2 * linux/kernel/time/tick-sched.c
4 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
5 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
6 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner
8 * No idle tick implementation for low and high resolution timers
10 * Started by: Thomas Gleixner and Ingo Molnar
12 * Distribute under GPLv2.
14 #include <linux/cpu.h>
15 #include <linux/err.h>
16 #include <linux/hrtimer.h>
17 #include <linux/interrupt.h>
18 #include <linux/kernel_stat.h>
19 #include <linux/percpu.h>
20 #include <linux/profile.h>
21 #include <linux/sched.h>
22 #include <linux/module.h>
23 #include <linux/irq_work.h>
24 #include <linux/posix-timers.h>
25 #include <linux/perf_event.h>
26 #include <linux/context_tracking.h>
28 #include <asm/irq_regs.h>
30 #include "tick-internal.h"
32 #include <trace/events/timer.h>
35 * Per cpu nohz control structure
37 static DEFINE_PER_CPU(struct tick_sched
, tick_cpu_sched
);
39 struct tick_sched
*tick_get_tick_sched(int cpu
)
41 return &per_cpu(tick_cpu_sched
, cpu
);
44 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
46 * The time, when the last jiffy update happened. Protected by jiffies_lock.
48 static ktime_t last_jiffies_update
;
51 * Must be called with interrupts disabled !
53 static void tick_do_update_jiffies64(ktime_t now
)
55 unsigned long ticks
= 0;
59 * Do a quick check without holding jiffies_lock:
61 delta
= ktime_sub(now
, last_jiffies_update
);
62 if (delta
.tv64
< tick_period
.tv64
)
65 /* Reevalute with jiffies_lock held */
66 write_seqlock(&jiffies_lock
);
68 delta
= ktime_sub(now
, last_jiffies_update
);
69 if (delta
.tv64
>= tick_period
.tv64
) {
71 delta
= ktime_sub(delta
, tick_period
);
72 last_jiffies_update
= ktime_add(last_jiffies_update
,
75 /* Slow path for long timeouts */
76 if (unlikely(delta
.tv64
>= tick_period
.tv64
)) {
77 s64 incr
= ktime_to_ns(tick_period
);
79 ticks
= ktime_divns(delta
, incr
);
81 last_jiffies_update
= ktime_add_ns(last_jiffies_update
,
86 /* Keep the tick_next_period variable up to date */
87 tick_next_period
= ktime_add(last_jiffies_update
, tick_period
);
89 write_sequnlock(&jiffies_lock
);
92 write_sequnlock(&jiffies_lock
);
97 * Initialize and return retrieve the jiffies update.
99 static ktime_t
tick_init_jiffy_update(void)
103 write_seqlock(&jiffies_lock
);
104 /* Did we start the jiffies update yet ? */
105 if (last_jiffies_update
.tv64
== 0)
106 last_jiffies_update
= tick_next_period
;
107 period
= last_jiffies_update
;
108 write_sequnlock(&jiffies_lock
);
113 static void tick_sched_do_timer(ktime_t now
)
115 int cpu
= smp_processor_id();
117 #ifdef CONFIG_NO_HZ_COMMON
119 * Check if the do_timer duty was dropped. We don't care about
120 * concurrency: This happens only when the cpu in charge went
121 * into a long sleep. If two cpus happen to assign themself to
122 * this duty, then the jiffies update is still serialized by
125 if (unlikely(tick_do_timer_cpu
== TICK_DO_TIMER_NONE
)
126 && !tick_nohz_full_cpu(cpu
))
127 tick_do_timer_cpu
= cpu
;
130 /* Check, if the jiffies need an update */
131 if (tick_do_timer_cpu
== cpu
)
132 tick_do_update_jiffies64(now
);
135 static void tick_sched_handle(struct tick_sched
*ts
, struct pt_regs
*regs
)
137 #ifdef CONFIG_NO_HZ_COMMON
139 * When we are idle and the tick is stopped, we have to touch
140 * the watchdog as we might not schedule for a really long
141 * time. This happens on complete idle SMP systems while
142 * waiting on the login prompt. We also increment the "start of
143 * idle" jiffy stamp so the idle accounting adjustment we do
144 * when we go busy again does not account too much ticks.
