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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/perf_event.h>
26#include <linux/context_tracking.h>
27
28#include <asm/irq_regs.h>
29
30#include "tick-internal.h"
31
32#include <trace/events/timer.h>
33
34/*
35 * Per cpu nohz control structure
36 */
37DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
38
39/*
40 * The time, when the last jiffy update happened. Protected by jiffies_lock.
41 */
42static ktime_t last_jiffies_update;
43
44struct tick_sched *tick_get_tick_sched(int cpu)
45{
46 return &per_cpu(tick_cpu_sched, cpu);
47}
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();
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
155#ifdef CONFIG_NO_HZ_FULL
156cpumask_var_t tick_nohz_full_mask;
157bool tick_nohz_full_running;
158
159static bool can_stop_full_tick(void)
160{
161 WARN_ON_ONCE(!irqs_disabled());
162
163 if (!sched_can_stop_tick()) {
164 trace_tick_stop(0, "more than 1 task in runqueue\n");
165 return false;
166 }
167
168 if (!posix_cpu_timers_can_stop_tick(current)) {
169 trace_tick_stop(0, "posix timers running\n");
170 return false;
171 }
172
173 if (!perf_event_can_stop_tick()) {
174 trace_tick_stop(0, "perf events running\n");
175 return false;
176 }
177
178 /* sched_clock_tick() needs us? */
179#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
180 /*
181 * TODO: kick full dynticks CPUs when
182 * sched_clock_stable is set.
183 */
184 if (!sched_clock_stable()) {
185 trace_tick_stop(0, "unstable sched clock\n");
186 /*
187 * Don't allow the user to think they can get
188 * full NO_HZ with this machine.
189 */
190 WARN_ONCE(tick_nohz_full_running,
191 "NO_HZ FULL will not work with unstable sched clock");
192 return false;
193 }
194#endif
195
196 return true;
197}
198
199static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
200
201/*
202 * Re-evaluate the need for the tick on the current CPU
203 * and restart it if necessary.
204 */
205void __tick_nohz_full_check(void)
206{
207 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
208
209 if (tick_nohz_full_cpu(smp_processor_id())) {
210 if (ts->tick_stopped && !is_idle_task(current)) {
211 if (!can_stop_full_tick())
212 tick_nohz_restart_sched_tick(ts, ktime_get());
213 }
214 }
215}
216
217static void nohz_full_kick_work_func(struct irq_work *work)
218{
219 __tick_nohz_full_check();
220}
221
222static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
223 .func = nohz_full_kick_work_func,
224};
225
226/*
227 * Kick the current CPU if it's full dynticks in order to force it to
228 * re-evaluate its dependency on the tick and restart it if necessary.
229 */
230void tick_nohz_full_kick(void)
231{
232 if (tick_nohz_full_cpu(smp_processor_id()))
233 irq_work_queue(&__get_cpu_var(nohz_full_kick_work));
234}
235
236static void nohz_full_kick_ipi(void *info)
237{
238 __tick_nohz_full_check();
239}
240
241/*
242 * Kick all full dynticks CPUs in order to force these to re-evaluate
243 * their dependency on the tick and restart it if necessary.
244 */
245void tick_nohz_full_kick_all(void)
246{
247 if (!tick_nohz_full_running)
248 return;
249
250 preempt_disable();
251 smp_call_function_many(tick_nohz_full_mask,
252 nohz_full_kick_ipi, NULL, false);
253 tick_nohz_full_kick();
254 preempt_enable();
255}
256
257/*
258 * Re-evaluate the need for the tick as we switch the current task.
259 * It might need the tick due to per task/process properties:
260 * perf events, posix cpu timers, ...
261 */
262void __tick_nohz_task_switch(struct task_struct *tsk)
263{
264 unsigned long flags;
265
266 local_irq_save(flags);
267
268 if (!tick_nohz_full_cpu(smp_processor_id()))
269 goto out;
270
271 if (tick_nohz_tick_stopped() && !can_stop_full_tick())
272 tick_nohz_full_kick();
273
274out:
275 local_irq_restore(flags);
276}
277
278/* Parse the boot-time nohz CPU list from the kernel parameters. */
279static int __init tick_nohz_full_setup(char *str)
280{
281 int cpu;
282
283 alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
284 if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
285 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
286 return 1;
287 }
288
289 cpu = smp_processor_id();
290 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
291 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
292 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
293 }
294 tick_nohz_full_running = true;
295
296 return 1;
297}
298__setup("nohz_full=", tick_nohz_full_setup);
299
300static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
301 unsigned long action,
302 void *hcpu)
303{
304 unsigned int cpu = (unsigned long)hcpu;
305
306 switch (action & ~CPU_TASKS_FROZEN) {
307 case CPU_DOWN_PREPARE:
308 /*
309 * If we handle the timekeeping duty for full dynticks CPUs,
310 * we can't safely shutdown that CPU.
