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To: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com>
cc: henrich@crh.cl.msu.edu (Charles Henrich), freebsd-hackers@freebsd.org
Subject: Re: A performance mystery 
In-reply-to: Your message of "Fri, 02 Jun 95 22:10:47 PDT."
             <199506030510.WAA09409@gndrsh.aac.dev.com> 
From: David Greenman <davidg@Root.COM>
Reply-To: davidg@Root.COM
Date: Fri, 02 Jun 1995 22:17:02 -0700
Sender: hackers-owner@freebsd.org
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>> > >     16      8192    3360694             2890287
>                                              ^^^^^^^
>
>How come *this* number and the number below are different by a factor
>of 7???  It should have been the same.  ``iozone 16 8192'' and the
>above line from ``iozone auto'' do exactly the same things yet we
>are seeing this *huge* descrepancy.

   Because there isn't enough 'free' memory at the time that he ran the test
to cache the entire file. Since it's read sequentially and the cache policy
for something like this is more or less LRU, it get pushed out of the cache
before it is read back.

-DG