Re: [Bug #12809] iozone regression with 2.6.29-rc6

Lin Ming
2009-03-16T05:13:15Z

On Sun, 2009-03-15 at 08:27 +0800, Linus Torvalds wrote:
>
> On Sat, 14 Mar 2009, Rafael J. Wysocki wrote:
> >
> > The following bug entry is on the current list of known regressions
> > from 2.6.28. Please verify if it still should be listed and let me know
> > (either way).
> >
> >
> > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=12809
> > Subject : iozone regression with 2.6.29-rc6
> > Submitter : Lin Ming <ming.m.lin@intel.com>
> > Date : 2009-02-27 9:13 (16 days old)
> > First-Bad-Commit: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1cf6e7d83bf334cc5916137862c920a97aabc018
> > References : http://marc.info/?l=linux-kernel&m=123572630504360&w=4
> > Handled-By : Wu Fengguang <fengguang.wu@intel.com>
>
> I suspect that I should just raise the default dirty limits. Wu reported
> that it fixed the regression, and while he picked some rather high
> percentages, I think we could certainly raise the rather aggressive
> default ones.
>
> After all, those default percentages were picked (a) with the old dirty
> logic and (b) largely at random and (c) designed to be aggressive. In
> particular, that (a) means that having fixed some of the dirty accounting,
> maybe the real bug is now that it was always too aggressive, just hidden
> by an accounting issue.
>
> If we raised the default ratio from 5/10 to 10/20, what happens to the
> iozone regression?

echo 10 > /proc/sys/vm/dirty_background_ratio
echo 20 > /proc/sys/vm/dirty_ratio

It fixed the regression of iozone (filesize 1200M) on 4P dual-core HT
machine(8G mem).

Lin Ming