or more processors  102  executes an application or process. Memory controller hub  116  also couples with an optional external graphics processor  112 , which may communicate with the one or more graphics processors  108  in processors  102  to perform graphics and media operations. 
     In some embodiments, ICH  130  enables peripherals to connect to memory device  120  and processor  102  via a high-speed I/O bus. The I/O peripherals include, but are not limited to, an audio controller  146 , a firmware interface  128 , a wireless transceiver  126  (e.g., Wi-Fi, Bluetooth), a data storage device  124  (e.g., hard disk drive, flash memory, etc.), and a legacy I/O controller  140  for coupling legacy (e.g., Personal System 2 (PS/2)) devices to the system. One or more Universal Serial Bus (USB) controllers  142  connect input devices, such as keyboard and mouse  144  combinations. A network controller  134  may also couple with ICH  130 . In some embodiments, a high-performance network controller (not shown) couples with processor bus  110 . It will be appreciated that the system  100  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  130  may be integrated within the one or more processor  102 , or the memory controller hub  116  and I/O controller hub  130  may be integrated into a discreet external graphics processor, such as the external graphics processor  112 . 
       FIG. 2  is a block diagram of an embodiment of a processor  200  having one or more processor cores  202 A- 202 N, an integrated memory controller  214 , and an integrated graphics processor  208 . Those elements of  FIG. 2  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  200  can include additional cores up to and including additional core  202 N represented by the dashed lined boxes. Each of processor cores  202 A- 202 N includes one or more internal cache units  204 A- 204 N. In some embodiments each processor core also has access to one or more shared cached units  206 . 
     The internal cache units  204 A- 204 N and shared cache units  206  represent a cache memory hierarchy within the processor  200 . 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  206  and  204 A- 204 N. 
     In some embodiments, processor  200  may also include a set of one or more bus controller units  216  and a system agent core  210 . The one or more bus controller units  216  manage a set of peripheral buses, such as one or more Peripheral Component Interconnect buses (e.g., PCI, PCI Express). System agent core  210  provides management functionality for the various processor components. In some embodiments, system agent core  210  includes one or more integrated memory controllers  214  to manage access to various external memory devices (not shown). 
     In some embodiments, one or more of the processor cores  202 A- 202 N include support for simultaneous multi-threading. In such embodiment, the system agent core  210  includes components for coordinating and operating cores  202 A- 202 N during multi-threaded processing. System agent core  210  may additionally include a power control unit (PCU), which includes logic and components to regulate the power state of processor cores  202 A- 202 N and graphics processor  208 . 
     In some embodiments, processor  200  additionally includes graphics processor  208  to execute graphics processing operations. In some embodiments, the graphics processor  208  couples with the set of shared cache units  206 , and the system agent core  210 , including the one or more integrated memory controllers  214 . In some embodiments, a display controller  211  is coupled with the graphics processor  208  to drive graphics processor output to one or more coupled displays. In some embodiments, display controller  211  may be a separate module coupled with the graphics processor via at least one interconnect, or may be integrated within the graphics processor  208  or system agent core  210 . 
     In some embodiments, a ring based interconnect unit  212  is used to couple the internal components of the processor  200 . 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  208  couples with the ring interconnect  212  via an I/O link  213 . 
     The exemplary I/O link  213  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  218 , such as an eDRAM module. In some embodiments, each of the processor cores  202 A- 202 N and graphics processor  208  use embedded memory modules  218  as a shared Last Level Cache. 
     In some embodiments, processor cores  202 A- 202 N are homogenous cores executing the same instruction set architecture. In another embodiment, processor cores  202 A- 202 N are heterogeneous in terms of instruction set architecture (ISA), where one or more of processor cores  202 A- 202 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  202 A- 202 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  200  can be implemented on one or more chips or as an SoC integrated circuit having the illustrated components, in addition to other components. 
       FIG. 3  is a block diagram of a graphics processor  300 , 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  300  includes a memory interface  314  to access memory. Memory interface  314  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  300  also includes a display controller  302  to drive display output data to a display device  320 . Display controller  302  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  300  includes a video codec engine  306  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) 421M/VC-1, and Joint Photographic Experts Group (JPEG) formats such as JPEG, and Motion JPEG (MJPEG) formats. 
     In some embodiments, graphics processor  300  includes a block image transfer (BLIT) engine  304  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)  310 . In some embodiments, GPE  310  is a compute engine for performing graphics operations, including three-dimensional (3D) graphics operations and media operations. 
     In some embodiments, GPE  310  includes a 3D pipeline  312  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  312  includes programmable and fixed function elements that perform various tasks within the element and/or spawn execution threads to a 3D/Media sub-system  315 . While 3D pipeline  312  can be used to perform media operations, an embodiment of GPE  310  also includes a media pipeline  316  that is specifically used to perform media operations, such as video post-processing and image enhancement. 
     In some embodiments, media pipeline  316  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  306 . In some embodiments, media pipeline  316  additionally includes a thread spawning unit to spawn threads for execution on 3D/Media sub-system  315 . The spawned threads perform computations for the media operations on one or more graphics execution units included in 3D/Media sub-system  315 . 
     In some embodiments, 3D/Media subsystem  315  includes logic for executing threads spawned by 3D pipeline  312  and media pipeline  316 . In one embodiment, the pipelines send thread execution requests to 3D/Media subsystem  315 , 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  315  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. 4  is a block diagram of a graphics processing engine  410  of a graphics processor in accordance with some embodiments. In one embodiment, the graphics processing engine (GPE)  410  is a version of the GPE  310  shown in  FIG. 3 . Elements of  FIG. 4  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  312  and media pipeline  316  of  FIG. 3  are illustrated. The media pipeline  316  is optional in some embodiments of the GPE  410  and may not be explicitly included within the GPE  410 . For example and in at least one embodiment, a separate media and/or image processor is coupled to the GPE  410 . 
     In some embodiments, GPE  410  couples with or includes a command streamer  403 , which provides a command stream to the 3D pipeline  312  and/or media pipelines  316 . In some embodiments, command streamer  403  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  403  receives commands from the memory and sends the commands to 3D pipeline  312  and/or media pipeline  316 . The commands are directives fetched from a ring buffer, which stores commands for the 3D pipeline  312  and media pipeline  316 . In one embodiment, the ring buffer can additionally include batch command buffers storing batches of multiple commands. The commands for the 3D pipeline  312  can also include references to data stored in memory, such as but not limited to vertex and geometry data for the 3D pipeline  312  and/or image data and memory objects for the media pipeline  316 . The 3D pipeline  312  and media pipeline  316  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  414 . 
     In various embodiments the 3D pipeline  312  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  414 . The graphics core array  414  provides a unified block of execution resources. Multi-purpose execution logic (e.g., execution units) within the graphic core array  414  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  414  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)  107  of  FIG. 1  or core  202 A- 202 N as in  FIG. 2 . 
     Output data generated by threads executing on the graphics core array  414  can output data to memory in a unified return buffer (URB)  418 . The URB  418  can store data for multiple threads. In some embodiments the URB  418  may be used to send data between different threads executing on the graphics core array  414 . In some embodiments the URB  418  may additionally be used for synchronization between threads on the graphics core array and fixed function logic within the shared function logic  420 . 
     In some embodiments, graphics core array  414  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  410 . In one embodiment the execution resources are dynamically scalable, such that execution resources may be enabled or disabled as needed. 
     The graphics core array  414  couples with shared function logic  420  that includes multiple resources that are shared between the graphics cores in the graphics core array. The shared functions within the shared function logic  420  are hardware logic units that provide specialized supplemental functionality to the graphics core array  414 . In various embodiments, shared function logic  420  includes but is not limited to sampler  421 , math  422 , and inter-thread communication (ITC)  423  logic. Additionally, some embodiments implement one or more cache(s)  425  within the shared function logic  420 . A shared function is implemented where the demand for a given specialized function is insufficient for inclusion within the graphics core array  414 . Instead a single instantiation of that specialized function is implemented as a stand-alone entity in the shared function logic  420  and shared among the execution resources within the graphics core array  414 . The precise set of functions that are shared between the graphics core array  414  and included within the graphics core array  414  varies between embodiments. 
       FIG. 5  is a block diagram of another embodiment of a graphics processor  500 . Elements of  FIG. 5  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  500  includes a ring interconnect  502 , a pipeline front-end  504 , a media engine  537 , and graphics cores  580 A- 580 N. In some embodiments, ring interconnect  502  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  500  receives batches of commands via ring interconnect  502 . The incoming commands are interpreted by a command streamer  503  in the pipeline front-end  504 . In some embodiments, graphics processor  500  includes scalable execution logic to perform 3D geometry processing and media processing via the graphics core(s)  580 A- 580 N. For 3D geometry processing commands, command streamer  503  supplies commands to geometry pipeline  536 . For at least some media processing commands, command streamer  503  supplies the commands to a video front end  534 , which couples with a media engine  537 . In some embodiments, media engine  537  includes a Video Quality Engine (VQE)  530  for video and image post-processing and a multi-format encode/decode (MFX)  533  engine to provide hardware-accelerated media data encode and decode. In some embodiments, geometry pipeline  536  and media engine  537  each generate execution threads for the thread execution resources provided by at least one graphics core  580 A. 
