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From: carter@iastate.edu (Michael Brannon Carter)
Newsgroups: comp.parallel
Subject: Re: Justifications for || processing
Keywords: Parallel Processing
Message-ID: <12325@hubcap.clemson.edu>
Date: 18 Dec 90 13:52:42 GMT
Sender: fpst@hubcap.clemson.edu
Reply-To: carter@iastate.edu (Michael Brannon Carter)
Organization: Iowa State University
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Approved: parallel@hubcap.clemson.edu

> I'm wondering how people in the application side of parallel processing
> justify coding for a parallel machine.  I would be very much interested
> in knowing how much complexity analysis plays a part in this.

For the applications I see at the Scalable Computing Facility at Ames
Laboratory,
the answer is simple: people want to run BIGGER problems.  They want to
run them
as fast as possible, but the primary emphasis, at least here, is on the
size of
the problem.  More atoms in the electrolyte, more atoms in the metallic
cluster,
etc.

When a physicist or chemist is told that he/she can have a bunch of time
on a parallel computer to run bigger problems, they usually jump at the
chance.  This is followed shortly thereafter by a lot of headscratching
trying to figure out how to make it parallel.  We find ourselves having
to help people along a lot because they just don't know how to program a
parallel computer.  (If anyone really KNOWS how...)  Granted, these are
researchers, so there are a lot of graduate students around to actually
do the work.  I can't speak to the commercial side of things.

As for complexity analysis, it remains on an intuitive level; not a
formal one.
We simply decide by obvious factors (%age runtime consumed by a
particular function) and experience what functions to make parallel, and
just how that is to be done.  Since we see mainly scientific
applications, the operations performed in them tend to be
well-understood algorithms: matrix math, global communications, etc.

> On a related note, how prevalent are compilers that parallelize code
?

There are none.  Note that I do *NOT* call the MIMDizer a parallelizing
compiler!
As far as I know, it only works for certain shared-memory by recognizing
very
specific constructs in FORTRAN.  Try this on for size: MIMDizer ~
||izing compiler
the way Expert System ~ AI.

--
Michael B. Carter