Messages in this thread | | | Date | Fri, 3 Feb 2023 17:27:10 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2 clocksource 6/7] clocksource: Verify HPET and PMTMR when TSC unverified |
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On Thu, Feb 02, 2023 at 08:57:39AM +0100, Thomas Gleixner wrote: > On Wed, Feb 01 2023 at 22:40, Waiman Long wrote: > > On 2/1/23 14:55, Paul E. McKenney wrote: > >>>>> Therefore, when watchdog verification of TSC is disabled, enable it for > >>>>> HPET and PMTMR (AKA ACPI PM timer). This provides the needed in-kernel > >>>>> time-skew diagnostic without degrading the system's performance. > >>>> I'm more than unhappy about this. We finally have a point where the TSC > >>>> watchdog overhead can go away without adding TSC=reliable to the kernel > >>>> commandline. > >>>> > >>>> Now you add an unconditionally enforce the watchdog again in a way which > >>>> even cannot be disabled on the kernel command line. > >>>> > >>>> Patently bad idea, no cookies for you! > >>> I have a similar concern about this patch as well. That is why I was > >>> suggesting to have this enabled for a limited time after boot for sanity > >>> checking purpose only. > >> Fair enough! > >> > >> If the watchdog checking of HPET and/or PMTMR against TSC only happens > >> only when the sysadm asks for it, would you still want to have the ability > >> to enable such watchdog checking at boot time, and then to disable it > >> once the system had been running for some limited time? > > > > Yes, being optional is another way to avoid the overhead for the > > majority of users. The paranoids can turn it on if they want to. > > Yes, opt-in is good enough.
I have added this commit to my clocksource branch:
2ff7dacc88b0 clocksource: Enable TSC watchdog checking of HPET and PMTMR only when requested
It is passing my internal tests, and if it does fine for a couple of days in -next, I will send an updated pull request.
Thanx, Paul
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The full clocksource branch:
beaa1ffe551c3 clocksource: Print clocksource name when clocksource is tested unstable c37e85c135cea clocksource: Loosen clocksource watchdog constraints f092eb34b3304 clocksource: Improve read-back-delay message dd029269947a3 clocksource: Improve "skew is too large" messages b7082cdfc464b clocksource: Suspend the watchdog temporarily when high read latency detected a7ec817d55421 x86/tsc: Add option to force frequency recalibration with HW timer efc8b329c7fdc clocksource: Verify HPET and PMTMR when TSC unverified 2ff7dacc88b0c clocksource: Enable TSC watchdog checking of HPET and PMTMR only when requested
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