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
);
40 * The time, when the last jiffy update happened. Protected by jiffies_lock.
42 static ktime_t last_jiffies_update
;
44 struct tick_sched
*tick_get_tick_sched(int cpu
)
46 return &per_cpu(tick_cpu_sched
, cpu
);
50 * Must be called with interrupts disabled !
52 static void tick_do_update_jiffies64(ktime_t now
)
54 unsigned long ticks
= 0;
58 * Do a quick check without holding jiffies_lock:
60 delta
= ktime_sub(now
, last_jiffies_update
);
61 if (delta
.tv64
< tick_period
.tv64
)
64 /* Reevalute with jiffies_lock held */
65 write_seqlock(&jiffies_lock
);
67 delta
= ktime_sub(now
, last_jiffies_update
);
68 if (delta
.tv64
>= tick_period
.tv64
) {
70 delta
= ktime_sub(delta
, tick_period
);
71 last_jiffies_update
= ktime_add(last_jiffies_update
,
74 /* Slow path for long timeouts */
75 if (unlikely(delta
.tv64
>= tick_period
.tv64
)) {
76 s64 incr
= ktime_to_ns(tick_period
);
78 ticks
= ktime_divns(delta
, incr
);
80 last_jiffies_update
= ktime_add_ns(last_jiffies_update
,
85 /* Keep the tick_next_period variable up to date */
86 tick_next_period
= ktime_add(last_jiffies_update
, tick_period
);
88 write_sequnlock(&jiffies_lock
);
91 write_sequnlock(&jiffies_lock
);
96 * Initialize and return retrieve the jiffies update.
98 static ktime_t
tick_init_jiffy_update(void)
102 write_seqlock(&jiffies_lock
);
103 /* Did we start the jiffies update yet ? */
104 if (last_jiffies_update
.tv64
== 0)
105 last_jiffies_update
= tick_next_period
;
106 period
= last_jiffies_update
;
107 write_sequnlock(&jiffies_lock
);
112 static void tick_sched_do_timer(ktime_t now
)
114 int cpu
= smp_processor_id();
116 #ifdef CONFIG_NO_HZ_COMMON
118 * Check if the do_timer duty was dropped. We don't care about
119 * concurrency: This happens only when the cpu in charge went
120 * into a long sleep. If two cpus happen to assign themself to
121 * this duty, then the jiffies update is still serialized by
124 if (unlikely(tick_do_timer_cpu
== TICK_DO_TIMER_NONE
)
125 && !tick_nohz_full_cpu(cpu
))
126 tick_do_timer_cpu
= cpu
;
129 /* Check, if the jiffies need an update */
130 if (tick_do_timer_cpu
== cpu
)
131 tick_do_update_jiffies64(now
);
134 static void tick_sched_handle(struct tick_sched
*ts
, struct pt_regs
*regs
)
136 #ifdef CONFIG_NO_HZ_COMMON
138 * When we are idle and the tick is stopped, we have to touch
139 * the watchdog as we might not schedule for a really long
140 * time. This happens on complete idle SMP systems while
141 * waiting on the login prompt. We also increment the "start of
142 * idle" jiffy stamp so the idle accounting adjustment we do
143 * when we go busy again does not account too much ticks.
145 if (ts
->tick_stopped
) {
146 touch_softlockup_watchdog();
147 if (is_idle_task(current
))
151 update_process_times(user_mode(regs
));
152 profile_tick(CPU_PROFILING
);
155 #ifdef CONFIG_NO_HZ_FULL
156 cpumask_var_t tick_nohz_full_mask
;
157 cpumask_var_t housekeeping_mask
;
158 bool tick_nohz_full_running
;
160 static bool can_stop_full_tick(void)
162 WARN_ON_ONCE(!irqs_disabled());
164 if (!sched_can_stop_tick()) {
165 trace_tick_stop(0, "more than 1 task in runqueue\n");
169 if (!posix_cpu_timers_can_stop_tick(current
)) {
170 trace_tick_stop(0, "posix timers running\n");
174 if (!perf_event_can_stop_tick()) {
175 trace_tick_stop(0, "perf events running\n");
179 /* sched_clock_tick() needs us? */
180 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
182 * TODO: kick full dynticks CPUs when
183 * sched_clock_stable is set.