311 */
312 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
313 return NOTIFY_BAD;
314 break;
315 }
316 return NOTIFY_OK;
317}
318
319/*
320 * Worst case string length in chunks of CPU range seems 2 steps
321 * separations: 0,2,4,6,...
322 * This is NR_CPUS + sizeof('\0')
323 */
324static char __initdata nohz_full_buf[NR_CPUS + 1];
325
326static int tick_nohz_init_all(void)
327{
328 int err = -1;
329
330#ifdef CONFIG_NO_HZ_FULL_ALL
331 if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
332 pr_err("NO_HZ: Can't allocate full dynticks cpumask\n");
333 return err;
334 }
335 err = 0;
336 cpumask_setall(tick_nohz_full_mask);
337 cpumask_clear_cpu(smp_processor_id(), tick_nohz_full_mask);
338 tick_nohz_full_running = true;
339#endif
340 return err;
341}
342
343void __init tick_nohz_init(void)
344{
345 int cpu;
346
347 if (!tick_nohz_full_running) {
348 if (tick_nohz_init_all() < 0)
349 return;
350 }
351
352 for_each_cpu(cpu, tick_nohz_full_mask)
353 context_tracking_cpu_set(cpu);
354
355 cpu_notifier(tick_nohz_cpu_down_callback, 0);
356 cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), tick_nohz_full_mask);
357 pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
358}
359#endif
360
361/*
362 * NOHZ - aka dynamic tick functionality
363 */
364#ifdef CONFIG_NO_HZ_COMMON
365/*
366 * NO HZ enabled ?
367 */
368static int tick_nohz_enabled __read_mostly = 1;
369int tick_nohz_active __read_mostly;
370/*
371 * Enable / Disable tickless mode
372 */
373static int __init setup_tick_nohz(char *str)
374{
375 if (!strcmp(str, "off"))
376 tick_nohz_enabled = 0;
377 else if (!strcmp(str, "on"))
378 tick_nohz_enabled = 1;
379 else
380 return 0;
381 return 1;
382}
383
384__setup("nohz=", setup_tick_nohz);
385
386/**
387 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
388 *
389 * Called from interrupt entry when the CPU was idle
390 *
391 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
392 * must be updated. Otherwise an interrupt handler could use a stale jiffy
393 * value. We do this unconditionally on any cpu, as we don't know whether the
394 * cpu, which has the update task assigned is in a long sleep.
395 */
396static void tick_nohz_update_jiffies(ktime_t now)
397{
398 unsigned long flags;
399
400 __this_cpu_write(tick_cpu_sched.idle_waketime, now);
401
402 local_irq_save(flags);
403 tick_do_update_jiffies64(now);
404 local_irq_restore(flags);
405
406 touch_softlockup_watchdog();
407}
408
409/*
410 * Updates the per cpu time idle statistics counters
411 */
412static void
413update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
414{
415 ktime_t delta;
416
417 if (ts->idle_active) {
418 delta = ktime_sub(now, ts->idle_entrytime);
419 if (nr_iowait_cpu(cpu) > 0)
420 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
421 else
422 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
423 ts->idle_entrytime = now;
424 }
425
426 if (last_update_time)
427 *last_update_time = ktime_to_us(now);
428
429}
430
431static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
432{
433 update_ts_time_stats(smp_processor_id(), ts, now, NULL);
434 ts->idle_active = 0;
435
436 sched_clock_idle_wakeup_event(0);
437}
438
439static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
440{
441 ktime_t now = ktime_get();
442
443 ts->idle_entrytime = now;
444 ts->idle_active = 1;
445 sched_clock_idle_sleep_event();
446 return now;
447}
448
449/**
450 * get_cpu_idle_time_us - get the total idle time of a cpu
451 * @cpu: CPU number to query
452 * @last_update_time: variable to store update time in. Do not update
453 * counters if NULL.
