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Date:   Thu, 3 Nov 2022 13:47:41 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Waiman Long <longman@redhat.com>
Cc:     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, feng.tang@intel.com,
        zhengjun.xing@intel.com, John Stultz <jstultz@google.com>
Subject: Re: [PATCH clocksource 1/2] clocksource: Add comments to classify
 bogus measurements
Message-ID: <20221103204741.GE5600@paulmck-ThinkPad-P17-Gen-1>
Reply-To: paulmck@kernel.org
References: <20221102184001.GA1306489@paulmck-ThinkPad-P17-Gen-1>
 <20221102184009.1306751-1-paulmck@kernel.org>
 <7339298b-1156-2d24-7dd9-e7fae690773c@redhat.com>
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On Wed, Nov 02, 2022 at 10:23:25PM -0400, Waiman Long wrote:
> On 11/2/22 14:40, Paul E. McKenney wrote:
> > An extremely busy system can delay the clocksource watchdog, so that
> > the corresponding too-long bogus-measurement error does not necessarily
> > imply an error in the system.  However, a too-short bogus-measurement
> > error likely indicates a bug in hardware, firmware or software.
> > 
> > Therefore, add comments clarifying these bogus-measurement pr_warn()s.
> > 
> > Reported-by: Feng Tang <feng.tang@intel.com>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > Cc: John Stultz <jstultz@google.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Stephen Boyd <sboyd@kernel.org>
> > Cc: Feng Tang <feng.tang@intel.com>
> > Cc: Waiman Long <longman@redhat.com>
> > ---
> >   kernel/time/clocksource.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> > index dcaf38c062161..3f5317faf891f 100644
> > --- a/kernel/time/clocksource.c
> > +++ b/kernel/time/clocksource.c
> > @@ -443,10 +443,12 @@ static void clocksource_watchdog(struct timer_list *unused)
> >   		/* Check for bogus measurements. */
> >   		wdi = jiffies_to_nsecs(WATCHDOG_INTERVAL);
> >   		if (wd_nsec < (wdi >> 2)) {
> > +			/* This usually indicates broken timer code or hardware. */
> >   			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)) {
> > +			/* This can happen on busy systems, which can delay the watchdog. */
> >   			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;
> >   		}
> 
> Looks good.
> 
> Reviewed-by: Waiman Long <longman@redhat.com>

Applied, thank you!

							Thanx, Paul