Newsgroups: comp.arch
Path: utzoo!utgpu!watserv1!watmath!watmsg!sccowan
From: sccowan@watmsg.uwaterloo.ca (S. Crispin Cowan)
Subject: Re: Superlinear Speedup (was Re: Scalability?)
Message-ID: <1990May3.230324.24376@watmath.waterloo.edu>
Sender: daemon@watmath.waterloo.edu (Owner of Many System Processes)
Organization: University of Waterloo
References: <2075@naucse.UUCP> <6897@odin.corp.sgi.com> <49622@lanl.gov> <1990May1.154558.24009@cs.rochester.edu> <1990May3.203405.23456@ecn.purdue.edu>
Date: Thu, 3 May 90 23:03:24 GMT
Lines: 34

In article <1990May3.203405.23456@ecn.purdue.edu> hankd@ee.ecn.purdue.edu (Hank Dietz) writes:
>In article <1990May1.154558.24009@cs.rochester.edu> crowl@cs.rochester.edu (Lawrence Crowl) writes:
>>In article <49622@lanl.gov> ryg@lanl.gov (Richard S Grandy) writes:
>>>I've got a glossy from SGI that shows the POWER center performance on 
>>>LINPACK (100x100, coded) as:
>>>		1 CPU	3.8 DP MFLOPS
>>>		4 CPU	16  DP MFLOPS
>>>Does this mean than with 4 cpus you really get GREATER than a linear speedup?? 
>I do research in optimizing/parallelizing compilers and the first benchmarks
>I did all yielded >n speedup.  Why?  BECAUSE WHEN A PROGRAM IS PARALLELIZED,
>IT ISN'T THE SAME PROGRAM -- it simply produces the same results.  In other
>words, it can be transformed to take advantage of various side benefits of
>parallel hardware & execution:

This all looks like a complicated way of noticing the (somewhat subtle)
point that a parallel machine with n processors _also_ has something
approximating n times the bandwidth to memory, because it has n times
the cache space with n fetch cycles and n centres of locality.

>						-hankd@ecn.purdue.edu

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