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

Michael T. Prinkey mprinkey at aeolusresearch.com
Mon Feb 14 15:39:06 EST 2005


Greg, based on your evaluation of the available MPI libraries, does this        
imply that overlapping communication and computation can really only be         
done by explicitly building two separate threads?                               
                                                                           
Mike 

On Mon, 14 Feb 2005, Greg Lindahl wrote:

> 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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