[Beowulf] Re: Re: Home beowulf - NIC latencies

Keith D. Underwood kdunder at sandia.gov
Tue Feb 15 09:31:12 EST 2005


> Looking for overlaping is actually not that hard:
> a) look for medium/large messages, don't waste time on small ones.

I contend that this particular item is bad advice.  If you send a lot of
small messages, you should use MPI_Isend there as well to give the MPI
implementation every opportunity to do the right thing.  As we go
forward, end-to-end acknowledgments are going to become a reality.  The
last thing you want is to spend a round-trip delay on every message you
send if you send a lot of them.  Yes, the implementation can copy on the
sending side to allow the send to complete, but that wastes memory and
time.  

					Keith


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