Messages in this thread |  | | Date | Mon, 21 Nov 2022 08:55:15 +0800 | From | Feng Tang <> | Subject | Re: [PATCH clocksource 1/3] clocksource: Reject bogus watchdog clocksource measurements |
| |
On Thu, Nov 17, 2022 at 03:09:10PM -0800, Paul E. McKenney wrote: > On Thu, Nov 17, 2022 at 10:57:34PM +0100, Thomas Gleixner wrote: > > Paul! > > > > On Mon, Nov 14 2022 at 15:28, Paul E. McKenney wrote: > > > > > > + /* Check for bogus measurements. */ > > > + wdi = jiffies_to_nsecs(WATCHDOG_INTERVAL); > > > + if (wd_nsec < (wdi >> 2)) { > > > + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced only %lld ns during %d-jiffy time interval, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL); > > > + continue; > > > + } > > > + if (wd_nsec > (wdi << 2)) { > > > + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced an excessive %lld ns during %d-jiffy time interval, probable CPU overutilization, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL); > > > + continue; > > > + } > > > > This is really getting ridiculous. > > I have absolutely no argument with this statement, and going back a > long time. ;-) > > But the set of systems that caused me to send this turned out to have > real divergence between HPET and TSC, and 40 milliseconds per second of > divergence at that. So not only do you hate this series, but it is also > the case that this series doesn't help with the problem at hand.
The drift is about 4% which is quite big. It seems that this is either problem of HPET/TSC's hardware/firmware, or the problem of frequency calibration for HPET/TSC. TSC calibration is complex, as it could be done from different methods depending on hardware and firmware, could you share the kernel boot log related with tsc/hpet and clocksource?
Also if your platform has acpi PM_TIMER, you may try "nohpet" to use PM_TIMER instead of HPET and check if there is also big drift between TSC and PM_TIMER.
Thanks, Feng
|  |