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Subject: Re: [OMPI users] Openmpi and processor affinity
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-06-03 12:02:49


On Jun 3, 2009, at 11:40 AM, Ashley Pittman wrote:

> Wasn't there a discussion about this recently on the list, OMPI binds
> during MPI_Init() so it's possible for memory to be allocated on the
> wrong quad, the discussion was about moving the binding to the orte
> process as I recall?
>

Yes. It's been fixed in OMPI devel trunk. I'm not sure it made it to
the v1.3 branch, but it's definitely not in a released version yet.

I *thought* that HPL did all allocation after MPI_INIT. But I could
be wrong. If so, then using numactl to bind before the MPI app starts
will likely give better results -- you're right (until we get our
fixes in such that we bind pre-main).

Regardless, if something is *changing* the affinity after MPI_INIT,
then there's little OMPI can do about that.

> >From my testing of process affinity you tend to get much more
> consistent
> results with it on and much more unpredictable results with it off,
> I'd
> questing that it's working properly if you are seeing a 88-93% range
> in
> the results.
>
> Ashley Pittman.
>
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-- 
Jeff Squyres
Cisco Systems