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Subject: [OMPI users] latency #2
From: Georges Markomanolis (georges.markomanolis_at_[hidden])
Date: 2010-09-13 07:20:20


Dear all,

Hi again, after using MPI_Ssend seems to be what I was looking for but I
would like to know more about MPI_Send.

For example sending 1 byte with MPI_Send it takes 8.69 microsec but with
MPI_Ssend it takes 152.9 microsec. I understand the difference but it
seems that from one message's size and after their difference is not so
big like trying for 518400 bytes where it needs 3515.78 microsec with
MPI_Send and 3584.1 microsec with MPI_Ssend. So has is there any rule to
figure out (of course it depends on the hardware) the threshold that
after this size the difference between the timings of MPI_Send and
MPI_Send is not so big or at least how to find it for my hardware?

Thanks a lot,
Best regards,
Georges