Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |   all Open MPI User's mailing list

Subject: Re: [OMPI users] Factor of 10 loss in performance with 1.3.x
From: Steve Kargl (sgk_at_[hidden])
Date: 2009-04-07 16:16:23


On Tue, Apr 07, 2009 at 01:40:13PM -0600, Ralph Castain wrote:
> I would really suggest looking at George's note first as I think you
> are chasing your tail here. It sounds like the most likely problem is
> that OMPI thinks you are oversubscribed and is setting sched_yield
> accordingly. which would fully account for these diffs.
>
> Note that the methods for setting sched yield are different between
> the various releases, so something could be catching you here. If you
> are sure you aren't oversubscribing, then set -mca mpi_yield_when_idle
> 0 on your cmd line to override any internal settings.
>

'-mca mpi_yield_when_idle 0' returns the performance of 1.3.1 to
that of 1.2.9. In fact, 1.3.1 may be marginally better. A comparison
can be see at

http://troutmask.apl.washington.edu/~kargl/ompi_cmp_yield.jpg

So, in what file is sched_yield set?

-- 
Steve