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>
25 #include <asm/irq_regs.h>
27 #include "tick-internal.h"
30 * Per cpu nohz control structure
32 DEFINE_PER_CPU(struct tick_sched
, tick_cpu_sched
);
35 * The time, when the last jiffy update happened. Protected by jiffies_lock.
37 static ktime_t last_jiffies_update
;
39 struct tick_sched
*tick_get_tick_sched(int cpu
)
41 return &per_cpu(tick_cpu_sched
, cpu
);
45 * Must be called with interrupts disabled !
47 static void tick_do_update_jiffies64(ktime_t now
)
49 unsigned long ticks
= 0;
53 * Do a quick check without holding jiffies_lock:
55 delta
= ktime_sub(now
, last_jiffies_update
);
56 if (delta
.tv64
< tick_period
.tv64
)
59 /* Reevalute with jiffies_lock held */
60 write_seqlock(&jiffies_lock
);
62 delta
= ktime_sub(now
, last_jiffies_update
);
63 if (delta
.tv64
>= tick_period
.tv64
) {
65 delta
= ktime_sub(delta
, tick_period
);
66 last_jiffies_update
= ktime_add(last_jiffies_update
,
69 /* Slow path for long timeouts */
70 if (unlikely(delta
.tv64
>= tick_period
.tv64
)) {
71 s64 incr
= ktime_to_ns(tick_period
);
73 ticks
= ktime_divns(delta
, incr
);
75 last_jiffies_update
= ktime_add_ns(last_jiffies_update
,
80 /* Keep the tick_next_period variable up to date */
81 tick_next_period
= ktime_add(last_jiffies_update
, tick_period
);
83 write_sequnlock(&jiffies_lock
);
87 * Initialize and return retrieve the jiffies update.
89 static ktime_t
tick_init_jiffy_update(void)
93 write_seqlock(&jiffies_lock
);
94 /* Did we start the jiffies update yet ? */
95 if (last_jiffies_update
.tv64
== 0)
96 last_jiffies_update
= tick_next_period
;
97 period
= last_jiffies_update
;
98 write_sequnlock(&jiffies_lock
);
103 static void tick_sched_do_timer(ktime_t now
)
105 int cpu
= smp_processor_id();
107 #ifdef CONFIG_NO_HZ_COMMON
109 * Check if the do_timer duty was dropped. We don't care about
110 * concurrency: This happens only when the cpu in charge went
111 * into a long sleep. If two cpus happen to assign themself to
112 * this duty, then the jiffies update is still serialized by
115 if (unlikely(tick_do_timer_cpu
== TICK_DO_TIMER_NONE
)
116 && !tick_nohz_full_cpu(cpu
))
117 tick_do_timer_cpu
= cpu
;
120 /* Check, if the jiffies need an update */
121 if (tick_do_timer_cpu
== cpu
)
122 tick_do_update_jiffies64(now
);
125 static void tick_sched_handle(struct tick_sched
*ts
, struct pt_regs
*regs
)
127 #ifdef CONFIG_NO_HZ_COMMON
129 * When we are idle and the tick is stopped, we have to touch
130 * the watchdog as we might not schedule for a really long
131 * time. This happens on complete idle SMP systems while
132 * waiting on the login prompt. We also increment the "start of
133 * idle" jiffy stamp so the idle accounting adjustment we do
134 * when we go busy again does not account too much ticks.
136 if (ts
->tick_stopped
) {
137 touch_softlockup_watchdog();
138 if (is_idle_task(current
))
142 update_process_times(user_mode(regs
));
143 profile_tick(CPU_PROFILING
);
146 #ifdef CONFIG_NO_HZ_FULL
147 static cpumask_var_t nohz_full_mask
;
148 bool have_nohz_full_mask
;
151 * Re-evaluate the need for the tick on the current CPU
152 * and restart it if necessary.
154 static void tick_nohz_full_check(void)
157 * STUB for now, will be filled with the full tick stop/restart
158 * infrastructure patches
162 static void nohz_full_kick_work_func(struct irq_work
*work
)
164 tick_nohz_full_check();
167 static DEFINE_PER_CPU(struct irq_work
, nohz_full_kick_work
) = {
168 .func
= nohz_full_kick_work_func
,
172 * Kick the current CPU if it's full dynticks in order to force it to
173 * re-evaluate its dependency on the tick and restart it if necessary.
