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Message-ID: <46BA6667.1070205@maths.otago.ac.nz>
Date: Thu, 09 Aug 2007 12:57:11 +1200
From: Greg Trounson <gregt@...hs.otago.ac.nz>
To: Ingo Molnar <mingo@...e.hu>
CC: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/23] per device dirty throttling -v8
Ingo Molnar wrote:
> * Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>
>>>> People just need to know about the performance differences - very
>>>> few realise its more than a fraction of a percent. I'm sure Gentoo
>>>> will use relatime the moment anyone knows its > 5% 8)
>>> noatime,nodiratime gave 50% of wall-clock kernel rpm build
>>> performance improvement for Dave Jones, on a beefy box. Unless i
>>> misunderstood what you meant under 'fraction of a percent' your
>>> numbers are _WAY_ off.
>> What numbers - I didn't quote any performance numbers ?
>
> ok, i misunderstood your "very few realise its more than a fraction of a
> percent" sentence, i thought you were saying it's a fraction of a
> percent.
>
> Measurements show that noatime helps 20-30% on regular desktop
> workloads, easily 50% for kernel builds and much more than that (in
> excess of 100%) for file-read-intense workloads. We cannot just walk
> past such a _huge_ performance impact so easily without even reacting to
> the performance arguments, and i'm happy Ubuntu picked up
> noatime,nodiratime and is whipping up the floor with Fedora on the
> desktop.
>
Sorry I'm just not seeing those gains here. With my filesystems mounted with atime
defaults the Quake sources build in 1m28.856s. A test with ls -ltu verifies that atime is
working as expected. When I remount my filesystems with:
mount [fs] -o remount,noatime,nodiratime
I get a compile time of 1m23.368s, a mere 6% improvement.
This is on a dual-core Athlon 4200+ box running 2.6.21, so I would have thought this to be
close to a best-case file I/O test.
Greg
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