1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright(C) 2005-2006, Linutronix GmbH, Thomas Gleixner <tglx@kernel.org>
4 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
5 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner
6 *
7 * NOHZ implementation for low and high resolution timers
8 *
9 * Started by: Thomas Gleixner and Ingo Molnar
10 */
11#include <linux/compiler.h>
12#include <linux/cpu.h>
13#include <linux/err.h>
14#include <linux/hrtimer.h>
15#include <linux/interrupt.h>
16#include <linux/kernel_stat.h>
17#include <linux/percpu.h>
18#include <linux/nmi.h>
19#include <linux/profile.h>
20#include <linux/sched/signal.h>
21#include <linux/sched/clock.h>
22#include <linux/sched/stat.h>
23#include <linux/sched/nohz.h>
24#include <linux/sched/loadavg.h>
25#include <linux/module.h>
26#include <linux/irq_work.h>
27#include <linux/posix-timers.h>
28#include <linux/context_tracking.h>
29#include <linux/mm.h>
30
31#include <asm/irq_regs.h>
32
33#include "tick-internal.h"
34
35#include <trace/events/timer.h>
36
37/*
38 * Per-CPU nohz control structure
39 */
40static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
41
42struct tick_sched *tick_get_tick_sched(int cpu)
43{
44 return &per_cpu(tick_cpu_sched, cpu);
45}
46
47/*
48 * The time when the last jiffy update happened. Write access must hold
49 * jiffies_lock and jiffies_seq. tick_nohz_next_event() needs to get a
50 * consistent view of jiffies and last_jiffies_update.
51 */
52static ktime_t last_jiffies_update;
53
54/*
55 * Must be called with interrupts disabled !
56 */
57static void tick_do_update_jiffies64(ktime_t now)
58{
59 unsigned long ticks = 1;
60 ktime_t delta, nextp;
61
62 /*
63 * 64-bit can do a quick check without holding the jiffies lock and
64 * without looking at the sequence count. The smp_load_acquire()
65 * pairs with the update done later in this function.
66 *
67 * 32-bit cannot do that because the store of 'tick_next_period'
68 * consists of two 32-bit stores, and the first store could be
69 * moved by the CPU to a random point in the future.
70 */
71 if (IS_ENABLED(CONFIG_64BIT)) {
72 if (ktime_before(cmp1: now, smp_load_acquire(&tick_next_period)))
73 return;
74 } else {
75 unsigned int seq;
76
77 /*
78 * Avoid contention on 'jiffies_lock' and protect the quick
79 * check with the sequence count.
80 */
81 do {
82 seq = read_seqcount_begin(&jiffies_seq);
83 nextp = tick_next_period;
84 } while (read_seqcount_retry(&jiffies_seq, seq));
85
86 if (ktime_before(cmp1: now, cmp2: nextp))
87 return;
88 }
89
90 /* Quick check failed, i.e. update is required. */
91 raw_spin_lock(&jiffies_lock);
92 /*
93 * Re-evaluate with the lock held. Another CPU might have done the
94 * update already.
95 */
96 if (ktime_before(cmp1: now, cmp2: tick_next_period)) {
97 raw_spin_unlock(&jiffies_lock);
98 return;
99 }
100
101 write_seqcount_begin(&jiffies_seq);
102
103 delta = ktime_sub(now, tick_next_period);
104 if (unlikely(delta >= TICK_NSEC)) {
105 /* Slow path for long idle sleep times */
106 s64 incr = TICK_NSEC;
107
108 ticks += ktime_divns(kt: delta, div: incr);
109
110 last_jiffies_update = ktime_add_ns(last_jiffies_update,
111 incr * ticks);
112 } else {
113 last_jiffies_update = ktime_add_ns(last_jiffies_update,
114 TICK_NSEC);
115 }
116
117 /* Advance jiffies to complete the 'jiffies_seq' protected job */
118 jiffies_64 += ticks;
119
120 /* Keep the tick_next_period variable up to date */
121 nextp = ktime_add_ns(last_jiffies_update, TICK_NSEC);
122
123 if (IS_ENABLED(CONFIG_64BIT)) {
124 /*
125 * Pairs with smp_load_acquire() in the lockless quick
126 * check above, and ensures that the update to 'jiffies_64' is
127 * not reordered vs. the store to 'tick_next_period', neither
128 * by the compiler nor by the CPU.
129 */
130 smp_store_release(&tick_next_period, nextp);
131 } else {
132 /*
133 * A plain store is good enough on 32-bit, as the quick check
134 * above is protected by the sequence count.
135 */
136 tick_next_period = nextp;
137 }
138
139 /*
140 * Release the sequence count. calc_global_load() below is not
141 * protected by it, but 'jiffies_lock' needs to be held to prevent
142 * concurrent invocations.
143 */
144 write_seqcount_end(&jiffies_seq);
145
146 calc_global_load();
147
148 raw_spin_unlock(&jiffies_lock);
149 update_wall_time();
150}
151
152/*
153 * Initialize and return retrieve the jiffies update.
154 */
155static ktime_t tick_init_jiffy_update(void)
156{
157 ktime_t period;
158
159 raw_spin_lock(&jiffies_lock);
160 write_seqcount_begin(&jiffies_seq);
161
162 /* Have we started the jiffies update yet ? */
163 if (last_jiffies_update == 0) {
164 u32 rem;
165
166 /*
167 * Ensure that the tick is aligned to a multiple of
168 * TICK_NSEC.
169 */
170 div_u64_rem(dividend: tick_next_period, TICK_NSEC, remainder: &rem);
171 if (rem)
172 tick_next_period += TICK_NSEC - rem;
173
174 last_jiffies_update = tick_next_period;
175 }
176 period = last_jiffies_update;
177
178 write_seqcount_end(&jiffies_seq);
179 raw_spin_unlock(&jiffies_lock);
180
181 return period;
182}
183
184static inline int tick_sched_flag_test(struct tick_sched *ts,
185 unsigned long flag)
186{
187 return !!(ts->flags & flag);
188}
189
190static inline void tick_sched_flag_set(struct tick_sched *ts,
191 unsigned long flag)
192{
193 lockdep_assert_irqs_disabled();
194 ts->flags |= flag;
195}
196
197static inline void tick_sched_flag_clear(struct tick_sched *ts,
198 unsigned long flag)
199{
200 lockdep_assert_irqs_disabled();
201 ts->flags &= ~flag;
202}
203
204/*
205 * Allow only one non-timekeeper CPU at a time update jiffies from
206 * the timer tick.
207 *
208 * Returns true if update was run.
209 */
210static bool tick_limited_update_jiffies64(struct tick_sched *ts, ktime_t now)
211{
212 static atomic_t in_progress;
213 int inp;
214
215 inp = atomic_read(v: &in_progress);
216 if (inp || !atomic_try_cmpxchg(v: &in_progress, old: &inp, new: 1))
217 return false;
218
219 if (ts->last_tick_jiffies == jiffies)
220 tick_do_update_jiffies64(now);
221 atomic_set(v: &in_progress, i: 0);
222 return true;
223}
224
225#define MAX_STALLED_JIFFIES 5
226
227static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
228{
229 int tick_cpu, cpu = smp_processor_id();
230
231 /*
232 * Check if the do_timer duty was dropped. We don't care about
233 * concurrency: This happens only when the CPU in charge went
234 * into a long sleep. If two CPUs happen to assign themselves to
235 * this duty, then the jiffies update is still serialized by
236 * 'jiffies_lock'.
