1// SPDX-License-Identifier: GPL-2.0
2/*
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
6 *
7 *  No idle tick implementation for low and high resolution timers
8 *
9 *  Started by: Thomas Gleixner and Ingo Molnar
10 */
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>
28#include <linux/mm.h>
29
30#include <asm/irq_regs.h>
31
32#include "tick-internal.h"
33
34#include <trace/events/timer.h>
35
36/*
37 * Per-CPU nohz control structure
38 */
39static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
40
41struct tick_sched *tick_get_tick_sched(int cpu)
42{
43	return &per_cpu(tick_cpu_sched, cpu);
44}
45
46#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
47/*
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.
51 */
52static ktime_t last_jiffies_update;
53
54/*
55 * Must be called with interrupts disabled !
56 */
57static void tick_do_update_jiffies64(ktime_t now)
58{
59	unsigned long ticks = 1;
60	ktime_t delta, nextp;
61
62	/*
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.
66	 *
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.
70	 */
71	if (IS_ENABLED(CONFIG_64BIT)) {
72		if (ktime_before(now, smp_load_acquire(&tick_next_period)))
73			return;
74	} else {
75		unsigned int seq;
76
77		/*
78		 * Avoid contention on jiffies_lock and protect the quick
79		 * check with the sequence count.
80		 */
81		do {
82			seq = read_seqcount_begin(&jiffies_seq);
83			nextp = tick_next_period;
84		} while (read_seqcount_retry(&jiffies_seq, seq));
85
86		if (ktime_before(now, nextp))
87			return;
88	}
89
90	/* Quick check failed, i.e. update is required. */
91	raw_spin_lock(&jiffies_lock);
92	/*
93	 * Reevaluate with the lock held. Another CPU might have done the
94	 * update already.
95	 */
96	if (ktime_before(now, tick_next_period)) {
97		raw_spin_unlock(&jiffies_lock);
98		return;
99	}
100
101	write_seqcount_begin(&jiffies_seq);
102
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;
107
108		ticks += ktime_divns(delta, incr);
109
110		last_jiffies_update = ktime_add_ns(last_jiffies_update,
111						   incr * ticks);
112	} else {
113		last_jiffies_update = ktime_add_ns(last_jiffies_update,
114						   TICK_NSEC);
115	}
116
117	/* Advance jiffies to complete the jiffies_seq protected job */
118	jiffies_64 += ticks;
119
120	/*
121	 * Keep the tick_next_period variable up to date.
122	 */
123	nextp = ktime_add_ns(last_jiffies_update, TICK_NSEC);
124
125	if (IS_ENABLED(CONFIG_64BIT)) {
126		/*
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.
131		 */
132		smp_store_release(&tick_next_period, nextp);
133	} else {
134		/*
135		 * A plain store is good enough on 32bit as the quick check
136		 * above is protected by the sequence count.
137		 */
138		tick_next_period = nextp;
139	}
140
141	/*
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.
145	 */
146	write_seqcount_end(&jiffies_seq);
147
148	calc_global_load();
149
150	raw_spin_unlock(&jiffies_lock);
151	update_wall_time();
152}
153
154/*
155 * Initialize and return retrieve the jiffies update.
156 */
157static ktime_t tick_init_jiffy_update(void)
158{
159	ktime_t period;
160
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)
165		last_jiffies_update = tick_next_period;
166	period = last_jiffies_update;
167	write_seqcount_end(&jiffies_seq);
168	raw_spin_unlock(&jiffies_lock);
169	return period;
170}
171
172#define MAX_STALLED_JIFFIES 5
173
174static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
175{
176	int cpu = smp_processor_id();
177
178#ifdef CONFIG_NO_HZ_COMMON
179	/*
180	 * Check if the do_timer duty was dropped. We don't care about
181	 * concurrency: This happens only when the CPU in charge went
182	 * into a long sleep. If two CPUs happen to assign themselves to
183	 * this duty, then the jiffies update is still serialized by
184	 * jiffies_lock.
185	 *
186	 * If nohz_full is enabled, this should not happen because the
187	 * tick_do_timer_cpu never relinquishes.
188	 */
189	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) {
190#ifdef CONFIG_NO_HZ_FULL
191		WARN_ON_ONCE(tick_nohz_full_running);
192#endif
193		tick_do_timer_cpu = cpu;
194	}
195#endif
196
197	/* Check, if the jiffies need an update */
198	if (tick_do_timer_cpu == cpu)
199		tick_do_update_jiffies64(now);
200
201	/*
202	 * If jiffies update stalled for too long (timekeeper in stop_machine()
203	 * or VMEXIT'ed for several msecs), force an update.
204	 */
205	if (ts->last_tick_jiffies != jiffies) {
206		ts->stalled_jiffies = 0;
207		ts->last_tick_jiffies = READ_ONCE(jiffies);
208	} else {
209		if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) {
210			tick_do_update_jiffies64(now);
211			ts->stalled_jiffies = 0;
212			ts->last_tick_jiffies = READ_ONCE(jiffies);
213		}
214	}
215
216	if (ts->inidle)
217		ts->got_idle_tick = 1;
218}
219
220static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
221{
222#ifdef CONFIG_NO_HZ_COMMON
223	/*
224	 * When we are idle and the tick is stopped, we have to touch
225	 * the watchdog as we might not schedule for a really long
226	 * time. This happens on complete idle SMP systems while
227	 * waiting on the login prompt. We also increment the "start of
228	 * idle" jiffy stamp so the idle accounting adjustment we do
229	 * when we go busy again does not account too much ticks.
230	 */
231	if (ts->tick_stopped) {
232		touch_softlockup_watchdog_sched();
233		if (is_idle_task(current))
234			ts->idle_jiffies++;
235		/*
236		 * In case the current tick fired too early past its expected
237		 * expiration, make sure we don't bypass the next clock reprogramming
238		 * to the same deadline.
