Re: [PATCH] x86/tsc: mark tsc reliable for qualified platforms

[Thomas Gleixner]

On Tue, Mar 02 2021 at 10:52, Feng Tang wrote:
> There are cases that tsc clocksource are wrongly judged as unstable by
> clocksource watchdogs like hpet, acpi_pm or 'refined-jiffies'. While
> there is hardly a general reliable way to check the validity of a
> watchdog, and to protect the innocent tsc, Thomas Gleixner proposed [1]:
>
> "I'm inclined to lift that requirement when the CPU has:
>
>     1) X86_FEATURE_CONSTANT_TSC
>     2) X86_FEATURE_NONSTOP_TSC
>     3) X86_FEATURE_NONSTOP_TSC_S3
>     4) X86_FEATURE_TSC_ADJUST
>     5) At max. 4 sockets
>
>  After two decades of horrors we're finally at a point where TSC seems
>  to be halfway reliable and less abused by BIOS tinkerers. TSC_ADJUST
>  was really key as we can now detect even small modifications reliably
>  and the important point is that we can cure them as well (not pretty
>  but better than all other options)."
>
> So implement it with slight change as discussed in the thread, and be
> more defensive to use maxim of 2 sockets.

Can you please explain the slight change in the changelog?

Thanks,

        tglx