Re: [OMPI users] Bad behavior in Allgatherv when a count is 0

[George Bosilca]

Kenneth,




  Thanks,
    george.

On Dec 13, 2007, at 6:58 PM, Moreland, Kenneth wrote:

I cannot replicate this weird behavior with the current version in the trunk. I guess it has been fixed since 1.2.4.

I have found that on rare occasion Allgatherv fails to pass the data to

all processes.  Given some magical combination of receive counts and
displacements, one or more processes are missing some or all of some
arrays in their receive buffer.  A necessary, but not sufficient,

below demonstrates the failure.  I have tried it on OpenMPI version

1.1.2, so the problem must have been introduced since then.

-Ken

  ****      Kenneth Moreland
   ***      Sandia National Laboratories
***********
*** *** ***  email: kmo...@sandia.gov
**  ***  **  phone: (505) 844-8919
   ***      fax:   (505) 845-0833



#include <mpi.h>

#include <stdlib.h>
#include <stdio.h>

int main(int argc, char **argv)
{
 int rank;
 int size;
 MPI_Comm smallComm;
 int senddata[5], recvdata[100];
 int lengths[3], offsets[3];
 int i, j;

 MPI_Init(&argc, &argv);

 MPI_Comm_rank(MPI_COMM_WORLD, &rank);
 MPI_Comm_size(MPI_COMM_WORLD, &size);
 if (size != 3)
   {
   printf("Need 3 processes.");
   MPI_Abort(MPI_COMM_WORLD, 1);
   }

 for (i = 0; i < 100; i++) recvdata[i] = -1;
 for (i = 0; i < 5; i++) senddata[i] = rank*10 + i;
 lengths[0] = 5;  lengths[1] = 0;  lengths[2] = 5;
 offsets[0] = 3;  offsets[1] = 9;  offsets[2] = 10;
 MPI_Allgatherv(senddata, lengths[rank], MPI_INT,
                recvdata, lengths, offsets, MPI_INT, MPI_COMM_WORLD);

 for (i = 0; i < size; i++)
   {
   for (j = 0; j < lengths[i]; j++)
     {
     if (recvdata[offsets[i]+j] != 10*i+j)
       {

j,
              recvdata[offsets[i]+j]);
       break;
       }
     }
   }

 MPI_Finalize();

 return 0;
}



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condition seems to be that one of the receive counts is 0. Beyond that I have not figured out any real pattern, but the example program listed 1.2.3 and 1.2.4; it fails on both. However, it works fine with version printf("%d: Got bad data from rank %d, index %d: %d\n", rank, i,

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