This should not happen. Typically, Intra node communication latency are way way cheaper than inter node.
Can you please tell us how u ran your application ?

Sent from my iPhone

On Jun 1, 2012, at 7:34 AM, Mudassar Majeed <> wrote:

Dear MPI people,
                               Can someone tell me why MPI_Ssend takes more time when two MPI processes are on same node ...... ?? the same two processes on different nodes take much less time for the same message exchange. I am using a supercomputing center and this happens. I was writing an algorithm to reduce the across node communication. But now I found that across node communication is cheaper than communication within a node (with 8 cores on each node).

best regards,

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