185 if (!sched_clock_stable()) {
186 trace_tick_stop(0, "unstable sched clock\n");
188 * Don't allow the user to think they can get
189 * full NO_HZ with this machine.
191 WARN_ONCE(tick_nohz_full_running
,
192 "NO_HZ FULL will not work with unstable sched clock");
200 static void nohz_full_kick_work_func(struct irq_work
*work
)
202 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
205 static DEFINE_PER_CPU(struct irq_work
, nohz_full_kick_work
) = {
206 .func
= nohz_full_kick_work_func
,
210 * Kick this CPU if it's full dynticks in order to force it to
211 * re-evaluate its dependency on the tick and restart it if necessary.
212 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
215 void tick_nohz_full_kick(void)
217 if (!tick_nohz_full_cpu(smp_processor_id()))
220 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work
));
224 * Kick the CPU if it's full dynticks in order to force it to
225 * re-evaluate its dependency on the tick and restart it if necessary.
227 void tick_nohz_full_kick_cpu(int cpu
)
229 if (!tick_nohz_full_cpu(cpu
))
232 irq_work_queue_on(&per_cpu(nohz_full_kick_work
, cpu
), cpu
);
235 static void nohz_full_kick_ipi(void *info
)
237 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
241 * Kick all full dynticks CPUs in order to force these to re-evaluate
242 * their dependency on the tick and restart it if necessary.
244 void tick_nohz_full_kick_all(void)
246 if (!tick_nohz_full_running
)
250 smp_call_function_many(tick_nohz_full_mask
,
251 nohz_full_kick_ipi
, NULL
, false);
252 tick_nohz_full_kick();
257 * Re-evaluate the need for the tick as we switch the current task.
258 * It might need the tick due to per task/process properties:
259 * perf events, posix cpu timers, ...
261 void __tick_nohz_task_switch(void)
265 local_irq_save(flags
);
267 if (!tick_nohz_full_cpu(smp_processor_id()))
270 if (tick_nohz_tick_stopped() && !can_stop_full_tick())
271 tick_nohz_full_kick();
274 local_irq_restore(flags
);
277 /* Parse the boot-time nohz CPU list from the kernel parameters. */
278 static int __init
tick_nohz_full_setup(char *str
)
280 alloc_bootmem_cpumask_var(&tick_nohz_full_mask
);
281 if (cpulist_parse(str
, tick_nohz_full_mask
) < 0) {
282 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
283 free_bootmem_cpumask_var(tick_nohz_full_mask
);
286 tick_nohz_full_running
= true;
290 __setup("nohz_full=", tick_nohz_full_setup
);
292 static int tick_nohz_cpu_down_callback(struct notifier_block
*nfb
,
293 unsigned long action
,
296 unsigned int cpu
= (unsigned long)hcpu
;
298 switch (action
& ~CPU_TASKS_FROZEN
) {
299 case CPU_DOWN_PREPARE
:
301 * The boot CPU handles housekeeping duty (unbound timers,
302 * workqueues, timekeeping, ...) on behalf of full dynticks
303 * CPUs. It must remain online when nohz full is enabled.