     In some embodiments, graphics processor  500  includes scalable thread execution resources featuring modular cores  580 A- 580 N (sometimes referred to as core slices), each having multiple sub-cores  550 A- 550 N,  560 A- 560 N (sometimes referred to as core sub-slices). In some embodiments, graphics processor  500  can have any number of graphics cores  580 A through  580 N. In some embodiments, graphics processor  500  includes a graphics core  580 A having at least a first sub-core  550 A and a second sub-core  560 A. In other embodiments, the graphics processor is a low power processor with a single sub-core (e.g.,  550 A). In some embodiments, graphics processor  500  includes multiple graphics cores  580 A- 580 N, each including a set of first sub-cores  550 A- 550 N and a set of second sub-cores  560 A- 560 N. Each sub-core in the set of first sub-cores  550 A- 550 N includes at least a first set of execution units  552 A- 552 N and media/texture samplers  554 A- 554 N. Each sub-core in the set of second sub-cores  560 A- 560 N includes at least a second set of execution units  562 A- 562 N and samplers  564 A- 564 N. In some embodiments, each sub-core  550 A- 550 N,  560 A- 560 N shares a set of shared resources  570 A- 570 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. 6  illustrates thread execution logic  600  including an array of processing elements employed in some embodiments of a GPE. Elements of  FIG. 6  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  600  includes a shader processor  602 , a thread dispatcher  604 , instruction cache  606 , a scalable execution unit array including a plurality of execution units  608 A- 608 N, a sampler  610 , a data cache  612 , and a data port  614 . 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  608 A,  608 B,  608 C,  608 D, through  608 N−1 and  608 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  600  includes one or more connections to memory, such as system memory or cache memory, through one or more of instruction cache  606 , data port  614 , sampler  610 , and execution units  608 A- 608 N. In some embodiments, each execution unit (e.g.  608 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  608 A- 608 N is scalable to include any number individual execution units. 
     In some embodiments, the execution units  608 A- 608 N are primarily used to execute shader programs. A shader processor  602  can process the various shader programs and dispatch execution threads associated with the shader programs via a thread dispatcher  604 . 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  608 A- 608 N. For example, the geometry pipeline (e.g.,  536  of  FIG. 5 ) can dispatch vertex, tessellation, or geometry shaders to the thread execution logic  600  ( FIG. 6 ) for processing. In some embodiments, thread dispatcher  604  can also process runtime thread spawning requests from the executing shader programs. 
     In some embodiments, the execution units  608 A- 608 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  608 A- 608 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  608 A- 608 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  608 A- 608 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  608 A- 608 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.,  606 ) are included in the thread execution logic  600  to cache thread instructions for the execution units. In some embodiments, one or more data caches (e.g.,  612 ) are included to cache thread data during thread execution. In some embodiments, a sampler  610  is included to provide texture sampling for 3D operations and media sampling for media operations. In some embodiments, sampler  610  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  600  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  602  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  602  then executes an application programming interface (API)-supplied pixel or fragment shader program. To execute the shader program, the shader processor  602  dispatches threads to an execution unit (e.g.,  608 A) via thread dispatcher  604 . In some embodiments, pixel shader  602  uses texture sampling logic in the sampler  610  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  614  provides a memory access mechanism for the thread execution logic  600  output processed data to memory for processing on a graphics processor output pipeline. In some embodiments, the data port  614  includes or couples to one or more cache memories (e.g., data cache  612 ) to cache data for memory access via the data port. 
       FIG. 7  is a block diagram illustrating a graphics processor instruction formats  700  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  700  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  710 . A 64-bit compacted instruction format  730  is available for some instructions based on the selected instruction, instruction options, and number of operands. The native 128-bit instruction format  710  provides access to all instruction options, while some options and operations are restricted in the 64-bit instruction format  730 . The native instructions available in the 64-bit instruction format  730  vary by embodiment. In some embodiments, the instruction is compacted in part using a set of index values in an index field  713 . 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  710 . 
     For each format, instruction opcode  712  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  714  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  710  an exec-size field  716  limits the number of data channels that will be executed in parallel. In some embodiments, exec-size field  716  is not available for use in the 64-bit compact instruction format  730 . 
     Some execution unit instructions have up to three operands including two source operands, src0  720 , src1  722 , and one destination  718 . 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., SRC2  724 ), where the instruction opcode  712  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  710  includes an access/address mode field  726  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  710  includes an access/address mode field  726 , 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  726  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  712  bit-fields to simplify Opcode decode  740 . 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  742  includes data movement and logic instructions (e.g., move (mov), compare (cmp)). In some embodiments, move and logic group  742  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  744  (e.g., call, jump (jmp)) includes instructions in the form of 0010xxxxb (e.g., 0x20). A miscellaneous instruction group  746  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  748  includes component-wise arithmetic instructions (e.g., add, multiply (mul)) in the form of 0100xxxxb (e.g., 0x40). The parallel math group  748  performs the arithmetic operations in parallel across data channels. The vector math group  750  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. 8  is a block diagram of another embodiment of a graphics processor  800 . Elements of  FIG. 8  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  800  includes a graphics pipeline  820 , a media pipeline  830 , a display engine  840 , thread execution logic  850 , and a render output pipeline  870 . In some embodiments, graphics processor  800  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  800  via a ring interconnect  802 . In some embodiments, ring interconnect  802  couples graphics processor  800  to other processing components, such as other graphics processors or general-purpose processors. Commands from ring interconnect  802  are interpreted by a command streamer  803 , which supplies instructions to individual components of graphics pipeline  820  or media pipeline  830 . 
     In some embodiments, command streamer  803  directs the operation of a vertex fetcher  805  that reads vertex data from memory and executes vertex-processing commands provided by command streamer  803 . In some embodiments, vertex fetcher  805  provides vertex data to a vertex shader  807 , which performs coordinate space transformation and lighting operations to each vertex. In some embodiments, vertex fetcher  805  and vertex shader  807  execute vertex-processing instructions by dispatching execution threads to execution units  852 A- 852 B via a thread dispatcher  831   
     In some embodiments, execution units  852 A- 852 B are an array of vector processors having an instruction set for performing graphics and media operations. In some embodiments, execution units  852 A- 852 B have an attached L1 cache  851  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  820  includes tessellation components to perform hardware-accelerated tessellation of 3D objects. In some embodiments, a programmable hull shader  811  configures the tessellation operations. A programmable domain shader  817  provides back-end evaluation of tessellation output. A tessellator  813  operates at the direction of hull shader  811  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  820 . In some embodiments, if tessellation is not used, tessellation components (e.g., hull shader  811 , tessellator  813 , and domain shader  817 ) can be bypassed. 
     In some embodiments, complete geometric objects can be processed by a geometry shader  819  via one or more threads dispatched to execution units  852 A- 852 B, or can proceed directly to the clipper  829 . 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  819  receives input from the vertex shader  807 . In some embodiments, geometry shader  819  is programmable by a geometry shader program to perform geometry tessellation if the tessellation units are disabled. 
     Before rasterization, a clipper  829  processes vertex data. The clipper  829  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  873  in the render output pipeline  870  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  850 . In some embodiments, an application can bypass the rasterizer and depth test component  873  and access un-rasterized vertex data via a stream out unit  823 . 
     The graphics processor  800  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  852 A- 852 B and associated cache(s)  851 , texture and media sampler  854 , and texture/sampler cache  858  interconnect via a data port  856  to perform memory access and communicate with render output pipeline components of the processor. In some embodiments, sampler  854 , caches  851 ,  858  and execution units  852 A- 852 B each have separate memory access paths. 
     In some embodiments, render output pipeline  870  contains a rasterizer and depth test component  873  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  878  and depth cache  879  are also available in some embodiments. A pixel operations component  877  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  841 , or substituted at display time by the display controller  843  using overlay display planes. In some embodiments, a shared L3 cache  875  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  830  includes a media engine  837  and a video front end  834 . In some embodiments, video front end  834  receives pipeline commands from the command streamer  803 . In some embodiments, media pipeline  830  includes a separate command streamer. In some embodiments, video front-end  834  processes media commands before sending the command to the media engine  837 . In some embodiments, media engine  837  includes thread spawning functionality to spawn threads for dispatch to thread execution logic  850  via thread dispatcher  831 . 
     In some embodiments, graphics processor  800  includes a display engine  840 . In some embodiments, display engine  840  is external to processor  800  and couples with the graphics processor via the ring interconnect  802 , or some other interconnect bus or fabric. In some embodiments, display engine  840  includes a 2D engine  841  and a display controller  843 . In some embodiments, display engine  840  contains special purpose logic capable of operating independently of the 3D pipeline. In some embodiments, display controller  843  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  820  and media pipeline  830  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. 9A  is a block diagram illustrating a graphics processor command format  900  according to some embodiments.  FIG. 9B  is a block diagram illustrating a graphics processor command sequence  910  according to an embodiment. The solid lined boxes in  FIG. 9A  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  900  of  FIG. 9A  includes data fields to identify a target client  902  of the command, a command operation code (opcode)  904 , and the relevant data  906  for the command. A sub-opcode  905  and a command size  908  are also included in some commands. 
