name	OpenCL
logo
author	Apple Inc.
developer	Khronos Group
latest release version	1.1
latest release date
operating system	Cross-platform
genre	API
license	Royalty Free
website	www.khronos.org/openclwww.khronos.org/webcl }}

OpenCL (Open Computing Language) is a framework for writing programs that execute across heterogeneous platforms consisting of CPUs, GPUs, and other processors. OpenCL includes a language (based on C99) for writing ''kernels'' (functions that execute on OpenCL devices), plus APIs that are used to define and then control the platforms. OpenCL provides parallel computing using task-based and data-based parallelism. It has been adopted by Intel, AMD, ATI, and ARM. OpenCL is an open standard defined by the Khronos Group.

OpenCL gives any application access to the graphics processing unit for non-graphical computing. Thus, OpenCL extends the power of the Graphics Processing Unit beyond graphics (general-purpose computing on graphics processing units). Academic researchers have investigated automatically compiling OpenCL programs into application-specific processors running on FPGAs, and commercial FPGA vendors are developing tools to translate OpenCL to run on their FPGA devices.

OpenCL is analogous to the open industry standards OpenGL and OpenAL, for 3D graphics and computer audio, respectively. OpenCL is managed by the non-profit technology consortium Khronos Group.

History

OpenCL was initially developed by Apple Inc., which holds trademark rights, and refined into an initial proposal in collaboration with technical teams at AMD, IBM, Intel, and Nvidia. Apple submitted this initial proposal to the Khronos Group. On June 16, 2008 the Khronos Compute Working Group was formed with representatives from CPU, GPU, embedded-processor, and software companies. This group worked for five months to finish the technical details of the specification for OpenCL 1.0 by November 18, 2008. This technical specification was reviewed by the Khronos members and approved for public release on December 8, 2008.

OpenCL 1.0 has been released with Mac OS X Snow Leopard. According to an Apple press release:

Snow Leopard further extends support for modern hardware with Open Computing Language (OpenCL), which lets any application tap into the vast gigaflops of GPU computing power previously available only to graphics applications. OpenCL is based on the C programming language and has been proposed as an open standard.

AMD has decided to support OpenCL (and DirectX 11) instead of the now deprecated Close to Metal in its Stream framework. RapidMind announced their adoption of OpenCL underneath their development platform, in order to support GPUs from multiple vendors with one interface. On December 9, 2008, Nvidia announced its intention to add full support for the OpenCL 1.0 specification to its GPU Computing Toolkit. On October 30, 2009, IBM released its first OpenCL implementation as a part of the XL compilers.

OpenCL 1.1 was ratified by the Khronos Group June 14, 2010 and adds significant functionality for enhanced parallel programming flexibility, functionality and performance including:

New data types including 3-component vectors and additional image formats;

Handling commands from multiple host threads and processing buffers across multiple devices;

Operations on regions of a buffer including read, write and copy of 1D, 2D or 3D rectangular regions;

Enhanced use of events to drive and control command execution;

Additional OpenCL built-in C functions such as integer clamp, shuffle and asynchronous strided copies;

Improved OpenGL interoperability through efficient sharing of images and buffers by linking OpenCL and OpenGL events.

The OpenCL specification is under development at Khronos, which is open to any interested company to join.

Implementation

On December 10, 2008, AMD and Nvidia held the first public OpenCL demonstration, a 75-minute presentation at Siggraph Asia 2008. AMD showed a CPU-accelerated OpenCL demo explaining the scalability of OpenCL on one or more cores while Nvidia showed a GPU-accelerated demo. On March 16, 2009, at the 4th Multicore Expo, Imagination Technologies announced the PowerVR SGX543MP, the first GPU of this company to feature OpenCL support. On March 26, 2009, at GDC 2009, AMD and Havok demonstrated the first working implementation for OpenCL accelerating Havok Cloth on AMD Radeon HD 4000 series GPU. On April 20, 2009, Nvidia announced the release of its OpenCL driver and SDK to developers participating in its OpenCL Early Access Program. On August 5, 2009, AMD unveiled the first development tools for its OpenCL platform as part of its ATI Stream SDK v2.0 Beta Program. On August 28, 2009, Apple released Mac OS X Snow Leopard, which contains a full implementation of OpenCL. :OpenCL in Snow Leopard is supported on the NVIDIA GeForce 320M, GeForce GT 330M, GeForce 9400M, GeForce 9600M GT, GeForce 8600M GT, GeForce GT 120, GeForce GT 130, GeForce GTX 285, GeForce 8800 GT, GeForce 8800 GS, Quadro FX 4800, Quadro FX5600, ATI Radeon HD 4670, ATI Radeon HD 4850, Radeon HD 4870, ATI Radeon HD 5670, ATI Radeon HD 5750, ATI Radeon HD 5770 and ATI Radeon HD 5870.

