CUDA support

Warning

This is an experimental feature, available starting with release 2.3.0. It is still incomplete and has only been tested on Linux on x86_64.

CUDA is supported by passing all JITed code through two pipelines: one for the CPU and one for the GPU. Use of the __CUDA__ pre-processor macro enables more fine-grained control over which pipeline sees what, which is used e.g. in the pre-compiled header: the GPU pipeline has the CUDA headers included, the CPU pipeline does not. Building the pre-compiled header will also pick up common CUDA libraries such as cuBLAS, if installed.

Each version of CUDA requires specific versions of Clang and the system compiler (e.g. gcc) for proper functioning. Since Cling as used by cppyy is still running Clang9 (work on the port to Clang13 is on-going) and since CUDA has changed the APIs for launching kernels in v11, the latest supported version of CUDA is v10.2. This is also the default for the binary distribution; use of a different version of CUDA (older than v10.2) will work but does require rebuilding cppyy-cling from source.

There are three environment variables to control Cling’s handling of CUDA:

  • CLING_ENABLE_CUDA (required): set to 1 to enable the CUDA backend.
  • CLING_CUDA_PATH (optional): set to the local CUDA installation if not in a standard location.
  • CLING_CUDA_ARCH (optional): set the architecture to target; default is sm_35 and Clang9 is limited to sm_75.

After enabling CUDA with CLING_ENABLE_CUDA=1 CUDA code can be used and kernels can be launched from JITed code by in cppyy.cppdef(). There is currently no syntax or helpers yet to launch kernels from Python.