[mpich-devel] MPI_Dist_graph_create self-edge

[Daniel Ibanez]

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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