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Subject: Re: [OMPI users] Over committing?
From: Ralph Castain (rhc_at_[hidden])
Date: 2011-04-13 10:34:03

On Apr 13, 2011, at 8:13 AM, Rushton Martin wrote:

> The bulk of our compute nodes are 8 cores (twin 4-core IBM x3550-m2).
> Jobs are submitted by Torque/MOAB. When run with up to np=8 there is
> good performance. Attempting to run with more processors brings
> problems, specifically if any one node of a group of nodes has all 8
> cores in use the job hangs. For instance running with 14 cores (7+7) is
> fine, but running with 16 (8+8) hangs.
>> From the FAQs I note the issues of over committing and aggressive
> scheduling. Is it possible for mpirun (or orted on the remote nodes) to
> be blocked from progressing by a fully committed node? We have a few
> x3755-m2 machines with 16 cores, and we have detected a similar issue
> with 16+16.

I'm not entirely sure I understand your notation, but we have never seen an issue when running with fully loaded nodes (i.e., where the number of MPI procs on the node = the number of cores).

What version of OMPI are you using? Are you binding the procs?

> Martin Rushton
> HPC System Manager, Weapons Technologies
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