On September 28, 2009, NVIDIA released its own OpenCL drivers and SDK implementation.

On October 13, 2009, AMD released the fourth beta of the ATI Stream SDK 2.0, which provides a complete OpenCL implementation on both R700/R800 GPUs and SSE3 capable CPUs. The SDK is available for both Linux and Windows.

On November 26, 2009, NVIDIA released drivers for OpenCL 1.0 (rev 48).

:The Apple, Nvidia, RapidMind and Gallium3D implementations of OpenCL are all based on the LLVM Compiler technology and use the Clang Compiler as its frontend. On October 27, 2009, S3 released their first product supporting native OpenCL 1.0 - the Chrome 5400E embedded graphics processor. On December 10, 2009, VIA released their first product supporting OpenCL 1.0 - ChromotionHD 2.0 video processor included in VN1000 chipset. On December 21, 2009, AMD released the production version of the ATI Stream SDK 2.0, which provides OpenCL 1.0 support for R800 GPUs and beta support for R700 GPUs. On June 1, 2010, ZiiLABS released details of their first OpenCL implementation for the ZMS processor for handheld, embedded and digital home products. On June 30, 2010, IBM released a fully conformant version of OpenCL 1.0. On September 13, 2010, Intel released details of their first OpenCL implementation for the Sandy Bridge chip architecture. Sandy Bridge will integrate Intel's newest graphics chip technology directly onto the central processing unit.

On November 15, 2010, Wolfram Research released Mathematica 8 with OpenCLLink package.

On March 3, 2011, Khronos Group announces the formation of the WebCL working group to explore defining a JavaScript binding to OpenCL. This creates the potential to harness GPU and multi-core CPU parallel processing from a Web browser. On March 31, 2011, IBM released a fully conformant version of OpenCL 1.1. On May 4, 2011, Nokia Research releases an open source WebCL extension for the Firefox web browser, providing a JavaScript binding to OpenCL. On July 1, 2011, Samsung Electronics releases an open source prototype implementation of WebCL for WebKit, providing a JavaScript binding to OpenCL. On August 8, 2011, AMD released the OpenCL-driven AMD Accelerated Parallel Processing (APP) Software Development Kit (SDK) v2.5, replacing the ATI Stream SDK as technology and concept.

OpenCL language

The programming language used to write computation kernels is based on C99 with some limitations and additions. It omits the use of function pointers, recursion, bit fields, variable-length arrays, and standard C99 header files. The language is extended to easily use parallelism with vector types and operations, synchronization, functions to work with work-items/groups. It has memory region qualifiers: __global, __local, __constant, and __private. Also, a lot of built-in functions are added.

Example

This example will load a Fast Fourier Transformation (FFT) and execute it: // create a compute context with GPU device context = clCreateContextFromType(NULL, CL_DEVICE_TYPE_GPU, NULL, NULL, NULL);

// create a command queue queue = clCreateCommandQueue(context, NULL, 0, NULL);

// allocate the buffer memory objects memobjs[0] = clCreateBuffer(context, CL_MEM_READ_ONLY | CL_MEM_COPY_HOST_PTR, sizeof(float)*2*num_entries, srcA, NULL); memobjs[1] = clCreateBuffer(context, CL_MEM_READ_WRITE, sizeof(float)*2*num_entries, NULL, NULL);

// create the compute program program = clCreateProgramWithSource(context, 1, &fft1D;_1024_kernel_src, NULL, NULL);

// build the compute program executable clBuildProgram(program, 0, NULL, NULL, NULL, NULL);

// create the compute kernel kernel = clCreateKernel(program, "fft1D_1024", NULL);

// set the args values clSetKernelArg(kernel, 0, sizeof(cl_mem), (void *)&memobjs;[0]); clSetKernelArg(kernel, 1, sizeof(cl_mem), (void *)&memobjs;[1]); clSetKernelArg(kernel, 2, sizeof(float)*(local_work_size[0]+1)*16, NULL); clSetKernelArg(kernel, 3, sizeof(float)*(local_work_size[0]+1)*16, NULL);

// create N-D range object with work-item dimensions and execute kernel global_work_size[0] = num_entries; local_work_size[0] = 64; clEnqueueNDRangeKernel(queue, kernel, 1, NULL, global_work_size, local_work_size, 0, NULL, NULL);

