Re: [PATCH] x86/intel: Disable HPET on another Intel Coffee Lake platform

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On Fri, Sep 17, 2021 at 11:11:49AM +0200, Peter Zijlstra wrote:
> On Thu, Sep 16, 2021 at 10:07:07AM -0500, Bjorn Helgaas wrote:
> > This seems to be an ongoing issue, not just a point defect in a single
> > product, and I really hate the onesy-twosy nature of this.  Is there
> > really no way to detect this issue automatically or fix whatever Linux
> > bug makes us trip over this?  I am no clock expert, so I have
> > absolutely no idea whether this is possible.
> 
> X86 is gifted with the grant total of _0_ reliable clocks. Given no
> accurate time, it is impossible to tell which one of them is broken
> worst. Although I suppose we could attempt to synchronize against the
> PMU or MPERF..
> 
> We could possibly disable the tsc watchdog for
> X86_FEATURE_TSC_KNOWN_FREQ && X86_FEATURE_TSC_ADJUST I suppose.
> 
> And then have people with 'creative' BIOS get to keep the pieces.

Alternatively, we can change what the TSC watchdog does for
X86_FEATURE_TSC_ADJUST machines. Instead of checking time against HPET
it can check if TSC_ADJUST changes. That should make it more resillient
vs HPET time itself being off.



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