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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(¤t->tick_dep_mask))
301 return false;
302
303 if (check_tick_dependency(¤t->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(¤t->tick_dep_mask) ||
517 atomic_read(¤t->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 ct_cpu_track_user(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}
1/*
2 * linux/kernel/time/tick-sched.c
3 *
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
7 *
8 * No idle tick implementation for low and high resolution timers
9 *
10 * Started by: Thomas Gleixner and Ingo Molnar
11 *
12 * Distribute under GPLv2.
13 */
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/nmi.h>
21#include <linux/profile.h>
22#include <linux/sched/signal.h>
23#include <linux/sched/clock.h>
24#include <linux/sched/stat.h>
25#include <linux/sched/nohz.h>
26#include <linux/module.h>
27#include <linux/irq_work.h>
28#include <linux/posix-timers.h>
29#include <linux/context_tracking.h>
30#include <linux/mm.h>
31
32#include <asm/irq_regs.h>
33
34#include "tick-internal.h"
35
36#include <trace/events/timer.h>
37
38/*
39 * Per-CPU nohz control structure
40 */
41static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
42
43struct tick_sched *tick_get_tick_sched(int cpu)
44{
45 return &per_cpu(tick_cpu_sched, cpu);
46}
47
48#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
49/*
50 * The time, when the last jiffy update happened. Protected by jiffies_lock.
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 = 0;
60 ktime_t delta;
61
62 /*
63 * Do a quick check without holding jiffies_lock:
64 */
65 delta = ktime_sub(now, last_jiffies_update);
66 if (delta < tick_period)
67 return;
68
69 /* Reevaluate with jiffies_lock held */
70 write_seqlock(&jiffies_lock);
71
72 delta = ktime_sub(now, last_jiffies_update);
73 if (delta >= tick_period) {
74
75 delta = ktime_sub(delta, tick_period);
76 last_jiffies_update = ktime_add(last_jiffies_update,
77 tick_period);
78
79 /* Slow path for long timeouts */
80 if (unlikely(delta >= tick_period)) {
81 s64 incr = ktime_to_ns(tick_period);
82
83 ticks = ktime_divns(delta, incr);
84
85 last_jiffies_update = ktime_add_ns(last_jiffies_update,
86 incr * ticks);
87 }
88 do_timer(++ticks);
89
90 /* Keep the tick_next_period variable up to date */
91 tick_next_period = ktime_add(last_jiffies_update, tick_period);
92 } else {
93 write_sequnlock(&jiffies_lock);
94 return;
95 }
96 write_sequnlock(&jiffies_lock);
97 update_wall_time();
98}
99
100/*
101 * Initialize and return retrieve the jiffies update.
102 */
103static ktime_t tick_init_jiffy_update(void)
104{
105 ktime_t period;
106
107 write_seqlock(&jiffies_lock);
108 /* Did we start the jiffies update yet ? */
109 if (last_jiffies_update == 0)
110 last_jiffies_update = tick_next_period;
111 period = last_jiffies_update;
112 write_sequnlock(&jiffies_lock);
113 return period;
114}
115
116static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
117{
118 int cpu = smp_processor_id();
119
120#ifdef CONFIG_NO_HZ_COMMON
121 /*
122 * Check if the do_timer duty was dropped. We don't care about
123 * concurrency: This happens only when the CPU in charge went
124 * into a long sleep. If two CPUs happen to assign themselves to
125 * this duty, then the jiffies update is still serialized by
126 * jiffies_lock.
127 */
128 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
129 && !tick_nohz_full_cpu(cpu))
130 tick_do_timer_cpu = cpu;
131#endif
132
133 /* Check, if the jiffies need an update */
134 if (tick_do_timer_cpu == cpu)
135 tick_do_update_jiffies64(now);
136
137 if (ts->inidle)
138 ts->got_idle_tick = 1;
139}
140
141static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
142{
143#ifdef CONFIG_NO_HZ_COMMON
144 /*
145 * When we are idle and the tick is stopped, we have to touch
146 * the watchdog as we might not schedule for a really long
147 * time. This happens on complete idle SMP systems while
148 * waiting on the login prompt. We also increment the "start of
149 * idle" jiffy stamp so the idle accounting adjustment we do
150 * when we go busy again does not account too much ticks.
151 */
152 if (ts->tick_stopped) {
153 touch_softlockup_watchdog_sched();
154 if (is_idle_task(current))
155 ts->idle_jiffies++;
156 /*
157 * In case the current tick fired too early past its expected
158 * expiration, make sure we don't bypass the next clock reprogramming
159 * to the same deadline.
