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Re: OpenMPI 5.0 to be 32-bit only ?

On 2023-02-07 10:54, Alastair McKinstry wrote:

I've been pinged by the upstream maintainer of OpenMPI    Jefff
Squyres as to our opinions on maintaining 32-bit support.

See a  thread here: https://github.com/open-mpi/ompi/pull/11282

Until now I've asked for OMPI to hold off going to 64-bit only; saying
we can help with the maintenance burden with our testing

But we're not well suited to run multi-node test jobs.

If Lucas Nussbaum thinks it's appropriate, one thing we could consider is setting up multinode tests on the Grid'5000 [1] infrastructure. It would take a bit of effort to set up, but once set up it should be able to run multinode tests routinely. Although, true, it would only allow for 64-bit testing, i.e. amd64 (plus also arm64 and ppc64el), so it might not help with the question of 32-bit support unless 32-bit chroots can be set up.

[1] https://www.grid5000.fr

If 32-bit support is dropped in OMPI we can switch to MPICH as the
default on those archs instead, but the core problem remains: how much
can we support and test on 32-bit?

Switching to mpich would in any case be supported by a lot of our upstream developers. In various different projects we hear them recommending mpich and occasionally expressing discontent with bugs in openmpi.

To make it simpler for ourselves, we could also consider just switching to mpich altogether as default. Are there reasons to prefer 64-bit OMPI over MPICH?


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