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List:       beowulf
Subject:    Re: [Beowulf] mpiexec task affinity
From:       Christopher Samuel <samuel () unimelb ! edu ! au>
Date:       2013-09-21 4:05:15
Message-ID: 523D1AFB.4040700 () unimelb ! edu ! au
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On 20/09/13 00:49, reza azimi wrote:

> Assume I want to run 24 thread on my Beowulf cluster which use
> MPICH2 as the MPI library. I run these 24 threads on six servers
> giving each 4 threads with "mpiexec" command. Can I change this
> configuration during the *run time* for example do it as 4*6 using
> 4 server and giving each 6 thread?

You should be able to use MPI_Comm_spawn() to launch other ranks on
the nodes you are already on, so you could grow but I am not sure
about shrinking on other nodes.

http://www.open-mpi.org/doc/v1.4/man3/MPI_Comm_spawn.3.php

Of course if you are running in a job system of some sort you'll have
needed to have asked for the maximum number of cores per node you're
going to end up using in the end at which point why not just use all
of them from the beginning? :-)

Caveat: I am a sysadmin, not a programmer.

cheers!
Chris
- -- 
 Christopher Samuel        Senior Systems Administrator
 VLSCI - Victorian Life Sciences Computation Initiative
 Email: samuel@unimelb.edu.au Phone: +61 (0)3 903 55545
 http://www.vlsci.org.au/      http://twitter.com/vlsci

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