305 if (tick_nohz_full_running
&& tick_do_timer_cpu
== cpu
)
312 static int tick_nohz_init_all(void)
316 #ifdef CONFIG_NO_HZ_FULL_ALL
317 if (!alloc_cpumask_var(&tick_nohz_full_mask
, GFP_KERNEL
)) {
318 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
322 cpumask_setall(tick_nohz_full_mask
);
323 tick_nohz_full_running
= true;
328 void __init
tick_nohz_init(void)
332 if (!tick_nohz_full_running
) {
333 if (tick_nohz_init_all() < 0)
337 if (!alloc_cpumask_var(&housekeeping_mask
, GFP_KERNEL
)) {
338 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
339 cpumask_clear(tick_nohz_full_mask
);
340 tick_nohz_full_running
= false;
345 * Full dynticks uses irq work to drive the tick rescheduling on safe
346 * locking contexts. But then we need irq work to raise its own
347 * interrupts to avoid circular dependency on the tick
349 if (!arch_irq_work_has_interrupt()) {
350 pr_warning("NO_HZ: Can't run full dynticks because arch doesn't "
351 "support irq work self-IPIs\n");
352 cpumask_clear(tick_nohz_full_mask
);
353 cpumask_copy(housekeeping_mask
, cpu_possible_mask
);
354 tick_nohz_full_running
= false;
358 cpu
= smp_processor_id();
360 if (cpumask_test_cpu(cpu
, tick_nohz_full_mask
)) {
361 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu
);
362 cpumask_clear_cpu(cpu
, tick_nohz_full_mask
);
365 cpumask_andnot(housekeeping_mask
,
366 cpu_possible_mask
, tick_nohz_full_mask
);
368 for_each_cpu(cpu
, tick_nohz_full_mask
)
369 context_tracking_cpu_set(cpu
);
371 cpu_notifier(tick_nohz_cpu_down_callback
, 0);
372 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
373 cpumask_pr_args(tick_nohz_full_mask
));
376 * We need at least one CPU to handle housekeeping work such
377 * as timekeeping, unbound timers, workqueues, ...
379 WARN_ON_ONCE(cpumask_empty(housekeeping_mask
));
384 * NOHZ - aka dynamic tick functionality
386 #ifdef CONFIG_NO_HZ_COMMON
390 int tick_nohz_enabled __read_mostly
= 1;
391 unsigned long tick_nohz_active __read_mostly
;
393 * Enable / Disable tickless mode
395 static int __init
setup_tick_nohz(char *str
)
397 if (!strcmp(str
, "off"))
398 tick_nohz_enabled
= 0;
399 else if (!strcmp(str
, "on"))
400 tick_nohz_enabled
= 1;
406 __setup("nohz=", setup_tick_nohz
);
408 int tick_nohz_tick_stopped(void)
410 return __this_cpu_read(tick_cpu_sched
.tick_stopped
);
414 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
416 * Called from interrupt entry when the CPU was idle
418 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
419 * must be updated. Otherwise an interrupt handler could use a stale jiffy
420 * value. We do this unconditionally on any cpu, as we don't know whether the
421 * cpu, which has the update task assigned is in a long sleep.
423 static void tick_nohz_update_jiffies(ktime_t now
)
427 __this_cpu_write(tick_cpu_sched
.idle_waketime
, now
);
429 local_irq_save(flags
);
430 tick_do_update_jiffies64(now
);
431 local_irq_restore(flags
);
433 touch_softlockup_watchdog();
437 * Updates the per cpu time idle statistics counters
440 update_ts_time_stats(int cpu
, struct tick_sched
*ts
, ktime_t now
, u64
*last_update_time
)
444 if (ts
->idle_active
) {
445 delta
= ktime_sub(now
, ts
->idle_entrytime
);
446 if (nr_iowait_cpu(cpu
) > 0)
447 ts
->iowait_sleeptime
= ktime_add(ts
->iowait_sleeptime
, delta
);
449 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
450 ts
->idle_entrytime
= now
;
453 if (last_update_time
)
454 *last_update_time
= ktime_to_us(now
);
458 static void tick_nohz_stop_idle(struct tick_sched
*ts
, ktime_t now
)
460 update_ts_time_stats(smp_processor_id(), ts
, now
, NULL
);
463 sched_clock_idle_wakeup_event(0);
466 static ktime_t
tick_nohz_start_idle(struct tick_sched
*ts
)
468 ktime_t now
= ktime_get();
470 ts
->idle_entrytime
= now
;
472 sched_clock_idle_sleep_event();
477 * get_cpu_idle_time_us - get the total idle time of a cpu
478 * @cpu: CPU number to query
479 * @last_update_time: variable to store update time in. Do not update
482 * Return the cummulative idle time (since boot) for a given
483 * CPU, in microseconds.