237 *
238 * If nohz_full is enabled, this should not happen because the
239 * 'tick_do_timer_cpu' CPU never relinquishes.
240 */
241 tick_cpu = READ_ONCE(tick_do_timer_cpu);
242
243 if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && unlikely(tick_cpu == TICK_DO_TIMER_NONE)) {
244#ifdef CONFIG_NO_HZ_FULL
245 WARN_ON_ONCE(tick_nohz_full_running);
246#endif
247 WRITE_ONCE(tick_do_timer_cpu, cpu);
248 tick_cpu = cpu;
249 }
250
251 /* Check if jiffies need an update */
252 if (tick_cpu == cpu)
253 tick_do_update_jiffies64(now);
254
255 /*
256 * If the jiffies update stalled for too long (timekeeper in stop_machine()
257 * or VMEXIT'ed for several msecs), force an update.
258 */
259 if (ts->last_tick_jiffies != jiffies) {
260 ts->stalled_jiffies = 0;
261 ts->last_tick_jiffies = READ_ONCE(jiffies);
262 } else {
263 if (++ts->stalled_jiffies >= MAX_STALLED_JIFFIES) {
264 if (tick_limited_update_jiffies64(ts, now)) {
265 ts->stalled_jiffies = 0;
266 ts->last_tick_jiffies = READ_ONCE(jiffies);
267 }
268 }
269 }
270
271 if (tick_sched_flag_test(ts, TS_FLAG_INIDLE))
272 ts->got_idle_tick = 1;
273}
274
275static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
276{
277 /*
278 * When we are idle and the tick is stopped, we have to touch
279 * the watchdog as we might not schedule for a really long
280 * time. This happens on completely idle SMP systems while
281 * waiting on the login prompt. We also increment the "start of
282 * idle" jiffy stamp so the idle accounting adjustment we do
283 * when we go busy again does not account too many ticks.
284 */
285 if (IS_ENABLED(CONFIG_NO_HZ_COMMON) &&
286 tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
287 touch_softlockup_watchdog_sched();
288 if (is_idle_task(current))
289 ts->idle_jiffies++;
290 /*
291 * In case the current tick fired too early past its expected
292 * expiration, make sure we don't bypass the next clock reprogramming
293 * to the same deadline.
294 */
295 ts->next_tick = 0;
296 }
297
298 update_process_times(user: user_mode(regs));
299 profile_tick(CPU_PROFILING);
300}
301
302/*
303 * We rearm the timer until we get disabled by the idle code.
304 * Called with interrupts disabled.
305 */
306static enum hrtimer_restart tick_nohz_handler(struct hrtimer *timer)
307{
308 struct tick_sched *ts = container_of(timer, struct tick_sched, sched_timer);
309 struct pt_regs *regs = get_irq_regs();
310 ktime_t now = ktime_get();
311
312 tick_sched_do_timer(ts, now);
313
314 /*
315 * Do not call when we are not in IRQ context and have
316 * no valid 'regs' pointer
317 */
318 if (regs)
319 tick_sched_handle(ts, regs);
320 else
321 ts->next_tick = 0;
322
323 /*
324 * In dynticks mode, tick reprogram is deferred:
325 * - to the idle task if in dynticks-idle
326 * - to IRQ exit if in full-dynticks.
327 */
328 if (unlikely(tick_sched_flag_test(ts, TS_FLAG_STOPPED)))
329 return HRTIMER_NORESTART;
330
331 hrtimer_forward(timer, now, TICK_NSEC);
332
333 return HRTIMER_RESTART;
334}
335
336#ifdef CONFIG_NO_HZ_FULL
337cpumask_var_t tick_nohz_full_mask;
338EXPORT_SYMBOL_GPL(tick_nohz_full_mask);
339bool tick_nohz_full_running;
340EXPORT_SYMBOL_GPL(tick_nohz_full_running);
341static atomic_t tick_dep_mask;
342
343static bool check_tick_dependency(atomic_t *dep)
344{
345 int val = atomic_read(dep);
346
347 if (val & TICK_DEP_MASK_POSIX_TIMER) {
348 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
349 return true;
350 }
351
352 if (val & TICK_DEP_MASK_PERF_EVENTS) {
353 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
354 return true;
355 }
356
357 if (val & TICK_DEP_MASK_SCHED) {
358 trace_tick_stop(0, TICK_DEP_MASK_SCHED);
359 return true;
360 }
361
362 if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
363 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
364 return true;
365 }
366
367 if (val & TICK_DEP_MASK_RCU) {
368 trace_tick_stop(0, TICK_DEP_MASK_RCU);
369 return true;
370 }
371
372 if (val & TICK_DEP_MASK_RCU_EXP) {
373 trace_tick_stop(0, TICK_DEP_MASK_RCU_EXP);
374 return true;
375 }
376
377 return false;
378}
379
380static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
381{
382 lockdep_assert_irqs_disabled();
383
384 if (unlikely(!cpu_online(cpu)))
385 return false;
386
387 if (check_tick_dependency(&tick_dep_mask))
388 return false;
389
390 if (check_tick_dependency(&ts->tick_dep_mask))
391 return false;
392
393 if (check_tick_dependency(&current->tick_dep_mask))
394 return false;
395
396 if (check_tick_dependency(&current->signal->tick_dep_mask))
397 return false;
398
399 return true;
400}
401
402static void nohz_full_kick_func(struct irq_work *work)
403{
404 /* Empty, the tick restart happens on tick_nohz_irq_exit() */
405}
406
407static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) =
408 IRQ_WORK_INIT_HARD(nohz_full_kick_func);
409
410/*
411 * Kick this CPU if it's full dynticks in order to force it to
412 * re-evaluate its dependency on the tick and restart it if necessary.
413 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
414 * is NMI safe.
415 */
416static void tick_nohz_full_kick(void)
417{
418 if (!tick_nohz_full_cpu(smp_processor_id()))
419 return;
420
421 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
422}
423
424/*
425 * Kick the CPU if it's full dynticks in order to force it to
426 * re-evaluate its dependency on the tick and restart it if necessary.
427 */
428void tick_nohz_full_kick_cpu(int cpu)
429{
430 if (!tick_nohz_full_cpu(cpu))
431 return;
432
433 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
434}
435
436static void tick_nohz_kick_task(struct task_struct *tsk)
437{
438 int cpu;
439
440 /*
441 * If the task is not running, run_posix_cpu_timers()
442 * has nothing to elapse, and an IPI can then be optimized out.
