linux-kernel - Re: [PATCH] x86/tsc: Add tsc_tuned_baseclk flag disabling CPUID.16h use for tsc calibration

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Date:   Fri, 17 Jan 2020 08:37:12 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Krzysztof Piecuch <piecuch@...tonmail.com>
Cc:     "corbet@....net" <corbet@....net>,
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Subject: Re: [PATCH] x86/tsc: Add tsc_tuned_baseclk flag disabling CPUID.16h use for tsc calibration



> On Jan 17, 2020, at 7:21 AM, Krzysztof Piecuch <piecuch@...tonmail.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.
> 

Wouldn’t it be better to have an option tsc_max_refinement= to increase the 1%?