GPGPU

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GPGPU stands for General-purpose computing on graphics processing units. In Linux, there are currently two major GPGPU frameworks: OpenCL and CUDA.

OpenCL

OpenCL (Open Computing Language) is an open, royalty-free parallel programming specification developed by the Khronos Group, a non-profit consortium.

The OpenCL specification describes a programming language, a general environment that is required to be present, and a C API to enable programmers to call into this environment.

Tip: The clinfo utility can be used to list OpenCL platforms, devices present and ICD loader properties.

OpenCL Runtime

To execute programs that use OpenCL, a compatible hardware runtime needs to be installed.

AMD/ATI

NVIDIA

Intel

  • intel-compute-runtime: a.k.a. the Neo OpenCL runtime, the open-source implementation for Intel HD Graphics GPU on Gen8 (Broadwell) and beyond.
  • beignet: the open-source implementation for Intel HD Graphics GPU on Gen7 (Ivy Bridge) and beyond, deprecated by Intel in favour of NEO OpenCL driver, remains recommended solution for legacy HW platforms (e.g. Ivy Bridge, Sandy Bridge, Haswell).
  • intel-openclAUR: the proprietary implementation for Intel HD Graphics GPU on Gen7 (Ivy Bridge) and beyond, deprecated by Intel in favour of NEO OpenCL driver, remains recommended solution for legacy HW platforms (e.g. Ivy Bridge, Sandy Bridge, Haswell).
  • intel-opencl-runtimeAUR: the implementation for Intel Core and Xeon processors. It also supports non-Intel CPUs.

Others

  • poclAUR: LLVM-based OpenCL implementation

OpenCL ICD loader (libOpenCL.so)

The OpenCL ICD loader is supposed to be a platform-agnostic library that provides the means to load device-specific drivers through the OpenCL API. Most OpenCL vendors provide their own implementation of an OpenCL ICD loader, and these should all work with the other vendors' OpenCL implementations. Unfortunately, most vendors do not provide completely up-to-date ICD loaders, and therefore Arch Linux has decided to provide this library from a separate project (ocl-icd) which currently provides a functioning implementation of the current OpenCL API.

The other ICD loader libraries are installed as part of each vendor's SDK. If you want to ensure the ICD loader from the ocl-icd package is used, you can create a file in /etc/ld.so.conf.d which adds /usr/lib to the dynamic program loader's search directories:

/etc/ld.so.conf.d/00-usrlib.conf
/usr/lib

This is necessary because all the SDKs add their runtime's lib directories to the search path through ld.so.conf.d files.

The available packages containing various OpenCL ICDs are:

  • ocl-icd: recommended, most up-to-date
  • libopenclAUR by AMD. Provides OpenCL 2.0. It is distributed by AMD under a restrictive license and therefore cannot be included into the official repositories.
  • intel-openclAUR by Intel. Provides OpenCL 2.0, deprecated in favour of intel-compute-runtime.
Note: ICD Loader's vendor is mentioned only to identify each loader, it is otherwise completely irrelevant. ICD loaders are vendor-agnostic and may be used interchangeably (as long as they are implemented correctly).

OpenCL Development

For OpenCL development, the bare minimum additional packages required, are:

  • ocl-icd: OpenCL ICD loader implementation, up to date with the latest OpenCL specification.
  • opencl-headers: OpenCL C/C++ API headers.

The vendors' SDKs provide a multitude of tools and support libraries:

  • intel-opencl-sdkAUR: Intel OpenCL SDK (old version, new OpenCL SDKs are included in the INDE and Intel Media Server Studio)
  • amdapp-sdkAUR: This package is installed as /opt/AMDAPP and apart from SDK files it also contains a number of code samples (/opt/AMDAPP/SDK/samples/). It also provides the clinfo utility which lists OpenCL platforms and devices present in the system and displays detailed information about them. As AMD APP SDK itself contains CPU OpenCL driver, no extra driver is needed to execute OpenCL on CPU devices (regardless of its vendor). GPU OpenCL drivers are provided by the catalystAUR package (an optional dependency).
  • cuda: Nvidia's GPU SDK which includes support for OpenCL 1.1.

