Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!haven!udel!princeton!notecnirp!mg
From: mg@notecnirp.Princeton.EDU (Michael Golan)
Newsgroups: comp.arch
Subject: Re: ATTACK OF KILLER MICROS (Actually parallel systems)
Message-ID: <20336@princeton.Princeton.EDU>
Date: 17 Oct 89 03:47:32 GMT
References: <35825@lll-winken.LLNL.GOV>
Sender: news@princeton.Princeton.EDU
Reply-To: mg@notecnirp.edu (Michael Golan)
Organization: Dept. of Computer Science, Princeton University
Lines: 47

This came for various people - the references are so confusing I removed them
so as not to put the wrong words in someone's mouth:

>>>Supercomputers of the future will be scalable multiprocessors made of many
>>>hundreds to thousands of commodity microprocessors.
>>
>This is the stuff of research papers right now, and rapid progress is being
>made in this area.  The key issue is not having the components which establish
>the interconnect cost much more than the micros, their off chip caches,
>I currently lean to scalable coherent cache systems which minimize programmer
>effort.  The exact protocols and hardware implementation which work best
>for real applications is a current research topic. 

Last year, I took a graduate level course in parallel computing here at
Princeton. I would like to make the following comments, which are my *own*:

1) There is no parallel machine currently the works faster than non-parallel
machines for the same price. The "fastest" machines are also non-parallel - 
these are vector processors.

2) A lot of research is going on - and went on for over 10 years now. As far
as I know, no *really* scalable parallel architecture with shared memory exists
that will scale far above 10 processors (i.e. 100). And it does not seems to
me this will be possible in the near future.
"A lot of research" does not imply any effective results - especially in CS -
just take a look how many people write articles improving time from 
O(N log log N) to O(Nlog log log N), which will never be practical for N<10^20
or so (the log log is just an example; you know what I mean).

3) personally I feel parallel computing has no real future as the single cpu
gets a 2-4 folds performance boost every few years, and parallel machines
constructions just can't keep up with that. It seems to me that for at least 
the next 10 years, non-parallel machines will still give the best performance 
and the best performance/cost.

4) I think Cray-like machines will be here for a long long time. People talk
about Cray-sharing. This is true, but when an engineer needs a simulation to
run and it takes 1 day each time, if you run it on a 2 or 3 day machine, he
sits doing nothing for that time, which costs you a lot, i.e. it is turn-around
time that really matters. And while computers get faster, its seems software
complexity and the need for faster and faster machines is growing even more
rapidly.

 Michael Golan
 mg@princeton.edu

The opinions expressed above are my *own*. You are welcome not to like them.