     In some embodiments, client  902  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  904  and, if present, sub-opcode  905  to determine the operation to perform. The client unit performs the command using information in data field  906 . For some commands an explicit command size  908  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. 9B  shows an exemplary graphics processor command sequence  910 . 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  910  may begin with a pipeline flush command  912  to cause any active graphics pipeline to complete the currently pending commands for the pipeline. In some embodiments, the 3D pipeline  922  and the media pipeline  924  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  912  can be used for pipeline synchronization or before placing the graphics processor into a low power state. 
     In some embodiments, a pipeline select command  913  is used when a command sequence requires the graphics processor to explicitly switch between pipelines. In some embodiments, a pipeline select command  913  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  912  is required immediately before a pipeline switch via the pipeline select command  913 . 
     In some embodiments, a pipeline control command  914  configures a graphics pipeline for operation and is used to program the 3D pipeline  922  and the media pipeline  924 . In some embodiments, pipeline control command  914  configures the pipeline state for the active pipeline. In one embodiment, the pipeline control command  914  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, commands for the return buffer state  916  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, configuring the return buffer state  916  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  920 , the command sequence is tailored to the 3D pipeline  922  beginning with the 3D pipeline state  930  or the media pipeline  924  beginning at the media pipeline state  940 . 
     The commands to configure the 3D pipeline state  930  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  930  commands are also able to selectively disable or bypass certain pipeline elements if those elements will not be used. 
     In some embodiments, 3D primitive  932  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  932  command are forwarded to the vertex fetch function in the graphics pipeline. The vertex fetch function uses the 3D primitive  932  command data to generate vertex data structures. The vertex data structures are stored in one or more return buffers. In some embodiments, 3D primitive  932  command is used to perform vertex operations on 3D primitives via vertex shaders. To process vertex shaders, 3D pipeline  922  dispatches shader execution threads to graphics processor execution units. 
     In some embodiments, 3D pipeline  922  is triggered via an execute  934  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  910  follows the media pipeline  924  path when performing media operations. In general, the specific use and manner of programming for the media pipeline  924  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  924  is configured in a similar manner as the 3D pipeline  922 . A set of commands to configure the media pipeline state  940  are dispatched or placed into a command queue before the media object commands  942 . In some embodiments, commands for the media pipeline state  940  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, commands for the media pipeline state  940  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  942  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  942 . Once the pipeline state is configured and media object commands  942  are queued, the media pipeline  924  is triggered via an execute command  944  or an equivalent execute event (e.g., register write). Output from media pipeline  924  may then be post processed by operations provided by the 3D pipeline  922  or the media pipeline  924 . In some embodiments, GPGPU operations are configured and executed in a similar manner as media operations. 
     Graphics Software Architecture 
       FIG. 10  illustrates exemplary graphics software architecture for a data processing system  1000  according to some embodiments. In some embodiments, software architecture includes a 3D graphics application  1010 , an operating system  1020 , and at least one processor  1030 . In some embodiments, processor  1030  includes a graphics processor  1032  and one or more general-purpose processor core(s)  1034 . The graphics application  1010  and operating system  1020  each execute in the system memory  1050  of the data processing system. 
     In some embodiments, 3D graphics application  1010  contains one or more shader programs including shader instructions  1012 . 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  1014  in a machine language suitable for execution by the general-purpose processor core  1034 . The application also includes graphics objects  1016  defined by vertex data. 
     In some embodiments, operating system  1020  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  1020  can support a graphics API  1022  such as the Direct3D API, the OpenGL API, or the Vulkan API. When the Direct3D API is in use, the operating system  1020  uses a front-end shader compiler  1024  to compile any shader instructions  1012  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  1010 . In some embodiments, the shader instructions  1012  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  1026  contains a back-end shader compiler  1027  to convert the shader instructions  1012  into a hardware specific representation. When the OpenGL API is in use, shader instructions  1012  in the GLSL high-level language are passed to a user mode graphics driver  1026  for compilation. In some embodiments, user mode graphics driver  1026  uses operating system kernel mode functions  1028  to communicate with a kernel mode graphics driver  1029 . In some embodiments, kernel mode graphics driver  1029  communicates with graphics processor  1032  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. 11  is a block diagram illustrating an IP core development system  1100  that may be used to manufacture an integrated circuit to perform operations according to an embodiment. The IP core development system  1100  may be used to generate modular, re-usable 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  1130  can generate a software simulation  1110  of an IP core design in a high level programming language (e.g., C/C++). The software simulation  1110  can be used to design, test, and verify the behavior of the IP core using a simulation model  1112 . The simulation model  1112  may include functional, behavioral, and/or timing simulations. A register transfer level (RTL) design  1115  can then be created or synthesized from the simulation model  1112 . The RTL design  1115  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  1115 , 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  1115  or equivalent may be further synthesized by the design facility into a hardware model  1120 , 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 3rd party fabrication facility  1165  using non-volatile memory  1140  (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  1150  or wireless connection  1160 . The fabrication facility  1165  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. 12-14  illustrate 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. 12  is a block diagram illustrating an exemplary system on a chip integrated circuit  1200  that may be fabricated using one or more IP cores, according to an embodiment. Exemplary integrated circuit  1200  includes one or more application processor(s)  1205  (e.g., CPUs), at least one graphics processor  1210 , and may additionally include an image processor  1215  and/or a video processor  1220 , any of which may be a modular IP core from the same or multiple different design facilities. Integrated circuit  1200  includes peripheral or bus logic including a USB controller  1225 , UART controller  1230 , an SPI/SDIO controller  1235 , and an I 2 S/I 2 C controller  1240 . Additionally, the integrated circuit can include a display device  1245  coupled to one or more of a high-definition multimedia interface (HDMI) controller  1250  and a mobile industry processor interface (MIPI) display interface  1255 . Storage may be provided by a flash memory subsystem  1260  including flash memory and a flash memory controller. Memory interface may be provided via a memory controller  1265  for access to SDRAM or SRAM memory devices. Some integrated circuits additionally include an embedded security engine  1270 . 
       FIG. 13  is a block diagram illustrating an exemplary graphics processor  1310  of a system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. Graphics processor  1310  can be a variant of the graphics processor  1210  of  FIG. 12 . Graphics processor  1310  includes a vertex processor  1305  and one or more fragment processor(s)  1315 A 1315 N (e.g.,  1315 A,  1315 B,  1315 C,  1315 D, through  1315 N−1, and  1315 N). Graphics processor  1310  can execute different shader programs via separate logic, such that the vertex processor  1305  is optimized to execute operations for vertex shader programs, while the one or more fragment processor(s)  1315 A- 1315 N execute fragment (e.g., pixel) shading operations for fragment or pixel shader programs. The vertex processor  1305  performs the vertex processing stage of the 3D graphics pipeline and generates primitives and vertex data. The fragment processor(s)  1315 A- 1315 N use the primitive and vertex data generated by the vertex processor  1305  to produce a framebuffer that is displayed on a display device. In one embodiment, the fragment processor(s)  1315 A- 1315 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  1310  additionally includes one or more memory management units (MMUs)  1320 A- 1320 B, cache(s)  1325 A- 1325 B, and circuit interconnect(s)  1330 A- 1330 B. The one or more MMU(s)  1320 A- 1320 B provide for virtual to physical address mapping for graphics processor  1310 , including for the vertex processor  1305  and/or fragment processor(s)  1315 A- 1315 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)  1325 A- 1325 B. In one embodiment the one or more MMU(s)  1320 A- 1320 B may be synchronized with other MMUs within the system, including one or more MMUs associated with the one or more application processor(s)  1205 , image processor  1215 , and/or video processor  1220  of  FIG. 12 , such that each processor  1205 - 1220  can participate in a shared or unified virtual memory system. The one or more circuit interconnect(s)  1330 A- 1330 B enable graphics processor  1310  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. 14  is a block diagram illustrating an additional exemplary graphics processor  1410  of a system on a chip integrated circuit that may be fabricated using one or more IP cores, according to an embodiment. Graphics processor  1410  can be a variant of the graphics processor  1210  of  FIG. 12 . Graphics processor  1410  includes the one or more MMU(s)  1320 A- 1320 B, cache(s)  1325 A- 1325 B, and circuit interconnect(s)  1330 A- 1330 B of the integrated circuit  1300  of  FIG. 13 . 
     Graphics processor  1410  includes one or more shader core(s)  1415 A- 1415 N (e.g.,  1415 A,  1415 B,  1415 C,  1415 D,  1415 E,  1415 F, through  1315 N−1, and  1315 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  1410  includes an inter-core task manager  1405 , which acts as a thread dispatcher to dispatch execution threads to one or more shader core(s)  1415 A- 1415 N and a tiling unit  1418  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. 