Implementations

To see which OpenCL implementations are currently active on your system, use the following command:

$ ls /etc/OpenCL/vendors

To find out all possible (known) properties of the OpenCL platform and devices available on the system, install clinfo.

Language bindings

SYCL

SYCL is another open and royalty-free standard by the Khronos Group that defines a single-source heterogeneous programming model for C++ on top of OpenCL 1.2.

SYCL consists of a runtime part and a C++ device compiler. The device compiler may target any number and kind of accelerators. The runtime is required to fall back to a pure CPU code path in case no OpenCL implementation can be found.

Implementations

  • computecppAUR Codeplay's proprietary implementation of SYCL 1.2.1. Can target SPIR, SPIR-V and experimentally PTX (NVIDIA) as device targets.
  • trisycl-gitAUR: Open source implementation mainly driven by Xilinx.
  • hipsycl-cuda-gitAUR and hipsycl-rocm-gitAUR: Free implementation built over AMD's HIP instead of OpenCL. Is able to run on AMD and NVIDIA GPUs.

Checking For SPIR Support

Most SYCL implementations are able to compile the accelerator code to SPIR or SPIR-V. Both are intermediate languages designed by Khronos that can be consumed by an OpenCL driver. To check whether SPIR or SPIR-V are supported clinfo can be used:

$ clinfo | grep -i spir
Platform Extensions                             cl_khr_icd cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_byte_addressable_store cl_khr_depth_images cl_khr_3d_image_writes cl_intel_exec_by_local_thread cl_khr_spir cl_khr_fp64 cl_khr_image2d_from_buffer cl_intel_vec_len_hint 
  IL version                                    SPIR-V_1.0
  SPIR versions                                 1.2

ComputeCpp additionally ships with a tool that summarizes the relevant system information:

$ computecpp_info
Device 0:

  Device is supported                     : UNTESTED - Untested OS
  CL_DEVICE_NAME                          : Intel(R) Core(TM) i7-4770K CPU @ 3.50GHz
  CL_DEVICE_VENDOR                        : Intel(R) Corporation
  CL_DRIVER_VERSION                       : 18.1.0.0920
  CL_DEVICE_TYPE                          : CL_DEVICE_TYPE_CPU 

Drivers known to at least partially support SPIR or SPIR-V include intel-compute-runtime, intel-opencl-runtimeAUR, poclAUR and amdgpu-pro-openclAUR.

SYCL Development

SYCL requires a working C++11 environment to be set up. There are a few open source libraries available:

CUDA

CUDA (Compute Unified Device Architecture) is NVIDIA's proprietary, closed-source parallel computing architecture and framework. It requires a NVIDIA GPU. It consists of several components:

  • required:
    • proprietary Nvidia kernel module
    • CUDA "driver" and "runtime" libraries
  • optional:
    • additional libraries: CUBLAS, CUFFT, CUSPARSE, etc.
    • CUDA toolkit, including the nvcc compiler
    • CUDA SDK, which contains many code samples and examples of CUDA and OpenCL programs

The kernel module and CUDA "driver" library are shipped in nvidia and opencl-nvidia. The "runtime" library and the rest of the CUDA toolkit are available in cuda. The library is available only in 64-bit version. cuda-gdb needs ncurses5-compat-libsAUR to be installed, see FS#46598.

Development

The cuda package installs all components in the directory /opt/cuda. For compiling CUDA code, add /opt/cuda/include to your include path in the compiler instructions. For example this can be accomplished by adding -I/opt/cuda/include to the compiler flags/options. To use nvcc, a gcc wrapper provided by NVIDIA, just add /opt/cuda/bin to your path.

To find whether the installation was successful and if cuda is up and running, you can compile the samples installed on /opt/cuda/samples (you can simply run make inside the directory, altough is a good practice to copy the /opt/cuda/samples directory to your home directory before compiling) and running the compiled examples. A nice way to check the installation is to run one of the examples, called deviceQuery.

Language bindings

List of GPGPU accelerated software

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: More application may support GPGPU. (Discuss in Talk:GPGPU#)

Links and references