Newsgroups: comp.parallel
From: srd320@cs.usask.ca (Satya Ranjan Dash)
Subject: Performance Issues in MPI
Organization: University of Saskatchewan
Date: 29 May 1995 16:09:46 GMT
Message-ID: <3qcrka$29c@usenet.srv.cis.pitt.edu>

Hi, I have been fiddling around with MPI-LAM.  I have hit a snag in
carrying out further development. The issue I am facing is an unre-
asonably high communication overhead.

On my Ethernet LAN I have run a little test program to measure  the
performance  for  transferring  double  precision  numbers (arrays)
across the MPI processor pool. I found that the cost for sending 1K
of double precision numbers is around 10-15 seconds on the  average
and  in  the  worst case about  25 seconds.  Clearly with such high
communication  overheads  serious computation in idling workstation
clusters is difficult.

The intention of this news item is to explore how other users of MPI
are fairing in their work and whether  either I am terribly  goofing
in my measurements or there are some possible optimizations which  I
am not implementing.

I have one idea worth trying but would appreciate other workers
approach and observations.
--
Cheers.								Dash

P.S.	If any one is interested in  either looking  in at my test
	program (to catch my leg) or to take measurements on their
	own;  pleae drop me  a line and I will mail back the code.
	It is written in a easily understandable way and  produces
	neatly formatted outputs.  However, it is trivial.