     Apparatus and Method for Implementing Bounding Volume Hierarchy Operations on Tesselation Hardware 
     Graphics tesselation units include hardware for subdividing a surface into a plurality of smaller surfaces. In particular, during tessellation, each surface is subdivided into additional primitives (triangles, lines, vertices). The number of primitives into which a surface is to be subdivided is specified by a set of tessellation factors (typically provided by a Hull Shader). The end result is that a relatively coarse mesh may be dynamically transformed into a finer mesh with more vertices and triangles. The finer mesh is then shaded and rendered on the display, resulting in improved image quality. 
     Bounding volume hierarchies are commonly used to improve the efficiency with which operations are performed on graphics primitives and other graphics objects. A BVH is a hierarchical tree structure which is built based on a set of geometric objects. At the top of the tree structure is the root node which encloses all of the geometric objects in a given scene. The individual geometric objects are wrapped in bounding volumes that form the leaf nodes of the tree. These nodes are then grouped as small sets and enclosed within larger bounding volumes. These, in turn, are also grouped and enclosed within other larger bounding volumes in a recursive fashion, eventually resulting in a tree structure with a single bounding volume, represented by the root node, at the top of the tree. Bounding volume hierarchies are used to efficiently support a variety of operations on sets of geometric objects, such as collision detection, primitive culling, and ray traversal/intersection operations used in ray tracing. 
     In one embodiment, the tessellation hardware generate a bounding volume hierarchy (BVH) for a set of primitives resulting from tessellation of a surface as it generates those primitives.  FIG. 15  illustrates an exemplary embodiment in which a tessellation unit  1502  of a GPU  1510  tesselates each input surface to generate a set of triangles or other primitives  1520  and concurrently generates a bounding volume hierarchy (BVH)  1521  associated with the new set of primitives. The tessellation unit  1520  receives surfaces and tessellation factors from a hull shader  1501 . Each surface may be defined, for example, by a plurality of vertices and the tessellation factors may specify how finely the surface is to be tessellated (e.g., how many triangles or other primitives to generate to represent the surface). 
     In one embodiment, as tessellation circuitry  1503  within the tessellation unit generates the primitives  1520 , BVH node generation circuitry  1504  generates a corresponding BVH  1521  based on the primitives using the same data required for tesselation. For example, the tessellation circuitry  1503  may first split the input surface into two halves, then split those two halves into halves, and so on, until the level of detail has been reached (as specified by the tessellation factors). The BVH node generation circuitry  1504  may define the root BVH node to include the entire input surface. When the input surface is split into two halves, the BVH node generation circuit  1504  may dynamically generate the first two child BVH nodes to include these two halves, then generate the next level of BVH nodes to include the next division and so on, until the entire BVH has been constructed concurrently with the tessellation operations. The results may be provided to a domain shader  1505  which performs shading operations on the new vertices/primitives. 
     An example is illustrated in  FIG. 16  for a set of primitives  1520  generated during tessellation. A first bounding box  1600  (the root node) encompasses the entire set of primitives. The next two boxes  1610 - 1611  encompass half of the primitives (splitting one primitive down the middle), and the next set of bounding boxes  1620 - 1623  each enclose an individual primitive (i.e., they are leaf nodes). Thus, given the similarities associated with tessellation and BVH generation, the same tessellation hardware may be used to perform BVH construction concurrently with tessellation. 
     Apparatus and Method for Fast Topological BVH Generation for Hardware Tesselation 
     In addition, one embodiment of the invention extends the tessellation hardware to perform ray-triangle intersections on the fly. For example, as illustrated in  FIG. 17 , the BVH node generation module  1504  may generate a BVH for a given surface as described above. The ray-surface intersection circuitry  1700  then uses the BVH to test the input surface and its primitives for intersection with a set of N rays before tessellation  1503 . If a particular set of primitives or potentially the entire surface is not intersected by any of the N rays, then this batch of primitives may be culled with respect to the N rays, thereby preserving bandwidth that would otherwise be consumed by the tessellation unit  1502  and other pipeline stages. 
     In one embodiment, the ray-surface intersection circuitry also includes BVH traversal circuitry to traverse the BVH to determine which primitives (if any) are intersected by one or more of the N rays. If only a subset of the primitives are intersected, then the tessellation circuitry  1503  may only tessellate that portion of the surface which includes primitives which may be intersected by a ray. 
     A method in accordance with one embodiment is illustrated in  FIG. 18 . The method may be implemented within the context of the system architectures described above, but is not limited to any particular processor or system architecture. 
     At  1800 , a bounding volume hierarchy (BVH) is generated for an input surface with tesselaton hardware. As mentioned, this may be accomplished using tessellation factors provided by a hull shader. At  1801 , intersection tests are performed for the input surface for using the BVH to determine whether any primitives of the surface are intersected by any of a set of rays. If not, then the entire input surface may be culled at  1803 . If so, then at  1804  tesselation circuitry is provided with tessellation factors for the surface and/or an indication of those primitives (or sets of primitives) which are intersected (or those which are not intersected). At  1805 , the tessellation circuitry tessellates the input surface to generate the primitives, potentially focusing on only those portions of the surface which are intersected. At  1806 , the results of the tessellation are output to a domain shader which may perform sharing at a primitive-level granularity. 
     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. 19  is a block diagram illustrating a computing system  1900  configured to implement one or more aspects of the embodiments described herein. The computing system  1900  includes a processing subsystem  1901  having one or more processor(s)  1902  and a system memory  1904  communicating via an interconnection path that may include a memory hub  1905 . The memory hub  1905  may be a separate component within a chipset component or may be integrated within the one or more processor(s)  1902 . The memory hub  1905  couples with an I/O subsystem  1911  via a communication link  1906 . The I/O subsystem  1911  includes an I/O hub  1907  that can enable the computing system  1900  to receive input from one or more input device(s)  1908 . Additionally, the I/O hub  1907  can enable a display controller, which may be included in the one or more processor(s)  1902 , to provide outputs to one or more display device(s)  1910 A. In one embodiment the one or more display device(s)  1910 A coupled with the I/O hub  1907  can include a local, internal, or embedded display device. 
     In one embodiment the processing subsystem  1901  includes one or more parallel processor(s)  1912  coupled to memory hub  1905  via a bus or other communication link  1913 . The communication link  1913  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)  1912  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)  1912  form a graphics processing subsystem that can output pixels to one of the one or more display device(s)  1910 A coupled via the I/O Hub  1907 . The one or more parallel processor(s)  1912  can also include a display controller and display interface (not shown) to enable a direct connection to one or more display device(s)  1910 B. 
     Within the I/O subsystem  1911 , a system storage unit  1914  can connect to the I/O hub  1907  to provide a storage mechanism for the computing system  1900 . An I/O switch  1916  can be used to provide an interface mechanism to enable connections between the I/O hub  1907  and other components, such as a network adapter  1918  and/or wireless network adapter  1919  that may be integrated into the platform, and various other devices that can be added via one or more add-in device(s)  1920 . The network adapter  1918  can be an Ethernet adapter or another wired network adapter. The wireless network adapter  1919  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  1900  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  1907 . Communication paths interconnecting the various components in  FIG. 19  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)  1912  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)  1912  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  1900  may be integrated with one or more other system elements on a single integrated circuit. For example, the one or more parallel processor(s),  1912  memory hub  1905 , processor(s)  1902 , and I/O hub  1907  can be integrated into a system on chip (SoC) integrated circuit. Alternatively, the components of the computing system  1900  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  1900  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  1900  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)  1902 , and the number of parallel processor(s)  1912 , may be modified as desired. For instance, in some embodiments, system memory  1904  is connected to the processor(s)  1902  directly rather than through a bridge, while other devices communicate with system memory  1904  via the memory hub  1905  and the processor(s)  1902 . In other alternative topologies, the parallel processor(s)  1912  are connected to the I/O hub  1907  or directly to one of the one or more processor(s)  1902 , rather than to the memory hub  1905 . In other embodiments, the I/O hub  1907  and memory hub  1905  may be integrated into a single chip. Some embodiments may include two or more sets of processor(s)  1902  attached via multiple sockets, which can couple with two or more instances of the parallel processor(s)  1912 . 
     Some of the particular components shown herein are optional and may not be included in all implementations of the computing system  1900 . 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. 19 . For example, the memory hub  1905  may be referred to as a Northbridge in some architectures, while the I/O hub  1907  may be referred to as a Southbridge. 
       FIG. 20A  illustrates a parallel processor  2000 , according to an embodiment. The various components of the parallel processor  2000  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  2000  is a variant of the one or more parallel processor(s)  1912  shown in  FIG. 19 , according to an embodiment. 
     In one embodiment the parallel processor  2000  includes a parallel processing unit  2002 . The parallel processing unit includes an I/O unit  2004  that enables communication with other devices, including other instances of the parallel processing unit  2002 . The I/O unit  2004  may be directly connected to other devices. In one embodiment the I/O unit  2004  connects with other devices via the use of a hub or switch interface, such as memory hub  1905 . The connections between the memory hub  1905  and the I/O unit  2004  form a communication link  1913 . Within the parallel processing unit  2002 , the I/O unit  2004  connects with a host interface  2006  and a memory crossbar  2016 , where the host interface  2006  receives commands directed to performing processing operations and the memory crossbar  2016  receives commands directed to performing memory operations. 