454 *
455 * Return the cummulative idle time (since boot) for a given
456 * CPU, in microseconds.
457 *
458 * This time is measured via accounting rather than sampling,
459 * and is as accurate as ktime_get() is.
460 *
461 * This function returns -1 if NOHZ is not enabled.
462 */
463u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
464{
465 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
466 ktime_t now, idle;
467
468 if (!tick_nohz_active)
469 return -1;
470
471 now = ktime_get();
472 if (last_update_time) {
473 update_ts_time_stats(cpu, ts, now, last_update_time);
474 idle = ts->idle_sleeptime;
475 } else {
476 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
477 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
478
479 idle = ktime_add(ts->idle_sleeptime, delta);
480 } else {
481 idle = ts->idle_sleeptime;
482 }
483 }
484
485 return ktime_to_us(idle);
486
487}
488EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
489
490/**
491 * get_cpu_iowait_time_us - get the total iowait time of a cpu
492 * @cpu: CPU number to query
493 * @last_update_time: variable to store update time in. Do not update
494 * counters if NULL.
495 *
496 * Return the cummulative iowait time (since boot) for a given
497 * CPU, in microseconds.
498 *
499 * This time is measured via accounting rather than sampling,
500 * and is as accurate as ktime_get() is.
501 *
502 * This function returns -1 if NOHZ is not enabled.
503 */
504u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
505{
506 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
507 ktime_t now, iowait;
508
509 if (!tick_nohz_active)
510 return -1;
511
512 now = ktime_get();
513 if (last_update_time) {
514 update_ts_time_stats(cpu, ts, now, last_update_time);
515 iowait = ts->iowait_sleeptime;
516 } else {
517 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
518 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
519
520 iowait = ktime_add(ts->iowait_sleeptime, delta);
521 } else {
522 iowait = ts->iowait_sleeptime;
523 }
524 }
525
526 return ktime_to_us(iowait);
527}
528EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
529
530static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
531 ktime_t now, int cpu)
532{
533 unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
534 ktime_t last_update, expires, ret = { .tv64 = 0 };
535 unsigned long rcu_delta_jiffies;
536 struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
537 u64 time_delta;
538
539 time_delta = timekeeping_max_deferment();
540
541 /* Read jiffies and the time when jiffies were updated last */
542 do {
543 seq = read_seqbegin(&jiffies_lock);
544 last_update = last_jiffies_update;
545 last_jiffies = jiffies;
546 } while (read_seqretry(&jiffies_lock, seq));
547
548 if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
549 arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
550 next_jiffies = last_jiffies + 1;
551 delta_jiffies = 1;
552 } else {
553 /* Get the next timer wheel timer */
554 next_jiffies = get_next_timer_interrupt(last_jiffies);
555 delta_jiffies = next_jiffies - last_jiffies;
556 if (rcu_delta_jiffies < delta_jiffies) {
557 next_jiffies = last_jiffies + rcu_delta_jiffies;
558 delta_jiffies = rcu_delta_jiffies;
559 }
560 }
561
562 /*
563 * Do not stop the tick, if we are only one off (or less)
564 * or if the cpu is required for RCU:
565 */
566 if (!ts->tick_stopped && delta_jiffies <= 1)
567 goto out;
568
569 /* Schedule the tick, if we are at least one jiffie off */
570 if ((long)delta_jiffies >= 1) {
571
572 /*
573 * If this cpu is the one which updates jiffies, then
574 * give up the assignment and let it be taken by the
575 * cpu which runs the tick timer next, which might be
576 * this cpu as well. If we don't drop this here the
577 * jiffies might be stale and do_timer() never
578 * invoked. Keep track of the fact that it was the one
579 * which had the do_timer() duty last. If this cpu is
580 * the one which had the do_timer() duty last, we
581 * limit the sleep time to the timekeeping
582 * max_deferement value which we retrieved
583 * above. Otherwise we can sleep as long as we want.