146 if (ts
->tick_stopped
) {
147 touch_softlockup_watchdog_sched();
148 if (is_idle_task(current
))
152 update_process_times(user_mode(regs
));
153 profile_tick(CPU_PROFILING
);
157 #ifdef CONFIG_NO_HZ_FULL
158 cpumask_var_t tick_nohz_full_mask
;
159 cpumask_var_t housekeeping_mask
;
160 bool tick_nohz_full_running
;
162 static bool can_stop_full_tick(void)
164 WARN_ON_ONCE(!irqs_disabled());
166 if (!sched_can_stop_tick()) {
167 trace_tick_stop(0, "more than 1 task in runqueue\n");
171 if (!posix_cpu_timers_can_stop_tick(current
)) {
172 trace_tick_stop(0, "posix timers running\n");
176 if (!perf_event_can_stop_tick()) {
177 trace_tick_stop(0, "perf events running\n");
181 /* sched_clock_tick() needs us? */
182 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
184 * TODO: kick full dynticks CPUs when
185 * sched_clock_stable is set.
187 if (!sched_clock_stable()) {
188 trace_tick_stop(0, "unstable sched clock\n");
190 * Don't allow the user to think they can get
191 * full NO_HZ with this machine.
193 WARN_ONCE(tick_nohz_full_running
,
194 "NO_HZ FULL will not work with unstable sched clock");
202 static void nohz_full_kick_work_func(struct irq_work
*work
)
204 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
207 static DEFINE_PER_CPU(struct irq_work
, nohz_full_kick_work
) = {
208 .func
= nohz_full_kick_work_func
,
212 * Kick this CPU if it's full dynticks in order to force it to
213 * re-evaluate its dependency on the tick and restart it if necessary.
214 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
217 void tick_nohz_full_kick(void)
219 if (!tick_nohz_full_cpu(smp_processor_id()))
222 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work
));
226 * Kick the CPU if it's full dynticks in order to force it to
227 * re-evaluate its dependency on the tick and restart it if necessary.
229 void tick_nohz_full_kick_cpu(int cpu
)
231 if (!tick_nohz_full_cpu(cpu
))
234 irq_work_queue_on(&per_cpu(nohz_full_kick_work
, cpu
), cpu
);
237 static void nohz_full_kick_ipi(void *info
)
239 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
243 * Kick all full dynticks CPUs in order to force these to re-evaluate
244 * their dependency on the tick and restart it if necessary.
246 void tick_nohz_full_kick_all(void)
248 if (!tick_nohz_full_running
)
252 smp_call_function_many(tick_nohz_full_mask
,
253 nohz_full_kick_ipi
, NULL
, false);
254 tick_nohz_full_kick();
259 * Re-evaluate the need for the tick as we switch the current task.
260 * It might need the tick due to per task/process properties:
261 * perf events, posix cpu timers, ...
263 void __tick_nohz_task_switch(void)
267 local_irq_save(flags
);
269 if (!tick_nohz_full_cpu(smp_processor_id()))
272 if (tick_nohz_tick_stopped() && !can_stop_full_tick())
273 tick_nohz_full_kick();
276 local_irq_restore(flags
);
279 /* Parse the boot-time nohz CPU list from the kernel parameters. */
280 static int __init
tick_nohz_full_setup(char *str
)
282 alloc_bootmem_cpumask_var(&tick_nohz_full_mask
);
283 if (cpulist_parse(str
, tick_nohz_full_mask
) < 0) {
284 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
285 free_bootmem_cpumask_var(tick_nohz_full_mask
);
288 tick_nohz_full_running
= true;
292 __setup("nohz_full=", tick_nohz_full_setup
);
294 static int tick_nohz_cpu_down_callback(struct notifier_block
*nfb
,
295 unsigned long action
,
298 unsigned int cpu
= (unsigned long)hcpu
;
300 switch (action
& ~CPU_TASKS_FROZEN
) {
301 case CPU_DOWN_PREPARE
:
303 * The boot CPU handles housekeeping duty (unbound timers,
304 * workqueues, timekeeping, ...) on behalf of full dynticks
305 * CPUs. It must remain online when nohz full is enabled.
