I guess this must depend on what BTL you're using. If I run all
processes on the same node, I get the behavior you expect. So, are you
running processes on the same node, or different nodes and, if
different, via TCP or IB?
Gregory D Abram wrote:
I have a little program which initializes, calls MPI_Bcast, prints
a message, waits five seconds, and finalized. I sure thought that each
participating process would print the message immediately, then all
would wait and exit - thats what happens with mvapich 1.0.0. On OpenMPI
1.2.5, though, I get the message immediately from proc 0, then 5
seconds later, from proc 1, and then 5 seconds later, it exits- as if
MPI_Finalize on proc 0 flushed the MPI_Bcast. If I add a MPI_Barrier
after the MPI_Bcast, it works as I'd expect. Is this behavior correct?
If so, I so I have a bunch of code to change in order to work correctly
on OpenMPI.
#include <stdlib.h>
#include <stdio.h>
#include <mpi.h>
main(int argc, char *argv[])
{
char hostname[256]; int r, s;
MPI_Init(&argc, &argv);
gethostname(hostname, sizeof(hostname));
MPI_Comm_rank(MPI_COMM_WORLD, &r);
MPI_Comm_size(MPI_COMM_WORLD, &s);
fprintf(stderr, "%d of %d: %s\n", r, s,
hostname);
int i = 99999;
MPI_Bcast(&i, sizeof(i), MPI_UNSIGNED_CHAR,
0,
MPI_COMM_WORLD);
//
MPI_Barrier(MPI_COMM_WORLD);
fprintf(stderr, "%d: got it\n", r);
sleep(5);
MPI_Finalize();
}
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