1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
4 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
5 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner
7 * No idle tick implementation for low and high resolution timers
9 * Started by: Thomas Gleixner and Ingo Molnar
11 #include <linux/cpu.h>
12 #include <linux/err.h>
13 #include <linux/hrtimer.h>
14 #include <linux/interrupt.h>
15 #include <linux/kernel_stat.h>
16 #include <linux/percpu.h>
17 #include <linux/nmi.h>
18 #include <linux/profile.h>
19 #include <linux/sched/signal.h>
20 #include <linux/sched/clock.h>
21 #include <linux/sched/stat.h>
22 #include <linux/sched/nohz.h>
23 #include <linux/sched/loadavg.h>
24 #include <linux/module.h>
25 #include <linux/irq_work.h>
26 #include <linux/posix-timers.h>
27 #include <linux/context_tracking.h>
30 #include <asm/irq_regs.h>
32 #include "tick-internal.h"
34 #include <trace/events/timer.h>
37 * Per-CPU nohz control structure
39 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
41 struct tick_sched *tick_get_tick_sched(int cpu)
43 return &per_cpu(tick_cpu_sched, cpu);
46 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
48 * The time, when the last jiffy update happened. Write access must hold
49 * jiffies_lock and jiffies_seq. tick_nohz_next_event() needs to get a
50 * consistent view of jiffies and last_jiffies_update.
52 static ktime_t last_jiffies_update;
55 * Must be called with interrupts disabled !
57 static void tick_do_update_jiffies64(ktime_t now)
59 unsigned long ticks = 1;
63 * 64bit can do a quick check without holding jiffies lock and
64 * without looking at the sequence count. The smp_load_acquire()
65 * pairs with the update done later in this function.
67 * 32bit cannot do that because the store of tick_next_period
68 * consists of two 32bit stores and the first store could move it
69 * to a random point in the future.
71 if (IS_ENABLED(CONFIG_64BIT)) {
72 if (ktime_before(now, smp_load_acquire(&tick_next_period)))
78 * Avoid contention on jiffies_lock and protect the quick
79 * check with the sequence count.
82 seq = read_seqcount_begin(&jiffies_seq);
83 nextp = tick_next_period;
84 } while (read_seqcount_retry(&jiffies_seq, seq));
86 if (ktime_before(now, nextp))
90 /* Quick check failed, i.e. update is required. */
91 raw_spin_lock(&jiffies_lock);
93 * Reevaluate with the lock held. Another CPU might have done the
96 if (ktime_before(now, tick_next_period)) {
97 raw_spin_unlock(&jiffies_lock);
101 write_seqcount_begin(&jiffies_seq);
103 delta = ktime_sub(now, tick_next_period);
104 if (unlikely(delta >= TICK_NSEC)) {
105 /* Slow path for long idle sleep times */
106 s64 incr = TICK_NSEC;
108 ticks += ktime_divns(delta, incr);
110 last_jiffies_update = ktime_add_ns(last_jiffies_update,
113 last_jiffies_update = ktime_add_ns(last_jiffies_update,
117 /* Advance jiffies to complete the jiffies_seq protected job */
121 * Keep the tick_next_period variable up to date.
123 nextp = ktime_add_ns(last_jiffies_update, TICK_NSEC);
125 if (IS_ENABLED(CONFIG_64BIT)) {
127 * Pairs with smp_load_acquire() in the lockless quick
128 * check above and ensures that the update to jiffies_64 is
129 * not reordered vs. the store to tick_next_period, neither
130 * by the compiler nor by the CPU.
132 smp_store_release(&tick_next_period, nextp);
135 * A plain store is good enough on 32bit as the quick check
136 * above is protected by the sequence count.
138 tick_next_period = nextp;
142 * Release the sequence count. calc_global_load() below is not
143 * protected by it, but jiffies_lock needs to be held to prevent
144 * concurrent invocations.
146 write_seqcount_end(&jiffies_seq);
150 raw_spin_unlock(&jiffies_lock);
155 * Initialize and return retrieve the jiffies update.
157 static ktime_t tick_init_jiffy_update(void)
161 raw_spin_lock(&jiffies_lock);
162 write_seqcount_begin(&jiffies_seq);
163 /* Did we start the jiffies update yet ? */
164 if (last_jiffies_update == 0) {
168 * Ensure that the tick is aligned to a multiple of
171 div_u64_rem(tick_next_period, TICK_NSEC, &rem);
173 tick_next_period += TICK_NSEC - rem;
175 last_jiffies_update = tick_next_period;
177 period = last_jiffies_update;
178 write_seqcount_end(&jiffies_seq);
179 raw_spin_unlock(&jiffies_lock);
183 #define MAX_STALLED_JIFFIES 5
185 static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
187 int cpu = smp_processor_id();
189 #ifdef CONFIG_NO_HZ_COMMON
191 * Check if the do_timer duty was dropped. We don't care about
192 * concurrency: This happens only when the CPU in charge went
193 * into a long sleep. If two CPUs happen to assign themselves to
194 * this duty, then the jiffies update is still serialized by
197 * If nohz_full is enabled, this should not happen because the
198 * tick_do_timer_cpu never relinquishes.
