Hey Patrick, Patrick Geoffray wrote: > Message aggregation would be much more beneficial in the context of > UPC, where the compiler will likely generates many small grain > communications to the same remote process. However, as Greg pointed > out, MPI applications often already aggregate messages themselves > (this is something even "challenged" application people understand > easily). Right ... > 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. Having the alternative of compiling to a pseudo-vector pipelined GASnet/ARMCI primitive (hiding latency in the pipeline) >or< an aggregation primitive (amortizing latency over a large data block) would seem to be a good thing depending on the number and distribution of remote memory references in your given kernel. The latency bubbles in interconnect- mediated remote memory references are of course much larger than in a hardware mediated global addresses space remote reference. This might change the effectiveness of pipelined based latency hiding. From what I know the Berkeley UPC compiler team is focused on optimization through aggregation rather than pipelining. Regardless, at this point our more GUPS-like direct remote memory reference patterns in our UPC codes, which perform well on the Cray X1E, must be manually aggregated to achieve performance on a cluster.
Regards, rbw -- Richard B. Walsh Project Manager Network Computing Services, Inc. Army High Performance Computing Research Center (AHPCRC) [EMAIL PROTECTED] | 612.337.3467 > > "The world is given to me only once, not one existing and one > perceived. The subject and object are but one." > > Erwin Schroedinger ----------------------------------------------------------------------- This message (including any attachments) may contain proprietary or privileged information, the use and disclosure of which is legally restricted. If you have received this message in error please notify the sender by reply message, do not otherwise distribute it, and delete this message, with all of its contents, from your files. ----------------------------------------------------------------------- _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
