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From: Michael Smith <msmith@atrad.adelaide.edu.au>
Message-Id: <199604301324.WAA21150@genesis.atrad.adelaide.edu.au>
Subject: Re: lmbench IDE anomaly
To: koshy@india.hp.com (A JOSEPH KOSHY)
Date: Tue, 30 Apr 1996 22:54:18 +0930 (CST)
Cc: hackers@freebsd.org, current@freebsd.org
In-Reply-To: <199604301053.AA141971583@fakir.india.hp.com> from "A JOSEPH KOSHY" at Apr 30, 96 04:23:03 pm
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A JOSEPH KOSHY stands accused of saying:
> 
> >> two simultaneous runs on the scsi disk
...
> The performance degradation per process is around 2x which is to be expected.
> The overall throughput is around the same as the single benchmark case.
> 
> However when the same exercise is repeated with the IDE disk:
...
> Here we see a 8x degradation per process; 4x in terms of total throughput.
> 
> Is this to be expected, or am i doing something wrong here? The system was 
> otherwise idle during these tests.

That's about right.  The SCSI disk gets the chance to sort the I/O to suit
itself, optimising its performance.  The IDE disk only gets to look at one
transaction at a time, so it's at the mercy of the disksorting code in
the operating system.  I don't know that FreeBSD's disksort stuff is 
terribly wonderful, but I'd happily stand corrected.

> Koshy

-- 
]] Mike Smith, Software Engineer        msmith@atrad.adelaide.edu.au    [[
]] Genesis Software                     genesis@atrad.adelaide.edu.au   [[
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