Or "I will only do gets and compare-and-swap", which is something a couple of graph codes I've looked at do. But I agree, we probably should have made it REPLACE, NO_OP, and 1 other op or not added it at all. Sigh :). Brian On 10/24/13 11:39 AM, "Jeff Hammond" <[email protected]> wrote:
I read same_op_no_op as "I will use only MPI_REPLACE and MPI_NO_OP" i.e. give me nothing more than atomic Put/Get, I do not want to actually accumulate anything.
Jeff
On Thu, Oct 24, 2013 at 12:34 PM, Underwood, Keith D <[email protected]> wrote:
Yes, that's the motivation, but I'm not sure if anybody does atomics without puts.... It seems to me like we should have included MPI_REPLACE in that list
-----Original Message----- From: mpiwg-rma [mailto:[email protected]] On Behalf Of Pavan Balaji Sent: Thursday, October 24, 2013 1:33 PM To: MPI WG Remote Memory Access working group Subject: Re: [mpiwg-rma] same_op_no_op and SHMEM
The motivation was that it's hard to maintain atomicity when different operations are done. For example, if the hardware only supports some atomic operations, but not all, this might result in some operations happening in hardware and some in software making atomicity hard. In such cases, the MPI implementation might need to fall back to software-only implementations.
-- Pavan
On Oct 24, 2013, at 12:23 PM, Jeff Hammond <[email protected]> wrote:
I recall that Brian and/or Keith wanted same_op_no_op because of SHMEM. However, SHMEM requires the use of MPI_NO_OP (for atomic Get via Get_accumulate), MPI_REPLACE (for atomic Put via Accumulate) and MPI_SUM (for add, fadd, inc and finc). So what is the benefit of same_op_no_op to SHMEM? Perhaps I remember completely wrong and the motivation was something that does not use the latter atomics. Or perhaps it is common for SHMEM codes to not use these and thus the assumption is MPI_SUM can be ignored.
Jeff
-- Jeff Hammond [email protected] _______________________________________________ mpiwg-rma mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
-- Pavan Balaji http://www.mcs.anl.gov/~balaji
_______________________________________________ mpiwg-rma mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
mpiwg-rma mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
-- Jeff Hammond [email protected] _______________________________________________ mpiwg-rma mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
-- Brian W. Barrett Scalable System Software Group Sandia National Laboratories