[mpich-discuss] Setting for max number of nonblocking messages?

[Adam Sylvester]

I have an application which runs 16 ranks, where there is a step in the
processing where each rank does an MPI_Irecv() and MPI_Isend() with every
other rank, then calls MPI_Waitall().  The code could likely be refactored
to use an MPI_Alltoallv() instead, but that's not my point here as this
portion of the code isn't a bottleneck.

I've previously been using Open MPI which has run this block of code
thousands of times without issues.  I just switched over to MPICH 3.2
(obviously recompiling my application) and it hangs in this block (there is
MPI communication involving at least as much data movement earlier in the
chain using a series of MPI_Ialltoallv() calls which completes without
issue).  I need to reduce the number of ranks down to 2 for it to make it
through the MPI_recv() / MPI_Isend() / MPI_Waitall() section.

I'm wondering if there's a setting for the max number of nonblocking
messages that defaults to a low value for MPICH.  Or any other thoughts on
what I could be running into?

Thanks.
-Adam
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