Re: cfq misbehaving on 2.6.11-1.14_FC3

From: Con Kolivas
Date: Thu Jun 23 2005 - 22:37:35 EST

On Fri, 24 Jun 2005 12:33, spaminos-ker@xxxxxxxxx wrote:
> --- Con Kolivas <kernel@xxxxxxxxxxx> wrote:
> > I found the same, and the effect was blunted by noatime and
> > journal_data_writeback (on ext3). Try them one at a time and see what you
> > get.
> I had to move to a different box, but get the same kind of results (for
> ext3 default mount options).
> Here are the latencies (all cfq) I get with different values for the mount
> parameters
> ext2 default
> 0.1s
> ext3 default
> 52.6s avg
> reiser defaults
> 29s avg 5 minutes
> then,
> 12.9s avg
> ext3 rw,noatime,data=writeback
> 0.1s avg
> reiser rw,noatime,data=writeback
> 4s avg for 20 seconds
> then 0.1 seconds avg
> So, indeed adding noatime,data=writeback to the mount options improves
> things a lot.
> I also tried without the noatime, and that doesn't make much difference to
> me.
> That looks like a good workaround, I'll now try with the actual server and
> see how things go.

That's more or less what I found, although I found noatime also helped my test
cases, but also less than the journal options. Coincidentally I only
discovered this recently and hadn't gotten around to telling anyone how
dramatic this was and this seemed as good a time as any. I am suspicious that
it wasn't this bad in past kernels but haven't been able to instrument
earlier kernels to check.


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