Re: [PATCH v2 0/4] clocksource: Avoid incorrect hpet fallback

[Waiman Long]

On 11/17/21 16:25, Paul E. McKenney wrote:
> On Wed, Nov 17, 2021 at 01:51:51PM -0500, Waiman Long wrote:
> > On 11/17/21 11:54, Paul E. McKenney wrote:
> > > On Tue, Nov 16, 2021 at 06:44:22PM -0500, Waiman Long wrote:
> > > A few questions:
> > >
> > > 1.	Once you have all the patches in place, is the increase in
> > > 	WATCHDOG_MAX_SKEW from 50us to 100us necessary?
> > I think so. Using Feng's reproducer, I was able to cause a hpet-hpet delay
> > of more than 90us on a 1-socket system. With a default 50us
> > WATCHDOG_MAX_SKEW, the chance of a warning showing up will be much higher.
> > Trying to minimize the chance that a warning may appear is my primary reason
> > to increase WATCHDOG_MAX_SKEW.
> Should we downgrade the "had to retry read" complain to pr_info(),
> and make the only real warning be the case where a large number of
> consecutive read attempts fail?  I believe that Heiner Kallweit was
> looking for something like this.
Sure. I will downgrade it to pr_info().
> > > 2.	The reason for having cs->uncertainty_margin set to
> > > 	2*WATCHDOG_MAX_SKEW was to allow for worst-case skew from both
> > > 	the previous and the current reading.  Are you sure that
> > > 	dropping back to WATCHDOG_MAX_SKEW avoids false positives?
> > I can remove the hunk of changing cs->uncertainty_margin. It is critical for
> > this patch.
> Assuming "not critical", good!

Yes, it is "not critical". Somehow I missed the "not" :-)

Cheers,
Longman