485 * This time is measured via accounting rather than sampling,
486 * and is as accurate as ktime_get() is.
488 * This function returns -1 if NOHZ is not enabled.
490 u64
get_cpu_idle_time_us(int cpu
, u64
*last_update_time
)
492 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
495 if (!tick_nohz_active
)
499 if (last_update_time
) {
500 update_ts_time_stats(cpu
, ts
, now
, last_update_time
);
501 idle
= ts
->idle_sleeptime
;
503 if (ts
->idle_active
&& !nr_iowait_cpu(cpu
)) {
504 ktime_t delta
= ktime_sub(now
, ts
->idle_entrytime
);
506 idle
= ktime_add(ts
->idle_sleeptime
, delta
);
508 idle
= ts
->idle_sleeptime
;
512 return ktime_to_us(idle
);
515 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us
);
518 * get_cpu_iowait_time_us - get the total iowait time of a cpu
519 * @cpu: CPU number to query
520 * @last_update_time: variable to store update time in. Do not update
523 * Return the cummulative iowait time (since boot) for a given
524 * CPU, in microseconds.
526 * This time is measured via accounting rather than sampling,
527 * and is as accurate as ktime_get() is.
529 * This function returns -1 if NOHZ is not enabled.
531 u64
get_cpu_iowait_time_us(int cpu
, u64
*last_update_time
)
533 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
536 if (!tick_nohz_active
)
540 if (last_update_time
) {
541 update_ts_time_stats(cpu
, ts
, now
, last_update_time
);
542 iowait
= ts
->iowait_sleeptime
;
544 if (ts
->idle_active
&& nr_iowait_cpu(cpu
) > 0) {
545 ktime_t delta
= ktime_sub(now
, ts
->idle_entrytime
);
547 iowait
= ktime_add(ts
->iowait_sleeptime
, delta
);
549 iowait
= ts
->iowait_sleeptime
;
553 return ktime_to_us(iowait
);
555 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us
);
557 static void tick_nohz_restart(struct tick_sched
*ts
, ktime_t now
)
559 hrtimer_cancel(&ts
->sched_timer
);
560 hrtimer_set_expires(&ts
->sched_timer
, ts
->last_tick
);
562 /* Forward the time to expire in the future */
563 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
565 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
566 hrtimer_start_expires(&ts
->sched_timer
, HRTIMER_MODE_ABS_PINNED
);
568 tick_program_event(hrtimer_get_expires(&ts
->sched_timer
), 1);
571 static ktime_t
tick_nohz_stop_sched_tick(struct tick_sched
*ts
,
572 ktime_t now
, int cpu
)
574 struct clock_event_device
*dev
= __this_cpu_read(tick_cpu_device
.evtdev
);
575 u64 basemono
, next_tick
, next_tmr
, next_rcu
, delta
, expires
;
576 unsigned long seq
, basejiff
;
579 /* Read jiffies and the time when jiffies were updated last */
581 seq
= read_seqbegin(&jiffies_lock
);
582 basemono
= last_jiffies_update
.tv64
;
584 } while (read_seqretry(&jiffies_lock
, seq
));
585 ts
->last_jiffies
= basejiff
;
587 if (rcu_needs_cpu(basemono
, &next_rcu
) ||
588 arch_needs_cpu() || irq_work_needs_cpu()) {
589 next_tick
= basemono
+ TICK_NSEC
;
592 * Get the next pending timer. If high resolution
593 * timers are enabled this only takes the timer wheel
594 * timers into account. If high resolution timers are
595 * disabled this also looks at the next expiring
598 next_tmr
= get_next_timer_interrupt(basejiff
, basemono
);
599 ts
->next_timer
= next_tmr
;
600 /* Take the next rcu event into account */
601 next_tick
= next_rcu
< next_tmr
? next_rcu
: next_tmr
;
605 * If the tick is due in the next period, keep it ticking or
608 delta
= next_tick
- basemono
;
609 if (delta
<= (u64
)TICK_NSEC
) {
611 if (!ts
->tick_stopped
)
614 /* Tick is stopped, but required now. Enforce it */
615 tick_nohz_restart(ts
, now
);
621 * If this cpu is the one which updates jiffies, then give up
622 * the assignment and let it be taken by the cpu which runs
623 * the tick timer next, which might be this cpu as well. If we
624 * don't drop this here the jiffies might be stale and
625 * do_timer() never invoked. Keep track of the fact that it
626 * was the one which had the do_timer() duty last. If this cpu
627 * is the one which had the do_timer() duty last, we limit the
628 * sleep time to the timekeeping max_deferement value.
