Path: utzoo!attcan!uunet!mfci!colwell
From: colwell@mfci.UUCP (Robert Colwell)
Newsgroups: comp.arch
Subject: Re: Don't look back
Message-ID: <671@m3.mfci.UUCP>
Date: 25 Feb 89 15:50:20 GMT
References: <13582@winchester.mips.COM> <20667@lll-winken.LLNL.GOV> <7330@pyr.gatech.EDU> <656@m3.mfci.UUCP> <20821@lll-winken.LLNL.GOV> <661@m3.mfci.UUCP> <20862@lll-winken.LLNL.GOV>
Sender: colwell@mfci.UUCP
Reply-To: colwell@mfci.UUCP (Robert Colwell)
Organization: Multiflow Computer Inc., Branford Ct. 06405
Lines: 38

In article <20862@lll-winken.LLNL.GOV> brooks@maddog.llnl.gov.UUCP (Eugene Brooks) writes:
>Some time back I posted a challenge to VLIW proponents to compile and run a
>parallel Monte Carlo code of mine and compare the performance to a box full
>of microprocessors.  There were no takers.  This challenge is still open.

As I'm sure you know, Eugene, if there were a potential sale behind this
challenge, our level of interest would rise considerably.  As it is, just
what do you think you'd be entitled to conclude if we DID run something
that was tailored for a vector box and came up short?  How about this:
nothing at all.  A VLIW isn't a replacement for a vector machine.  It's
a different way of computing that does very well on vector code, but also
does well on code that chokes a vector machine.  Because of Amdahl's law,
this situation arises more often than not.  So what's your point?

>I would also like to see a detailed justification for the statement that VLIW
>processors will displace vector processors at what they do best.  A VLIW
>machine has not yet outrun a vector processor yet on its favorite workload
>and I do not see any technology trend that leads to this conclusion even for
>the long term.

The first answer is to wait and see.  What is your rejoinder when it is
pointed out that the TRACE (as an example of a VLIW) routinely achieves
fractions of a Cray XM/P far out of proportion to the difference in 
cycle times?  I'd imagine the only thing you can say is that you suspect
there's something fundamental in the design of a VLIW that will always
make it require a much longer cycle time.  You can think that if you
want to.  If you want the opinions of the folks who designed the TRACE,
we think that's hogwash.

Arguing in your style, name me a vector machine that can touch a dedicated
single-algorithm digital signal processor on IT'S favorite workload. 
Right, none.  Did I just prove that digital signal processors are the
wave of all computing in the future?

Bob Colwell               ..!uunet!mfci!colwell
Multiflow Computer     or colwell@multiflow.com
175 N. Main St.
Branford, CT 06405     203-488-6090