Hi,
I tried openmpi-3.0.0rc1.tar.gz using Intel Fortran 2017 and gcc on a current
MacOS system. For this version, it seems to me that MPI_IN_PLACE returns
incorrect results (while other MPI implementations, including some past OpenMPI
versions, work fine).
This can be seen with a simple Fortran example code, shown below. In the test,
the values of all entries of an array “test_data” should be 1.0d0 if the
behavior were as intended. However, the version of OpenMPI I have returns 0.d0
instead.
I’ve seen this behavior on some other compute platforms too, in the past, so it
wasn’t new to me. Still, I thought that this time, I’d ask. Any thoughts?
Thank you,
Best wishes
Volker
! size of test data array
integer :: n_data
! array that contains test data for MPI_IN_PLACE
real*8, allocatable :: test_data(:)
integer :: mpierr
n_data = 10
allocate(test_data(n_data),stat=mpierr)
! seed test data array for allreduce call below
if (myid.eq.0) then
test_data(:) = 1.d0
else
test_data(:) = 0.d0
end if
! Sum the test_data array over all MPI tasks
call MPI_ALLREDUCE(MPI_IN_PLACE, &
test_data(:), &
n_data, &
MPI_DOUBLE_PRECISION, &
MPI_SUM, &
mpi_comm_global, &
mpierr )
! The value of all entries of test_data should now be 1.d0 on all MPI tasks.
! If that is not the case, then the MPI_IN_PLACE flag may be broken.
Volker Blum
Associate Professor
Ab Initio Materials Simulations
Duke University, MEMS Department
144 Hudson Hall, Box 90300, Duke University, Durham, NC 27708, USA
volker.b...@duke.edu
https://aims.pratt.duke.edu
+1 (919) 660 5279
Twitter: Aimsduke
Office: 1111 Hudson Hall
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