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README.md

LIBSMM

The LIBSMM library implements the ACC LIBSMM interface, and depends on the OpenCL backend.

Compile-time settings are (implicitly) documented and can be adjusted by editing opencl_libsmm.h, e.g., OPENCL_LIBSMM_VALIDATE is disabled by default but can be enabled for debug purpose. The OPENCL_LIBSMM_VALIDATE compile-time setting enables side-by-side validation of matrix transpose and multiply operations between device and host. For example, running DBCSR's unit tests with OPENCL_LIBSMM_VALIDATE enabled produces console output that allows to pin-point a kernel which misses validation. Runtime settings are made by the means of environment variables. The OpenCL backend provides acc_getenv.sh to list all occurrences of getenv categorized into "OpenCL Backend environment variables" and "OpenCL LIBSMM environment variables".

There are two categories for the two domains in LIBSMM, i.e., matrix transpose (OPENCL_LIBSMM_TRANS_*) and matrix multiplication (OPENCL_LIBSMM_SMM_*). For transposing matrices, the settings are:

  • OPENCL_LIBSMM_TRANS_BUILDOPTS: character string with build options (compile and link) supplied to the OpenCL runtime compiler.
  • OPENCL_LIBSMM_TRANS_INPLACE: Boolean value (zero or non-zero integer) for in-place matrix transpose (no local memory needed).
  • OPENCL_LIBSMM_TRANS_BM: non-negative integer number (less/equal than the M-extent) denoting the blocksize in M-direction.

The most common settings for multiplying matrices are:

  • OPENCL_LIBSMM_SMM_BUILDOPTS: character string with build options (compile and link) supplied to the OpenCL runtime compiler.
  • OPENCL_LIBSMM_SMM_PARAMS: Disable embedded/auto-tuned parameters (0), or load CSV-file (e.g., path/to/tune_multiply.csv).
  • OPENCL_LIBSMM_SMM_BS: non-negative integer number denoting the intra-kernel (mini-)batchsize mainly used to amortize atomic updates of data in global/main memory. The remainder with respect to the "stacksize" is handled by the kernel.
  • OPENCL_LIBSMM_SMM_BM: non-negative integer number (less/equal than the M-extent) denoting the blocksize in M-direction.
  • OPENCL_LIBSMM_SMM_BN: non-negative integer number (less/equal than the N-extent) denoting the blocksize in N-direction.
  • OPENCL_LIBSMM_SMM_AP: specifies access to array of parameters (batch or "stack").
  • OPENCL_LIBSMM_SMM_AA: specifies access to array of A-matrices.
  • OPENCL_LIBSMM_SMM_AB: specifies access to array of B-matrices.
  • OPENCL_LIBSMM_SMM_AC: specifies access to array of C-matrices.

The full list of tunable parameters and some explanation can be received with smm/tune_multiply.py --help, i.e., short description, default settings, and accepted values.

NOTE: LIBSMM's tunable runtime settings can be non-smooth like producing distinct code-paths, e.g., OPENCL_LIBSMM_SMM_BS=1 vs. OPENCL_LIBSMM_SMM_BS=2.

Auto Tuning

To tune and optimize a kernel and generating kernel parameters, please refer to the Auto Tuning guide. To update or retune an entire set of kernels (optimized parameters), please refer to the Bulk Tuning guide.