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Subject: Re: [OMPI devel] Fwd: [OMPI bugs] [Open MPI] #1250: Performance problem on SM
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-07-23 11:50:28


Fixed in r19001. Please re-test; it fixes the problem for me (i.e.,
no need to manually specify sched_yield=0).

BTW, this never came up before because:

- the ODLS used to use paffinity, but before PLPA supported the
topology stuff and therefore always returned the number of processors
- when we updated PLPA, the ODLS wasn't using paffinity anymore
- we only re-updated ODLS to use paffinity recently, and that's when
this problem surfaced

On Jul 23, 2008, at 11:32 AM, Jeff Squyres wrote:

> On Jul 23, 2008, at 10:37 AM, Terry Dontje wrote:
>
>> This seems to work for me too. What is interesting is my
>> experiments have shown that if you run on RH5.1 you don't need to
>> set mpi_yield_when_idle to 0.
>
> Yes, this makes sense -- on RHEL5.1, it's a much newer Linux kernel
> and PLPA works as expected there. So ODLS uses the values that PLPA
> passes back and all is good.
>
> On older Linux kernels, we're effectively returning "not supported"
> from paffinity, and therefore ODLS (rightly) assumes that it can't
> know anything and puts us into the "oversubscribed" state.
>
> I'm working on a fix.
>
> --
> Jeff Squyres
> Cisco Systems
>
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-- 
Jeff Squyres
Cisco Systems