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@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@gmail.com>
Reply-To: "devel@mpich.org" <devel@mpich.org>
Date: Saturday, October 24, 2015 at 5:05 PM
To: "devel@mpich.org" <devel@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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