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TOMOYO Linux Cross Reference
Linux/kernel/time/tick-sched.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
  4  *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
  5  *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
  6  *
  7  *  No idle tick implementation for low and high resolution timers
  8  *
  9  *  Started by: Thomas Gleixner and Ingo Molnar
 10  */
 11 #include <linux/cpu.h>
 12 #include <linux/err.h>
 13 #include <linux/hrtimer.h>
 14 #include <linux/interrupt.h>
 15 #include <linux/kernel_stat.h>
 16 #include <linux/percpu.h>
 17 #include <linux/nmi.h>
 18 #include <linux/profile.h>
 19 #include <linux/sched/signal.h>
 20 #include <linux/sched/clock.h>
 21 #include <linux/sched/stat.h>
 22 #include <linux/sched/nohz.h>
 23 #include <linux/module.h>
 24 #include <linux/irq_work.h>
 25 #include <linux/posix-timers.h>
 26 #include <linux/context_tracking.h>
 27 #include <linux/mm.h>
 28 
 29 #include <asm/irq_regs.h>
 30 
 31 #include "tick-internal.h"
 32 
 33 #include <trace/events/timer.h>
 34 
 35 /*
 36  * Per-CPU nohz control structure
 37  */
 38 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 39 
 40 struct tick_sched *tick_get_tick_sched(int cpu)
 41 {
 42         return &per_cpu(tick_cpu_sched, cpu);
 43 }
 44 
 45 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
 46 /*
 47  * The time, when the last jiffy update happened. Protected by jiffies_lock.
 48  */
 49 static ktime_t last_jiffies_update;
 50 
 51 /*
 52  * Must be called with interrupts disabled !
 53  */
 54 static void tick_do_update_jiffies64(ktime_t now)
 55 {
 56         unsigned long ticks = 0;
 57         ktime_t delta;
 58 
 59         /*
 60          * Do a quick check without holding jiffies_lock:
 61          */
 62         delta = ktime_sub(now, last_jiffies_update);
 63         if (delta < tick_period)
 64                 return;
 65 
 66         /* Reevaluate with jiffies_lock held */
 67         write_seqlock(&jiffies_lock);
 68 
 69         delta = ktime_sub(now, last_jiffies_update);
 70         if (delta >= tick_period) {
 71 
 72                 delta = ktime_sub(delta, tick_period);
 73                 last_jiffies_update = ktime_add(last_jiffies_update,
 74                                                 tick_period);
 75 
 76                 /* Slow path for long timeouts */
 77                 if (unlikely(delta >= tick_period)) {
 78                         s64 incr = ktime_to_ns(tick_period);
 79 
 80                         ticks = ktime_divns(delta, incr);
 81 
 82                         last_jiffies_update = ktime_add_ns(last_jiffies_update,
 83                                                            incr * ticks);
 84                 }
 85                 do_timer(++ticks);
 86 
 87                 /* Keep the tick_next_period variable up to date */
 88                 tick_next_period = ktime_add(last_jiffies_update, tick_period);
 89         } else {
 90                 write_sequnlock(&jiffies_lock);
 91                 return;
 92         }
 93         write_sequnlock(&jiffies_lock);
 94         update_wall_time();
 95 }
 96 
 97 /*
 98  * Initialize and return retrieve the jiffies update.
 99  */
100 static ktime_t tick_init_jiffy_update(void)
101 {
102         ktime_t period;
103 
104         write_seqlock(&jiffies_lock);
105         /* Did we start the jiffies update yet ? */
106         if (last_jiffies_update == 0)
107                 last_jiffies_update = tick_next_period;
108         period = last_jiffies_update;
109         write_sequnlock(&jiffies_lock);
110         return period;
111 }
112 
113 static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
114 {
115         int cpu = smp_processor_id();
116 
117 #ifdef CONFIG_NO_HZ_COMMON
118         /*
119          * Check if the do_timer duty was dropped. We don't care about
120          * concurrency: This happens only when the CPU in charge went
121          * into a long sleep. If two CPUs happen to assign themselves to
122          * this duty, then the jiffies update is still serialized by
123          * jiffies_lock.
124          */
125         if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
126             && !tick_nohz_full_cpu(cpu))
127                 tick_do_timer_cpu = cpu;
128 #endif
129 
130         /* Check, if the jiffies need an update */
131         if (tick_do_timer_cpu == cpu)
132                 tick_do_update_jiffies64(now);
133 
134         if (ts->inidle)
135                 ts->got_idle_tick = 1;
136 }
137 
138 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
139 {
140 #ifdef CONFIG_NO_HZ_COMMON
141         /*
142          * When we are idle and the tick is stopped, we have to touch
143          * the watchdog as we might not schedule for a really long
144          * time. This happens on complete idle SMP systems while
145          * waiting on the login prompt. We also increment the "start of
146          * idle" jiffy stamp so the idle accounting adjustment we do
147          * when we go busy again does not account too much ticks.
148          */
149         if (ts->tick_stopped) {
150                 touch_softlockup_watchdog_sched();
151                 if (is_idle_task(current))
152                         ts->idle_jiffies++;
153                 /*
154                  * In case the current tick fired too early past its expected
155                  * expiration, make sure we don't bypass the next clock reprogramming
156                  * to the same deadline.
