Subject: Re: Fw: CCL:Scaling of G98 on Clusters

From: "Robert G. Brown" <[email-masked]>
Date: Fri, 31 Mar 2000 08:52:01 -0500 (EST)

On Thu, 30 Mar 2000, Phillip Matz wrote:

> > And one last comment, I was completely amazed at how easy and accurate it
> > was to model my G98 beowulf's performance based on the simple equations
> > found in Dr. Brown's beowulf profiling guide - so thank you Dr. Brown!
> >
> > Respectfully,
> > Phillip Matz

Aw, you'll make me blush...;-) Remember, I didn't really derive any of
that stuff, I just digested the work of many other people in the talk.
I've also been trying to update the brahma site with a few even simpler
talks, this time with scaling figures.  The real moral of the exercise
is that beowulfery is really truly a form of parallel computing, and one
can (with a bit of effort) understand the way various (e.g. IPC) times
limit parallel scaling in a calculation.  It is therefore worth getting
a book or two on parallel computing or using the online book by Ian
Foster at:

   http://www-unix.mcs.anl.gov/dbpp/

to learn about parallel algorithms and so forth.  

I've tried to summarize in simple form a lot of the very simple
per-processor scaling so people can understand why it might be stupid to
build a 128 node beowulf (even if they can afford it easily) to tackle a
problem that has a peak speedup at only 8 nodes for their chosen
hardware.  On the other hand, spending all that money on 4x more
expensive hardware with much faster networking, they might not reach
their peak speedup until 32 nodes.  However, there is a lot more to
learn about things like the scaling of algorithms with problem size.
That's what real computer scientists are for -- they work out all this
stuff for us, if only we'd take the time to learn about what they've
done.

    rgb

Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:[email-masked]

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