443 *
444 * activate_task() STORE p->tick_dep_mask
445 * STORE p->on_rq
446 * __schedule() (switch to task 'p') smp_mb() (atomic_fetch_or())
447 * LOCK rq->lock LOAD p->on_rq
448 * smp_mb__after_spin_lock()
449 * tick_nohz_task_switch()
450 * LOAD p->tick_dep_mask
451 *
452 * XXX given a task picks up the dependency on schedule(), should we
453 * only care about tasks that are currently on the CPU instead of all
454 * that are on the runqueue?
455 *
456 * That is, does this want to be: task_on_cpu() / task_curr()?
457 */
458 if (!sched_task_on_rq(tsk))
459 return;
460
461 /*
462 * If the task concurrently migrates to another CPU,
463 * we guarantee it sees the new tick dependency upon
464 * schedule.
465 *
466 * set_task_cpu(p, cpu);
467 * STORE p->cpu = @cpu
468 * __schedule() (switch to task 'p')
469 * LOCK rq->lock
470 * smp_mb__after_spin_lock() STORE p->tick_dep_mask
471 * tick_nohz_task_switch() smp_mb() (atomic_fetch_or())
472 * LOAD p->tick_dep_mask LOAD p->cpu
473 */
474 cpu = task_cpu(tsk);
475
476 preempt_disable();
477 if (cpu_online(cpu))
478 tick_nohz_full_kick_cpu(cpu);
479 preempt_enable();
480}
481
482/*
483 * Kick all full dynticks CPUs in order to force these to re-evaluate
484 * their dependency on the tick and restart it if necessary.
485 */
486static void tick_nohz_full_kick_all(void)
487{
488 int cpu;
489
490 if (!tick_nohz_full_running)
491 return;
492
493 preempt_disable();
494 for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
495 tick_nohz_full_kick_cpu(cpu);
496 preempt_enable();
497}
498
499static void tick_nohz_dep_set_all(atomic_t *dep,
500 enum tick_dep_bits bit)
501{
502 int prev;
503
504 prev = atomic_fetch_or(BIT(bit), dep);
505 if (!prev)
506 tick_nohz_full_kick_all();
507}
508
509/*
510 * Set a global tick dependency. Used by perf events that rely on freq and
511 * unstable clocks.
512 */
513void tick_nohz_dep_set(enum tick_dep_bits bit)
514{
515 tick_nohz_dep_set_all(&tick_dep_mask, bit);
516}
517
518void tick_nohz_dep_clear(enum tick_dep_bits bit)
519{
520 atomic_andnot(BIT(bit), &tick_dep_mask);
521}
522
523/*
524 * Set per-CPU tick dependency. Used by scheduler and perf events in order to
525 * manage event-throttling.
526 */
527void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
528{
529 int prev;
530 struct tick_sched *ts;
531
532 ts = per_cpu_ptr(&tick_cpu_sched, cpu);
533
534 prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
535 if (!prev) {
536 preempt_disable();
537 /* Perf needs local kick that is NMI safe */
538 if (cpu == smp_processor_id()) {
539 tick_nohz_full_kick();
540 } else {
541 /* Remote IRQ work not NMI-safe */
542 if (!WARN_ON_ONCE(in_nmi()))
543 tick_nohz_full_kick_cpu(cpu);
544 }
545 preempt_enable();
546 }
547}
548EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu);
549
550void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
551{
552 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
553
554 atomic_andnot(BIT(bit), &ts->tick_dep_mask);
555}
556EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu);
557
558/*
559 * Set a per-task tick dependency. RCU needs this. Also posix CPU timers
560 * in order to elapse per task timers.
561 */
562void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
563{
564 if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask))
565 tick_nohz_kick_task(tsk);
566}
567EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task);
568
569void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
570{
571 atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
572}
573EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_task);
574
575/*
576 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
577 * per process timers.
578 */
579void tick_nohz_dep_set_signal(struct task_struct *tsk,
580 enum tick_dep_bits bit)
581{
582 int prev;
583 struct signal_struct *sig = tsk->signal;
584
585 prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask);
586 if (!prev) {
587 struct task_struct *t;
588
589 lockdep_assert_held(&tsk->sighand->siglock);
590 __for_each_thread(sig, t)
591 tick_nohz_kick_task(t);
592 }
593}
594
595void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
596{
597 atomic_andnot(BIT(bit), &sig->tick_dep_mask);
598}
599
600/*
601 * Re-evaluate the need for the tick as we switch the current task.
602 * It might need the tick due to per task/process properties:
603 * perf events, posix CPU timers, ...
604 */
605void __tick_nohz_task_switch(void)
606{
607 struct tick_sched *ts;
608
609 if (!tick_nohz_full_cpu(smp_processor_id()))
610 return;
611
612 ts = this_cpu_ptr(&tick_cpu_sched);
613
614 if (tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
615 if (atomic_read(&current->tick_dep_mask) ||
616 atomic_read(&current->signal->tick_dep_mask))
617 tick_nohz_full_kick();
618 }
619}
620
621/* Get the boot-time nohz CPU list from the kernel parameters. */
622void __init tick_nohz_full_setup(cpumask_var_t cpumask)
623{
624 alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
625 cpumask_copy(tick_nohz_full_mask, cpumask);
626 tick_nohz_full_running = true;
627}
628
629bool tick_nohz_cpu_hotpluggable(unsigned int cpu)
630{
631 /*
632 * The 'tick_do_timer_cpu' CPU handles housekeeping duty (unbound
633 * timers, workqueues, timekeeping, ...) on behalf of full dynticks
634 * CPUs. It must remain online when nohz full is enabled.
635 */
636 if (tick_nohz_full_running && READ_ONCE(tick_do_timer_cpu) == cpu)
637 return false;
638 return true;
639}
640
641static int tick_nohz_cpu_down(unsigned int cpu)
642{
643 return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY;
644}
645
646void __init tick_nohz_init(void)
647{
648 int cpu, ret;
649
650 if (!tick_nohz_full_running)
651 return;
652
653 /*
654 * Full dynticks uses IRQ work to drive the tick rescheduling on safe
655 * locking contexts. But then we need IRQ work to raise its own
656 * interrupts to avoid circular dependency on the tick.
657 */
658 if (!arch_irq_work_has_interrupt()) {
659 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support IRQ work self-IPIs\n");
660 cpumask_clear(tick_nohz_full_mask);
661 tick_nohz_full_running = false;
662 return;
663 }
664
665 if (IS_ENABLED(CONFIG_PM_SLEEP_SMP) &&
666 !IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU)) {
667 cpu = smp_processor_id();
668
669 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
670 pr_warn("NO_HZ: Clearing %d from nohz_full range "
671 "for timekeeping\n", cpu);
672 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
673 }
674 }
675
676 for_each_cpu(cpu, tick_nohz_full_mask)
677 ct_cpu_track_user(cpu);
678
679 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
680 "kernel/nohz:predown", NULL,
681 tick_nohz_cpu_down);
682 WARN_ON(ret < 0);
683 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
684 cpumask_pr_args(tick_nohz_full_mask));
685}
686#endif /* #ifdef CONFIG_NO_HZ_FULL */
687
688/*
689 * NOHZ - aka dynamic tick functionality
690 */
691#ifdef CONFIG_NO_HZ_COMMON
692/*
693 * NO HZ enabled ?
