Dispatch

Microbenchmark

This code sample benchmarks the performance of (1) the dispatch mechanism, and (2) the time needed to JIT-generate code for the first time. Both mechanisms are relevant when replacing GEMM calls (see Call Wrapper section of the reference documentation), or in any case of calling LIBXSMM’s native GEMM functionality.

Command Line Interface (CLI)

Optionally takes the number of dispatches/code-generations (default: 10000).
Optionally takes the number of threads (default: 1).

Measurements (Benchmark)

Duration of an empty function call (serves as a reference timing).
Duration to find an already generated kernel (cached/non-cached).
Duration to JIT-generate a GEMM kernel.

In case of a multi-threaded benchmark, the timings represent a highly contended request (worst case). For thread-scaling, it can be observed that read-only accesses (code dispatch) stay roughly with a constant duration whereas write-accesses (code generation) are serialized and hence the duration scales linearly with the number of threads.

The Fortran example (dispatch.f) could use libxsmm_dmmdispatch (or similar) like the C code (dispatch.c) but intentionally shows the lower-level dispatch interface libxsmm_xmmdispatch and also omits using the LIBXSMM module. Not using the module confirms: the same task can be achieved by relying only on FORTRAN 77 language level.

User-Data Dispatch

Further, another Fortran example about user-data dispatch is not exactly a benchmark. Dispatching user-data containing multiple kernels can obviously save multiple singular dispatches. The C interface for dispatching user-data is designed to follow the same flow as the Fortran interface.