Hi,
I have openmpi-2.0.2 builds on two different machines and I have a test
code which works on one machine and does not on the other machine. I'm
struggling to understand why and I hope that by posting here someone may
have some insight.
The test is using mpi derived data types and mpi_alltoallw on 4 tasks. On
the machine that fails it appears to ignore the displacement in the derived
datatype defined on task 0 and just send 0-3 to all tasks. The failing
machine is built against gcc 5.4.0, the working machine has both intel
16.0.3 and gcc 6.3.0 builds.
#include "mpi.h"
#include <stdio.h>
int main(int argc, char *argv[])
{
int rank, size;
MPI_Datatype type[4], type2[4];
int displacement[1];
int sbuffer[16];
int rbuffer[4];
MPI_Status status;
int scnts[4], sdispls[4], rcnts[4], rdispls[4];
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &size);
if (size < 4)
{
printf("Please run with 4 processes.\n");
MPI_Finalize();
return 1;
}
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
/* task 0 has sbuffer of size 16 and we are going to send 4 values to
each of tasks 0-3, offsetting in each
case so that the expected result is
task[0] 0-3
task[1] 4-7
task[2] 8-11
task[3] 12-15
*/
for( int i=0; i<size; i++){
if (rank == 0){
scnts[i] = 1;
}else{
scnts[i] = 0;
}
sdispls[i] = 0;
rcnts[i] = 0;
rdispls[i] = 0;
}
rcnts[0] = 1;
for (int i=0; i<size; i++){
type[i] = MPI_INT;
type2[i] = MPI_INT;
rbuffer[i] = -1;
}
/* on the recv side we create a data type which is a single block of
4 integers for the recv from 0
otherwise we use MPI_INT as a placeholder for the type
(openmpi does not want us to use MPI_DATATYPE_NULL a stupid
misinterpretation of the standard imho )*/
displacement[0] = 0;
MPI_Type_create_indexed_block(1, 4, displacement, MPI_INT, type2);
MPI_Type_commit(type2);
if (rank == 0)
{
for( int i=0; i<size; i++){
displacement[0] = i*4;
/* we create a datatype which is a single block of 4 integers with offset 4
from the start of sbuffer */
MPI_Type_create_indexed_block(1, 4, displacement, MPI_INT, type + i);
MPI_Type_commit(type+i);
}
for (int i=0; i<16; i++)
sbuffer[i] = i;
}
for (int i=0; i<size; i++)
printf("rank %d i=%d: scnts %d sdispls %d stype %d rcnts %d rdispls
%d rtype %d\n", rank, i, scnts[i], sdispls[i], type[i], rcnts[i],
rdispls[i], type2[i]);
MPI_Alltoallw(sbuffer, scnts, sdispls, type, rbuffer, rcnts, rdispls,
type2, MPI_COMM_WORLD);
for (int i=0; i<4; i++)
printf("rbuffer[%d] = %d\n", i, rbuffer[i]);
fflush(stdout);
MPI_Finalize();
return 0;
}
--
Jim Edwards
CESM Software Engineer
National Center for Atmospheric Research
Boulder, CO
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