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Subject: Re: [OMPI users] Optimal 3-D Cartesian processor mapping
From: Jeffrey Squyres (jsquyres_at_[hidden])
Date: 2012-04-24 15:11:19

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.

Jeff Squyres
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