[Mpi3-rma] [EXTERNAL] Re: MPI-3 UNIFIED model clarification

Pavan Balaji balaji at mcs.anl.gov
Sun Aug 4 18:02:58 CDT 2013


On 08/04/2013 05:56 PM, Barrett, Brian W wrote:
> So, I guess I really don't see a problem with what we have today.  As
> soon as you require a target side WIN_SYNC, there's no point in using
> Unified; the user and the implementation can live quite happily with
> SEPARATE.  And, I believe, make SEPARATE go fast on platforms that only
> need a memory barrier to ensure target side ordering, rather than a
> complicated cache protocol.

That's not true.  If two processes are accessing nonoverlapping memory 
locations (PUT/GETs and load/stores), it would still be very useful. 
With SEPARATE additional synchronization would be required for such 

UNIFIED is too complex if the user mostly cares about nonoverlapping 
memory regions, and doesn't mind paying a small penalty for overlapping 

SEPARATE is too expensive for such cases.

  -- Pavan

Pavan Balaji

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