Try removing the barrier.
On May 4, 2012, at 5:52 AM, Jorge Chiva Segura 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?
>
> More specific data of the case and cluster:
> Number of processors: 320
> Max size of the message: 6800 floats (27200 bytes)
> Number of cores by node: 32
> File system: lustre
> Resource manager: slurm
> OMPI version: 1.4.4
> Operative system: Ubuntu 10.04.4 LTS
> Kernel: RHEL 6.2 2.6.32-220.4.2
> Infiniband: OFED 1.4.2
> InfiniBand: Mellanox Technologies MT26428 [ConnectX VPI PCIe 2.0 5GT/s - IB
> QDR / 10GigE] (rev b0)
>
> Thank you for your time,
> Jorge
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