linux-kernel - Re: Linux disk performance.

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Message-Id: <1166530686.3365.1238.camel@laptopd505.fenrus.org>
Date:	Tue, 19 Dec 2006 13:18:06 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Manish Regmi <regmi.manish@...il.com>,
	Erik Mouw <mouw@...linux.org>, kernelnewbies@...linux.org,
	linux-kernel@...r.kernel.org
Subject: Re: Linux disk performance.

On Tue, 2006-12-19 at 17:38 +1100, Nick Piggin wrote:
> Manish Regmi wrote:
> 
> > Nick Piggin:
> > 
> >> but
> >> they look like they might be a (HZ quantised) delay coming from
> >> block layer plugging.
> > 
> > 
> > Sorry i didn´t understand what you mean.
> 
> When you submit a request to an empty block device queue, it can
> get "plugged" for a number of timer ticks before any IO is actually
> started. This is done for efficiency reasons and is independent of
> the IO scheduler used.

however the O_DIRECT codepath unplugs the queues always immediately..



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