157                  */
158                 ts->next_tick = 0;
159         }
160 #endif
161         update_process_times(user_mode(regs));
162         profile_tick(CPU_PROFILING);
163 }
164 #endif
165 
166 #ifdef CONFIG_NO_HZ_FULL
167 cpumask_var_t tick_nohz_full_mask;
168 bool tick_nohz_full_running;
169 static atomic_t tick_dep_mask;
170 
171 static bool check_tick_dependency(atomic_t *dep)
172 {
173         int val = atomic_read(dep);
174 
175         if (val & TICK_DEP_MASK_POSIX_TIMER) {
176                 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
177                 return true;
178         }
179 
180         if (val & TICK_DEP_MASK_PERF_EVENTS) {
181                 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
182                 return true;
183         }
184 
185         if (val & TICK_DEP_MASK_SCHED) {
186                 trace_tick_stop(0, TICK_DEP_MASK_SCHED);
187                 return true;
188         }
189 
190         if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
191                 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
192                 return true;
193         }
194 
195         return false;
196 }
197 
198 static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
199 {
200         lockdep_assert_irqs_disabled();
201 
202         if (unlikely(!cpu_online(cpu)))
203                 return false;
204 
205         if (check_tick_dependency(&tick_dep_mask))
206                 return false;
207 
208         if (check_tick_dependency(&ts->tick_dep_mask))
209                 return false;
210 
211         if (check_tick_dependency(&current->tick_dep_mask))
212                 return false;
213 
214         if (check_tick_dependency(&current->signal->tick_dep_mask))
215                 return false;
216 
217         return true;
218 }
219 
220 static void nohz_full_kick_func(struct irq_work *work)
221 {
222         /* Empty, the tick restart happens on tick_nohz_irq_exit() */
223 }
224 
225 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
226         .func = nohz_full_kick_func,
227 };
228 
229 /*
230  * Kick this CPU if it's full dynticks in order to force it to
231  * re-evaluate its dependency on the tick and restart it if necessary.
232  * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
233  * is NMI safe.
234  */
235 static void tick_nohz_full_kick(void)
236 {
237         if (!tick_nohz_full_cpu(smp_processor_id()))
238                 return;
239 
240         irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
241 }
242 
243 /*
244  * Kick the CPU if it's full dynticks in order to force it to
245  * re-evaluate its dependency on the tick and restart it if necessary.
246  */
247 void tick_nohz_full_kick_cpu(int cpu)
248 {
249         if (!tick_nohz_full_cpu(cpu))
250                 return;
251 
252         irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
253 }
254 
255 /*
256  * Kick all full dynticks CPUs in order to force these to re-evaluate
257  * their dependency on the tick and restart it if necessary.
258  */
259 static void tick_nohz_full_kick_all(void)
260 {
261         int cpu;
262 
263         if (!tick_nohz_full_running)
264                 return;
265 
266         preempt_disable();
267         for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
268                 tick_nohz_full_kick_cpu(cpu);
269         preempt_enable();
270 }
271 
272 static void tick_nohz_dep_set_all(atomic_t *dep,
273                                   enum tick_dep_bits bit)
274 {
275         int prev;
276 
277         prev = atomic_fetch_or(BIT(bit), dep);
278         if (!prev)
279                 tick_nohz_full_kick_all();
280 }
281 
282 /*
283  * Set a global tick dependency. Used by perf events that rely on freq and
284  * by unstable clock.
285  */
286 void tick_nohz_dep_set(enum tick_dep_bits bit)
287 {
288         tick_nohz_dep_set_all(&tick_dep_mask, bit);
289 }
290 
291 void tick_nohz_dep_clear(enum tick_dep_bits bit)
292 {
293         atomic_andnot(BIT(bit), &tick_dep_mask);
294 }
295 
296 /*
297  * Set per-CPU tick dependency. Used by scheduler and perf events in order to
298  * manage events throttling.
299  */
300 void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
301 {
302         int prev;
303         struct tick_sched *ts;
304 
305         ts = per_cpu_ptr(&tick_cpu_sched, cpu);
306 
307         prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
308         if (!prev) {
309                 preempt_disable();
310                 /* Perf needs local kick that is NMI safe */
311                 if (cpu == smp_processor_id()) {
312                         tick_nohz_full_kick();
313                 } else {
314                         /* Remote irq work not NMI-safe */
315                         if (!WARN_ON_ONCE(in_nmi()))
316                                 tick_nohz_full_kick_cpu(cpu);
317                 }
318                 preempt_enable();
319         }
320 }
321 
322 void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
323 {
324         struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
325 
326         atomic_andnot(BIT(bit), &ts->tick_dep_mask);
327 }
328 
329 /*
330  * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
331  * per task timers.
332  */
333 void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
334 {
335         /*
336          * We could optimize this with just kicking the target running the task
337          * if that noise matters for nohz full users.
338          */
339         tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
340 }
341 
342 void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
343 {
344         atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
345 }
346 
347 /*
348  * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
349  * per process timers.