239		 */
240		ts->next_tick = 0;
241	}
242#endif
243	update_process_times(user_mode(regs));
244	profile_tick(CPU_PROFILING);
245}
246#endif
247
248#ifdef CONFIG_NO_HZ_FULL
249cpumask_var_t tick_nohz_full_mask;
250EXPORT_SYMBOL_GPL(tick_nohz_full_mask);
251bool tick_nohz_full_running;
252EXPORT_SYMBOL_GPL(tick_nohz_full_running);
253static atomic_t tick_dep_mask;
254
255static bool check_tick_dependency(atomic_t *dep)
256{
257	int val = atomic_read(dep);
258
259	if (val & TICK_DEP_MASK_POSIX_TIMER) {
260		trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
261		return true;
262	}
263
264	if (val & TICK_DEP_MASK_PERF_EVENTS) {
265		trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
266		return true;
267	}
268
269	if (val & TICK_DEP_MASK_SCHED) {
270		trace_tick_stop(0, TICK_DEP_MASK_SCHED);
271		return true;
272	}
273
274	if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
275		trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
276		return true;
277	}
278
279	if (val & TICK_DEP_MASK_RCU) {
280		trace_tick_stop(0, TICK_DEP_MASK_RCU);
281		return true;
282	}
283
284	return false;
285}
286
287static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
288{
289	lockdep_assert_irqs_disabled();
290
291	if (unlikely(!cpu_online(cpu)))
292		return false;
293
294	if (check_tick_dependency(&tick_dep_mask))
295		return false;
296
297	if (check_tick_dependency(&ts->tick_dep_mask))
298		return false;
299
300	if (check_tick_dependency(&current->tick_dep_mask))
301		return false;
302
303	if (check_tick_dependency(&current->signal->tick_dep_mask))
304		return false;
305
306	return true;
307}
308
309static void nohz_full_kick_func(struct irq_work *work)
310{
311	/* Empty, the tick restart happens on tick_nohz_irq_exit() */
312}
313
314static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) =
315	IRQ_WORK_INIT_HARD(nohz_full_kick_func);
316
317/*
318 * Kick this CPU if it's full dynticks in order to force it to
319 * re-evaluate its dependency on the tick and restart it if necessary.
320 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
321 * is NMI safe.
322 */
323static void tick_nohz_full_kick(void)
324{
325	if (!tick_nohz_full_cpu(smp_processor_id()))
326		return;
327
328	irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
329}
330
331/*
332 * Kick the CPU if it's full dynticks in order to force it to
333 * re-evaluate its dependency on the tick and restart it if necessary.
334 */
335void tick_nohz_full_kick_cpu(int cpu)
336{
337	if (!tick_nohz_full_cpu(cpu))
338		return;
339
340	irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
341}
342
343static void tick_nohz_kick_task(struct task_struct *tsk)
344{
345	int cpu;
346
347	/*
348	 * If the task is not running, run_posix_cpu_timers()
349	 * has nothing to elapse, IPI can then be spared.
350	 *
351	 * activate_task()                      STORE p->tick_dep_mask
352	 *   STORE p->on_rq
353	 * __schedule() (switch to task 'p')    smp_mb() (atomic_fetch_or())
354	 *   LOCK rq->lock                      LOAD p->on_rq
355	 *   smp_mb__after_spin_lock()
356	 *   tick_nohz_task_switch()
357	 *     LOAD p->tick_dep_mask
358	 */
359	if (!sched_task_on_rq(tsk))
360		return;
361
362	/*
363	 * If the task concurrently migrates to another CPU,
364	 * we guarantee it sees the new tick dependency upon
365	 * schedule.
366	 *
367	 * set_task_cpu(p, cpu);
368	 *   STORE p->cpu = @cpu
369	 * __schedule() (switch to task 'p')
370	 *   LOCK rq->lock
371	 *   smp_mb__after_spin_lock()          STORE p->tick_dep_mask
372	 *   tick_nohz_task_switch()            smp_mb() (atomic_fetch_or())
373	 *      LOAD p->tick_dep_mask           LOAD p->cpu
374	 */
375	cpu = task_cpu(tsk);
376
377	preempt_disable();
378	if (cpu_online(cpu))
379		tick_nohz_full_kick_cpu(cpu);
380	preempt_enable();
381}
382
383/*
384 * Kick all full dynticks CPUs in order to force these to re-evaluate
385 * their dependency on the tick and restart it if necessary.
386 */
387static void tick_nohz_full_kick_all(void)
388{
389	int cpu;
390
391	if (!tick_nohz_full_running)
392		return;
393
394	preempt_disable();
395	for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
396		tick_nohz_full_kick_cpu(cpu);
397	preempt_enable();
398}
399
400static void tick_nohz_dep_set_all(atomic_t *dep,
401				  enum tick_dep_bits bit)
402{
403	int prev;
404
405	prev = atomic_fetch_or(BIT(bit), dep);
406	if (!prev)
407		tick_nohz_full_kick_all();
408}
409
410/*
411 * Set a global tick dependency. Used by perf events that rely on freq and
412 * by unstable clock.
413 */
414void tick_nohz_dep_set(enum tick_dep_bits bit)
415{
416	tick_nohz_dep_set_all(&tick_dep_mask, bit);
417}
418
419void tick_nohz_dep_clear(enum tick_dep_bits bit)
420{
421	atomic_andnot(BIT(bit), &tick_dep_mask);
422}
423
424/*
425 * Set per-CPU tick dependency. Used by scheduler and perf events in order to
426 * manage events throttling.