200 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) {
201 #ifdef CONFIG_NO_HZ_FULL
202 WARN_ON_ONCE(tick_nohz_full_running);
204 tick_do_timer_cpu = cpu;
208 /* Check, if the jiffies need an update */
209 if (tick_do_timer_cpu == cpu)
210 tick_do_update_jiffies64(now);
213 * If jiffies update stalled for too long (timekeeper in stop_machine()
214 * or VMEXIT'ed for several msecs), force an update.
216 if (ts->last_tick_jiffies != jiffies) {
217 ts->stalled_jiffies = 0;
218 ts->last_tick_jiffies = READ_ONCE(jiffies);
220 if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) {
221 tick_do_update_jiffies64(now);
222 ts->stalled_jiffies = 0;
223 ts->last_tick_jiffies = READ_ONCE(jiffies);
228 ts->got_idle_tick = 1;
231 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
233 #ifdef CONFIG_NO_HZ_COMMON
235 * When we are idle and the tick is stopped, we have to touch
236 * the watchdog as we might not schedule for a really long
237 * time. This happens on complete idle SMP systems while
238 * waiting on the login prompt. We also increment the "start of
239 * idle" jiffy stamp so the idle accounting adjustment we do
240 * when we go busy again does not account too much ticks.
242 if (ts->tick_stopped) {
243 touch_softlockup_watchdog_sched();
244 if (is_idle_task(current))
247 * In case the current tick fired too early past its expected
248 * expiration, make sure we don't bypass the next clock reprogramming
249 * to the same deadline.
254 update_process_times(user_mode(regs));
255 profile_tick(CPU_PROFILING);
259 #ifdef CONFIG_NO_HZ_FULL
260 cpumask_var_t tick_nohz_full_mask;
261 EXPORT_SYMBOL_GPL(tick_nohz_full_mask);
262 bool tick_nohz_full_running;
263 EXPORT_SYMBOL_GPL(tick_nohz_full_running);
264 static atomic_t tick_dep_mask;
266 static bool check_tick_dependency(atomic_t *dep)
268 int val = atomic_read(dep);
270 if (val & TICK_DEP_MASK_POSIX_TIMER) {
271 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
275 if (val & TICK_DEP_MASK_PERF_EVENTS) {
276 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
280 if (val & TICK_DEP_MASK_SCHED) {
281 trace_tick_stop(0, TICK_DEP_MASK_SCHED);
285 if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
286 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
290 if (val & TICK_DEP_MASK_RCU) {
291 trace_tick_stop(0, TICK_DEP_MASK_RCU);
295 if (val & TICK_DEP_MASK_RCU_EXP) {
296 trace_tick_stop(0, TICK_DEP_MASK_RCU_EXP);
303 static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
305 lockdep_assert_irqs_disabled();
307 if (unlikely(!cpu_online(cpu)))
310 if (check_tick_dependency(&tick_dep_mask))
313 if (check_tick_dependency(&ts->tick_dep_mask))
316 if (check_tick_dependency(¤t->tick_dep_mask))
319 if (check_tick_dependency(¤t->signal->tick_dep_mask))
325 static void nohz_full_kick_func(struct irq_work *work)
327 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
330 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) =
331 IRQ_WORK_INIT_HARD(nohz_full_kick_func);
334 * Kick this CPU if it's full dynticks in order to force it to
335 * re-evaluate its dependency on the tick and restart it if necessary.
336 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
339 static void tick_nohz_full_kick(void)
341 if (!tick_nohz_full_cpu(smp_processor_id()))
344 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
348 * Kick the CPU if it's full dynticks in order to force it to
349 * re-evaluate its dependency on the tick and restart it if necessary.
351 void tick_nohz_full_kick_cpu(int cpu)
353 if (!tick_nohz_full_cpu(cpu))
356 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
359 static void tick_nohz_kick_task(struct task_struct *tsk)
364 * If the task is not running, run_posix_cpu_timers()
365 * has nothing to elapse, IPI can then be spared.
367 * activate_task() STORE p->tick_dep_mask
369 * __schedule() (switch to task 'p') smp_mb() (atomic_fetch_or())
370 * LOCK rq->lock LOAD p->on_rq
371 * smp_mb__after_spin_lock()
372 * tick_nohz_task_switch()
373 * LOAD p->tick_dep_mask
375 if (!sched_task_on_rq(tsk))
379 * If the task concurrently migrates to another CPU,
380 * we guarantee it sees the new tick dependency upon
383 * set_task_cpu(p, cpu);
384 * STORE p->cpu = @cpu
385 * __schedule() (switch to task 'p')
387 * smp_mb__after_spin_lock() STORE p->tick_dep_mask
388 * tick_nohz_task_switch() smp_mb() (atomic_fetch_or())
389 * LOAD p->tick_dep_mask LOAD p->cpu
395 tick_nohz_full_kick_cpu(cpu);
400 * Kick all full dynticks CPUs in order to force these to re-evaluate
401 * their dependency on the tick and restart it if necessary.
