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Subject: [OMPI users] efficient strategy with temporary message copy
From: christophe petit (christophe.petit09_at_[hidden])
Date: 2014-03-16 22:24:10


Hello,

I am studying the optimization strategy when the number of communication
functions in a code
is high.

My courses on MPI say two things for optimization which are contradictory :

1*) You have to use temporary message copy to allow non-blocking sending
and uncouple the sending and receiving

2*) Avoid using temporary message copy because the copy will add extra cost
on execution time.

And then, we are adviced to do :

- replace MPI_SEND by MPI_SSEND (synchroneous blocking sending) : it is
said that execution is divided by a factor 2

- use MPI_ISSEND and MPI_IRECV with MPI_WAIT function to synchronize
(synchroneous non-blocking sending) : it is said that execution is divided
by a factor 3

So what's the best optimization ? Do we have to use temporary message copy
or not and if yes, what's the case for ?

Thanks