Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |  

This web mail archive is frozen.

This page is part of a frozen web archive of this mailing list.

You can still navigate around this archive, but know that no new mails have been added to it since July of 2016.

Click here to be taken to the new web archives of this list; it includes all the mails that are in this frozen archive plus all new mails that have been sent to the list since it was migrated to the new archives.

Subject: [OMPI users] MPI_Alltoall with Vector Datatype
From: Spenser Gilliland (spenser_at_[hidden])
Date: 2014-05-07 04:48:39


Hi,

I've recently started working with MPI and I noticed that when a
Alltoall is utilized with a vector datatype, the call only uses the
extent to determine the location for the back to back transactions.
This makes using the vector type with collective communicators
difficult.

For Example:
Using the code at the bottom. I think I should get

 0 1 8 9
 4 5 12 13
 2 3 10 11
 6 7 14 15

However, the result is

 0 1 2 3
 4 5 8 9
 6 7 10 11
 x x 14 15

Is this the way it is supposed to be?

FYI: This is version 1.6.2 in Rocks 6

Thanks,
Spenser

float A[4][4];
int wsize, wrank;
MPI_Comm_size(MPI_COMM_WORLD, &wsize); // Assume 2
MPI_Comm_rank(MPI_COMM_WORLD, &wrank);
MPI_Type_vector(4/wsize, 4/wsize, 4, MPI_FLOAT, &mpi_all_t);
MPI_Type_commit(&mpi_all_t);

for(int i = 0; i < 4; i++) for (j = 0; j < 4; j++) {
   A[i][j] = i*4+j;
}

MPI_Alltoall(A[rank*4/wsize*4], 1, mpi_all_t,
                     A[rank*4/wsize*4], 1, mpi_all_t,
                     MPI_COMM_WORLD);

for(int i = 0; i < 4; i++) {
   for (j = 0; j < 4; j++) {
      printf("%6.2g")
   }
   printf("\n");
}

-- 
Spenser Gilliland
Computer Engineer
Doctoral Candidate