403 static void tick_nohz_full_kick_all(void)
407 if (!tick_nohz_full_running)
411 for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
412 tick_nohz_full_kick_cpu(cpu);
416 static void tick_nohz_dep_set_all(atomic_t *dep,
417 enum tick_dep_bits bit)
421 prev = atomic_fetch_or(BIT(bit), dep);
423 tick_nohz_full_kick_all();
427 * Set a global tick dependency. Used by perf events that rely on freq and
430 void tick_nohz_dep_set(enum tick_dep_bits bit)
432 tick_nohz_dep_set_all(&tick_dep_mask, bit);
435 void tick_nohz_dep_clear(enum tick_dep_bits bit)
437 atomic_andnot(BIT(bit), &tick_dep_mask);
441 * Set per-CPU tick dependency. Used by scheduler and perf events in order to
442 * manage events throttling.
444 void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
447 struct tick_sched *ts;
449 ts = per_cpu_ptr(&tick_cpu_sched, cpu);
451 prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
454 /* Perf needs local kick that is NMI safe */
455 if (cpu == smp_processor_id()) {
456 tick_nohz_full_kick();
458 /* Remote irq work not NMI-safe */
459 if (!WARN_ON_ONCE(in_nmi()))
460 tick_nohz_full_kick_cpu(cpu);
465 EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu);
467 void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
469 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
471 atomic_andnot(BIT(bit), &ts->tick_dep_mask);
473 EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu);
476 * Set a per-task tick dependency. RCU need this. Also posix CPU timers
477 * in order to elapse per task timers.
479 void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
481 if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask))
482 tick_nohz_kick_task(tsk);
484 EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task);
486 void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
488 atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
490 EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_task);
493 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
494 * per process timers.
496 void tick_nohz_dep_set_signal(struct task_struct *tsk,
497 enum tick_dep_bits bit)
500 struct signal_struct *sig = tsk->signal;
502 prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask);
504 struct task_struct *t;
506 lockdep_assert_held(&tsk->sighand->siglock);
507 __for_each_thread(sig, t)
508 tick_nohz_kick_task(t);
512 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
514 atomic_andnot(BIT(bit), &sig->tick_dep_mask);
518 * Re-evaluate the need for the tick as we switch the current task.
519 * It might need the tick due to per task/process properties:
520 * perf events, posix CPU timers, ...
522 void __tick_nohz_task_switch(void)
524 struct tick_sched *ts;
526 if (!tick_nohz_full_cpu(smp_processor_id()))
529 ts = this_cpu_ptr(&tick_cpu_sched);
531 if (ts->tick_stopped) {
532 if (atomic_read(¤t->tick_dep_mask) ||
533 atomic_read(¤t->signal->tick_dep_mask))
534 tick_nohz_full_kick();
538 /* Get the boot-time nohz CPU list from the kernel parameters. */
539 void __init tick_nohz_full_setup(cpumask_var_t cpumask)
541 alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
542 cpumask_copy(tick_nohz_full_mask, cpumask);
543 tick_nohz_full_running = true;
546 bool tick_nohz_cpu_hotpluggable(unsigned int cpu)
549 * The tick_do_timer_cpu CPU handles housekeeping duty (unbound
550 * timers, workqueues, timekeeping, ...) on behalf of full dynticks
551 * CPUs. It must remain online when nohz full is enabled.
553 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
558 static int tick_nohz_cpu_down(unsigned int cpu)
560 return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY;
563 void __init tick_nohz_init(void)
567 if (!tick_nohz_full_running)
571 * Full dynticks uses irq work to drive the tick rescheduling on safe
572 * locking contexts. But then we need irq work to raise its own
573 * interrupts to avoid circular dependency on the tick
575 if (!arch_irq_work_has_interrupt()) {
576 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
577 cpumask_clear(tick_nohz_full_mask);
578 tick_nohz_full_running = false;
582 if (IS_ENABLED(CONFIG_PM_SLEEP_SMP) &&
583 !IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU)) {
584 cpu = smp_processor_id();
586 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
587 pr_warn("NO_HZ: Clearing %d from nohz_full range "
588 "for timekeeping\n", cpu);
589 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
593 for_each_cpu(cpu, tick_nohz_full_mask)
594 ct_cpu_track_user(cpu);
596 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
597 "kernel/nohz:predown", NULL,
600 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
601 cpumask_pr_args(tick_nohz_full_mask));
606 * NOHZ - aka dynamic tick functionality
608 #ifdef CONFIG_NO_HZ_COMMON
612 bool tick_nohz_enabled __read_mostly = true;
613 unsigned long tick_nohz_active __read_mostly;
615 * Enable / Disable tickless mode
617 static int __init setup_tick_nohz(char *str)
619 return (kstrtobool(str, &tick_nohz_enabled) == 0);
622 __setup("nohz=", setup_tick_nohz);
624 bool tick_nohz_tick_stopped(void)
626 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
628 return ts->tick_stopped;
631 bool tick_nohz_tick_stopped_cpu(int cpu)
633 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
635 return ts->tick_stopped;
639 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
641 * Called from interrupt entry when the CPU was idle
643 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
644 * must be updated. Otherwise an interrupt handler could use a stale jiffy
645 * value. We do this unconditionally on any CPU, as we don't know whether the
646 * CPU, which has the update task assigned is in a long sleep.