160 */
161 ts->next_tick = 0;
162 }
163#endif
164 update_process_times(user_mode(regs));
165 profile_tick(CPU_PROFILING);
166}
167#endif
168
169#ifdef CONFIG_NO_HZ_FULL
170cpumask_var_t tick_nohz_full_mask;
171bool tick_nohz_full_running;
172static atomic_t tick_dep_mask;
173
174static bool check_tick_dependency(atomic_t *dep)
175{
176 int val = atomic_read(dep);
177
178 if (val & TICK_DEP_MASK_POSIX_TIMER) {
179 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
180 return true;
181 }
182
183 if (val & TICK_DEP_MASK_PERF_EVENTS) {
184 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
185 return true;
186 }
187
188 if (val & TICK_DEP_MASK_SCHED) {
189 trace_tick_stop(0, TICK_DEP_MASK_SCHED);
190 return true;
191 }
192
193 if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
194 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
195 return true;
196 }
197
198 return false;
199}
200
201static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
202{
203 lockdep_assert_irqs_disabled();
204
205 if (unlikely(!cpu_online(cpu)))
206 return false;
207
208 if (check_tick_dependency(&tick_dep_mask))
209 return false;
210
211 if (check_tick_dependency(&ts->tick_dep_mask))
212 return false;
213
214 if (check_tick_dependency(¤t->tick_dep_mask))
215 return false;
216
217 if (check_tick_dependency(¤t->signal->tick_dep_mask))
218 return false;
219
220 return true;
221}
222
223static void nohz_full_kick_func(struct irq_work *work)
224{
225 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
226}
227
228static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
229 .func = nohz_full_kick_func,
230};
231
232/*
233 * Kick this CPU if it's full dynticks in order to force it to
234 * re-evaluate its dependency on the tick and restart it if necessary.
235 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
236 * is NMI safe.
237 */
238static void tick_nohz_full_kick(void)
239{
240 if (!tick_nohz_full_cpu(smp_processor_id()))
241 return;
242
243 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
244}
245
246/*
247 * Kick the CPU if it's full dynticks in order to force it to
248 * re-evaluate its dependency on the tick and restart it if necessary.
249 */
250void tick_nohz_full_kick_cpu(int cpu)
251{
252 if (!tick_nohz_full_cpu(cpu))
253 return;
254
255 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
256}
257
258/*
259 * Kick all full dynticks CPUs in order to force these to re-evaluate
260 * their dependency on the tick and restart it if necessary.
261 */
262static void tick_nohz_full_kick_all(void)
263{
264 int cpu;
265
266 if (!tick_nohz_full_running)
267 return;
268
269 preempt_disable();
270 for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
271 tick_nohz_full_kick_cpu(cpu);
272 preempt_enable();
273}
274
275static void tick_nohz_dep_set_all(atomic_t *dep,
276 enum tick_dep_bits bit)
277{
278 int prev;
279
280 prev = atomic_fetch_or(BIT(bit), dep);
281 if (!prev)
282 tick_nohz_full_kick_all();
283}
284
285/*
286 * Set a global tick dependency. Used by perf events that rely on freq and
287 * by unstable clock.
288 */
289void tick_nohz_dep_set(enum tick_dep_bits bit)
290{
291 tick_nohz_dep_set_all(&tick_dep_mask, bit);
292}
293
294void tick_nohz_dep_clear(enum tick_dep_bits bit)
295{
296 atomic_andnot(BIT(bit), &tick_dep_mask);
297}
298
299/*
300 * Set per-CPU tick dependency. Used by scheduler and perf events in order to
301 * manage events throttling.
302 */
303void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
304{
305 int prev;
306 struct tick_sched *ts;
307
308 ts = per_cpu_ptr(&tick_cpu_sched, cpu);
309
310 prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
311 if (!prev) {
312 preempt_disable();
313 /* Perf needs local kick that is NMI safe */
314 if (cpu == smp_processor_id()) {
315 tick_nohz_full_kick();
316 } else {
317 /* Remote irq work not NMI-safe */
318 if (!WARN_ON_ONCE(in_nmi()))
319 tick_nohz_full_kick_cpu(cpu);
320 }
321 preempt_enable();
322 }
323}
324
325void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
326{
327 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
328
329 atomic_andnot(BIT(bit), &ts->tick_dep_mask);
330}
331
332/*
333 * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
334 * per task timers.
335 */
336void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
337{
338 /*
339 * We could optimize this with just kicking the target running the task
340 * if that noise matters for nohz full users.
341 */
342 tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
343}
344
345void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
346{
347 atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
348}
349
350/*
351 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
352 * per process timers.
353 */
354void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
355{
356 tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
357}
358
359void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
360{
361 atomic_andnot(BIT(bit), &sig->tick_dep_mask);
362}
363
364/*
365 * Re-evaluate the need for the tick as we switch the current task.
366 * It might need the tick due to per task/process properties:
367 * perf events, posix CPU timers, ...
