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Optimization of Collective Communication Operations in MPICH
Ist Teil von
The international journal of high performance computing applications, 2005-04, Vol.19 (1), p.49-66
Ort / Verlag
Thousand Oaks, CA: Sage Publications
Erscheinungsjahr
2005
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
We describe our work on improving the performance of collective communication
operations in MPICH for clusters connected by switched networks. For each collective
operation, we use multiple algorithms depending on the message size, with the goal
of minimizing latency for short messages and minimizing bandwidth use for long
messages. Although we have implemented new algorithms for all MPI (Message Passing
Interface) collective operations, because of limited space we describe only the
algorithms for allgather, broadcast, all-to-all, reduce-scatter, reduce, and
allreduce. Performance results on a Myrinet-connected Linux cluster and an IBM SP
indicate that, in all cases, the new algorithms significantly outperform the old
algorithms used in MPICH on the Myrinet cluster, and, in many cases, they outperform
the algorithms used in IBM's MPI on the SP. We also explore in further
detail the optimization of two of the most commonly used collective operations,
allreduce and reduce, particularly for long messages and nonpower-of-two numbers of
processes. The optimized algorithms for these operations perform several times
better than the native algorithms on a Myrinet cluster, IBM SP, and Cray T3E. Our
results indicate that to achieve the best performance for a collective communication
operation, one needs to use a number of different algorithms and select the right
algorithm for a particular message size and number of processes.