648 static void tick_nohz_update_jiffies(ktime_t now)
652 __this_cpu_write(tick_cpu_sched.idle_waketime, now);
654 local_irq_save(flags);
655 tick_do_update_jiffies64(now);
656 local_irq_restore(flags);
658 touch_softlockup_watchdog_sched();
661 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
665 if (WARN_ON_ONCE(!ts->idle_active))
668 delta = ktime_sub(now, ts->idle_entrytime);
670 write_seqcount_begin(&ts->idle_sleeptime_seq);
671 if (nr_iowait_cpu(smp_processor_id()) > 0)
672 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
674 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
676 ts->idle_entrytime = now;
678 write_seqcount_end(&ts->idle_sleeptime_seq);
680 sched_clock_idle_wakeup_event();
683 static void tick_nohz_start_idle(struct tick_sched *ts)
685 write_seqcount_begin(&ts->idle_sleeptime_seq);
686 ts->idle_entrytime = ktime_get();
688 write_seqcount_end(&ts->idle_sleeptime_seq);
690 sched_clock_idle_sleep_event();
693 static u64 get_cpu_sleep_time_us(struct tick_sched *ts, ktime_t *sleeptime,
694 bool compute_delta, u64 *last_update_time)
699 if (!tick_nohz_active)
703 if (last_update_time)
704 *last_update_time = ktime_to_us(now);
707 seq = read_seqcount_begin(&ts->idle_sleeptime_seq);
709 if (ts->idle_active && compute_delta) {
710 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
712 idle = ktime_add(*sleeptime, delta);
716 } while (read_seqcount_retry(&ts->idle_sleeptime_seq, seq));
718 return ktime_to_us(idle);
723 * get_cpu_idle_time_us - get the total idle time of a CPU
724 * @cpu: CPU number to query
725 * @last_update_time: variable to store update time in. Do not update
728 * Return the cumulative idle time (since boot) for a given
729 * CPU, in microseconds. Note this is partially broken due to
730 * the counter of iowait tasks that can be remotely updated without
731 * any synchronization. Therefore it is possible to observe backward
732 * values within two consecutive reads.
734 * This time is measured via accounting rather than sampling,
735 * and is as accurate as ktime_get() is.
737 * This function returns -1 if NOHZ is not enabled.
739 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
741 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
743 return get_cpu_sleep_time_us(ts, &ts->idle_sleeptime,
744 !nr_iowait_cpu(cpu), last_update_time);
746 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
749 * get_cpu_iowait_time_us - get the total iowait time of a CPU
750 * @cpu: CPU number to query
751 * @last_update_time: variable to store update time in. Do not update
754 * Return the cumulative iowait time (since boot) for a given
755 * CPU, in microseconds. Note this is partially broken due to
756 * the counter of iowait tasks that can be remotely updated without
757 * any synchronization. Therefore it is possible to observe backward
758 * values within two consecutive reads.
760 * This time is measured via accounting rather than sampling,
761 * and is as accurate as ktime_get() is.
763 * This function returns -1 if NOHZ is not enabled.
765 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
767 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
769 return get_cpu_sleep_time_us(ts, &ts->iowait_sleeptime,
770 nr_iowait_cpu(cpu), last_update_time);
772 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
774 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
776 hrtimer_cancel(&ts->sched_timer);
777 hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
779 /* Forward the time to expire in the future */
780 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
782 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
783 hrtimer_start_expires(&ts->sched_timer,
784 HRTIMER_MODE_ABS_PINNED_HARD);
786 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
790 * Reset to make sure next tick stop doesn't get fooled by past
791 * cached clock deadline.
796 static inline bool local_timer_softirq_pending(void)
798 return local_softirq_pending() & BIT(TIMER_SOFTIRQ);
801 static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
803 u64 basemono, next_tick, delta, expires;
804 unsigned long basejiff;
807 /* Read jiffies and the time when jiffies were updated last */
809 seq = read_seqcount_begin(&jiffies_seq);
810 basemono = last_jiffies_update;
812 } while (read_seqcount_retry(&jiffies_seq, seq));
813 ts->last_jiffies = basejiff;
814 ts->timer_expires_base = basemono;
817 * Keep the periodic tick, when RCU, architecture or irq_work
819 * Aside of that check whether the local timer softirq is
820 * pending. If so its a bad idea to call get_next_timer_interrupt()
821 * because there is an already expired timer, so it will request
822 * immediate expiry, which rearms the hardware timer with a
823 * minimal delta which brings us back to this place
824 * immediately. Lather, rinse and repeat...
