From your description, I don't see any reason why MPICH would hang if the user code is correct. Can you send us a small test code that reproduces this problem? Halim www.mcs.anl.gov/~aamer On 11/3/17 10:27 AM, Adam Sylvester wrote:

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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