175 void tick_nohz_full_kick(void)
177 if (tick_nohz_full_cpu(smp_processor_id()))
178 irq_work_queue(&__get_cpu_var(nohz_full_kick_work
));
181 static void nohz_full_kick_ipi(void *info
)
183 tick_nohz_full_check();
187 * Kick all full dynticks CPUs in order to force these to re-evaluate
188 * their dependency on the tick and restart it if necessary.
190 void tick_nohz_full_kick_all(void)
192 if (!have_nohz_full_mask
)
196 smp_call_function_many(nohz_full_mask
,
197 nohz_full_kick_ipi
, NULL
, false);
201 int tick_nohz_full_cpu(int cpu
)
203 if (!have_nohz_full_mask
)
206 return cpumask_test_cpu(cpu
, nohz_full_mask
);
209 /* Parse the boot-time nohz CPU list from the kernel parameters. */
210 static int __init
tick_nohz_full_setup(char *str
)
214 alloc_bootmem_cpumask_var(&nohz_full_mask
);
215 if (cpulist_parse(str
, nohz_full_mask
) < 0) {
216 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
220 cpu
= smp_processor_id();
221 if (cpumask_test_cpu(cpu
, nohz_full_mask
)) {
222 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu
);
223 cpumask_clear_cpu(cpu
, nohz_full_mask
);
225 have_nohz_full_mask
= true;
229 __setup("nohz_full=", tick_nohz_full_setup
);
231 static int __cpuinit
tick_nohz_cpu_down_callback(struct notifier_block
*nfb
,
232 unsigned long action
,
235 unsigned int cpu
= (unsigned long)hcpu
;
237 switch (action
& ~CPU_TASKS_FROZEN
) {
238 case CPU_DOWN_PREPARE
:
240 * If we handle the timekeeping duty for full dynticks CPUs,
241 * we can't safely shutdown that CPU.
243 if (have_nohz_full_mask
&& tick_do_timer_cpu
== cpu
)
251 * Worst case string length in chunks of CPU range seems 2 steps
252 * separations: 0,2,4,6,...
253 * This is NR_CPUS + sizeof('\0')
255 static char __initdata nohz_full_buf
[NR_CPUS
+ 1];
257 static int tick_nohz_init_all(void)
261 #ifdef CONFIG_NO_HZ_FULL_ALL
262 if (!alloc_cpumask_var(&nohz_full_mask
, GFP_KERNEL
)) {
263 pr_err("NO_HZ: Can't allocate full dynticks cpumask\n");
267 cpumask_setall(nohz_full_mask
);
268 cpumask_clear_cpu(smp_processor_id(), nohz_full_mask
);
269 have_nohz_full_mask
= true;
274 void __init
tick_nohz_init(void)
278 if (!have_nohz_full_mask
) {
279 if (tick_nohz_init_all() < 0)
283 cpu_notifier(tick_nohz_cpu_down_callback
, 0);
285 /* Make sure full dynticks CPU are also RCU nocbs */
286 for_each_cpu(cpu
, nohz_full_mask
) {
287 if (!rcu_is_nocb_cpu(cpu
)) {
288 pr_warning("NO_HZ: CPU %d is not RCU nocb: "
289 "cleared from nohz_full range", cpu
);
290 cpumask_clear_cpu(cpu
, nohz_full_mask
);
294 cpulist_scnprintf(nohz_full_buf
, sizeof(nohz_full_buf
), nohz_full_mask
);
295 pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf
);
298 #define have_nohz_full_mask (0)
302 * NOHZ - aka dynamic tick functionality
304 #ifdef CONFIG_NO_HZ_COMMON
308 int tick_nohz_enabled __read_mostly
= 1;
311 * Enable / Disable tickless mode
313 static int __init
setup_tick_nohz(char *str
)
315 if (!strcmp(str
, "off"))
316 tick_nohz_enabled
= 0;
317 else if (!strcmp(str
, "on"))
318 tick_nohz_enabled
= 1;
324 __setup("nohz=", setup_tick_nohz
);
327 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
329 * Called from interrupt entry when the CPU was idle
331 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
332 * must be updated. Otherwise an interrupt handler could use a stale jiffy
333 * value. We do this unconditionally on any cpu, as we don't know whether the
334 * cpu, which has the update task assigned is in a long sleep.
