Hi,
It have read that FAQ. 
Does it mean shared memory communication is used when send messages 
between the processes in same node in default?
No need any options and configuration for OpenMPI shared memory?

THANK YOU!



From: Eugene Loh <Eugene.Loh@sun.com>
To: Open MPI Users <users@open-mpi.org>
Sent: Thursday, April 23, 2009 2:08:33 PM
Subject: Re: [OMPI users] SHARED Memory----------------

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?