Hi Patrick I think tab(i,:) is not contiguous in memory, but has a stride of nbcpus. Since the MPI type you are passing is just the barebones MPI_INTEGER, MPI_BCAST expects the four integers to be contiguous in memory, I guess. The MPI calls don't have any idea of the Fortran90 memory layout, and the tab(i,:) that you pass to MPI_BCAST means only the address for the *first* MPI_INTEGER to be broadcast (sent and received).
My impression is that you could either: 1) Declare your table transposed, i.e, tab(4,nbcpus-1), and make a few adjustments in the code to adapt to this change, which would make tab(:,i) contiguous in memory. or 2) Keep your current declaration of 'tab', but declare an MPI_TYPE_VECTOR with the appropriate stride (nbcpus) and use it in your MPI_BCAST call. For MPI user defined types see Ch. 3 of "MPI, The Complete Reference, Vol.1, The MPI Core, 2nd Ed." by M. Snir et. al. I hope this helps, Gus Correa On Dec 12, 2011, at 10:35 AM, Patrick Begou wrote: > I've got a strange problem with Fortran90 and MPI_BCAST call on a large > application. I've isolated the problem in this short program samples. > With fortran we can use subarrays in functions calls. Example, with passing a > subarray to the "change" procedure: > > MODULE mymod > IMPLICIT NONE > CONTAINS > SUBROUTINE change(tab,i) > IMPLICIT NONE > INTEGER, INTENT(INOUT),DIMENSION(:)::tab > INTEGER, INTENT(IN) :: i > tab(:)=i > END SUBROUTINE change > END MODULE mymod > > PROGRAM toto > USE mymod > IMPLICIT NONE > INTEGER, PARAMETER::nx=6, ny=4 > INTEGER, DIMENSION(nx,ny):: tab > INTEGER::i > > tab=-1 > DO i=1,nx > CALL change(tab(i,:),i) > ENDDO > PRINT*,tab > END PROGRAM toto > > But If I use subarrays with MPI_BCAST() like in this example: > > PROGRAM bide > USE mpi > IMPLICIT NONE > INTEGER :: nbcpus > INTEGER :: my_rank > INTEGER :: ierr,i,buf > INTEGER, ALLOCATABLE:: tab(:,:) > > CALL MPI_INIT(ierr) > CALL MPI_COMM_RANK(MPI_COMM_WORLD,my_rank,ierr) > CALL MPI_COMM_SIZE(MPI_COMM_WORLD,nbcpus,ierr) > > ALLOCATE (tab(0:nbcpus-1,4)) > > tab(:,:)=-1 > tab(my_rank,:)=my_rank > DO i=0,nbcpus-1 > CALL MPI_BCAST(tab(i,:),4,MPI_INTEGER,i,MPI_COMM_WORLD,ierr) > ENDDO > IF (my_rank .EQ. 0) print*,tab > CALL MPI_FINALIZE(ierr) > > END PROGRAM bide > > It doesn't work! With openMPI 1.2.8 (OpenSuse 11.4 X86_64) I have random > segfault: it works sometime, with few cpus (2, 4, 8...) and does'nt work > sometime with a larger number of cpus (32, 48, 64...). With OpenMPI 1.4.4 > (build from sources) it hangs (most of the array tab remains at the -1 > initialization value). > Such procedure calls are allowed with fortran90 so I do not understand why > they fail here. I have to use a buffer array (called tabl in the following > program) to solve the problem. > > PROGRAM bide > USE mpi > IMPLICIT NONE > INTEGER :: nbcpus > INTEGER :: my_rank > INTEGER :: ierr,i,buf > INTEGER, ALLOCATABLE:: tab(:,:) > INTEGER::tab1(4) > > CALL MPI_INIT(ierr) > CALL MPI_COMM_RANK(MPI_COMM_WORLD,my_rank,ierr) > CALL MPI_COMM_SIZE(MPI_COMM_WORLD,nbcpus,ierr) > > ALLOCATE (tab(0:nbcpus-1,4)) > > tab=-1 > tab1=-1 > DO i=0,nbcpus-1 > IF(my_rank.EQ.i) tab1=my_rank > CALL MPI_BCAST(tab1,4,MPI_INTEGER,i,MPI_COMM_WORLD,ierr) > tab(i,:)=tab1 > ENDDO > IF (my_rank .EQ. 0) print*,tab > CALL MPI_FINALIZE(ierr) > > END PROGRAM bide > > Any idea about this behavior ? > > Patrick > -- > =============================================================== > | Equipe M.O.S.T. | > http://most.hmg.inpg.fr > | > | Patrick BEGOU | ------------ | > | LEGI | > mailto:patrick.be...@hmg.inpg.fr > | > | BP 53 X | Tel 04 76 82 51 35 | > | 38041 GRENOBLE CEDEX | Fax 04 76 82 52 71 | > =============================================================== > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
