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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/profile.h>
21#include <linux/sched.h>
22#include <linux/module.h>
23#include <linux/irq_work.h>
24#include <linux/posix-timers.h>
25#include <linux/context_tracking.h>
26
27#include <asm/irq_regs.h>
28
29#include "tick-internal.h"
30
31#include <trace/events/timer.h>
32
33/*
34 * Per cpu nohz control structure
35 */
36static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
37
38struct tick_sched *tick_get_tick_sched(int cpu)
39{
40 return &per_cpu(tick_cpu_sched, cpu);
41}
42
43#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
44/*
45 * The time, when the last jiffy update happened. Protected by jiffies_lock.
46 */
47static ktime_t last_jiffies_update;
48
49/*
50 * Must be called with interrupts disabled !
51 */
52static void tick_do_update_jiffies64(ktime_t now)
53{
54 unsigned long ticks = 0;
55 ktime_t delta;
56
57 /*
58 * Do a quick check without holding jiffies_lock:
59 */
60 delta = ktime_sub(now, last_jiffies_update);
61 if (delta.tv64 < tick_period.tv64)
62 return;
63
64 /* Reevalute with jiffies_lock held */
65 write_seqlock(&jiffies_lock);
66
67 delta = ktime_sub(now, last_jiffies_update);
68 if (delta.tv64 >= tick_period.tv64) {
69
70 delta = ktime_sub(delta, tick_period);
71 last_jiffies_update = ktime_add(last_jiffies_update,
72 tick_period);
73
74 /* Slow path for long timeouts */
75 if (unlikely(delta.tv64 >= tick_period.tv64)) {
76 s64 incr = ktime_to_ns(tick_period);
77
78 ticks = ktime_divns(delta, incr);
79
80 last_jiffies_update = ktime_add_ns(last_jiffies_update,
81 incr * ticks);
82 }
83 do_timer(++ticks);
84
85 /* Keep the tick_next_period variable up to date */
86 tick_next_period = ktime_add(last_jiffies_update, tick_period);
87 } else {
88 write_sequnlock(&jiffies_lock);
89 return;
90 }
91 write_sequnlock(&jiffies_lock);
92 update_wall_time();
93}
94
95/*
96 * Initialize and return retrieve the jiffies update.
97 */
98static ktime_t tick_init_jiffy_update(void)
99{
100 ktime_t period;
101
102 write_seqlock(&jiffies_lock);
103 /* Did we start the jiffies update yet ? */
104 if (last_jiffies_update.tv64 == 0)
105 last_jiffies_update = tick_next_period;
106 period = last_jiffies_update;
107 write_sequnlock(&jiffies_lock);
108 return period;
109}
110
111
112static void tick_sched_do_timer(ktime_t now)
113{
114 int cpu = smp_processor_id();
115
116#ifdef CONFIG_NO_HZ_COMMON
117 /*
118 * Check if the do_timer duty was dropped. We don't care about
119 * concurrency: This happens only when the cpu in charge went
120 * into a long sleep. If two cpus happen to assign themself to
121 * this duty, then the jiffies update is still serialized by
122 * jiffies_lock.
123 */
124 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
125 && !tick_nohz_full_cpu(cpu))
126 tick_do_timer_cpu = cpu;
127#endif
128
129 /* Check, if the jiffies need an update */
130 if (tick_do_timer_cpu == cpu)
131 tick_do_update_jiffies64(now);
132}
133
134static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
135{
136#ifdef CONFIG_NO_HZ_COMMON
137 /*
138 * When we are idle and the tick is stopped, we have to touch
139 * the watchdog as we might not schedule for a really long
140 * time. This happens on complete idle SMP systems while
141 * waiting on the login prompt. We also increment the "start of
142 * idle" jiffy stamp so the idle accounting adjustment we do
143 * when we go busy again does not account too much ticks.
144 */
145 if (ts->tick_stopped) {
146 touch_softlockup_watchdog_sched();
147 if (is_idle_task(current))
148 ts->idle_jiffies++;
149 }
150#endif
151 update_process_times(user_mode(regs));
152 profile_tick(CPU_PROFILING);
153}
154#endif
155
156#ifdef CONFIG_NO_HZ_FULL
157cpumask_var_t tick_nohz_full_mask;
158cpumask_var_t housekeeping_mask;
159bool tick_nohz_full_running;
160static atomic_t tick_dep_mask;
161
162static bool check_tick_dependency(atomic_t *dep)
163{
164 int val = atomic_read(dep);
165
166 if (val & TICK_DEP_MASK_POSIX_TIMER) {
167 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
168 return true;
169 }
170
171 if (val & TICK_DEP_MASK_PERF_EVENTS) {
172 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
173 return true;
174 }
175
176 if (val & TICK_DEP_MASK_SCHED) {
177 trace_tick_stop(0, TICK_DEP_MASK_SCHED);
178 return true;
179 }
180
181 if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
182 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
183 return true;
184 }
185
186 return false;
187}
188
189static bool can_stop_full_tick(struct tick_sched *ts)
190{
191 WARN_ON_ONCE(!irqs_disabled());
192
193 if (check_tick_dependency(&tick_dep_mask))
194 return false;
195
196 if (check_tick_dependency(&ts->tick_dep_mask))
197 return false;
198
199 if (check_tick_dependency(¤t->tick_dep_mask))
200 return false;
201
202 if (check_tick_dependency(¤t->signal->tick_dep_mask))
203 return false;
204
205 return true;
206}
207
208static void nohz_full_kick_func(struct irq_work *work)
209{
210 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
211}
212
213static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
214 .func = nohz_full_kick_func,
215};
216
217/*
218 * Kick this CPU if it's full dynticks in order to force it to
219 * re-evaluate its dependency on the tick and restart it if necessary.
220 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
221 * is NMI safe.
222 */
223static void tick_nohz_full_kick(void)
224{
225 if (!tick_nohz_full_cpu(smp_processor_id()))
226 return;
227
228 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
229}
230
231/*
232 * Kick the CPU if it's full dynticks in order to force it to
233 * re-evaluate its dependency on the tick and restart it if necessary.
234 */
235void tick_nohz_full_kick_cpu(int cpu)
236{
237 if (!tick_nohz_full_cpu(cpu))
238 return;
239
240 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
241}
242
243/*
244 * Kick all full dynticks CPUs in order to force these to re-evaluate
245 * their dependency on the tick and restart it if necessary.
246 */
247static void tick_nohz_full_kick_all(void)
248{
249 int cpu;
250
251 if (!tick_nohz_full_running)
252 return;
253
254 preempt_disable();
255 for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
256 tick_nohz_full_kick_cpu(cpu);
257 preempt_enable();
258}
259
260static void tick_nohz_dep_set_all(atomic_t *dep,
261 enum tick_dep_bits bit)
262{
263 int prev;
264
265 prev = atomic_fetch_or(dep, BIT(bit));
266 if (!prev)
267 tick_nohz_full_kick_all();
268}
269
270/*
271 * Set a global tick dependency. Used by perf events that rely on freq and
272 * by unstable clock.
273 */
274void tick_nohz_dep_set(enum tick_dep_bits bit)
275{
276 tick_nohz_dep_set_all(&tick_dep_mask, bit);
277}
278
279void tick_nohz_dep_clear(enum tick_dep_bits bit)
280{
281 atomic_andnot(BIT(bit), &tick_dep_mask);
282}
283
284/*
285 * Set per-CPU tick dependency. Used by scheduler and perf events in order to
286 * manage events throttling.
287 */
288void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
289{
290 int prev;
291 struct tick_sched *ts;
292
293 ts = per_cpu_ptr(&tick_cpu_sched, cpu);
294
295 prev = atomic_fetch_or(&ts->tick_dep_mask, BIT(bit));
296 if (!prev) {
297 preempt_disable();
298 /* Perf needs local kick that is NMI safe */
299 if (cpu == smp_processor_id()) {
300 tick_nohz_full_kick();
301 } else {
302 /* Remote irq work not NMI-safe */
303 if (!WARN_ON_ONCE(in_nmi()))
304 tick_nohz_full_kick_cpu(cpu);
305 }
306 preempt_enable();
307 }
308}
309
310void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
311{
312 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
313
314 atomic_andnot(BIT(bit), &ts->tick_dep_mask);
315}
316
317/*
318 * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
319 * per task timers.
320 */
321void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
322{
323 /*
324 * We could optimize this with just kicking the target running the task
325 * if that noise matters for nohz full users.
326 */
327 tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
328}
329
330void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
331{
332 atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
333}
334
335/*
336 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
337 * per process timers.
