linux-kernel - [PATCH v2] Clocksource:Avoid misjudgment of clocksource

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Message-Id: <20211009104240.46406-1-yanghui.def@bytedance.com>
Date:   Sat,  9 Oct 2021 18:42:40 +0800
From:   yanghui <yanghui.def@...edance.com>
To:     john.stultz@...aro.org
Cc:     tglx@...utronix.de, sboyd@...nel.org, linux-kernel@...r.kernel.org,
        yanghui <yanghui.def@...edance.com>
Subject: [PATCH v2] Clocksource:Avoid misjudgment of clocksource

Function clocksource_watchdog() is executed every WATCHDOG_INTERVAL(0.5s)
by Timer. But sometimes system is very busy and the Timer cannot be
executed in 0.5sec. For example,if clocksource_watchdog be executed
after 10sec, the calculated value of abs(cs_nsec - wd_nsec) will
be magnified. Then the current clocksource will be misjudged as
unstable. So we add conditions to prevent the clocksource from
being misjudged.

Signed-off-by: yanghui <yanghui.def@...edance.com>
---
Change in v2:
    Remove the check on cs_nsec.

 kernel/time/clocksource.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index b8a14d2fb5ba..c35bb708e030 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -136,8 +136,10 @@ static void __clocksource_change_rating(struct clocksource *cs, int rating);
 
 /*
  * Interval: 0.5sec.
+ * MaxInterval: 1s.
  */
 #define WATCHDOG_INTERVAL (HZ >> 1)
+#define WATCHDOG_MAX_INTERVAL_NS (NSEC_PER_SEC)
 
 static void clocksource_watchdog_work(struct work_struct *work)
 {
@@ -404,7 +406,8 @@ static void clocksource_watchdog(struct timer_list *unused)
 
 		/* Check the deviation from the watchdog clocksource. */
 		md = cs->uncertainty_margin + watchdog->uncertainty_margin;
-		if (abs(cs_nsec - wd_nsec) > md) {
+		if ((abs(cs_nsec - wd_nsec) > md) &&
+		    wd_nsec < WATCHDOG_MAX_INTERVAL_NS) {
 			pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
 				smp_processor_id(), cs->name);
 			pr_warn("                      '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
-- 
2.20.1