307 if (tick_nohz_full_running
&& tick_do_timer_cpu
== cpu
)
314 static int tick_nohz_init_all(void)
318 #ifdef CONFIG_NO_HZ_FULL_ALL
319 if (!alloc_cpumask_var(&tick_nohz_full_mask
, GFP_KERNEL
)) {
320 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
324 cpumask_setall(tick_nohz_full_mask
);
325 tick_nohz_full_running
= true;
330 void __init
tick_nohz_init(void)
334 if (!tick_nohz_full_running
) {
335 if (tick_nohz_init_all() < 0)
339 if (!alloc_cpumask_var(&housekeeping_mask
, GFP_KERNEL
)) {
340 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
341 cpumask_clear(tick_nohz_full_mask
);
342 tick_nohz_full_running
= false;
347 * Full dynticks uses irq work to drive the tick rescheduling on safe
348 * locking contexts. But then we need irq work to raise its own
349 * interrupts to avoid circular dependency on the tick
351 if (!arch_irq_work_has_interrupt()) {
352 pr_warning("NO_HZ: Can't run full dynticks because arch doesn't "
353 "support irq work self-IPIs\n");
354 cpumask_clear(tick_nohz_full_mask
);
355 cpumask_copy(housekeeping_mask
, cpu_possible_mask
);
356 tick_nohz_full_running
= false;
360 cpu
= smp_processor_id();
362 if (cpumask_test_cpu(cpu
, tick_nohz_full_mask
)) {
363 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu
);
364 cpumask_clear_cpu(cpu
, tick_nohz_full_mask
);
367 cpumask_andnot(housekeeping_mask
,
368 cpu_possible_mask
, tick_nohz_full_mask
);
370 for_each_cpu(cpu
, tick_nohz_full_mask
)
371 context_tracking_cpu_set(cpu
);
373 cpu_notifier(tick_nohz_cpu_down_callback
, 0);
374 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
375 cpumask_pr_args(tick_nohz_full_mask
));
378 * We need at least one CPU to handle housekeeping work such
379 * as timekeeping, unbound timers, workqueues, ...
381 WARN_ON_ONCE(cpumask_empty(housekeeping_mask
));
386 * NOHZ - aka dynamic tick functionality
388 #ifdef CONFIG_NO_HZ_COMMON
392 int tick_nohz_enabled __read_mostly
= 1;
393 unsigned long tick_nohz_active __read_mostly
;
395 * Enable / Disable tickless mode
397 static int __init
setup_tick_nohz(char *str
)
399 if (!strcmp(str
, "off"))
400 tick_nohz_enabled
= 0;
401 else if (!strcmp(str
, "on"))
402 tick_nohz_enabled
= 1;
408 __setup("nohz=", setup_tick_nohz
);
410 int tick_nohz_tick_stopped(void)
412 return __this_cpu_read(tick_cpu_sched
.tick_stopped
);
416 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
418 * Called from interrupt entry when the CPU was idle
420 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
421 * must be updated. Otherwise an interrupt handler could use a stale jiffy
422 * value. We do this unconditionally on any cpu, as we don't know whether the
423 * cpu, which has the update task assigned is in a long sleep.
425 static void tick_nohz_update_jiffies(ktime_t now
)
429 __this_cpu_write(tick_cpu_sched
.idle_waketime
, now
);
431 local_irq_save(flags
);
432 tick_do_update_jiffies64(now
);
433 local_irq_restore(flags
);
435 touch_softlockup_watchdog_sched();
439 * Updates the per cpu time idle statistics counters
442 update_ts_time_stats(int cpu
, struct tick_sched
*ts
, ktime_t now
, u64
*last_update_time
)
446 if (ts
->idle_active
) {
447 delta
= ktime_sub(now
, ts
->idle_entrytime
);
448 if (nr_iowait_cpu(cpu
) > 0)
449 ts
->iowait_sleeptime
= ktime_add(ts
->iowait_sleeptime
, delta
);
451 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
452 ts
->idle_entrytime
= now
;
455 if (last_update_time
)
456 *last_update_time
= ktime_to_us(now
);
460 static void tick_nohz_stop_idle(struct tick_sched
*ts
, ktime_t now
)
462 update_ts_time_stats(smp_processor_id(), ts
, now
, NULL
);
465 sched_clock_idle_wakeup_event(0);
468 static ktime_t
tick_nohz_start_idle(struct tick_sched
*ts
)
470 ktime_t now
= ktime_get();
472 ts
->idle_entrytime
= now
;
474 sched_clock_idle_sleep_event();
479 * get_cpu_idle_time_us - get the total idle time of a cpu
480 * @cpu: CPU number to query
481 * @last_update_time: variable to store update time in. Do not update
484 * Return the cummulative idle time (since boot) for a given
485 * CPU, in microseconds.