368 */
369void __tick_nohz_task_switch(void)
370{
371 unsigned long flags;
372 struct tick_sched *ts;
373
374 local_irq_save(flags);
375
376 if (!tick_nohz_full_cpu(smp_processor_id()))
377 goto out;
378
379 ts = this_cpu_ptr(&tick_cpu_sched);
380
381 if (ts->tick_stopped) {
382 if (atomic_read(¤t->tick_dep_mask) ||
383 atomic_read(¤t->signal->tick_dep_mask))
384 tick_nohz_full_kick();
385 }
386out:
387 local_irq_restore(flags);
388}
389
390/* Get the boot-time nohz CPU list from the kernel parameters. */
391void __init tick_nohz_full_setup(cpumask_var_t cpumask)
392{
393 alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
394 cpumask_copy(tick_nohz_full_mask, cpumask);
395 tick_nohz_full_running = true;
396}
397
398static int tick_nohz_cpu_down(unsigned int cpu)
399{
400 /*
401 * The boot CPU handles housekeeping duty (unbound timers,
402 * workqueues, timekeeping, ...) on behalf of full dynticks
403 * CPUs. It must remain online when nohz full is enabled.
404 */
405 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
406 return -EBUSY;
407 return 0;
408}
409
410void __init tick_nohz_init(void)
411{
412 int cpu, ret;
413
414 if (!tick_nohz_full_running)
415 return;
416
417 /*
418 * Full dynticks uses irq work to drive the tick rescheduling on safe
419 * locking contexts. But then we need irq work to raise its own
420 * interrupts to avoid circular dependency on the tick
421 */
422 if (!arch_irq_work_has_interrupt()) {
423 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
424 cpumask_clear(tick_nohz_full_mask);
425 tick_nohz_full_running = false;
426 return;
427 }
428
429 cpu = smp_processor_id();
430
431 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
432 pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
433 cpu);
434 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
435 }
436
437 for_each_cpu(cpu, tick_nohz_full_mask)
438 context_tracking_cpu_set(cpu);
439
440 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
441 "kernel/nohz:predown", NULL,
442 tick_nohz_cpu_down);
443 WARN_ON(ret < 0);
444 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
445 cpumask_pr_args(tick_nohz_full_mask));
446}
447#endif
448
449/*
450 * NOHZ - aka dynamic tick functionality
451 */
452#ifdef CONFIG_NO_HZ_COMMON
453/*
454 * NO HZ enabled ?
455 */
456bool tick_nohz_enabled __read_mostly = true;
457unsigned long tick_nohz_active __read_mostly;
458/*
459 * Enable / Disable tickless mode
460 */
461static int __init setup_tick_nohz(char *str)
462{
463 return (kstrtobool(str, &tick_nohz_enabled) == 0);
464}
465
466__setup("nohz=", setup_tick_nohz);
467
468bool tick_nohz_tick_stopped(void)
469{
470 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
471
472 return ts->tick_stopped;
473}
474
475bool tick_nohz_tick_stopped_cpu(int cpu)
476{
477 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
478
479 return ts->tick_stopped;
480}
481
482/**
483 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
484 *
485 * Called from interrupt entry when the CPU was idle
486 *
487 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
488 * must be updated. Otherwise an interrupt handler could use a stale jiffy
489 * value. We do this unconditionally on any CPU, as we don't know whether the
490 * CPU, which has the update task assigned is in a long sleep.
491 */
492static void tick_nohz_update_jiffies(ktime_t now)
493{
494 unsigned long flags;
495
496 __this_cpu_write(tick_cpu_sched.idle_waketime, now);
497
498 local_irq_save(flags);
499 tick_do_update_jiffies64(now);
500 local_irq_restore(flags);
501
502 touch_softlockup_watchdog_sched();
503}
504
505/*
506 * Updates the per-CPU time idle statistics counters
507 */
508static void
509update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
510{
511 ktime_t delta;
512
513 if (ts->idle_active) {
514 delta = ktime_sub(now, ts->idle_entrytime);
515 if (nr_iowait_cpu(cpu) > 0)
516 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
517 else
518 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
519 ts->idle_entrytime = now;
520 }
521
522 if (last_update_time)
523 *last_update_time = ktime_to_us(now);
524
525}
526
527static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
528{
529 update_ts_time_stats(smp_processor_id(), ts, now, NULL);
530 ts->idle_active = 0;
531
532 sched_clock_idle_wakeup_event();
533}
534
535static void tick_nohz_start_idle(struct tick_sched *ts)
536{
537 ts->idle_entrytime = ktime_get();
538 ts->idle_active = 1;
539 sched_clock_idle_sleep_event();
540}
541
542/**
543 * get_cpu_idle_time_us - get the total idle time of a CPU
544 * @cpu: CPU number to query
545 * @last_update_time: variable to store update time in. Do not update
546 * counters if NULL.
547 *
548 * Return the cumulative idle time (since boot) for a given
549 * CPU, in microseconds.