694 */
695bool tick_nohz_enabled __read_mostly = true;
696unsigned long tick_nohz_active __read_mostly;
697/*
698 * Enable / Disable tickless mode
699 */
700static int __init setup_tick_nohz(char *str)
701{
702 return (kstrtobool(s: str, res: &tick_nohz_enabled) == 0);
703}
704
705__setup("nohz=", setup_tick_nohz);
706
707bool tick_nohz_tick_stopped(void)
708{
709 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
710
711 return tick_sched_flag_test(ts, TS_FLAG_STOPPED);
712}
713
714bool tick_nohz_tick_stopped_cpu(int cpu)
715{
716 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
717
718 return tick_sched_flag_test(ts, TS_FLAG_STOPPED);
719}
720
721/**
722 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
723 * @now: current ktime_t
724 *
725 * Called from interrupt entry when the CPU was idle
726 *
727 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
728 * must be updated. Otherwise an interrupt handler could use a stale jiffy
729 * value. We do this unconditionally on any CPU, as we don't know whether the
730 * CPU, which has the update task assigned, is in a long sleep.
731 */
732static void tick_nohz_update_jiffies(ktime_t now)
733{
734 unsigned long flags;
735
736 __this_cpu_write(tick_cpu_sched.idle_waketime, now);
737
738 local_irq_save(flags);
739 tick_do_update_jiffies64(now);
740 local_irq_restore(flags);
741
742 touch_softlockup_watchdog_sched();
743}
744
745static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
746{
747 ktime_t delta;
748
749 if (WARN_ON_ONCE(!tick_sched_flag_test(ts, TS_FLAG_IDLE_ACTIVE)))
750 return;
751
752 delta = ktime_sub(now, ts->idle_entrytime);
753
754 write_seqcount_begin(&ts->idle_sleeptime_seq);
755 if (nr_iowait_cpu(smp_processor_id()) > 0)
756 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
757 else
758 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
759
760 ts->idle_entrytime = now;
761 tick_sched_flag_clear(ts, TS_FLAG_IDLE_ACTIVE);
762 write_seqcount_end(&ts->idle_sleeptime_seq);
763
764 sched_clock_idle_wakeup_event();
765}
766
767static void tick_nohz_start_idle(struct tick_sched *ts)
768{
769 write_seqcount_begin(&ts->idle_sleeptime_seq);
770 ts->idle_entrytime = ktime_get();
771 tick_sched_flag_set(ts, TS_FLAG_IDLE_ACTIVE);
772 write_seqcount_end(&ts->idle_sleeptime_seq);
773
774 sched_clock_idle_sleep_event();
775}
776
777static u64 get_cpu_sleep_time_us(struct tick_sched *ts, ktime_t *sleeptime,
778 bool compute_delta, u64 *last_update_time)
779{
780 ktime_t now, idle;
781 unsigned int seq;
782
783 if (!tick_nohz_active)
784 return -1;
785
786 now = ktime_get();
787 if (last_update_time)
788 *last_update_time = ktime_to_us(kt: now);
789
790 do {
791 seq = read_seqcount_begin(&ts->idle_sleeptime_seq);
792
793 if (tick_sched_flag_test(ts, TS_FLAG_IDLE_ACTIVE) && compute_delta) {
794 ktime_t delta = ktime_sub(now, ts->idle_entrytime);
795
796 idle = ktime_add(*sleeptime, delta);
797 } else {
798 idle = *sleeptime;
799 }
800 } while (read_seqcount_retry(&ts->idle_sleeptime_seq, seq));
801
802 return ktime_to_us(kt: idle);
803
804}
805
806/**
807 * get_cpu_idle_time_us - get the total idle time of a CPU
808 * @cpu: CPU number to query
809 * @last_update_time: variable to store update time in. Do not update
810 * counters if NULL.
811 *
812 * Return the cumulative idle time (since boot) for a given
813 * CPU, in microseconds. Note that this is partially broken due to
814 * the counter of iowait tasks that can be remotely updated without
815 * any synchronization. Therefore it is possible to observe backward
816 * values within two consecutive reads.
817 *
818 * This time is measured via accounting rather than sampling,
819 * and is as accurate as ktime_get() is.
820 *
821 * Return: -1 if NOHZ is not enabled, else total idle time of the @cpu
822 */
823u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
824{
825 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
826
827 return get_cpu_sleep_time_us(ts, sleeptime: &ts->idle_sleeptime,
828 compute_delta: !nr_iowait_cpu(cpu), last_update_time);
829}
830EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
831
832/**
833 * get_cpu_iowait_time_us - get the total iowait time of a CPU
834 * @cpu: CPU number to query
835 * @last_update_time: variable to store update time in. Do not update
836 * counters if NULL.
837 *
838 * Return the cumulative iowait time (since boot) for a given
839 * CPU, in microseconds. Note this is partially broken due to
840 * the counter of iowait tasks that can be remotely updated without
841 * any synchronization. Therefore it is possible to observe backward
842 * values within two consecutive reads.
843 *
844 * This time is measured via accounting rather than sampling,
845 * and is as accurate as ktime_get() is.
846 *
847 * Return: -1 if NOHZ is not enabled, else total iowait time of @cpu
848 */
849u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
850{
851 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
852
853 return get_cpu_sleep_time_us(ts, sleeptime: &ts->iowait_sleeptime,
854 compute_delta: nr_iowait_cpu(cpu), last_update_time);
855}
856EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
857
858static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
859{
860 hrtimer_cancel(timer: &ts->sched_timer);
861 hrtimer_set_expires(timer: &ts->sched_timer, time: ts->last_tick);
862
863 /* Forward the time to expire in the future */
864 hrtimer_forward(timer: &ts->sched_timer, now, TICK_NSEC);
865
866 if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES)) {
867 hrtimer_start_expires(timer: &ts->sched_timer,
868 mode: HRTIMER_MODE_ABS_PINNED_HARD);
869 } else {
870 tick_program_event(expires: hrtimer_get_expires(timer: &ts->sched_timer), force: 1);
871 }
872
873 /*
874 * Reset to make sure the next tick stop doesn't get fooled by past
875 * cached clock deadline.
876 */
877 ts->next_tick = 0;
878}
879
880static inline bool local_timer_softirq_pending(void)
881{
882 return local_timers_pending() & BIT(TIMER_SOFTIRQ);
883}
884
885/*
886 * Read jiffies and the time when jiffies were updated last
887 */
888u64 get_jiffies_update(unsigned long *basej)
889{
890 unsigned long basejiff;
891 unsigned int seq;
892 u64 basemono;
893
894 do {
895 seq = read_seqcount_begin(&jiffies_seq);
896 basemono = last_jiffies_update;
897 basejiff = jiffies;
898 } while (read_seqcount_retry(&jiffies_seq, seq));
899 *basej = basejiff;
900 return basemono;
901}
902
903/**
904 * tick_nohz_next_event() - return the clock monotonic based next event
905 * @ts: pointer to tick_sched struct
906 * @cpu: CPU number
907 *
908 * Return:
909 * *%0 - When the next event is a maximum of TICK_NSEC in the future
910 * and the tick is not stopped yet
911 * *%next_event - Next event based on clock monotonic
912 */
913static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
914{
915 u64 basemono, next_tick, delta, expires;
916 unsigned long basejiff;
917 int tick_cpu;
918
919 basemono = get_jiffies_update(basej: &basejiff);
920 ts->last_jiffies = basejiff;
921 ts->timer_expires_base = basemono;
922
923 /*
924 * Keep the periodic tick, when RCU, architecture or irq_work
925 * requests it.
