Date: Sun, 5 Aug 2007 13:33:01 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: =?ISO-8859-1?B?SvZybg==?= Engel <joern@logfs.org>
Cc: Ingo Molnar <mingo@elte.hu>, Arjan van de Ven <arjan@infradead.org>,
       Willy Tarreau <w@1wt.eu>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Jeff Garzik <jeff@garzik.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-mm@kvack.org,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       miklos@szeredi.hu, neilb@suse.de, dgc@sgi.com,
       tomoki.sekiyama.qu@hitachi.com, nikita@clusterfs.com,
       trond.myklebust@fys.uio.no, yingchao.zhou@gmail.com,
       richard@rsk.demon.co.uk, david@lang.hm
Subject: Re: [PATCH 00/23] per device dirty throttling -v8
Message-Id: <20070805133301.107ce725.akpm@linux-foundation.org>
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On Sun, 5 Aug 2007 22:21:12 +0200 J?rn Engel <joern@logfs.org> wrote:

> On Sun, 5 August 2007 20:37:14 +0200, J?rn 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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