     When the host interface  2006  receives a command buffer via the I/O unit  2004 , the host interface  2006  can direct work operations to perform those commands to a front end  2008 . In one embodiment the front end  2008  couples with a scheduler  2010 , which is configured to distribute commands or other work items to a processing cluster array  2012 . In one embodiment the scheduler  2010  ensures that the processing cluster array  2012  is properly configured and in a valid state before tasks are distributed to the processing clusters of the processing cluster array  2012 . In one embodiment the scheduler  2010  is implemented via firmware logic executing on a microcontroller. The microcontroller implemented scheduler  2010  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  2012 . In one embodiment, the host software can prove workloads for scheduling on the processing array  2012  via one of multiple graphics processing doorbells. The workloads can then be automatically distributed across the processing array  2012  by the scheduler  2010  logic within the scheduler microcontroller. 
     The processing cluster array  2012  can include up to “N” processing clusters (e.g., cluster  2014 A, cluster  2014 B, through cluster  2014 N). Each cluster  2014 A- 2014 N of the processing cluster array  2012  can execute a large number of concurrent threads. The scheduler  2010  can allocate work to the clusters  2014 A- 2014 N of the processing cluster array  2012  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  2010 , or can be assisted in part by compiler logic during compilation of program logic configured for execution by the processing cluster array  2012 . In one embodiment, different clusters  2014 A- 2014 N of the processing cluster array  2012  can be allocated for processing different types of programs or for performing different types of computations. 
     The processing cluster array  2012  can be configured to perform various types of parallel processing operations. In one embodiment the processing cluster array  2012  is configured to perform general-purpose parallel compute operations. For example, the processing cluster array  2012  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  2012  is configured to perform parallel graphics processing operations. In embodiments in which the parallel processor  2000  is configured to perform graphics processing operations, the processing cluster array  2012  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  2012  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  2002  can transfer data from system memory via the I/O unit  2004  for processing. During processing the transferred data can be stored to on-chip memory (e.g., parallel processor memory  2022 ) during processing, then written back to system memory. 
     In one embodiment, when the parallel processing unit  2002  is used to perform graphics processing, the scheduler  2010  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  2014 A- 2014 N of the processing cluster array  2012 . In some embodiments, portions of the processing cluster array  2012  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  2014 A- 2014 N may be stored in buffers to allow the intermediate data to be transmitted between clusters  2014 A- 2014 N for further processing. 
     During operation, the processing cluster array  2012  can receive processing tasks to be executed via the scheduler  2010 , which receives commands defining processing tasks from front end  2008 . 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  2010  may be configured to fetch the indices corresponding to the tasks or may receive the indices from the front end  2008 . The front end  2008  can be configured to ensure the processing cluster array  2012  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  2002  can couple with parallel processor memory  2022 . The parallel processor memory  2022  can be accessed via the memory crossbar  2016 , which can receive memory requests from the processing cluster array  2012  as well as the I/O unit  2004 . The memory crossbar  2016  can access the parallel processor memory  2022  via a memory interface  2018 . The memory interface  2018  can include multiple partition units (e.g., partition unit  2020 A, partition unit  2020 B, through partition unit  2020 N) that can each couple to a portion (e.g., memory unit) of parallel processor memory  2022 . In one implementation the number of partition units  2020 A- 2020 N is configured to be equal to the number of memory units, such that a first partition unit  2020 A has a corresponding first memory unit  2024 A, a second partition unit  2020 B has a corresponding memory unit  2024 B, and an Nth partition unit  2020 N has a corresponding Nth memory unit  2024 N. In other embodiments, the number of partition units  2020 A- 2020 N may not be equal to the number of memory devices. 
     In various embodiments, the memory units  2024 A- 2024 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  2024 A- 2024 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  2024 A- 2024 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  2024 A- 2024 N, allowing partition units  2020 A- 2020 N to write portions of each render target in parallel to efficiently use the available bandwidth of parallel processor memory  2022 . In some embodiments, a local instance of the parallel processor memory  2022  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  2014 A- 2014 N of the processing cluster array  2012  can process data that will be written to any of the memory units  2024 A- 2024 N within parallel processor memory  2022 . The memory crossbar  2016  can be configured to transfer the output of each cluster  2014 A- 2014 N to any partition unit  2020 A- 2020 N or to another cluster  2014 A- 2014 N, which can perform additional processing operations on the output. Each cluster  2014 A- 2014 N can communicate with the memory interface  2018  through the memory crossbar  2016  to read from or write to various external memory devices. In one embodiment the memory crossbar  2016  has a connection to the memory interface  2018  to communicate with the I/O unit  2004 , as well as a connection to a local instance of the parallel processor memory  2022 , enabling the processing units within the different processing clusters  2014 A- 2014 N to communicate with system memory or other memory that is not local to the parallel processing unit  2002 . In one embodiment the memory crossbar  2016  can use virtual channels to separate traffic streams between the clusters  2014 A- 2014 N and the partition units  2020 A- 2020 N. 
     While a single instance of the parallel processing unit  2002  is illustrated within the parallel processor  2000 , any number of instances of the parallel processing unit  2002  can be included. For example, multiple instances of the parallel processing unit  2002  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  2002  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  2002  can include higher precision floating point units relative to other instances. Systems incorporating one or more instances of the parallel processing unit  2002  or the parallel processor  2000  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. 20B  is a block diagram of a partition unit  2020 , according to an embodiment. In one embodiment the partition unit  2020  is an instance of one of the partition units  2020 A- 2020 N of  FIG. 20A . As illustrated, the partition unit  2020  includes an L2 cache  2021 , a frame buffer interface  2025 , and a ROP  2026  (raster operations unit). The L2 cache  2021  is a read/write cache that is configured to perform load and store operations received from the memory crossbar  2016  and ROP  2026 . Read misses and urgent write-back requests are output by L2 cache  2021  to frame buffer interface  2025  for processing. Updates can also be sent to the frame buffer via the frame buffer interface  2025  for processing. In one embodiment the frame buffer interface  2025  interfaces with one of the memory units in parallel processor memory, such as the memory units  2024 A- 2024 N of  FIG. 20  (e.g., within parallel processor memory  2022 ). 
     In graphics applications, the ROP  2026  is a processing unit that performs raster operations such as stencil, z test, blending, and the like. The ROP  2026  then outputs processed graphics data that is stored in graphics memory. In some embodiments the ROP  2026  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  2026  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  2026  is included within each processing cluster (e.g., cluster  2014 A- 2014 N of  FIG. 20 ) instead of within the partition unit  2020 . In such embodiment, read and write requests for pixel data are transmitted over the memory crossbar  2016  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)  1910  of  FIG. 19 , routed for further processing by the processor(s)  1902 , or routed for further processing by one of the processing entities within the parallel processor  2000  of  FIG. 20A . 
       FIG. 20C  is a block diagram of a processing cluster  2014  within a parallel processing unit, according to an embodiment. In one embodiment the processing cluster is an instance of one of the processing clusters  2014 A- 2014 N of  FIG. 20 . The processing cluster  2014  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  2014  can be controlled via a pipeline manager  2032  that distributes processing tasks to SIMT parallel processors. The pipeline manager  2032  receives instructions from the scheduler  2010  of  FIG. 20  and manages execution of those instructions via a graphics multiprocessor  2034  and/or a texture unit  2036 . The illustrated graphics multiprocessor  2034  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  2014 . One or more instances of the graphics multiprocessor  2034  can be included within a processing cluster  2014 . The graphics multiprocessor  2034  can process data and a data crossbar  2040  can be used to distribute the processed data to one of multiple possible destinations, including other shader units. The pipeline manager  2032  can facilitate the distribution of processed data by specifying destinations for processed data to be distributed vis the data crossbar  2040 . 
     Each graphics multiprocessor  2034  within the processing cluster  2014  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  2014  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  2034 . A thread group may include fewer threads than the number of processing engines within the graphics multiprocessor  2034 . 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  2034 . When the thread group includes more threads than the number of processing engines within the graphics multiprocessor  2034 , processing can be performed over consecutive clock cycles. In one embodiment multiple thread groups can be executed concurrently on a graphics multiprocessor  2034 . 
     In one embodiment the graphics multiprocessor  2034  includes an internal cache memory to perform load and store operations. In one embodiment, the graphics multiprocessor  2034  can forego an internal cache and use a cache memory (e.g., L1 cache  2108 ) within the processing cluster  2014 . Each graphics multiprocessor  2034  also has access to L2 caches within the partition units (e.g., partition units  2020 A- 2020 N of  FIG. 20 ) that are shared among all processing clusters  2014  and may be used to transfer data between threads. The graphics multiprocessor  2034  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  2002  may be used as global memory. Embodiments in which the processing cluster  2014  includes multiple instances of the graphics multiprocessor  2034  can share common instructions and data, which may be stored in the L1 cache  2108 . 