584 */
585 if (cpu == tick_do_timer_cpu) {
586 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
587 ts->do_timer_last = 1;
588 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
589 time_delta = KTIME_MAX;
590 ts->do_timer_last = 0;
591 } else if (!ts->do_timer_last) {
592 time_delta = KTIME_MAX;
593 }
594
595#ifdef CONFIG_NO_HZ_FULL
596 if (!ts->inidle) {
597 time_delta = min(time_delta,
598 scheduler_tick_max_deferment());
599 }
600#endif
601
602 /*
603 * calculate the expiry time for the next timer wheel
604 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
605 * that there is no timer pending or at least extremely
606 * far into the future (12 days for HZ=1000). In this
607 * case we set the expiry to the end of time.
608 */
609 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
610 /*
611 * Calculate the time delta for the next timer event.
612 * If the time delta exceeds the maximum time delta
613 * permitted by the current clocksource then adjust
614 * the time delta accordingly to ensure the
615 * clocksource does not wrap.
616 */
617 time_delta = min_t(u64, time_delta,
618 tick_period.tv64 * delta_jiffies);
619 }
620
621 if (time_delta < KTIME_MAX)
622 expires = ktime_add_ns(last_update, time_delta);
623 else
624 expires.tv64 = KTIME_MAX;
625
626 /* Skip reprogram of event if its not changed */
627 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
628 goto out;
629
630 ret = expires;
631
632 /*
633 * nohz_stop_sched_tick can be called several times before
634 * the nohz_restart_sched_tick is called. This happens when
635 * interrupts arrive which do not cause a reschedule. In the
636 * first call we save the current tick time, so we can restart
637 * the scheduler tick in nohz_restart_sched_tick.
638 */
639 if (!ts->tick_stopped) {
640 nohz_balance_enter_idle(cpu);
641 calc_load_enter_idle();
642
643 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
644 ts->tick_stopped = 1;
645 trace_tick_stop(1, " ");
646 }
647
648 /*
649 * If the expiration time == KTIME_MAX, then
650 * in this case we simply stop the tick timer.
651 */
652 if (unlikely(expires.tv64 == KTIME_MAX)) {
653 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
654 hrtimer_cancel(&ts->sched_timer);
655 goto out;
656 }
657
658 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
659 hrtimer_start(&ts->sched_timer, expires,
660 HRTIMER_MODE_ABS_PINNED);
661 /* Check, if the timer was already in the past */
662 if (hrtimer_active(&ts->sched_timer))
663 goto out;
664 } else if (!tick_program_event(expires, 0))
665 goto out;
666 /*
667 * We are past the event already. So we crossed a
668 * jiffie boundary. Update jiffies and raise the
669 * softirq.
670 */
671 tick_do_update_jiffies64(ktime_get());
672 }
673 raise_softirq_irqoff(TIMER_SOFTIRQ);
674out:
675 ts->next_jiffies = next_jiffies;
676 ts->last_jiffies = last_jiffies;
677 ts->sleep_length = ktime_sub(dev->next_event, now);
678
679 return ret;
680}
681
682static void tick_nohz_full_stop_tick(struct tick_sched *ts)
683{
684#ifdef CONFIG_NO_HZ_FULL
685 int cpu = smp_processor_id();
686
687 if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
688 return;
689
690 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
691 return;
692
693 if (!can_stop_full_tick())
694 return;
695
696 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
697#endif
698}
699
700static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
701{
702 /*
703 * If this cpu is offline and it is the one which updates
704 * jiffies, then give up the assignment and let it be taken by
705 * the cpu which runs the tick timer next. If we don't drop
706 * this here the jiffies might be stale and do_timer() never
707 * invoked.
708 */
709 if (unlikely(!cpu_online(cpu))) {
710 if (cpu == tick_do_timer_cpu)
711 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
712 return false;
713 }
714
715 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
716 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
717 return false;
718 }
719
720 if (need_resched())
721 return false;
722
723 if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
724 static int ratelimit;
725
726 if (ratelimit < 10 &&
727 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
728 pr_warn("NOHZ: local_softirq_pending %02x\n",
729 (unsigned int) local_softirq_pending());
730 ratelimit++;
731 }
732 return false;
733 }
734
735 if (tick_nohz_full_enabled()) {
736 /*
737 * Keep the tick alive to guarantee timekeeping progression
738 * if there are full dynticks CPUs around
739 */
740 if (tick_do_timer_cpu == cpu)
741 return false;
742 /*
743 * Boot safety: make sure the timekeeping duty has been
744 * assigned before entering dyntick-idle mode,
745 */
746 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
747 return false;
748 }
749
750 return true;
751}
752
753static void __tick_nohz_idle_enter(struct tick_sched *ts)
754{
755 ktime_t now, expires;
756 int cpu = smp_processor_id();
757
758 now = tick_nohz_start_idle(ts);
759
760 if (can_stop_idle_tick(cpu, ts)) {
761 int was_stopped = ts->tick_stopped;
762
763 ts->idle_calls++;
764
765 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
766 if (expires.tv64 > 0LL) {
767 ts->idle_sleeps++;
768 ts->idle_expires = expires;
769 }
770
771 if (!was_stopped && ts->tick_stopped)
772 ts->idle_jiffies = ts->last_jiffies;
773 }
774}
775
776/**
777 * tick_nohz_idle_enter - stop the idle tick from the idle task
778 *
779 * When the next event is more than a tick into the future, stop the idle tick
780 * Called when we start the idle loop.