336 static void tick_nohz_update_jiffies(ktime_t now
)
338 int cpu
= smp_processor_id();
339 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
342 ts
->idle_waketime
= now
;
344 local_irq_save(flags
);
345 tick_do_update_jiffies64(now
);
346 local_irq_restore(flags
);
348 touch_softlockup_watchdog();
352 * Updates the per cpu time idle statistics counters
355 update_ts_time_stats(int cpu
, struct tick_sched
*ts
, ktime_t now
, u64
*last_update_time
)
359 if (ts
->idle_active
) {
360 delta
= ktime_sub(now
, ts
->idle_entrytime
);
361 if (nr_iowait_cpu(cpu
) > 0)
362 ts
->iowait_sleeptime
= ktime_add(ts
->iowait_sleeptime
, delta
);
364 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
365 ts
->idle_entrytime
= now
;
368 if (last_update_time
)
369 *last_update_time
= ktime_to_us(now
);
373 static void tick_nohz_stop_idle(int cpu
, ktime_t now
)
375 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
377 update_ts_time_stats(cpu
, ts
, now
, NULL
);
380 sched_clock_idle_wakeup_event(0);
383 static ktime_t
tick_nohz_start_idle(int cpu
, struct tick_sched
*ts
)
385 ktime_t now
= ktime_get();
387 ts
->idle_entrytime
= now
;
389 sched_clock_idle_sleep_event();
394 * get_cpu_idle_time_us - get the total idle time of a cpu
395 * @cpu: CPU number to query
396 * @last_update_time: variable to store update time in. Do not update
399 * Return the cummulative idle time (since boot) for a given
400 * CPU, in microseconds.
402 * This time is measured via accounting rather than sampling,
403 * and is as accurate as ktime_get() is.
405 * This function returns -1 if NOHZ is not enabled.
407 u64
get_cpu_idle_time_us(int cpu
, u64
*last_update_time
)
409 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
412 if (!tick_nohz_enabled
)
416 if (last_update_time
) {
417 update_ts_time_stats(cpu
, ts
, now
, last_update_time
);
418 idle
= ts
->idle_sleeptime
;
420 if (ts
->idle_active
&& !nr_iowait_cpu(cpu
)) {
421 ktime_t delta
= ktime_sub(now
, ts
->idle_entrytime
);
423 idle
= ktime_add(ts
->idle_sleeptime
, delta
);
425 idle
= ts
->idle_sleeptime
;
429 return ktime_to_us(idle
);
432 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us
);
435 * get_cpu_iowait_time_us - get the total iowait time of a cpu
436 * @cpu: CPU number to query
437 * @last_update_time: variable to store update time in. Do not update
440 * Return the cummulative iowait time (since boot) for a given
441 * CPU, in microseconds.
443 * This time is measured via accounting rather than sampling,
444 * and is as accurate as ktime_get() is.
446 * This function returns -1 if NOHZ is not enabled.
448 u64
get_cpu_iowait_time_us(int cpu
, u64
*last_update_time
)
450 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
453 if (!tick_nohz_enabled
)
457 if (last_update_time
) {
458 update_ts_time_stats(cpu
, ts
, now
, last_update_time
);
459 iowait
= ts
->iowait_sleeptime
;
461 if (ts
->idle_active
&& nr_iowait_cpu(cpu
) > 0) {
462 ktime_t delta
= ktime_sub(now
, ts
->idle_entrytime
);
464 iowait
= ktime_add(ts
->iowait_sleeptime
, delta
);
466 iowait
= ts
->iowait_sleeptime
;
470 return ktime_to_us(iowait
);
472 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us
);
474 static ktime_t
tick_nohz_stop_sched_tick(struct tick_sched
*ts
,
475 ktime_t now
, int cpu
)
477 unsigned long seq
, last_jiffies
, next_jiffies
, delta_jiffies
;
478 ktime_t last_update
, expires
, ret
= { .tv64
= 0 };
479 unsigned long rcu_delta_jiffies
