Ed Peddycoart wrote:
I need to do some performance tests on my mpi app. I simply want
to determine how long it takes for my sends from one process to be
received by another process.
Here is the code I used as my example for non-blocking send/receive...
if( myrank == 0 ) {
/* Post a receive, send a message, then wait */
MPI_Irecv( b, 100, MPI_DOUBLE, 1, 19, MPI_COMM_WORLD, &request );
MPI_Isend( a, 100, MPI_DOUBLE, 1, 17, MPI_COMM_WORLD );
MPI_Wait( &request, &status );
}
else if( myrank == 1 ) {
/* Post a receive, send a message, then wait */
MPI_Irecv( b, 100, MPI_DOUBLE, 0, 17, MPI_COMM_WORLD, &request
);
MPI_Isend( a, 100, MPI_DOUBLE, 0, 19, MPI_COMM_WORLD );
MPI_Wait( &request, &status );
}
First of all, you should also complete the Isend request. One option
is to turn it into a blocking Send. Another option is to add a request
to the Isend call (which is required by the API) and then turn the Wait
call into a Waitall call on both requests.
I originally thought to just put a timer call before affer the
rank=0 receive, but that doesn't seem to capture the complete time...
see the following code.
if( myrank == 0 ) {
timer.start();
/* Post a receive, send a message, then wait */
MPI_Irecv( b, 100, MPI_DOUBLE, 1, 19, MPI_COMM_WORLD, &request );
MPI_Isend( a, 100, MPI_DOUBLE, 1, 17, MPI_COMM_WORLD );
MPI_Wait( &request, &status );
timer.stop();
elapsedTime = getElapsedTime();
}
else if( myrank == 1 ) {
/* Post a receive, send a message, then wait */
MPI_Irecv( b, 100, MPI_DOUBLE, 0, 17, MPI_COMM_WORLD, &request
);
MPI_Isend( a, 100, MPI_DOUBLE, 0, 19, MPI_COMM_WORLD );
MPI_Wait( &request, &status );
}
That should work once the code is corrected. Can you use MPI_Wtime()?
(Not necessarily a big deal, but should be a portable way of getting
high-quality timings in MPI programs.) In what sense does it not
capture the complete time?
How do others time this process? Should I send a msg from one app
to the other to initiate timing, send the data I want to time?
It's common to ping-pong many times back and forth. There may be one
or more "warm-up" iterations (to make sure both processes are ready and
all resources used have been touched and warmed/woken up) and other
iterations to check reproducibility of results. Also, one might have
many iterations between the timer calls to amortize the overhead of the
timer call.
if( myrank == 0 ) {
MPI_Irecv( b, 100, MPI_DOUBLE, 1,
startTimeTag, MPI_COMM_WORLD, &request );
MPI_Wait( &request, &status );
timer.start();
MPI_Irecv( b, 100, MPI_DOUBLE, 1, dataTag, MPI_COMM_WORLD,
&request );
MPI_Wait( &request, &status );
timer.stop();
elapsedTime = getElapsedTime();
}
else if( myrank == 1 ) {
MPI_Isend( a, 100, MPI_DOUBLE, 0,
startTimerTag, MPI_COMM_WORLD );
MPI_Wait( &request, &status );
MPI_Isend( b, 100, MPI_DOUBLE, 0, dataTag , MPI_COMM_WORLD,
&request );
MPI_Wait( &request, &status );
}
Ed
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