Section: New Results

Communication and computation overlap

To amortize the cost of communication in HPC application, programmers want to overlap communications with computation. To do so, they assume non-blocking MPI communications will progress in background. NewMadeleine, our communication library, is actually able to make communication progress in background so as to actually have overlap happen. However, not all MPI implementations are able to overlap communication and computation.

We have proposed [8] a benchmark to measure what really happens when trying to overlap non-blocking point-to-point communications with computation. The benchmark measures how much overlap happen in various cases: sender-side, receiver-side, datatypes likely to be offloaded onto NIC or not, multi-threaded computation, multi-threaded communication or not. We have benchmarked a wide panel of MPI libraries and hardware platforms, and thanks to low-level traces, explained the results.