Re: huge improvement with per-device dirty throttling

Martin Knoblauch
2007-09-06T09:50:10Z

--- Martin Knoblauch <knobi@knobisoft.de> wrote:

>
> --- Leroy van Logchem <leroy.vanlogchem@wldelft.nl> wrote:
>
> > Andrea Arcangeli wrote:
> > > On Wed, Aug 22, 2007 at 01:05:13PM +0200, Andi Kleen wrote:
> > >> Ok perhaps the new adaptive dirty limits helps your single disk
> > >> a lot too. But your improvements seem to be more "collateral
> > damage" @)
> > >>
> > >> But if that was true it might be enough to just change the dirty
> > limits
> > >> to get the same effect on your system. You might want to play
> with
> > >> /proc/sys/vm/dirty_*
> > >
> > > The adaptive dirty limit is per task so it can't be reproduced
> with
> > > global sysctl. It made quite some difference when I researched
> into
> > it
> > > in function of time. This isn't in function of time but it
> > certainly
> > > makes a lot of difference too, actually it's the most important
> > part
> > > of the patchset for most people, the rest is for the corner cases
> > that
> > > aren't handled right currently (writing to a slow device with
> > > writeback cache has always been hanging the whole thing).
> >
> >
> > Self-tuning > static sysctl's. The last years we needed to use very
>
> > small values for dirty_ratio and dirty_background_ratio to soften
> the
> >
> > latency problems we have during sustained writes. Imo these patches
>
> > really help in many cases, please commit to mainline.
> >
> > --
> > Leroy
> >
>
> while it helps in some situations, I did some tests today with
> 2.6.22.6+bdi-v9 (Peter was so kind) which seem to indicate that it
> hurts NFS writes. Anyone seen similar effects?
>
> Otherwise I would just second your request. It definitely helps the
> problematic performance of my CCISS based RAID5 volume.
>

please disregard my comment about NFS write performance. What I have
seen is caused by some other stuff I am toying with.

So, I second your request to push this forward.

Martin

------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www: http://www.knobisoft.de