;
480 struct clock_event_device
*dev
= __get_cpu_var(tick_cpu_device
).evtdev
;
483 /* Read jiffies and the time when jiffies were updated last */
485 seq
= read_seqbegin(&jiffies_lock
);
486 last_update
= last_jiffies_update
;
487 last_jiffies
= jiffies
;
488 time_delta
= timekeeping_max_deferment();
489 } while (read_seqretry(&jiffies_lock
, seq
));
491 if (rcu_needs_cpu(cpu
, &rcu_delta_jiffies
) ||
492 arch_needs_cpu(cpu
) || irq_work_needs_cpu()) {
493 next_jiffies
= last_jiffies
+ 1;
496 /* Get the next timer wheel timer */
497 next_jiffies
= get_next_timer_interrupt(last_jiffies
);
498 delta_jiffies
= next_jiffies
- last_jiffies
;
499 if (rcu_delta_jiffies
< delta_jiffies
) {
500 next_jiffies
= last_jiffies
+ rcu_delta_jiffies
;
501 delta_jiffies
= rcu_delta_jiffies
;
505 * Do not stop the tick, if we are only one off
506 * or if the cpu is required for rcu
508 if (!ts
->tick_stopped
&& delta_jiffies
== 1)
511 /* Schedule the tick, if we are at least one jiffie off */
512 if ((long)delta_jiffies
>= 1) {
515 * If this cpu is the one which updates jiffies, then
516 * give up the assignment and let it be taken by the
517 * cpu which runs the tick timer next, which might be
518 * this cpu as well. If we don't drop this here the
519 * jiffies might be stale and do_timer() never
520 * invoked. Keep track of the fact that it was the one
521 * which had the do_timer() duty last. If this cpu is
522 * the one which had the do_timer() duty last, we
523 * limit the sleep time to the timekeeping
524 * max_deferement value which we retrieved
525 * above. Otherwise we can sleep as long as we want.
527 if (cpu
== tick_do_timer_cpu
) {
528 tick_do_timer_cpu
= TICK_DO_TIMER_NONE
;
529 ts
->do_timer_last
= 1;
530 } else if (tick_do_timer_cpu
!= TICK_DO_TIMER_NONE
) {
531 time_delta
= KTIME_MAX
;
532 ts
->do_timer_last
= 0;
533 } else if (!ts
->do_timer_last
) {
534 time_delta
= KTIME_MAX
;
538 * calculate the expiry time for the next timer wheel
539 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
540 * that there is no timer pending or at least extremely
541 * far into the future (12 days for HZ=1000). In this
542 * case we set the expiry to the end of time.
544 if (likely(delta_jiffies
< NEXT_TIMER_MAX_DELTA
)) {
546 * Calculate the time delta for the next timer event.
547 * If the time delta exceeds the maximum time delta
548 * permitted by the current clocksource then adjust
549 * the time delta accordingly to ensure the
550 * clocksource does not wrap.
552 time_delta
= min_t(u64
, time_delta
,
553 tick_period
.tv64
* delta_jiffies
);
556 if (time_delta
< KTIME_MAX
)
557 expires
= ktime_add_ns(last_update
, time_delta
);
559 expires
.tv64
= KTIME_MAX
;
561 /* Skip reprogram of event if its not changed */
562 if (ts
->tick_stopped
&& ktime_equal(expires
, dev
->next_event
))
568 * nohz_stop_sched_tick can be called several times before
569 * the nohz_restart_sched_tick is called. This happens when
570 * interrupts arrive which do not cause a reschedule. In the
571 * first call we save the current tick time, so we can restart
572 * the scheduler tick in nohz_restart_sched_tick.
574 if (!ts
->tick_stopped
) {
575 nohz_balance_enter_idle(cpu
);
576 calc_load_enter_idle();
578 ts
->last_tick
= hrtimer_get_expires(&ts
->sched_timer
);
579 ts
->tick_stopped
= 1;
583 * If the expiration time == KTIME_MAX, then
584 * in this case we simply stop the tick timer.
