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/
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
> > 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
> in collaborating in such project. Can you give me more details about
> 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
> >> 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.
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