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Subject: Re: [OMPI users] Shared Memory (SM) module and sharedcache implications
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-06-25 08:49:09


FWIW: there's also work going on to use direct process-to-process
copies (vs. using shared memory bounce buffers). Various MPI
implementations have had this technology for a while (e.g., QLogic's
PSM-based MPI); the Open-MX guys are publishing the knem open source
kernel module for this purpose these days (http://runtime.bordeaux.inria.fr/knem/
), etc.

On Jun 25, 2009, at 8:31 AM, Simone Pellegrini wrote:

> Ralph Castain wrote:
> > At the moment, I believe the answer is the main memory route. We
> have
> > a project just starting here (LANL) to implement the cache-level
> > exchange, but it won't be ready for release for awhile.
> Interesting, actually I am a PhD student and my topic is
> optimization of
> MPI applications on multi-core architectures. I will be very
> interested
> in collaborating in such project. Can you give me more details about
> it
> (links/pointers)?
>
> regards, Simone
> >
> >
> > On Jun 25, 2009, at 2:39 AM, Simone Pellegrini wrote:
> >
> >> Hello,
> >> I have a simple question for the shared memory (sm) module
> developers
> >> of Open MPI.
> >>
> >> In the current implementation, is there any advantage of having
> >> shared cache among processes communicating?
> >> For example let say we have P1 and P2 placed in the same CPU on 2
> >> different physical cores with shared cache, P1 wants to send a
> >> message to P2 and the message is already in the cache.
> >>
> >> How the message is being actually exchanged? Is the cache line
> >> invalidated, written to main memory and exchanged by using some DMA
> >> transfer... or is the message in the cache used (avoiding access to
> >> the main memory)?
> >>
> >> thanks in advance, Simone P.
> >> _______________________________________________
> >> users mailing list
> >> users_at_[hidden]
> >> http://www.open-mpi.org/mailman/listinfo.cgi/users
> >
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
> _______________________________________________
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>

-- 
Jeff Squyres
Cisco Systems