629 * Otherwise we can sleep as long as we want.
631 delta
= timekeeping_max_deferment();
632 if (cpu
== tick_do_timer_cpu
) {
633 tick_do_timer_cpu
= TICK_DO_TIMER_NONE
;
634 ts
->do_timer_last
= 1;
635 } else if (tick_do_timer_cpu
!= TICK_DO_TIMER_NONE
) {
637 ts
->do_timer_last
= 0;
638 } else if (!ts
->do_timer_last
) {
642 #ifdef CONFIG_NO_HZ_FULL
643 /* Limit the tick delta to the maximum scheduler deferment */
645 delta
= min(delta
, scheduler_tick_max_deferment());
648 /* Calculate the next expiry time */
649 if (delta
< (KTIME_MAX
- basemono
))
650 expires
= basemono
+ delta
;
654 expires
= min_t(u64
, expires
, next_tick
);
657 /* Skip reprogram of event if its not changed */
658 if (ts
->tick_stopped
&& (expires
== dev
->next_event
.tv64
))
662 * nohz_stop_sched_tick can be called several times before
663 * the nohz_restart_sched_tick is called. This happens when
664 * interrupts arrive which do not cause a reschedule. In the
665 * first call we save the current tick time, so we can restart
666 * the scheduler tick in nohz_restart_sched_tick.
668 if (!ts
->tick_stopped
) {
669 nohz_balance_enter_idle(cpu
);
670 calc_load_enter_idle();
672 ts
->last_tick
= hrtimer_get_expires(&ts
->sched_timer
);
673 ts
->tick_stopped
= 1;
674 trace_tick_stop(1, " ");
678 * If the expiration time == KTIME_MAX, then we simply stop
681 if (unlikely(expires
== KTIME_MAX
)) {
682 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
683 hrtimer_cancel(&ts
->sched_timer
);
687 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
688 hrtimer_start(&ts
->sched_timer
, tick
, HRTIMER_MODE_ABS_PINNED
);
690 tick_program_event(tick
, 1);
692 /* Update the estimated sleep length */
693 ts
->sleep_length
= ktime_sub(dev
->next_event
, now
);
697 static void tick_nohz_restart_sched_tick(struct tick_sched
*ts
, ktime_t now
)
699 /* Update jiffies first */
700 tick_do_update_jiffies64(now
);
701 update_cpu_load_nohz();
703 calc_load_exit_idle();
704 touch_softlockup_watchdog();
706 * Cancel the scheduled timer and restore the tick
708 ts
->tick_stopped
= 0;
709 ts
->idle_exittime
= now
;
711 tick_nohz_restart(ts
, now
);
714 static void tick_nohz_full_update_tick(struct tick_sched
*ts
)
716 #ifdef CONFIG_NO_HZ_FULL
717 int cpu
= smp_processor_id();
719 if (!tick_nohz_full_cpu(cpu
))
722 if (!ts
->tick_stopped
&& ts
->nohz_mode
== NOHZ_MODE_INACTIVE
)
725 if (can_stop_full_tick())
726 tick_nohz_stop_sched_tick(ts
, ktime_get(), cpu
);
727 else if (ts
->tick_stopped
)
728 tick_nohz_restart_sched_tick(ts
, ktime_get());
732 static bool can_stop_idle_tick(int cpu
, struct tick_sched
*ts
)
735 * If this cpu is offline and it is the one which updates
736 * jiffies, then give up the assignment and let it be taken by
737 * the cpu which runs the tick timer next. If we don't drop
738 * this here the jiffies might be stale and do_timer() never
741 if (unlikely(!cpu_online(cpu
))) {
742 if (cpu
== tick_do_timer_cpu
)
743 tick_do_timer_cpu
= TICK_DO_TIMER_NONE
;
747 if (unlikely(ts
->nohz_mode
