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Subject: Re: [OMPI users] SHARED Memory----------------
From: Eugene Loh (Eugene.Loh_at_[hidden])
Date: 2009-04-23 01:08:33


shan axida wrote:
What I am asking is if I use MPI_Send and MPI_Recv between processes in 
a node, does it mean using shared memory or not?
It (typically) does.  (Some edge cases could occur.)  Your question is addressed by the FAQ I mentioned.
if not, how to use 
shared memory among processes which are runing in a node?
________________________________
From: Eugene Loh <Eugene.Loh@sun.com>
To: Open MPI Users <users@open-mpi.org>
Sent: Thursday, April 23, 2009 1:20:05 PM
Subject: Re: [OMPI users] SHARED Memory----------------

Just to clarify (since "send to self" strikes me as confusing)...

If you're talking about using shared memory for point-to-point MPI
message passing, OMPI typically uses it automatically between two
processes on the same node.  It is *not* used for a process sending to
itself.  There is a well-written FAQ (in my arrogant opinion!) at
http://www.open-mpi.org/faq/?category=sm -- e.g.,
http://www.open-mpi.org/faq/?category=sm#sm-btl .

If you're talking about some other use of shared memory, let us know
what you had in mind.

Elvedin Trnjanin wrote:
Shared memory is used for send-to-self scenarios such as if you're
making use of multiple slots on the same machine.

shan axida wrote:
Any body know how to make use of shared memory in OpenMPI
implementation?