On Fri, Aug 14, 2009 at 1:32 AM, Eugene Loh <eugene....@sun.com> wrote:
> amjad ali wrote: > > I am parallelizing a CFD 2D code in FORTRAN+OPENMPI. Suppose that the grid > (all triangles) is partitioned among 8 processes using METIS. Each process > has different number of neighboring processes. Suppose each process has n > elements/faces whose data it needs to sends to corresponding neighboring > processes, and it has m number of elements/faces on which it needs to get > data from corresponding neighboring processes. Values of n and m are > different for each process. Another aim is to hide the communication behind > computation. For this I do the following for each process: > > > > DO j = 1 to n > > CALL MPI_ISEND (send_data, num, type, dest(j), tag, MPI_COMM_WORLD, > ireq(j), ierr) > > ENDDO > > > > DO k = 1 to m > > CALL MPI_RECV(recv_data, num, type, source(k), tag, MPI_COMM_WORLD, > status, ierr) > > ENDDO > > > > This solves my problem. But it gives memory leakage; Ram gets filled after > few thousands of iteration. What is the solution/remedy? How should I tackle > this? > > > > In another CFD code I removed this problem of memory-filling by following > (in that code n=m) : > > > > DO j = 1 to n > > CALL MPI_ISEND (send_data, num, type, dest(j), tag, MPI_COMM_WORLD, > ireq(j), ierr) > > ENDDO > > > > CALL MPI_WAITALL(n,ireq,status,ierr) > > > > DO k = 1 to n > > CALL MPI_RECV(recv_data, num, type, source(k), tag, MPI_COMM_WORLD, > status, ierr) > > ENDDO > > > > But this is not working in current code; and the previous code was not > giving correct results with large number of processes. > > I don't know how literally to read the code you sent. Maybe your actual > code "does the right thing", but just to confirm I think the correct code > should look like this: > > DO J=1, N > CALL MPI_ISEND(...) > END DO > > DO K=1, M > CALL MPI_RECV(...) > END DO > > CALL MPI_WAITALL(...) > > That is, you start all non-blocking sends. Then you perform receives. > Then you complete the sends. More commonly, one would post all receives > first using non-blocking calls (MPI_IRECV), then perform all sends > (MPI_SEND), then complete the receives with MPI_WAITALL. > > Yet another option is to post non-blocking receives, then non-blocking > sends, then complete all sends and receives with a WAITALL call that has M+N > requests. > > Sorry if you already knew all this and I'm just overreacting to the > simplified code you sent out. > No its OK; your sayings are really fine. Please tell me that if have multiple such ISEND-RECV squrntially for sending receiving data then DO we need to declare separate status(MPI_STATUS_SIZE) with for example status1, status2, ....; or a single declaration of it will work for all?? Regards, Amjad Ali. > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users >