550 *
551 * This time is measured via accounting rather than sampling,
552 * and is as accurate as ktime_get() is.
553 *
554 * This function returns -1 if NOHZ is not enabled.
555 */
556u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
557{
558 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
559 ktime_t now, idle;
560
561 if (!tick_nohz_active)
562 return -1;
563
564 now = ktime_get();
565 if (last_update_time) {
566 update_ts_time_stats(cpu, ts, now, last_update_time);
567 idle = ts->idle_sleeptime;
568 } else {
569 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
570 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
571
572 idle = ktime_add(ts->idle_sleeptime, delta);
573 } else {
574 idle = ts->idle_sleeptime;
575 }
576 }
577
578 return ktime_to_us(idle);
579
580}
581EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
582
583/**
584 * get_cpu_iowait_time_us - get the total iowait time of a CPU
585 * @cpu: CPU number to query
586 * @last_update_time: variable to store update time in. Do not update
587 * counters if NULL.
588 *
589 * Return the cumulative iowait time (since boot) for a given
590 * CPU, in microseconds.
591 *
592 * This time is measured via accounting rather than sampling,
593 * and is as accurate as ktime_get() is.
594 *
595 * This function returns -1 if NOHZ is not enabled.
596 */
597u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
598{
599 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
600 ktime_t now, iowait;
601
602 if (!tick_nohz_active)
603 return -1;
604
605 now = ktime_get();
606 if (last_update_time) {
607 update_ts_time_stats(cpu, ts, now, last_update_time);
608 iowait = ts->iowait_sleeptime;
609 } else {
610 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
611 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
612
613 iowait = ktime_add(ts->iowait_sleeptime, delta);
614 } else {
615 iowait = ts->iowait_sleeptime;
616 }
617 }
618
619 return ktime_to_us(iowait);
620}
621EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
622
623static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
624{
625 hrtimer_cancel(&ts->sched_timer);
626 hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
627
628 /* Forward the time to expire in the future */
629 hrtimer_forward(&ts->sched_timer, now, tick_period);
630
631 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
632 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
633 else
634 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
635
636 /*
637 * Reset to make sure next tick stop doesn't get fooled by past
638 * cached clock deadline.
639 */
640 ts->next_tick = 0;
641}
642
643static inline bool local_timer_softirq_pending(void)
644{
645 return local_softirq_pending() & TIMER_SOFTIRQ;
646}
647
648static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
649{
650 u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
651 unsigned long seq, basejiff;
652
653 /* Read jiffies and the time when jiffies were updated last */
654 do {
655 seq = read_seqbegin(&jiffies_lock);
656 basemono = last_jiffies_update;
657 basejiff = jiffies;
658 } while (read_seqretry(&jiffies_lock, seq));
659 ts->last_jiffies = basejiff;
660 ts->timer_expires_base = basemono;
661
662 /*
663 * Keep the periodic tick, when RCU, architecture or irq_work
664 * requests it.
665 * Aside of that check whether the local timer softirq is
666 * pending. If so its a bad idea to call get_next_timer_interrupt()
667 * because there is an already expired timer, so it will request
668 * immeditate expiry, which rearms the hardware timer with a
669 * minimal delta which brings us back to this place
670 * immediately. Lather, rinse and repeat...
671 */
672 if (rcu_needs_cpu(basemono, &next_rcu) || arch_needs_cpu() ||
673 irq_work_needs_cpu() || local_timer_softirq_pending()) {
674 next_tick = basemono + TICK_NSEC;
675 } else {
676 /*
677 * Get the next pending timer. If high resolution
678 * timers are enabled this only takes the timer wheel
679 * timers into account. If high resolution timers are
680 * disabled this also looks at the next expiring
681 * hrtimer.
682 */
683 next_tmr = get_next_timer_interrupt(basejiff, basemono);
684 ts->next_timer = next_tmr;
685 /* Take the next rcu event into account */
686 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
687 }
688
689 /*
690 * If the tick is due in the next period, keep it ticking or
691 * force prod the timer.
692 */
693 delta = next_tick - basemono;
694 if (delta <= (u64)TICK_NSEC) {
695 /*
696 * Tell the timer code that the base is not idle, i.e. undo
697 * the effect of get_next_timer_interrupt():
698 */
699 timer_clear_idle();
700 /*
701 * We've not stopped the tick yet, and there's a timer in the
702 * next period, so no point in stopping it either, bail.
703 */
704 if (!ts->tick_stopped) {
705 ts->timer_expires = 0;
706 goto out;
707 }
708 }
709
710 /*
711 * If this CPU is the one which had the do_timer() duty last, we limit
712 * the sleep time to the timekeeping max_deferment value.
713 * Otherwise we can sleep as long as we want.
