From: "Paul E. McKenney" <paulmck@kernel.org>
To: tglx@linutronix.de
Cc: 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,
"Paul E. McKenney" <paulmck@kernel.org>,
Chris Mason <clm@meta.com>, John Stultz <jstultz@google.com>,
Waiman Long <longman@redhat.com>
Subject: [PATCH clocksource 1/3] clocksource: Reject bogus watchdog clocksource measurements
Date: Mon, 14 Nov 2022 15:28:24 -0800 [thread overview]
Message-ID: <20221114232827.835599-1-paulmck@kernel.org> (raw)
In-Reply-To: <20221114232807.GA834337@paulmck-ThinkPad-P17-Gen-1>
One remaining clocksource-skew issue involves extreme CPU overcommit,
which can cause the clocksource watchdog measurements to be delayed by
tens of seconds. This in turn means that a clock-skew criterion that
is appropriate for a 500-millisecond interval will instead give lots of
false positives.
Therefore, check for the watchdog clocksource reporting much larger or
much less than the time specified by WATCHDOG_INTERVAL. In these cases,
print a pr_warn() warning and refrain from marking the clocksource under
test as being unstable.
Reported-by: Chris Mason <clm@meta.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 | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 8058bec87acee..dcaf38c062161 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -386,7 +386,7 @@ EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
static void clocksource_watchdog(struct timer_list *unused)
{
- u64 csnow, wdnow, cslast, wdlast, delta;
+ u64 csnow, wdnow, cslast, wdlast, delta, wdi;
int next_cpu, reset_pending;
int64_t wd_nsec, cs_nsec;
struct clocksource *cs;
@@ -440,6 +440,17 @@ static void clocksource_watchdog(struct timer_list *unused)
if (atomic_read(&watchdog_reset_pending))
continue;
+ /* 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;
+ }
+
/* Check the deviation from the watchdog clocksource. */
md = cs->uncertainty_margin + watchdog->uncertainty_margin;
if (abs(cs_nsec - wd_nsec) > md) {
--
2.31.1.189.g2e36527f23
next prev parent reply other threads:[~2022-11-14 23:28 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 ` Paul E. McKenney [this message]
2022-11-17 21:57 ` [PATCH clocksource 1/3] clocksource: " 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
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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