Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 15 Jan 2020 12:15:36 -0800 | Subject | Re: [PATCH] x86/tsc: Add tsc_guess flag disabling CPUID.16h use for tsc calibration |
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On Tue, Jan 14, 2020 at 6:39 AM Krzysztof Piecuch <piecuch@protonmail.com> wrote: > > Changing base clock frequency directly impacts tsc hz but not CPUID.16h > values. An overclocked CPU supporting CPUID.16h and partial CPUID.15h > support will set tsc hz according to "best guess" given by CPUID.16h > relying on tsc_refine_calibration_work to give better numbers later. > tsc_refine_calibration_work will refuse to do its work when the outcome is > off the early tsc hz value by more than 1% which is certain to happen on an > overclocked system. > > Signed-off-by: Krzysztof Piecuch <piecuch@protonmail.com> > --- > Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ > arch/x86/kernel/tsc.c | 12 ++++++++++-- > 2 files changed, 16 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index ade4e6ec23e0..54ae9e153a19 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -4905,6 +4905,12 @@ > interruptions from clocksource watchdog are not > acceptable). > > + tsc_guess= [X86,INTEL] Don't use data provided by CPUID.16h during > + early tsc calibration. Disabling this may be useful for > + CPUs with altered base clocks. > + Format: <bool> (1/Y/y=enable, 0/N/n=disable) > + default: enabled
This has more negatives than makes sense. I also think it's wrong. How about:
tsc_guess= ... Use data provided by CPUID.16h ...
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