926 * Aside of that, check whether the local timer softirq is
927 * pending. If so, its a bad idea to call get_next_timer_interrupt(),
928 * because there is an already expired timer, so it will request
929 * immediate expiry, which rearms the hardware timer with a
930 * minimal delta, which brings us back to this place
931 * immediately. Lather, rinse and repeat...
932 */
933 if (rcu_needs_cpu() || arch_needs_cpu() ||
934 irq_work_needs_cpu() || local_timer_softirq_pending()) {
935 next_tick = basemono + TICK_NSEC;
936 } else {
937 /*
938 * Get the next pending timer. If high resolution
939 * timers are enabled this only takes the timer wheel
940 * timers into account. If high resolution timers are
941 * disabled this also looks at the next expiring
942 * hrtimer.
943 */
944 next_tick = get_next_timer_interrupt(basej: basejiff, basem: basemono);
945 ts->next_timer = next_tick;
946 }
947
948 /* Make sure next_tick is never before basemono! */
949 if (WARN_ON_ONCE(basemono > next_tick))
950 next_tick = basemono;
951
952 /*
953 * If the tick is due in the next period, keep it ticking or
954 * force prod the timer.
955 */
956 delta = next_tick - basemono;
957 if (delta <= (u64)TICK_NSEC) {
958 /*
959 * We've not stopped the tick yet, and there's a timer in the
960 * next period, so no point in stopping it either, bail.
961 */
962 if (!tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
963 ts->timer_expires = 0;
964 goto out;
965 }
966 }
967
968 /*
969 * If this CPU is the one which had the do_timer() duty last, we limit
970 * the sleep time to the timekeeping 'max_deferment' value.
971 * Otherwise we can sleep as long as we want.
972 */
973 delta = timekeeping_max_deferment();
974 tick_cpu = READ_ONCE(tick_do_timer_cpu);
975 if (tick_cpu != cpu &&
976 (tick_cpu != TICK_DO_TIMER_NONE || !tick_sched_flag_test(ts, TS_FLAG_DO_TIMER_LAST)))
977 delta = KTIME_MAX;
978
979 /* Calculate the next expiry time */
980 if (delta < (KTIME_MAX - basemono))
981 expires = basemono + delta;
982 else
983 expires = KTIME_MAX;
984
985 ts->timer_expires = min_t(u64, expires, next_tick);
986
987out:
988 return ts->timer_expires;
989}
990
991static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
992{
993 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
994 unsigned long basejiff = ts->last_jiffies;
995 u64 basemono = ts->timer_expires_base;
996 bool timer_idle = tick_sched_flag_test(ts, TS_FLAG_STOPPED);
997 int tick_cpu;
998 u64 expires;
999
1000 /* Make sure we won't be trying to stop it twice in a row. */
1001 ts->timer_expires_base = 0;
1002
1003 /*
1004 * Now the tick should be stopped definitely - so the timer base needs
1005 * to be marked idle as well to not miss a newly queued timer.
1006 */
1007 expires = timer_base_try_to_set_idle(basej: basejiff, basem: basemono, idle: &timer_idle);
1008 if (expires > ts->timer_expires) {
1009 /*
1010 * This path could only happen when the first timer was removed
1011 * between calculating the possible sleep length and now (when
1012 * high resolution mode is not active, timer could also be a
1013 * hrtimer).
1014 *
1015 * We have to stick to the original calculated expiry value to
1016 * not stop the tick for too long with a shallow C-state (which
1017 * was programmed by cpuidle because of an early next expiration
1018 * value).
1019 */
1020 expires = ts->timer_expires;
1021 }
1022
1023 /* If the timer base is not idle, retain the not yet stopped tick. */
1024 if (!timer_idle)
1025 return;
1026
1027 /*
1028 * If this CPU is the one which updates jiffies, then give up
1029 * the assignment and let it be taken by the CPU which runs
1030 * the tick timer next, which might be this CPU as well. If we
1031 * don't drop this here, the jiffies might be stale and
1032 * do_timer() never gets invoked. Keep track of the fact that it
1033 * was the one which had the do_timer() duty last.
1034 */
1035 tick_cpu = READ_ONCE(tick_do_timer_cpu);
1036 if (tick_cpu == cpu) {
1037 WRITE_ONCE(tick_do_timer_cpu, TICK_DO_TIMER_NONE);
1038 tick_sched_flag_set(ts, TS_FLAG_DO_TIMER_LAST);
1039 } else if (tick_cpu != TICK_DO_TIMER_NONE) {
1040 tick_sched_flag_clear(ts, TS_FLAG_DO_TIMER_LAST);
1041 }
1042
1043 /* Skip reprogram of event if it's not changed */
1044 if (tick_sched_flag_test(ts, TS_FLAG_STOPPED) && (expires == ts->next_tick)) {
1045 /* Sanity check: make sure clockevent is actually programmed */
1046 if (expires == KTIME_MAX || ts->next_tick == hrtimer_get_expires(timer: &ts->sched_timer))
1047 return;
1048
1049 WARN_ONCE(1, "basemono: %llu ts->next_tick: %llu dev->next_event: %llu "
1050 "timer->active: %d timer->expires: %llu\n", basemono, ts->next_tick,
1051 dev->next_event, hrtimer_active(&ts->sched_timer),
1052 hrtimer_get_expires(&ts->sched_timer));
1053 }
1054
1055 /*
1056 * tick_nohz_stop_tick() can be called several times before
1057 * tick_nohz_restart_sched_tick() is called. This happens when
1058 * interrupts arrive which do not cause a reschedule. In the first
1059 * call we save the current tick time, so we can restart the
1060 * scheduler tick in tick_nohz_restart_sched_tick().
1061 */
1062 if (!tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
1063 calc_load_nohz_start();
1064 quiet_vmstat();
1065
1066 ts->last_tick = hrtimer_get_expires(timer: &ts->sched_timer);
1067 tick_sched_flag_set(ts, TS_FLAG_STOPPED);
1068 trace_tick_stop(success: 1, TICK_DEP_MASK_NONE);
1069 }
1070
1071 ts->next_tick = expires;
1072
1073 /*
1074 * If the expiration time == KTIME_MAX, then we simply stop
1075 * the tick timer.
