I'm sure it was a latency optimization, just like the old test behavior.
Personally, I'd call opal_progress blindly, then walk through the queue.
Doing the walk the queue, call opal_progress, walk the queue thing seems
like too much work for iprobe. Test, sure. iProbe... eh.
Brian
On Wed, 18 Jun 2008, Jeff Squyres wrote:
Perhaps we did that as a latency optimization...?
George / Brian / Galen -- do you guys know/remember why this was done?
On the surface, it looks like it would be ok to call progress and check again
to see if it found the match. Can anyone think of a deeper reason not to?
On Jun 17, 2008, at 11:43 AM, Terry Dontje wrote:
I've ran into an issue while running hpl where a message has been sent (in
shared memory in this case) and the receiver calls iprobe but doesn't see
said message the first call to iprobe (even though it is there) but does
see it the second call to iprobe. Looking at mca_pml_ob1_iprobe function
and the calls it makes it looks like it checks the unexpected queue for
matches and if it doesn't find one it sets the flag to 0 (no matches), then
calls opal_progress and return. This seems wrong to me since I would
expect that the call to opal_progress probably would pull in the message
that the iprobe is waiting for.
Am I correct in my reading of the code? It seems that maybe some sort of
check needs to be done after the call to opal_progress in
mca_pml_ob1_iprobe.
Attached is a simple program that shows the issue I am running into:
#include <mpi.h>
int main() {
int rank, src[2], dst[2], flag = 0;
int nxfers;
MPI_Status status;
MPI_Init(NULL, NULL);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
if (0 == rank) {
for (nxfers = 0; nxfers < 5; nxfers++)
MPI_Send(src, 2, MPI_INT, 1, 0, MPI_COMM_WORLD);
} else if (1 == rank) {
for (nxfers = 0; nxfers < 5; nxfers++) {
sleep(5);
flag = 0;
while (!flag) {
printf("iprobe...");
MPI_Iprobe(0, 0, MPI_COMM_WORLD, &flag, &status);
}
printf("\n");
MPI_Recv(dst, 2, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
}
}
MPI_Finalize();
}
--td
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