350  */
351 void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
352 {
353         tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
354 }
355 
356 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
357 {
358         atomic_andnot(BIT(bit), &sig->tick_dep_mask);
359 }
360 
361 /*
362  * Re-evaluate the need for the tick as we switch the current task.
363  * It might need the tick due to per task/process properties:
364  * perf events, posix CPU timers, ...
365  */
366 void __tick_nohz_task_switch(void)
367 {
368         unsigned long flags;
369         struct tick_sched *ts;
370 
371         local_irq_save(flags);
372 
373         if (!tick_nohz_full_cpu(smp_processor_id()))
374                 goto out;
375 
376         ts = this_cpu_ptr(&tick_cpu_sched);
377 
378         if (ts->tick_stopped) {
379                 if (atomic_read(&current->tick_dep_mask) ||
380                     atomic_read(&current->signal->tick_dep_mask))
381                         tick_nohz_full_kick();
382         }
383 out:
384         local_irq_restore(flags);
385 }
386 
387 /* Get the boot-time nohz CPU list from the kernel parameters. */
388 void __init tick_nohz_full_setup(cpumask_var_t cpumask)
389 {
390         alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
391         cpumask_copy(tick_nohz_full_mask, cpumask);
392         tick_nohz_full_running = true;
393 }
394 
395 static int tick_nohz_cpu_down(unsigned int cpu)
396 {
397         /*
398          * The boot CPU handles housekeeping duty (unbound timers,
399          * workqueues, timekeeping, ...) on behalf of full dynticks
400          * CPUs. It must remain online when nohz full is enabled.
401          */
402         if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
403                 return -EBUSY;
404         return 0;
405 }
406 
407 void __init tick_nohz_init(void)
408 {
409         int cpu, ret;
410 
411         if (!tick_nohz_full_running)
412                 return;
413 
414         /*
415          * Full dynticks uses irq work to drive the tick rescheduling on safe
416          * locking contexts. But then we need irq work to raise its own
417          * interrupts to avoid circular dependency on the tick
418          */
419         if (!arch_irq_work_has_interrupt()) {
420                 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
421                 cpumask_clear(tick_nohz_full_mask);
422                 tick_nohz_full_running = false;
423                 return;
424         }
425 
426         cpu = smp_processor_id();
427 
428         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
429                 pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
430                         cpu);
431                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
432         }
433 
434         for_each_cpu(cpu, tick_nohz_full_mask)
435                 context_tracking_cpu_set(cpu);
436 
437         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
438                                         "kernel/nohz:predown", NULL,
439                                         tick_nohz_cpu_down);
440         WARN_ON(ret < 0);
441         pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
442                 cpumask_pr_args(tick_nohz_full_mask));
443 }
444 #endif
445 
446 /*
447  * NOHZ - aka dynamic tick functionality
448  */
449 #ifdef CONFIG_NO_HZ_COMMON
450 /*
451  * NO HZ enabled ?
452  */
453 bool tick_nohz_enabled __read_mostly  = true;
454 unsigned long tick_nohz_active  __read_mostly;
455 /*
456  * Enable / Disable tickless mode
457  */
458 static int __init setup_tick_nohz(char *str)
459 {
460         return (kstrtobool(str, &tick_nohz_enabled) == 0);
461 }
462 
463 __setup("nohz=", setup_tick_nohz);
464 
465 bool tick_nohz_tick_stopped(void)
466 {
467         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
468 
469         return ts->tick_stopped;
470 }
471 
472 bool tick_nohz_tick_stopped_cpu(int cpu)
473 {
474         struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
475 
476         return ts->tick_stopped;
477 }
478 
479 /**
480  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
481  *
482  * Called from interrupt entry when the CPU was idle
483  *
484  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
485  * must be updated. Otherwise an interrupt handler could use a stale jiffy
486  * value. We do this unconditionally on any CPU, as we don't know whether the
487  * CPU, which has the update task assigned is in a long sleep.
488  */
489 static void tick_nohz_update_jiffies(ktime_t now)
490 {
491         unsigned long flags;
492 
493         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
494 
495         local_irq_save(flags);
496         tick_do_update_jiffies64(now);
497         local_irq_restore(flags);
498 
499         touch_softlockup_watchdog_sched();
500 }
501 
502 /*
503  * Updates the per-CPU time idle statistics counters
504  */
505 static void
506 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
507 {
508         ktime_t delta;
509 
510         if (ts->idle_active) {
511                 delta = ktime_sub(now, ts->idle_entrytime);
512                 if (nr_iowait_cpu(cpu) > 0)
513                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
514                 else
515                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
516                 ts->idle_entrytime = now;
517         }
518 
519         if (last_update_time)
520                 *last_update_time = ktime_to_us(now);
521 
522 }
523 
524 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
525 {
526         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
527         ts->idle_active = 0;
528 
529         sched_clock_idle_wakeup_event();
530 }
531 
532 static void tick_nohz_start_idle(struct tick_sched *ts)
533 {
534         ts->idle_entrytime = ktime_get();
535         ts->idle_active = 1;
536         sched_clock_idle_sleep_event();
537 }
538 
539 /**
540  * get_cpu_idle_time_us - get the total idle time of a CPU
541  * @cpu: CPU number to query
542  * @last_update_time: variable to store update time in. Do not update
543  * counters if NULL.