== NOHZ_MODE_INACTIVE
)) {
748 ts
->sleep_length
= (ktime_t
) { .tv64
= NSEC_PER_SEC
/HZ
};
755 if (unlikely(local_softirq_pending() && cpu_online(cpu
))) {
756 static int ratelimit
;
758 if (ratelimit
< 10 &&
759 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK
)) {
760 pr_warn("NOHZ: local_softirq_pending %02x\n",
761 (unsigned int) local_softirq_pending());
767 if (tick_nohz_full_enabled()) {
769 * Keep the tick alive to guarantee timekeeping progression
770 * if there are full dynticks CPUs around
772 if (tick_do_timer_cpu
== cpu
)
775 * Boot safety: make sure the timekeeping duty has been
776 * assigned before entering dyntick-idle mode,
778 if (tick_do_timer_cpu
== TICK_DO_TIMER_NONE
)
785 static void __tick_nohz_idle_enter(struct tick_sched
*ts
)
787 ktime_t now
, expires
;
788 int cpu
= smp_processor_id();
790 now
= tick_nohz_start_idle(ts
);
792 if (can_stop_idle_tick(cpu
, ts
)) {
793 int was_stopped
= ts
->tick_stopped
;
797 expires
= tick_nohz_stop_sched_tick(ts
, now
, cpu
);
798 if (expires
.tv64
> 0LL) {
800 ts
->idle_expires
= expires
;
803 if (!was_stopped
&& ts
->tick_stopped
)
804 ts
->idle_jiffies
= ts
->last_jiffies
;
809 * tick_nohz_idle_enter - stop the idle tick from the idle task
811 * When the next event is more than a tick into the future, stop the idle tick
812 * Called when we start the idle loop.
814 * The arch is responsible of calling:
816 * - rcu_idle_enter() after its last use of RCU before the CPU is put
818 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
820 void tick_nohz_idle_enter(void)
822 struct tick_sched
*ts
;
824 WARN_ON_ONCE(irqs_disabled());
827 * Update the idle state in the scheduler domain hierarchy
828 * when tick_nohz_stop_sched_tick() is called from the idle loop.
829 * State will be updated to busy during the first busy tick after
832 set_cpu_sd_state_idle();
836 ts
= this_cpu_ptr(&tick_cpu_sched
);
838 __tick_nohz_idle_enter(ts
);
844 * tick_nohz_irq_exit - update next tick event from interrupt exit
846 * When an interrupt fires while we are idle and it doesn't cause
847 * a reschedule, it may still add, modify or delete a timer, enqueue
848 * an RCU callback, etc...
849 * So we need to re-calculate and reprogram the next tick event.
851 void tick_nohz_irq_exit(void)
853 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
856 __tick_nohz_idle_enter(ts
);
858 tick_nohz_full_update_tick(ts
);
862 * tick_nohz_get_sleep_length - return the length of the current sleep
864 * Called from power state control code with interrupts disabled
866 ktime_t
tick_nohz_get_sleep_length(void)
868 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
870 return ts
->sleep_length
;
873 static void tick_nohz_account_idle_ticks(struct tick_sched
*ts
)
875 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
878 if (vtime_accounting_enabled())
881 * We stopped the tick in idle. Update process times would miss the
882 * time we slept as update_process_times does only a 1 tick
883 * accounting. Enforce that this is accounted to idle !