826 if (rcu_needs_cpu() || arch_needs_cpu() ||
827 irq_work_needs_cpu() || local_timer_softirq_pending()) {
828 next_tick = basemono + TICK_NSEC;
831 * Get the next pending timer. If high resolution
832 * timers are enabled this only takes the timer wheel
833 * timers into account. If high resolution timers are
834 * disabled this also looks at the next expiring
837 next_tick = get_next_timer_interrupt(basejiff, basemono);
838 ts->next_timer = next_tick;
842 * If the tick is due in the next period, keep it ticking or
843 * force prod the timer.
845 delta = next_tick - basemono;
846 if (delta <= (u64)TICK_NSEC) {
848 * Tell the timer code that the base is not idle, i.e. undo
849 * the effect of get_next_timer_interrupt():
853 * We've not stopped the tick yet, and there's a timer in the
854 * next period, so no point in stopping it either, bail.
856 if (!ts->tick_stopped) {
857 ts->timer_expires = 0;
863 * If this CPU is the one which had the do_timer() duty last, we limit
864 * the sleep time to the timekeeping max_deferment value.
865 * Otherwise we can sleep as long as we want.
867 delta = timekeeping_max_deferment();
868 if (cpu != tick_do_timer_cpu &&
869 (tick_do_timer_cpu != TICK_DO_TIMER_NONE || !ts->do_timer_last))
872 /* Calculate the next expiry time */
873 if (delta < (KTIME_MAX - basemono))
874 expires = basemono + delta;
878 ts->timer_expires = min_t(u64, expires, next_tick);
881 return ts->timer_expires;
884 static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
886 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
887 u64 basemono = ts->timer_expires_base;
888 u64 expires = ts->timer_expires;
889 ktime_t tick = expires;
891 /* Make sure we won't be trying to stop it twice in a row. */
892 ts->timer_expires_base = 0;
895 * If this CPU is the one which updates jiffies, then give up
896 * the assignment and let it be taken by the CPU which runs
897 * the tick timer next, which might be this CPU as well. If we
898 * don't drop this here the jiffies might be stale and
899 * do_timer() never invoked. Keep track of the fact that it
900 * was the one which had the do_timer() duty last.
902 if (cpu == tick_do_timer_cpu) {
903 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
904 ts->do_timer_last = 1;
905 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
906 ts->do_timer_last = 0;
909 /* Skip reprogram of event if its not changed */
910 if (ts->tick_stopped && (expires == ts->next_tick)) {
911 /* Sanity check: make sure clockevent is actually programmed */
912 if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer))
916 printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n",
917 basemono, ts->next_tick, dev->next_event,
918 hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer));
922 * nohz_stop_sched_tick can be called several times before
923 * the nohz_restart_sched_tick is called. This happens when
924 * interrupts arrive which do not cause a reschedule. In the
925 * first call we save the current tick time, so we can restart
926 * the scheduler tick in nohz_restart_sched_tick.
928 if (!ts->tick_stopped) {
929 calc_load_nohz_start();
932 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
933 ts->tick_stopped = 1;
934 trace_tick_stop(1, TICK_DEP_MASK_NONE);
937 ts->next_tick = tick;
940 * If the expiration time == KTIME_MAX, then we simply stop
943 if (unlikely(expires == KTIME_MAX)) {
944 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
945 hrtimer_cancel(&ts->sched_timer);
947 tick_program_event(KTIME_MAX, 1);
951 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
952 hrtimer_start(&ts->sched_timer, tick,
953 HRTIMER_MODE_ABS_PINNED_HARD);
955 hrtimer_set_expires(&ts->sched_timer, tick);
956 tick_program_event(tick, 1);
960 static void tick_nohz_retain_tick(struct tick_sched *ts)
962 ts->timer_expires_base = 0;
965 #ifdef CONFIG_NO_HZ_FULL
966 static void tick_nohz_stop_sched_tick(struct tick_sched *ts, int cpu)
968 if (tick_nohz_next_event(ts, cpu))
969 tick_nohz_stop_tick(ts, cpu);
971 tick_nohz_retain_tick(ts);
973 #endif /* CONFIG_NO_HZ_FULL */
975 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
977 /* Update jiffies first */
978 tick_do_update_jiffies64(now);
981 * Clear the timer idle flag, so we avoid IPIs on remote queueing and
982 * the clock forward checks in the enqueue path:
986 calc_load_nohz_stop();
987 touch_softlockup_watchdog_sched();
989 * Cancel the scheduled timer and restore the tick
991 ts->tick_stopped = 0;
992 tick_nohz_restart(ts, now);
995 static void __tick_nohz_full_update_tick(struct tick_sched *ts,
998 #ifdef CONFIG_NO_HZ_FULL
999 int cpu = smp_processor_id();
1001 if (can_stop_full_tick(cpu, ts))
1002 tick_nohz_stop_sched_tick(ts, cpu);
1003 else if (ts->tick_stopped)
1004 tick_nohz_restart_sched_tick(ts, now);
1008 static void tick_nohz_full_update_tick(struct tick_sched *ts)
1010 if (!tick_nohz_full_cpu(smp_processor_id()))
1013 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
1016 __tick_nohz_full_update_tick(ts, ktime_get());
1020 * A pending softirq outside an IRQ (or softirq disabled section) context
1021 * should be waiting for ksoftirqd to handle it. Therefore we shouldn't
1022 * reach here due to the need_resched() early check in can_stop_idle_tick().
