From: "Paul E. McKenney" <paulmck@kernel.org>
To: Feng Tang <feng.tang@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, john.stultz@linaro.org,
sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com,
maz@kernel.org, kernel-team@meta.com, neeraju@codeaurora.org,
ak@linux.intel.com, zhengjun.xing@intel.com,
Chris Mason <clm@meta.com>, John Stultz <jstultz@google.com>,
Waiman Long <longman@redhat.com>
Subject: Re: [PATCH clocksource 1/3] clocksource: Reject bogus watchdog clocksource measurements
Date: Mon, 21 Nov 2022 07:21:07 -0800 [thread overview]
Message-ID: <20221121152107.GI4001@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <Y3rMc2VbgVLHN9db@feng-clx>
On Mon, Nov 21, 2022 at 08:55:15AM +0800, Feng Tang wrote:
> On Thu, Nov 17, 2022 at 03:09:10PM -0800, Paul E. McKenney wrote:
> > On Thu, Nov 17, 2022 at 10:57:34PM +0100, Thomas Gleixner wrote:
> > > Paul!
> > >
> > > On Mon, Nov 14 2022 at 15:28, Paul E. McKenney wrote:
> > > >
> > > > + /* Check for bogus measurements. */
> > > > + wdi = jiffies_to_nsecs(WATCHDOG_INTERVAL);
> > > > + if (wd_nsec < (wdi >> 2)) {
> > > > + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced only %lld ns during %d-jiffy time interval, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL);
> > > > + continue;
> > > > + }
> > > > + if (wd_nsec > (wdi << 2)) {
> > > > + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced an excessive %lld ns during %d-jiffy time interval, probable CPU overutilization, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL);
> > > > + continue;
> > > > + }
> > >
> > > This is really getting ridiculous.
> >
> > I have absolutely no argument with this statement, and going back a
> > long time. ;-)
> >
> > But the set of systems that caused me to send this turned out to have
> > real divergence between HPET and TSC, and 40 milliseconds per second of
> > divergence at that. So not only do you hate this series, but it is also
> > the case that this series doesn't help with the problem at hand.
>
> The drift is about 4% which is quite big. It seems that this is
> either problem of HPET/TSC's hardware/firmware, or the problem of
> frequency calibration for HPET/TSC. TSC calibration is complex,
> as it could be done from different methods depending on hardware
> and firmware, could you share the kernel boot log related with
> tsc/hpet and clocksource?
Thank you for looking into this!
Knucklehead here failed to save away the dmesg. Let me see what
I can drum up.
> Also if your platform has acpi PM_TIMER, you may try "nohpet"
> to use PM_TIMER instead of HPET and check if there is also big
> drift between TSC and PM_TIMER.
Let me see about giving this a go, and again, thank you!
Thanx, Paul
next prev parent reply other threads:[~2022-11-21 15:22 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-14 23:28 [PATCH clocksource 0/3] Reject bogus watchdog clocksource measurements Paul E. McKenney
2022-11-14 23:28 ` [PATCH clocksource 1/3] clocksource: " Paul E. McKenney
2022-11-17 21:57 ` Thomas Gleixner
2022-11-17 23:09 ` Paul E. McKenney
2022-11-21 0:55 ` Feng Tang
2022-11-21 15:21 ` Paul E. McKenney [this message]
2022-11-21 18:14 ` Paul E. McKenney
2022-11-22 15:55 ` Feng Tang
2022-11-22 22:07 ` Paul E. McKenney
2022-11-23 2:36 ` Feng Tang
2022-11-23 21:23 ` Paul E. McKenney
2022-11-28 2:15 ` Feng Tang
2022-11-29 19:29 ` Paul E. McKenney
2022-11-30 1:38 ` Feng Tang
2022-11-30 4:12 ` Paul E. McKenney
2022-11-30 4:49 ` Feng Tang
2022-11-30 5:16 ` Paul E. McKenney
2022-11-30 5:35 ` Feng Tang
2022-11-30 5:50 ` Paul E. McKenney
2022-11-30 6:00 ` Feng Tang
2022-12-01 17:24 ` Paul E. McKenney
2022-12-02 1:10 ` Feng Tang
2022-12-02 1:44 ` Paul E. McKenney
2022-12-02 2:02 ` Feng Tang
2022-12-02 22:24 ` Paul E. McKenney
2022-12-03 2:51 ` Feng Tang
2022-11-14 23:28 ` [PATCH clocksource 2/3] clocksource: Add comments to classify bogus measurements Paul E. McKenney
2022-11-14 23:28 ` [PATCH clocksource 3/3] clocksource: Exponential backoff for load-induced bogus watchdog reads Paul E. McKenney
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