586 if (unlikely(expires
.tv64
== KTIME_MAX
)) {
587 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
588 hrtimer_cancel(&ts
->sched_timer
);
592 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
593 hrtimer_start(&ts
->sched_timer
, expires
,
594 HRTIMER_MODE_ABS_PINNED
);
595 /* Check, if the timer was already in the past */
596 if (hrtimer_active(&ts
->sched_timer
))
598 } else if (!tick_program_event(expires
, 0))
601 * We are past the event already. So we crossed a
602 * jiffie boundary. Update jiffies and raise the
605 tick_do_update_jiffies64(ktime_get());
607 raise_softirq_irqoff(TIMER_SOFTIRQ
);
609 ts
->next_jiffies
= next_jiffies
;
610 ts
->last_jiffies
= last_jiffies
;
611 ts
->sleep_length
= ktime_sub(dev
->next_event
, now
);
616 static bool can_stop_idle_tick(int cpu
, struct tick_sched
*ts
)
619 * If this cpu is offline and it is the one which updates
620 * jiffies, then give up the assignment and let it be taken by
621 * the cpu which runs the tick timer next. If we don't drop
622 * this here the jiffies might be stale and do_timer() never
625 if (unlikely(!cpu_online(cpu
))) {
626 if (cpu
== tick_do_timer_cpu
)
627 tick_do_timer_cpu
= TICK_DO_TIMER_NONE
;
630 if (unlikely(ts
->nohz_mode
== NOHZ_MODE_INACTIVE
))
636 if (unlikely(local_softirq_pending() && cpu_online(cpu
))) {
637 static int ratelimit
;
639 if (ratelimit
< 10 &&
640 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK
)) {
641 printk(KERN_ERR
"NOHZ: local_softirq_pending %02x\n",
642 (unsigned int) local_softirq_pending());
648 if (have_nohz_full_mask
) {
650 * Keep the tick alive to guarantee timekeeping progression
651 * if there are full dynticks CPUs around
653 if (tick_do_timer_cpu
== cpu
)
656 * Boot safety: make sure the timekeeping duty has been
657 * assigned before entering dyntick-idle mode,
659 if (tick_do_timer_cpu
== TICK_DO_TIMER_NONE
)
666 static void __tick_nohz_idle_enter(struct tick_sched
*ts
)
668 ktime_t now
, expires
;
669 int cpu
= smp_processor_id();
671 now
= tick_nohz_start_idle(cpu
, ts
);
673 if (can_stop_idle_tick(cpu
, ts
)) {
674 int was_stopped
= ts
->tick_stopped
;
678 expires
= tick_nohz_stop_sched_tick(ts
, now
, cpu
);
679 if (expires
.tv64
> 0LL) {
681 ts
->idle_expires
= expires
;
684 if (!was_stopped
&& ts
->tick_stopped
)
685 ts
->idle_jiffies
= ts
->last_jiffies
;
690 * tick_nohz_idle_enter - stop the idle tick from the idle task
692 * When the next event is more than a tick into the future, stop the idle tick
693 * Called when we start the idle loop.
695 * The arch is responsible of calling:
697 * - rcu_idle_enter() after its last use of RCU before the CPU is put
699 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
701 void tick_nohz_idle_enter(void)
703 struct tick_sched
*ts
;
705 WARN_ON_ONCE(irqs_disabled());
708 * Update the idle state in the scheduler domain hierarchy
709 * when tick_nohz_stop_sched_tick() is called from the idle loop.
710 * State will be updated to busy during the first busy tick after
713 set_cpu_sd_state_idle();
717 ts
= &__get_cpu_var(tick_cpu_sched
);
719 * set ts->inidle unconditionally. even if the system did not
720 * switch to nohz mode the cpu frequency governers rely on the
721 * update of the idle time accounting in tick_nohz_start_idle().
724 __tick_nohz_idle_enter(ts
);
728 EXPORT_SYMBOL_GPL(tick_nohz_idle_enter
);
731 * tick_nohz_irq_exit - update next tick event from interrupt exit
733 * When an interrupt fires while we are idle and it doesn't cause
734 * a reschedule, it may still add, modify or delete a timer, enqueue
735 * an RCU callback, etc...
736 * So we need to re-calculate and reprogram the next tick event.
738 void tick_nohz_irq_exit(void)
740 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
745 /* Cancel the timer because CPU already waken up from the C-states*/
746 menu_hrtimer_cancel();
747 __tick_nohz_idle_enter(ts
);
751 * tick_nohz_get_sleep_length - return the length of the current sleep
753 * Called from power state control code with interrupts disabled
755 ktime_t
tick_nohz_get_sleep_length(void)
757 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
759 return ts
->sleep_length
;
762 static void tick_nohz_restart(struct tick_sched
*ts
, ktime_t now
)
764 hrtimer_cancel(&ts
->sched_timer
);
765 hrtimer_set_expires(&ts
->sched_timer
, ts
->last_tick
);
768 /* Forward the time to expire in the future */
769 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
771 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
772 hrtimer_start_expires(&ts
->sched_timer
,
773 HRTIMER_MODE_ABS_PINNED
);
774 /* Check, if the timer was already in the past */
775 if (hrtimer_active(&ts
->sched_timer
))
778 if (!tick_program_event(
779 hrtimer_get_expires(&ts
->sched_timer
), 0))
782 /* Reread time and update jiffies */
784 tick_do_update_jiffies64(now
);
788 static void tick_nohz_restart_sched_tick(struct tick_sched
*ts
, ktime_t now
)
790 /* Update jiffies first */
791 tick_do_update_jiffies64(now
);
792 update_cpu_load_nohz();
794 calc_load_exit_idle();
795 touch_softlockup_watchdog();
797 * Cancel the scheduled timer and restore the tick
799 ts
->tick_stopped
= 0;
800 ts
->idle_exittime
= now
;
802 tick_nohz_restart(ts
, now
);
805 static void tick_nohz_account_idle_ticks(struct tick_sched
*ts
)
807 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
810 if (vtime_accounting_enabled())
813 * We stopped the tick in idle. Update process times would miss the
814 * time we slept as update_process_times does only a 1 tick
815 * accounting. Enforce that this is accounted to idle !