885 ticks
= jiffies
- ts
->idle_jiffies
;
887 * We might be one off. Do not randomly account a huge number of ticks!
889 if (ticks
&& ticks
< LONG_MAX
)
890 account_idle_ticks(ticks
);
895 * tick_nohz_idle_exit - restart the idle tick from the idle task
897 * Restart the idle tick when the CPU is woken up from idle
898 * This also exit the RCU extended quiescent state. The CPU
899 * can use RCU again after this function is called.
901 void tick_nohz_idle_exit(void)
903 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
908 WARN_ON_ONCE(!ts
->inidle
);
912 if (ts
->idle_active
|| ts
->tick_stopped
)
916 tick_nohz_stop_idle(ts
, now
);
918 if (ts
->tick_stopped
) {
919 tick_nohz_restart_sched_tick(ts
, now
);
920 tick_nohz_account_idle_ticks(ts
);
927 * The nohz low res interrupt handler
929 static void tick_nohz_handler(struct clock_event_device
*dev
)
931 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
932 struct pt_regs
*regs
= get_irq_regs();
933 ktime_t now
= ktime_get();
935 dev
->next_event
.tv64
= KTIME_MAX
;
937 tick_sched_do_timer(now
);
938 tick_sched_handle(ts
, regs
);
940 /* No need to reprogram if we are running tickless */
941 if (unlikely(ts
->tick_stopped
))
944 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
945 tick_program_event(hrtimer_get_expires(&ts
->sched_timer
), 1);
948 static inline void tick_nohz_activate(struct tick_sched
*ts
, int mode
)
950 if (!tick_nohz_enabled
)
952 ts
->nohz_mode
= mode
;
953 /* One update is enough */
954 if (!test_and_set_bit(0, &tick_nohz_active
))
955 timers_update_migration(true);
959 * tick_nohz_switch_to_nohz - switch to nohz mode
961 static void tick_nohz_switch_to_nohz(void)
963 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
966 if (!tick_nohz_enabled
)
969 if (tick_switch_to_oneshot(tick_nohz_handler
))
973 * Recycle the hrtimer in ts, so we can share the
974 * hrtimer_forward with the highres code.
976 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
977 /* Get the next period */
978 next
= tick_init_jiffy_update();
980 hrtimer_forward_now(&ts
->sched_timer
, tick_period
);
981 hrtimer_set_expires(&ts
->sched_timer
, next
);
982 tick_program_event(next
, 1);
983 tick_nohz_activate(ts
, NOHZ_MODE_LOWRES
);
987 * When NOHZ is enabled and the tick is stopped, we need to kick the
988 * tick timer from irq_enter() so that the jiffies update is kept
989 * alive during long running softirqs. That's ugly as hell, but
990 * correctness is key even if we need to fix the offending softirq in
993 * Note, this is different to tick_nohz_restart. We just kick the
994 * timer and do not touch the other magic bits which need to be done
997 static void tick_nohz_kick_tick(struct tick_sched
*ts
, ktime_t now
)
1000 /* Switch back to 2.6.27 behaviour */
1004 * Do not touch the tick device, when the next expiry is either
1005 * already reached or less/equal than the tick period.
1007 delta
= ktime_sub(hrtimer_get_expires(&ts
->sched_timer
), now
);
1008 if (delta
.tv64
<= tick_period
.tv64
)
1011 tick_nohz_restart(ts
, now
);
1015 static inline void tick_nohz_irq_enter(void)
1017 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
1020 if (!ts
->idle_active
&& !ts
->tick_stopped
)
1023 if (ts
->idle_active
)
1024 tick_nohz_stop_idle(ts
, now
);
1025 if (ts
->tick_stopped
) {
1026 tick_nohz_update_jiffies(now
);
1027 tick_nohz_kick_tick(ts
, now
);
1033 static inline void tick_nohz_switch_to_nohz(void) { }
1034 static inline void tick_nohz_irq_enter(void) { }
1035 static inline void tick_nohz_activate(struct tick_sched
*ts
, int mode
) { }
1037 #endif /* CONFIG_NO_HZ_COMMON */
1040 * Called from irq_enter to notify about the possible interruption of idle()
1042 void tick_irq_enter(void)
1044 tick_check_oneshot_broadcast_this_cpu();
1045 tick_nohz_irq_enter();
1049 * High resolution timer specific code
1051 #ifdef CONFIG_HIGH_RES_TIMERS
1053 * We rearm the timer until we get disabled by the idle code.