     Each processing cluster  2014  may include an MMU  2045  (memory management unit) that is configured to map virtual addresses into physical addresses. In other embodiments, one or more instances of the MMU  2045  may reside within the memory interface  2018  of  FIG. 20 . The MMU  2045  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  2045  may include address translation lookaside buffers (TLB) or caches that may reside within the graphics multiprocessor  2034  or the L1 cache or processing cluster  2014 . 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  2014  may be configured such that each graphics multiprocessor  2034  is coupled to a texture unit  2036  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  2034  and is fetched from an L2 cache, local parallel processor memory, or system memory, as needed. Each graphics multiprocessor  2034  outputs processed tasks to the data crossbar  2040  to provide the processed task to another processing cluster  2014  for further processing or to store the processed task in an L2 cache, local parallel processor memory, or system memory via the memory crossbar  2016 . A preROP  2042  (pre-raster operations unit) is configured to receive data from graphics multiprocessor  2034 , direct data to ROP units, which may be located with partition units as described herein (e.g., partition units  2020 A- 2020 N of  FIG. 20 ). The preROP  2042  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  2034 , texture units  2036 , preROPs  2042 , etc., may be included within a processing cluster  2014 . Further, while only one processing cluster  2014  is shown, a parallel processing unit as described herein may include any number of instances of the processing cluster  2014 . In one embodiment, each processing cluster  2014  can be configured to operate independently of other processing clusters  2014  using separate and distinct processing units, L1 caches, etc. 
       FIG. 20D  shows a graphics multiprocessor  2034 , according to one embodiment. In such embodiment the graphics multiprocessor  2034  couples with the pipeline manager  2032  of the processing cluster  2014 . The graphics multiprocessor  2034  has an execution pipeline including but not limited to an instruction cache  2052 , an instruction unit  2054 , an address mapping unit  2056 , a register file  2058 , one or more general purpose graphics processing unit (GPGPU) cores  2062 , and one or more load/store units  2066 . The GPGPU cores  2062  and load/store units  2066  are coupled with cache memory  2072  and shared memory  2070  via a memory and cache interconnect  2068 . 
     In one embodiment, the instruction cache  2052  receives a stream of instructions to execute from the pipeline manager  2032 . The instructions are cached in the instruction cache  2052  and dispatched for execution by the instruction unit  2054 . The instruction unit  2054  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  2062 . 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  2056  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  2066 . 
     The register file  2058  provides a set of registers for the functional units of the graphics multiprocessor  2124 . The register file  2058  provides temporary storage for operands connected to the data paths of the functional units (e.g., GPGPU cores  2062 , load/store units  2066 ) of the graphics multiprocessor  2124 . In one embodiment, the register file  2058  is divided between each of the functional units such that each functional unit is allocated a dedicated portion of the register file  2058 . In one embodiment, the register file  2058  is divided between the different warps being executed by the graphics multiprocessor  2124 . 
     The GPGPU cores  2062  can each include floating point units (FPUs) and/or integer arithmetic logic units (ALUs) that are used to execute instructions of the graphics multiprocessor  2124 . The GPGPU cores  2062  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  2062  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  2124  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  2062  include SIMD logic capable of performing a single instruction on multiple sets of data. In one embodiment GPGPU cores  2062  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  2068  is an interconnect network that connects each of the functional units of the graphics multiprocessor  2124  to the register file  2058  and to the shared memory  2070 . In one embodiment, the memory and cache interconnect  2068  is a crossbar interconnect that allows the load/store unit  2066  to implement load and store operations between the shared memory  2070  and the register file  2058 . The register file  2058  can operate at the same frequency as the GPGPU cores  2062 , thus data transfer between the GPGPU cores  2062  and the register file  2058  is very low latency. The shared memory  2070  can be used to enable communication between threads that execute on the functional units within the graphics multiprocessor  2034 . The cache memory  2072  can be used as a data cache for example, to cache texture data communicated between the functional units and the texture unit  2036 . The shared memory  2070  can also be used as a program managed cached. Threads executing on the GPGPU cores  2062  can programmatically store data within the shared memory in addition to the automatically cached data that is stored within the cache memory  2072 . 
       FIGS. 21A-21B  illustrate additional graphics multiprocessors, according to embodiments. The illustrated graphics multiprocessors  2125 ,  2150  are variants of the graphics multiprocessor  2034  of  FIG. 20C . The illustrated graphics multiprocessors  2125 ,  2150  can be configured as a streaming multiprocessor (SM) capable of simultaneous execution of a large number of execution threads. 
       FIG. 21A  shows a graphics multiprocessor  2125  according to an additional embodiment. The graphics multiprocessor  2125  includes multiple additional instances of execution resource units relative to the graphics multiprocessor  2034  of  FIG. 20D . For example, the graphics multiprocessor  2125  can include multiple instances of the instruction unit  2132 A- 2132 B, register file  2134 A- 2134 B, and texture unit(s)  2144 A- 2144 B. The graphics multiprocessor  2125  also includes multiple sets of graphics or compute execution units (e.g., GPGPU core  2136 A- 2136 B, GPGPU core  2137 A- 2137 B, GPGPU core  2138 A- 2138 B) and multiple sets of load/store units  2140 A- 2140 B. In one embodiment the execution resource units have a common instruction cache  2130 , texture and/or data cache memory  2142 , and shared memory  2146 . 
     The various components can communicate via an interconnect fabric  2127 . In one embodiment the interconnect fabric  2127  includes one or more crossbar switches to enable communication between the various components of the graphics multiprocessor  2125 . In one embodiment the interconnect fabric  2127  is a separate, high-speed network fabric layer upon which each component of the graphics multiprocessor  2125  is stacked. The components of the graphics multiprocessor  2125  communicate with remote components via the interconnect fabric  2127 . For example, the GPGPU cores  2136 A- 2136 B,  2137 A- 2137 B, and  21378 A- 2138 B can each communicate with shared memory  2146  via the interconnect fabric  2127 . The interconnect fabric  2127  can arbitrate communication within the graphics multiprocessor  2125  to ensure a fair bandwidth allocation between components. 
       FIG. 21B  shows a graphics multiprocessor  2150  according to an additional embodiment. The graphics processor includes multiple sets of execution resources  2156 A- 2156 D, where each set of execution resource includes multiple instruction units, register files, GPGPU cores, and load store units, as illustrated in  FIG. 20D  and  FIG. 21A . The execution resources  2156 A- 2156 D can work in concert with texture unit(s)  2160 A- 2160 D for texture operations, while sharing an instruction cache  2154 , and shared memory  2162 . In one embodiment the execution resources  2156 A- 2156 D can share an instruction cache  2154  and shared memory  2162 , as well as multiple instances of a texture and/or data cache memory  2158 A- 2158 B. The various components can communicate via an interconnect fabric  2152  similar to the interconnect fabric  2127  of  FIG. 21A . 
     Persons skilled in the art will understand that the architecture described in  FIGS. 19, 20A-20D, and 21A-21B  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. 22A  illustrates an exemplary architecture in which a plurality of GPUs  2210 - 2213  are communicatively coupled to a plurality of multi-core processors  2205 - 2206  over high-speed links  2240 - 2243  (e.g., buses, point-to-point interconnects, etc.). In one embodiment, the high-speed links  2240 - 2243  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  2210 - 2213  are interconnected over high-speed links  2244 - 2245 , which may be implemented using the same or different protocols/links than those used for high-speed links  2240 - 2243 . Similarly, two or more of the multi-core processors  2205 - 2206  may be connected over high speed link  2233  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. 22A  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  2205 - 2206  is communicatively coupled to a processor memory  2201 - 2202 , via memory interconnects  2230 - 2231 , respectively, and each GPU  2210 - 2213  is communicatively coupled to GPU memory  2220 - 2223  over GPU memory interconnects  2250 - 2253 , respectively. The memory interconnects  2230 - 2231  and  2250 - 2253  may utilize the same or different memory access technologies. By way of example, and not limitation, the processor memories  2201 - 2202  and GPU memories  2220 - 2223  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  2205 - 2206  and GPUs  2210 - 2213  may be physically coupled to a particular memory  2201 - 2202 ,  2220 - 2223 , 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  2201 - 2202  may each comprise 64 GB of the system memory address space and GPU memories  2220 - 2223  may each comprise 32 GB of the system memory address space (resulting in a total of 256 GB addressable memory in this example). 
       FIG. 22B  illustrates additional details for an interconnection between a multi-core processor  2207  and a graphics acceleration module  2246  in accordance with one embodiment. The graphics acceleration module  2246  may include one or more GPU chips integrated on a line card which is coupled to the processor  2207  via the high-speed link  2240 . Alternatively, the graphics acceleration module  2246  may be integrated on the same package or chip as the processor  2207 . 