338 */
339void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
340{
341 tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
342}
343
344void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
345{
346 atomic_andnot(BIT(bit), &sig->tick_dep_mask);
347}
348
349/*
350 * Re-evaluate the need for the tick as we switch the current task.
351 * It might need the tick due to per task/process properties:
352 * perf events, posix cpu timers, ...
353 */
354void __tick_nohz_task_switch(void)
355{
356 unsigned long flags;
357 struct tick_sched *ts;
358
359 local_irq_save(flags);
360
361 if (!tick_nohz_full_cpu(smp_processor_id()))
362 goto out;
363
364 ts = this_cpu_ptr(&tick_cpu_sched);
365
366 if (ts->tick_stopped) {
367 if (atomic_read(¤t->tick_dep_mask) ||
368 atomic_read(¤t->signal->tick_dep_mask))
369 tick_nohz_full_kick();
370 }
371out:
372 local_irq_restore(flags);
373}
374
375/* Parse the boot-time nohz CPU list from the kernel parameters. */
376static int __init tick_nohz_full_setup(char *str)
377{
378 alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
379 if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
380 pr_warn("NO_HZ: Incorrect nohz_full cpumask\n");
381 free_bootmem_cpumask_var(tick_nohz_full_mask);
382 return 1;
383 }
384 tick_nohz_full_running = true;
385
386 return 1;
387}
388__setup("nohz_full=", tick_nohz_full_setup);
389
390static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
391 unsigned long action,
392 void *hcpu)
393{
394 unsigned int cpu = (unsigned long)hcpu;
395
396 switch (action & ~CPU_TASKS_FROZEN) {
397 case CPU_DOWN_PREPARE:
398 /*
399 * The boot CPU handles housekeeping duty (unbound timers,
400 * workqueues, timekeeping, ...) on behalf of full dynticks
401 * CPUs. It must remain online when nohz full is enabled.
402 */
403 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
404 return NOTIFY_BAD;
405 break;
406 }
407 return NOTIFY_OK;
408}
409
410static int tick_nohz_init_all(void)
411{
412 int err = -1;
413
414#ifdef CONFIG_NO_HZ_FULL_ALL
415 if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
416 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
417 return err;
418 }
419 err = 0;
420 cpumask_setall(tick_nohz_full_mask);
421 tick_nohz_full_running = true;
422#endif
423 return err;
424}
425
426void __init tick_nohz_init(void)
427{
428 int cpu;
429
430 if (!tick_nohz_full_running) {
431 if (tick_nohz_init_all() < 0)
432 return;
433 }
434
435 if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
436 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
437 cpumask_clear(tick_nohz_full_mask);
438 tick_nohz_full_running = false;
439 return;
440 }
441
442 /*
443 * Full dynticks uses irq work to drive the tick rescheduling on safe
444 * locking contexts. But then we need irq work to raise its own
445 * interrupts to avoid circular dependency on the tick
446 */
447 if (!arch_irq_work_has_interrupt()) {
448 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
449 cpumask_clear(tick_nohz_full_mask);
450 cpumask_copy(housekeeping_mask, cpu_possible_mask);
451 tick_nohz_full_running = false;
452 return;
453 }
454
455 cpu = smp_processor_id();
456
457 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
458 pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
459 cpu);
460 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
461 }
462
463 cpumask_andnot(housekeeping_mask,
464 cpu_possible_mask, tick_nohz_full_mask);
465
466 for_each_cpu(cpu, tick_nohz_full_mask)
467 context_tracking_cpu_set(cpu);
468
469 cpu_notifier(tick_nohz_cpu_down_callback, 0);
470 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
471 cpumask_pr_args(tick_nohz_full_mask));
472
473 /*
474 * We need at least one CPU to handle housekeeping work such
475 * as timekeeping, unbound timers, workqueues, ...
476 */
477 WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
478}
479#endif
480
481/*
482 * NOHZ - aka dynamic tick functionality
483 */
484#ifdef CONFIG_NO_HZ_COMMON
485/*
486 * NO HZ enabled ?
487 */
488bool tick_nohz_enabled __read_mostly = true;
489unsigned long tick_nohz_active __read_mostly;
490/*
491 * Enable / Disable tickless mode
492 */
493static int __init setup_tick_nohz(char *str)
494{
495 return (kstrtobool(str, &tick_nohz_enabled) == 0);
496}
497
498__setup("nohz=", setup_tick_nohz);
499
500int tick_nohz_tick_stopped(void)
501{
502 return __this_cpu_read(tick_cpu_sched.tick_stopped);
503}
504
505/**
506 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
507 *
508 * Called from interrupt entry when the CPU was idle
509 *
510 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
511 * must be updated. Otherwise an interrupt handler could use a stale jiffy
512 * value. We do this unconditionally on any cpu, as we don't know whether the
513 * cpu, which has the update task assigned is in a long sleep.
514 */
515static void tick_nohz_update_jiffies(ktime_t now)
516{
517 unsigned long flags;
518
519 __this_cpu_write(tick_cpu_sched.idle_waketime, now);
520
521 local_irq_save(flags);
522 tick_do_update_jiffies64(now);
523 local_irq_restore(flags);
524
525 touch_softlockup_watchdog_sched();
526}
527
528/*
529 * Updates the per cpu time idle statistics counters
530 */
531static void
532update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
533{
534 ktime_t delta;
535
536 if (ts->idle_active) {
537 delta = ktime_sub(now, ts->idle_entrytime);
538 if (nr_iowait_cpu(cpu) > 0)
539 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
540 else
541 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
542 ts->idle_entrytime = now;
543 }
544
545 if (last_update_time)
546 *last_update_time = ktime_to_us(now);
547
548}
549
550static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
551{
552 update_ts_time_stats(smp_processor_id(), ts, now, NULL);
553 ts->idle_active = 0;
554
555 sched_clock_idle_wakeup_event(0);
556}
557
558static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
559{
560 ktime_t now = ktime_get();
561
562 ts->idle_entrytime = now;
563 ts->idle_active = 1;
564 sched_clock_idle_sleep_event();
565 return now;
566}
567
568/**
569 * get_cpu_idle_time_us - get the total idle time of a cpu
570 * @cpu: CPU number to query
571 * @last_update_time: variable to store update time in. Do not update
572 * counters if NULL.
573 *
574 * Return the cummulative idle time (since boot) for a given
575 * CPU, in microseconds.
576 *
577 * This time is measured via accounting rather than sampling,
578 * and is as accurate as ktime_get() is.
579 *
580 * This function returns -1 if NOHZ is not enabled.
581 */
582u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
583{
584 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
585 ktime_t now, idle;
586
587 if (!tick_nohz_active)
588 return -1;
589
590 now = ktime_get();
591 if (last_update_time) {
592 update_ts_time_stats(cpu, ts, now, last_update_time);
593 idle = ts->idle_sleeptime;
594 } else {
595 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
596 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
597
598 idle = ktime_add(ts->idle_sleeptime, delta);
599 } else {
600 idle = ts->idle_sleeptime;
601 }
602 }
603
604 return ktime_to_us(idle);
605
606}
607EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
608
609/**
610 * get_cpu_iowait_time_us - get the total iowait time of a cpu
611 * @cpu: CPU number to query
612 * @last_update_time: variable to store update time in. Do not update
613 * counters if NULL.
614 *
615 * Return the cummulative iowait time (since boot) for a given
616 * CPU, in microseconds.
617 *
618 * This time is measured via accounting rather than sampling,
619 * and is as accurate as ktime_get() is.
620 *
621 * This function returns -1 if NOHZ is not enabled.
622 */
623u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
624{
625 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
626 ktime_t now, iowait;
627
628 if (!tick_nohz_active)
629 return -1;
630
631 now = ktime_get();
632 if (last_update_time) {
633 update_ts_time_stats(cpu, ts, now, last_update_time);
634 iowait = ts->iowait_sleeptime;
635 } else {
636 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
637 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
638
639 iowait = ktime_add(ts->iowait_sleeptime, delta);
640 } else {
641 iowait = ts->iowait_sleeptime;
642 }
643 }
644
645 return ktime_to_us(iowait);
646}
647EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
648
649static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
650{
651 hrtimer_cancel(&ts->sched_timer);
652 hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
653
654 /* Forward the time to expire in the future */
655 hrtimer_forward(&ts->sched_timer, now, tick_period);
656
657 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
658 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
659 else
660 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
661}
662
663static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
664 ktime_t now, int cpu)
665{
666 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
667 u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
668 unsigned long seq, basejiff;
669 ktime_t tick;
670
671 /* Read jiffies and the time when jiffies were updated last */
672 do {
673 seq = read_seqbegin(&jiffies_lock);
674 basemono = last_jiffies_update.tv64;
675 basejiff = jiffies;
676 } while (read_seqretry(&jiffies_lock, seq));
677 ts->last_jiffies = basejiff;
678
679 if (rcu_needs_cpu(basemono, &next_rcu) ||
680 arch_needs_cpu() || irq_work_needs_cpu()) {
681 next_tick = basemono + TICK_NSEC;
682 } else {
683 /*
684 * Get the next pending timer. If high resolution
685 * timers are enabled this only takes the timer wheel
686 * timers into account. If high resolution timers are
687 * disabled this also looks at the next expiring
688 * hrtimer.
