Re: Regression in v5.0-rc1 with autosuspend hrtimers

Tony Lindgren
2019-01-09T17:02:06Z

* Vincent Guittot <vincent.guittot@linaro.org> [190109 16:56]:
> On Wed, 9 Jan 2019 at 17:50, Tony Lindgren <tony@atomide.com> wrote:
> >
> > * Vincent Guittot <vincent.guittot@linaro.org> [190109 16:48]:
> > > On Wed, 9 Jan 2019 at 17:28, Tony Lindgren <tony@atomide.com> wrote:
> > > >
> > > > * Rafael J. Wysocki <rafael@kernel.org> [190109 09:44]:
> > > > > On Wed, Jan 9, 2019 at 2:51 AM Tony Lindgren <tony@atomide.com> wrote:
> > > > > >
> > > > > > * Vincent Guittot <vincent.guittot@linaro.org> [190109 01:42]:
> > > > > > > Le Tuesday 08 Jan 2019 à 13:37:43 (-0800), Tony Lindgren a écrit :
> > > > > > > > Lowering the autosuspend_delay_ms to 2100 ms makes things work again.
> > > > > > > > Anything higher than 2200 ms seems to somehow time out immediately
> > > > > > > > now :)
> > > > > > >
> > > > > > > This is quite close to the max ns of an int on arm 32bits
> > > > > > >
> > > > > > > Could you try the patch below ?
> > > > > >
> > > > > > Yup great thanks, that's it:
> > > > > >
> > > > > > Tested-by: Tony Lindgren <tony@atomide.com>
> > > > >
> > > > > Cool. Thanks for getting to the bottom of this!
> > > >
> > > > No problem.
> > > >
> > > > One more thing I noticed: The 25% slack can get noticeable
> > > > for larger values. For things like a 3 second uart console
> > > > timeout slack of 750 ms is quite large variation.
> > > >
> > > > Should we have a limit of max 100 ms for the slack?
> > >
> > > Keep in mind that when jiffies were used, expires was rounded to a
> > > full second when delay was greater than a second. So you could already
> > > have difference of up 990ms on arm before this patch
> > > And i don't take into account the rework of timer infra which add
> > > another level of variation, something like up to 640 ms more when the
> > > timer is greater than 2880 ms for arm IIRC
> >
> > I think it was rounded up earlier.
> >
> > Don't we get rounded down now also?
>
> We still round up. In hrtimer we have :
> timer->_softexpires = time;
> timer->node.expires = ktime_add_safe(time, delta);
> so the hrtimer will expire between "time" and "time+delta"

OK thanks for checking it. In that case we should be good to go :)

Tony