817 ticks
= jiffies
- ts
->idle_jiffies
;
819 * We might be one off. Do not randomly account a huge number of ticks!
821 if (ticks
&& ticks
< LONG_MAX
)
822 account_idle_ticks(ticks
);
827 * tick_nohz_idle_exit - restart the idle tick from the idle task
829 * Restart the idle tick when the CPU is woken up from idle
830 * This also exit the RCU extended quiescent state. The CPU
831 * can use RCU again after this function is called.
833 void tick_nohz_idle_exit(void)
835 int cpu
= smp_processor_id();
836 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
841 WARN_ON_ONCE(!ts
->inidle
);
845 /* Cancel the timer because CPU already waken up from the C-states*/
846 menu_hrtimer_cancel();
847 if (ts
->idle_active
|| ts
->tick_stopped
)
851 tick_nohz_stop_idle(cpu
, now
);
853 if (ts
->tick_stopped
) {
854 tick_nohz_restart_sched_tick(ts
, now
);
855 tick_nohz_account_idle_ticks(ts
);
860 EXPORT_SYMBOL_GPL(tick_nohz_idle_exit
);
862 static int tick_nohz_reprogram(struct tick_sched
*ts
, ktime_t now
)
864 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
865 return tick_program_event(hrtimer_get_expires(&ts
->sched_timer
), 0);
869 * The nohz low res interrupt handler
871 static void tick_nohz_handler(struct clock_event_device
*dev
)
873 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
874 struct pt_regs
*regs
= get_irq_regs();
875 ktime_t now
= ktime_get();
877 dev
->next_event
.tv64
= KTIME_MAX
;
879 tick_sched_do_timer(now
);
880 tick_sched_handle(ts
, regs
);
882 while (tick_nohz_reprogram(ts
, now
)) {
884 tick_do_update_jiffies64(now
);
889 * tick_nohz_switch_to_nohz - switch to nohz mode
891 static void tick_nohz_switch_to_nohz(void)
893 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
896 if (!tick_nohz_enabled
)
900 if (tick_switch_to_oneshot(tick_nohz_handler
)) {
905 ts
->nohz_mode
= NOHZ_MODE_LOWRES
;
908 * Recycle the hrtimer in ts, so we can share the
909 * hrtimer_forward with the highres code.
911 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
912 /* Get the next period */
913 next
= tick_init_jiffy_update();
916 hrtimer_set_expires(&ts
->sched_timer
, next
);
917 if (!tick_program_event(next
, 0))
919 next
= ktime_add(next
, tick_period
);
925 * When NOHZ is enabled and the tick is stopped, we need to kick the
926 * tick timer from irq_enter() so that the jiffies update is kept
927 * alive during long running softirqs. That's ugly as hell, but
928 * correctness is key even if we need to fix the offending softirq in
931 * Note, this is different to tick_nohz_restart. We just kick the
932 * timer and do not touch the other magic bits which need to be done
935 static void tick_nohz_kick_tick(int cpu
, ktime_t now
)
938 /* Switch back to 2.6.27 behaviour */
940 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
944 * Do not touch the tick device, when the next expiry is either
945 * already reached or less/equal than the tick period.
