At 11:52 04/05/2012, you wrote:
Hi all,
I have a program that executes a communication loop similar to this one:
1: for(int p1=0; p1<np; ++p1) {
2: for(int p2=0; p2<np; ++p2) {
3: if(me==p1) {
4: if(sendSize(p2))
MPI_Ssend(sendBuffer[p2],sendSize(p2),MPI_FLOAT,p2,0,myw);
5: if(recvSize(p2))
MPI_Recv(recvBuffer[p2],recvSize(p2),MPI_FLOAT,p2,0,myw,&status);
6: } else if(yo==p2) {
7: if(recvSize(p1))
MPI_Recv(recvBuffer[p1],recvSize(p1),MPI_FLOAT,p2,0,myw,&status);
8: if(sendSize(p1))
MPI_Ssend(sendBuffer[p1],sendSize(p1),MPI_FLOAT,p2,0,myw);
9: }
10: MPI_Barrier(myw);
11: }
12: }
The program is an iterative process that makes some calculations,
communicates and then continues with the next iteration. The problem
is that after making 30 successful iterations the program hangs.
With padb I have seen that one of the processors waits at line 5 for
the reception of data that was already sent and the rest of the
processors are waiting at the barrier in line 10. The size of the
messages and buffers is the same for all the iterations.
My real program makes use of asynchronous communications for obvious
performance reasons and it worked without problems when the case to
solve was smaller (lower number of processors and memory), but I
found that for this case the program hanged and that is why a
changed the communication routine using synchronous communications
to see where is the problem. Now I know where the program hangs, but
I don't understand what I am doing wrong.
Any suggestions?
All messages has p2 as destination. So, p1 is waiting for a message
that hasn't been sended for him. He shouldn't be waiting any
messages. Don't know the logic of your program, so can't tell more
suggestions or clues.