427 */
428void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
429{
430	int prev;
431	struct tick_sched *ts;
432
433	ts = per_cpu_ptr(&tick_cpu_sched, cpu);
434
435	prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
436	if (!prev) {
437		preempt_disable();
438		/* Perf needs local kick that is NMI safe */
439		if (cpu == smp_processor_id()) {
440			tick_nohz_full_kick();
441		} else {
442			/* Remote irq work not NMI-safe */
443			if (!WARN_ON_ONCE(in_nmi()))
444				tick_nohz_full_kick_cpu(cpu);
445		}
446		preempt_enable();
447	}
448}
449EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu);
450
451void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
452{
453	struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
454
455	atomic_andnot(BIT(bit), &ts->tick_dep_mask);
456}
457EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu);
458
459/*
460 * Set a per-task tick dependency. RCU need this. Also posix CPU timers
461 * in order to elapse per task timers.
462 */
463void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
464{
465	if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask))
466		tick_nohz_kick_task(tsk);
467}
468EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task);
469
470void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
471{
472	atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
473}
474EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_task);
475
476/*
477 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
478 * per process timers.
479 */
480void tick_nohz_dep_set_signal(struct task_struct *tsk,
481			      enum tick_dep_bits bit)
482{
483	int prev;
484	struct signal_struct *sig = tsk->signal;
485
486	prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask);
487	if (!prev) {
488		struct task_struct *t;
489
490		lockdep_assert_held(&tsk->sighand->siglock);
491		__for_each_thread(sig, t)
492			tick_nohz_kick_task(t);
493	}
494}
495
496void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
497{
498	atomic_andnot(BIT(bit), &sig->tick_dep_mask);
499}
500
501/*
502 * Re-evaluate the need for the tick as we switch the current task.
503 * It might need the tick due to per task/process properties:
504 * perf events, posix CPU timers, ...
505 */
506void __tick_nohz_task_switch(void)
507{
508	struct tick_sched *ts;
509
510	if (!tick_nohz_full_cpu(smp_processor_id()))
511		return;
512
513	ts = this_cpu_ptr(&tick_cpu_sched);
514
515	if (ts->tick_stopped) {
516		if (atomic_read(&current->tick_dep_mask) ||
517		    atomic_read(&current->signal->tick_dep_mask))
518			tick_nohz_full_kick();
519	}
520}
521
522/* Get the boot-time nohz CPU list from the kernel parameters. */
523void __init tick_nohz_full_setup(cpumask_var_t cpumask)
524{
525	alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
526	cpumask_copy(tick_nohz_full_mask, cpumask);
527	tick_nohz_full_running = true;
528}
529
530static int tick_nohz_cpu_down(unsigned int cpu)
531{
532	/*
533	 * The tick_do_timer_cpu CPU handles housekeeping duty (unbound
534	 * timers, workqueues, timekeeping, ...) on behalf of full dynticks
535	 * CPUs. It must remain online when nohz full is enabled.
536	 */
537	if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
538		return -EBUSY;
539	return 0;
540}
541
542void __init tick_nohz_init(void)
543{
544	int cpu, ret;
545
546	if (!tick_nohz_full_running)
547		return;
548
549	/*
550	 * Full dynticks uses irq work to drive the tick rescheduling on safe
551	 * locking contexts. But then we need irq work to raise its own
552	 * interrupts to avoid circular dependency on the tick
553	 */
554	if (!arch_irq_work_has_interrupt()) {
555		pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
556		cpumask_clear(tick_nohz_full_mask);
557		tick_nohz_full_running = false;
558		return;
559	}
560
561	if (IS_ENABLED(CONFIG_PM_SLEEP_SMP) &&
562			!IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU)) {
563		cpu = smp_processor_id();
564
565		if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
566			pr_warn("NO_HZ: Clearing %d from nohz_full range "
567				"for timekeeping\n", cpu);
568			cpumask_clear_cpu(cpu, tick_nohz_full_mask);
569		}
570	}
571
572	for_each_cpu(cpu, tick_nohz_full_mask)
573		context_tracking_cpu_set(cpu);
574
575	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
576					"kernel/nohz:predown", NULL,
577					tick_nohz_cpu_down);
578	WARN_ON(ret < 0);
579	pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
580		cpumask_pr_args(tick_nohz_full_mask));
581}
582#endif
583
584/*
585 * NOHZ - aka dynamic tick functionality
586 */
587#ifdef CONFIG_NO_HZ_COMMON
588/*
589 * NO HZ enabled ?
590 */
591bool tick_nohz_enabled __read_mostly  = true;
592unsigned long tick_nohz_active  __read_mostly;
593/*
594 * Enable / Disable tickless mode
595 */
596static int __init setup_tick_nohz(char *str)
597{
598	return (kstrtobool(str, &tick_nohz_enabled) == 0);
599}
600
601__setup("nohz=", setup_tick_nohz);
602
603bool tick_nohz_tick_stopped(void)
604{
605	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
606
607	return ts->tick_stopped;
608}
609
610bool tick_nohz_tick_stopped_cpu(int cpu)
611{
612	struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
613
614	return ts->tick_stopped;
615}
616
617/**
618 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
619 *
620 * Called from interrupt entry when the CPU was idle
621 *
622 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
623 * must be updated. Otherwise an interrupt handler could use a stale jiffy
624 * value. We do this unconditionally on any CPU, as we don't know whether the
625 * CPU, which has the update task assigned is in a long sleep.