947 delta
= ktime_sub(hrtimer_get_expires(&ts
->sched_timer
), now
);
948 if (delta
.tv64
<= tick_period
.tv64
)
951 tick_nohz_restart(ts
, now
);
955 static inline void tick_check_nohz(int cpu
)
957 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
960 if (!ts
->idle_active
&& !ts
->tick_stopped
)
964 tick_nohz_stop_idle(cpu
, now
);
965 if (ts
->tick_stopped
) {
966 tick_nohz_update_jiffies(now
);
967 tick_nohz_kick_tick(cpu
, now
);
973 static inline void tick_nohz_switch_to_nohz(void) { }
974 static inline void tick_check_nohz(int cpu
) { }
976 #endif /* CONFIG_NO_HZ_COMMON */
979 * Called from irq_enter to notify about the possible interruption of idle()
981 void tick_check_idle(int cpu
)
983 tick_check_oneshot_broadcast(cpu
);
984 tick_check_nohz(cpu
);
988 * High resolution timer specific code
990 #ifdef CONFIG_HIGH_RES_TIMERS
992 * We rearm the timer until we get disabled by the idle code.
993 * Called with interrupts disabled.
995 static enum hrtimer_restart
tick_sched_timer(struct hrtimer
*timer
)
997 struct tick_sched
*ts
=
998 container_of(timer
, struct tick_sched
, sched_timer
);
999 struct pt_regs
*regs
= get_irq_regs();
1000 ktime_t now
= ktime_get();
1002 tick_sched_do_timer(now
);
1005 * Do not call, when we are not in irq context and have
1006 * no valid regs pointer
1009 tick_sched_handle(ts
, regs
);
1011 hrtimer_forward(timer
, now
, tick_period
);
1013 return HRTIMER_RESTART
;
1016 static int sched_skew_tick
;
1018 static int __init
skew_tick(char *str
)
1020 get_option(&str
, &sched_skew_tick
);
1024 early_param("skew_tick", skew_tick
);
1027 * tick_setup_sched_timer - setup the tick emulation timer
1029 void tick_setup_sched_timer(void)
1031 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
1032 ktime_t now
= ktime_get();
1035 * Emulate tick processing via per-CPU hrtimers:
1037 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
1038 ts
->sched_timer
.function
= tick_sched_timer
;
1040 /* Get the next period (per cpu) */
1041 hrtimer_set_expires(&ts
->sched_timer
, tick_init_jiffy_update());
1043 /* Offset the tick to avert jiffies_lock contention. */
1044 if (sched_skew_tick
) {
1045 u64 offset
= ktime_to_ns(tick_period
) >> 1;
1046 do_div(offset
, num_possible_cpus());
1047 offset
*= smp_processor_id();
1048 hrtimer_add_expires_ns(&ts
->sched_timer
, offset
);
1052 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
1053 hrtimer_start_expires(&ts
->sched_timer
,
1054 HRTIMER_MODE_ABS_PINNED
);
1055 /* Check, if the timer was already in the past */
1056 if (hrtimer_active(&ts
->sched_timer
))
1061 #ifdef CONFIG_NO_HZ_COMMON
1062 if (tick_nohz_enabled
)
1063 ts
->nohz_mode
= NOHZ_MODE_HIGHRES
;
1066 #endif /* HIGH_RES_TIMERS */
1068 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1069 void tick_cancel_sched_timer(int cpu
)
1071 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
1073 # ifdef CONFIG_HIGH_RES_TIMERS
1074 if (ts
->sched_timer
.base
)
1075 hrtimer_cancel(&ts
->sched_timer
);
1078 ts
->nohz_mode
= NOHZ_MODE_INACTIVE
;
1083 * Async notification about clocksource changes
1085 void tick_clock_notify(void)
1089 for_each_possible_cpu(cpu
)
1090 set_bit(0, &per_cpu(tick_cpu_sched
, cpu
).check_clocks
);
1094 * Async notification about clock event changes
1096 void tick_oneshot_notify(void)
1098 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
1100 set_bit(0, &ts
->check_clocks
);
1104 * Check, if a change happened, which makes oneshot possible.
1106 * Called cyclic from the hrtimer softirq (driven by the timer
1107 * softirq) allow_nohz signals, that we can switch into low-res nohz
1108 * mode, because high resolution timers are disabled (either compile
1111 int tick_check_oneshot_change(int allow_nohz
)
1113 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
1115 if (!test_and_clear_bit(0, &ts
->check_clocks
))
1118 if (ts
->nohz_mode
!= NOHZ_MODE_INACTIVE
)
1121 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1127 tick_nohz_switch_to_nohz();