689 */
690 next_tmr = get_next_timer_interrupt(basejiff, basemono);
691 ts->next_timer = next_tmr;
692 /* Take the next rcu event into account */
693 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
694 }
695
696 /*
697 * If the tick is due in the next period, keep it ticking or
698 * force prod the timer.
699 */
700 delta = next_tick - basemono;
701 if (delta <= (u64)TICK_NSEC) {
702 tick.tv64 = 0;
703 /*
704 * We've not stopped the tick yet, and there's a timer in the
705 * next period, so no point in stopping it either, bail.
706 */
707 if (!ts->tick_stopped)
708 goto out;
709
710 /*
711 * If, OTOH, we did stop it, but there's a pending (expired)
712 * timer reprogram the timer hardware to fire now.
713 *
714 * We will not restart the tick proper, just prod the timer
715 * hardware into firing an interrupt to process the pending
716 * timers. Just like tick_irq_exit() will not restart the tick
717 * for 'normal' interrupts.
718 *
719 * Only once we exit the idle loop will we re-enable the tick,
720 * see tick_nohz_idle_exit().
721 */
722 if (delta == 0) {
723 tick_nohz_restart(ts, now);
724 goto out;
725 }
726 }
727
728 /*
729 * If this cpu is the one which updates jiffies, then give up
730 * the assignment and let it be taken by the cpu which runs
731 * the tick timer next, which might be this cpu as well. If we
732 * don't drop this here the jiffies might be stale and
733 * do_timer() never invoked. Keep track of the fact that it
734 * was the one which had the do_timer() duty last. If this cpu
735 * is the one which had the do_timer() duty last, we limit the
736 * sleep time to the timekeeping max_deferement value.
737 * Otherwise we can sleep as long as we want.
738 */
739 delta = timekeeping_max_deferment();
740 if (cpu == tick_do_timer_cpu) {
741 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
742 ts->do_timer_last = 1;
743 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
744 delta = KTIME_MAX;
745 ts->do_timer_last = 0;
746 } else if (!ts->do_timer_last) {
747 delta = KTIME_MAX;
748 }
749
750#ifdef CONFIG_NO_HZ_FULL
751 /* Limit the tick delta to the maximum scheduler deferment */
752 if (!ts->inidle)
753 delta = min(delta, scheduler_tick_max_deferment());
754#endif
755
756 /* Calculate the next expiry time */
757 if (delta < (KTIME_MAX - basemono))
758 expires = basemono + delta;
759 else
760 expires = KTIME_MAX;
761
762 expires = min_t(u64, expires, next_tick);
763 tick.tv64 = expires;
764
765 /* Skip reprogram of event if its not changed */
766 if (ts->tick_stopped && (expires == dev->next_event.tv64))
767 goto out;
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 nohz_balance_enter_idle(cpu);
778 calc_load_enter_idle();
779
780 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
781 ts->tick_stopped = 1;
782 trace_tick_stop(1, TICK_DEP_MASK_NONE);
783 }
784
785 /*
786 * If the expiration time == KTIME_MAX, then we simply stop
787 * the tick timer.
788 */
789 if (unlikely(expires == KTIME_MAX)) {
790 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
791 hrtimer_cancel(&ts->sched_timer);
792 goto out;
793 }
794
795 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
796 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
797 else
798 tick_program_event(tick, 1);
799out:
800 /* Update the estimated sleep length */
801 ts->sleep_length = ktime_sub(dev->next_event, now);
802 return tick;
803}
804
805static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now, int active)
806{
807 /* Update jiffies first */
808 tick_do_update_jiffies64(now);
809 update_cpu_load_nohz(active);
810
811 calc_load_exit_idle();
812 touch_softlockup_watchdog_sched();
813 /*
814 * Cancel the scheduled timer and restore the tick
815 */
816 ts->tick_stopped = 0;
817 ts->idle_exittime = now;
818
819 tick_nohz_restart(ts, now);
820}
821
822static void tick_nohz_full_update_tick(struct tick_sched *ts)
823{
824#ifdef CONFIG_NO_HZ_FULL
825 int cpu = smp_processor_id();
826
827 if (!tick_nohz_full_cpu(cpu))
828 return;
829
830 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
831 return;
832
833 if (can_stop_full_tick(ts))
834 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
835 else if (ts->tick_stopped)
836 tick_nohz_restart_sched_tick(ts, ktime_get(), 1);
837#endif
838}
839
840static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
841{
842 /*
843 * If this cpu is offline and it is the one which updates
844 * jiffies, then give up the assignment and let it be taken by
845 * the cpu which runs the tick timer next. If we don't drop
846 * this here the jiffies might be stale and do_timer() never
847 * invoked.
848 */
849 if (unlikely(!cpu_online(cpu))) {
850 if (cpu == tick_do_timer_cpu)
851 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
852 return false;
853 }
854
855 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
856 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
857 return false;
858 }
859
860 if (need_resched())
861 return false;
862
863 if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
864 static int ratelimit;
865
866 if (ratelimit < 10 &&
867 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
868 pr_warn("NOHZ: local_softirq_pending %02x\n",
869 (unsigned int) local_softirq_pending());
870 ratelimit++;
871 }
872 return false;
873 }
874
875 if (tick_nohz_full_enabled()) {
876 /*
877 * Keep the tick alive to guarantee timekeeping progression
878 * if there are full dynticks CPUs around
879 */
880 if (tick_do_timer_cpu == cpu)
881 return false;
882 /*
883 * Boot safety: make sure the timekeeping duty has been
884 * assigned before entering dyntick-idle mode,
885 */
886 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
887 return false;
888 }
889
890 return true;
891}
892
893static void __tick_nohz_idle_enter(struct tick_sched *ts)
894{
895 ktime_t now, expires;
896 int cpu = smp_processor_id();
897
898 now = tick_nohz_start_idle(ts);
899
900 if (can_stop_idle_tick(cpu, ts)) {
901 int was_stopped = ts->tick_stopped;
902
903 ts->idle_calls++;
904
905 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
906 if (expires.tv64 > 0LL) {
907 ts->idle_sleeps++;
908 ts->idle_expires = expires;
909 }
910
911 if (!was_stopped && ts->tick_stopped)
912 ts->idle_jiffies = ts->last_jiffies;
913 }
914}
915
916/**
917 * tick_nohz_idle_enter - stop the idle tick from the idle task
918 *
919 * When the next event is more than a tick into the future, stop the idle tick
920 * Called when we start the idle loop.
921 *
922 * The arch is responsible of calling:
923 *
924 * - rcu_idle_enter() after its last use of RCU before the CPU is put
925 * to sleep.
926 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
927 */
928void tick_nohz_idle_enter(void)
929{
930 struct tick_sched *ts;
931
932 WARN_ON_ONCE(irqs_disabled());
933
934 /*
935 * Update the idle state in the scheduler domain hierarchy
936 * when tick_nohz_stop_sched_tick() is called from the idle loop.
937 * State will be updated to busy during the first busy tick after
938 * exiting idle.
939 */
940 set_cpu_sd_state_idle();
941
942 local_irq_disable();
943
944 ts = this_cpu_ptr(&tick_cpu_sched);
945 ts->inidle = 1;
946 __tick_nohz_idle_enter(ts);
947
948 local_irq_enable();
949}
950
951/**
952 * tick_nohz_irq_exit - update next tick event from interrupt exit
953 *
954 * When an interrupt fires while we are idle and it doesn't cause
955 * a reschedule, it may still add, modify or delete a timer, enqueue
956 * an RCU callback, etc...
957 * So we need to re-calculate and reprogram the next tick event.
958 */
959void tick_nohz_irq_exit(void)
960{
961 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
962
963 if (ts->inidle)
964 __tick_nohz_idle_enter(ts);
965 else
966 tick_nohz_full_update_tick(ts);
967}
968
969/**
970 * tick_nohz_get_sleep_length - return the length of the current sleep
971 *
972 * Called from power state control code with interrupts disabled
973 */
974ktime_t tick_nohz_get_sleep_length(void)
975{
976 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
977
978 return ts->sleep_length;
979}
980
981static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
982{
983#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
984 unsigned long ticks;
985
986 if (vtime_accounting_cpu_enabled())
987 return;
988 /*
989 * We stopped the tick in idle. Update process times would miss the
990 * time we slept as update_process_times does only a 1 tick
991 * accounting. Enforce that this is accounted to idle !
