Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH v3 2/2] x86/tsc: skip tsc watchdog checking for qualified platforms | Date | Tue, 30 Nov 2021 22:55:45 +0100 |
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On Tue, Nov 30 2021 at 12:47, Paul E. McKenney wrote: > On Tue, Nov 30, 2021 at 09:39:32PM +0100, Thomas Gleixner wrote: >> 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.
Older machines also have pm_timer. But those beasts seem to have lost that too.
>> 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. ;-)
Well, I rather put a bet on the hardware, which has become reasonable over the last decade, than on trying to solve a circular dependency problem with tons of heuristics which won't ever work correctly.
TSC_ADJUST is a reasonable safety net and since its invention the amount of BIOS wreckage has been massively reduced. Seems the nastigram in dmesg when detecting a change in TSC_ADJUST had an effect or maybe Microsoft enforces a tinkerfree TSC by now and we get the benefit. :)
I still wish to have a knob to lock down TSC to read only, but that's probably for christmas 2030 or later. :)
Thanks,
tglx
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