[Mpi-forum] Discussion points from the MPI-<next> discussion today

Jed Brown jedbrown at mcs.anl.gov
Fri Sep 21 08:34:28 CDT 2012

On Thu, Sep 20, 2012 at 12:14 PM, Jeff Hammond <jhammond at alcf.anl.gov>wrote:

> P2P)
> I would like MPI_(I)RECV_REDUCE, which - as you might guess - does a
> reduction to the receive buffer instead of a simple write.  This
> allows one to avoid having to manually buffer incoming messages to be
> reduced at the receiver.  Torsten and I have discussed it and it seems
> there are at least a few use cases.

If you do this, _please_ allow a user-defined MPI_Op to be used in the
reduction (i.e., don't cripple it like one-sided).

Jeff Squyres, I don't know what "fix grequest" meant in your list, but I
hope that means: "provide a mechanism for users to implement nonblocking
operations with the same progress semantics as built-in nonblocking
operations". After writing the blog post below, I learned about additional
exemplar use cases in dense linear algebra. Lack of this specific feature
is causing a lot of important applications and libraries to systematically
over-synchronize and preventing them from hiding communication latency.

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