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Subject: Re: [OMPI users] Low performance of Open MPI-1.3 over Gigabit
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-03-05 15:29:47

On Mar 5, 2009, at 1:54 AM, Sangamesh B wrote:

> The fortran application I'm using here is the CPMD-3.11.
> I don't think the processor is Nehalem:
> Intel(R) Xeon(R) CPU X5472 @ 3.00GHz
> Installation procedure was same on both the clusters. I've not set
> mpi_affinity.
> This is a memory intensive application, but this job was not using
> that much amount of memory.
> Regarding CPU & ELAPSED TIMEs, the CPU TIME should be greater than
> ELAPSED TIME in general (for a parallel program). Right?

It depends on exactly what you're reporting for ELAPSED time. Is that
wall clock time? Or user time? Or something else?

Ralph and I disagree on this point, but my opinion is that the only
meaningful time reported in a parallel application is the wall clock
time. The CPU time can be badly skewed by a variety of things, such
as any filesystem IO, network activity (depending on whether you have
an OS-bypass network or not), etc.

Jeff Squyres
Cisco Systems