For the web archives: this same question was posted and answered on
the users list. See this thread:
http://www.open-mpi.org/community/lists/users/2008/11/7222.php
On Nov 6, 2008, at 1:00 PM, vladimir marjanovic wrote:
I am new user of Open MPI, I've used MPICH before.
I've tried on the user list but they couldn't help me.
There is performance bug with the following scenario:
proc_B: MPI_Isend(...,proc_A,..,&request)
do{
sleep(1);
MPI_Test(..,&flag,&request);
count++
}while(!flag);
proc_A: MPI_Recv(...,proc_B);
For message size 8MB, proc_B calls MPI_Test 88 times. It means
that point to point communication costs 88 seconds.
Btw, bandwidth isn't the problem (interconnection network:
InfiniBand)
Obviously, there is the problem with progress of the asynchronous
messages. In order to overlap communication and computation I
don't want to use MPI_Wait. Probably, the message is being
decomposed into chucks and the size of chuck is probably defined by
environment variable.
How can I advance the message more aggressively or can I control
size of chunk?
Thank you very much
Vladimir
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Cisco Systems
