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Subject: Re: [OMPI users] Question about collective messages implementation
From: Jerome Reybert (jreybert_at_[hidden])
Date: 2010-11-08 10:48:36


Ashley Pittman <ashley <at> pittman.co.uk> writes:

> MPI_Comm_split() is an expensive operation, sure the manual says it's low cost
but it shouldn't be used
> inside any critical loops so be sure you are doing the Comm_Split() at startup
and then re-using it as and
> when needed.
>
> Any blocking call into OpenMPI will poll consuming CPU cycles until the call
is complete, you can mitigate
> against this by telling OpenMPI to aggressively call yield whilst polling
which would mean that your
> parallel Lapack function could get the CPU resources it required. Have a look
at this FAQ entry for details
> of the option and what you can expect it to do.
>
> http://www.open-mpi.org/faq/?category=running#force-aggressive-degraded
>
> Ashley.
>

Thanks for your detailed responses. Actually, the problem came from a stupied
error of me...

However, I'll have a depth look about the active waiting you describe. I'll try
to see if it affects my performances.

Jérôme