1076 */
1077 if (unlikely(expires == KTIME_MAX)) {
1078 if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES))
1079 hrtimer_cancel(timer: &ts->sched_timer);
1080 else
1081 tick_program_event(KTIME_MAX, force: 1);
1082 return;
1083 }
1084
1085 if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES)) {
1086 hrtimer_start(timer: &ts->sched_timer, tim: expires,
1087 mode: HRTIMER_MODE_ABS_PINNED_HARD);
1088 } else {
1089 hrtimer_set_expires(timer: &ts->sched_timer, time: expires);
1090 tick_program_event(expires, force: 1);
1091 }
1092}
1093
1094static void tick_nohz_retain_tick(struct tick_sched *ts)
1095{
1096 ts->timer_expires_base = 0;
1097}
1098
1099#ifdef CONFIG_NO_HZ_FULL
1100static void tick_nohz_full_stop_tick(struct tick_sched *ts, int cpu)
1101{
1102 if (tick_nohz_next_event(ts, cpu))
1103 tick_nohz_stop_tick(ts, cpu);
1104 else
1105 tick_nohz_retain_tick(ts);
1106}
1107#endif /* CONFIG_NO_HZ_FULL */
1108
1109static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
1110{
1111 /* Update jiffies first */
1112 tick_do_update_jiffies64(now);
1113
1114 /*
1115 * Clear the timer idle flag, so we avoid IPIs on remote queueing and
1116 * the clock forward checks in the enqueue path:
1117 */
1118 timer_clear_idle();
1119
1120 calc_load_nohz_stop();
1121 touch_softlockup_watchdog_sched();
1122
1123 /* Cancel the scheduled timer and restore the tick: */
1124 tick_sched_flag_clear(ts, TS_FLAG_STOPPED);
1125 tick_nohz_restart(ts, now);
1126}
1127
1128static void __tick_nohz_full_update_tick(struct tick_sched *ts,
1129 ktime_t now)
1130{
1131#ifdef CONFIG_NO_HZ_FULL
1132 int cpu = smp_processor_id();
1133
1134 if (can_stop_full_tick(cpu, ts))
1135 tick_nohz_full_stop_tick(ts, cpu);
1136 else if (tick_sched_flag_test(ts, TS_FLAG_STOPPED))
1137 tick_nohz_restart_sched_tick(ts, now);
1138#endif
1139}
1140
1141static void tick_nohz_full_update_tick(struct tick_sched *ts)
1142{
1143 if (!tick_nohz_full_cpu(smp_processor_id()))
1144 return;
1145
1146 if (!tick_sched_flag_test(ts, TS_FLAG_NOHZ))
1147 return;
1148
1149 __tick_nohz_full_update_tick(ts, now: ktime_get());
1150}
1151
1152/*
1153 * A pending softirq outside an IRQ (or softirq disabled section) context
1154 * should be waiting for ksoftirqd to handle it. Therefore we shouldn't
1155 * reach this code due to the need_resched() early check in can_stop_idle_tick().
1156 *
1157 * However if we are between CPUHP_AP_SMPBOOT_THREADS and CPU_TEARDOWN_CPU on the
1158 * cpu_down() process, softirqs can still be raised while ksoftirqd is parked,
1159 * triggering the code below, since wakep_softirqd() is ignored.
1160 *
1161 */
1162static bool report_idle_softirq(void)
1163{
1164 static int ratelimit;
1165 unsigned int pending = local_softirq_pending();
1166
1167 if (likely(!pending))
1168 return false;
1169
1170 /* Some softirqs claim to be safe against hotplug and ksoftirqd parking */
1171 if (!cpu_active(smp_processor_id())) {
1172 pending &= ~SOFTIRQ_HOTPLUG_SAFE_MASK;
1173 if (!pending)
1174 return false;
1175 }
1176
1177 /* On RT, softirq handling may be waiting on some lock */
1178 if (local_bh_blocked())
1179 return false;
1180
1181 if (ratelimit < 10) {
1182 pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n",
1183 pending);
1184 ratelimit++;
1185 }
1186
1187 return true;
1188}
1189
1190static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
1191{
1192 WARN_ON_ONCE(cpu_is_offline(cpu));
1193
1194 if (unlikely(!tick_sched_flag_test(ts, TS_FLAG_NOHZ)))
1195 return false;
1196
1197 if (need_resched())
1198 return false;
1199
1200 if (unlikely(report_idle_softirq()))
1201 return false;
1202
1203 if (tick_nohz_full_enabled()) {
1204 int tick_cpu = READ_ONCE(tick_do_timer_cpu);
1205
1206 /*
1207 * Keep the tick alive to guarantee timekeeping progression
1208 * if there are full dynticks CPUs around
1209 */
1210 if (tick_cpu == cpu)
1211 return false;
1212
1213 /* Should not happen for nohz-full */
1214 if (WARN_ON_ONCE(tick_cpu == TICK_DO_TIMER_NONE))
1215 return false;
1216 }
1217
1218 return true;
1219}
1220
1221/**
1222 * tick_nohz_idle_stop_tick - stop the idle tick from the idle task
1223 *
1224 * When the next event is more than a tick into the future, stop the idle tick
1225 */
1226void tick_nohz_idle_stop_tick(void)
1227{
1228 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1229 int cpu = smp_processor_id();
1230 ktime_t expires;
1231
1232 /*
1233 * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the
1234 * tick timer expiration time is known already.
1235 */
1236 if (ts->timer_expires_base)
1237 expires = ts->timer_expires;
1238 else if (can_stop_idle_tick(cpu, ts))
1239 expires = tick_nohz_next_event(ts, cpu);
1240 else
1241 return;
1242
1243 ts->idle_calls++;
1244
1245 if (expires > 0LL) {
1246 int was_stopped = tick_sched_flag_test(ts, TS_FLAG_STOPPED);
1247
1248 tick_nohz_stop_tick(ts, cpu);
1249
1250 ts->idle_sleeps++;
1251 ts->idle_expires = expires;
1252
1253 if (!was_stopped && tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
1254 ts->idle_jiffies = ts->last_jiffies;
1255 nohz_balance_enter_idle(cpu);
1256 }
1257 } else {
1258 tick_nohz_retain_tick(ts);
1259 }
1260}
1261
1262void tick_nohz_idle_retain_tick(void)
1263{
1264 tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched));
1265}
1266
1267/**
1268 * tick_nohz_idle_enter - prepare for entering idle on the current CPU
1269 *
1270 * Called when we start the idle loop.
1271 */
1272void tick_nohz_idle_enter(void)
1273{
1274 struct tick_sched *ts;
1275
1276 lockdep_assert_irqs_enabled();
1277
1278 local_irq_disable();
1279
1280 ts = this_cpu_ptr(&tick_cpu_sched);
1281
1282 WARN_ON_ONCE(ts->timer_expires_base);
1283
1284 tick_sched_flag_set(ts, TS_FLAG_INIDLE);
1285 tick_nohz_start_idle(ts);
1286
1287 local_irq_enable();
1288}
1289
1290/**
1291 * tick_nohz_irq_exit - Notify the tick about IRQ exit
1292 *
1293 * A timer may have been added/modified/deleted either by the current IRQ,
1294 * or by another place using this IRQ as a notification. This IRQ may have
1295 * also updated the RCU callback list. These events may require a
1296 * re-evaluation of the next tick. Depending on the context:
1297 *
1298 * 1) If the CPU is idle and no resched is pending, just proceed with idle
1299 * time accounting. The next tick will be re-evaluated on the next idle
1300 * loop iteration.
