linux-kernel - Re: [PATCH v14 08/25] x86/kvmclock: Avoid TSC recalibration

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Message-ID: <CAGM2reY_uf2C2ox4kEmTSuSDm1PbXazTYHuT4shYiZ3WK3vTdQ@mail.gmail.com>
Date:   Wed, 18 Jul 2018 09:33:36 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     pbonzini@...hat.com
Cc:     Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        John Stultz <john.stultz@...aro.org>, sboyd@...eaurora.org,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        douly.fnst@...fujitsu.com, peterz@...radead.org, prarit@...hat.com,
        feng.tang@...el.com, Petr Mladek <pmladek@...e.com>,
        gnomes@...rguk.ukuu.org.uk, linux-s390@...r.kernel.org,
        boris.ostrovsky@...cle.com, jgross@...e.com
Subject: Re: [PATCH v14 08/25] x86/kvmclock: Avoid TSC recalibration

Thank you Paolo for letting me know. I will remove this patch from the
series, or it can be removed by whomever adds the series.

Thank you,
Pavel
On Wed, Jul 18, 2018 at 7:14 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 18/07/2018 04:21, Pavel Tatashin wrote:
> > From: Peter Zijlstra <peterz@...radead.org>
> >
> > If the host gives us a TSC rate, assume it is good and don't try and
> > recalibrate things against virtual timer hardware.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
> > ---
> >  arch/x86/kernel/kvmclock.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> > index ed170171fe49..da0ede8ac8f6 100644
> > --- a/arch/x86/kernel/kvmclock.c
> > +++ b/arch/x86/kernel/kvmclock.c
> > @@ -141,7 +141,16 @@ static inline void kvm_sched_clock_init(bool stable)
> >   */
> >  static unsigned long kvm_get_tsc_khz(void)
> >  {
> > -     return pvclock_tsc_khz(this_cpu_pvti());
> > +     unsigned long tsc_khz = pvclock_tsc_khz(this_cpu_pvti());
> > +
> > +     /*
> > +      * TSC frequency is reported by the host; calibration against (virtual)
> > +      * HPET/PM-timer in a guest is dodgy and pointless since the host
> > +      * already did it for us where required.
> > +      */
> > +     setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
> > +
> > +     return tsc_khz;
> >  }
> >
> >  static void kvm_get_preset_lpj(void)
> >
>
> This patch (really a similar one) has just been sent to Linus.
>
> Paolo