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Message-ID: <loom.20070706T120931-601@post.gmane.org>
Date: Fri, 6 Jul 2007 10:15:52 +0000 (UTC)
From: Brice Figureau <brice+lklm@...sofwonder.com>
To: linux-kernel@...r.kernel.org
Subject: Re: Understanding I/O behaviour
Martin Knoblauch <spamtrap <at> knobisoft.de> writes:
> --- Jesper Juhl <jesper.juhl <at> gmail.com> wrote:
>
> > On 06/07/07, Robert Hancock <hancockr <at> shaw.ca> wrote:
> > [snip]
> > >
> > > Try playing with reducing /proc/sys/vm/dirty_ratio and see how that
> > > helps. This workload will fill up memory with dirty data very
> > quickly,
> > > and it seems like system responsiveness often goes down the toilet
> > when
> > > this happens and the system is going crazy trying to write it all
> > out.
> > >
> >
> > Perhaps trying out a different elevator would also be worthwhile.
> >
>
> AS seems to be the best one (NOOP and DeadLine seem to be equally OK).
> CFQ gives less (about 10-15%) throughput except for the kernel with the
> cfs cpu scheduler, where CFQ is on par with the other IO schedulers.
>
Please have a look to kernel bug #7372:
http://bugzilla.kernel.org/show_bug.cgi?id=7372
It seems I encountered the almost same issue.
The fix on my side, beside running 2.6.17 (which was working fine for me) was to:
1) have /proc/sys/vm/vfs_cache_pressure=1
2) have /proc/sys/vm/dirty_ratio=1 and /proc/sys/vm/dirty_background_ratio=1
3) have /proc/sys/vm/swappiness=2
4) run Peter Zijlstra: per dirty device throttling patch on the top of 2.6.21.5:
http://www.ussg.iu.edu/hypermail/linux/kernel/0706.1/2776.html
Hope that helps,
--
Brice Figureau
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