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Subject: Re: [OMPI users] Shared Memory (SM) module and sharedcache implications
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-06-25 09:12:39


Doesn't that still pull the message off-socket? I thought it went
through the kernel for that method, which means moving it to main
memory.

On Jun 25, 2009, at 6:49 AM, Jeff Squyres wrote:

> 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
>> >
>> > _______________________________________________
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>>
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>
>
> --
> Jeff Squyres
> Cisco Systems
>
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