[Mpi-forum] MPI One-Sided Communication

Hubert Ritzdorf ritzdorf at it.neclab.eu
Mon Apr 27 09:38:10 CDT 2009

Underwood, Keith D wrote:
>> On the Earth Simulator, there are/were several application codes which are
>> using one-sided communication (instead of 2-sided). They used one-sided
>> communication especially to overlap communication and computation.
>> When I remember correctly, at least one of this applications won a Gordon
>> Bell Award of SC.
> The ambiguity of the progress rule notwithstanding, there is no particular reason that one-sided should give you better overlap than two-sided.  If this is the reason that people use one-sided, maybe we should revisit the progress rule ;-)
The application codes can overlap communication and computation also for pt2pt on the Earth Simulator.
The raw performance of MPI pt2pt and one-sided communication is similar. 
Which communication is selected, should depend on the application code. And there are
application codes which benefit on the one-sided communication model.

But the usage of the MPI-2 one-sided library is not zero and
one-sided comm is not "always" slower than 2-sided.


PS: Nevertheless, also the Earth Simulator application programmers have asked
for simpler synchronization functions for one-sided comms.  

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