544  *
545  * Return the cumulative idle time (since boot) for a given
546  * CPU, in microseconds.
547  *
548  * This time is measured via accounting rather than sampling,
549  * and is as accurate as ktime_get() is.
550  *
551  * This function returns -1 if NOHZ is not enabled.
552  */
553 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
554 {
555         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
556         ktime_t now, idle;
557 
558         if (!tick_nohz_active)
559                 return -1;
560 
561         now = ktime_get();
562         if (last_update_time) {
563                 update_ts_time_stats(cpu, ts, now, last_update_time);
564                 idle = ts->idle_sleeptime;
565         } else {
566                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
567                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
568 
569                         idle = ktime_add(ts->idle_sleeptime, delta);
570                 } else {
571                         idle = ts->idle_sleeptime;
572                 }
573         }
574 
575         return ktime_to_us(idle);
576 
577 }
578 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
579 
580 /**
581  * get_cpu_iowait_time_us - get the total iowait time of a CPU
582  * @cpu: CPU number to query
583  * @last_update_time: variable to store update time in. Do not update
584  * counters if NULL.
585  *
586  * Return the cumulative iowait time (since boot) for a given
587  * CPU, in microseconds.
588  *
589  * This time is measured via accounting rather than sampling,
590  * and is as accurate as ktime_get() is.
591  *
592  * This function returns -1 if NOHZ is not enabled.
593  */
594 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
595 {
596         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
597         ktime_t now, iowait;
598 
599         if (!tick_nohz_active)
600                 return -1;
601 
602         now = ktime_get();
603         if (last_update_time) {
604                 update_ts_time_stats(cpu, ts, now, last_update_time);
605                 iowait = ts->iowait_sleeptime;
606         } else {
607                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
608                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
609 
610                         iowait = ktime_add(ts->iowait_sleeptime, delta);
611                 } else {
612                         iowait = ts->iowait_sleeptime;
613                 }
614         }
615 
616         return ktime_to_us(iowait);
617 }
618 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
619 
620 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
621 {
622         hrtimer_cancel(&ts->sched_timer);
623         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
624 
625         /* Forward the time to expire in the future */
626         hrtimer_forward(&ts->sched_timer, now, tick_period);
627 
628         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
629                 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
630         else
631                 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
632 
633         /*
634          * Reset to make sure next tick stop doesn't get fooled by past
635          * cached clock deadline.
636          */
637         ts->next_tick = 0;
638 }
639 
640 static inline bool local_timer_softirq_pending(void)
641 {
642         return local_softirq_pending() & BIT(TIMER_SOFTIRQ);
643 }
644 
645 static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
646 {
647         u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
648         unsigned long seq, basejiff;
649 
650         /* Read jiffies and the time when jiffies were updated last */
651         do {
652                 seq = read_seqbegin(&jiffies_lock);
653                 basemono = last_jiffies_update;
654                 basejiff = jiffies;
655         } while (read_seqretry(&jiffies_lock, seq));
656         ts->last_jiffies = basejiff;
657         ts->timer_expires_base = basemono;
658 
659         /*
660          * Keep the periodic tick, when RCU, architecture or irq_work
661          * requests it.
662          * Aside of that check whether the local timer softirq is
663          * pending. If so its a bad idea to call get_next_timer_interrupt()
664          * because there is an already expired timer, so it will request
665          * immeditate expiry, which rearms the hardware timer with a
666          * minimal delta which brings us back to this place
667          * immediately. Lather, rinse and repeat...
668          */
669         if (rcu_needs_cpu(basemono, &next_rcu) || arch_needs_cpu() ||
670             irq_work_needs_cpu() || local_timer_softirq_pending()) {
671                 next_tick = basemono + TICK_NSEC;
672         } else {
673                 /*
674                  * Get the next pending timer. If high resolution
675                  * timers are enabled this only takes the timer wheel
676                  * timers into account. If high resolution timers are
677                  * disabled this also looks at the next expiring
678                  * hrtimer.
679                  */
680                 next_tmr = get_next_timer_interrupt(basejiff, basemono);
681                 ts->next_timer = next_tmr;
682                 /* Take the next rcu event into account */
683                 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
684         }
685 
686         /*
687          * If the tick is due in the next period, keep it ticking or
688          * force prod the timer.
689          */
690         delta = next_tick - basemono;
691         if (delta <= (u64)TICK_NSEC) {
692                 /*
693                  * Tell the timer code that the base is not idle, i.e. undo
694                  * the effect of get_next_timer_interrupt():
695                  */
696                 timer_clear_idle();
697                 /*
698                  * We've not stopped the tick yet, and there's a timer in the
699                  * next period, so no point in stopping it either, bail.
700                  */
701                 if (!ts->tick_stopped) {
702                         ts->timer_expires = 0;
703                         goto out;
704                 }
705         }
706 
707         /*
708          * If this CPU is the one which had the do_timer() duty last, we limit
709          * the sleep time to the timekeeping max_deferment value.
