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To: Peter Edwards <peadar.edwards@gmail.com>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Mon, 10 Oct 2005 11:56:34 BST."
	<34cb7c840510100356t1b93e679v6479afda16277afa@mail.gmail.com> 
Date: Mon, 10 Oct 2005 13:01:50 +0200
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Cc: src-committers@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org>,
	Peter Edwards <peadar@freebsd.org>, cvs-src@freebsd.org,
	cvs-all@freebsd.org, S?ren Schmidt <sos@freebsd.org>
Subject: Re: cvs commit: src/sys/dev/ata atapi-cd.c 
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In message <34cb7c840510100356t1b93e679v6479afda16277afa@mail.gmail.com>, Peter
 Edwards writes:
>> +> Please see geom_disk.c
>>
>I think an advantage to Poul-Henning's approach is that it reduces
>latency: the I/O can start immediately, rather than requiring all the
>bio's to be allocated first. The very fact that the race condition was
>triggered indicates that the IO devices can overtake the CPU. You
>might waste some time in the failure case, but that's obviously a
>small price to pay for improved performance in the normal run of
>things.

Agreed.

I've started wondering if I should actually put this code in a
function so we don't have to reinvent it all over the place.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.