linux-kernel - Re: updated: ext3 IO latency measurements on v2.6.30-rc1

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Message-Id: <E1M65q3-0006up-M2@approx.mit.edu>
Date:	Mon, 18 May 2009 12:37:19 -0400
From:	Sanjoy Mahajan <sanjoy@....EDU>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>, David Rees <drees76@...il.com>,
	Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>
Subject: Re: updated: ext3 IO latency measurements on v2.6.30-rc1 

To test the ext3 improvements in 2.6.30-rc5, I tried my previous test of
starting an rxvt while findutils or 'aptitude dist-upgrade' is madly
spinning the disk.

With vanilla 2.6.29 in those circumstances, starting an rxvt took 4
seconds on an otherwise unloaded system (Thinkpad T60 w/ 1.83GHz
dual-core CPU, 1.5GB RAM, 5400 rpm drive).  The second rxvt came up
right away.  So the first rxvt probably stalled until /usr/bin/rxvt
could be grabbed from disk.

With 2.6.30-rc5, the rxvt showed up much faster -- either right away
(maybe it was still in the cache) or after about 0.5 seconds (probably
the uncached case).

Other tests were also snappy, like opening a 10MB PDF file in Emacs,
adding a newline at the beginning, and saving it (while findutils was
running).  I hadn't done the same test with 2.6.29, but I'm pretty sure
it would have been painfully slow if findutils was running.

So, relative to 2.6.29, I see a large improvement in interactive
behavior under high IO load.

-Sanjoy

`Until lions have their historians, tales of the hunt shall always
 glorify the hunters.'  --African Proverb
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