710          * Otherwise we can sleep as long as we want.
711          */
712         delta = timekeeping_max_deferment();
713         if (cpu != tick_do_timer_cpu &&
714             (tick_do_timer_cpu != TICK_DO_TIMER_NONE || !ts->do_timer_last))
715                 delta = KTIME_MAX;
716 
717         /* Calculate the next expiry time */
718         if (delta < (KTIME_MAX - basemono))
719                 expires = basemono + delta;
720         else
721                 expires = KTIME_MAX;
722 
723         ts->timer_expires = min_t(u64, expires, next_tick);
724 
725 out:
726         return ts->timer_expires;
727 }
728 
729 static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
730 {
731         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
732         u64 basemono = ts->timer_expires_base;
733         u64 expires = ts->timer_expires;
734         ktime_t tick = expires;
735 
736         /* Make sure we won't be trying to stop it twice in a row. */
737         ts->timer_expires_base = 0;
738 
739         /*
740          * If this CPU is the one which updates jiffies, then give up
741          * the assignment and let it be taken by the CPU which runs
742          * the tick timer next, which might be this CPU as well. If we
743          * don't drop this here the jiffies might be stale and
744          * do_timer() never invoked. Keep track of the fact that it
745          * was the one which had the do_timer() duty last.
746          */
747         if (cpu == tick_do_timer_cpu) {
748                 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
749                 ts->do_timer_last = 1;
750         } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
751                 ts->do_timer_last = 0;
752         }
753 
754         /* Skip reprogram of event if its not changed */
755         if (ts->tick_stopped && (expires == ts->next_tick)) {
756                 /* Sanity check: make sure clockevent is actually programmed */
757                 if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer))
758                         return;
759 
760                 WARN_ON_ONCE(1);
761                 printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n",
762                             basemono, ts->next_tick, dev->next_event,
763                             hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer));
764         }
765 
766         /*
767          * nohz_stop_sched_tick can be called several times before
768          * the nohz_restart_sched_tick is called. This happens when
769          * interrupts arrive which do not cause a reschedule. In the
770          * first call we save the current tick time, so we can restart
771          * the scheduler tick in nohz_restart_sched_tick.
772          */
773         if (!ts->tick_stopped) {
774                 calc_load_nohz_start();
775                 cpu_load_update_nohz_start();
776                 quiet_vmstat();
777 
778                 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
779                 ts->tick_stopped = 1;
780                 trace_tick_stop(1, TICK_DEP_MASK_NONE);
781         }
782 
783         ts->next_tick = tick;
784 
785         /*
786          * If the expiration time == KTIME_MAX, then we simply stop
787          * the tick timer.
788          */
789         if (unlikely(expires == KTIME_MAX)) {
790                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
791                         hrtimer_cancel(&ts->sched_timer);
792                 return;
793         }
794 
795         if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
796                 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
797         } else {
798                 hrtimer_set_expires(&ts->sched_timer, tick);
799                 tick_program_event(tick, 1);
800         }
801 }
802 
803 static void tick_nohz_retain_tick(struct tick_sched *ts)
804 {
805         ts->timer_expires_base = 0;
806 }
807 
808 #ifdef CONFIG_NO_HZ_FULL
809 static void tick_nohz_stop_sched_tick(struct tick_sched *ts, int cpu)
810 {
811         if (tick_nohz_next_event(ts, cpu))
812                 tick_nohz_stop_tick(ts, cpu);
813         else
814                 tick_nohz_retain_tick(ts);
815 }
816 #endif /* CONFIG_NO_HZ_FULL */
817 
818 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
819 {
820         /* Update jiffies first */
821         tick_do_update_jiffies64(now);
822         cpu_load_update_nohz_stop();
823 
824         /*
825          * Clear the timer idle flag, so we avoid IPIs on remote queueing and
826          * the clock forward checks in the enqueue path:
827          */
828         timer_clear_idle();
829 
830         calc_load_nohz_stop();
831         touch_softlockup_watchdog_sched();
832         /*
833          * Cancel the scheduled timer and restore the tick
834          */
835         ts->tick_stopped  = 0;
836         ts->idle_exittime = now;
837 
838         tick_nohz_restart(ts, now);
839 }
840 
841 static void tick_nohz_full_update_tick(struct tick_sched *ts)
842 {
843 #ifdef CONFIG_NO_HZ_FULL
844         int cpu = smp_processor_id();
845 
846         if (!tick_nohz_full_cpu(cpu))
847                 return;
848 
849         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
850                 return;
851 
852         if (can_stop_full_tick(cpu, ts))
853                 tick_nohz_stop_sched_tick(ts, cpu);
854         else if (ts->tick_stopped)
855                 tick_nohz_restart_sched_tick(ts, ktime_get());
856 #endif
857 }
858 
859 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
860 {
861         /*
862          * If this CPU is offline and it is the one which updates
863          * jiffies, then give up the assignment and let it be taken by
864          * the CPU which runs the tick timer next. If we don't drop
865          * this here the jiffies might be stale and do_timer() never
866          * invoked.