1054 * Called with interrupts disabled.
1056 static enum hrtimer_restart
tick_sched_timer(struct hrtimer
*timer
)
1058 struct tick_sched
*ts
=
1059 container_of(timer
, struct tick_sched
, sched_timer
);
1060 struct pt_regs
*regs
= get_irq_regs();
1061 ktime_t now
= ktime_get();
1063 tick_sched_do_timer(now
);
1066 * Do not call, when we are not in irq context and have
1067 * no valid regs pointer
1070 tick_sched_handle(ts
, regs
);
1072 /* No need to reprogram if we are in idle or full dynticks mode */
1073 if (unlikely(ts
->tick_stopped
))
1074 return HRTIMER_NORESTART
;
1076 hrtimer_forward(timer
, now
, tick_period
);
1078 return HRTIMER_RESTART
;
1081 static int sched_skew_tick
;
1083 static int __init
skew_tick(char *str
)
1085 get_option(&str
, &sched_skew_tick
);
1089 early_param("skew_tick", skew_tick
);
1092 * tick_setup_sched_timer - setup the tick emulation timer
1094 void tick_setup_sched_timer(void)
1096 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
1097 ktime_t now
= ktime_get();
1100 * Emulate tick processing via per-CPU hrtimers:
1102 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
1103 ts
->sched_timer
.function
= tick_sched_timer
;
1105 /* Get the next period (per cpu) */
1106 hrtimer_set_expires(&ts
->sched_timer
, tick_init_jiffy_update());
1108 /* Offset the tick to avert jiffies_lock contention. */
1109 if (sched_skew_tick
) {
1110 u64 offset
= ktime_to_ns(tick_period
) >> 1;
1111 do_div(offset
, num_possible_cpus());
1112 offset
*= smp_processor_id();
1113 hrtimer_add_expires_ns(&ts
->sched_timer
, offset
);
1116 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
1117 hrtimer_start_expires(&ts
->sched_timer
, HRTIMER_MODE_ABS_PINNED
);
1118 tick_nohz_activate(ts
, NOHZ_MODE_HIGHRES
);
1120 #endif /* HIGH_RES_TIMERS */
1122 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1123 void tick_cancel_sched_timer(int cpu
)
1125 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
1127 # ifdef CONFIG_HIGH_RES_TIMERS
1128 if (ts
->sched_timer
.base
)
1129 hrtimer_cancel(&ts
->sched_timer
);
1132 memset(ts
, 0, sizeof(*ts
));
1137 * Async notification about clocksource changes
1139 void tick_clock_notify(void)
1143 for_each_possible_cpu(cpu
)
1144 set_bit(0, &per_cpu(tick_cpu_sched
, cpu
).check_clocks
);
1148 * Async notification about clock event changes
1150 void tick_oneshot_notify(void)
1152 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
1154 set_bit(0, &ts
->check_clocks
);
1158 * Check, if a change happened, which makes oneshot possible.
1160 * Called cyclic from the hrtimer softirq (driven by the timer
1161 * softirq) allow_nohz signals, that we can switch into low-res nohz
1162 * mode, because high resolution timers are disabled (either compile
1163 * or runtime). Called with interrupts disabled.
1165 int tick_check_oneshot_change(int allow_nohz
)
1167 struct tick_sched
*ts
= this_cpu_ptr(&tick_cpu_sched
);
1169 if (!test_and_clear_bit(0, &ts
->check_clocks
))
1172 if (ts
->nohz_mode
!= NOHZ_MODE_INACTIVE
)
1175 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1181 tick_nohz_switch_to_nohz();