linux-kernel - Re: [PATCH v5 13/14] x86/tsc: Mark Secure TSC as reliable clocksource

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Message-ID: <20231106130356.5mppou4pzxmldy22@box.shutemov.name>
Date:   Mon, 6 Nov 2023 16:03:56 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     "Nikunj A. Dadhania" <nikunj@....com>
Cc:     seanjc@...gle.com, pbonzini@...hat.com,
        Dave Hansen <dave.hansen@...el.com>,
        linux-kernel@...r.kernel.org, thomas.lendacky@....com,
        x86@...nel.org, kvm@...r.kernel.org, bp@...en8.de,
        mingo@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com,
        dionnaglaze@...gle.com, pgonda@...gle.com
Subject: Re: [PATCH v5 13/14] x86/tsc: Mark Secure TSC as reliable clocksource

On Mon, Nov 06, 2023 at 05:23:44PM +0530, Nikunj A. Dadhania wrote:
> > Maybe kvmclock rating has to be even lower after detecting sane TSC?
> 
> If I set kvmclock rating to 298, I do see exact behavior as you have seen on the bare-metal.
> 
> [    0.004520] clocksource: clocksource_enqueue: name kvm-clock rating 298
> [...]
> [    1.827422] clocksource: clocksource_enqueue: name tsc-early rating 299
> [...]
> [    3.485059] clocksource: Switched to clocksource tsc-early
> [...]
> [    3.623625] clocksource: clocksource_enqueue: name tsc rating 300
> [    3.628954] clocksource: Switched to clocksource tsc

This looks more reasonable to me. But I don't really understand
timekeeping. It would be nice to hear from someone who knows what he
saying.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov