[Mpi3-rma] Use cases for RMA

[Bronis R. de Supinski]

Bill:

One use case that I am familiar with at LLNL is to
distribute large read-only (write-once) tables. We
have libraries with this access pattern; the current
method is to replicate the tables in all MPI processes.
We have done a prototype implementation using GAs to
distribute the table. We also need support for caching
values locally. I think a good RMA implementation
would allow us to build a generic implementation of
the distribute and cache functionality...

Bronis


On Wed, 3 Mar 2010, William Gropp wrote:

> I went through the mail that was sent out in response to our request
> for use cases, and I must say it was underwhelming.  I've included a
> short summary below; based on this, we aren't looking at the correct
> needs.  I don't think that these are representative of *all* of the
> needs of RMA, but without good use cases, I don't see how we can
> justify any but the most limited extensions/changes to the current
> design.  Please (a) let me know if I overlooked something and (b) send
> me (and the list) additional use cases.  For example, we haven't
> included any of the issues needed to implement PGAS languages, nor
> have we addressed the existing SHMEM codes.  Do we simply say that a
> high-quality implementation will permit interoperation with whatever
> OpenSHMEM is?  And what do we do about the RMI issue that one of the
> two use cases that we have raises?
>
> Basically, I received two detailed notes for the area of Quantum
> Chemistry.  In brief:
>
> MPI-2 RMA is already adequate for most parts, as long as the
> implementation makes progress (as it is required to) on passive
> updates.  Requires get or accumulate; rarely requires put.
> Dynamic load balancing (a related but separate issue) needs some sort
> of RMW.  (Thanks to Jeff Hammond)
>
> More complex algorithms and data structures appear to require remote
> method invocation (RMI).  Sparse tree updates provide one example.
> (Thanks to Robert Harrison)
>
> Bill
>
>
> William Gropp
> Deputy Director for Research
> Institute for Advanced Computing Applications and Technologies
> Paul and Cynthia Saylor Professor of Computer Science
> University of Illinois Urbana-Champaign
>
>
>
>
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