626 */
627static void tick_nohz_update_jiffies(ktime_t now)
628{
629	unsigned long flags;
630
631	__this_cpu_write(tick_cpu_sched.idle_waketime, now);
632
633	local_irq_save(flags);
634	tick_do_update_jiffies64(now);
635	local_irq_restore(flags);
636
637	touch_softlockup_watchdog_sched();
638}
639
640/*
641 * Updates the per-CPU time idle statistics counters
642 */
643static void
644update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
645{
646	ktime_t delta;
647
648	if (ts->idle_active) {
649		delta = ktime_sub(now, ts->idle_entrytime);
650		if (nr_iowait_cpu(cpu) > 0)
651			ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
652		else
653			ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
654		ts->idle_entrytime = now;
655	}
656
657	if (last_update_time)
658		*last_update_time = ktime_to_us(now);
659
660}
661
662static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
663{
664	update_ts_time_stats(smp_processor_id(), ts, now, NULL);
665	ts->idle_active = 0;
666
667	sched_clock_idle_wakeup_event();
668}
669
670static void tick_nohz_start_idle(struct tick_sched *ts)
671{
672	ts->idle_entrytime = ktime_get();
673	ts->idle_active = 1;
674	sched_clock_idle_sleep_event();
675}
676
677/**
678 * get_cpu_idle_time_us - get the total idle time of a CPU
679 * @cpu: CPU number to query
680 * @last_update_time: variable to store update time in. Do not update
681 * counters if NULL.
682 *
683 * Return the cumulative idle time (since boot) for a given
684 * CPU, in microseconds.
685 *
686 * This time is measured via accounting rather than sampling,
687 * and is as accurate as ktime_get() is.
688 *
689 * This function returns -1 if NOHZ is not enabled.
690 */
691u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
692{
693	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
694	ktime_t now, idle;
695
696	if (!tick_nohz_active)
697		return -1;
698
699	now = ktime_get();
700	if (last_update_time) {
701		update_ts_time_stats(cpu, ts, now, last_update_time);
702		idle = ts->idle_sleeptime;
703	} else {
704		if (ts->idle_active && !nr_iowait_cpu(cpu)) {
705			ktime_t delta = ktime_sub(now, ts->idle_entrytime);
706
707			idle = ktime_add(ts->idle_sleeptime, delta);
708		} else {
709			idle = ts->idle_sleeptime;
710		}
711	}
712
713	return ktime_to_us(idle);
714
715}
716EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
717
718/**
719 * get_cpu_iowait_time_us - get the total iowait time of a CPU
720 * @cpu: CPU number to query
721 * @last_update_time: variable to store update time in. Do not update
722 * counters if NULL.
723 *
724 * Return the cumulative iowait time (since boot) for a given
725 * CPU, in microseconds.
726 *
727 * This time is measured via accounting rather than sampling,
728 * and is as accurate as ktime_get() is.
729 *
730 * This function returns -1 if NOHZ is not enabled.
731 */
732u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
733{
734	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
735	ktime_t now, iowait;
736
737	if (!tick_nohz_active)
738		return -1;
739
740	now = ktime_get();
741	if (last_update_time) {
742		update_ts_time_stats(cpu, ts, now, last_update_time);
743		iowait = ts->iowait_sleeptime;
744	} else {
745		if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
746			ktime_t delta = ktime_sub(now, ts->idle_entrytime);
747
748			iowait = ktime_add(ts->iowait_sleeptime, delta);
749		} else {
750			iowait = ts->iowait_sleeptime;
751		}
752	}
753
754	return ktime_to_us(iowait);
755}
756EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
757
758static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
759{
760	hrtimer_cancel(&ts->sched_timer);
761	hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
762
763	/* Forward the time to expire in the future */
764	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
765
766	if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
767		hrtimer_start_expires(&ts->sched_timer,
768				      HRTIMER_MODE_ABS_PINNED_HARD);
769	} else {
770		tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
771	}
772
773	/*
774	 * Reset to make sure next tick stop doesn't get fooled by past
775	 * cached clock deadline.
776	 */
777	ts->next_tick = 0;
778}
779
780static inline bool local_timer_softirq_pending(void)
781{
782	return local_softirq_pending() & BIT(TIMER_SOFTIRQ);
783}
784
785static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
786{
787	u64 basemono, next_tick, delta, expires;
788	unsigned long basejiff;
789	unsigned int seq;
790
791	/* Read jiffies and the time when jiffies were updated last */
792	do {
793		seq = read_seqcount_begin(&jiffies_seq);
794		basemono = last_jiffies_update;
795		basejiff = jiffies;
796	} while (read_seqcount_retry(&jiffies_seq, seq));
797	ts->last_jiffies = basejiff;
798	ts->timer_expires_base = basemono;
799
800	/*
801	 * Keep the periodic tick, when RCU, architecture or irq_work
802	 * requests it.
803	 * Aside of that check whether the local timer softirq is
804	 * pending. If so its a bad idea to call get_next_timer_interrupt()
805	 * because there is an already expired timer, so it will request
806	 * immediate expiry, which rearms the hardware timer with a
807	 * minimal delta which brings us back to this place
808	 * immediately. Lather, rinse and repeat...
809	 */
810	if (rcu_needs_cpu() || arch_needs_cpu() ||
811	    irq_work_needs_cpu() || local_timer_softirq_pending()) {
812		next_tick = basemono + TICK_NSEC;
813	} else {
814		/*
815		 * Get the next pending timer. If high resolution
816		 * timers are enabled this only takes the timer wheel
817		 * timers into account. If high resolution timers are
818		 * disabled this also looks at the next expiring
819		 * hrtimer.
820		 */
821		next_tick = get_next_timer_interrupt(basejiff, basemono);
822		ts->next_timer = next_tick;
823	}
824
825	/*
826	 * If the tick is due in the next period, keep it ticking or
827	 * force prod the timer.
828	 */
829	delta = next_tick - basemono;
830	if (delta <= (u64)TICK_NSEC) {
831		/*
832		 * Tell the timer code that the base is not idle, i.e. undo
833		 * the effect of get_next_timer_interrupt():
834		 */
835		timer_clear_idle();
836		/*
837		 * We've not stopped the tick yet, and there's a timer in the
838		 * next period, so no point in stopping it either, bail.
