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tick: Detect and fix jiffies update stall

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On some rare cases, the timekeeper CPU may be delaying its jiffies
update duty for a while. Known causes include:

* The timekeeper is waiting on stop_machine in a MULTI_STOP_DISABLE_IRQ
  or MULTI_STOP_RUN state. Disabled interrupts prevent from timekeeping
  updates while waiting for the target CPU to complete its
  stop_machine() callback.

* The timekeeper vcpu has VMEXIT'ed for a long while due to some overload
  on the host.

Detect and fix these situations with emergency timekeeping catchups.

Original-patch-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Frederic Weisbecker 2022-02-02 01:01:07 +01:00
parent 58dedf0a47
commit a1ff03cd6f
2 changed files with 21 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

17
kernel/time/tick-sched.c
View file

@ -169,6 +169,8 @@ static ktime_t tick_init_jiffy_update(void)
return period; return period;
} }
#define MAX_STALLED_JIFFIES 5
static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now) static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
{ {
int cpu = smp_processor_id(); int cpu = smp_processor_id();
@ -196,6 +198,21 @@ static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
if (tick_do_timer_cpu == cpu) if (tick_do_timer_cpu == cpu)
tick_do_update_jiffies64(now); tick_do_update_jiffies64(now);
/*
* If jiffies update stalled for too long (timekeeper in stop_machine()
* or VMEXIT'ed for several msecs), force an update.
*/
if (ts->last_tick_jiffies != jiffies) {
ts->stalled_jiffies = 0;
ts->last_tick_jiffies = READ_ONCE(jiffies);
} else {
if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) {
tick_do_update_jiffies64(now);
ts->stalled_jiffies = 0;
ts->last_tick_jiffies = READ_ONCE(jiffies);
}
}
if (ts->inidle) if (ts->inidle)
ts->got_idle_tick = 1; ts->got_idle_tick = 1;
} }

4
kernel/time/tick-sched.h
View file

@ -49,6 +49,8 @@ enum tick_nohz_mode {
* @timer_expires_base: Base time clock monotonic for @timer_expires * @timer_expires_base: Base time clock monotonic for @timer_expires
* @next_timer: Expiry time of next expiring timer for debugging purpose only * @next_timer: Expiry time of next expiring timer for debugging purpose only
* @tick_dep_mask: Tick dependency mask - is set, if someone needs the tick * @tick_dep_mask: Tick dependency mask - is set, if someone needs the tick
* @last_tick_jiffies: Value of jiffies seen on last tick
* @stalled_jiffies: Number of stalled jiffies detected across ticks
*/ */
struct tick_sched { struct tick_sched {
struct hrtimer sched_timer; struct hrtimer sched_timer;
@ -77,6 +79,8 @@ struct tick_sched {
u64 next_timer; u64 next_timer;
ktime_t idle_expires; ktime_t idle_expires;
atomic_t tick_dep_mask; atomic_t tick_dep_mask;
unsigned long last_tick_jiffies;
unsigned int stalled_jiffies;
}; };
extern struct tick_sched *tick_get_tick_sched(int cpu); extern struct tick_sched *tick_get_tick_sched(int cpu);