[Mpi3-rma] MPI-3.1 consideration slides

[Jim Dinan]

Hubert,

Thanks for your comment -- in general, the RMA group is thinking about 
the vector systems.  Is there a desire from users to have shared memory 
windows defined for this platform?  Keeping in mind that the 
synchronization required will be harder to reason about than get/put?

  ~Jim.

On 12/3/12 10:24 AM, Hubert Ritzdorf wrote:
> NEC SX (including the Earth Simulator) memory is not cache coherent and
> MPI-2 RMA is working since many years on these systems.
>
> Hubert
> ________________________________________
> From: mpi3-rma-bounces at lists.mpi-forum.org [mpi3-rma-bounces at lists.mpi-forum.org] on behalf of Jim Dinan [dinan at mcs.anl.gov]
> Sent: Monday, December 03, 2012 4:39 PM
> To: mpi3-rma at lists.mpi-forum.org
> Subject: Re: [Mpi3-rma] MPI-3.1 consideration slides
>
> 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.
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