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

Greg Lindahl lindahl at pathscale.com
Fri Feb 11 16:21:38 EST 2005


On Fri, Feb 11, 2005 at 02:39:29PM -0600, Isaac Dooley wrote:

> Using MPI_ISend() allows programs to not waste 
> CPU cycles waiting on the completion of a message transaction. This is 
> critical for some tightly coupled fine grained applications.

We do pretty much the same thing for MPI_Send and MPI_ISend for small
packets: they're nearly on the wire when the routine returns, and
the subsequent MPI_Wait is a no-op. This is actually pretty common
among MPI implementations.

The problem with trying to generalize about what MPI calls do is that
different implementations do different things with them. Reading
the standard won't teach you much about implementations.

-- greg
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