[mpich-discuss] mpiexec ignoring host setting in configfile

Alexander Rast alex.rast.technical at gmail.com
Thu Jun 22 09:55:22 CDT 2017

I'm getting a very suprising result with the attached application and
configfile. As you can see, I'm asking MPI to run 2 processes on
Shakespeare, and 2 on Burns. But when I ran the program using mpiexec
-configfile ./MPI_config.txt what I actually get is the output shown in
MPI_IO_Test.txt. Furthermore I can confirm that this is genuine: I shut
down Burns altogether and the same result ensues. It's as if mpiexec is
taking the -host field as advisory but not required, that is, it might
execute on the host asked for, but then again if it decides not to, it
doesn't interpret the -host field as a requirement. I get the distinct
impression, indeed, that instead of interpreting the host as a requirement,
it uses a greedy process allocation: if it can spawn all of the processes
on the invoking host (the one that ran mpiexec) it does so, and only once
the resources there are exhausted does it look at other possible hosts.

Clearly if you specify a -host the intention is that the process should be
placed there. This looks like a bug in mpiexec.
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-n 2 -host Shakespeare ./mpi_io_test
-n 2 -host Burns ./mpi_io_test

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Process 00 (of 04) on Shakespeare alive
[Rank 0]: IO access from any rank
Process 01 (of 04) on Shakespeare alive
[Rank 1]: IO access from any rank
Process 02 (of 04) on Shakespeare alive
Process 03 (of 04) on Shakespeare alive
[Rank 2]: IO access from any rank
[Rank 3]: IO access from any rank
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