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 <[email protected]> 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 <[email protected]> Reply-To: "[email protected]" <[email protected]> Date: Saturday, October 24, 2015 at 5:05 PM To: "[email protected]" <[email protected]> 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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