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Subject: [OMPI devel] Speedup for MPI_Dims_create()
From: Andreas Schäfer (gentryx_at_[hidden])
Date: 2013-12-19 09:37:59

Dear all,

please find attached a (trivial) patch to MPI_Dims_create(). When
computing the prime factors of nnodes, it is sufficient to check for
primes less or equal to sqrt(nnodes).

This was not so much of a problem in the past, but now that Tier 0
systems are capable of running O(10^6) MPI processes, the difference
in execution time is on the order of seconds (e.g. 8.86s vs. 0.04s on
my notebook, with nnproc = 10^6).


PS: oh, and the patch removes some trailing whitespace. Yuck. :-)

Andreas Schäfer
HPC and Grid Computing
Chair of Computer Science 3
Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
+49 9131 85-27910
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