867          */
868         if (unlikely(!cpu_online(cpu))) {
869                 if (cpu == tick_do_timer_cpu)
870                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
871                 /*
872                  * Make sure the CPU doesn't get fooled by obsolete tick
873                  * deadline if it comes back online later.
874                  */
875                 ts->next_tick = 0;
876                 return false;
877         }
878 
879         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
880                 return false;
881 
882         if (need_resched())
883                 return false;
884 
885         if (unlikely(local_softirq_pending())) {
886                 static int ratelimit;
887 
888                 if (ratelimit < 10 &&
889                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
890                         pr_warn("NOHZ: local_softirq_pending %02x\n",
891                                 (unsigned int) local_softirq_pending());
892                         ratelimit++;
893                 }
894                 return false;
895         }
896 
897         if (tick_nohz_full_enabled()) {
898                 /*
899                  * Keep the tick alive to guarantee timekeeping progression
900                  * if there are full dynticks CPUs around
901                  */
902                 if (tick_do_timer_cpu == cpu)
903                         return false;
904                 /*
905                  * Boot safety: make sure the timekeeping duty has been
906                  * assigned before entering dyntick-idle mode,
907                  */
908                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
909                         return false;
910         }
911 
912         return true;
913 }
914 
915 static void __tick_nohz_idle_stop_tick(struct tick_sched *ts)
916 {
917         ktime_t expires;
918         int cpu = smp_processor_id();
919 
920         /*
921          * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the
922          * tick timer expiration time is known already.
923          */
924         if (ts->timer_expires_base)
925                 expires = ts->timer_expires;
926         else if (can_stop_idle_tick(cpu, ts))
927                 expires = tick_nohz_next_event(ts, cpu);
928         else
929                 return;
930 
931         ts->idle_calls++;
932 
933         if (expires > 0LL) {
934                 int was_stopped = ts->tick_stopped;
935 
936                 tick_nohz_stop_tick(ts, cpu);
937 
938                 ts->idle_sleeps++;
939                 ts->idle_expires = expires;
940 
941                 if (!was_stopped && ts->tick_stopped) {
942                         ts->idle_jiffies = ts->last_jiffies;
943                         nohz_balance_enter_idle(cpu);
944                 }
945         } else {
946                 tick_nohz_retain_tick(ts);
947         }
948 }
949 
950 /**
951  * tick_nohz_idle_stop_tick - stop the idle tick from the idle task
952  *
953  * When the next event is more than a tick into the future, stop the idle tick
954  */
955 void tick_nohz_idle_stop_tick(void)
956 {
957         __tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched));
958 }
959 
960 void tick_nohz_idle_retain_tick(void)
961 {
962         tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched));
963         /*
964          * Undo the effect of get_next_timer_interrupt() called from
965          * tick_nohz_next_event().
966          */
967         timer_clear_idle();
968 }
969 
970 /**
971  * tick_nohz_idle_enter - prepare for entering idle on the current CPU
972  *
973  * Called when we start the idle loop.
974  */
975 void tick_nohz_idle_enter(void)
976 {
977         struct tick_sched *ts;
978 
979         lockdep_assert_irqs_enabled();
980 
981         local_irq_disable();
982 
983         ts = this_cpu_ptr(&tick_cpu_sched);
984 
985         WARN_ON_ONCE(ts->timer_expires_base);
986 
987         ts->inidle = 1;
988         tick_nohz_start_idle(ts);
989 
990         local_irq_enable();
991 }
992 
993 /**
994  * tick_nohz_irq_exit - update next tick event from interrupt exit
995  *
996  * When an interrupt fires while we are idle and it doesn't cause
997  * a reschedule, it may still add, modify or delete a timer, enqueue
998  * an RCU callback, etc...
999  * So we need to re-calculate and reprogram the next tick event.
1000  */
1001 void tick_nohz_irq_exit(void)
1002 {
1003         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1004 
1005         if (ts->inidle)
1006                 tick_nohz_start_idle(ts);
1007         else
1008                 tick_nohz_full_update_tick(ts);
1009 }
1010 
1011 /**
1012  * tick_nohz_idle_got_tick - Check whether or not the tick handler has run
1013  */
1014 bool tick_nohz_idle_got_tick(void)
1015 {
1016         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1017 
1018         if (ts->got_idle_tick) {
1019                 ts->got_idle_tick = 0;
1020                 return true;
1021         }
1022         return false;
1023 }
1024 
1025 /**
1026  * tick_nohz_get_sleep_length - return the expected length of the current sleep
1027  * @delta_next: duration until the next event if the tick cannot be stopped
1028  *
1029  * Called from power state control code with interrupts disabled
1030  */
1031 ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
1032 {
1033         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
1034         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1035         int cpu = smp_processor_id();
1036         /*
1037          * The idle entry time is expected to be a sufficient approximation of
1038          * the current time at this point.
