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Subject: [OMPI users] Making MPI_Send to behave as blocking for all the sizes of the messages
From: George Markomanolis (george_at_[hidden])
Date: 2010-11-18 04:56:11


Dear all,

I am trying to disable the eager mode in OpenMPI 1.3.3 and I don't see a
real difference between the timings.
I would like to execute a ping (rank 0 sends a message to rank 1) and to
measure the duration of the MPI_Send on rank 0 and the duration of
MPI_Recv on rank 1. I have the following results.

Without changing the eager mode:

bytes MPI_Send (in msec) MPI_Recv (in msec)
1 5.8 52.2
2 5.6 51.0
4 5.4 51.1
8 5.6 51.6
16 5.5 49.7
32 5.4 52.1
64 5.3 53.3

with disabled the eager mode:

ompi_info --param btl tcp | grep eager
MCA btl: parameter "btl_tcp_eager_limit" (current value: "0", data
source: environment)

bytes MPI_Send (in msec) MPI_Recv (in msec)
1 5.4 52.3
2 5.4 51.0
4 5.4 52.1
8 5.4 50.7
16 5.0 50.2
32 5.1 50.1
64 5.4 52.8

However I was expecting that with disabled the eager mode the duration
of MPI_Send should be longer. Am I wrong? Is there any option for making
the MPI_Send to behave like blocking command for all the sizes of the
messages?

Thanks a lot,
Best regards,
George Markomanolis