839		 */
840		if (!ts->tick_stopped) {
841			ts->timer_expires = 0;
842			goto out;
843		}
844	}
845
846	/*
847	 * If this CPU is the one which had the do_timer() duty last, we limit
848	 * the sleep time to the timekeeping max_deferment value.
849	 * Otherwise we can sleep as long as we want.
850	 */
851	delta = timekeeping_max_deferment();
852	if (cpu != tick_do_timer_cpu &&
853	    (tick_do_timer_cpu != TICK_DO_TIMER_NONE || !ts->do_timer_last))
854		delta = KTIME_MAX;
855
856	/* Calculate the next expiry time */
857	if (delta < (KTIME_MAX - basemono))
858		expires = basemono + delta;
859	else
860		expires = KTIME_MAX;
861
862	ts->timer_expires = min_t(u64, expires, next_tick);
863
864out:
865	return ts->timer_expires;
866}
867
868static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
869{
870	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
871	u64 basemono = ts->timer_expires_base;
872	u64 expires = ts->timer_expires;
873	ktime_t tick = expires;
874
875	/* Make sure we won't be trying to stop it twice in a row. */
876	ts->timer_expires_base = 0;
877
878	/*
879	 * If this CPU is the one which updates jiffies, then give up
880	 * the assignment and let it be taken by the CPU which runs
881	 * the tick timer next, which might be this CPU as well. If we
882	 * don't drop this here the jiffies might be stale and
883	 * do_timer() never invoked. Keep track of the fact that it
884	 * was the one which had the do_timer() duty last.
885	 */
886	if (cpu == tick_do_timer_cpu) {
887		tick_do_timer_cpu = TICK_DO_TIMER_NONE;
888		ts->do_timer_last = 1;
889	} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
890		ts->do_timer_last = 0;
891	}
892
893	/* Skip reprogram of event if its not changed */
894	if (ts->tick_stopped && (expires == ts->next_tick)) {
895		/* Sanity check: make sure clockevent is actually programmed */
896		if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer))
897			return;
898
899		WARN_ON_ONCE(1);
900		printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n",
901			    basemono, ts->next_tick, dev->next_event,
902			    hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer));
903	}
904
905	/*
906	 * nohz_stop_sched_tick can be called several times before
907	 * the nohz_restart_sched_tick is called. This happens when
908	 * interrupts arrive which do not cause a reschedule. In the
909	 * first call we save the current tick time, so we can restart
910	 * the scheduler tick in nohz_restart_sched_tick.
911	 */
912	if (!ts->tick_stopped) {
913		calc_load_nohz_start();
914		quiet_vmstat();
915
916		ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
917		ts->tick_stopped = 1;
918		trace_tick_stop(1, TICK_DEP_MASK_NONE);
919	}
920
921	ts->next_tick = tick;
922
923	/*
924	 * If the expiration time == KTIME_MAX, then we simply stop
925	 * the tick timer.
926	 */
927	if (unlikely(expires == KTIME_MAX)) {
928		if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
929			hrtimer_cancel(&ts->sched_timer);
930		else
931			tick_program_event(KTIME_MAX, 1);
932		return;
933	}
934
935	if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
936		hrtimer_start(&ts->sched_timer, tick,
937			      HRTIMER_MODE_ABS_PINNED_HARD);
938	} else {
939		hrtimer_set_expires(&ts->sched_timer, tick);
940		tick_program_event(tick, 1);
941	}
942}
943
944static void tick_nohz_retain_tick(struct tick_sched *ts)
945{
946	ts->timer_expires_base = 0;
947}
948
949#ifdef CONFIG_NO_HZ_FULL
950static void tick_nohz_stop_sched_tick(struct tick_sched *ts, int cpu)
951{
952	if (tick_nohz_next_event(ts, cpu))
953		tick_nohz_stop_tick(ts, cpu);
954	else
955		tick_nohz_retain_tick(ts);
956}
957#endif /* CONFIG_NO_HZ_FULL */
958
959static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
960{
961	/* Update jiffies first */
962	tick_do_update_jiffies64(now);
963
964	/*
965	 * Clear the timer idle flag, so we avoid IPIs on remote queueing and
966	 * the clock forward checks in the enqueue path:
967	 */
968	timer_clear_idle();
969
970	calc_load_nohz_stop();
971	touch_softlockup_watchdog_sched();
972	/*
973	 * Cancel the scheduled timer and restore the tick
974	 */
975	ts->tick_stopped  = 0;
976	tick_nohz_restart(ts, now);
977}
978
979static void __tick_nohz_full_update_tick(struct tick_sched *ts,
980					 ktime_t now)
981{
982#ifdef CONFIG_NO_HZ_FULL
983	int cpu = smp_processor_id();
984
985	if (can_stop_full_tick(cpu, ts))
986		tick_nohz_stop_sched_tick(ts, cpu);
987	else if (ts->tick_stopped)
988		tick_nohz_restart_sched_tick(ts, now);
989#endif
990}
991
992static void tick_nohz_full_update_tick(struct tick_sched *ts)
993{
994	if (!tick_nohz_full_cpu(smp_processor_id()))
995		return;
996
997	if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
998		return;
999
1000	__tick_nohz_full_update_tick(ts, ktime_get());
1001}
1002
1003/*
1004 * A pending softirq outside an IRQ (or softirq disabled section) context
1005 * should be waiting for ksoftirqd to handle it. Therefore we shouldn't
1006 * reach here due to the need_resched() early check in can_stop_idle_tick().
1007 *
1008 * However if we are between CPUHP_AP_SMPBOOT_THREADS and CPU_TEARDOWN_CPU on the
1009 * cpu_down() process, softirqs can still be raised while ksoftirqd is parked,
1010 * triggering the below since wakep_softirqd() is ignored.