992 */
993 ticks = jiffies - ts->idle_jiffies;
994 /*
995 * We might be one off. Do not randomly account a huge number of ticks!
996 */
997 if (ticks && ticks < LONG_MAX)
998 account_idle_ticks(ticks);
999#endif
1000}
1001
1002/**
1003 * tick_nohz_idle_exit - restart the idle tick from the idle task
1004 *
1005 * Restart the idle tick when the CPU is woken up from idle
1006 * This also exit the RCU extended quiescent state. The CPU
1007 * can use RCU again after this function is called.
1008 */
1009void tick_nohz_idle_exit(void)
1010{
1011 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1012 ktime_t now;
1013
1014 local_irq_disable();
1015
1016 WARN_ON_ONCE(!ts->inidle);
1017
1018 ts->inidle = 0;
1019
1020 if (ts->idle_active || ts->tick_stopped)
1021 now = ktime_get();
1022
1023 if (ts->idle_active)
1024 tick_nohz_stop_idle(ts, now);
1025
1026 if (ts->tick_stopped) {
1027 tick_nohz_restart_sched_tick(ts, now, 0);
1028 tick_nohz_account_idle_ticks(ts);
1029 }
1030
1031 local_irq_enable();
1032}
1033
1034/*
1035 * The nohz low res interrupt handler
1036 */
1037static void tick_nohz_handler(struct clock_event_device *dev)
1038{
1039 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1040 struct pt_regs *regs = get_irq_regs();
1041 ktime_t now = ktime_get();
1042
1043 dev->next_event.tv64 = KTIME_MAX;
1044
1045 tick_sched_do_timer(now);
1046 tick_sched_handle(ts, regs);
1047
1048 /* No need to reprogram if we are running tickless */
1049 if (unlikely(ts->tick_stopped))
1050 return;
1051
1052 hrtimer_forward(&ts->sched_timer, now, tick_period);
1053 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1054}
1055
1056static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1057{
1058 if (!tick_nohz_enabled)
1059 return;
1060 ts->nohz_mode = mode;
1061 /* One update is enough */
1062 if (!test_and_set_bit(0, &tick_nohz_active))
1063 timers_update_migration(true);
1064}
1065
1066/**
1067 * tick_nohz_switch_to_nohz - switch to nohz mode
1068 */
1069static void tick_nohz_switch_to_nohz(void)
1070{
1071 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1072 ktime_t next;
1073
1074 if (!tick_nohz_enabled)
1075 return;
1076
1077 if (tick_switch_to_oneshot(tick_nohz_handler))
1078 return;
1079
1080 /*
1081 * Recycle the hrtimer in ts, so we can share the
1082 * hrtimer_forward with the highres code.
1083 */
1084 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1085 /* Get the next period */
1086 next = tick_init_jiffy_update();
1087
1088 hrtimer_set_expires(&ts->sched_timer, next);
1089 hrtimer_forward_now(&ts->sched_timer, tick_period);
1090 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1091 tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1092}
1093
1094/*
1095 * When NOHZ is enabled and the tick is stopped, we need to kick the
1096 * tick timer from irq_enter() so that the jiffies update is kept
1097 * alive during long running softirqs. That's ugly as hell, but
1098 * correctness is key even if we need to fix the offending softirq in
1099 * the first place.
1100 *
1101 * Note, this is different to tick_nohz_restart. We just kick the
1102 * timer and do not touch the other magic bits which need to be done
1103 * when idle is left.
1104 */
1105static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1106{
1107#if 0
1108 /* Switch back to 2.6.27 behaviour */
1109 ktime_t delta;
1110
1111 /*
1112 * Do not touch the tick device, when the next expiry is either
1113 * already reached or less/equal than the tick period.
1114 */
1115 delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1116 if (delta.tv64 <= tick_period.tv64)
1117 return;
1118
1119 tick_nohz_restart(ts, now);
1120#endif
1121}
1122
1123static inline void tick_nohz_irq_enter(void)
1124{
1125 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1126 ktime_t now;
1127
1128 if (!ts->idle_active && !ts->tick_stopped)
1129 return;
1130 now = ktime_get();
1131 if (ts->idle_active)
1132 tick_nohz_stop_idle(ts, now);
1133 if (ts->tick_stopped) {
1134 tick_nohz_update_jiffies(now);
1135 tick_nohz_kick_tick(ts, now);
1136 }
1137}
1138
1139#else
1140
1141static inline void tick_nohz_switch_to_nohz(void) { }
1142static inline void tick_nohz_irq_enter(void) { }
1143static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1144
1145#endif /* CONFIG_NO_HZ_COMMON */
1146
1147/*
1148 * Called from irq_enter to notify about the possible interruption of idle()
1149 */
1150void tick_irq_enter(void)
1151{
1152 tick_check_oneshot_broadcast_this_cpu();
1153 tick_nohz_irq_enter();
1154}
1155
1156/*
1157 * High resolution timer specific code
1158 */
1159#ifdef CONFIG_HIGH_RES_TIMERS
1160/*
1161 * We rearm the timer until we get disabled by the idle code.
1162 * Called with interrupts disabled.
1163 */
1164static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1165{
1166 struct tick_sched *ts =
1167 container_of(timer, struct tick_sched, sched_timer);
1168 struct pt_regs *regs = get_irq_regs();
1169 ktime_t now = ktime_get();
1170
1171 tick_sched_do_timer(now);
1172
1173 /*
1174 * Do not call, when we are not in irq context and have
1175 * no valid regs pointer
1176 */
1177 if (regs)
1178 tick_sched_handle(ts, regs);
1179
1180 /* No need to reprogram if we are in idle or full dynticks mode */
1181 if (unlikely(ts->tick_stopped))
1182 return HRTIMER_NORESTART;
1183
1184 hrtimer_forward(timer, now, tick_period);
1185
1186 return HRTIMER_RESTART;
1187}
1188
1189static int sched_skew_tick;
1190
1191static int __init skew_tick(char *str)
1192{
1193 get_option(&str, &sched_skew_tick);
1194
1195 return 0;
1196}
1197early_param("skew_tick", skew_tick);
1198
1199/**
1200 * tick_setup_sched_timer - setup the tick emulation timer
1201 */
1202void tick_setup_sched_timer(void)
1203{
1204 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1205 ktime_t now = ktime_get();
1206
1207 /*
1208 * Emulate tick processing via per-CPU hrtimers:
1209 */
1210 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1211 ts->sched_timer.function = tick_sched_timer;
1212
1213 /* Get the next period (per cpu) */
1214 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1215
1216 /* Offset the tick to avert jiffies_lock contention. */
1217 if (sched_skew_tick) {
1218 u64 offset = ktime_to_ns(tick_period) >> 1;
1219 do_div(offset, num_possible_cpus());
1220 offset *= smp_processor_id();
1221 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1222 }
1223
1224 hrtimer_forward(&ts->sched_timer, now, tick_period);
1225 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1226 tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1227}
1228#endif /* HIGH_RES_TIMERS */
1229
1230#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1231void tick_cancel_sched_timer(int cpu)
1232{
1233 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1234
1235# ifdef CONFIG_HIGH_RES_TIMERS
1236 if (ts->sched_timer.base)
1237 hrtimer_cancel(&ts->sched_timer);
1238# endif
1239
1240 memset(ts, 0, sizeof(*ts));
1241}
1242#endif
1243
1244/**
1245 * Async notification about clocksource changes
1246 */
1247void tick_clock_notify(void)
1248{
1249 int cpu;
1250
1251 for_each_possible_cpu(cpu)
1252 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1253}
1254
1255/*
1256 * Async notification about clock event changes
1257 */
1258void tick_oneshot_notify(void)
1259{
1260 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1261
1262 set_bit(0, &ts->check_clocks);
1263}
1264
1265/**
1266 * Check, if a change happened, which makes oneshot possible.
1267 *
1268 * Called cyclic from the hrtimer softirq (driven by the timer
1269 * softirq) allow_nohz signals, that we can switch into low-res nohz
1270 * mode, because high resolution timers are disabled (either compile
1271 * or runtime). Called with interrupts disabled.
