[Beowulf] Performance characterising a HPC application

Richard Walsh rbw at ahpcrc.org
Wed Apr 4 09:25:45 EDT 2007


Ashley Pittman wrote:
> Patrick Geoffray wrote:
>   
>> I would bet that UPC could more efficiently leverage a strided or vector
>> communication primitive instead of message aggregation. I don't know if
>> GasNet provides one, I know ARMCI does.
>>     
>
> GasNet does however get extra credit for having a asynchronous
> collective, namely barrier.  Unfortunately when you read the spec it's
> actually a special case asynchronous reduce which is almost impossible
> to optimise anything like as well as barrier which is a shame.
>   
All,

Berkeley's recent paper on the some optimization techniques that they have applied within their UPC compiler emphasizes reducing and hoisting shared pointer references, maximally split-phased reads and writes (implying that GASnet can do what Ashley suggests), and aggregating-
coalescing communication.  I have only read half of it, but no mention of pipelining or pseudo-vector operations (too bad) ... this would seem to be harder to do as it would required whole loop analysis.

You may be interested in Googling for it:

"Communication Optimizations for Fine-Grained UPC Applications"

Wei-Yu Chen  Costin Iancu  Kathy Yelick

Regards,

rbw

--

Richard B. Walsh

Project Manager
Network Computing Services, Inc.
Army High Performance Computing Research Center (AHPCRC)
rbw at ahpcrc.org  |  612.337.3467

>
>  "Making predictions is hard, especially about the future."
>
>   Nils Bohr

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