Installation of OpenCL ====================== OpenCL is one of the backends that PyNUFFT supports. Up to the present, PyNUFFT has used OpenCL-1.2. One missing feature of OpenCL-1.2 is `atomicAdd` for the array with floating point numbers. PyNUFFT makes use of `atomic_cmpxchg` (compare and exchange) to implement the atomic_add_float subroutine, which can be seen in the `pynufft.src.re_subroutine.atomic_add`. This code has appeared in many resources, e.g. `http://simpleopencl.blogspot.com/2013/05/atomic-operations-and-floats-in-opencl.html` and `https://github.com/clMathLibraries/clSPARSE/blob/master/src/library/kernels/csrmv_adaptive.cl`. Note that the OpenCL standard is still evolving and all of the OpenCL supports may change quickly. Old sdk may not work with the newest Intel chipsets. Please try different versions of the hardware and software. The current compiler version is gcc version 7.3.0. Other compilers may be used on the target system but I haven't tested any of them. **Intel OpenCL** Intel HD graphics after the Skylake generation usually support OpenCL as long as the suitable intel-sdk is installed. One OpenCL example is a Gigabyte aero 15 Gentoo Linux on a machine with Intel Corporation HD Graphics 530 (rev 06). The dev-util/intel-ocl-sdk-4.4.0.117-r1 installed the `intel_sdk_for_ocl_applications_2014_ubuntu_4.4.0.117_x64.tgz` opencl package. The `clinfo` command shows :: Platform Name Intel(R) OpenCL Number of devices 1 Device Name Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz Device Vendor Intel(R) Corporation Device Vendor ID 0x8086 Device Version OpenCL 1.2 (Build 117) Driver Version 1.2.0.117 Device OpenCL C Version OpenCL C 1.2 Device Type CPU Device Profile FULL_PROFILE Device Available Yes Compiler Available Yes Linker Available Yes Max compute units 8 Max clock frequency 2600MHz Device Partition (core) Max number of sub-devices 8 Supported partition types by counts, equally, by names (Intel) Supported affinity domains (n/a) Max work item dimensions 3 Max work item sizes 8192x8192x8192 Max work group size 8192 Preferred work group size multiple 128 Preferred / native vector sizes char 1 / 32 short 1 / 16 int 1 / 8 long 1 / 4 half 0 / 0 (n/a) float 1 / 8 double 1 / 4 (cl_khr_fp64) Half-precision Floating-point support (n/a) Single-precision Floating-point support (core) Denormals Yes Infinity and NANs Yes Round to nearest Yes Round to zero No Round to infinity No IEEE754-2008 fused multiply-add No Support is emulated in software No Correctly-rounded divide and sqrt operations No Double-precision Floating-point support (cl_khr_fp64) Denormals Yes Infinity and NANs Yes Round to nearest Yes Round to zero Yes Round to infinity Yes IEEE754-2008 fused multiply-add Yes Support is emulated in software No Address bits 64, Little-Endian Global memory size 33613447168 (31.3GiB) Error Correction support No Max memory allocation 8403361792 (7.826GiB) Unified memory for Host and Device Yes Minimum alignment for any data type 128 bytes Alignment of base address 1024 bits (128 bytes) Global Memory cache type Read/Write Global Memory cache size 262144 (256KiB) Global Memory cache line size 64 bytes Image support Yes Max number of samplers per kernel 480 Max size for 1D images from buffer 525210112 pixels Max 1D or 2D image array size 2048 images Max 2D image size 16384x16384 pixels Max 3D image size 2048x2048x2048 pixels Max number of read image args 480 Max number of write image args 480 Local memory type Global Local memory size 32768 (32KiB) Max number of constant args 480 Max constant buffer size 131072 (128KiB) Max size of kernel argument 3840 (3.75KiB) Queue properties Out-of-order execution Yes Profiling Yes Local thread execution (Intel) Yes Prefer user sync for interop No Profiling timer resolution 1ns Execution capabilities Run OpenCL kernels Yes Run