[Mpi3-rma] MPI-3 UNIFIED model updates
balaji at mcs.anl.gov
Mon Aug 5 21:20:38 CDT 2013
Based on the very long email thread on "MPI-3 UNIFIED model
clarification", I think we now agree that something needs to change in
the MPI standard to allow for cache-coherent architectures that don't
quite give the level of hardware support that is required for UNIFIED.
We came down to one of two solutions for this --
1. We weaken the UNIFIED model to say that a WIN_SYNC is required for
data to be used. I liked Jim's wording best, so I'm listing it here:
Unified does not guarantee that "public win == private win". It
guarantees that they are *eventually* the same, not immediately and
always the same.
I would add that the user can force the windows to be the same using
WIN_SYNC, just like in SEPARATE.
2. We leave UNIFIED as-is, and create a new memory model. I'm going to
use KIND_OF_UNIFIED here for discussion, though someone else will need
to come up with a better name eventually.
The KIND_OF_UNIFIED memory model would not have the above described
I, personally, am OK with either option. But I look forward to hearing
others thoughts on these models.
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