Re: Understanding I/O behaviour

[Brice Figureau <brice+lklm@daysofwonder.com>]

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