714 */
715 delta = timekeeping_max_deferment();
716 if (cpu != tick_do_timer_cpu &&
717 (tick_do_timer_cpu != TICK_DO_TIMER_NONE || !ts->do_timer_last))
718 delta = KTIME_MAX;
719
720 /* Calculate the next expiry time */
721 if (delta < (KTIME_MAX - basemono))
722 expires = basemono + delta;
723 else
724 expires = KTIME_MAX;
725
726 ts->timer_expires = min_t(u64, expires, next_tick);
727
728out:
729 return ts->timer_expires;
730}
731
732static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
733{
734 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
735 u64 basemono = ts->timer_expires_base;
736 u64 expires = ts->timer_expires;
737 ktime_t tick = expires;
738
739 /* Make sure we won't be trying to stop it twice in a row. */
740 ts->timer_expires_base = 0;
741
742 /*
743 * If this CPU is the one which updates jiffies, then give up
744 * the assignment and let it be taken by the CPU which runs
745 * the tick timer next, which might be this CPU as well. If we
746 * don't drop this here the jiffies might be stale and
747 * do_timer() never invoked. Keep track of the fact that it
748 * was the one which had the do_timer() duty last.
749 */
750 if (cpu == tick_do_timer_cpu) {
751 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
752 ts->do_timer_last = 1;
753 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
754 ts->do_timer_last = 0;
755 }
756
757 /* Skip reprogram of event if its not changed */
758 if (ts->tick_stopped && (expires == ts->next_tick)) {
759 /* Sanity check: make sure clockevent is actually programmed */
760 if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer))
761 return;
762
763 WARN_ON_ONCE(1);
764 printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n",
765 basemono, ts->next_tick, dev->next_event,
766 hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer));
767 }
768
769 /*
770 * nohz_stop_sched_tick can be called several times before
771 * the nohz_restart_sched_tick is called. This happens when
772 * interrupts arrive which do not cause a reschedule. In the
773 * first call we save the current tick time, so we can restart
774 * the scheduler tick in nohz_restart_sched_tick.
775 */
776 if (!ts->tick_stopped) {
777 calc_load_nohz_start();
778 cpu_load_update_nohz_start();
779 quiet_vmstat();
780
781 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
782 ts->tick_stopped = 1;
783 trace_tick_stop(1, TICK_DEP_MASK_NONE);
784 }
785
786 ts->next_tick = tick;
787
788 /*
789 * If the expiration time == KTIME_MAX, then we simply stop
790 * the tick timer.
791 */
792 if (unlikely(expires == KTIME_MAX)) {
793 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
794 hrtimer_cancel(&ts->sched_timer);
795 return;
796 }
797
798 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
799 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
800 } else {
801 hrtimer_set_expires(&ts->sched_timer, tick);
802 tick_program_event(tick, 1);
803 }
804}
805
806static void tick_nohz_retain_tick(struct tick_sched *ts)
807{
808 ts->timer_expires_base = 0;
809}
810
811#ifdef CONFIG_NO_HZ_FULL
812static void tick_nohz_stop_sched_tick(struct tick_sched *ts, int cpu)
813{
814 if (tick_nohz_next_event(ts, cpu))
815 tick_nohz_stop_tick(ts, cpu);
816 else
817 tick_nohz_retain_tick(ts);
818}
819#endif /* CONFIG_NO_HZ_FULL */
820
821static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
822{
823 /* Update jiffies first */
824 tick_do_update_jiffies64(now);
825 cpu_load_update_nohz_stop();
826
827 /*
828 * Clear the timer idle flag, so we avoid IPIs on remote queueing and
829 * the clock forward checks in the enqueue path:
830 */
831 timer_clear_idle();
832
833 calc_load_nohz_stop();
834 touch_softlockup_watchdog_sched();
835 /*
836 * Cancel the scheduled timer and restore the tick
837 */
838 ts->tick_stopped = 0;
839 ts->idle_exittime = now;
840
841 tick_nohz_restart(ts, now);
842}
843
844static void tick_nohz_full_update_tick(struct tick_sched *ts)
845{
846#ifdef CONFIG_NO_HZ_FULL
847 int cpu = smp_processor_id();
848
849 if (!tick_nohz_full_cpu(cpu))
850 return;
851
852 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
853 return;
854
855 if (can_stop_full_tick(cpu, ts))
856 tick_nohz_stop_sched_tick(ts, cpu);
857 else if (ts->tick_stopped)
858 tick_nohz_restart_sched_tick(ts, ktime_get());
859#endif
860}
861
862static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
863{
864 /*
865 * If this CPU is offline and it is the one which updates
866 * jiffies, then give up the assignment and let it be taken by
867 * the CPU which runs the tick timer next. If we don't drop
868 * this here the jiffies might be stale and do_timer() never
869 * invoked.
870 */
871 if (unlikely(!cpu_online(cpu))) {
872 if (cpu == tick_do_timer_cpu)
873 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
874 /*
875 * Make sure the CPU doesn't get fooled by obsolete tick
876 * deadline if it comes back online later.
