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Date: Thu, 22 Jun 2017 17:33:02 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Kan Liang <kan.liang@intel.com>
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Subject: Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups
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On Wed, 21 Jun 2017, Thomas Gleixner wrote:

> On Wed, 21 Jun 2017, kan.liang@intel.com wrote:
> > We now have more and more systems where the Turbo range is wide enough
> > that the NMI watchdog expires faster than the soft watchdog timer that
> > updates the interrupt tick the NMI watchdog relies on.
> > 
> > This problem was originally added by commit 58687acba592
> > ("lockup_detector: Combine nmi_watchdog and softlockup detector").
> > Previously the NMI watchdog would always check jiffies, which were
> > ticking fast enough. But now the backing is quite slow so the expire
> > time becomes more sensitive.
> 
> And slapping a factor 3 on the NMI period is the wrong answer to the
> problem. The simple solution would be to increase the hrtimer frequency,
> but that's not really desired either.

Thinking a bit more about it. Increasing the hrtimer frequency and
maintaining the current frequency of softlockup_watchdog wakeups, would be
probably the most trivial workaround for now.

Thanks,

	tglx