1011 *
1012 */
1013static bool report_idle_softirq(void)
1014{
1015	static int ratelimit;
1016	unsigned int pending = local_softirq_pending();
1017
1018	if (likely(!pending))
1019		return false;
1020
1021	/* Some softirqs claim to be safe against hotplug and ksoftirqd parking */
1022	if (!cpu_active(smp_processor_id())) {
1023		pending &= ~SOFTIRQ_HOTPLUG_SAFE_MASK;
1024		if (!pending)
1025			return false;
1026	}
1027
1028	if (ratelimit < 10)
1029		return false;
1030
1031	/* On RT, softirqs handling may be waiting on some lock */
1032	if (!local_bh_blocked())
1033		return false;
1034
1035	pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n",
1036		pending);
1037	ratelimit++;
1038
1039	return true;
1040}
1041
1042static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
1043{
1044	/*
1045	 * If this CPU is offline and it is the one which updates
1046	 * jiffies, then give up the assignment and let it be taken by
1047	 * the CPU which runs the tick timer next. If we don't drop
1048	 * this here the jiffies might be stale and do_timer() never
1049	 * invoked.
1050	 */
1051	if (unlikely(!cpu_online(cpu))) {
1052		if (cpu == tick_do_timer_cpu)
1053			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
1054		/*
1055		 * Make sure the CPU doesn't get fooled by obsolete tick
1056		 * deadline if it comes back online later.
1057		 */
1058		ts->next_tick = 0;
1059		return false;
1060	}
1061
1062	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
1063		return false;
1064
1065	if (need_resched())
1066		return false;
1067
1068	if (unlikely(report_idle_softirq()))
1069		return false;
1070
1071	if (tick_nohz_full_enabled()) {
1072		/*
1073		 * Keep the tick alive to guarantee timekeeping progression
1074		 * if there are full dynticks CPUs around
1075		 */
1076		if (tick_do_timer_cpu == cpu)
1077			return false;
1078
1079		/* Should not happen for nohz-full */
1080		if (WARN_ON_ONCE(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
1081			return false;
1082	}
1083
1084	return true;
1085}
1086
1087static void __tick_nohz_idle_stop_tick(struct tick_sched *ts)
1088{
1089	ktime_t expires;
1090	int cpu = smp_processor_id();
1091
1092	/*
1093	 * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the
1094	 * tick timer expiration time is known already.
1095	 */
1096	if (ts->timer_expires_base)
1097		expires = ts->timer_expires;
1098	else if (can_stop_idle_tick(cpu, ts))
1099		expires = tick_nohz_next_event(ts, cpu);
1100	else
1101		return;
1102
1103	ts->idle_calls++;
1104
1105	if (expires > 0LL) {
1106		int was_stopped = ts->tick_stopped;
1107
1108		tick_nohz_stop_tick(ts, cpu);
1109
1110		ts->idle_sleeps++;
1111		ts->idle_expires = expires;
1112
1113		if (!was_stopped && ts->tick_stopped) {
1114			ts->idle_jiffies = ts->last_jiffies;
1115			nohz_balance_enter_idle(cpu);
1116		}
1117	} else {
1118		tick_nohz_retain_tick(ts);
1119	}
1120}
1121
1122/**
1123 * tick_nohz_idle_stop_tick - stop the idle tick from the idle task
1124 *
1125 * When the next event is more than a tick into the future, stop the idle tick
1126 */
1127void tick_nohz_idle_stop_tick(void)
1128{
1129	__tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched));
1130}
1131
1132void tick_nohz_idle_retain_tick(void)
1133{
1134	tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched));
1135	/*
1136	 * Undo the effect of get_next_timer_interrupt() called from
1137	 * tick_nohz_next_event().
1138	 */
1139	timer_clear_idle();
1140}
1141
1142/**
1143 * tick_nohz_idle_enter - prepare for entering idle on the current CPU
1144 *
1145 * Called when we start the idle loop.
1146 */
1147void tick_nohz_idle_enter(void)
1148{
1149	struct tick_sched *ts;
1150
1151	lockdep_assert_irqs_enabled();
1152
1153	local_irq_disable();
1154
1155	ts = this_cpu_ptr(&tick_cpu_sched);
1156
1157	WARN_ON_ONCE(ts->timer_expires_base);
1158
1159	ts->inidle = 1;
1160	tick_nohz_start_idle(ts);
1161
1162	local_irq_enable();
1163}
1164
1165/**
1166 * tick_nohz_irq_exit - update next tick event from interrupt exit
1167 *
1168 * When an interrupt fires while we are idle and it doesn't cause
1169 * a reschedule, it may still add, modify or delete a timer, enqueue
1170 * an RCU callback, etc...
1171 * So we need to re-calculate and reprogram the next tick event.
1172 */
1173void tick_nohz_irq_exit(void)
1174{
1175	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1176
1177	if (ts->inidle)
1178		tick_nohz_start_idle(ts);
1179	else
1180		tick_nohz_full_update_tick(ts);
1181}
1182
1183/**
1184 * tick_nohz_idle_got_tick - Check whether or not the tick handler has run
1185 */
1186bool tick_nohz_idle_got_tick(void)
1187{
1188	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1189
1190	if (ts->got_idle_tick) {
1191		ts->got_idle_tick = 0;
1192		return true;
1193	}
1194	return false;
1195}
1196
1197/**
1198 * tick_nohz_get_next_hrtimer - return the next expiration time for the hrtimer
1199 * or the tick, whatever that expires first. Note that, if the tick has been
1200 * stopped, it returns the next hrtimer.
