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

From: Tony Lindgren <[email-masked]>
Date: Wed, 9 Jan 2019 08:50:04 -0800

* Vincent Guittot <[email-masked]> [190109 16:48]:
> On Wed, 9 Jan 2019 at 17:28, Tony Lindgren <[email-masked]> wrote:
> >
> > * Rafael J. Wysocki <[email-masked]> [190109 09:44]:
> > > On Wed, Jan 9, 2019 at 2:51 AM Tony Lindgren <[email-masked]> wrote:
> > > >
> > > > * Vincent Guittot <[email-masked]> [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 <[email-masked]>
> > >
> > > 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?

Regards,

Tony

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