Messages in this thread | | | Subject | Re: [PATCH v2] clocksource: Warn if too many missing ticks are detected | From | Waiman Long <> | Date | Mon, 24 Sep 2018 11:35:14 -0400 |
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On 09/19/2018 03:53 AM, Thomas Gleixner wrote: > On Tue, 18 Sep 2018, Waiman Long wrote: > >> The clocksource watchdog, when running, is scheduled on all the CPUs in >> the system sequentially on a round-robin fashion with a period of 0.5s. >> A bug in the 4.18 kernel is causing missing ticks when nohz_full >> is specified. Under some circumstances, this causes the watchdog to >> incorrectly state that the TSC is unstable because of counter overflow >> in the hpet watchdog clock source after a few minutes delay. >> >> That particular bug is fixed by the 4.19 commit 7059b36636beab ("sched: >> idle: Avoid retaining the tick when it has been stopped"). To make it >> easier to catch this kind of bug in the future, a check is added to see >> if there is too much delay in the invocation of the watchdog callback >> and print a warning once if it happens. > Second thoughts on this. Putting the check into the clocksource watchdog is > the wrong place as it's just checking at a place where the symptom > shows. What about putting it right to the source, i.e. in the timer wheel > as it does not depend on the clocksource watchdog being active. The > clocksource watchdog triggering is just one of the symptoms, but in general > timers being massively late is not a good thing. > > Thanks, > > tglx > It looks like there are more complications to deal with in order to do the proper check. I will leave the check in the watchdog for the time being and see how thing works out.
-Longman
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