877 */
878 ts->next_tick = 0;
879 return false;
880 }
881
882 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
883 return false;
884
885 if (need_resched())
886 return false;
887
888 if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
889 static int ratelimit;
890
891 if (ratelimit < 10 &&
892 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
893 pr_warn("NOHZ: local_softirq_pending %02x\n",
894 (unsigned int) local_softirq_pending());
895 ratelimit++;
896 }
897 return false;
898 }
899
900 if (tick_nohz_full_enabled()) {
901 /*
902 * Keep the tick alive to guarantee timekeeping progression
903 * if there are full dynticks CPUs around
904 */
905 if (tick_do_timer_cpu == cpu)
906 return false;
907 /*
908 * Boot safety: make sure the timekeeping duty has been
909 * assigned before entering dyntick-idle mode,
910 */
911 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
912 return false;
913 }
914
915 return true;
916}
917
918static void __tick_nohz_idle_stop_tick(struct tick_sched *ts)
919{
920 ktime_t expires;
921 int cpu = smp_processor_id();
922
923 /*
924 * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the
925 * tick timer expiration time is known already.
926 */
927 if (ts->timer_expires_base)
928 expires = ts->timer_expires;
929 else if (can_stop_idle_tick(cpu, ts))
930 expires = tick_nohz_next_event(ts, cpu);
931 else
932 return;
933
934 ts->idle_calls++;
935
936 if (expires > 0LL) {
937 int was_stopped = ts->tick_stopped;
938
939 tick_nohz_stop_tick(ts, cpu);
940
941 ts->idle_sleeps++;
942 ts->idle_expires = expires;
943
944 if (!was_stopped && ts->tick_stopped) {
945 ts->idle_jiffies = ts->last_jiffies;
946 nohz_balance_enter_idle(cpu);
947 }
948 } else {
949 tick_nohz_retain_tick(ts);
950 }
951}
952
953/**
954 * tick_nohz_idle_stop_tick - stop the idle tick from the idle task
955 *
956 * When the next event is more than a tick into the future, stop the idle tick
957 */
958void tick_nohz_idle_stop_tick(void)
959{
960 __tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched));
961}
962
963void tick_nohz_idle_retain_tick(void)
964{
965 tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched));
966 /*
967 * Undo the effect of get_next_timer_interrupt() called from
968 * tick_nohz_next_event().
969 */
970 timer_clear_idle();
971}
972
973/**
974 * tick_nohz_idle_enter - prepare for entering idle on the current CPU
975 *
976 * Called when we start the idle loop.
977 */
978void tick_nohz_idle_enter(void)
979{
980 struct tick_sched *ts;
981
982 lockdep_assert_irqs_enabled();
983
984 local_irq_disable();
985
986 ts = this_cpu_ptr(&tick_cpu_sched);
987
988 WARN_ON_ONCE(ts->timer_expires_base);
989
990 ts->inidle = 1;
991 tick_nohz_start_idle(ts);
992
993 local_irq_enable();
994}
995
996/**
997 * tick_nohz_irq_exit - update next tick event from interrupt exit
998 *
999 * When an interrupt fires while we are idle and it doesn't cause
1000 * a reschedule, it may still add, modify or delete a timer, enqueue
1001 * an RCU callback, etc...
1002 * So we need to re-calculate and reprogram the next tick event.
1003 */
1004void tick_nohz_irq_exit(void)
1005{
1006 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1007
1008 if (ts->inidle)
1009 tick_nohz_start_idle(ts);
1010 else
1011 tick_nohz_full_update_tick(ts);
1012}
1013
1014/**
1015 * tick_nohz_idle_got_tick - Check whether or not the tick handler has run
1016 */
1017bool tick_nohz_idle_got_tick(void)
1018{
1019 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1020
1021 if (ts->got_idle_tick) {
1022 ts->got_idle_tick = 0;
1023 return true;
1024 }
1025 return false;
1026}
1027
1028/**
1029 * tick_nohz_get_sleep_length - return the expected length of the current sleep
1030 * @delta_next: duration until the next event if the tick cannot be stopped
1031 *
1032 * Called from power state control code with interrupts disabled
1033 */
1034ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
1035{
1036 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
1037 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1038 int cpu = smp_processor_id();
1039 /*
1040 * The idle entry time is expected to be a sufficient approximation of
1041 * the current time at this point.
1042 */
1043 ktime_t now = ts->idle_entrytime;
1044 ktime_t next_event;
1045
1046 WARN_ON_ONCE(!ts->inidle);
1047
1048 *delta_next = ktime_sub(dev->next_event, now);
1049
1050 if (!can_stop_idle_tick(cpu, ts))
1051 return *delta_next;
1052
1053 next_event = tick_nohz_next_event(ts, cpu);
1054 if (!next_event)
1055 return *delta_next;
1056
1057 /*
1058 * If the next highres timer to expire is earlier than next_event, the
1059 * idle governor needs to know that.
