Re: [PATCH RFC] x86/tsc: Make recalibration default on for TSC_KNOWN_FREQ cases

[Thomas Gleixner]

On Mon, May 22 2023 at 11:30, Feng Tang wrote:
> Commit a7ec817d5542 ("x86/tsc: Add option to force frequency
> recalibration with HW timer") was added to handle cases that the
> firmware has bug and provides a wrong TSC frequency number, and it
> is optional given that this kind of firmware issue rarely happens
> (Paul reported once [1]).
>
> But Rui reported that some Sapphire Rapids platform met this issue
> again recently, and as firmware is also a kind of 'software' which
> can't be bug free, make the recalibration default on. When the
> values from firmware and HW timer's calibration have big gap,
> raise a warning and let vendor to check which side is broken.

Sure firmware can have bugs, but if firmware validation does not even
catch such a trivially to detect bug, then their validation is nothing
else than rubber stamping. Seriously.

Are any of these affected platforms shipping already or is this just
Intel internal muck?

> One downside is, many VMs also has X86_FEATURE_TSC_KNOWN_FREQ set,
> and they will also do this recalibration.

It's also pointless for those SoCs which lack legacy hardware.

So why do you force this on everyone?

Thanks,

        tglx