1039          */
1040         ktime_t now = ts->idle_entrytime;
1041         ktime_t next_event;
1042 
1043         WARN_ON_ONCE(!ts->inidle);
1044 
1045         *delta_next = ktime_sub(dev->next_event, now);
1046 
1047         if (!can_stop_idle_tick(cpu, ts))
1048                 return *delta_next;
1049 
1050         next_event = tick_nohz_next_event(ts, cpu);
1051         if (!next_event)
1052                 return *delta_next;
1053 
1054         /*
1055          * If the next highres timer to expire is earlier than next_event, the
1056          * idle governor needs to know that.
1057          */
1058         next_event = min_t(u64, next_event,
1059                            hrtimer_next_event_without(&ts->sched_timer));
1060 
1061         return ktime_sub(next_event, now);
1062 }
1063 
1064 /**
1065  * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
1066  * for a particular CPU.
1067  *
1068  * Called from the schedutil frequency scaling governor in scheduler context.
1069  */
1070 unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
1071 {
1072         struct tick_sched *ts = tick_get_tick_sched(cpu);
1073 
1074         return ts->idle_calls;
1075 }
1076 
1077 /**
1078  * tick_nohz_get_idle_calls - return the current idle calls counter value
1079  *
1080  * Called from the schedutil frequency scaling governor in scheduler context.
1081  */
1082 unsigned long tick_nohz_get_idle_calls(void)
1083 {
1084         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1085 
1086         return ts->idle_calls;
1087 }
1088 
1089 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
1090 {
1091 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1092         unsigned long ticks;
1093 
1094         if (vtime_accounting_cpu_enabled())
1095                 return;
1096         /*
1097          * We stopped the tick in idle. Update process times would miss the
1098          * time we slept as update_process_times does only a 1 tick
1099          * accounting. Enforce that this is accounted to idle !
1100          */
1101         ticks = jiffies - ts->idle_jiffies;
1102         /*
1103          * We might be one off. Do not randomly account a huge number of ticks!
1104          */
1105         if (ticks && ticks < LONG_MAX)
1106                 account_idle_ticks(ticks);
1107 #endif
1108 }
1109 
1110 static void __tick_nohz_idle_restart_tick(struct tick_sched *ts, ktime_t now)
1111 {
1112         tick_nohz_restart_sched_tick(ts, now);
1113         tick_nohz_account_idle_ticks(ts);
1114 }
1115 
1116 void tick_nohz_idle_restart_tick(void)
1117 {
1118         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1119 
1120         if (ts->tick_stopped)
1121                 __tick_nohz_idle_restart_tick(ts, ktime_get());
1122 }
1123 
1124 /**
1125  * tick_nohz_idle_exit - restart the idle tick from the idle task
1126  *
1127  * Restart the idle tick when the CPU is woken up from idle
1128  * This also exit the RCU extended quiescent state. The CPU
1129  * can use RCU again after this function is called.
1130  */
1131 void tick_nohz_idle_exit(void)
1132 {
1133         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1134         bool idle_active, tick_stopped;
1135         ktime_t now;
1136 
1137         local_irq_disable();
1138 
1139         WARN_ON_ONCE(!ts->inidle);
1140         WARN_ON_ONCE(ts->timer_expires_base);
1141 
1142         ts->inidle = 0;
1143         idle_active = ts->idle_active;
1144         tick_stopped = ts->tick_stopped;
1145 
1146         if (idle_active || tick_stopped)
1147                 now = ktime_get();
1148 
1149         if (idle_active)
1150                 tick_nohz_stop_idle(ts, now);
1151 
1152         if (tick_stopped)
1153                 __tick_nohz_idle_restart_tick(ts, now);
1154 
1155         local_irq_enable();
1156 }
1157 
1158 /*
1159  * The nohz low res interrupt handler
1160  */
1161 static void tick_nohz_handler(struct clock_event_device *dev)
1162 {
1163         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1164         struct pt_regs *regs = get_irq_regs();
1165         ktime_t now = ktime_get();
1166 
1167         dev->next_event = KTIME_MAX;
1168 
1169         tick_sched_do_timer(ts, now);
1170         tick_sched_handle(ts, regs);
1171 
1172         /* No need to reprogram if we are running tickless  */
1173         if (unlikely(ts->tick_stopped))
1174                 return;
1175 
1176         hrtimer_forward(&ts->sched_timer, now, tick_period);
1177         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1178 }
1179 
1180 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1181 {
1182         if (!tick_nohz_enabled)
1183                 return;
1184         ts->nohz_mode = mode;
1185         /* One update is enough */
1186         if (!test_and_set_bit(0, &tick_nohz_active))
1187                 timers_update_nohz();
1188 }
1189 
1190 /**
1191  * tick_nohz_switch_to_nohz - switch to nohz mode
1192  */
1193 static void tick_nohz_switch_to_nohz(void)
1194 {
1195         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1196         ktime_t next;
1197 
1198         if (!tick_nohz_enabled)
1199                 return;
1200 
1201         if (tick_switch_to_oneshot(tick_nohz_handler))
1202                 return;
1203 
1204         /*
1205          * Recycle the hrtimer in ts, so we can share the
1206          * hrtimer_forward with the highres code.