1272 */
1273int tick_check_oneshot_change(int allow_nohz)
1274{
1275 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1276
1277 if (!test_and_clear_bit(0, &ts->check_clocks))
1278 return 0;
1279
1280 if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1281 return 0;
1282
1283 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1284 return 0;
1285
1286 if (!allow_nohz)
1287 return 1;
1288
1289 tick_nohz_switch_to_nohz();
1290 return 0;
1291}
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/profile.h>
21#include <linux/sched.h>
22#include <linux/module.h>
23#include <linux/irq_work.h>
24#include <linux/posix-timers.h>
25#include <linux/context_tracking.h>
26
27#include <asm/irq_regs.h>
28
29#include "tick-internal.h"
30
31#include <trace/events/timer.h>
32
33/*
34 * Per-CPU nohz control structure
35 */
36static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
37
38struct tick_sched *tick_get_tick_sched(int cpu)
39{
40 return &per_cpu(tick_cpu_sched, cpu);
41}
42
43#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
44/*
45 * The time, when the last jiffy update happened. Protected by jiffies_lock.
46 */
47static ktime_t last_jiffies_update;
48
49/*
50 * Must be called with interrupts disabled !
51 */
52static void tick_do_update_jiffies64(ktime_t now)
53{
54 unsigned long ticks = 0;
55 ktime_t delta;
56
57 /*
58 * Do a quick check without holding jiffies_lock:
59 */
60 delta = ktime_sub(now, last_jiffies_update);
61 if (delta < tick_period)
62 return;
63
64 /* Reevaluate with jiffies_lock held */
65 write_seqlock(&jiffies_lock);
66
67 delta = ktime_sub(now, last_jiffies_update);
68 if (delta >= tick_period) {
69
70 delta = ktime_sub(delta, tick_period);
71 last_jiffies_update = ktime_add(last_jiffies_update,
72 tick_period);
73
74 /* Slow path for long timeouts */
75 if (unlikely(delta >= tick_period)) {
76 s64 incr = ktime_to_ns(tick_period);
77
78 ticks = ktime_divns(delta, incr);
79
80 last_jiffies_update = ktime_add_ns(last_jiffies_update,
81 incr * ticks);
82 }
83 do_timer(++ticks);
84
85 /* Keep the tick_next_period variable up to date */
86 tick_next_period = ktime_add(last_jiffies_update, tick_period);
87 } else {
88 write_sequnlock(&jiffies_lock);
89 return;
90 }
91 write_sequnlock(&jiffies_lock);
92 update_wall_time();
93}
94
95/*
96 * Initialize and return retrieve the jiffies update.
97 */
98static ktime_t tick_init_jiffy_update(void)
99{
100 ktime_t period;
101
102 write_seqlock(&jiffies_lock);
103 /* Did we start the jiffies update yet ? */
104 if (last_jiffies_update == 0)
105 last_jiffies_update = tick_next_period;
106 period = last_jiffies_update;
107 write_sequnlock(&jiffies_lock);
108 return period;
109}
110
111
112static void tick_sched_do_timer(ktime_t now)
113{
114 int cpu = smp_processor_id();
115
116#ifdef CONFIG_NO_HZ_COMMON
117 /*
118 * Check if the do_timer duty was dropped. We don't care about
119 * concurrency: This happens only when the CPU in charge went
120 * into a long sleep. If two CPUs happen to assign themselves to
121 * this duty, then the jiffies update is still serialized by
122 * jiffies_lock.
123 */
124 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
125 && !tick_nohz_full_cpu(cpu))
126 tick_do_timer_cpu = cpu;
127#endif
128
129 /* Check, if the jiffies need an update */
130 if (tick_do_timer_cpu == cpu)
131 tick_do_update_jiffies64(now);
132}
133
134static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
135{
136#ifdef CONFIG_NO_HZ_COMMON
137 /*
138 * When we are idle and the tick is stopped, we have to touch
139 * the watchdog as we might not schedule for a really long
140 * time. This happens on complete idle SMP systems while
141 * waiting on the login prompt. We also increment the "start of
142 * idle" jiffy stamp so the idle accounting adjustment we do
143 * when we go busy again does not account too much ticks.
144 */
145 if (ts->tick_stopped) {
146 touch_softlockup_watchdog_sched();
147 if (is_idle_task(current))
148 ts->idle_jiffies++;
149 }
150#endif
151 update_process_times(user_mode(regs));
152 profile_tick(CPU_PROFILING);
153}
154#endif
155
156#ifdef CONFIG_NO_HZ_FULL
157cpumask_var_t tick_nohz_full_mask;
158cpumask_var_t housekeeping_mask;
159bool tick_nohz_full_running;
160static atomic_t tick_dep_mask;
161
162static bool check_tick_dependency(atomic_t *dep)
163{
164 int val = atomic_read(dep);
165
166 if (val & TICK_DEP_MASK_POSIX_TIMER) {
167 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
168 return true;
169 }
170
171 if (val & TICK_DEP_MASK_PERF_EVENTS) {
172 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
173 return true;
174 }
175
176 if (val & TICK_DEP_MASK_SCHED) {
177 trace_tick_stop(0, TICK_DEP_MASK_SCHED);
178 return true;
179 }
180
181 if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
182 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
183 return true;
184 }
185
186 return false;
187}
188
189static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
190{
191 WARN_ON_ONCE(!irqs_disabled());
192
193 if (unlikely(!cpu_online(cpu)))
194 return false;
195
196 if (check_tick_dependency(&tick_dep_mask))
197 return false;
198
199 if (check_tick_dependency(&ts->tick_dep_mask))
200 return false;
201
202 if (check_tick_dependency(¤t->tick_dep_mask))
203 return false;
204
205 if (check_tick_dependency(¤t->signal->tick_dep_mask))
206 return false;
207
208 return true;
209}
210
211static void nohz_full_kick_func(struct irq_work *work)
212{
213 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
214}
215
216static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
217 .func = nohz_full_kick_func,
218};
219
220/*
221 * Kick this CPU if it's full dynticks in order to force it to
222 * re-evaluate its dependency on the tick and restart it if necessary.
223 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
224 * is NMI safe.
225 */
226static void tick_nohz_full_kick(void)
227{
228 if (!tick_nohz_full_cpu(smp_processor_id()))
229 return;
230
231 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
232}
233
234/*
235 * Kick the CPU if it's full dynticks in order to force it to
236 * re-evaluate its dependency on the tick and restart it if necessary.
237 */
238void tick_nohz_full_kick_cpu(int cpu)
239{
240 if (!tick_nohz_full_cpu(cpu))
241 return;
242
243 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
244}
245
246/*
247 * Kick all full dynticks CPUs in order to force these to re-evaluate
248 * their dependency on the tick and restart it if necessary.
249 */
250static void tick_nohz_full_kick_all(void)
251{
252 int cpu;
253
254 if (!tick_nohz_full_running)
255 return;
256
257 preempt_disable();
258 for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
259 tick_nohz_full_kick_cpu(cpu);
260 preempt_enable();
261}
262
263static void tick_nohz_dep_set_all(atomic_t *dep,
264 enum tick_dep_bits bit)
265{
266 int prev;
267
268 prev = atomic_fetch_or(BIT(bit), dep);
269 if (!prev)
270 tick_nohz_full_kick_all();
271}
272
273/*
274 * Set a global tick dependency. Used by perf events that rely on freq and
275 * by unstable clock.
276 */
277void tick_nohz_dep_set(enum tick_dep_bits bit)
278{
279 tick_nohz_dep_set_all(&tick_dep_mask, bit);
280}
281
282void tick_nohz_dep_clear(enum tick_dep_bits bit)
283{
284 atomic_andnot(BIT(bit), &tick_dep_mask);
285}
286
287/*
288 * Set per-CPU tick dependency. Used by scheduler and perf events in order to
289 * manage events throttling.
290 */
291void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
292{
293 int prev;
294 struct tick_sched *ts;
295
296 ts = per_cpu_ptr(&tick_cpu_sched, cpu);
297
298 prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
299 if (!prev) {
300 preempt_disable();
301 /* Perf needs local kick that is NMI safe */
302 if (cpu == smp_processor_id()) {
303 tick_nohz_full_kick();
304 } else {
305 /* Remote irq work not NMI-safe */
306 if (!WARN_ON_ONCE(in_nmi()))
307 tick_nohz_full_kick_cpu(cpu);
308 }
309 preempt_enable();
310 }
311}
312
313void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
314{
315 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
316
317 atomic_andnot(BIT(bit), &ts->tick_dep_mask);
318}
319
320/*
321 * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
322 * per task timers.
323 */
324void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
325{
326 /*
327 * We could optimize this with just kicking the target running the task
328 * if that noise matters for nohz full users.
