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Subject: Re: [OMPI users] Optimal 3-D Cartesian processor mapping
From: Ralph Castain (rhc_at_[hidden])
Date: 2012-04-24 15:36:13

Add --display-map to your mpirun cmd line

On Apr 24, 2012, at 1:33 PM, Tom Rosmond wrote:

> Jeff,
> Yes, I would be interested in such a plugin. But be advised that I am
> strictly a fortran programmer, so if it requires any C/C++ talent, I
> would be in trouble. So maybe, before jumping into that, I would like
> to be able to look at what processor/node mapping Open-mpi is actually
> giving me. Is there an environmental variable or an MCA option I can
> add to my 'mpirun' command line that would give that to me? I am
> running 1.5.4.
> T. Rosmond
> On Tue, 2012-04-24 at 15:11 -0400, Jeffrey Squyres wrote:
>> On Apr 24, 2012, at 3:01 PM, Tom Rosmond wrote:
>>> My question is this: If the cartesian mapping is done so the two
>>> spacial dimensions are the 'most rapidly varying' in equivalent 1-D
>>> processor mapping, will Open-mpi automatically assign those 2 dimensions
>>> 'on-node', and assign the 'ensemble' dimension as the slowest varying
>>> and across nodes? If not, how can we guarantee this to happen?
>> Sadly, the MPI mapping functions in Open MPI are effectively no-ops -- if you ask for re-ordering, OMPI says "sure!" but then gives you back exactly the same mapping. :-(
>> That being said, the mapping functionality is actually a plugin in Open MPI (in the "topo" framework). It would not be too difficult to write a plugin for the mapping that you want.
>> Would this be of interest to you? I'd be happy to talk you through the process of writing such a plugin.
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