linux-kernel - Re: [PATCH 00/23] per device dirty throttling -v8

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Date:	Sun, 5 Aug 2007 13:33:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jörn Engel <joern@...fs.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	Willy Tarreau <w@....eu>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	miklos@...redi.hu, neilb@...e.de, dgc@....com,
	tomoki.sekiyama.qu@...achi.com, nikita@...sterfs.com,
	trond.myklebust@....uio.no, yingchao.zhou@...il.com,
	richard@....demon.co.uk, david@...g.hm
Subject: Re: [PATCH 00/23] per device dirty throttling -v8

On Sun, 5 Aug 2007 22:21:12 +0200 Jörn Engel <joern@...fs.org> wrote:

> On Sun, 5 August 2007 20:37:14 +0200, Jörn Engel wrote:
> > 
> > Guess I should throw in a kernel compile test as well, just to get a
> > feel for the performance.
> 
> Three runs each of noatime, relatime and atime, both with cold caches
> and with warm caches.  Scripts below.  Run on a Thinkpad T40, 1.5GHz,
> 2GiB RAM, 60GB 2.5" IDE disk, ext3.
> 
> Biggest difference between atime and noatime (median run, cold cache) is
> ~2.3%, nowhere near the numbers claimed by Ingo.  Ingo, how did you
> measure 10% and more?

Ingo had CONFIG_DEBUG_INFO=y, which generates heaps more writeout,
but no additional atime updates.

Ingo had a faster computer ;)  That will generate many more MB/sec
write traffic, so the cost of those atime seeks becomes proportionally
higher.  Basically: you're CPU-limited, Ingo is seek-limited.
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