329 */
330 tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
331}
332
333void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
334{
335 atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
336}
337
338/*
339 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
340 * per process timers.
341 */
342void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
343{
344 tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
345}
346
347void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
348{
349 atomic_andnot(BIT(bit), &sig->tick_dep_mask);
350}
351
352/*
353 * Re-evaluate the need for the tick as we switch the current task.
354 * It might need the tick due to per task/process properties:
355 * perf events, posix CPU timers, ...
356 */
357void __tick_nohz_task_switch(void)
358{
359 unsigned long flags;
360 struct tick_sched *ts;
361
362 local_irq_save(flags);
363
364 if (!tick_nohz_full_cpu(smp_processor_id()))
365 goto out;
366
367 ts = this_cpu_ptr(&tick_cpu_sched);
368
369 if (ts->tick_stopped) {
370 if (atomic_read(¤t->tick_dep_mask) ||
371 atomic_read(¤t->signal->tick_dep_mask))
372 tick_nohz_full_kick();
373 }
374out:
375 local_irq_restore(flags);
376}
377
378/* Parse the boot-time nohz CPU list from the kernel parameters. */
379static int __init tick_nohz_full_setup(char *str)
380{
381 alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
382 if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
383 pr_warn("NO_HZ: Incorrect nohz_full cpumask\n");
384 free_bootmem_cpumask_var(tick_nohz_full_mask);
385 return 1;
386 }
387 tick_nohz_full_running = true;
388
389 return 1;
390}
391__setup("nohz_full=", tick_nohz_full_setup);
392
393static int tick_nohz_cpu_down(unsigned int cpu)
394{
395 /*
396 * The boot CPU handles housekeeping duty (unbound timers,
397 * workqueues, timekeeping, ...) on behalf of full dynticks
398 * CPUs. It must remain online when nohz full is enabled.
399 */
400 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
401 return -EBUSY;
402 return 0;
403}
404
405static int tick_nohz_init_all(void)
406{
407 int err = -1;
408
409#ifdef CONFIG_NO_HZ_FULL_ALL
410 if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
411 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
412 return err;
413 }
414 err = 0;
415 cpumask_setall(tick_nohz_full_mask);
416 tick_nohz_full_running = true;
417#endif
418 return err;
419}
420
421void __init tick_nohz_init(void)
422{
423 int cpu, ret;
424
425 if (!tick_nohz_full_running) {
426 if (tick_nohz_init_all() < 0)
427 return;
428 }
429
430 if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
431 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
432 cpumask_clear(tick_nohz_full_mask);
433 tick_nohz_full_running = false;
434 return;
435 }
436
437 /*
438 * Full dynticks uses irq work to drive the tick rescheduling on safe
439 * locking contexts. But then we need irq work to raise its own
440 * interrupts to avoid circular dependency on the tick
441 */
442 if (!arch_irq_work_has_interrupt()) {
443 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
444 cpumask_clear(tick_nohz_full_mask);
445 cpumask_copy(housekeeping_mask, cpu_possible_mask);
446 tick_nohz_full_running = false;
447 return;
448 }
449
450 cpu = smp_processor_id();
451
452 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
453 pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
454 cpu);
455 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
456 }
457
458 cpumask_andnot(housekeeping_mask,
459 cpu_possible_mask, tick_nohz_full_mask);
460
461 for_each_cpu(cpu, tick_nohz_full_mask)
462 context_tracking_cpu_set(cpu);
463
464 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
465 "kernel/nohz:predown", NULL,
466 tick_nohz_cpu_down);
467 WARN_ON(ret < 0);
468 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
469 cpumask_pr_args(tick_nohz_full_mask));
470
471 /*
472 * We need at least one CPU to handle housekeeping work such
473 * as timekeeping, unbound timers, workqueues, ...
474 */
475 WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
476}
477#endif
478
479/*
480 * NOHZ - aka dynamic tick functionality
481 */
482#ifdef CONFIG_NO_HZ_COMMON
483/*
484 * NO HZ enabled ?
485 */
486bool tick_nohz_enabled __read_mostly = true;
487unsigned long tick_nohz_active __read_mostly;
488/*
489 * Enable / Disable tickless mode
490 */
491static int __init setup_tick_nohz(char *str)
492{
493 return (kstrtobool(str, &tick_nohz_enabled) == 0);
494}
495
496__setup("nohz=", setup_tick_nohz);
497
498int tick_nohz_tick_stopped(void)
499{
500 return __this_cpu_read(tick_cpu_sched.tick_stopped);
501}
502
503/**
504 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
505 *
506 * Called from interrupt entry when the CPU was idle
507 *
508 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
509 * must be updated. Otherwise an interrupt handler could use a stale jiffy
510 * value. We do this unconditionally on any CPU, as we don't know whether the
511 * CPU, which has the update task assigned is in a long sleep.
512 */
513static void tick_nohz_update_jiffies(ktime_t now)
514{
515 unsigned long flags;
516
517 __this_cpu_write(tick_cpu_sched.idle_waketime, now);
518
519 local_irq_save(flags);
520 tick_do_update_jiffies64(now);
521 local_irq_restore(flags);
522
523 touch_softlockup_watchdog_sched();
524}
525
526/*
527 * Updates the per-CPU time idle statistics counters
528 */
529static void
530update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
531{
532 ktime_t delta;
533
534 if (ts->idle_active) {
535 delta = ktime_sub(now, ts->idle_entrytime);
536 if (nr_iowait_cpu(cpu) > 0)
537 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
538 else
539 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
540 ts->idle_entrytime = now;
541 }
542
543 if (last_update_time)
544 *last_update_time = ktime_to_us(now);
545
546}
547
548static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
549{
550 update_ts_time_stats(smp_processor_id(), ts, now, NULL);
551 ts->idle_active = 0;
552
553 sched_clock_idle_wakeup_event(0);
554}
555
556static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
557{
558 ktime_t now = ktime_get();
559
560 ts->idle_entrytime = now;
561 ts->idle_active = 1;
562 sched_clock_idle_sleep_event();
563 return now;
564}
565
566/**
567 * get_cpu_idle_time_us - get the total idle time of a CPU
568 * @cpu: CPU number to query
569 * @last_update_time: variable to store update time in. Do not update
570 * counters if NULL.
571 *
572 * Return the cumulative idle time (since boot) for a given
573 * CPU, in microseconds.
574 *
575 * This time is measured via accounting rather than sampling,
576 * and is as accurate as ktime_get() is.
577 *
578 * This function returns -1 if NOHZ is not enabled.
579 */
580u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
581{
582 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
583 ktime_t now, idle;
584
585 if (!tick_nohz_active)
586 return -1;
587
588 now = ktime_get();
589 if (last_update_time) {
590 update_ts_time_stats(cpu, ts, now, last_update_time);
591 idle = ts->idle_sleeptime;
592 } else {
593 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
594 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
595
596 idle = ktime_add(ts->idle_sleeptime, delta);
597 } else {
598 idle = ts->idle_sleeptime;
599 }
600 }
601
602 return ktime_to_us(idle);
603
604}
605EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
606
607/**
608 * get_cpu_iowait_time_us - get the total iowait time of a CPU
609 * @cpu: CPU number to query
610 * @last_update_time: variable to store update time in. Do not update
611 * counters if NULL.
612 *
613 * Return the cumulative iowait time (since boot) for a given
614 * CPU, in microseconds.
615 *
616 * This time is measured via accounting rather than sampling,
617 * and is as accurate as ktime_get() is.
618 *
619 * This function returns -1 if NOHZ is not enabled.
620 */
621u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
622{
623 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
624 ktime_t now, iowait;
625
626 if (!tick_nohz_active)
627 return -1;
628
629 now = ktime_get();
630 if (last_update_time) {
631 update_ts_time_stats(cpu, ts, now, last_update_time);
632 iowait = ts->iowait_sleeptime;
633 } else {
634 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
635 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
636
637 iowait = ktime_add(ts->iowait_sleeptime, delta);
638 } else {
639 iowait = ts->iowait_sleeptime;
640 }
641 }
642
643 return ktime_to_us(iowait);
644}
645EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
646
647static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
648{
649 hrtimer_cancel(&ts->sched_timer);
650 hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
651
652 /* Forward the time to expire in the future */
653 hrtimer_forward(&ts->sched_timer, now, tick_period);
654
655 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
656 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
657 else
658 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
659}
660
661static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
662 ktime_t now, int cpu)
663{
664 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
665 u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
666 unsigned long seq, basejiff;
667 ktime_t tick;
668
669 /* Read jiffies and the time when jiffies were updated last */
670 do {
671 seq = read_seqbegin(&jiffies_lock);
672 basemono = last_jiffies_update;
673 basejiff = jiffies;
674 } while (read_seqretry(&jiffies_lock, seq));
675 ts->last_jiffies = basejiff;
676
677 if (rcu_needs_cpu(basemono, &next_rcu) ||
678 arch_needs_cpu() || irq_work_needs_cpu()) {
679 next_tick = basemono + TICK_NSEC;
680 } else {
681 /*
682 * Get the next pending timer. If high resolution
683 * timers are enabled this only takes the timer wheel
684 * timers into account. If high resolution timers are
685 * disabled this also looks at the next expiring
686 * hrtimer.
