> > > > From: Kan Liang <Kan.liang@xxxxxxxxx> > > > > > > > > Some users reported spurious NMI watchdog timeouts. > > > > > > > > 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. > > > > > > AFAIR the watchdog doesn't rely on deferred timers so this would > > > suggest that a standard hrtimer can expire much later than programmed, > right? > > > > The softlockup watchdog relies on hrtimers. > > The hardlockup watchdog (NMI watchdog) relies on perf subsystem and > > using unhalted CPU cycles. > > When the softlockup watchdog expires, it updates the hrtimer_interrupts. > > When the NMI watchdog expires, it will check the hrtimer_interrupts, > > and determine if it's a hardlockup. > > The design was to make the softlockup watchdog runs with 2.5 times the > > rate of NMI watchdog. So it guarantees that the hrtimer_interrupts is > > updated before the NMI watchdog expires. > > That works well if Turbo-Mode is disabled. > > However, when Turbo-Mode is enabled, unhalted CPU cycles might run > > much faster than expected, even faster than softlockup watchdog. > > So the softlockup watchdog will not get a chance to update the > > hrtimer_interrupts, which will trigger false positives. > > So it is not the hrtimer which doesn't fire but rather the NMI events fire too > quickly, right? Yes, the NMI fires too quickly. Thanks, Kan