I finally managed to track down some issues in mpi4py's test suite
using Open MPI 1.8+. The code below should be enough to reproduce the
problem. Run it under valgrind to make sense of my following
diagnostics.
In this code I'm creating a 2D, periodic Cartesian topology out of
COMM_SELF. In this case, the process in COMM_SELF has 4 logical in/out
links to itself. So we have size=1 but indegree=outdegree=4. However,
in ompi/mca/coll/basic/coll_basic_module.c, "size * 2" request are
being allocated to manage communication:
if (OMPI_COMM_IS_INTER(comm)) {
size = ompi_comm_remote_size(comm);
} else {
size = ompi_comm_size(comm);
}
basic_module->mccb_num_reqs = size * 2;
basic_module->mccb_reqs = (ompi_request_t**)
malloc(sizeof(ompi_request_t *) * basic_module->mccb_num_reqs);
I guess you have to also special-case for topologies and allocate
indegree+outdegree requests (not sure about this number, just
guessing).
#include <stdio.h>
#include <mpi.h>
int main(int argc, char *argv[])
{
MPI_Comm comm;
int ndims = 2, dims[2] = {1,1}, periods[2] = {1,1};
int sendbuf = 7, recvbuf[5] = {0,0,0,0,0};
MPI_Init(&argc, &argv);
MPI_Cart_create(MPI_COMM_SELF, ndims, dims, periods, 0, &comm);
MPI_Neighbor_allgather(&sendbuf, 1, MPI_INT,
recvbuf, 1, MPI_INT,
comm);
{int i; for (i=0;i<5;i++) printf("%d ",recvbuf[i]); printf("\n");}
MPI_Finalize();
return 0;
}
--
Lisandro Dalcin
============
Research Scientist
Computer, Electrical and Mathematical Sciences & Engineering (CEMSE)
Numerical Porous Media Center (NumPor)
King Abdullah University of Science and Technology (KAUST)
http://numpor.kaust.edu.sa/
4700 King Abdullah University of Science and Technology
al-Khawarizmi Bldg (Bldg 1), Office # 4332
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http://www.kaust.edu.sa
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