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From: bruce@seismo.gps.caltech.edu (Bruce Worden)
Newsgroups: comp.sys.transputer
Subject: Re: i860s and the like
Keywords: i860, Meiko
Message-ID: <1990Aug9.045851.7448@laguna.ccsf.caltech.edu>
Date: 9 Aug 90 04:58:51 GMT
References: <8439.9008081138@prg.oxford.ac.uk>
Sender: bruce@seismo.gps.caltech.edu
Organization: California Institute of Technology, CA
Lines: 56

In article <8439.9008081138@prg.oxford.ac.uk> ARCR1@biology.cambridge.ac.uk (Andy Raine) writes:
>...
>Meiko, Transtech, Microway etc. etc. sell boards that have an intel i860 
>procesor interfaced to one or two t800's.
>...
>but one thing bothers me: 
>Consider:  Meiko claim that their board can do a 1024x32bit complex FFT in 
>1.3 ms.  

This FFT (Meiko's) is hand-coded and the data is just the right size (8k)
to be wired down into the cache.  (I talked to the guy who was working 
on it.)  There is no way a compiled, general-purpose code will ever 
reach this kind of performance level.

>...
>I suggest that what is needed for a large number of scientific calculations 
>is a 'fine grain' processor.  In other words, if the ratio of communication 
>speed to compute speed of the t800 is taken to be 1:1, then what is needed 
>is a processor where the ratio is 10:1.  The i860 & vector boards achieve a 
>ratio of 1:10 (The wrong way!), and the H1 transputer maintains the t800 
>ratio at 1:1.

Different applications need different ratios.  Also, the ratio isn't as
important as the absolute values.  E.g. if the t800 gives 1:1 then
a t800 running at 2Mhz would give the 10:1 you want, but I don't think
that is what you have in mind.  In any given application, one thing or the
other will be the bottleneck.  What is needed is an i860 with proportionally 
fast message passing.

>If a manufacturer produced boards with a t800 coupled with link driver 
>hardware that ran at 10 times the speed of the t800's links, then I would 
>be able to use ten times as many processors, and get 10 times the 
>performance.  What about it?

Why not just scrap the t800 completely?  Take the i860 hook it to
some memory with a hardware message router (like Ametek had) and let
it rip.  It would blow the transputer networks out of the water.  Look
at what Intel is doing with the IPSC.

A couple of points:
1. With a faster processor, you don't need as many processors, hence there
is less message passing to begin with.  That is exactly what happened to 
us--the T800's were not very fast and just adding more of them would 
have created a communication nightmare.  The i860's with the extra links 
solved two problems for us.  We could do the problem with just a few
(from 8 to 32) processors, and the multi-hop overhead and link
contention went away.  If you continue the trend, you can eliminate
the need for parallel/multi-computers in the first place.  

2. In general, I agree with you.  I harassed every multicomputer
vendor I talked to about speeding up their communications, but all of them
just said "we're working on it."  More bandwidth means more applications
become parallelizable.  You think they would work a little harder, then 
maybe they would sell more machines. 

Bruce Worden bruce@seismo.gps.caltech.edu