1301 *
1302 * 2) If the CPU is nohz_full:
1303 *
1304 * 2.1) If there is any tick dependency, restart the tick if stopped.
1305 *
1306 * 2.2) If there is no tick dependency, (re-)evaluate the next tick and
1307 * stop/update it accordingly.
1308 */
1309void tick_nohz_irq_exit(void)
1310{
1311 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1312
1313 if (tick_sched_flag_test(ts, TS_FLAG_INIDLE))
1314 tick_nohz_start_idle(ts);
1315 else
1316 tick_nohz_full_update_tick(ts);
1317}
1318
1319/**
1320 * tick_nohz_idle_got_tick - Check whether or not the tick handler has run
1321 *
1322 * Return: %true if the tick handler has run, otherwise %false
1323 */
1324bool tick_nohz_idle_got_tick(void)
1325{
1326 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1327
1328 if (ts->got_idle_tick) {
1329 ts->got_idle_tick = 0;
1330 return true;
1331 }
1332 return false;
1333}
1334
1335/**
1336 * tick_nohz_get_next_hrtimer - return the next expiration time for the hrtimer
1337 * or the tick, whichever expires first. Note that, if the tick has been
1338 * stopped, it returns the next hrtimer.
1339 *
1340 * Called from power state control code with interrupts disabled
1341 *
1342 * Return: the next expiration time
1343 */
1344ktime_t tick_nohz_get_next_hrtimer(void)
1345{
1346 return __this_cpu_read(tick_cpu_device.evtdev)->next_event;
1347}
1348
1349/**
1350 * tick_nohz_get_sleep_length - return the expected length of the current sleep
1351 * @delta_next: duration until the next event if the tick cannot be stopped
1352 *
1353 * Called from power state control code with interrupts disabled.
1354 *
1355 * The return value of this function and/or the value returned by it through the
1356 * @delta_next pointer can be negative which must be taken into account by its
1357 * callers.
1358 *
1359 * Return: the expected length of the current sleep
1360 */
1361ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
1362{
1363 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
1364 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1365 int cpu = smp_processor_id();
1366 /*
1367 * The idle entry time is expected to be a sufficient approximation of
1368 * the current time at this point.
1369 */
1370 ktime_t now = ts->idle_entrytime;
1371 ktime_t next_event;
1372
1373 WARN_ON_ONCE(!tick_sched_flag_test(ts, TS_FLAG_INIDLE));
1374
1375 *delta_next = ktime_sub(dev->next_event, now);
1376
1377 if (!can_stop_idle_tick(cpu, ts))
1378 return *delta_next;
1379
1380 next_event = tick_nohz_next_event(ts, cpu);
1381 if (!next_event)
1382 return *delta_next;
1383
1384 /*
1385 * If the next highres timer to expire is earlier than 'next_event', the
1386 * idle governor needs to know that.
1387 */
1388 next_event = min_t(u64, next_event,
1389 hrtimer_next_event_without(&ts->sched_timer));
1390
1391 return ktime_sub(next_event, now);
1392}
1393
1394/**
1395 * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
1396 * for a particular CPU.
1397 * @cpu: target CPU number
1398 *
1399 * Called from the schedutil frequency scaling governor in scheduler context.
1400 *
1401 * Return: the current idle calls counter value for @cpu
1402 */
1403unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
1404{
1405 struct tick_sched *ts = tick_get_tick_sched(cpu);
1406
1407 return ts->idle_calls;
1408}
1409
1410static void tick_nohz_account_idle_time(struct tick_sched *ts,
1411 ktime_t now)
1412{
1413 unsigned long ticks;
1414
1415 ts->idle_exittime = now;
1416
1417 if (vtime_accounting_enabled_this_cpu())
1418 return;
1419 /*
1420 * We stopped the tick in idle. update_process_times() would miss the
1421 * time we slept, as it does only a 1 tick accounting.
1422 * Enforce that this is accounted to idle !
1423 */
1424 ticks = jiffies - ts->idle_jiffies;
1425 /*
1426 * We might be one off. Do not randomly account a huge number of ticks!
1427 */
1428 if (ticks && ticks < LONG_MAX)
1429 account_idle_ticks(ticks);
1430}
1431
1432void tick_nohz_idle_restart_tick(void)
1433{
1434 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1435
1436 if (tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
1437 ktime_t now = ktime_get();
1438 tick_nohz_restart_sched_tick(ts, now);
1439 tick_nohz_account_idle_time(ts, now);
1440 }
1441}
1442
1443static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now)
1444{
1445 if (tick_nohz_full_cpu(smp_processor_id()))
1446 __tick_nohz_full_update_tick(ts, now);
1447 else
1448 tick_nohz_restart_sched_tick(ts, now);
1449
1450 tick_nohz_account_idle_time(ts, now);
1451}
1452
1453/**
1454 * tick_nohz_idle_exit - Update the tick upon idle task exit
1455 *
1456 * When the idle task exits, update the tick depending on the
1457 * following situations:
1458 *
1459 * 1) If the CPU is not in nohz_full mode (most cases), then
1460 * restart the tick.
1461 *
1462 * 2) If the CPU is in nohz_full mode (corner case):
1463 * 2.1) If the tick can be kept stopped (no tick dependencies)
1464 * then re-evaluate the next tick and try to keep it stopped
1465 * as long as possible.
1466 * 2.2) If the tick has dependencies, restart the tick.
1467 *
1468 */
1469void tick_nohz_idle_exit(void)
1470{
1471 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1472 bool idle_active, tick_stopped;
1473 ktime_t now;
1474
1475 local_irq_disable();
1476
1477 WARN_ON_ONCE(!tick_sched_flag_test(ts, TS_FLAG_INIDLE));
1478 WARN_ON_ONCE(ts->timer_expires_base);
1479
1480 tick_sched_flag_clear(ts, TS_FLAG_INIDLE);
1481 idle_active = tick_sched_flag_test(ts, TS_FLAG_IDLE_ACTIVE);
1482 tick_stopped = tick_sched_flag_test(ts, TS_FLAG_STOPPED);
1483
1484 if (idle_active || tick_stopped)
1485 now = ktime_get();
1486
1487 if (idle_active)
1488 tick_nohz_stop_idle(ts, now);
1489
1490 if (tick_stopped)
1491 tick_nohz_idle_update_tick(ts, now);
1492
1493 local_irq_enable();
1494}
1495
1496/*
1497 * In low-resolution mode, the tick handler must be implemented directly
1498 * at the clockevent level. hrtimer can't be used instead, because its
1499 * infrastructure actually relies on the tick itself as a backend in
1500 * low-resolution mode (see hrtimer_run_queues()).
