Hi Hugo, Jeff, list
Hugo: I think David Zhang's suggestion was to use
MPI_REAL8 not MPI_REAL, instead of MPI_DOUBLE_PRECISION in your
MPI_Allreduce call.
Still, to me it looks like OpenMPI is making double precision 4-byte
long, which shorter than I expected it be (8 bytes),
at least when looking at the output of ompi_info --all.
I always get get a size 4 for dbl prec in my x86_64 machine,
from ompi_info --all.
I confirmed this in six builds of OpenMPI 1.4.2: gcc+gfortran,
gcc+pgf90, gcc+ifort, icc+ifort, pgcc+pgf90, and opencc+openf95.
Although the output of ompi_info never says this is actually the size
of MPI_DOUBLE_PRECISION, just of "dbl prec", which is a bit ambiguous.
FWIW, I include the output below. Note that alignment for gcc+ifort
is 1, all others are 4.
Jeff: Is this correct?
Thanks,
Gus Correa
$ openmpi/1.4.2/open64-4.2.3-0/bin/ompi_info --all | grep -i dbl
Fort dbl prec size: 4
Fort dbl cplx size: 4
Fort dbl prec align: 4
Fort dbl cplx align: 4
$ openmpi/1.4.2/gnu-4.1.2/bin/ompi_info --all | grep -i dbl
Fort dbl prec size: 4
Fort dbl cplx size: 4
Fort dbl prec align: 4
Fort dbl cplx align: 4
$ openmpi/1.4.2/gnu-4.1.2-intel-10.1.017/bin/ompi_info --all | grep -i dbl
Fort dbl prec size: 4
Fort dbl cplx size: 4
Fort dbl prec align: 1
Fort dbl cplx align: 1
$ openmpi/1.4.2/gnu-4.1.2-pgi-8.0-4/bin/ompi_info --all | grep -i dbl
Fort dbl prec size: 4
Fort dbl cplx size: 4
Fort dbl prec align: 4
Fort dbl cplx align: 4
$ openmpi/1.4.2/pgi-8.0-4/bin/ompi_info --all | grep -i dbl
Fort dbl prec size: 4
Fort dbl cplx size: 4
Fort dbl prec align: 4
Fort dbl cplx align: 4
Hugo Gagnon wrote:
And how do I know how big my data buffer is? I ran MPI_TYPE_EXTENT of
And how do I know how big my data buffer is? I ran MPI_TYPE_EXTENT of
MPI_DOUBLE_PRECISION and the result was 8. So I changed my program to:
1 program test
2
3 use mpi
4
5 implicit none
6
7 integer :: ierr, nproc, myrank
8 !integer, parameter :: dp = kind(1.d0)
9 real(kind=8) :: inside(5), outside(5)
10
11 call mpi_init(ierr)
12 call mpi_comm_size(mpi_comm_world, nproc, ierr)
13 call mpi_comm_rank(mpi_comm_world, myrank, ierr)
14
15 inside = (/ 1., 2., 3., 4., 5. /)
16 call mpi_allreduce(inside, outside, 5, mpi_real, mpi_sum,
mpi_comm_world, ierr)
17
18 if (myrank == 0) then
19 print*, outside
20 end if
21
22 call mpi_finalize(ierr)
23
24 end program test
but I still get a SIGSEGV fault:
forrtl: severe (174): SIGSEGV, segmentation fault occurred
Image PC Routine Line
Source
libmpi.0.dylib 00000001001BB4B7 Unknown Unknown
Unknown
libmpi_f77.0.dyli 00000001000AF046 Unknown Unknown
Unknown
a.out 0000000100000D87 _MAIN__ 16
test.f90
a.out 0000000100000C9C Unknown Unknown
Unknown
a.out 0000000100000C34 Unknown Unknown
Unknown
forrtl: severe (174): SIGSEGV, segmentation fault occurred
Image PC Routine Line
Source
libmpi.0.dylib 00000001001BB4B7 Unknown Unknown
Unknown
libmpi_f77.0.dyli 00000001000AF046 Unknown Unknown
Unknown
a.out 0000000100000D87 _MAIN__ 16
test.f90
a.out 0000000100000C9C Unknown Unknown
Unknown
a.out 0000000100000C34 Unknown Unknown
Unknown
What is wrong now?
