[mpich-discuss] Support for MIC in MPICH 3.0.4

Jed Brown jedbrown at mcs.anl.gov
Tue Jul 9 13:19:25 CDT 2013

Jeff Hammond <jeff.science at gmail.com> writes:

> You're going to have to convert to MPI+Threads eventually so you might
> as well start now.  It is completely unreasonable to expect that
> MPI-only is reasonable usage on a 60-core chip with a ring
> interconnect.

This is something that endpoints is supposed to address.  Note that
OpenMP doesn't have any decent way to do reductions scoped across
subsets of threads, so for many applications, it's not even a reasonable
level of expressivity.

> I am so convinced of the impossibility that MPI_Allreduce scales to
>>100 MPI procs in shared memory that I will learn Ada as punishment if
> I'm wrong.

Does 30 microsecond MPI_Allreduce at 512 cores qualify as "impossible to

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