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Subject: Re: [OMPI users] Shared Memory (SM) module and shared cache implications
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-06-25 07:43:29


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.

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.
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