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From: Gleb Natapov (glebn_at_[hidden])
Date: 2006-12-01 09:23:42


On Fri, Dec 01, 2006 at 04:14:31PM +0200, Gleb Natapov wrote:
> On Fri, Dec 01, 2006 at 11:51:24AM +0100, Peter Kjellstrom wrote:
> > On Saturday 25 November 2006 15:31, shaposh_at_[hidden] wrote:
> > > Hello,
> > > i cant figure out, is there a way with open-mpi to bind all
> > > threads on a given node to a specified subset of CPUs.
> > > For example, on a multi-socket multi-core machine, i want to use
> > > only a single core on each CPU.
> > > Thank You.
> >
> > This might be a bit naive but, if you spawn two procs on a dual core dual
> > socket system then the linux kernel should automagically schedule them this
> > way.
> >
> > I actually think this applies to most of the situations discussed in this
> > thread. Explicitly assigning processes to cores may actually get it wrong
> > more often than the normal linux scheduler.
> >
> If you run two single threaded ranks on the dual core dual socket node
> you better be placing them on the same core. Shared memory communication
I mean "same socket" here and not "same core" of cause.

> will be much faster (especially if two cores shares cache).
>
> > /Peter (who may be putting a bit too much faith in the linux scheduler...)
> Linux scheduler does its best assuming the processes are unrelated. This is
> not the case with MPI ranks.
>
> --
> Gleb.
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--
			Gleb.