The actual calculation: (Based on Fitting FFT onto the G80 Architecture) // This kernel computes FFT of length 1024. The 1024 length FFT is decomposed into // calls to a radix 16 function, another radix 16 function and then a radix 4 function

__kernel void fft1D_1024 (__global float2 *in, __global float2 *out, __local float *sMemx, __local float *sMemy) { int tid = get_local_id(0); int blockIdx = get_group_id(0) * 1024 + tid; float2 data[16];

// starting index of data to/from global memory in = in + blockIdx; out = out + blockIdx;

globalLoads(data, in, 64); // coalesced global reads fftRadix16Pass(data); // in-place radix-16 pass twiddleFactorMul(data, tid, 1024, 0);

// local shuffle using local memory localShuffle(data, sMemx, sMemy, tid, (((tid & 15) * 65) + (tid >> 4))); fftRadix16Pass(data); // in-place radix-16 pass twiddleFactorMul(data, tid, 64, 4); // twiddle factor multiplication

localShuffle(data, sMemx, sMemy, tid, (((tid >> 4) * 64) + (tid & 15)));

// four radix-4 function calls fftRadix4Pass(data); // radix-4 function number 1 fftRadix4Pass(data + 4); // radix-4 function number 2 fftRadix4Pass(data + 8); // radix-4 function number 3 fftRadix4Pass(data + 12); // radix-4 function number 4

// coalesced global writes globalStores(data, out, 64); } A full, open source implementation of an OpenCL FFT can be found on Apple's website

OpenCL Conformant Products

The Khronos Group announces an extended list of OpenCL conformant products, see OpenCL Conformant Products.

Synopsis of OpenCL conformant products
AMD APP SDK (supports OpenCL CPU and Accelerated processing unit Devices)		AMD Fusion E-350, E-240, C-50, C-30 with HD 6310/HD 6250	AMD Radeon/Mobility HD 6800, HD 5x00 series GPU, iGPU HD 6310/HD 6250	ATI FirePro Vx800 series GPU
Intel OpenCL SDK 1.1 (supports only OpenCL Intel Core based CPU Device)	Intel CPUs with SSE 4.1, SSE 4.2 or AVX support. Microsoft Windows, Linux	Intel Core i7, i5, i3; 2nd Generation Intel Core i7/5/3				IBM BladeCenter JS2x, JS43	IBM BladeCenter QS22
NVIDIA OpenCL Driver	[[NVIDIA">Intel Core (microarchitecture)	[[Xeon#Core-based_Xeon
!style="text-align:left"			IBM BladeCenter JS2x, JS43	IBM BladeCenter QS22
NVIDIA OpenCL Driver	[[NVIDIA Tesla C/D/S	NVIDIA GeForce GTS/GT/GTX	NVIDIA ION	NVIDIA Quadro FX/NVX/Plex

See also

GPGPU

CUDA

OpenHMPP

DirectCompute

FireStream

Larrabee

Close to Metal

BrookGPU

Lib Sh

CLyther

References

External links

Documentation

OpenCL 1.1 Specification

OpenCL 1.1 Reference Pages

OpenCL 1.1 Quick Reference card

Drivers

OpenCL for Nvidia (Download page)

OpenCL for AMD (Download page)

OpenCL for Intel (Download Page)

OpenCL for IBM (Download page)

Libraries

OpenCLLink package for Mathematica

OpenCL toolbox for MATLAB

AMD Accelerated Parallel Processing Math Libraries

ViennaCL

GPU Automatically Tuned Linear Algebra Software

OpenCL Data Parallel Primitives Library

Language Bindings and Wrappers

WebCL JavaScript bindings for Firefox

WebCL JavaScript bindings for WebKit

cl4d D bindings

JOCL Java bindings

JogAmp Java bindings

PyOpenCL Python bindings

PyOpenCL Python bindings

The Open Toolkit library cross-platform C#, OpenGL, OpenAL and OpenCL wrapper for Mono/.NET

Tools

gDEBugger CL debugger

clcc Open-source, cross-platform OpenCL compiler and API entry point loader

Fixstars OpenCL Cross Compiler Source-to-source compiler from OpenCL C to readable C code

MinGW Package with OpenCL support

OpenCL definition language for Notepad++

GPU Caps Viewer

OpenCL-Z

Scalable Heterogeneous Computing (SHOC) Benchmark Suite

OpenCL Studio integrated development environment

CLyther extension language

ImageMagick

MandelGPU, SmallptGPU, and JuliaGPU

Eyeon Fusion

Category:GPGPU

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