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Subject: Re: [OMPI users] CPU burning in Wait state
From: Eugene Loh (Eugene.Loh_at_[hidden])
Date: 2008-09-04 11:35:26


Jeff Squyres wrote:

> OMPI currently polls for message passing progress. While you're in
> MPI_BCAST, it's quite possible/ likely that OMPI will poll hard until
> the BCAST is done. It is possible that a future version of OMPI will
> use a hybrid polling+non- polling approach for progress, such that if
> you call MPI_BCAST, we'll poll for a while. And if nothing
> "interesting" happens after a while (i.e., the BCAST hasn't finished
> and nothing else seems to be happening), we'll allow OMPI's internal
> progression engine to block/go to sleep until something interesting
> happens.

There are many alternatives to polling hard. One is to yield the CPU if
someone else is asking for it. Again, Open MPI has some support for
this today with the "mpi_yield_when_idle" variable. Right? Might not
be all of what someone wants, but the above discussion just seems not to
account for this. In any case, I verified that it does do something
useful in at least one case.