687 */
688 next_tmr = get_next_timer_interrupt(basejiff, basemono);
689 ts->next_timer = next_tmr;
690 /* Take the next rcu event into account */
691 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
692 }
693
694 /*
695 * If the tick is due in the next period, keep it ticking or
696 * force prod the timer.
697 */
698 delta = next_tick - basemono;
699 if (delta <= (u64)TICK_NSEC) {
700 tick = 0;
701
702 /*
703 * Tell the timer code that the base is not idle, i.e. undo
704 * the effect of get_next_timer_interrupt():
705 */
706 timer_clear_idle();
707 /*
708 * We've not stopped the tick yet, and there's a timer in the
709 * next period, so no point in stopping it either, bail.
710 */
711 if (!ts->tick_stopped)
712 goto out;
713
714 /*
715 * If, OTOH, we did stop it, but there's a pending (expired)
716 * timer reprogram the timer hardware to fire now.
717 *
718 * We will not restart the tick proper, just prod the timer
719 * hardware into firing an interrupt to process the pending
720 * timers. Just like tick_irq_exit() will not restart the tick
721 * for 'normal' interrupts.
722 *
723 * Only once we exit the idle loop will we re-enable the tick,
724 * see tick_nohz_idle_exit().
725 */
726 if (delta == 0) {
727 tick_nohz_restart(ts, now);
728 goto out;
729 }
730 }
731
732 /*
733 * If this CPU is the one which updates jiffies, then give up
734 * the assignment and let it be taken by the CPU which runs
735 * the tick timer next, which might be this CPU as well. If we
736 * don't drop this here the jiffies might be stale and
737 * do_timer() never invoked. Keep track of the fact that it
738 * was the one which had the do_timer() duty last. If this CPU
739 * is the one which had the do_timer() duty last, we limit the
740 * sleep time to the timekeeping max_deferment value.
741 * Otherwise we can sleep as long as we want.
742 */
743 delta = timekeeping_max_deferment();
744 if (cpu == tick_do_timer_cpu) {
745 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
746 ts->do_timer_last = 1;
747 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
748 delta = KTIME_MAX;
749 ts->do_timer_last = 0;
750 } else if (!ts->do_timer_last) {
751 delta = KTIME_MAX;
752 }
753
754#ifdef CONFIG_NO_HZ_FULL
755 /* Limit the tick delta to the maximum scheduler deferment */
756 if (!ts->inidle)
757 delta = min(delta, scheduler_tick_max_deferment());
758#endif
759
760 /* Calculate the next expiry time */
761 if (delta < (KTIME_MAX - basemono))
762 expires = basemono + delta;
763 else
764 expires = KTIME_MAX;
765
766 expires = min_t(u64, expires, next_tick);
767 tick = expires;
768
769 /* Skip reprogram of event if its not changed */
770 if (ts->tick_stopped && (expires == dev->next_event))
771 goto out;
772
773 /*
774 * nohz_stop_sched_tick can be called several times before
775 * the nohz_restart_sched_tick is called. This happens when
776 * interrupts arrive which do not cause a reschedule. In the
777 * first call we save the current tick time, so we can restart
778 * the scheduler tick in nohz_restart_sched_tick.
779 */
780 if (!ts->tick_stopped) {
781 nohz_balance_enter_idle(cpu);
782 calc_load_enter_idle();
783 cpu_load_update_nohz_start();
784
785 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
786 ts->tick_stopped = 1;
787 trace_tick_stop(1, TICK_DEP_MASK_NONE);
788 }
789
790 /*
791 * If the expiration time == KTIME_MAX, then we simply stop
792 * the tick timer.
793 */
794 if (unlikely(expires == KTIME_MAX)) {
795 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
796 hrtimer_cancel(&ts->sched_timer);
797 goto out;
798 }
799
800 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
801 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
802 else
803 tick_program_event(tick, 1);
804out:
805 /* Update the estimated sleep length */
806 ts->sleep_length = ktime_sub(dev->next_event, now);
807 return tick;
808}
809
810static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
811{
812 /* Update jiffies first */
813 tick_do_update_jiffies64(now);
814 cpu_load_update_nohz_stop();
815
816 /*
817 * Clear the timer idle flag, so we avoid IPIs on remote queueing and
818 * the clock forward checks in the enqueue path:
819 */
820 timer_clear_idle();
821
822 calc_load_exit_idle();
823 touch_softlockup_watchdog_sched();
824 /*
825 * Cancel the scheduled timer and restore the tick
826 */
827 ts->tick_stopped = 0;
828 ts->idle_exittime = now;
829
830 tick_nohz_restart(ts, now);
831}
832
833static void tick_nohz_full_update_tick(struct tick_sched *ts)
834{
835#ifdef CONFIG_NO_HZ_FULL
836 int cpu = smp_processor_id();
837
838 if (!tick_nohz_full_cpu(cpu))
839 return;
840
841 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
842 return;
843
844 if (can_stop_full_tick(cpu, ts))
845 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
846 else if (ts->tick_stopped)
847 tick_nohz_restart_sched_tick(ts, ktime_get());
848#endif
849}
850
851static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
852{
853 /*
854 * If this CPU is offline and it is the one which updates
855 * jiffies, then give up the assignment and let it be taken by
856 * the CPU which runs the tick timer next. If we don't drop
857 * this here the jiffies might be stale and do_timer() never
858 * invoked.
859 */
860 if (unlikely(!cpu_online(cpu))) {
861 if (cpu == tick_do_timer_cpu)
862 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
863 return false;
864 }
865
866 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
867 ts->sleep_length = NSEC_PER_SEC / HZ;
868 return false;
869 }
870
871 if (need_resched())
872 return false;
873
874 if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
875 static int ratelimit;
876
877 if (ratelimit < 10 &&
878 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
879 pr_warn("NOHZ: local_softirq_pending %02x\n",
880 (unsigned int) local_softirq_pending());
881 ratelimit++;
882 }
883 return false;
884 }
885
886 if (tick_nohz_full_enabled()) {
887 /*
888 * Keep the tick alive to guarantee timekeeping progression
889 * if there are full dynticks CPUs around
890 */
891 if (tick_do_timer_cpu == cpu)
892 return false;
893 /*
894 * Boot safety: make sure the timekeeping duty has been
895 * assigned before entering dyntick-idle mode,
896 */
897 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
898 return false;
899 }
900
901 return true;
902}
903
904static void __tick_nohz_idle_enter(struct tick_sched *ts)
905{
906 ktime_t now, expires;
907 int cpu = smp_processor_id();
908
909 now = tick_nohz_start_idle(ts);
910
911 if (can_stop_idle_tick(cpu, ts)) {
912 int was_stopped = ts->tick_stopped;
913
914 ts->idle_calls++;
915
916 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
917 if (expires > 0LL) {
918 ts->idle_sleeps++;
919 ts->idle_expires = expires;
920 }
921
922 if (!was_stopped && ts->tick_stopped)
923 ts->idle_jiffies = ts->last_jiffies;
924 }
925}
926
927/**
928 * tick_nohz_idle_enter - stop the idle tick from the idle task
929 *
930 * When the next event is more than a tick into the future, stop the idle tick
931 * Called when we start the idle loop.
932 *
933 * The arch is responsible of calling:
934 *
935 * - rcu_idle_enter() after its last use of RCU before the CPU is put
936 * to sleep.
937 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
938 */
939void tick_nohz_idle_enter(void)
940{
941 struct tick_sched *ts;
942
943 WARN_ON_ONCE(irqs_disabled());
944
945 /*
946 * Update the idle state in the scheduler domain hierarchy
947 * when tick_nohz_stop_sched_tick() is called from the idle loop.
948 * State will be updated to busy during the first busy tick after
949 * exiting idle.
950 */
951 set_cpu_sd_state_idle();
952
953 local_irq_disable();
954
955 ts = this_cpu_ptr(&tick_cpu_sched);
956 ts->inidle = 1;
957 __tick_nohz_idle_enter(ts);
958
959 local_irq_enable();
960}
961
962/**
963 * tick_nohz_irq_exit - update next tick event from interrupt exit
964 *
965 * When an interrupt fires while we are idle and it doesn't cause
966 * a reschedule, it may still add, modify or delete a timer, enqueue
967 * an RCU callback, etc...
