linux-kernel - Re: [RFC PATCH v4 17/21] x86/tsc: Switch to perf-based hardlockup detector if TSC become unstable

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Date:   Fri, 7 Jun 2019 07:14:16 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Ashok Raj <ashok.raj@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Andi Kleen <andi.kleen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org,
        Ricardo Neri <ricardo.neri@...el.com>
Subject: Re: [RFC PATCH v4 17/21] x86/tsc: Switch to perf-based hardlockup
 detector if TSC become unstable

On Thu, Jun 06, 2019 at 05:35:51PM -0700, Stephane Eranian wrote:
> Hi Ricardo,

Hi Stephane,

> Thanks for your contribution here. It is very important to move the
> watchdog out of the PMU wherever possible.

Indeed, using the PMU for the hardlockup detector is still the default
option. This patch series proposes a new kernel command line to switch
to use the HPET.

> 
> On Thu, May 23, 2019 at 6:17 PM Ricardo Neri
> <ricardo.neri-calderon@...ux.intel.com> wrote:
> >
> > The HPET-based hardlockup detector relies on the TSC to determine if an
> > observed NMI interrupt was originated by HPET timer. Hence, this detector
> > can no longer be used with an unstable TSC.
> >
> > In such case, permanently stop the HPET-based hardlockup detector and
> > start the perf-based detector.
> >
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> > ---
> >  arch/x86/include/asm/hpet.h    | 2 ++
> >  arch/x86/kernel/tsc.c          | 2 ++
> >  arch/x86/kernel/watchdog_hld.c | 7 +++++++
> >  3 files changed, 11 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h
> > index fd99f2390714..a82cbe17479d 100644
> > --- a/arch/x86/include/asm/hpet.h
> > +++ b/arch/x86/include/asm/hpet.h
> > @@ -128,6 +128,7 @@ extern int hardlockup_detector_hpet_init(void);
> >  extern void hardlockup_detector_hpet_stop(void);
> >  extern void hardlockup_detector_hpet_enable(unsigned int cpu);
> >  extern void hardlockup_detector_hpet_disable(unsigned int cpu);
> > +extern void hardlockup_detector_switch_to_perf(void);
> >  #else
> >  static inline struct hpet_hld_data *hpet_hardlockup_detector_assign_timer(void)
> >  { return NULL; }
> > @@ -136,6 +137,7 @@ static inline int hardlockup_detector_hpet_init(void)
> >  static inline void hardlockup_detector_hpet_stop(void) {}
> >  static inline void hardlockup_detector_hpet_enable(unsigned int cpu) {}
> >  static inline void hardlockup_detector_hpet_disable(unsigned int cpu) {}
> > +static void harrdlockup_detector_switch_to_perf(void) {}
> >  #endif /* CONFIG_X86_HARDLOCKUP_DETECTOR_HPET */
> >
> This does not compile for me when CONFIG_X86_HARDLOCKUP_DETECTOR_HPET
> is not enabled.
> because:
>    1- you have a typo on the function name
>     2- you are missing the inline keyword

I am sorry. This was an oversight on my side. I have corrected this in
preparation for a v5.

Thanks and BR,
Ricardo