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Subject: Re: [OMPI users] Do MPI calls ever sleep?
From: Jed Brown (jed_at_[hidden])
Date: 2010-07-21 15:54:52

On Wed, 21 Jul 2010 15:20:24 -0400, David Ronis <David.Ronis_at_[hidden]> wrote:
> Hi Jed,
> Thanks for the reply and suggestion. I tried adding -mca
> yield_when_idle 1 (and later mpi_yield_when_idle 1 which is what
> ompi_info reports the variable as) but it seems to have had 0 effect.
> My master goes into fftw planning routines for a minute or so (I see the
> threads being created), but the overall usage of the slaves remains
> close to 100% during this time. Just to be sure, I put the slaves into
> a MPI_Barrier(MPI_COMM_WORLD) while they were waiting for the fftw
> planner to finish. It also didn't help.

They still spin (instead of using e.g. select()), but call sched_yield()
so should only be actively spinning when nothing else is trying to run.
Are you sure that the planner is always running in parallel? What OS
and OMPI version are you using?