1201 *
1202 * Called from power state control code with interrupts disabled
1203 */
1204ktime_t tick_nohz_get_next_hrtimer(void)
1205{
1206	return __this_cpu_read(tick_cpu_device.evtdev)->next_event;
1207}
1208
1209/**
1210 * tick_nohz_get_sleep_length - return the expected length of the current sleep
1211 * @delta_next: duration until the next event if the tick cannot be stopped
1212 *
1213 * Called from power state control code with interrupts disabled.
1214 *
1215 * The return value of this function and/or the value returned by it through the
1216 * @delta_next pointer can be negative which must be taken into account by its
1217 * callers.
1218 */
1219ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
1220{
1221	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
1222	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1223	int cpu = smp_processor_id();
1224	/*
1225	 * The idle entry time is expected to be a sufficient approximation of
1226	 * the current time at this point.
1227	 */
1228	ktime_t now = ts->idle_entrytime;
1229	ktime_t next_event;
1230
1231	WARN_ON_ONCE(!ts->inidle);
1232
1233	*delta_next = ktime_sub(dev->next_event, now);
1234
1235	if (!can_stop_idle_tick(cpu, ts))
1236		return *delta_next;
1237
1238	next_event = tick_nohz_next_event(ts, cpu);
1239	if (!next_event)
1240		return *delta_next;
1241
1242	/*
1243	 * If the next highres timer to expire is earlier than next_event, the
1244	 * idle governor needs to know that.
1245	 */
1246	next_event = min_t(u64, next_event,
1247			   hrtimer_next_event_without(&ts->sched_timer));
1248
1249	return ktime_sub(next_event, now);
1250}
1251
1252/**
1253 * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
1254 * for a particular CPU.
1255 *
1256 * Called from the schedutil frequency scaling governor in scheduler context.
1257 */
1258unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
1259{
1260	struct tick_sched *ts = tick_get_tick_sched(cpu);
1261
1262	return ts->idle_calls;
1263}
1264
1265/**
1266 * tick_nohz_get_idle_calls - return the current idle calls counter value
1267 *
1268 * Called from the schedutil frequency scaling governor in scheduler context.
1269 */
1270unsigned long tick_nohz_get_idle_calls(void)
1271{
1272	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1273
1274	return ts->idle_calls;
1275}
1276
1277static void tick_nohz_account_idle_time(struct tick_sched *ts,
1278					ktime_t now)
1279{
1280	unsigned long ticks;
1281
1282	ts->idle_exittime = now;
1283
1284	if (vtime_accounting_enabled_this_cpu())
1285		return;
1286	/*
1287	 * We stopped the tick in idle. Update process times would miss the
1288	 * time we slept as update_process_times does only a 1 tick
1289	 * accounting. Enforce that this is accounted to idle !
1290	 */
1291	ticks = jiffies - ts->idle_jiffies;
1292	/*
1293	 * We might be one off. Do not randomly account a huge number of ticks!
1294	 */
1295	if (ticks && ticks < LONG_MAX)
1296		account_idle_ticks(ticks);
1297}
1298
1299void tick_nohz_idle_restart_tick(void)
1300{
1301	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1302
1303	if (ts->tick_stopped) {
1304		ktime_t now = ktime_get();
1305		tick_nohz_restart_sched_tick(ts, now);
1306		tick_nohz_account_idle_time(ts, now);
1307	}
1308}
1309
1310static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now)
1311{
1312	if (tick_nohz_full_cpu(smp_processor_id()))
1313		__tick_nohz_full_update_tick(ts, now);
1314	else
1315		tick_nohz_restart_sched_tick(ts, now);
1316
1317	tick_nohz_account_idle_time(ts, now);
1318}
1319
1320/**
1321 * tick_nohz_idle_exit - restart the idle tick from the idle task
1322 *
1323 * Restart the idle tick when the CPU is woken up from idle
1324 * This also exit the RCU extended quiescent state. The CPU
1325 * can use RCU again after this function is called.
1326 */
1327void tick_nohz_idle_exit(void)
1328{
1329	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1330	bool idle_active, tick_stopped;
1331	ktime_t now;
1332
1333	local_irq_disable();
1334
1335	WARN_ON_ONCE(!ts->inidle);
1336	WARN_ON_ONCE(ts->timer_expires_base);
1337
1338	ts->inidle = 0;
1339	idle_active = ts->idle_active;
1340	tick_stopped = ts->tick_stopped;
1341
1342	if (idle_active || tick_stopped)
1343		now = ktime_get();
1344
1345	if (idle_active)
1346		tick_nohz_stop_idle(ts, now);
1347
1348	if (tick_stopped)
1349		tick_nohz_idle_update_tick(ts, now);
1350
1351	local_irq_enable();
1352}
1353
1354/*
1355 * The nohz low res interrupt handler
1356 */
1357static void tick_nohz_handler(struct clock_event_device *dev)
1358{
1359	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1360	struct pt_regs *regs = get_irq_regs();
1361	ktime_t now = ktime_get();
1362
1363	dev->next_event = KTIME_MAX;
1364
1365	tick_sched_do_timer(ts, now);
1366	tick_sched_handle(ts, regs);
1367
1368	if (unlikely(ts->tick_stopped)) {
1369		/*
1370		 * The clockevent device is not reprogrammed, so change the
1371		 * clock event device to ONESHOT_STOPPED to avoid spurious
1372		 * interrupts on devices which might not be truly one shot.