487 * This time is measured via accounting rather than sampling,
488 * and is as accurate as ktime_get() is.
490 * This function returns -1 if NOHZ is not enabled.
492 u64
get_cpu_idle_time_us(int cpu
, u64
*last_update_time
)
494 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
497 if (!tick_nohz_active
)
501 if (last_update_time
) {
502 update_ts_time_stats(cpu
, ts
, now
, last_update_time
);
503 idle
= ts
->idle_sleeptime
;
505 if (ts
->idle_active
&& !nr_iowait_cpu(cpu
)) {
506 ktime_t delta
= ktime_sub(now
, ts
->idle_entrytime
);
508 idle
= ktime_add(ts
->idle_sleeptime
, delta
);
510 idle
= ts
->idle_sleeptime
;
514 return ktime_to_us(idle
);
517 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us
);
520 * get_cpu_iowait_time_us - get the total iowait time of a cpu
521 * @cpu: CPU number to query
522 * @last_update_time: variable to store update time in. Do not update
525 * Return the cummulative iowait time (since boot) for a given
526 * CPU, in microseconds.
528 * This time is measured via accounting rather than sampling,
529 * and is as accurate as ktime_get() is.
531 * This function returns -1 if NOHZ is not enabled.
533 u64
get_cpu_iowait_time_us(int cpu
, u64
*last_update_time
)
535 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
538 if (!tick_nohz_active
)
542 if (last_update_time
) {
543 update_ts_time_stats(cpu
, ts
, now
, last_update_time
);
544 iowait
= ts
->iowait_sleeptime
;
546 if (ts
->idle_active
&& nr_iowait_cpu(cpu
) > 0) {
547 ktime_t delta
= ktime_sub(now
, ts
->idle_entrytime
);
549 iowait
= ktime_add(ts
->iowait_sleeptime
, delta
);
551 iowait
= ts
->iowait_sleeptime
;
555 return ktime_to_us(iowait
);
557 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us
);
559 static void tick_nohz_restart(struct tick_sched
*ts
, ktime_t now
)
561 hrtimer_cancel(&ts
->sched_timer
);
562 hrtimer_set_expires(&ts
->sched_timer
, ts
->last_tick
);
564 /* Forward the time to expire in the future */
565 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
567 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
568 hrtimer_start_expires(&ts
->sched_timer
, HRTIMER_MODE_ABS_PINNED
);
570 tick_program_event(hrtimer_get_expires(&ts
->sched_timer
), 1);
573 static ktime_t
tick_nohz_stop_sched_tick(struct tick_sched
*ts
,
574 ktime_t now
, int cpu
)
576 struct clock_event_device
*dev
= __this_cpu_read(tick_cpu_device
.evtdev
);
577 u64 basemono
, next_tick
, next_tmr
, next_rcu
, delta
, expires
;
578 unsigned long seq
, basejiff
;
581 /* Read jiffies and the time when jiffies were updated last */
583 seq
= read_seqbegin(&jiffies_lock
);
584 basemono
= last_jiffies_update
.tv64
;
586 } while (read_seqretry(&jiffies_lock
, seq
));
587 ts
->last_jiffies
= basejiff
;
589 if (rcu_needs_cpu(basemono
, &next_rcu
) ||
590 arch_needs_cpu() || irq_work_needs_cpu()) {
591 next_tick
= basemono
+ TICK_NSEC
;
594 * Get the next pending timer. If high resolution
595 * timers are enabled this only takes the timer wheel
596 * timers into account. If high resolution timers are
597 * disabled this also looks at the next expiring
600 next_tmr
= get_next_timer_interrupt(basejiff
, basemono
);
601 ts
->next_timer
= next_tmr
;
602 /* Take the next rcu event into account */
603 next_tick
= next_rcu
< next_tmr
? next_rcu
: next_tmr
;
607 * If the tick is due in the next period, keep it ticking or
608 * force prod the timer.
