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From: johnw@astroatc.UUCP
Newsgroups: comp.sys.m68k,comp.sys.intel,comp.arch
Subject: locality of reference (was Re: Recent Motorola ad seen in Byte)
Message-ID: <234@astroatc.UUCP>
Date: Wed, 15-Apr-87 16:07:45 EST
Article-I.D.: astroatc.234
Posted: Wed Apr 15 16:07:45 1987
Date-Received: Fri, 17-Apr-87 03:45:09 EST
References: <362@sbcs.UUCP> <1466@ncr-sd.SanDiego.NCR.COM> <580@plx.UUCP> <513@omen.UUCP> <285@winchester.mips.UUCP> <518@omen.UUCP>
Reply-To: johnw@astroatc.UUCP (John F. Wardale)
Distribution: comp
Organization: Astronautics Technology Cntr, Madison, WI
Lines: 38
Keywords: Sieve, 68020 vs. 80386
Xref: utgpu comp.sys.m68k:332 comp.sys.intel:139 comp.arch:886
Summary: everything helps

In article <518@omen.UUCP> caf@.UUCP (PUT omen's NAME HERE) writes:

>While it is conceivable that Motorola put the 256 byte cache in the 68020
>just to help certain benchmarks,  it is more likely that the cache
>actually improves performance rather inexpensively.
>
>Does somebody have real data on how the 68020's cache improves performance
>on sieve, troff, sort, and other Unix CPU hogs?

For a graduate architecture course, I did a paper that studied 
"locality of reference" for a large program.  (I traced the 
running of a compiler.)  My data was a list of address and
reference-count pair (sorted highest to lowest ref-cnt).

The results were not sruprizing.  The distribution was a nice
exponectioal decay, with a cumulate dist that approced 100%.

As I remember the data:
The 8/10/16 most used accounted for a large (but not half) the
references.  In the 200-300 most frequently accessed locations
accounted for most (but definatly under 90%) of the references.
I think the 1000 most used were in the low 90's% after 200 you
have to add alot more before you see an appreciable increase in
the "cumulative distribution function"

If anyone wants more details, send mail....I'll sum...


			John W

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Name:	John F. Wardale
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