From: glindahl@hpti.com (Greg Lindahl)
Newsgroups: comp.parallel.mpi
Subject: Re: [Q] Multiple packs vs. multiple sends
Date: 5 Apr 1999 22:03:22 GMT
Organization: a guest of Shadow Island Games
Message-Id: <7ebbvb$1gbl@news3.newsguy.com>
References: <7eao0m$5ru$1@mozo.cc.purdue.edu>
Xref: ukc comp.parallel.mpi:4885


jonesbr@roger.ecn.purdue.edu (Brian R. Jones) writes:

> In general, is there any performance benefit in packing multiple
> variable arrays into a single message under MPI?  The central example that
> I'm considering packs 18 variable arrays into a single message that will
> typically require 10s of Kilobytes (potentially 100's of KB on larger
> problems).

In general, yes. A system using ethernet for communications has a
rather high latency to send messages. This shows up most for tiny
messages, or things like reductions, which are always synchronous. In
your particular example above, it sounds like the messages are large
enough that you don't need to worry.

-- g