[mpich-devel] MPI_Dist_graph_create self-edge

[Daniel Ibanez]

Pavan,

Here is a short program that reproduces the issue:



#include <mpi.h>
#include <assert.h>

int main(int argc, char** argv)
{
  MPI_Init(&argc, &argv);
  int size;
  MPI_Comm_size(MPI_COMM_WORLD, &size);
  assert(size == 2);
  int rank;
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm newcomm;
  if (rank == 0) {
    int sources[1] = {0};
    int degrees[1] = {2};
    int destinations[2] = {1,0};
    int weights[2] = {2,1};
    MPI_Dist_graph_create(MPI_COMM_WORLD, 2, sources, degrees, destinations,
        weights, MPI_INFO_NULL, 0, &newcomm);
  } else {
    int sources[1] = {1};
    int degrees[1] = {1};
    int destinations[1] = {0};
    int weights[1] = {2};
    MPI_Dist_graph_create(MPI_COMM_WORLD, 1, sources, degrees, destinations,
        weights, MPI_INFO_NULL, 0, &newcomm);
  }
  MPI_Comm_free(&newcomm);
  MPI_Finalize();
}




Thanks,

Dan

On Sat, Oct 24, 2015 at 7:21 PM, Balaji, Pavan <balaji at anl.gov> wrote:

> Daniel,
>
> Do you have a test program that shows these errors?
>
> The algorithms are a first cut, for now, but we are hoping to optimize
> them in 2016 (together with one of our vendor partners, who will be
> contributing code for it).
>
> Thanks,
>
>   -- Pavan
>
> From: Daniel Ibanez <dan.a.ibanez at gmail.com>
> Reply-To: "devel at mpich.org" <devel at mpich.org>
> Date: Saturday, October 24, 2015 at 5:05 PM
> To: "devel at mpich.org" <devel at mpich.org>
> Subject: [mpich-devel] MPI_Dist_graph_create self-edge
>
> Hello,
>
> Using MPICH 3.1.4, I'm getting internal assertions of this kind
> of when using MPI_Dist_graph_create :
>
> Assertion failed in file src/mpi/topo/dist_gr_create.c at line 223: s_rank
> >= 0
> Assertion failed in file src/mpi/topo/dist_gr_create.c at line 195:
> sources[i] < comm_size
>
> I've checked that ranks passed in are in the proper range,
> rather I think the issue is caused by requesting an edge
> from rank 0 to itself.
> (Another hint is that its non-deterministic which assertion
> I get; it depends on the order in which the ranks get scheduled
> by the OS, so there is a bit of a bug in the implementation,
> or at least no check for self-edges).
>
> Does the MPI standard allow for self-edges in these graphs ?
>
> Thank you,
>
> P.S. - I'll throw in a bigger question while I'm at it: are
> MPI_Dist_graph_create and MPI_Neighbor_alltoallv
> implemented with optimally scalable algorithms ?
> I'm betting my scalability on them being roughly
> O(log(P)) where P is communicator size, assuming
> neighborhood sizes and message sizes are constant.
>
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