linux-ext4 - Re: [Bug 14830] When other IO is running sync times go to 10 to 20 minutes

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Date:	Thu, 28 Jan 2010 02:53:28 -0500
From:	tytso@....edu
To:	Andre Noll <maan@...temlinux.org>
Cc:	Michael Godfrey <godfrey@....stanford.edu>,
	linux-ext4@...r.kernel.org, bugzilla-daemon@...zilla.kernel.org
Subject: Re: [Bug 14830] When other IO is running sync times go to 10 to 20
 minutes

On Wed, Jan 27, 2010 at 02:06:25PM +0100, Andre Noll wrote:
> On 11:19, bugzilla-daemon@...zilla.kernel.org wrote:
> > After kill -9 of the sync run it took about 20 minutes before 
> > it died.
> 
> I was seeing similar behaviour on one of our servers, and changing
> the io scheduler to noop fixed things for me. So it seems to be an
> issue with cfq which is somehow triggered by ext4 but not by ext3.
> 
> To change the IO scheduler, just execute
> 
> 	echo noop > /sys/block/sda/queue/scheduler
> 
> (replace sda if necessary).

Andre or Michael.  If switching away from cfq helps, that's
definitely... interesting.  Given that cfq is the default scheduler, I
definitely want to understand what might be going on here.  Are either
if you able to run blktrace so we can get a sense of what is going on
under the cfq and deadline/noop I/O schedulers?

And in both of your cases, were you using a new file system freshly
created using mke2fs -t ext4, or was this a ext2/ext3 filesystem that
was converted for use under ext4?

Thanks,

					- Ted
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