Path: utzoo!attcan!uunet!decwrl!sdd.hp.com!hplabs!hpfcso!hpfcdj!kinsell
From: kinsell@hpfcdj.HP.COM (Dave Kinsell)
Newsgroups: comp.arch
Subject: Re: Workstation Disk I/O
Message-ID: <16870002@hpfcdj.HP.COM>
Date: 11 Oct 90 02:09:54 GMT
References: <14900016@hpdmd48.boi.hp.com>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 36



>If the benchmark truly represents what "really goes on in systems"
>this suggests that the disk cache design was very clever and useful;
>not that the results are "skewed".

>The $64K question is always, does the benchmark reflect real system
>loads.

Well, if your real system workload consists of one trivially small
program that reads the same data file over and over, then yes, this
sort of benchmark will accurately predict system performance.

If, on the other hand, you have large programs constantly getting knocked
out of main RAM by all the caching of the data files, then these benchmarks
do a somewhat less accurate job of predicting "real" performance.  Would
this qualify as the understatement of the century?

Being careful to keep the buffer cache much smaller than the test file,
you can easily prove to yourself that systems with memory mapped
files are superior by factors of 20X or so.  I've also seen systems with
buffer caches give substantially better benchmark results than those with
mapped files, if the buffer cache was sized appropriately.  It all depends
on what you're trying to prove.



>--
>----------------------------------------------------------------
>Keith H. Bierman    kbierman@Eng.Sun.COM | khb@chiba.Eng.Sun.COM
>SMI 2550 Garcia 12-33			 | (415 336 2648)   
>    Mountain View, CA 94043
>----------

Dave Kinsell
kinsell@hpfcmb.hp.com