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

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