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Subject: Re: [hwloc-users] Thread core affinity
From: Gabriele Fatigati (g.fatigati_at_[hidden])
Date: 2011-08-04 11:41:05


Well,

now it's more clear.

Thanks for the informations!

Regards.

2011/8/4 Samuel Thibault <samuel.thibault_at_[hidden]>

> Gabriele Fatigati, le Thu 04 Aug 2011 16:56:22 +0200, a écrit :
> > L#0 and L#1 are physically near because hwloc consider shared caches map
> when
> > build topology?
>
> Yes. That's the whole point of sorting objects topologically first, and
> numbering them afterwards. See the glossary entry for "logical index":
>
> “The ordering is based on topology first, and then on OS CPU numbers”
>
> I.e. OS CPU numbers are only used when no topology information (shared
> cache etc.) provides any better sorting.
>
> > Because if not, i don't know how hwloc understand the physical
> > proximity of cores :(
>
> Physical proximity of cores does not mean logical proximity. cores can
> be next one to the other, and still share no cache at all. Forget the
> expression "physical proximity", it does not provide any interesting
> information. What matters is logical proximity. And that's *precisely*
> what logical indexes express.
>
> Samuel
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>

-- 
Ing. Gabriele Fatigati
HPC specialist
SuperComputing Applications and Innovation Department
Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
www.cineca.it                    Tel:   +39 051 6171722
g.fatigati [AT] cineca.it