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Subject: [OMPI users] How to time data transfers?
From: Ed Peddycoart (EPeddycoart_at_[hidden])
Date: 2010-10-13 13:59:40


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 );
 }

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 );
 }

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?

 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