[PATCH clocksource 1/2] clocksource: Add comments to classify bogus measurements
From: Paul E. McKenney
Date: Wed Nov 02 2022 - 14:40:19 EST
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@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: John Stultz <jstultz@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
Cc: Feng Tang <feng.tang@xxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
---
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;
}
--
2.31.1.189.g2e36527f23