Messages in this thread | | | Date | Tue, 30 Nov 2021 12:47:21 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v3 2/2] x86/tsc: skip tsc watchdog checking for qualified platforms |
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On Tue, Nov 30, 2021 at 09:39:32PM +0100, Thomas Gleixner wrote: > > Can you folks please trim your replies? Finding content in the middle of > quoted nonsense becomes harder with every mail in this thread. > > On Tue, Nov 30 2021 at 08:28, Paul E. McKenney wrote: > > On Tue, Nov 30, 2021 at 11:02:56PM +0800, Feng Tang wrote: > >> For this case, I don't have access to the HW and only have the > >> dmesg log, from which it seems the watchdog timer has been postponed > >> a very long time from running. > > > > Thank you for the analysis! > > > > One approach to handle this situation would be to avoid checking for > > clock skew if the time since the last watchdog read was more than (say) > > twice the desired watchdog spacing. This does leave open the question of > > exactly which clocksource to use to measure the time between successive > > clocksource reads. My thought is to check this only once upon entry to > > the handler and to use the designated-good clocksource. > > > > Does that make sense, or would something else work better? > > Seriously. Jiffies is not usable as watchdog simply because lost ticks > cannot be compensated and you cannot use TSC to bridge them because you > are not trusting TSC. This is simply a circulus vitiosus.
OK, HPET or nothing, then.
> We really need to remove the watchdog requirement for modern hardware. > Let me stare at those patches and get them merged.
You are more trusting of modern hardware than I am, but for all I know, maybe rightfully so. ;-)
Thanx, Paul
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