1024 * However if we are between CPUHP_AP_SMPBOOT_THREADS and CPU_TEARDOWN_CPU on the
1025 * cpu_down() process, softirqs can still be raised while ksoftirqd is parked,
1026 * triggering the below since wakep_softirqd() is ignored.
1029 static bool report_idle_softirq(void)
1031 static int ratelimit;
1032 unsigned int pending = local_softirq_pending();
1034 if (likely(!pending))
1037 /* Some softirqs claim to be safe against hotplug and ksoftirqd parking */
1038 if (!cpu_active(smp_processor_id())) {
1039 pending &= ~SOFTIRQ_HOTPLUG_SAFE_MASK;
1044 if (ratelimit >= 10)
1047 /* On RT, softirqs handling may be waiting on some lock */
1048 if (local_bh_blocked())
1051 pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n",
1058 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
1061 * If this CPU is offline and it is the one which updates
1062 * jiffies, then give up the assignment and let it be taken by
1063 * the CPU which runs the tick timer next. If we don't drop
1064 * this here the jiffies might be stale and do_timer() never
1067 if (unlikely(!cpu_online(cpu))) {
1068 if (cpu == tick_do_timer_cpu)
1069 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
1071 * Make sure the CPU doesn't get fooled by obsolete tick
1072 * deadline if it comes back online later.
1078 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
1084 if (unlikely(report_idle_softirq()))
1087 if (tick_nohz_full_enabled()) {
1089 * Keep the tick alive to guarantee timekeeping progression
1090 * if there are full dynticks CPUs around
1092 if (tick_do_timer_cpu == cpu)
1095 /* Should not happen for nohz-full */
1096 if (WARN_ON_ONCE(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
1104 * tick_nohz_idle_stop_tick - stop the idle tick from the idle task
1106 * When the next event is more than a tick into the future, stop the idle tick
1108 void tick_nohz_idle_stop_tick(void)
1110 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1111 int cpu = smp_processor_id();
1115 * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the
1116 * tick timer expiration time is known already.
1118 if (ts->timer_expires_base)
1119 expires = ts->timer_expires;
1120 else if (can_stop_idle_tick(cpu, ts))
1121 expires = tick_nohz_next_event(ts, cpu);
1127 if (expires > 0LL) {
1128 int was_stopped = ts->tick_stopped;
1130 tick_nohz_stop_tick(ts, cpu);
1133 ts->idle_expires = expires;
1135 if (!was_stopped && ts->tick_stopped) {
1136 ts->idle_jiffies = ts->last_jiffies;
1137 nohz_balance_enter_idle(cpu);
1140 tick_nohz_retain_tick(ts);
1144 void tick_nohz_idle_retain_tick(void)
1146 tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched));
1148 * Undo the effect of get_next_timer_interrupt() called from
1149 * tick_nohz_next_event().
1155 * tick_nohz_idle_enter - prepare for entering idle on the current CPU
1157 * Called when we start the idle loop.
1159 void tick_nohz_idle_enter(void)
1161 struct tick_sched *ts;
1163 lockdep_assert_irqs_enabled();
1165 local_irq_disable();
1167 ts = this_cpu_ptr(&tick_cpu_sched);
1169 WARN_ON_ONCE(ts->timer_expires_base);
1172 tick_nohz_start_idle(ts);
1178 * tick_nohz_irq_exit - update next tick event from interrupt exit
1180 * When an interrupt fires while we are idle and it doesn't cause
1181 * a reschedule, it may still add, modify or delete a timer, enqueue
1182 * an RCU callback, etc...
1183 * So we need to re-calculate and reprogram the next tick event.
1185 void tick_nohz_irq_exit(void)
1187 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1190 tick_nohz_start_idle(ts);
1192 tick_nohz_full_update_tick(ts);
1196 * tick_nohz_idle_got_tick - Check whether or not the tick handler has run
1198 bool tick_nohz_idle_got_tick(void)
1200 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1202 if (ts->got_idle_tick) {
1203 ts->got_idle_tick = 0;
1210 * tick_nohz_get_next_hrtimer - return the next expiration time for the hrtimer
1211 * or the tick, whatever that expires first. Note that, if the tick has been
1212 * stopped, it returns the next hrtimer.
