Re: [PATCH clocksource 1/2] clocksource: Add comments to classify bogus measurements

[Waiman Long <longman@redhat.com>]

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>