     The illustrated processor  2207  includes a plurality of cores  2260 A- 2260 D, each with a translation lookaside buffer  2261 A- 2261 D and one or more caches  2262 A- 2262 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  2262 A- 2262 D may comprise level 1 (L1) and level 2 (L2) caches. In addition, one or more shared caches  2226  may be included in the caching hierarchy and shared by sets of the cores  2260 A- 2260 D. For example, one embodiment of the processor  2207  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  2207  and the graphics accelerator integration module  2246  connect with system memory  2241 , which may include processor memories  2201 - 2202   
     Coherency is maintained for data and instructions stored in the various caches  2262 A- 2262 D,  2256  and system memory  2241  via inter-core communication over a coherence bus  2264 . For example, each cache may have cache coherency logic/circuitry associated therewith to communicate to over the coherence bus  2264  in response to detected reads or writes to particular cache lines. In one implementation, a cache snooping protocol is implemented over the coherence bus  2264  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  2225  communicatively couples the graphics acceleration module  2246  to the coherence bus  2264 , allowing the graphics acceleration module  2246  to participate in the cache coherence protocol as a peer of the cores. In particular, an interface  2235  provides connectivity to the proxy circuit  2225  over high-speed link  2240  (e.g., a PCIe bus, NVLink, etc.) and an interface  2237  connects the graphics acceleration module  2246  to the link  2240 . 
     In one implementation, an accelerator integration circuit  2236  provides cache management, memory access, context management, and interrupt management services on behalf of a plurality of graphics processing engines  2231 ,  2232 , N of the graphics acceleration module  2246 . The graphics processing engines  2231 ,  2232 , N may each comprise a separate graphics processing unit (GPU). Alternatively, the graphics processing engines  2231 ,  2232 , 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  2231 - 2232 , N or the graphics processing engines  2231 - 2232 , N may be individual GPUs integrated on a common package, line card, or chip. 
     In one embodiment, the accelerator integration circuit  2236  includes a memory management unit (MMU)  2239  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  2241 . The MMU  2239  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  2238  stores commands and data for efficient access by the graphics processing engines  2231 - 2232 , N. In one embodiment, the data stored in cache  2238  and graphics memories  2233 - 2234 , N is kept coherent with the core caches  2262 A- 2262 D,  2256  and system memory  2211 . As mentioned, this may be accomplished via proxy circuit  2225  which takes part in the cache coherency mechanism on behalf of cache  2238  and memories  2233 - 2234 , N (e.g., sending updates to the cache  2238  related to modifications/accesses of cache lines on processor caches  2262 A- 2262 D,  2256  and receiving updates from the cache  2238 ). 
     A set of registers  2245  store context data for threads executed by the graphics processing engines  2231 - 2232 , N and a context management circuit  2248  manages the thread contexts. For example, the context management circuit  2248  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  2248  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  2247  receives and processes interrupts received from system devices. 
     In one implementation, virtual/effective addresses from a graphics processing engine  2231  are translated to real/physical addresses in system memory  2211  by the MMU  2239 . One embodiment of the accelerator integration circuit  2236  supports multiple (e.g., 4, 8, 16) graphics accelerator modules  2246  and/or other accelerator devices. The graphics accelerator module  2246  may be dedicated to a single application executed on the processor  2207  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  2231 - 2232 , 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  2246  and provides address translation and system memory cache services. In addition, the accelerator integration circuit  2236  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  2231 - 2232 , N are mapped explicitly to the real address space seen by the host processor  2207 , any host processor can address these resources directly using an effective address value. One function of the accelerator integration circuit  2236 , in one embodiment, is the physical separation of the graphics processing engines  2231 - 2232 , N so that they appear to the system as independent units. 
     As mentioned, in the illustrated embodiment, one or more graphics memories  2233 - 2234 , M are coupled to each of the graphics processing engines  2231 - 2232 , N, respectively. The graphics memories  2233 - 2234 , M store instructions and data being processed by each of the graphics processing engines  2231 - 2232 , N. The graphics memories  2233 - 2234 , 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  2240 , biasing techniques are used to ensure that the data stored in graphics memories  2233 - 2234 , M is data which will be used most frequently by the graphics processing engines  2231 - 2232 , N and preferably not used by the cores  2260 A- 2260 D (at least not frequently). Similarly, the biasing mechanism attempts to keep data needed by the cores (and preferably not the graphics processing engines  2231 - 2232 , N) within the caches  2262 A- 2262 D,  2256  of the cores and system memory  2211 . 
       FIG. 22C  illustrates another embodiment in which the accelerator integration circuit  2236  is integrated within the processor  2207 . In this embodiment, the graphics processing engines  2231 - 2232 , N communicate directly over the high-speed link  2240  to the accelerator integration circuit  2236  via interface  2237  and interface  2235  (which, again, may be utilize any form of bus or interface protocol). The accelerator integration circuit  2236  may perform the same operations as those described with respect to  FIG. 22B , but potentially at a higher throughput given its close proximity to the coherency bus  2262  and caches  2262 A- 2262 D,  2226 . 
     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  2236  and programming models which are controlled by the graphics acceleration module  2246 . 
     In one embodiment of the dedicated process model, graphics processing engines  2231 - 2232 , 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  2231 - 2232 , N, providing virtualization within a VM/partition. 
     In the dedicated-process programming models, the graphics processing engines  2231 - 2232 , N, may be shared by multiple VM/application partitions. The shared models require a system hypervisor to virtualize the graphics processing engines  2231 - 2232 , N to allow access by each operating system. For single-partition systems without a hypervisor, the graphics processing engines  2231 - 2232 , N are owned by the operating system. In both cases, the operating system can virtualize the graphics processing engines  2231 - 2232 , N to provide access to each process or application. 
     For the shared programming model, the graphics acceleration module  2246  or an individual graphics processing engine  2231 - 2232 , N selects a process element using a process handle. In one embodiment, process elements are stored in system memory  2211  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  2231 - 2232 , 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. 22D  illustrates an exemplary accelerator integration slice  2290 . As used herein, a “slice” comprises a specified portion of the processing resources of the accelerator integration circuit  2236 . Application effective address space  2282  within system memory  2211  stores process elements  2283 . In one embodiment, the process elements  2283  are stored in response to GPU invocations  2281  from applications  2280  executed on the processor  2207 . A process element  2283  contains the process state for the corresponding application  2280 . A work descriptor (WD)  2284  contained in the process element  2283  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  2284  is a pointer to the job request queue in the application&#39;s address space  2282 . 
     The graphics acceleration module  2246  and/or the individual graphics processing engines  2231 - 2232 , 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  2284  to a graphics acceleration module  2246  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  2246  or an individual graphics processing engine  2231 . Because the graphics acceleration module  2246  is owned by a single process, the hypervisor initializes the accelerator integration circuit  2236  for the owning partition and the operating system initializes the accelerator integration circuit  2236  for the owning process at the time when the graphics acceleration module  2246  is assigned. 
     In operation, a WD fetch unit  2291  in the accelerator integration slice  2290  fetches the next WD  2284  which includes an indication of the work to be done by one of the graphics processing engines of the graphics acceleration module  2246 . Data from the WD  2284  may be stored in registers  2245  and used by the MMU  2239 , interrupt management circuit  2247  and/or context management circuit  2246  as illustrated. For example, one embodiment of the MMU  2239  includes segment/page walk circuitry for accessing segment/page tables  2286  within the OS virtual address space  2285 . The interrupt management circuit  2247  may process interrupt events  2292  received from the graphics acceleration module  2246 . When performing graphics operations, an effective address  2293  generated by a graphics processing engine  2231 - 2232 , N is translated to a real address by the MMU  2239 . 
     In one embodiment, the same set of registers  2245  are duplicated for each graphics processing engine  2231 - 2232 , N and/or graphics acceleration module  2246  and may be initialized by the hypervisor or operating system. Each of these duplicated registers may be included in an accelerator integration slice  2290 . 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  2284  is specific to a particular graphics acceleration module  2246  and/or graphics processing engine  2231 - 2232 , N. It contains all the information a graphics processing engine  2231 - 2232 , 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. 22E  illustrates additional details for one embodiment of a shared model. This embodiment includes a hypervisor real address space  2298  in which a process element list  2299  is stored. The hypervisor real address space  2298  is accessible via a hypervisor  2296  which virtualizes the graphics acceleration module engines for the operating system  2295 . 
     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  2246 . There are two programming models where the graphics acceleration module  2246  is shared by multiple processes and partitions: time-sliced shared and graphics directed shared. 
     In this model, the system hypervisor  2296  owns the graphics acceleration module  2246  and makes its function available to all operating systems  2295 . For a graphics acceleration module  2246  to support virtualization by the system hypervisor  2296 , the graphics acceleration module  2246  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  2246  must provide a context save and restore mechanism. 2) An application&#39;s job request is guaranteed by the graphics acceleration module  2246  to complete in a specified amount of time, including any translation faults, or the graphics acceleration module  2246  provides the ability to preempt the processing of the job. 3) The graphics acceleration module  2246  must be guaranteed fairness between processes when operating in the directed shared programming model. 
