[mpiwg-rma] FW: [Mpi3-rma] [EXTERNAL] Re: MPI-3 UNIFIED model updates

[Underwood, Keith D]

> On 08/27/2013 07:15 AM, Underwood, Keith D wrote:
> >>> I prefer option #1 -- that a window synchronization (e.g. Win_sync)
> >>> can be used to order load/store operations with respect to actions
> >>> performed by other processes in the target's window.  If no ordering
> >>> is enforced, the MPI standard does not define what is seen by load
> >>> operations at the target process.  As a rationale, the local process'
> >>> view of the window may not be consistent with the window because of
> >>> performance optimizations or the consistency model of the underlying
> >>> architecture.  This would allow e.g. SHMEM implementations to still
> >>> use MPI-3 RMA, but they would have to rely on a behavior that is
> >>> defined by the architecture/implementation, as they currently do.
> >
> > My statement:  this seems to be what SHMEM does - except they don't
> > provide the equivalent of Win_sync.  If we are going to hack on the
> > text, I would prefer that we be *very* careful in our wording.
> > Specifically, we need to make it very clear that the SHMEM approach is
> > *legal*, but the burden is on the user to do potentially
> > implementation specific things to make it work right.
> 
> Hmm.  OK.  Just so there's no confusion, by "SHMEM approach", you are
> saying that the application can use its own platform-specific memory
> consistency calls and avoid using WIN_SYNC, correct?

Yes.  WIN_SYNC will do that for them, but they can do everything without calling WIN_SYNC as long as they call the right platform-specific things and the platform-specific approach might be faster/lower overhead.