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Published in:
2010 | OriginalPaper | Chapter
A Scalable MPI_Comm_split Algorithm for Exascale Computing
Authors : Paul Sack, William Gropp
Published in: Recent Advances in the Message Passing Interface
Publisher: Springer Berlin Heidelberg
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Existing algorithms for creating communicators in MPI programs will not scale well to future exascale supercomputers containing millions of cores. In this work, we present a novel communicator-creation algorithm that does scale well into millions of processes using three techniques: replacing the sorting at the end of
MPI_Comm_split
with merging as the color and key table is built, sorting the color and key table in parallel, and using a distributed table to store the output communicator data rather than a replicated table. This reduces the time cost of
MPI_Comm_split
in the worst case we consider from 22 seconds to 0.37 second. Existing algorithms build a table with as many entries as processes, using vast amounts of memory. Our algorithm uses a small, fixed amount of memory per communicator after
MPI_Comm_split
has finished and uses a fraction of the memory used by the conventional algorithm for temporary storage during the execution of
MPI_Comm_split
.