Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!aplcen!uakari.primate.wisc.edu!uflorida!stat!mccalpin
From: mccalpin@stat.fsu.edu (John Mccalpin)
Newsgroups: comp.arch
Subject: Re: The Killer Micro From Hell
Summary: Cray's are still fast!
Keywords: cpu starvation, memory bandwidth
Message-ID: <788@stat.fsu.edu>
Date: 30 Dec 89 17:26:01 GMT
References: <158@csinc.UUCP> <787@stat.fsu.edu> <42701@lll-winken.LLNL.GOV>
Reply-To: mccalpin@stat.fsu.edu (John Mccalpin)
Organization: Supercomputer Computations Research Institute
Lines: 44

In article <787@stat.fsu.edu> I wrote:
>By the way, I estimate the the (soon-to-be-installed) FSU Cray
>Y/MP-4/432 will only be about 125 times as fast as the new MIPS "KILLER
>MICRO from HELL" on my code.  Yep, they are closing the gap all right....

In article <42701@lll-winken.LLNL.GOV> brooks@maddog.llnl.gov (Eugene Brooks)
asked:
>Would you care to enlighten the masses with regard to the basis for
>this estimate? 
>brooks@maddog.llnl.gov, brooks@maddog.uucp

The estimate is based on the _observed_ performance of an 8-processor
Cray Y/MP vs a 25 MHz R-3000 (SGI 4D/2x0).  The speed ratio in that
case is 536:1, and this Cray is an internal machine with a 6.5 ns
clock, rather than the 6 ns clock that will be installed at FSU.

So applying some scaling suggests that a 4-cpu Cray Y/MP at 6 ns will
be about 290 times as fast as the R-3000 box.  Then scale the MIPS cpu
speed by the ratio of the clocks of the R-6000 to R-3000 to reduce this
ratio to about 120:1.  (I am assuming a 60 MHz clock on the R-6000 ---
I don't know what the exact value will be....).

Since the code is highly parallelizable, a multi-processor R-6000 based
machine will show good speedups up to about 16 processors.  The experience
on the Cray and Ardent machines suggests that a speedup of 12x should be
possible on a 16-cpu system.  However, multi-processor Cray Y/MP's exist
today, and multi-processor R-6000 machines do not....

The code is a hybrid finite-element/finite-difference ocean circulation
model written in portable FORTRAN-77.  The calculations are all done in
64-bit precision, and require 64-bits for reasonable accuracy.

This is all just as excuse to remind Eugene :-) that some users will
still be able to make effective use of vector supercomputers.  In
Price/Performance ratios, the scalar KILLER MICRO's are not even
significantly ahead of the traditional supercomputers on optimal
codes.  They are certainly not _yet_ competitive with regard to 
turnaround time on large vector jobs, though I agree that that will
change soon as 8-16 cpu machines in the R-6000 class become available.

My next project is porting this code to a Connection Machine CM-2.
I anticipate about the same performance as the 8-processor Y/MP,
but in a much more scalable architecture, and at about 1/4 of the
price.