[mpiwg-rma] same_op_no_op and SHMEM

[Underwood, Keith D]

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
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> 
> --
> Pavan Balaji
> http://www.mcs.anl.gov/~balaji
> 
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