Re: [mpich-discuss] Is it allowed to attach automatic array for remote access with MPI_Win_attach?

19 Apr 2016

      This is simplified version of my routine. It may look odd but I am
trying to migrate from send/recv scheme to one sided pscw and that
is the reason for buffers etc. As long as dynamic windows are not used,
it works fine (I believe). When I switch to dynamic windows it fails
with segmentation fault. I would appreciate any comment and suggestion
how to improve this.

SUBROUTINE swap_simple_rma(field, row_length, rows, levels, halo_size)

USE mpi

IMPLICIT NONE

INTEGER, INTENT(IN) :: row_length
INTEGER, INTENT(IN) :: rows
INTEGER, INTENT(IN) :: levels
INTEGER, INTENT(IN) :: halo_size
REAL(KIND=8), INTENT(INOUT) :: field(1:row_length, 1:rows, levels)
REAL(KIND=8) :: send_buffer(halo_size, rows, levels)
REAL(KIND=8) :: recv_buffer(halo_size, rows, levels)
INTEGER  :: buffer_size
INTEGER ::  i,j,k
INTEGER(kind=MPI_INTEGER_KIND)  :: ierror
INTEGER(kind=MPI_INTEGER_KIND) :: my_rank, comm_size
Integer(kind=MPI_INTEGER_KIND) :: win, win_info
Integer(kind=MPI_INTEGER_KIND) :: my_group, origin_group, target_group
Integer(kind=MPI_INTEGER_KIND), DIMENSION(1) :: target_rank, origin_rank
Integer(kind=MPI_ADDRESS_KIND) :: win_size, disp

  CALL MPI_Comm_Rank(MPI_COMM_WORLD, my_rank, ierror)
  CALL MPI_Comm_Size(MPI_COMM_WORLD, comm_size, ierror)

  buffer_size = halo_size * rows * levels

  CALL MPI_Info_create(win_info, ierror)
  CALL MPI_Info_set(win_info, "no_locks", "true", ierror)

  CALL MPI_Comm_group(MPI_COMM_WORLD, my_group, ierror)

  If (my_rank /= comm_size - 1) Then
    origin_rank = my_rank + 1
    CALL MPI_Group_incl(my_group, 1, origin_rank, origin_group, ierror)
    win_size = 8*buffer_size
  Else
    origin_group = MPI_GROUP_EMPTY
    win_size = 0
  End If

  CALL MPI_Win_create_dynamic(win_info, MPI_COMM_WORLD, win, ierror)
!! CALL MPI_Win_create(recv_buffer, win_size,      &
!!        8, win_info, MPI_COMM_WORLD, win, ierror)
  CALL MPI_Win_attach(win, recv_buffer, win_size, ierror)

  CALL MPI_Barrier(MPI_COMM_WORLD, ierror)

  CALL MPI_Win_post(origin_group, MPI_MODE_NOSTORE, win, ierror)

  ! Prepare buffer
     DO k=1,levels
       DO j=1,rows
         DO i=1,halo_size
           send_buffer(i,j,k)=field(i,j,k)
         END DO ! I
        END DO ! J
      END DO ! K

  If (my_rank /= 0 ) Then
     target_rank = my_rank - 1
     CALL MPI_Group_incl(my_group, 1, target_rank, target_group, ierror)
  Else
     target_group = MPI_GROUP_EMPTY
  End If

  CALL MPI_Win_start(target_group, 0, win, ierror)

  disp = 0

  If (my_rank /= 0) Then
    CALL MPI_Put(send_buffer, buffer_size, MPI_REAL8,   &
        my_rank - 1, disp, buffer_size, MPI_REAL8, win, ierror)
  End If
  CALL MPI_Win_complete(win, ierror)

  CALL MPI_Barrier(MPI_COMM_WORLD, ierror)
  write (0,*) 'Put OK'
  CALL MPI_Barrier(MPI_COMM_WORLD, ierror)

  CALL MPI_Win_wait(win, ierror)

  ! Read from buffer
  If (my_rank /= comm_size -1 ) Then
      DO k=1,levels
        DO j=1,rows
          DO i=1,halo_size
            field(row_length+i,j,k) =  recv_buffer(i,j,k)
          END DO
        END DO
      END DO
  End if

  CALL MPI_Win_detach(win, recv_buffer, ierror)
  CALL MPI_Win_free(win, ierror)

END SUBROUTINE swap_simple_rma

Best Regards,
Maciej

W dniu 14.04.2016 o 19:21, Thakur, Rajeev pisze:
...
After the Win_attach, did you add a barrier or some other form of synchronization? The put shouldn’t happen before Win_attach returns.
Rajeev
...
On Apr 14, 2016, at 10:56 AM, Maciej Szpindler <[email protected]> wrote:
Dear All,
I am trying to use dynamic RMA windows in fortran. In my case I would
like to attach automatic array to dynamic window. The question is if
it is correct and allowed in MPICH. I feel that it is not working, at
least in cray-mpich/7.3.2.
I have a subroutine that use RMA windows:
SUBROUTINE foo(x, y, z , ...)
USE mpi
...
INTEGER, INTENT(IN) :: x, y, z
REAL(KIND=8) :: buffer(x, y, z)
INTEGER(kind=MPI_INTEGER_KIND) :: win_info, win, comm
INTEGER(kind=MPI_INTEGER_KIND) :: buff_size
...
buff_size = x*y*z*8
CALL MPI_Info_create(win_info, ierror)
CALL MPI_Info_set(win_info, "no_locks", "true", ierror)
CALL MPI_Win_create_dynamic(win_info, comm, win, ierror)
CALL MPI_Win_attach(win, buffer, buff_size, ierror)
...
This produces segmentation fault when MPI_Put is called on a window,
while exactly the same routine code with static MPI_Win_create on
buffer instead of create_dynamic+attach works fine. As far as I
understand buffer is in this case "simply contiguous" in a sense of
the MPI Standard. Any help would be appreciated!
Best Regards,
Maciej
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Maciej Szpindler

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