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Subject: Re: [hwloc-devel] multiple simultaneous topology inits?
From: Jeff Squyres (jsquyres) (jsquyres_at_[hidden])
Date: 2011-03-01 06:34:59

FWIW OMPI is moving to a model like that.

Sent from my phone. No type good.

On Mar 1, 2011, at 4:47 AM, "Bernd Kallies" <kallies_at_[hidden]> wrote:

> On Mon, 2011-02-28 at 22:17 +0100, Brice Goglin wrote:
>> Le 28/02/2011 22:04, Jeff Squyres a écrit :
>>> That being said, someone cited on this list a long time ago that running the hwloc detection on very large machines (e.g., SGI machines with 1000+ cores) takes on the order of seconds (because it traverses /sys, etc.). So if you want your tool to be used on machines like that, then it might be better to do the discovery once and share that data among your threads.
>> People running on such large machines should really export the machine
>> topology to XML once and reload from there all the time.
> Btw. lstopo on such a large machine (64 NUMA nodes, 1024 logical CPUs)
> takes about 0.6 seconds at our site.
> This is accepteable for scripts, that run only frequently. It is also
> accepteable for executables that need the topology info at start time
> (e.g. pbs_mom of Torque).
> To calculate topology-based pinning schemes and do process pinning (like
> done e.g. by OpenMPI or MVAPICH2) this is too long, when every process
> (MPI task) or thread loads the topology in parallel. But exporting an
> XML topology and using this for this purpose is inaccepteable, when
> Linux cpusets are used, because one needs the topology of a subset of
> the machine depending on the caller context. What we currently do is to
> let only one process per machine load the topology, and distribute the
> essentials needed for pinning to the remaining processes.
> BK
>> Brice
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> Tel: +49-30-84185-270
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