linux-kernel - Re: Noatime vs relatime

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Date:	Fri, 10 Aug 2007 16:44:35 +0200
From:	Xavier Bestel <xavier.bestel@...e.fr>
To:	Vlad <vladc6@...oo.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Noatime vs relatime

On Fri, 2007-08-10 at 07:26 -0700, Vlad wrote:
> Relatime seems to be wasteful of both IO resources _and_ CPU cycles.
> Instead of performing a single IO operation (as atime does), relatime
> performs at least three IO operations and three CPU-dependent
> operations:
> 
> 1) a read IO operation to find out the old atime
> 2) a read IO operation to find out the old ctime
> 3) a read IO operation to find out the old mtime
> 4) Comparison of "old atime is <= than mtime/ctime"
> 5) Find out current time
> 6) Comparison of "current time minus old atime is > X"

As all [acm]times are stored in the same block (inode), I bet all this
is one single IO, plus some insignificant computation (3 comparisons
plus reading time is really smaller than one block IO).

	Xav


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