Re: [Bug #23902] [BUG] 2.6.37-rc3 massive interactivity regression on ARM

Rafael J. Wysocki
2010-12-06T22:28:59Z

On Saturday, December 04, 2010, Mikael Pettersson wrote:
> Mikael Pettersson writes:
> > Rafael J. Wysocki wrote:
> > > This message has been generated automatically as a part of a summary report
> > > of recent regressions.
> > >
> > > The following bug entry is on the current list of known regressions
> > > from 2.6.36. Please verify if it still should be listed and let the tracking team
> > > know (either way).
> > >
> > >
> > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=23902
> > > Subject : [BUG] 2.6.37-rc3 massive interactivity regression on ARM
> > > Submitter : Mikael Pettersson <mikpe-1zs4UD6AkMk@public.gmane.org>
> > > Date : 2010-11-27 15:16 (6 days old)
> > > Message-ID : <19697.8378.717761.236202-tgku4HJDRZih8lFjZTKsyTAV6s6igYVG@public.gmane.org>
> > > References : http://marc.info/?l=linux-kernel&m=129087098911837&w=2
> >
> > The bug is still present in 2.6.37-rc4. I'm currently trying to bisect it.
>
> git bisect identified
>
> [305e6835e05513406fa12820e40e4a8ecb63743c] sched: Do not account irq time to current task
>
> as the cause of this regression. Reverting it from 2.6.37-rc4 (requires some
> hackery due to subsequent changes in the same area) restores sane behaviour.
>
> (Author of original patch cc:d.)
>
> The original patch submission talks about irq-heavy scenarios. My case is the
> exact opposite: UP, !PREEMPT, NO_HZ, very low irq rate, essentially 100% CPU
> bound in userspace but expected to schedule quickly when needed (e.g. running
> top or ps or just hitting CR in one shell while another runs a compile job).

Thanks, added the first bad commit information to the bug entry.

Rafael