[MPICH] Problem with MPI_Gather

[Dmitri Chubarov]

Hello, Jonathan!

I have tested your example with mpich2 1.0.6 the previous stable release of
mpich2 and
found the example work correctly. I have compiled your program with
mpich2-1.0.6p1 with
gather.c taken from src/mpi/coll of mpich2-1.0.6 distribution and found the
example to work
as well. The problem with 1.0.6p1 seems to show only with messages of size
greater than the
value of MPIR_GATHER_VSMALL_MSG set in mpiimpl.h . Currently this constant
is set to
1024 bytes which explains why reducing DATASIZE to less than 256 removes the
bug on
32 bit machines. I hope someone from the developers will come up with a fix
soon, since
the algorithm seems to have been slightly modified in 1.0.6p1.

Best regards,
  Dima
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