Scientific Reports:

A. Carpen-Amarie, S. Hunold, J. Träff:
"MPI Derived Datatypes: Performance Expectations and Status Quo";
Report for CoRR - Computing Research Repository; Report No. arXiv:1607.00178, 2016; 46 pages.

English abstract:
We examine natural expectations on communication performance using MPI derived datatypes in comparison to the baseline, "raw" performance of communicating simple, non-contiguous data layouts. We show that common MPI libraries sometimes violate these datatype performance expectations, and discuss reasons why this happens, but also show cases where MPI libraries perform well. Our findings are in many ways surprising and disappointing. First, the performance of derived datatypes is sometimes worse than the semantically equivalent packing and unpacking using the corresponding MPI functionality. Second, the communication performance equivalence stated in the MPI standard between a single contiguous datatype and the repetition of its constituent datatype does not hold universally. Third, the heuristics that are typically employed by MPI libraries at type-commit time are insufficient to enforce natural performance guidelines, and better type normalization heuristics may have a significant performance impact. We show cases where all the MPI type constructors are necessary to achieve the expected performance for certain data layouts. We describe our benchmarking approach to verify the datatype performance guidelines, and present extensive verification results for different MPI libraries.

Related Projects:
Project Head Jesper Larsson Träff:

Project Head Jesper Larsson Träff:

Created from the Publication Database of the Vienna University of Technology.