968 * So we need to re-calculate and reprogram the next tick event.
969 */
970void tick_nohz_irq_exit(void)
971{
972 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
973
974 if (ts->inidle)
975 __tick_nohz_idle_enter(ts);
976 else
977 tick_nohz_full_update_tick(ts);
978}
979
980/**
981 * tick_nohz_get_sleep_length - return the length of the current sleep
982 *
983 * Called from power state control code with interrupts disabled
984 */
985ktime_t tick_nohz_get_sleep_length(void)
986{
987 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
988
989 return ts->sleep_length;
990}
991
992static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
993{
994#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
995 unsigned long ticks;
996
997 if (vtime_accounting_cpu_enabled())
998 return;
999 /*
1000 * We stopped the tick in idle. Update process times would miss the
1001 * time we slept as update_process_times does only a 1 tick
1002 * accounting. Enforce that this is accounted to idle !
1003 */
1004 ticks = jiffies - ts->idle_jiffies;
1005 /*
1006 * We might be one off. Do not randomly account a huge number of ticks!
1007 */
1008 if (ticks && ticks < LONG_MAX)
1009 account_idle_ticks(ticks);
1010#endif
1011}
1012
1013/**
1014 * tick_nohz_idle_exit - restart the idle tick from the idle task
1015 *
1016 * Restart the idle tick when the CPU is woken up from idle
1017 * This also exit the RCU extended quiescent state. The CPU
1018 * can use RCU again after this function is called.
1019 */
1020void tick_nohz_idle_exit(void)
1021{
1022 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1023 ktime_t now;
1024
1025 local_irq_disable();
1026
1027 WARN_ON_ONCE(!ts->inidle);
1028
1029 ts->inidle = 0;
1030
1031 if (ts->idle_active || ts->tick_stopped)
1032 now = ktime_get();
1033
1034 if (ts->idle_active)
1035 tick_nohz_stop_idle(ts, now);
1036
1037 if (ts->tick_stopped) {
1038 tick_nohz_restart_sched_tick(ts, now);
1039 tick_nohz_account_idle_ticks(ts);
1040 }
1041
1042 local_irq_enable();
1043}
1044
1045/*
1046 * The nohz low res interrupt handler
1047 */
1048static void tick_nohz_handler(struct clock_event_device *dev)
1049{
1050 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1051 struct pt_regs *regs = get_irq_regs();
1052 ktime_t now = ktime_get();
1053
1054 dev->next_event = KTIME_MAX;
1055
1056 tick_sched_do_timer(now);
1057 tick_sched_handle(ts, regs);
1058
1059 /* No need to reprogram if we are running tickless */
1060 if (unlikely(ts->tick_stopped))
1061 return;
1062
1063 hrtimer_forward(&ts->sched_timer, now, tick_period);
1064 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1065}
1066
1067static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1068{
1069 if (!tick_nohz_enabled)
1070 return;
1071 ts->nohz_mode = mode;
1072 /* One update is enough */
1073 if (!test_and_set_bit(0, &tick_nohz_active))
1074 timers_update_migration(true);
1075}
1076
1077/**
1078 * tick_nohz_switch_to_nohz - switch to nohz mode
1079 */
1080static void tick_nohz_switch_to_nohz(void)
1081{
1082 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1083 ktime_t next;
1084
1085 if (!tick_nohz_enabled)
1086 return;
1087
1088 if (tick_switch_to_oneshot(tick_nohz_handler))
1089 return;
1090
1091 /*
1092 * Recycle the hrtimer in ts, so we can share the
1093 * hrtimer_forward with the highres code.
1094 */
1095 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1096 /* Get the next period */
1097 next = tick_init_jiffy_update();
1098
1099 hrtimer_set_expires(&ts->sched_timer, next);
1100 hrtimer_forward_now(&ts->sched_timer, tick_period);
1101 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1102 tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1103}
1104
1105static inline void tick_nohz_irq_enter(void)
1106{
1107 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1108 ktime_t now;
1109
1110 if (!ts->idle_active && !ts->tick_stopped)
1111 return;
1112 now = ktime_get();
1113 if (ts->idle_active)
1114 tick_nohz_stop_idle(ts, now);
1115 if (ts->tick_stopped)
1116 tick_nohz_update_jiffies(now);
1117}
1118
1119#else
1120
1121static inline void tick_nohz_switch_to_nohz(void) { }
1122static inline void tick_nohz_irq_enter(void) { }
1123static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1124
1125#endif /* CONFIG_NO_HZ_COMMON */
1126
1127/*
1128 * Called from irq_enter to notify about the possible interruption of idle()
1129 */
1130void tick_irq_enter(void)
1131{
1132 tick_check_oneshot_broadcast_this_cpu();
1133 tick_nohz_irq_enter();
1134}
1135
1136/*
1137 * High resolution timer specific code
1138 */
1139#ifdef CONFIG_HIGH_RES_TIMERS
1140/*
1141 * We rearm the timer until we get disabled by the idle code.
1142 * Called with interrupts disabled.
1143 */
1144static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1145{
1146 struct tick_sched *ts =
1147 container_of(timer, struct tick_sched, sched_timer);
1148 struct pt_regs *regs = get_irq_regs();
1149 ktime_t now = ktime_get();
1150
1151 tick_sched_do_timer(now);
1152
1153 /*
1154 * Do not call, when we are not in irq context and have
1155 * no valid regs pointer
1156 */
1157 if (regs)
1158 tick_sched_handle(ts, regs);
1159
1160 /* No need to reprogram if we are in idle or full dynticks mode */
1161 if (unlikely(ts->tick_stopped))
1162 return HRTIMER_NORESTART;
1163
1164 hrtimer_forward(timer, now, tick_period);
1165
1166 return HRTIMER_RESTART;
1167}
1168
1169static int sched_skew_tick;
1170
1171static int __init skew_tick(char *str)
1172{
1173 get_option(&str, &sched_skew_tick);
1174
1175 return 0;
1176}
1177early_param("skew_tick", skew_tick);
1178
1179/**
1180 * tick_setup_sched_timer - setup the tick emulation timer
1181 */
1182void tick_setup_sched_timer(void)
1183{
1184 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1185 ktime_t now = ktime_get();
1186
1187 /*
1188 * Emulate tick processing via per-CPU hrtimers:
1189 */
1190 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1191 ts->sched_timer.function = tick_sched_timer;
1192
1193 /* Get the next period (per-CPU) */
1194 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1195
1196 /* Offset the tick to avert jiffies_lock contention. */
1197 if (sched_skew_tick) {
1198 u64 offset = ktime_to_ns(tick_period) >> 1;
1199 do_div(offset, num_possible_cpus());
1200 offset *= smp_processor_id();
1201 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1202 }
1203
1204 hrtimer_forward(&ts->sched_timer, now, tick_period);
1205 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1206 tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1207}
1208#endif /* HIGH_RES_TIMERS */
1209
1210#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1211void tick_cancel_sched_timer(int cpu)
1212{
1213 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1214
1215# ifdef CONFIG_HIGH_RES_TIMERS
1216 if (ts->sched_timer.base)
1217 hrtimer_cancel(&ts->sched_timer);
1218# endif
1219
1220 memset(ts, 0, sizeof(*ts));
1221}
1222#endif
1223
1224/**
1225 * Async notification about clocksource changes
1226 */
1227void tick_clock_notify(void)
1228{
1229 int cpu;
1230
1231 for_each_possible_cpu(cpu)
1232 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1233}
1234
1235/*
1236 * Async notification about clock event changes
1237 */
1238void tick_oneshot_notify(void)
1239{
1240 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1241
1242 set_bit(0, &ts->check_clocks);
1243}
1244
1245/**
1246 * Check, if a change happened, which makes oneshot possible.
1247 *
1248 * Called cyclic from the hrtimer softirq (driven by the timer
1249 * softirq) allow_nohz signals, that we can switch into low-res nohz
1250 * mode, because high resolution timers are disabled (either compile
1251 * or runtime). Called with interrupts disabled.
1252 */
1253int tick_check_oneshot_change(int allow_nohz)
1254{
1255 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1256
1257 if (!test_and_clear_bit(0, &ts->check_clocks))
1258 return 0;
1259
1260 if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1261 return 0;
1262
1263 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1264 return 0;
1265
1266 if (!allow_nohz)
1267 return 1;
1268
1269 tick_nohz_switch_to_nohz();
1270 return 0;
1271}