610 delta
= next_tick
- basemono
;
611 if (delta
<= (u64
)TICK_NSEC
) {
614 * We've not stopped the tick yet, and there's a timer in the
615 * next period, so no point in stopping it either, bail.
617 if (!ts
->tick_stopped
)
621 * If, OTOH, we did stop it, but there's a pending (expired)
622 * timer reprogram the timer hardware to fire now.
624 * We will not restart the tick proper, just prod the timer
625 * hardware into firing an interrupt to process the pending
626 * timers. Just like tick_irq_exit() will not restart the tick
627 * for 'normal' interrupts.
629 * Only once we exit the idle loop will we re-enable the tick,
630 * see tick_nohz_idle_exit().
633 tick_nohz_restart(ts
, now
);
639 * If this cpu is the one which updates jiffies, then give up
640 * the assignment and let it be taken by the cpu which runs
641 * the tick timer next, which might be this cpu as well. If we
642 * don't drop this here the jiffies might be stale and
643 * do_timer() never invoked. Keep track of the fact that it
644 * was the one which had the do_timer() duty last. If this cpu
645 * is the one which had the do_timer() duty last, we limit the
646 * sleep time to the timekeeping max_deferement value.
647 * Otherwise we can sleep as long as we want.
649 delta
= timekeeping_max_deferment();
650 if (cpu
== tick_do_timer_cpu
) {
651 tick_do_timer_cpu
= TICK_DO_TIMER_NONE
;
652 ts
->do_timer_last
= 1;
653 } else if (tick_do_timer_cpu
!= TICK_DO_TIMER_NONE
) {
655 ts
->do_timer_last
= 0;
656 } else if (!ts
->do_timer_last
) {
660 #ifdef CONFIG_NO_HZ_FULL
661 /* Limit the tick delta to the maximum scheduler deferment */
663 delta
= min(delta
, scheduler_tick_max_deferment());
666 /* Calculate the next expiry time */
667 if (delta
< (KTIME_MAX
- basemono
))
668 expires
= basemono
+ delta
;
672 expires
= min_t(u64
, expires
, next_tick
);
675 /* Skip reprogram of event if its not changed */
676 if (ts
->tick_stopped
&& (expires
== dev
->next_event
.tv64
))
680 * nohz_stop_sched_tick can be called several times before
681 * the nohz_restart_sched_tick is called. This happens when
682 * interrupts arrive which do not cause a reschedule. In the
683 * first call we save the current tick time, so we can restart
684 * the scheduler tick in nohz_restart_sched_tick.
686 if (!ts
->tick_stopped
) {
687 nohz_balance_enter_idle(cpu
);
688 calc_load_enter_idle();
690 ts
->last_tick
= hrtimer_get_expires(&ts
->sched_timer
);
691 ts
->tick_stopped
= 1;
692 trace_tick_stop(1, " ");
696 * If the expiration time == KTIME_MAX, then we simply stop
699 if (unlikely(expires
== KTIME_MAX
)) {
700 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
701 hrtimer_cancel(&ts
->sched_timer
);
705 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
706 hrtimer_start(&ts
->sched_timer
, tick
, HRTIMER_MODE_ABS_PINNED
);
708 tick_program_event(tick
, 1);
710 /* Update the estimated sleep length */
711 ts
->sleep_length
= ktime_sub(dev
->next_event
, now
);
715 static void tick_nohz_restart_sched_tick(struct tick_sched
*ts
, ktime_t now
, int active
)
717 /* Update jiffies first */
718 tick_do_update_jiffies64(now
);
719 update_cpu_load_nohz(active
);
721 calc_load_exit_idle();
722 touch_softlockup_watchdog_sched();
724 * Cancel the scheduled timer and restore the tick
726 ts
->tick_stopped
= 0;
727 ts
->idle_exittime
= now
;
729 tick_nohz_restart(ts
, now
);
732 static void tick_nohz_full_update_tick(struct tick_sched
*ts
)
734 #ifdef CONFIG_NO_HZ_FULL
735 int cpu
= smp_processor_id();
737 if (!tick_nohz_full_cpu(cpu
))
740 if (!ts
->tick_stopped
&& ts
->nohz_mode
== NOHZ_MODE_INACTIVE
)
743 if (can_stop_full_tick())