     In one embodiment, for the shared model, the application  2280  is required to make an operating system  2295  system call with a graphics acceleration module  2246  type, a work descriptor (WD), an authority mask register (AMR) value, and a context save/restore area pointer (CSRP). The graphics acceleration module  2246  type describes the targeted acceleration function for the system call. The graphics acceleration module  2246  type may be a system-specific value. The WD is formatted specifically for the graphics acceleration module  2246  and can be in the form of a graphics acceleration module  2246  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  2246 . 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  2236  and graphics acceleration module  2246  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  2296  may optionally apply the current Authority Mask Override Register (AMOR) value before placing the AMR into the process element  2283 . In one embodiment, the CSRP is one of the registers  2245  containing the effective address of an area in the application&#39;s address space  2282  for the graphics acceleration module  2246  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  2295  may verify that the application  2280  has registered and been given the authority to use the graphics acceleration module  2246 . The operating system  2295  then calls the hypervisor  2296  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  2296  verifies that the operating system  2295  has registered and been given the authority to use the graphics acceleration module  2246 . The hypervisor  2296  then puts the process element  2283  into the process element linked list for the corresponding graphics acceleration module  2246  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  2290  registers  2245 . 
     As illustrated in  FIG. 22F , one embodiment of the invention employs a unified memory addressable via a common virtual memory address space used to access the physical processor memories  2201 - 2202  and GPU memories  2220 - 2223 . In this implementation, operations executed on the GPUs  2210 - 2213  utilize the same virtual/effective memory address space to access the processors memories  2201 - 2202  and vice versa, thereby simplifying programmability. In one embodiment, a first portion of the virtual/effective address space is allocated to the processor memory  2201 , a second portion to the second processor memory  2202 , a third portion to the GPU memory  2220 , 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  2201 - 2202  and GPU memories  2220 - 2223 , 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  2294 A- 2294 E within one or more of the MMUs  2239 A- 2239 E ensures cache coherence between the caches of the host processors (e.g.,  2205 ) and the GPUs  2210 - 2213  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  2294 A- 2294 E are illustrated in  FIG. 22F , the bias/coherence circuitry may be implemented within the MMU of one or more host processors  2205  and/or within the accelerator integration circuit  2236 . 
     One embodiment allows GPU-attached memory  2220 - 2223  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  2220 - 2223  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  2205  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  2220 - 2223  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  2210 - 2213 . 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  2220 - 2223 , with or without a bias cache in the GPU  2210 - 2213  (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  2220 - 2223  is accessed prior the actual access to the GPU memory, causing the following operations. First, local requests from the GPU  2210 - 2213  that find their page in GPU bias are forwarded directly to a corresponding GPU memory  2220 - 2223 . Local requests from the GPU that find their page in host bias are forwarded to the processor  2205  (e.g., over a high-speed link as discussed above). In one embodiment, requests from the processor  2205  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  2210 - 2213 . 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  2205  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  2205 . To access these pages, the processor  2205  may request access from the GPU  2210  which may or may not grant access right away, depending on the implementation. Thus, to reduce communication between the processor  2205  and GPU  2210  it is beneficial to ensure that GPU-biased pages are those which are required by the GPU but not the host processor  2205  and vice versa. 
     Graphics Processing Pipeline 
       FIG. 23  illustrates a graphics processing pipeline  2300 , according to an embodiment. In one embodiment a graphics processor can implement the illustrated graphics processing pipeline  2300 . The graphics processor can be included within the parallel processing subsystems as described herein, such as the parallel processor  2000  of  FIG. 20 , which, in one embodiment, is a variant of the parallel processor(s)  1912  of  FIG. 19 . The various parallel processing systems can implement the graphics processing pipeline  2300  via one or more instances of the parallel processing unit (e.g., parallel processing unit  2002  of  FIG. 20 ) as described herein. For example, a shader unit (e.g., graphics multiprocessor  2034  of  FIG. 21 ) may be configured to perform the functions of one or more of a vertex processing unit  2304 , a tessellation control processing unit  2308 , a tessellation evaluation processing unit  2312 , a geometry processing unit  2316 , and a fragment/pixel processing unit  2324 . The functions of data assembler  2302 , primitive assemblers  2306 ,  2314 ,  2318 , tessellation unit  2310 , rasterizer  2322 , and raster operations unit  2326  may also be performed by other processing engines within a processing cluster (e.g., processing cluster  2014  of  FIG. 21 ) and a corresponding partition unit (e.g., partition unit  2020 A- 2020 N of  FIG. 20 ). The graphics processing pipeline  2300  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  2300  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  2300  can access on-chip memory (e.g., parallel processor memory  2022  as in  FIG. 20 ) via a memory interface  2328 , which may be an instance of the memory interface  2018  of  FIG. 20 . 
     In one embodiment the data assembler  2302  is a processing unit that collects vertex data for surfaces and primitives. The data assembler  2302  then outputs the vertex data, including the vertex attributes, to the vertex processing unit  2304 . The vertex processing unit  2304  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  2304  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  2306  receives vertex attributes from the vertex processing unit  230 . The primitive assembler  2306  readings stored vertex attributes as needed and constructs graphics primitives for processing by tessellation control processing unit  2308 . 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  2308  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  2312 . The tessellation control processing unit  2308  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  2310  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  2312 . The tessellation evaluation processing unit  2312  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  2314  receives vertex attributes from the tessellation evaluation processing unit  2312 , reading stored vertex attributes as needed, and constructs graphics primitives for processing by the geometry processing unit  2316 . The geometry processing unit  2316  is a programmable execution unit that executes geometry shader programs to transform graphics primitives received from primitive assembler  2314  as specified by the geometry shader programs. In one embodiment the geometry processing unit  2316  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  2316  can add or delete elements in the geometry stream. The geometry processing unit  2316  outputs the parameters and vertices specifying new graphics primitives to primitive assembler  2318 . The primitive assembler  2318  receives the parameters and vertices from the geometry processing unit  2316  and constructs graphics primitives for processing by a viewport scale, cull, and clip unit  2320 . The geometry processing unit  2316  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  2320  performs clipping, culling, and viewport scaling and outputs processed graphics primitives to a rasterizer  2322 . 
     The rasterizer  2322  can perform depth culling and other depth-based optimizations. The rasterizer  2322  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  2324 . The fragment/pixel processing unit  2324  is a programmable execution unit that is configured to execute fragment shader programs or pixel shader programs. The fragment/pixel processing unit  2324  transforming fragments or pixels received from rasterizer  2322 , as specified by the fragment or pixel shader programs. For example, the fragment/pixel processing unit  2324  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  2326 . The fragment/pixel processing unit  2324  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  2326  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  2022  as in  FIG. 20 , and/or system memory  1904  as in  FIG. 19 , to be displayed on the one or more display device(s)  1910  or for further processing by one of the one or more processor(s)  1902  or parallel processor(s)  1912 . In some embodiments the raster operations unit  2326  is configured to compress z or color data that is written to memory and decompress z or color data that is read from memory. 
     In embodiments, the term “engine” or “module” or “logic” may refer to, be part of, or include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. In embodiments, an engine or a module may be implemented in firmware, hardware, software, or any combination of firmware, hardware, and software. 
     Embodiments of the invention may include various steps, which have been described above. The steps may be embodied in machine-executable instructions which may be used to cause a general-purpose or special-purpose processor to perform the steps. Alternatively, these steps may be performed by specific hardware components that contain hardwired logic for performing the steps, or by any combination of programmed computer components and custom hardware components. 
     As described herein, instructions may refer to specific configurations of hardware such as application specific integrated circuits (ASICs) configured to perform certain operations or having a predetermined functionality or software instructions stored in memory embodied in a non-transitory computer readable medium. Thus, the techniques shown in the figures can be implemented using code and data stored and executed on one or more electronic devices (e.g., an end station, a network element, etc.). Such electronic devices store and communicate (internally and/or with other electronic devices over a network) code and data using computer machine-readable media, such as non-transitory computer machine-readable storage media (e.g., magnetic disks; optical disks; random access memory; read only memory; flash memory devices; phase-change memory) and transitory computer machine-readable communication media (e.g., electrical, optical, acoustical or other form of propagated signals—such as carrier waves, infrared signals, digital signals, etc.). 
     In addition, such electronic devices typically include a set of one or more processors coupled to one or more other components, such as one or more storage devices (non-transitory machine-readable storage media), user input/output devices (e.g., a keyboard, a touchscreen, and/or a display), and network connections. The coupling of the set of processors and other components is typically through one or more busses and bridges (also termed as bus controllers). The storage device and signals carrying the network traffic respectively represent one or more machine-readable storage media and machine-readable communication media. Thus, the storage device of a given electronic device typically stores code and/or data for execution on the set of one or more processors of that electronic device. Of course, one or more parts of an embodiment of the invention may be implemented using different combinations of software, firmware, and/or hardware. Throughout this detailed description, for the purposes of explanation, numerous specific details were set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without some of these specific details. In certain instances, well known structures and functions were not described in elaborate detail in order to avoid obscuring the subject matter of the present invention. Accordingly, the scope and spirit of the invention should be judged in terms of the claims which follow.