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Subject: Re: [OMPI devel] processor affinity -- OpenMPI/batch system integration
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-09-30 14:58:00


On Sep 30, 2008, at 2:51 PM, Rayson Ho wrote:

> Restarting this discussion. A new update version of Grid Engine 6.2
> will come out early next year [1], and I really hope that we can get
> at least the interface defined.

Great!

> At the minimum, is it enough for the batch system to tell OpenMPI via
> an env variable which core (or virtual core, in the SMT case) to start
> binding the first MPI task?? I guess an added bonus would be
> information about the number of processors to skip (the stride)
> between the sibling tasks?? Stride of one is usually the case, but
> something larger than one would allow the batch system to control the
> level of cache and memory bandwidth sharing between the MPI tasks...

Wouldn't it be better to give us a specific list of cores to bind to?
As core counts go up in servers, I think we may see a re-emergence of
having multiple MPI jobs on a single server. And as core counts go
even *higher*, then fragmentation of available cores over time is
possible/likely.

Would you be giving us a list of *relative* cores to bind to (i.e.,
"bind to the Nth online core on the machine" -- which may be different
than the OS's ID for that processor) or will you be giving us the
actual OS virtual processor ID(s) to bind to?

-- 
Jeff Squyres
Cisco Systems