1501 */
1502static void tick_nohz_lowres_handler(struct clock_event_device *dev)
1503{
1504 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1505
1506 dev->next_event = KTIME_MAX;
1507
1508 if (likely(tick_nohz_handler(&ts->sched_timer) == HRTIMER_RESTART))
1509 tick_program_event(expires: hrtimer_get_expires(timer: &ts->sched_timer), force: 1);
1510}
1511
1512static inline void tick_nohz_activate(struct tick_sched *ts)
1513{
1514 if (!tick_nohz_enabled)
1515 return;
1516 tick_sched_flag_set(ts, TS_FLAG_NOHZ);
1517 /* One update is enough */
1518 if (!test_and_set_bit(nr: 0, addr: &tick_nohz_active))
1519 timers_update_nohz();
1520}
1521
1522/**
1523 * tick_nohz_switch_to_nohz - switch to NOHZ mode
1524 */
1525static void tick_nohz_switch_to_nohz(void)
1526{
1527 if (!tick_nohz_enabled)
1528 return;
1529
1530 if (tick_switch_to_oneshot(handler: tick_nohz_lowres_handler))
1531 return;
1532
1533 /*
1534 * Recycle the hrtimer in 'ts', so we can share the
1535 * highres code.
1536 */
1537 tick_setup_sched_timer(hrtimer: false);
1538}
1539
1540static inline void tick_nohz_irq_enter(void)
1541{
1542 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1543 ktime_t now;
1544
1545 if (!tick_sched_flag_test(ts, TS_FLAG_STOPPED | TS_FLAG_IDLE_ACTIVE))
1546 return;
1547 now = ktime_get();
1548 if (tick_sched_flag_test(ts, TS_FLAG_IDLE_ACTIVE))
1549 tick_nohz_stop_idle(ts, now);
1550 /*
1551 * If all CPUs are idle we may need to update a stale jiffies value.
1552 * Note nohz_full is a special case: a timekeeper is guaranteed to stay
1553 * alive but it might be busy looping with interrupts disabled in some
1554 * rare case (typically stop machine). So we must make sure we have a
1555 * last resort.
1556 */
1557 if (tick_sched_flag_test(ts, TS_FLAG_STOPPED))
1558 tick_nohz_update_jiffies(now);
1559}
1560
1561#else
1562
1563static inline void tick_nohz_switch_to_nohz(void) { }
1564static inline void tick_nohz_irq_enter(void) { }
1565static inline void tick_nohz_activate(struct tick_sched *ts) { }
1566
1567#endif /* CONFIG_NO_HZ_COMMON */
1568
1569/*
1570 * Called from irq_enter() to notify about the possible interruption of idle()
1571 */
1572void tick_irq_enter(void)
1573{
1574 tick_check_oneshot_broadcast_this_cpu();
1575 tick_nohz_irq_enter();
1576}
1577
1578static int sched_skew_tick;
1579
1580static int __init skew_tick(char *str)
1581{
1582 get_option(str: &str, pint: &sched_skew_tick);
1583
1584 return 0;
1585}
1586early_param("skew_tick", skew_tick);
1587
1588/**
1589 * tick_setup_sched_timer - setup the tick emulation timer
1590 * @hrtimer: whether to use the hrtimer or not
1591 */
1592void tick_setup_sched_timer(bool hrtimer)
1593{
1594 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1595
1596 /* Emulate tick processing via per-CPU hrtimers: */
1597 hrtimer_setup(timer: &ts->sched_timer, function: tick_nohz_handler, CLOCK_MONOTONIC, mode: HRTIMER_MODE_ABS_HARD);
1598
1599 if (IS_ENABLED(CONFIG_HIGH_RES_TIMERS) && hrtimer)
1600 tick_sched_flag_set(ts, TS_FLAG_HIGHRES);
1601
1602 /* Get the next period (per-CPU) */
1603 hrtimer_set_expires(timer: &ts->sched_timer, time: tick_init_jiffy_update());
1604
1605 /* Offset the tick to avert 'jiffies_lock' contention. */
1606 if (sched_skew_tick) {
1607 u64 offset = TICK_NSEC >> 1;
1608 do_div(offset, num_possible_cpus());
1609 offset *= smp_processor_id();
1610 hrtimer_add_expires_ns(timer: &ts->sched_timer, ns: offset);
1611 }
1612
1613 hrtimer_forward_now(timer: &ts->sched_timer, TICK_NSEC);
1614 if (IS_ENABLED(CONFIG_HIGH_RES_TIMERS) && hrtimer)
1615 hrtimer_start_expires(timer: &ts->sched_timer, mode: HRTIMER_MODE_ABS_PINNED_HARD);
1616 else
1617 tick_program_event(expires: hrtimer_get_expires(timer: &ts->sched_timer), force: 1);
1618 tick_nohz_activate(ts);
1619}
1620
1621/*
1622 * Shut down the tick and make sure the CPU won't try to retake the timekeeping
1623 * duty before disabling IRQs in idle for the last time.
1624 */
1625void tick_sched_timer_dying(int cpu)
1626{
1627 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1628 ktime_t idle_sleeptime, iowait_sleeptime;
1629 unsigned long idle_calls, idle_sleeps;
1630
1631 /* This must happen before hrtimers are migrated! */
1632 if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES))
1633 hrtimer_cancel(timer: &ts->sched_timer);
1634
1635 idle_sleeptime = ts->idle_sleeptime;
1636 iowait_sleeptime = ts->iowait_sleeptime;
1637 idle_calls = ts->idle_calls;
1638 idle_sleeps = ts->idle_sleeps;
1639 memset(ts, 0, sizeof(*ts));
1640 ts->idle_sleeptime = idle_sleeptime;
1641 ts->iowait_sleeptime = iowait_sleeptime;
1642 ts->idle_calls = idle_calls;
1643 ts->idle_sleeps = idle_sleeps;
1644}
1645
1646/*
1647 * Async notification about clocksource changes
1648 */
1649void tick_clock_notify(void)
1650{
1651 int cpu;
1652
1653 for_each_possible_cpu(cpu)
1654 set_bit(nr: 0, addr: &per_cpu(tick_cpu_sched, cpu).check_clocks);
1655}
1656
1657/*
1658 * Async notification about clock event changes
1659 */
1660void tick_oneshot_notify(void)
1661{
1662 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1663
1664 set_bit(nr: 0, addr: &ts->check_clocks);
1665}
1666
1667/*
1668 * Check if a change happened, which makes oneshot possible.
1669 *
1670 * Called cyclically from the hrtimer softirq (driven by the timer
1671 * softirq). 'allow_nohz' signals that we can switch into low-res NOHZ
1672 * mode, because high resolution timers are disabled (either compile
1673 * or runtime). Called with interrupts disabled.
1674 */
1675int tick_check_oneshot_change(int allow_nohz)
1676{
1677 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1678
1679 if (!test_and_clear_bit(nr: 0, addr: &ts->check_clocks))
1680 return 0;
1681
1682 if (tick_sched_flag_test(ts, TS_FLAG_NOHZ))
1683 return 0;
1684
1685 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1686 return 0;
1687
1688 if (!allow_nohz)
1689 return 1;
1690
1691 tick_nohz_switch_to_nohz();
1692 return 0;
1693}
1694

source code of linux/kernel/time/tick-sched.c