Messages in this thread | | | Date | Wed, 1 Dec 2021 09:26:55 +0800 | From | Feng Tang <> | 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 03:37:26PM -0800, Paul E. McKenney wrote: > 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? ;-)
For HPET, it's a long story :) Back in 2012 or so, the HPET on Baytrail platform has a new feature that it will stop counting in PC10 (a cpuidle state), which prevent it to be a clocksource, and we have to disable HPET explicitly for that platform. Since then, some new platforms also have the same feature, and their HPET got disabled too.
Thanks, Feng
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