781 *
782 * The arch is responsible of calling:
783 *
784 * - rcu_idle_enter() after its last use of RCU before the CPU is put
785 * to sleep.
786 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
787 */
788void tick_nohz_idle_enter(void)
789{
790 struct tick_sched *ts;
791
792 WARN_ON_ONCE(irqs_disabled());
793
794 /*
795 * Update the idle state in the scheduler domain hierarchy
796 * when tick_nohz_stop_sched_tick() is called from the idle loop.
797 * State will be updated to busy during the first busy tick after
798 * exiting idle.
799 */
800 set_cpu_sd_state_idle();
801
802 local_irq_disable();
803
804 ts = &__get_cpu_var(tick_cpu_sched);
805 ts->inidle = 1;
806 __tick_nohz_idle_enter(ts);
807
808 local_irq_enable();
809}
810EXPORT_SYMBOL_GPL(tick_nohz_idle_enter);
811
812/**
813 * tick_nohz_irq_exit - update next tick event from interrupt exit
814 *
815 * When an interrupt fires while we are idle and it doesn't cause
816 * a reschedule, it may still add, modify or delete a timer, enqueue
817 * an RCU callback, etc...
818 * So we need to re-calculate and reprogram the next tick event.
819 */
820void tick_nohz_irq_exit(void)
821{
822 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
823
824 if (ts->inidle)
825 __tick_nohz_idle_enter(ts);
826 else
827 tick_nohz_full_stop_tick(ts);
828}
829
830/**
831 * tick_nohz_get_sleep_length - return the length of the current sleep
832 *
833 * Called from power state control code with interrupts disabled
834 */
835ktime_t tick_nohz_get_sleep_length(void)
836{
837 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
838
839 return ts->sleep_length;
840}
841
842static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
843{
844 hrtimer_cancel(&ts->sched_timer);
845 hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
846
847 while (1) {
848 /* Forward the time to expire in the future */
849 hrtimer_forward(&ts->sched_timer, now, tick_period);
850
851 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
852 hrtimer_start_expires(&ts->sched_timer,
853 HRTIMER_MODE_ABS_PINNED);
854 /* Check, if the timer was already in the past */
855 if (hrtimer_active(&ts->sched_timer))
856 break;
857 } else {
858 if (!tick_program_event(
859 hrtimer_get_expires(&ts->sched_timer), 0))
860 break;
861 }
862 /* Reread time and update jiffies */
863 now = ktime_get();
864 tick_do_update_jiffies64(now);
865 }
866}
867
868static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
869{
870 /* Update jiffies first */
871 tick_do_update_jiffies64(now);
872 update_cpu_load_nohz();
873
874 calc_load_exit_idle();
875 touch_softlockup_watchdog();
876 /*
877 * Cancel the scheduled timer and restore the tick
878 */
879 ts->tick_stopped = 0;
880 ts->idle_exittime = now;
881
882 tick_nohz_restart(ts, now);
883}
884
885static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
886{
887#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
888 unsigned long ticks;
889
890 if (vtime_accounting_enabled())
891 return;
892 /*
893 * We stopped the tick in idle. Update process times would miss the
894 * time we slept as update_process_times does only a 1 tick
895 * accounting. Enforce that this is accounted to idle !
896 */
897 ticks = jiffies - ts->idle_jiffies;
898 /*
899 * We might be one off. Do not randomly account a huge number of ticks!
