[mvapich-discuss] gather receive order

[Andrew Senin]

Hi Krishna, 

 

Thanks for your answer! I'm using mvapich2-1.6. And setting the variables
fixes the problem, that's exactly what I need! 

 

Thanks again.

-Andrew 

 

From: krishna.kandalla at gmail.com [mailto:krishna.kandalla at gmail.com] On
Behalf Of Krishna Kandalla
Sent: Wednesday, May 25, 2011 12:28 AM
To: Andrew Senin
Cc: mvapich-discuss at cse.ohio-state.edu
Subject: Re: [mvapich-discuss] gather receive order

 

Hello Andrew, 
          Thank you for reporting this issue.  We have a fix for this in our
current development version. Can you please let us know which version of
mvapich2 you are using? I can generate a patch for your version and send it
over. Meanwhile, you can also try setting the following run-time flags to 0:

MV2_USE_DIRECT_GATHER
<http://mvapich.cse.ohio-state.edu/support/user_guide_mvapich2-1.7_alpha.htm
l#x1-20100011.75>  and 
MV2_USE_TWO_LEVEL_GATHER
<http://mvapich.cse.ohio-state.edu/support/user_guide_mvapich2-1.7_alpha.htm
l#x1-22300011.97> . 

Regards,
Krishna
             

On Tue, May 24, 2011 at 6:02 AM, Andrew Senin <andrew.senin at itseez.com>
wrote:

Hello list, 

 

I have an application which uses MPI_Gather. It worked perfectly with
openmpi-1.4.3 and mpich2-1.3.2p1. However when I switched to mvapich2 it
starts failing. After investigation I found that MPI_Gather does receives
array in rank order while the other 2 implementations do. Is this an issue
in mvapich2? The standard says that "The root process receives the messages
and stores them in rank order".

 

Here is the output I receive from 4 ranks:

rank 2 sent (4,5,)

rank 3 sent (6,7,)

rank 0 sent (0,1,)

rank 0 received 0 1 6 7 2 3 4 5 , expected 0 1 2 3 4 5 6 7

rank 1 sent (2,3,)

 

And the test which generates this output:

#include "mpi.h"

#include <string.h>

#include "stdio.h"

 

#define num_el 2

#define num_ranks 4

 

int main(int argc, char *argv[])

{

    int i = 0;

    int rank;

    int size; 

    int gather_send[num_el] = {0};

    int gather_recv[num_el * num_ranks] = {0};

    

    MPI_Init(&argc, &argv);

 

    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    MPI_Comm_size(MPI_COMM_WORLD, &size);

 

    if (size != num_ranks)

    {

        printf("This sample works with only %i ranks\n", num_ranks);

        goto FreeMemory;

    }

  

    for (i = 0; i < num_el; i++)

    {

        gather_send[i] = num_el * rank + i;

    }

 

    MPI_Gather(gather_send, num_el, MPI_INT, 

               gather_recv, num_el, MPI_INT, 

               0, MPI_COMM_WORLD);

 

    printf("rank %i sent (",rank);

    for (i = 0; i < num_el; i++)

    {

        printf("%i,", gather_send[i]);

    }

    printf(")\n");

 

    if (rank == 0)

    {

        int i = 0;

 

        char buffer_received[10000] = {0};

        char buffer_expected[10000] = {0};

 

        for(i = 0; i < num_el * num_ranks; i++)

        {

            char temp_received[128] = {0};

            char temp_expected[128] = {0};

 

            sprintf(temp_received, "%i ", gather_recv[i]);

            sprintf(temp_expected, "%i ", i);

 

            strcat(buffer_expected, temp_expected);

            strcat(buffer_received, temp_received);

        }

 

        printf("rank %i received %s, expected %s\n", 

                rank, 

                buffer_received, 

                buffer_expected);

    }

 

 

FreeMemory:

    MPI_Finalize();

 

    return 0;

}

 

Thanks, 

Andrew.

 

 


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