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Date: Tue, 17 Feb 2009 13:46:20 -0700
From: Scott Long <scottl@samsco.org>
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To: Bruce Evans <brde@optusnet.com.au>
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Cc: FreeBSD@FreeBSD.org, FreeBSD Current <freebsd-current@FreeBSD.org>,
	Stable <freebsd-stable@FreeBSD.org>,
	Gary Jennejohn <gary.jennejohn@freenet.de>, scsi@FreeBSD.org
Subject: Re: HEADS UP: More CAM fixes.
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Bruce Evans wrote:
> On Tue, 17 Feb 2009, Gary Jennejohn wrote:
> 
>> I tested this with an Adaptec 29160.  I saw no real improvement in
>> performance, but also no regressions.
>>
>> I suspect that the old disk I had attached just didn't have enough
>> performance reserves to show an improvement.
>>
>> My test scenario was buildworld.  Since /usr/src and /usr/obj were both
>> on the one disk it got a pretty good workout.
>                                   ^^^^ low
>>
>> AMD64 X2 (2.5 GHz) with 4GB of RAM.
> 
> Buildworld hardly uses the disk at all.  It reads and writes a few hundred
> MB.  Ideally the i/o should go at disk speeds of 50-200MB/S and thus take
> between 20 and 5 seconds.  In practice, it will take a few more seconds.
> physically but perhaps even less virtually due to parallelism.
> 
> Bruce

Yes, on modern machines, buildworld is bound almost completely by disk
latency, and not at all by disk or controller bandwidth.

Scott