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Subject: Re: [OMPI users] OpenMPI problem on Fedora Core 12
From: Ashley Pittman (ashley_at_[hidden])
Date: 2009-12-14 14:22:43

On Sun, 2009-12-13 at 19:04 +0100, Gijsbert Wiesenekker wrote:
> The following routine gives a problem after some (not reproducible)
> time on Fedora Core 12. The routine is a CPU usage friendly version of
> MPI_Barrier.

There are some proposals for Non-blocking collectives before the MPI
forum currently and I believe a working implementation which can be used
as a plug-in for OpenMPI, I would urge you to look at these rather than
try and implement your own.

> My question is: is there a problem with this routine that I overlooked
> that somehow did not show up until now

Your code both does all-to-all communication and also uses probe, both
of these can easily be avoided when implementing Barrier.

> Is there a way to see which messages have been sent/received/are
> pending?

Yes, there is a message queue interface allowing tools to peek inside
the MPI library and see these queues. That I know of there are three
tools which use this, either TotalView, DDT or my own tool, padb.
TotalView and DDT are both full-featured graphical debuggers and
commercial products, padb is a open-source text based tool.


Ashley Pittman, Bath, UK.
Padb - A parallel job inspection tool for cluster computing