On Thu, Sep 20, 2012 at 12:14 PM, Jeff Hammond <[email protected]>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. https://www.ieeetcsc.org/activities/blog/user_defined_nonblocking_collective...