744 tick_nohz_stop_sched_tick(ts
, ktime_get(), cpu
);
745 else if (ts
->tick_stopped
)
746 tick_nohz_restart_sched_tick(ts
, ktime_get(), 1);
750 static bool can_stop_idle_tick(int cpu
, struct tick_sched
*ts
)
753 * If this cpu is offline and it is the one which updates
754 * jiffies, then give up the assignment and let it be taken by
755 * the cpu which runs the tick timer next. If we don't drop
756 * this here the jiffies might be stale and do_timer() never
759 if (unlikely(!cpu_online(cpu
))) {
760 if (cpu
== tick_do_timer_cpu
)
761 tick_do_timer_cpu
= TICK_DO_TIMER_NONE
;
765 if (unlikely(ts
->nohz_mode
== NOHZ_MODE_INACTIVE
)) {
766 ts
->sleep_length
= (ktime_t
) { .tv64
= NSEC_PER_SEC
/HZ
};
773 if (unlikely(local_softirq_pending() && cpu_online(cpu
))) {
774 static int ratelimit
;
776 if (ratelimit
< 10 &&
777 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK
)) {
778 pr_warn("NOHZ: local_softirq_pending %02x\n",
779 (unsigned int) local_softirq_pending());
785 if (tick_nohz_full_enabled()) {
787 * Keep the tick alive to guarantee timekeeping progression
788 * if there are full dynticks CPUs around
790 if (tick_do_timer_cpu
== cpu
)
793 * Boot safety: make sure the timekeeping duty has been
794 * assigned before entering dyntick-idle mode,
796 if (tick_do_timer_cpu
== TICK_DO_TIMER_NONE
)
803 static void __tick_nohz_idle_enter(struct tick_sched
*ts
)
805 ktime_t now
, expires
;
806 int cpu
= smp_processor_id();
808 now
= tick_nohz_start_idle(ts
);
810 if (can_stop_idle_tick(cpu
, ts
)) {
811 int was_stopped
= ts
->tick_stopped
;
815 expires
= tick_nohz_stop_sched_tick(ts
, now
, cpu
);
816 if (expires
.tv64
> 0LL) {
818 ts
->idle_expires
= expires
;
821 if (!was_stopped
&& ts
->tick_stopped
)
822 ts
->idle_jiffies
= ts
->last_jiffies
;
827 * tick_nohz_idle_enter - stop the idle tick from the idle task
829 * When the next event is more than a tick into the future, stop the idle tick
830 * Called when we start the idle loop.
832 * The arch is responsible of calling:
834 * - rcu_idle_enter() after its last use of RCU before the CPU is put
836 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
838 void tick_nohz_idle_enter(void)
840 struct tick_sched
*ts
;
842 WARN_ON_ONCE(irqs_disabled());
845 * Update the idle state in the scheduler domain hierarchy
846 * when tick_nohz_stop_sched_tick() is called from the idle loop.
847 * State will be updated to busy during the first busy tick after
850 set_cpu_sd_state_idle();
854 ts
= this_cpu_ptr(&tick_cpu_sched
);
856 __tick_nohz_idle_enter(ts
);
862 * tick_nohz_irq_exit - update next tick event from interrupt exit
864 * When an interrupt fires while we are idle and it doesn't cause
865 * a reschedule, it may still add, modify or delete a timer, enqueue
866 * an RCU callback, etc...
867 * So we need to re-calculate and reprogram the next tick event.
869 void tick_nohz_irq_exit(void)
871 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
874 __tick_nohz_idle_enter(ts
);
876 tick_nohz_full_update_tick(ts
);
880 * tick_nohz_get_sleep_length - return the length of the current sleep
882 * Called from power state control code with interrupts disabled
884 ktime_t
tick_nohz_get_sleep_length(void)
886 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
888 return ts
->sleep_length
;
891 static void tick_nohz_account_idle_ticks(struct tick_sched
*ts
)
893 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
896 if (vtime_accounting_cpu_enabled())
899 * We stopped the tick in idle. Update process times would miss the
900 * time we slept as update_process_times does only a 1 tick
901 * accounting. Enforce that this is accounted to idle !
