[mpich-devel] MPI_Dist_graph_create self-edge

[Thakur, Rajeev]

On rank 0, if you are passing n=2, shouldn’t the sources and degrees arrays be of size 2?

Rajeev

> On Oct 24, 2015, at 6:37 PM, Daniel Ibanez <dan.a.ibanez at gmail.com> wrote:
> 
> 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.
> 
> _______________________________________________
> To manage subscription options or unsubscribe:
> https://lists.mpich.org/mailman/listinfo/devel
> 
> _______________________________________________
> To manage subscription options or unsubscribe:
> https://lists.mpich.org/mailman/listinfo/devel