900 */
901 if (ticks && ticks < LONG_MAX)
902 account_idle_ticks(ticks);
903#endif
904}
905
906/**
907 * tick_nohz_idle_exit - restart the idle tick from the idle task
908 *
909 * Restart the idle tick when the CPU is woken up from idle
910 * This also exit the RCU extended quiescent state. The CPU
911 * can use RCU again after this function is called.
912 */
913void tick_nohz_idle_exit(void)
914{
915 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
916 ktime_t now;
917
918 local_irq_disable();
919
920 WARN_ON_ONCE(!ts->inidle);
921
922 ts->inidle = 0;
923
924 if (ts->idle_active || ts->tick_stopped)
925 now = ktime_get();
926
927 if (ts->idle_active)
928 tick_nohz_stop_idle(ts, now);
929
930 if (ts->tick_stopped) {
931 tick_nohz_restart_sched_tick(ts, now);
932 tick_nohz_account_idle_ticks(ts);
933 }
934
935 local_irq_enable();
936}
937EXPORT_SYMBOL_GPL(tick_nohz_idle_exit);
938
939static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
940{
941 hrtimer_forward(&ts->sched_timer, now, tick_period);
942 return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
943}
944
945/*
946 * The nohz low res interrupt handler
947 */
948static void tick_nohz_handler(struct clock_event_device *dev)
949{
950 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
951 struct pt_regs *regs = get_irq_regs();
952 ktime_t now = ktime_get();
953
954 dev->next_event.tv64 = KTIME_MAX;
955
956 tick_sched_do_timer(now);
957 tick_sched_handle(ts, regs);
958
959 while (tick_nohz_reprogram(ts, now)) {
960 now = ktime_get();
961 tick_do_update_jiffies64(now);
962 }
963}
964
965/**
966 * tick_nohz_switch_to_nohz - switch to nohz mode
967 */
968static void tick_nohz_switch_to_nohz(void)
969{
970 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
971 ktime_t next;
972
973 if (!tick_nohz_enabled)
974 return;
975
976 local_irq_disable();
977 if (tick_switch_to_oneshot(tick_nohz_handler)) {
978 local_irq_enable();
979 return;
980 }
981 tick_nohz_active = 1;
982 ts->nohz_mode = NOHZ_MODE_LOWRES;
983
984 /*
985 * Recycle the hrtimer in ts, so we can share the
986 * hrtimer_forward with the highres code.
987 */
988 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
989 /* Get the next period */
990 next = tick_init_jiffy_update();
991
992 for (;;) {
993 hrtimer_set_expires(&ts->sched_timer, next);
994 if (!tick_program_event(next, 0))
995 break;
996 next = ktime_add(next, tick_period);
997 }
998 local_irq_enable();
999}
1000
1001/*
1002 * When NOHZ is enabled and the tick is stopped, we need to kick the
1003 * tick timer from irq_enter() so that the jiffies update is kept
1004 * alive during long running softirqs. That's ugly as hell, but
1005 * correctness is key even if we need to fix the offending softirq in
1006 * the first place.
1007 *
1008 * Note, this is different to tick_nohz_restart. We just kick the
1009 * timer and do not touch the other magic bits which need to be done
1010 * when idle is left.
1011 */
1012static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1013{
1014#if 0
1015 /* Switch back to 2.6.27 behaviour */
1016 ktime_t delta;
1017
1018 /*
1019 * Do not touch the tick device, when the next expiry is either
1020 * already reached or less/equal than the tick period.
1021 */
1022 delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1023 if (delta.tv64 <= tick_period.tv64)
1024 return;
1025
1026 tick_nohz_restart(ts, now);
1027#endif
1028}
1029
1030static inline void tick_nohz_irq_enter(void)
1031{
1032 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1033 ktime_t now;
1034
1035 if (!ts->idle_active && !ts->tick_stopped)
1036 return;
1037 now = ktime_get();
1038 if (ts->idle_active)
1039 tick_nohz_stop_idle(ts, now);
1040 if (ts->tick_stopped) {
1041 tick_nohz_update_jiffies(now);
1042 tick_nohz_kick_tick(ts, now);
1043 }
1044}
1045
1046#else
1047
1048static inline void tick_nohz_switch_to_nohz(void) { }
1049static inline void tick_nohz_irq_enter(void) { }
1050
1051#endif /* CONFIG_NO_HZ_COMMON */
1052
1053/*
1054 * Called from irq_enter to notify about the possible interruption of idle()
1055 */
1056void tick_irq_enter(void)
1057{
1058 tick_check_oneshot_broadcast_this_cpu();
1059 tick_nohz_irq_enter();
1060}
1061
1062/*
1063 * High resolution timer specific code
1064 */
1065#ifdef CONFIG_HIGH_RES_TIMERS
1066/*
1067 * We rearm the timer until we get disabled by the idle code.
