[mpiwg-rma] same_op_no_op and SHMEM

[Jeff Hammond]

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
<keith.d.underwood at intel.com> 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:mpiwg-rma-bounces at lists.mpi-forum.org] 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 <jeff.science at gmail.com>
>> 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
>> > jeff.science at gmail.com
>> > _______________________________________________
>> > mpiwg-rma mailing list
>> > mpiwg-rma at lists.mpi-forum.org
>> > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
>>
>> --
>> Pavan Balaji
>> http://www.mcs.anl.gov/~balaji
>>
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-- 
Jeff Hammond
jeff.science at gmail.com