1207          */
1208         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1209         /* Get the next period */
1210         next = tick_init_jiffy_update();
1211 
1212         hrtimer_set_expires(&ts->sched_timer, next);
1213         hrtimer_forward_now(&ts->sched_timer, tick_period);
1214         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1215         tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1216 }
1217 
1218 static inline void tick_nohz_irq_enter(void)
1219 {
1220         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1221         ktime_t now;
1222 
1223         if (!ts->idle_active && !ts->tick_stopped)
1224                 return;
1225         now = ktime_get();
1226         if (ts->idle_active)
1227                 tick_nohz_stop_idle(ts, now);
1228         if (ts->tick_stopped)
1229                 tick_nohz_update_jiffies(now);
1230 }
1231 
1232 #else
1233 
1234 static inline void tick_nohz_switch_to_nohz(void) { }
1235 static inline void tick_nohz_irq_enter(void) { }
1236 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1237 
1238 #endif /* CONFIG_NO_HZ_COMMON */
1239 
1240 /*
1241  * Called from irq_enter to notify about the possible interruption of idle()
1242  */
1243 void tick_irq_enter(void)
1244 {
1245         tick_check_oneshot_broadcast_this_cpu();
1246         tick_nohz_irq_enter();
1247 }
1248 
1249 /*
1250  * High resolution timer specific code
1251  */
1252 #ifdef CONFIG_HIGH_RES_TIMERS
1253 /*
1254  * We rearm the timer until we get disabled by the idle code.
1255  * Called with interrupts disabled.
1256  */
1257 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1258 {
1259         struct tick_sched *ts =
1260                 container_of(timer, struct tick_sched, sched_timer);
1261         struct pt_regs *regs = get_irq_regs();
1262         ktime_t now = ktime_get();
1263 
1264         tick_sched_do_timer(ts, now);
1265 
1266         /*
1267          * Do not call, when we are not in irq context and have
1268          * no valid regs pointer
1269          */
1270         if (regs)
1271                 tick_sched_handle(ts, regs);
1272         else
1273                 ts->next_tick = 0;
1274 
1275         /* No need to reprogram if we are in idle or full dynticks mode */
1276         if (unlikely(ts->tick_stopped))
1277                 return HRTIMER_NORESTART;
1278 
1279         hrtimer_forward(timer, now, tick_period);
1280 
1281         return HRTIMER_RESTART;
1282 }
1283 
1284 static int sched_skew_tick;
1285 
1286 static int __init skew_tick(char *str)
1287 {
1288         get_option(&str, &sched_skew_tick);
1289 
1290         return 0;
1291 }
1292 early_param("skew_tick", skew_tick);
1293 
1294 /**
1295  * tick_setup_sched_timer - setup the tick emulation timer
1296  */
1297 void tick_setup_sched_timer(void)
1298 {
1299         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1300         ktime_t now = ktime_get();
1301 
1302         /*
1303          * Emulate tick processing via per-CPU hrtimers:
1304          */
1305         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1306         ts->sched_timer.function = tick_sched_timer;
1307 
1308         /* Get the next period (per-CPU) */
1309         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1310 
1311         /* Offset the tick to avert jiffies_lock contention. */
1312         if (sched_skew_tick) {
1313                 u64 offset = ktime_to_ns(tick_period) >> 1;
1314                 do_div(offset, num_possible_cpus());
1315                 offset *= smp_processor_id();
1316                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1317         }
1318 
1319         hrtimer_forward(&ts->sched_timer, now, tick_period);
1320         hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1321         tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1322 }
1323 #endif /* HIGH_RES_TIMERS */
1324 
1325 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1326 void tick_cancel_sched_timer(int cpu)
1327 {
1328         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1329 
1330 # ifdef CONFIG_HIGH_RES_TIMERS
1331         if (ts->sched_timer.base)
1332                 hrtimer_cancel(&ts->sched_timer);
1333 # endif
1334 
1335         memset(ts, 0, sizeof(*ts));
1336 }
1337 #endif
1338 
1339 /**
1340  * Async notification about clocksource changes
1341  */
1342 void tick_clock_notify(void)
1343 {
1344         int cpu;
1345 
1346         for_each_possible_cpu(cpu)
1347                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1348 }
1349 
1350 /*
1351  * Async notification about clock event changes
1352  */
1353 void tick_oneshot_notify(void)
1354 {
1355         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1356 
1357         set_bit(0, &ts->check_clocks);
1358 }
1359 
1360 /**
1361  * Check, if a change happened, which makes oneshot possible.
1362  *
1363  * Called cyclic from the hrtimer softirq (driven by the timer
1364  * softirq) allow_nohz signals, that we can switch into low-res nohz
1365  * mode, because high resolution timers are disabled (either compile
1366  * or runtime). Called with interrupts disabled.
1367  */
1368 int tick_check_oneshot_change(int allow_nohz)
1369 {
1370         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1371 
1372         if (!test_and_clear_bit(0, &ts->check_clocks))
1373                 return 0;
1374 
1375         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1376                 return 0;
1377 
1378         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1379                 return 0;
1380 
1381         if (!allow_nohz)
1382                 return 1;
1383 
1384         tick_nohz_switch_to_nohz();
1385         return 0;
1386 }
1387 

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