1214 * Called from power state control code with interrupts disabled
1216 ktime_t tick_nohz_get_next_hrtimer(void)
1218 return __this_cpu_read(tick_cpu_device.evtdev)->next_event;
1222 * tick_nohz_get_sleep_length - return the expected length of the current sleep
1223 * @delta_next: duration until the next event if the tick cannot be stopped
1225 * Called from power state control code with interrupts disabled.
1227 * The return value of this function and/or the value returned by it through the
1228 * @delta_next pointer can be negative which must be taken into account by its
1231 ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
1233 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
1234 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1235 int cpu = smp_processor_id();
1237 * The idle entry time is expected to be a sufficient approximation of
1238 * the current time at this point.
1240 ktime_t now = ts->idle_entrytime;
1243 WARN_ON_ONCE(!ts->inidle);
1245 *delta_next = ktime_sub(dev->next_event, now);
1247 if (!can_stop_idle_tick(cpu, ts))
1250 next_event = tick_nohz_next_event(ts, cpu);
1255 * If the next highres timer to expire is earlier than next_event, the
1256 * idle governor needs to know that.
1258 next_event = min_t(u64, next_event,
1259 hrtimer_next_event_without(&ts->sched_timer));
1261 return ktime_sub(next_event, now);
1265 * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
1266 * for a particular CPU.
1268 * Called from the schedutil frequency scaling governor in scheduler context.
1270 unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
1272 struct tick_sched *ts = tick_get_tick_sched(cpu);
1274 return ts->idle_calls;
1278 * tick_nohz_get_idle_calls - return the current idle calls counter value
1280 * Called from the schedutil frequency scaling governor in scheduler context.
1282 unsigned long tick_nohz_get_idle_calls(void)
1284 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1286 return ts->idle_calls;
1289 static void tick_nohz_account_idle_time(struct tick_sched *ts,
1292 unsigned long ticks;
1294 ts->idle_exittime = now;
1296 if (vtime_accounting_enabled_this_cpu())
1299 * We stopped the tick in idle. Update process times would miss the
1300 * time we slept as update_process_times does only a 1 tick
1301 * accounting. Enforce that this is accounted to idle !
1303 ticks = jiffies - ts->idle_jiffies;
1305 * We might be one off. Do not randomly account a huge number of ticks!
1307 if (ticks && ticks < LONG_MAX)
1308 account_idle_ticks(ticks);
1311 void tick_nohz_idle_restart_tick(void)
1313 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1315 if (ts->tick_stopped) {
1316 ktime_t now = ktime_get();
1317 tick_nohz_restart_sched_tick(ts, now);
1318 tick_nohz_account_idle_time(ts, now);
1322 static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now)
1324 if (tick_nohz_full_cpu(smp_processor_id()))
1325 __tick_nohz_full_update_tick(ts, now);
1327 tick_nohz_restart_sched_tick(ts, now);
1329 tick_nohz_account_idle_time(ts, now);
1333 * tick_nohz_idle_exit - restart the idle tick from the idle task
1335 * Restart the idle tick when the CPU is woken up from idle
1336 * This also exit the RCU extended quiescent state. The CPU
1337 * can use RCU again after this function is called.
1339 void tick_nohz_idle_exit(void)
1341 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1342 bool idle_active, tick_stopped;
1345 local_irq_disable();
1347 WARN_ON_ONCE(!ts->inidle);
1348 WARN_ON_ONCE(ts->timer_expires_base);
1351 idle_active = ts->idle_active;
1352 tick_stopped = ts->tick_stopped;
1354 if (idle_active || tick_stopped)
1358 tick_nohz_stop_idle(ts, now);
1361 tick_nohz_idle_update_tick(ts, now);
1367 * The nohz low res interrupt handler
1369 static void tick_nohz_handler(struct clock_event_device *dev)
1371 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1372 struct pt_regs *regs = get_irq_regs();
1373 ktime_t now = ktime_get();
1375 dev->next_event = KTIME_MAX;
1377 tick_sched_do_timer(ts, now);
1378 tick_sched_handle(ts, regs);
1380 if (unlikely(ts->tick_stopped)) {
1382 * The clockevent device is not reprogrammed, so change the
1383 * clock event device to ONESHOT_STOPPED to avoid spurious
1384 * interrupts on devices which might not be truly one shot.
1386 tick_program_event(KTIME_MAX, 1);
1390 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
1391 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1394 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1396 if (!tick_nohz_enabled)
1398 ts->nohz_mode = mode;
1399 /* One update is enough */
1400 if (!test_and_set_bit(0, &tick_nohz_active))
1401 timers_update_nohz();
1405 * tick_nohz_switch_to_nohz - switch to nohz mode
1407 static void tick_nohz_switch_to_nohz(void)
1409 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1412 if (!tick_nohz_enabled)
1415 if (tick_switch_to_oneshot(tick_nohz_handler))
1419 * Recycle the hrtimer in ts, so we can share the
1420 * hrtimer_forward with the highres code.