903 ticks
= jiffies
- ts
->idle_jiffies
;
905 * We might be one off. Do not randomly account a huge number of ticks!
907 if (ticks
&& ticks
< LONG_MAX
)
908 account_idle_ticks(ticks
);
913 * tick_nohz_idle_exit - restart the idle tick from the idle task
915 * Restart the idle tick when the CPU is woken up from idle
916 * This also exit the RCU extended quiescent state. The CPU
917 * can use RCU again after this function is called.
919 void tick_nohz_idle_exit(void)
921 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
926 WARN_ON_ONCE(!ts
->inidle
);
930 if (ts
->idle_active
|| ts
->tick_stopped
)
934 tick_nohz_stop_idle(ts
, now
);
936 if (ts
->tick_stopped
) {
937 tick_nohz_restart_sched_tick(ts
, now
, 0);
938 tick_nohz_account_idle_ticks(ts
);
945 * The nohz low res interrupt handler
947 static void tick_nohz_handler(struct clock_event_device
*dev
)
949 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
950 struct pt_regs
*regs
= get_irq_regs();
951 ktime_t now
= ktime_get();
953 dev
->next_event
.tv64
= KTIME_MAX
;
955 tick_sched_do_timer(now
);
956 tick_sched_handle(ts
, regs
);
958 /* No need to reprogram if we are running tickless */
959 if (unlikely(ts
->tick_stopped
))
962 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
963 tick_program_event(hrtimer_get_expires(&ts
->sched_timer
), 1);
966 static inline void tick_nohz_activate(struct tick_sched
*ts
, int mode
)
968 if (!tick_nohz_enabled
)
970 ts
->nohz_mode
= mode
;
971 /* One update is enough */
972 if (!test_and_set_bit(0, &tick_nohz_active
))
973 timers_update_migration(true);
977 * tick_nohz_switch_to_nohz - switch to nohz mode
979 static void tick_nohz_switch_to_nohz(void)
981 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
984 if (!tick_nohz_enabled
)
987 if (tick_switch_to_oneshot(tick_nohz_handler
))
991 * Recycle the hrtimer in ts, so we can share the
992 * hrtimer_forward with the highres code.
994 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
995 /* Get the next period */
996 next
= tick_init_jiffy_update();
998 hrtimer_set_expires(&ts
->sched_timer
, next
);
999 hrtimer_forward_now(&ts
->sched_timer
, tick_period
);
1000 tick_program_event(hrtimer_get_expires(&ts
->sched_timer
), 1);
1001 tick_nohz_activate(ts
, NOHZ_MODE_LOWRES
);
1005 * When NOHZ is enabled and the tick is stopped, we need to kick the
1006 * tick timer from irq_enter() so that the jiffies update is kept
1007 * alive during long running softirqs. That's ugly as hell, but
1008 * correctness is key even if we need to fix the offending softirq in
1011 * Note, this is different to tick_nohz_restart. We just kick the
1012 * timer and do not touch the other magic bits which need to be done
1013 * when idle is left.
1015 static void tick_nohz_kick_tick(struct tick_sched
*ts
, ktime_t now
)
1018 /* Switch back to 2.6.27 behaviour */
1022 * Do not touch the tick device, when the next expiry is either
1023 * already reached or less/equal than the tick period.