native kernels Yes SPIR versions 1.2 printf() buffer size 1048576 (1024KiB) Built-in kernels (n/a) Device 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_spir cl_intel_exec_by_local_thread cl_khr_depth_images cl_khr_3d_image_writes cl_khr_fp64 Pure CPU system without Intel HD graphics may require the newest Intel SDK for OpenCL `https://software.intel.com/en-us/intel-opencl` and `https://software.intel.com/en-us/articles/opencl-drivers`. One pure CPU system with Intel i7 7900X can make use of Intel Studio 2019. **Nvidia OpenCL** NVIDIA also supports OpenCL 1.2. A successful installation made use of nvidia-driver 417.18 and CUDA-SDK-9.2.88 and gcc 7.3.0. clinfo shows :: Platform Name NVIDIA CUDA Number of devices 1 Device Name GeForce GTX 1060 Device Vendor NVIDIA Corporation Device Vendor ID 0x10de Device Version OpenCL 1.2 CUDA Driver Version 415.18 Device OpenCL C Version OpenCL C 1.2 Device Type GPU Device Topology (NV) PCI-E, 01:00.0 Device Profile FULL_PROFILE Device Available Yes Compiler Available Yes Linker Available Yes Max compute units 10 Max clock frequency 1670MHz Compute Capability (NV) 6.1 Device Partition (core) Max number of sub-devices 1 Supported partition types None Supported affinity domains (n/a) Max work item dimensions 3 Max work item sizes 1024x1024x64 Max work group size 1024 Preferred work group size multiple 32 Warp size (NV) 32 Preferred / native vector sizes char 1 / 1 short 1 / 1 int 1 / 1 long 1 / 1 half 0 / 0 (n/a) float 1 / 1 double 1 / 1 (cl_khr_fp64) Half-precision Floating-point support (n/a) Single-precision Floating-point support (core) Denormals Yes Infinity and NANs Yes Round to nearest Yes Round to zero Yes Round to infinity Yes IEEE754-2008 fused multiply-add Yes Support is emulated in software No Correctly-rounded divide and sqrt operations Yes Double-precision Floating-point support (cl_khr_fp64) Denormals Yes Infinity and NANs Yes Round to nearest Yes Round to zero Yes Round to infinity Yes IEEE754-2008 fused multiply-add Yes Support is emulated in software No Address bits 64, Little-Endian Global memory size 6373572608 (5.936GiB) Error Correction support No Max memory allocation 1593393152 (1.484GiB) Unified memory for Host and Device No Integrated memory (NV) No Minimum alignment for any data type 128 bytes Alignment of base address 4096 bits (512 bytes) Global Memory cache type Read/Write Global Memory cache size 163840 (160KiB) Global Memory cache line size 128 bytes Image support Yes Max number of samplers per kernel 32 Max size for 1D images from buffer 134217728 pixels Max 1D or 2D image array size 2048 images Max 2D image size 16384x32768 pixels Max 3D image size 16384x16384x16384 pixels Max number of read image args 256 Max number of write image args 16 Local memory type Local Local memory size 49152 (48KiB) Registers per block (NV) 65536 Max number of constant args 9 Max constant buffer size 65536 (64KiB) Max size of kernel argument 4352 (4.25KiB) Queue properties Out-of-order execution Yes Profiling Yes Prefer user sync for interop No Profiling timer resolution 1000ns Execution capabilities Run OpenCL kernels Yes Run native kernels No Kernel execution timeout (NV) No Concurrent copy and kernel execution (NV) Yes Number of async copy engines 2 printf() buffer size 1048576 (1024KiB) Built-in kernels (n/a) Device Extensions 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_fp64 cl_khr_byte_addressable_store cl_khr_icd cl_khr_gl_sharing cl_nv_compiler_options cl_nv_device_attribute_query cl_nv_pragma_unroll cl_nv_copy_opts cl_nv_create_buffer **AMD GPU** AMD has a very good support for OpenCL. See AMDGPU-PRO driver. AMD usually performs very well for fp64 (double precision PyNUFFT is available on request). **Open-source Intel Compute OpenCL (Intel-NEO and Intel SDK)** Try to install Intel's proprietary OpenCL sdk.