IIRC, the argument for RMA was that we had not wanted to require the MPI library to maintain a reference to the request. There could be many RMA operations pending and the MPI library maintaining a list of pending operations could be a significant source of overhead. I seem to recall this having been the general sentiment at the time and it may have also applied to NBC.
~Jim. On Sat, Aug 8, 2020 at 7:15 PM Jeff Hammond via mpi-forum < mpi-forum@lists.mpi-forum.org> wrote: > We should fix the RMA chapter with an erratum. I care less about NBC but > share your ignorance of why it was done that way. > > Sent from my iPhone > > On Aug 8, 2020, at 6:51 AM, Balaji, Pavan via mpi-forum < > mpi-forum@lists.mpi-forum.org> wrote: > > Folks, > > Does someone remember why we disallowed users from calling > MPI_Request_free on nonblocking collective requests? I remember the > reasoning for not allowing cancel (i.e., the operation might have completed > on some processes, but not all), but not for Request_free. AFAICT, > allowing the users to free the request doesn’t make any difference to the > MPI library. The MPI library would simply maintain its own refcount to the > request and continue forward till the operation completes. One of our > users would like to free NBC requests so they don’t have to wait for the > operation to complete in some situations. > > Unfortunately, when I added the Rput/Rget operations in the RMA chapter, I > copy-pasted that text into RMA as well without thinking too hard about it. > My bad! Either the RMA committee missed it too, or they thought of a > reason that I can’t think of now. > > Can someone clarify or remind me what the reason was? > > Regards, > > — Pavan > > MPI-3.1 standard, page 197, lines 26-27: > > “It is erroneous to call MPI_REQUEST_FREE or MPI_CANCEL for a request > associated with a nonblocking collective operation.” > > _______________________________________________ > mpi-forum mailing list > mpi-forum@lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-forum > > _______________________________________________ > mpi-forum mailing list > mpi-forum@lists.mpi-forum.org > https://lists.mpi-forum.org/mailman/listinfo/mpi-forum >
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