1068 * Called with interrupts disabled.
1069 */
1070static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1071{
1072 struct tick_sched *ts =
1073 container_of(timer, struct tick_sched, sched_timer);
1074 struct pt_regs *regs = get_irq_regs();
1075 ktime_t now = ktime_get();
1076
1077 tick_sched_do_timer(now);
1078
1079 /*
1080 * Do not call, when we are not in irq context and have
1081 * no valid regs pointer
1082 */
1083 if (regs)
1084 tick_sched_handle(ts, regs);
1085
1086 hrtimer_forward(timer, now, tick_period);
1087
1088 return HRTIMER_RESTART;
1089}
1090
1091static int sched_skew_tick;
1092
1093static int __init skew_tick(char *str)
1094{
1095 get_option(&str, &sched_skew_tick);
1096
1097 return 0;
1098}
1099early_param("skew_tick", skew_tick);
1100
1101/**
1102 * tick_setup_sched_timer - setup the tick emulation timer
1103 */
1104void tick_setup_sched_timer(void)
1105{
1106 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1107 ktime_t now = ktime_get();
1108
1109 /*
1110 * Emulate tick processing via per-CPU hrtimers:
1111 */
1112 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1113 ts->sched_timer.function = tick_sched_timer;
1114
1115 /* Get the next period (per cpu) */
1116 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1117
1118 /* Offset the tick to avert jiffies_lock contention. */
1119 if (sched_skew_tick) {
1120 u64 offset = ktime_to_ns(tick_period) >> 1;
1121 do_div(offset, num_possible_cpus());
1122 offset *= smp_processor_id();
1123 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1124 }
1125
1126 for (;;) {
1127 hrtimer_forward(&ts->sched_timer, now, tick_period);
1128 hrtimer_start_expires(&ts->sched_timer,
1129 HRTIMER_MODE_ABS_PINNED);
1130 /* Check, if the timer was already in the past */
1131 if (hrtimer_active(&ts->sched_timer))
1132 break;
1133 now = ktime_get();
1134 }
1135
1136#ifdef CONFIG_NO_HZ_COMMON
1137 if (tick_nohz_enabled) {
1138 ts->nohz_mode = NOHZ_MODE_HIGHRES;
1139 tick_nohz_active = 1;
1140 }
1141#endif
1142}
1143#endif /* HIGH_RES_TIMERS */
1144
1145#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1146void tick_cancel_sched_timer(int cpu)
1147{
1148 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1149
1150# ifdef CONFIG_HIGH_RES_TIMERS
1151 if (ts->sched_timer.base)
1152 hrtimer_cancel(&ts->sched_timer);
1153# endif
1154
1155 memset(ts, 0, sizeof(*ts));
1156}
1157#endif
1158
1159/**
1160 * Async notification about clocksource changes
1161 */
1162void tick_clock_notify(void)
1163{
1164 int cpu;
1165
1166 for_each_possible_cpu(cpu)
1167 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1168}
1169
1170/*
1171 * Async notification about clock event changes
1172 */
1173void tick_oneshot_notify(void)
1174{
1175 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1176
1177 set_bit(0, &ts->check_clocks);
1178}
1179
1180/**
1181 * Check, if a change happened, which makes oneshot possible.
1182 *
1183 * Called cyclic from the hrtimer softirq (driven by the timer
1184 * softirq) allow_nohz signals, that we can switch into low-res nohz
1185 * mode, because high resolution timers are disabled (either compile
1186 * or runtime).
1187 */
1188int tick_check_oneshot_change(int allow_nohz)
1189{
1190 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1191
1192 if (!test_and_clear_bit(0, &ts->check_clocks))
1193 return 0;
1194
1195 if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1196 return 0;
1197
1198 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1199 return 0;
1200
1201 if (!allow_nohz)
1202 return 1;
1203
1204 tick_nohz_switch_to_nohz();
1205 return 0;
1206}
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}