1060 */
1061 next_event = min_t(u64, next_event,
1062 hrtimer_next_event_without(&ts->sched_timer));
1063
1064 return ktime_sub(next_event, now);
1065}
1066
1067/**
1068 * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
1069 * for a particular CPU.
1070 *
1071 * Called from the schedutil frequency scaling governor in scheduler context.
1072 */
1073unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
1074{
1075 struct tick_sched *ts = tick_get_tick_sched(cpu);
1076
1077 return ts->idle_calls;
1078}
1079
1080/**
1081 * tick_nohz_get_idle_calls - return the current idle calls counter value
1082 *
1083 * Called from the schedutil frequency scaling governor in scheduler context.
1084 */
1085unsigned long tick_nohz_get_idle_calls(void)
1086{
1087 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1088
1089 return ts->idle_calls;
1090}
1091
1092static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
1093{
1094#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1095 unsigned long ticks;
1096
1097 if (vtime_accounting_cpu_enabled())
1098 return;
1099 /*
1100 * We stopped the tick in idle. Update process times would miss the
1101 * time we slept as update_process_times does only a 1 tick
1102 * accounting. Enforce that this is accounted to idle !
1103 */
1104 ticks = jiffies - ts->idle_jiffies;
1105 /*
1106 * We might be one off. Do not randomly account a huge number of ticks!
1107 */
1108 if (ticks && ticks < LONG_MAX)
1109 account_idle_ticks(ticks);
1110#endif
1111}
1112
1113static void __tick_nohz_idle_restart_tick(struct tick_sched *ts, ktime_t now)
1114{
1115 tick_nohz_restart_sched_tick(ts, now);
1116 tick_nohz_account_idle_ticks(ts);
1117}
1118
1119void tick_nohz_idle_restart_tick(void)
1120{
1121 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1122
1123 if (ts->tick_stopped)
1124 __tick_nohz_idle_restart_tick(ts, ktime_get());
1125}
1126
1127/**
1128 * tick_nohz_idle_exit - restart the idle tick from the idle task
1129 *
1130 * Restart the idle tick when the CPU is woken up from idle
1131 * This also exit the RCU extended quiescent state. The CPU
1132 * can use RCU again after this function is called.
1133 */
1134void tick_nohz_idle_exit(void)
1135{
1136 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1137 bool idle_active, tick_stopped;
1138 ktime_t now;
1139
1140 local_irq_disable();
1141
1142 WARN_ON_ONCE(!ts->inidle);
1143 WARN_ON_ONCE(ts->timer_expires_base);
1144
1145 ts->inidle = 0;
1146 idle_active = ts->idle_active;
1147 tick_stopped = ts->tick_stopped;
1148
1149 if (idle_active || tick_stopped)
1150 now = ktime_get();
1151
1152 if (idle_active)
1153 tick_nohz_stop_idle(ts, now);
1154
1155 if (tick_stopped)
1156 __tick_nohz_idle_restart_tick(ts, now);
1157
1158 local_irq_enable();
1159}
1160
1161/*
1162 * The nohz low res interrupt handler
1163 */
1164static void tick_nohz_handler(struct clock_event_device *dev)
1165{
1166 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1167 struct pt_regs *regs = get_irq_regs();
1168 ktime_t now = ktime_get();
1169
1170 dev->next_event = KTIME_MAX;
1171
1172 tick_sched_do_timer(ts, now);
1173 tick_sched_handle(ts, regs);
1174
1175 /* No need to reprogram if we are running tickless */
1176 if (unlikely(ts->tick_stopped))
1177 return;
1178
1179 hrtimer_forward(&ts->sched_timer, now, tick_period);
1180 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1181}
1182
1183static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1184{
1185 if (!tick_nohz_enabled)
1186 return;
1187 ts->nohz_mode = mode;
1188 /* One update is enough */
1189 if (!test_and_set_bit(0, &tick_nohz_active))
1190 timers_update_nohz();
1191}
1192
1193/**
1194 * tick_nohz_switch_to_nohz - switch to nohz mode
1195 */
1196static void tick_nohz_switch_to_nohz(void)
1197{
1198 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1199 ktime_t next;
1200
1201 if (!tick_nohz_enabled)
1202 return;
1203
1204 if (tick_switch_to_oneshot(tick_nohz_handler))
1205 return;
1206
1207 /*
1208 * Recycle the hrtimer in ts, so we can share the
1209 * hrtimer_forward with the highres code.
