Messages in this thread | | | Date | Tue, 30 Nov 2021 15:37:26 -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 Wed, Dec 01, 2021 at 12:19:43AM +0100, Thomas Gleixner wrote: > On Tue, Nov 30 2021 at 14:48, Paul E. McKenney wrote: > > On Tue, Nov 30, 2021 at 10:55:45PM +0100, Thomas Gleixner wrote: > >> > OK, HPET or nothing, then. > >> > >> Older machines also have pm_timer. But those beasts seem to have lost > >> that too. > > > > I suppose that one way of avoiding clock-skew messages is to have only > > one clock. > > Indeed. It's a complete mystery why it takes ages to implement reliable > clocks in hardware.
That one is easy. It is because the previous clocksource watchdog was too lenient. ;-)
(Sorry, couldn't resist...)
> >> >> 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. > > > > Use of HPET to check the interval length would not be circular, right? > > As long as the HPET works reliably :)
Is it also a complete mystery why clocksources previously deemed reliable no longer work reliably? ;-)
> >> 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. :) > > > > Indeed. How would BIOS writers hide their SMI handlers? :-/ > > TSC_ADJUST already ruined that party.
Give the BIOS writers time, they will figure something else out. :-(
Thanx, Paul
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