[mpich2-dev] MPI_Dims_create specification question

[Joe Ratterman]

The system that we are building has a Cartesian network layout, so we want
to optimize the results of the MPI_Dims_create() function to most closely
reflect the physical layout of the nodes on the network.  Recently, we had a
bug report from a customer who noted that when running on 8 nodes (an
example), MPI_Dims_create(3, [0, 0, 0]) doesn't always return [2,2,2].  They
consider this an error and quote the spec.

Looking at the spec (latest 2.1 version :
http://www.hlrs.de/organization/par/services/models/mpi/mpi21/doc/mpi-report-2.1draft-2008-06-13.pdf
username and password "mpi21") on page 247, the customer appears to be
correct.  There is no indication that we are allowed to attempt to make the
results reflect the HW.  Beyond the "must" requirements, there is this one
more: "The dimensions are set to be as close to each other as possible,
using an appropriate divisibility algorithm."  Why is there no mention of
the physical HW?

Thanks,
Joe Ratterman
jratt at us.ibm.com
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