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Subject: Re: [OMPI users] machines swapping in running job[Scanned]
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-05-08 07:36:11

On May 7, 2008, at 12:08 PM, Arif Ali wrote:

> thanks, that's great, that worked
> we are also using IBM machines (IBM x3455) but we are using the gcc
> compiler that comes default with SLES 10
> I have successfully run the HPCC using values 2048, 4096 and 8192; I
> have kept this now at 2048 and continue testing.
> Is it better if this value to be high or low?

It depends. :-)

The purpose of this value is to limit how much memory Open MPI uses
internally. If you have lots of memory, setting it high shouldn't be
a problem. If you're memory-constrained, then setting it to a lower
number would be good. The best thing to do would be to check the
overall performance of both values -- limiting OMPI's memory *can*
impact performance if it introduces message passing stalls, etc.

So it's unfortunately not a simple question to answer: it essentially
is [can be] a tradeoff of space vs. time, and that very much depends
on your specific hardware setup, the message passing patterns of your
application, etc.

Jeff Squyres
Cisco Systems