1025 delta
= ktime_sub(hrtimer_get_expires(&ts
->sched_timer
), now
);
1026 if (delta
.tv64
<= tick_period
.tv64
)
1029 tick_nohz_restart(ts
, now
);
1033 static inline void tick_nohz_irq_enter(void)
1035 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
1038 if (!ts
->idle_active
&& !ts
->tick_stopped
)
1041 if (ts
->idle_active
)
1042 tick_nohz_stop_idle(ts
, now
);
1043 if (ts
->tick_stopped
) {
1044 tick_nohz_update_jiffies(now
);
1045 tick_nohz_kick_tick(ts
, now
);
1051 static inline void tick_nohz_switch_to_nohz(void) { }
1052 static inline void tick_nohz_irq_enter(void) { }
1053 static inline void tick_nohz_activate(struct tick_sched
*ts
, int mode
) { }
1055 #endif /* CONFIG_NO_HZ_COMMON */
1058 * Called from irq_enter to notify about the possible interruption of idle()
1060 void tick_irq_enter(void)
1062 tick_check_oneshot_broadcast_this_cpu();
1063 tick_nohz_irq_enter();
1067 * High resolution timer specific code
1069 #ifdef CONFIG_HIGH_RES_TIMERS
1071 * We rearm the timer until we get disabled by the idle code.
1072 * Called with interrupts disabled.
1074 static enum hrtimer_restart
tick_sched_timer(struct hrtimer
*timer
)
1076 struct tick_sched
*ts
=
1077 container_of(timer
, struct tick_sched
, sched_timer
);
1078 struct pt_regs
*regs
= get_irq_regs();
1079 ktime_t now
= ktime_get();
1081 tick_sched_do_timer(now
);
1084 * Do not call, when we are not in irq context and have
1085 * no valid regs pointer
1088 tick_sched_handle(ts
, regs
);
1090 /* No need to reprogram if we are in idle or full dynticks mode */
1091 if (unlikely(ts
->tick_stopped
))
1092 return HRTIMER_NORESTART
;
1094 hrtimer_forward(timer
, now
, tick_period
);
1096 return HRTIMER_RESTART
;
1099 static int sched_skew_tick
;
1101 static int __init
skew_tick(char *str
)
1103 get_option(&str
, &sched_skew_tick
);
1107 early_param("skew_tick", skew_tick
);
1110 * tick_setup_sched_timer - setup the tick emulation timer
1112 void tick_setup_sched_timer(void)
1114 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
1115 ktime_t now
= ktime_get();
1118 * Emulate tick processing via per-CPU hrtimers:
1120 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
1121 ts
->sched_timer
.function
= tick_sched_timer
;
1123 /* Get the next period (per cpu) */
1124 hrtimer_set_expires(&ts
->sched_timer
, tick_init_jiffy_update());
1126 /* Offset the tick to avert jiffies_lock contention. */
1127 if (sched_skew_tick
) {
1128 u64 offset
= ktime_to_ns(tick_period
) >> 1;
1129 do_div(offset
, num_possible_cpus());
1130 offset
*= smp_processor_id();
1131 hrtimer_add_expires_ns(&ts
->sched_timer
, offset
);
1134 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
1135 hrtimer_start_expires(&ts
->sched_timer
, HRTIMER_MODE_ABS_PINNED
);
1136 tick_nohz_activate(ts
, NOHZ_MODE_HIGHRES
);
1138 #endif /* HIGH_RES_TIMERS */
1140 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1141 void tick_cancel_sched_timer(int cpu
)
1143 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
1145 # ifdef CONFIG_HIGH_RES_TIMERS
1146 if (ts
->sched_timer
.base
)
1147 hrtimer_cancel(&ts
->sched_timer
);
1150 memset(ts
, 0, sizeof(*ts
));
1155 * Async notification about clocksource changes
1157 void tick_clock_notify(void)
1161 for_each_possible_cpu(cpu
)
1162 set_bit(0, &per_cpu(tick_cpu_sched
, cpu
).check_clocks
);
1166 * Async notification about clock event changes
1168 void tick_oneshot_notify(void)
1170 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
1172 set_bit(0, &ts
->check_clocks
);
1176 * Check, if a change happened, which makes oneshot possible.
1178 * Called cyclic from the hrtimer softirq (driven by the timer
1179 * softirq) allow_nohz signals, that we can switch into low-res nohz
1180 * mode, because high resolution timers are disabled (either compile
1181 * or runtime). Called with interrupts disabled.
1183 int tick_check_oneshot_change(int allow_nohz
)
1185 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
1187 if (!test_and_clear_bit(0, &ts
->check_clocks
))
1190 if (ts
->nohz_mode
!= NOHZ_MODE_INACTIVE
)
1193 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1199 tick_nohz_switch_to_nohz();