[Mpi3-rma] MPI-3 UNIFIED model clarification

Pavan Balaji balaji at mcs.anl.gov
Wed Jul 31 18:30:38 CDT 2013

On 07/31/2013 12:58 PM, Sur, Sayantan wrote:
>> On 07/31/2013 12:00 PM, Jim Dinan wrote:
>>> I would bet that past Jim suggested striking the
>>> polling/eventually visibile clause and relying on window
>>> synchronization to see updates. :)
>> Yup, so did past, present, and future Pavan.  IMO, that's a useless
>> guarantee.
>>> The downside to this is that libraries like SHMEM that rely on
>>> passive progress and polling, would not be implementable on top
>>> of Unified.
>> It's pretty useless even for SHMEM, since the user doesn't know
>> when the data is valid.  You could poll on a byte for it to turn to
>> one, but at that point you only know about that one byte and
>> nothing else.
> Past Sayantan had missed this discussion, but present Sayantan does
> agree that "eventually" as defined is useless. But he is also
> confused by the guarantee given by MPI_Win_flush, that when the call
> returns, all previously issued RMA ops are complete locally and
> remotely + UNIFIED (public win == private win).

Unfortunately, that part slipped the checks of the folks who believed 
you need a WIN_SYNC.  So the standard is inconsistent.  We have now made 
a full circle and gotten back to where this email thread started :-).

Pavan Balaji

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