[Mpi3-rma] MPI-3.1 consideration slides

[Jim Dinan]

On 12/2/12 7:44 AM, Jeff Hammond wrote:
>>> (1) Define semantics of shared memory windows in separate model.
>>>
>>> In Section 11.2.3 it says "MPI does not define semantics for accessing
>>> shared memory windows in the separate memory model."
>>>
>>> I would like to try to define these semantics in MPI 3.1.  Shouldn't
>>> it at least be possible to use MPI_WIN_(UN)LOCK with
>>> MPI_LOCK_EXCLUSIVE here?
>>>
>>> I believe that supporting RMA for weakly- or non- coherent memory
>>> architectures is vital for future systems.
>> I agree. We had this discussion and decided to postpone it because we
>> had other more pressing issues. Now may be the time. A discussion would
>> be good.
>
> Yes, there was no urgency.  I'm glad the standard left this issue wide
> open instead of defining something restrictive.

IMHO, defining shared memory windows in the separate model is not a 
worthy use of the Forum's time.  This will be hard to get right, and 
AFAIK no (reasonable) system requires it.  As we've currently left it, 
if this functionality is needed, one can define the semantics as an MPI 
extension.  I think this is a better option that defining a new model in 
the absence of a platform that uses it.

  ~Jim.