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