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

Greg Lindahl lindahl at pathscale.com
Mon Feb 14 14:07:37 EST 2005


On Mon, Feb 14, 2005 at 06:47:15PM +0300, Mikhail Kuzminsky wrote:

> Let me ask some stupid's question: which MPI implementations allow
> really
>  
> a) to overlap MPI_Isend w/computations
> and/or 
> b) to perform a set of subsequent MPI_Isend calls faster than "the 
> same" set of MPI_Send calls ?
> 
> I say only about sending of large messages.

For large messages, everyone does (b) at least partly right. (a) is
pretty rare. It's difficult to get (a) right without hurting short
message performance. One of the commercial MPIs, at first release, had
very slow short message performance because they thought getting (a)
right was more important. They've improved their short message
performance since, but I still haven't seen any real application
benchmarks that show benefit from their approach.

-- greg
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