1210 */
1211 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1212 /* Get the next period */
1213 next = tick_init_jiffy_update();
1214
1215 hrtimer_set_expires(&ts->sched_timer, next);
1216 hrtimer_forward_now(&ts->sched_timer, tick_period);
1217 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1218 tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1219}
1220
1221static inline void tick_nohz_irq_enter(void)
1222{
1223 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1224 ktime_t now;
1225
1226 if (!ts->idle_active && !ts->tick_stopped)
1227 return;
1228 now = ktime_get();
1229 if (ts->idle_active)
1230 tick_nohz_stop_idle(ts, now);
1231 if (ts->tick_stopped)
1232 tick_nohz_update_jiffies(now);
1233}
1234
1235#else
1236
1237static inline void tick_nohz_switch_to_nohz(void) { }
1238static inline void tick_nohz_irq_enter(void) { }
1239static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1240
1241#endif /* CONFIG_NO_HZ_COMMON */
1242
1243/*
1244 * Called from irq_enter to notify about the possible interruption of idle()
1245 */
1246void tick_irq_enter(void)
1247{
1248 tick_check_oneshot_broadcast_this_cpu();
1249 tick_nohz_irq_enter();
1250}
1251
1252/*
1253 * High resolution timer specific code
1254 */
1255#ifdef CONFIG_HIGH_RES_TIMERS
1256/*
1257 * We rearm the timer until we get disabled by the idle code.
1258 * Called with interrupts disabled.
1259 */
1260static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1261{
1262 struct tick_sched *ts =
1263 container_of(timer, struct tick_sched, sched_timer);
1264 struct pt_regs *regs = get_irq_regs();
1265 ktime_t now = ktime_get();
1266
1267 tick_sched_do_timer(ts, now);
1268
1269 /*
1270 * Do not call, when we are not in irq context and have
1271 * no valid regs pointer
1272 */
1273 if (regs)
1274 tick_sched_handle(ts, regs);
1275 else
1276 ts->next_tick = 0;
1277
1278 /* No need to reprogram if we are in idle or full dynticks mode */
1279 if (unlikely(ts->tick_stopped))
1280 return HRTIMER_NORESTART;
1281
1282 hrtimer_forward(timer, now, tick_period);
1283
1284 return HRTIMER_RESTART;
1285}
1286
1287static int sched_skew_tick;
1288
1289static int __init skew_tick(char *str)
1290{
1291 get_option(&str, &sched_skew_tick);
1292
1293 return 0;
1294}
1295early_param("skew_tick", skew_tick);
1296
1297/**
1298 * tick_setup_sched_timer - setup the tick emulation timer
1299 */
1300void tick_setup_sched_timer(void)
1301{
1302 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1303 ktime_t now = ktime_get();
1304
1305 /*
1306 * Emulate tick processing via per-CPU hrtimers:
1307 */
1308 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1309 ts->sched_timer.function = tick_sched_timer;
1310
1311 /* Get the next period (per-CPU) */
1312 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1313
1314 /* Offset the tick to avert jiffies_lock contention. */
1315 if (sched_skew_tick) {
1316 u64 offset = ktime_to_ns(tick_period) >> 1;
1317 do_div(offset, num_possible_cpus());
1318 offset *= smp_processor_id();
1319 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1320 }
1321
1322 hrtimer_forward(&ts->sched_timer, now, tick_period);
1323 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1324 tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1325}
1326#endif /* HIGH_RES_TIMERS */
1327
1328#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1329void tick_cancel_sched_timer(int cpu)
1330{
1331 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1332
1333# ifdef CONFIG_HIGH_RES_TIMERS
1334 if (ts->sched_timer.base)
1335 hrtimer_cancel(&ts->sched_timer);
1336# endif
1337
1338 memset(ts, 0, sizeof(*ts));
1339}
1340#endif
1341
1342/**
1343 * Async notification about clocksource changes
1344 */
1345void tick_clock_notify(void)
1346{
1347 int cpu;
1348
1349 for_each_possible_cpu(cpu)
1350 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1351}
1352
1353/*
1354 * Async notification about clock event changes
1355 */
1356void tick_oneshot_notify(void)
1357{
1358 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1359
1360 set_bit(0, &ts->check_clocks);
1361}
1362
1363/**
1364 * Check, if a change happened, which makes oneshot possible.
1365 *
1366 * Called cyclic from the hrtimer softirq (driven by the timer
1367 * softirq) allow_nohz signals, that we can switch into low-res nohz
1368 * mode, because high resolution timers are disabled (either compile
1369 * or runtime). Called with interrupts disabled.
1370 */
1371int tick_check_oneshot_change(int allow_nohz)
1372{
1373 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1374
1375 if (!test_and_clear_bit(0, &ts->check_clocks))
1376 return 0;
1377
1378 if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1379 return 0;
1380
1381 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1382 return 0;
1383
1384 if (!allow_nohz)
1385 return 1;
1386
1387 tick_nohz_switch_to_nohz();
1388 return 0;
1389}