On Tue, Sep 21 2021 at 20:05, Rafael J. Wysocki wrote:

On 9/19/2021 2:14 AM, Thomas Gleixner wrote:

quoted

What's the proper way to figure out whether PC10 is supported?

I can't say without research.  I think it'd be sufficient to check if 
C10 is supported, because asking for it is the only way to get PC10.

Do we have a common function for that or do I need to implement the
gazillionst CPUID query for that?

However, even if it is supported, the problem is not there until the 
kernel asks for C10.  So instead, I'd disable the TSC watchdog on the 
first attempt to ask the processor for C10 from the cpuidle code and I'd 
do that from the relevant drivers (intel_idle and ACPI idle).

There would be no TSC watchdog for the C10 users, but wouldn't that be a 
fair game?

Not really because that makes any other HPET usage broken as well and we
can't pull the rug under that. So we are better off to disable it
upfront.

Thanks,

        tglx