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

[Vincent Guittot]

On Wed, 9 Jan 2019 at 17:50, Tony Lindgren <tony@xxxxxxxxxxx> wrote:
>
> * Vincent Guittot <vincent.guittot@xxxxxxxxxx> [190109 16:48]:
> > On Wed, 9 Jan 2019 at 17:28, Tony Lindgren <tony@xxxxxxxxxxx> wrote:
> > >
> > > * Rafael J. Wysocki <rafael@xxxxxxxxxx> [190109 09:44]:
> > > > On Wed, Jan 9, 2019 at 2:51 AM Tony Lindgren <tony@xxxxxxxxxxx> wrote:
> > > > >
> > > > > * Vincent Guittot <vincent.guittot@xxxxxxxxxx> [190109 01:42]:
> > > > > > Le Tuesday 08 Jan 2019 Ã 13:37:43 (-0800), Tony Lindgren a Ãcrit :
> > > > > > > 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@xxxxxxxxxxx>
> > > >
> > > > 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"

>
> Regards,
>
> Tony