1373		 */
1374		tick_program_event(KTIME_MAX, 1);
1375		return;
1376	}
1377
1378	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
1379	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1380}
1381
1382static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1383{
1384	if (!tick_nohz_enabled)
1385		return;
1386	ts->nohz_mode = mode;
1387	/* One update is enough */
1388	if (!test_and_set_bit(0, &tick_nohz_active))
1389		timers_update_nohz();
1390}
1391
1392/**
1393 * tick_nohz_switch_to_nohz - switch to nohz mode
1394 */
1395static void tick_nohz_switch_to_nohz(void)
1396{
1397	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1398	ktime_t next;
1399
1400	if (!tick_nohz_enabled)
1401		return;
1402
1403	if (tick_switch_to_oneshot(tick_nohz_handler))
1404		return;
1405
1406	/*
1407	 * Recycle the hrtimer in ts, so we can share the
1408	 * hrtimer_forward with the highres code.
1409	 */
1410	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
1411	/* Get the next period */
1412	next = tick_init_jiffy_update();
1413
1414	hrtimer_set_expires(&ts->sched_timer, next);
1415	hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);
1416	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1417	tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1418}
1419
1420static inline void tick_nohz_irq_enter(void)
1421{
1422	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1423	ktime_t now;
1424
1425	if (!ts->idle_active && !ts->tick_stopped)
1426		return;
1427	now = ktime_get();
1428	if (ts->idle_active)
1429		tick_nohz_stop_idle(ts, now);
1430	/*
1431	 * If all CPUs are idle. We may need to update a stale jiffies value.
1432	 * Note nohz_full is a special case: a timekeeper is guaranteed to stay
1433	 * alive but it might be busy looping with interrupts disabled in some
1434	 * rare case (typically stop machine). So we must make sure we have a
1435	 * last resort.
1436	 */
1437	if (ts->tick_stopped)
1438		tick_nohz_update_jiffies(now);
1439}
1440
1441#else
1442
1443static inline void tick_nohz_switch_to_nohz(void) { }
1444static inline void tick_nohz_irq_enter(void) { }
1445static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1446
1447#endif /* CONFIG_NO_HZ_COMMON */
1448
1449/*
1450 * Called from irq_enter to notify about the possible interruption of idle()
1451 */
1452void tick_irq_enter(void)
1453{
1454	tick_check_oneshot_broadcast_this_cpu();
1455	tick_nohz_irq_enter();
1456}
1457
1458/*
1459 * High resolution timer specific code
1460 */
1461#ifdef CONFIG_HIGH_RES_TIMERS
1462/*
1463 * We rearm the timer until we get disabled by the idle code.
1464 * Called with interrupts disabled.
1465 */
1466static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1467{
1468	struct tick_sched *ts =
1469		container_of(timer, struct tick_sched, sched_timer);
1470	struct pt_regs *regs = get_irq_regs();
1471	ktime_t now = ktime_get();
1472
1473	tick_sched_do_timer(ts, now);
1474
1475	/*
1476	 * Do not call, when we are not in irq context and have
1477	 * no valid regs pointer
1478	 */
1479	if (regs)
1480		tick_sched_handle(ts, regs);
1481	else
1482		ts->next_tick = 0;
1483
1484	/* No need to reprogram if we are in idle or full dynticks mode */
1485	if (unlikely(ts->tick_stopped))
1486		return HRTIMER_NORESTART;
1487
1488	hrtimer_forward(timer, now, TICK_NSEC);
1489
1490	return HRTIMER_RESTART;
1491}
1492
1493static int sched_skew_tick;
1494
1495static int __init skew_tick(char *str)
1496{
1497	get_option(&str, &sched_skew_tick);
1498
1499	return 0;
1500}
1501early_param("skew_tick", skew_tick);
1502
1503/**
1504 * tick_setup_sched_timer - setup the tick emulation timer
1505 */
1506void tick_setup_sched_timer(void)
1507{
1508	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1509	ktime_t now = ktime_get();
1510
1511	/*
1512	 * Emulate tick processing via per-CPU hrtimers:
1513	 */
1514	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
1515	ts->sched_timer.function = tick_sched_timer;
1516
1517	/* Get the next period (per-CPU) */
1518	hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1519
1520	/* Offset the tick to avert jiffies_lock contention. */
1521	if (sched_skew_tick) {
1522		u64 offset = TICK_NSEC >> 1;
1523		do_div(offset, num_possible_cpus());
1524		offset *= smp_processor_id();
1525		hrtimer_add_expires_ns(&ts->sched_timer, offset);
1526	}
1527
1528	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
1529	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
1530	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1531}
1532#endif /* HIGH_RES_TIMERS */
1533
1534#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1535void tick_cancel_sched_timer(int cpu)
1536{
1537	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1538
1539# ifdef CONFIG_HIGH_RES_TIMERS
1540	if (ts->sched_timer.base)
1541		hrtimer_cancel(&ts->sched_timer);
1542# endif
1543
1544	memset(ts, 0, sizeof(*ts));
1545}
1546#endif
1547
1548/*
1549 * Async notification about clocksource changes
1550 */
1551void tick_clock_notify(void)
1552{
1553	int cpu;
1554
1555	for_each_possible_cpu(cpu)
1556		set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1557}
1558
1559/*
1560 * Async notification about clock event changes
1561 */
1562void tick_oneshot_notify(void)
1563{
1564	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1565
1566	set_bit(0, &ts->check_clocks);
1567}
1568
1569/*
1570 * Check, if a change happened, which makes oneshot possible.
1571 *
1572 * Called cyclic from the hrtimer softirq (driven by the timer
1573 * softirq) allow_nohz signals, that we can switch into low-res nohz
1574 * mode, because high resolution timers are disabled (either compile
1575 * or runtime). Called with interrupts disabled.
1576 */
1577int tick_check_oneshot_change(int allow_nohz)
1578{
1579	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1580
1581	if (!test_and_clear_bit(0, &ts->check_clocks))
1582		return 0;
1583
1584	if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1585		return 0;
1586
1587	if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1588		return 0;
1589
1590	if (!allow_nohz)
1591		return 1;
1592
1593	tick_nohz_switch_to_nohz();
1594	return 0;
1595}
1596