1422 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
1423 /* Get the next period */
1424 next = tick_init_jiffy_update();
1426 hrtimer_set_expires(&ts->sched_timer, next);
1427 hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);
1428 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1429 tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1432 static inline void tick_nohz_irq_enter(void)
1434 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1437 if (!ts->idle_active && !ts->tick_stopped)
1440 if (ts->idle_active)
1441 tick_nohz_stop_idle(ts, now);
1443 * If all CPUs are idle. We may need to update a stale jiffies value.
1444 * Note nohz_full is a special case: a timekeeper is guaranteed to stay
1445 * alive but it might be busy looping with interrupts disabled in some
1446 * rare case (typically stop machine). So we must make sure we have a
1449 if (ts->tick_stopped)
1450 tick_nohz_update_jiffies(now);
1455 static inline void tick_nohz_switch_to_nohz(void) { }
1456 static inline void tick_nohz_irq_enter(void) { }
1457 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1459 #endif /* CONFIG_NO_HZ_COMMON */
1462 * Called from irq_enter to notify about the possible interruption of idle()
1464 void tick_irq_enter(void)
1466 tick_check_oneshot_broadcast_this_cpu();
1467 tick_nohz_irq_enter();
1471 * High resolution timer specific code
1473 #ifdef CONFIG_HIGH_RES_TIMERS
1475 * We rearm the timer until we get disabled by the idle code.
1476 * Called with interrupts disabled.
1478 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1480 struct tick_sched *ts =
1481 container_of(timer, struct tick_sched, sched_timer);
1482 struct pt_regs *regs = get_irq_regs();
1483 ktime_t now = ktime_get();
1485 tick_sched_do_timer(ts, now);
1488 * Do not call, when we are not in irq context and have
1489 * no valid regs pointer
1492 tick_sched_handle(ts, regs);
1496 /* No need to reprogram if we are in idle or full dynticks mode */
1497 if (unlikely(ts->tick_stopped))
1498 return HRTIMER_NORESTART;
1500 hrtimer_forward(timer, now, TICK_NSEC);
1502 return HRTIMER_RESTART;
1505 static int sched_skew_tick;
1507 static int __init skew_tick(char *str)
1509 get_option(&str, &sched_skew_tick);
1513 early_param("skew_tick", skew_tick);
1516 * tick_setup_sched_timer - setup the tick emulation timer
1518 void tick_setup_sched_timer(void)
1520 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1521 ktime_t now = ktime_get();
1524 * Emulate tick processing via per-CPU hrtimers:
1526 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
1527 ts->sched_timer.function = tick_sched_timer;
1529 /* Get the next period (per-CPU) */
1530 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1532 /* Offset the tick to avert jiffies_lock contention. */
1533 if (sched_skew_tick) {
1534 u64 offset = TICK_NSEC >> 1;
1535 do_div(offset, num_possible_cpus());
1536 offset *= smp_processor_id();
1537 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1540 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
1541 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
1542 tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1544 #endif /* HIGH_RES_TIMERS */
1546 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1547 void tick_cancel_sched_timer(int cpu)
1549 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1550 ktime_t idle_sleeptime, iowait_sleeptime;
1551 unsigned long idle_calls, idle_sleeps;
1553 # ifdef CONFIG_HIGH_RES_TIMERS
1554 if (ts->sched_timer.base)
1555 hrtimer_cancel(&ts->sched_timer);
1558 idle_sleeptime = ts->idle_sleeptime;
1559 iowait_sleeptime = ts->iowait_sleeptime;
1560 idle_calls = ts->idle_calls;
1561 idle_sleeps = ts->idle_sleeps;
1562 memset(ts, 0, sizeof(*ts));
1563 ts->idle_sleeptime = idle_sleeptime;
1564 ts->iowait_sleeptime = iowait_sleeptime;
1565 ts->idle_calls = idle_calls;
1566 ts->idle_sleeps = idle_sleeps;
1571 * Async notification about clocksource changes
1573 void tick_clock_notify(void)
1577 for_each_possible_cpu(cpu)
1578 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1582 * Async notification about clock event changes
1584 void tick_oneshot_notify(void)
1586 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1588 set_bit(0, &ts->check_clocks);
1592 * Check, if a change happened, which makes oneshot possible.
1594 * Called cyclic from the hrtimer softirq (driven by the timer
1595 * softirq) allow_nohz signals, that we can switch into low-res nohz
1596 * mode, because high resolution timers are disabled (either compile
1597 * or runtime). Called with interrupts disabled.
1599 int tick_check_oneshot_change(int allow_nohz)
1601 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1603 if (!test_and_clear_bit(0, &ts->check_clocks))
1606 if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1609 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1615 tick_nohz_switch_to_nohz();