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tick: Detect and fix jiffies update stall
commit a1ff03cd6f
upstream.
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>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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2 changed files with 21 additions and 0 deletions
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@ -148,6 +148,8 @@ static ktime_t tick_init_jiffy_update(void)
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return period;
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return period;
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}
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}
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#define MAX_STALLED_JIFFIES 5
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static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
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static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
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{
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{
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int cpu = smp_processor_id();
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int cpu = smp_processor_id();
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@ -175,6 +177,21 @@ static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
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if (tick_do_timer_cpu == cpu)
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if (tick_do_timer_cpu == cpu)
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tick_do_update_jiffies64(now);
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tick_do_update_jiffies64(now);
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/*
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* If jiffies update stalled for too long (timekeeper in stop_machine()
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* or VMEXIT'ed for several msecs), force an update.
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*/
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if (ts->last_tick_jiffies != jiffies) {
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ts->stalled_jiffies = 0;
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ts->last_tick_jiffies = READ_ONCE(jiffies);
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} else {
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if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) {
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tick_do_update_jiffies64(now);
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ts->stalled_jiffies = 0;
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ts->last_tick_jiffies = READ_ONCE(jiffies);
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}
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}
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if (ts->inidle)
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if (ts->inidle)
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ts->got_idle_tick = 1;
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ts->got_idle_tick = 1;
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}
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}
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@ -49,6 +49,8 @@ enum tick_nohz_mode {
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* @timer_expires_base: Base time clock monotonic for @timer_expires
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* @timer_expires_base: Base time clock monotonic for @timer_expires
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* @next_timer: Expiry time of next expiring timer for debugging purpose only
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* @next_timer: Expiry time of next expiring timer for debugging purpose only
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* @tick_dep_mask: Tick dependency mask - is set, if someone needs the tick
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* @tick_dep_mask: Tick dependency mask - is set, if someone needs the tick
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* @last_tick_jiffies: Value of jiffies seen on last tick
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* @stalled_jiffies: Number of stalled jiffies detected across ticks
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*/
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*/
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struct tick_sched {
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struct tick_sched {
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struct hrtimer sched_timer;
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struct hrtimer sched_timer;
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@ -77,6 +79,8 @@ struct tick_sched {
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u64 next_timer;
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u64 next_timer;
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ktime_t idle_expires;
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ktime_t idle_expires;
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atomic_t tick_dep_mask;
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atomic_t tick_dep_mask;
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unsigned long last_tick_jiffies;
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unsigned int stalled_jiffies;
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};
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};
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extern struct tick_sched *tick_get_tick_sched(int cpu);
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extern struct tick_sched *tick_get_tick_sched(int cpu);
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