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Linux/kernel/time/tick-sched.c

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  1 /*
  2  *  linux/kernel/time/tick-sched.c
  3  *
  4  *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
  5  *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
  6  *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
  7  *
  8  *  No idle tick implementation for low and high resolution timers
  9  *
 10  *  Started by: Thomas Gleixner and Ingo Molnar
 11  *
 12  *  Distribute under GPLv2.
 13  */
 14 #include <linux/cpu.h>
 15 #include <linux/err.h>
 16 #include <linux/hrtimer.h>
 17 #include <linux/interrupt.h>
 18 #include <linux/kernel_stat.h>
 19 #include <linux/percpu.h>
 20 #include <linux/nmi.h>
 21 #include <linux/profile.h>
 22 #include <linux/sched/signal.h>
 23 #include <linux/sched/clock.h>
 24 #include <linux/sched/stat.h>
 25 #include <linux/sched/nohz.h>
 26 #include <linux/module.h>
 27 #include <linux/irq_work.h>
 28 #include <linux/posix-timers.h>
 29 #include <linux/context_tracking.h>
 30 #include <linux/mm.h>
 31 
 32 #include <asm/irq_regs.h>
 33 
 34 #include "tick-internal.h"
 35 
 36 #include <trace/events/timer.h>
 37 
 38 /*
 39  * Per-CPU nohz control structure
 40  */
 41 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 42 
 43 struct tick_sched *tick_get_tick_sched(int cpu)
 44 {
 45         return &per_cpu(tick_cpu_sched, cpu);
 46 }
 47 
 48 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
 49 /*
 50  * The time, when the last jiffy update happened. Protected by jiffies_lock.
 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 = 0;
 60         ktime_t delta;
 61 
 62         /*
 63          * Do a quick check without holding jiffies_lock:
 64          */
 65         delta = ktime_sub(now, last_jiffies_update);
 66         if (delta < tick_period)
 67                 return;
 68 
 69         /* Reevaluate with jiffies_lock held */
 70         write_seqlock(&jiffies_lock);
 71 
 72         delta = ktime_sub(now, last_jiffies_update);
 73         if (delta >= tick_period) {
 74 
 75                 delta = ktime_sub(delta, tick_period);
 76                 last_jiffies_update = ktime_add(last_jiffies_update,
 77                                                 tick_period);
 78 
 79                 /* Slow path for long timeouts */
 80                 if (unlikely(delta >= tick_period)) {
 81                         s64 incr = ktime_to_ns(tick_period);
 82 
 83                         ticks = ktime_divns(delta, incr);
 84 
 85                         last_jiffies_update = ktime_add_ns(last_jiffies_update,
 86                                                            incr * ticks);
 87                 }
 88                 do_timer(++ticks);
 89 
 90                 /* Keep the tick_next_period variable up to date */
 91                 tick_next_period = ktime_add(last_jiffies_update, tick_period);
 92         } else {
 93                 write_sequnlock(&jiffies_lock);
 94                 return;
 95         }
 96         write_sequnlock(&jiffies_lock);
 97         update_wall_time();
 98 }
 99 
100 /*
101  * Initialize and return retrieve the jiffies update.
102  */
103 static ktime_t tick_init_jiffy_update(void)
104 {
105         ktime_t period;
106 
107         write_seqlock(&jiffies_lock);
108         /* Did we start the jiffies update yet ? */
109         if (last_jiffies_update == 0)
110                 last_jiffies_update = tick_next_period;
111         period = last_jiffies_update;
112         write_sequnlock(&jiffies_lock);
113         return period;
114 }
115 
116 static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
117 {
118         int cpu = smp_processor_id();
119 
120 #ifdef CONFIG_NO_HZ_COMMON
121         /*
122          * Check if the do_timer duty was dropped. We don't care about
123          * concurrency: This happens only when the CPU in charge went
124          * into a long sleep. If two CPUs happen to assign themselves to
125          * this duty, then the jiffies update is still serialized by
126          * jiffies_lock.
127          */
128         if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
129             && !tick_nohz_full_cpu(cpu))
130                 tick_do_timer_cpu = cpu;
131 #endif
132 
133         /* Check, if the jiffies need an update */
134         if (tick_do_timer_cpu == cpu)
135                 tick_do_update_jiffies64(now);
136 
137         if (ts->inidle)
138                 ts->got_idle_tick = 1;
139 }
140 
141 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
142 {
143 #ifdef CONFIG_NO_HZ_COMMON
144         /*
145          * When we are idle and the tick is stopped, we have to touch
146          * the watchdog as we might not schedule for a really long
147          * time. This happens on complete idle SMP systems while
148          * waiting on the login prompt. We also increment the "start of
149          * idle" jiffy stamp so the idle accounting adjustment we do
150          * when we go busy again does not account too much ticks.
151          */
152         if (ts->tick_stopped) {
153                 touch_softlockup_watchdog_sched();
154                 if (is_idle_task(current))
155                         ts->idle_jiffies++;
156                 /*
157                  * In case the current tick fired too early past its expected
158                  * expiration, make sure we don't bypass the next clock reprogramming
159                  * to the same deadline.
160                  */
161                 ts->next_tick = 0;
162         }
163 #endif
164         update_process_times(user_mode(regs));
165         profile_tick(CPU_PROFILING);
166 }
167 #endif
168 
169 #ifdef CONFIG_NO_HZ_FULL
170 cpumask_var_t tick_nohz_full_mask;
171 bool tick_nohz_full_running;
172 static atomic_t tick_dep_mask;
173 
174 static bool check_tick_dependency(atomic_t *dep)
175 {
176         int val = atomic_read(dep);
177 
178         if (val & TICK_DEP_MASK_POSIX_TIMER) {
179                 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
180                 return true;
181         }
182 
183         if (val & TICK_DEP_MASK_PERF_EVENTS) {
184                 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
185                 return true;
186         }
187 
188         if (val & TICK_DEP_MASK_SCHED) {
189                 trace_tick_stop(0, TICK_DEP_MASK_SCHED);
190                 return true;
191         }
192 
193         if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
194                 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
195                 return true;
196         }
197 
198         return false;
199 }
200 
201 static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
202 {
203         lockdep_assert_irqs_disabled();
204 
205         if (unlikely(!cpu_online(cpu)))
206                 return false;
207 
208         if (check_tick_dependency(&tick_dep_mask))
209                 return false;
210 
211         if (check_tick_dependency(&ts->tick_dep_mask))
212                 return false;
213 
214         if (check_tick_dependency(&current->tick_dep_mask))
215                 return false;
216 
217         if (check_tick_dependency(&current->signal->tick_dep_mask))
218                 return false;
219 
220         return true;
221 }
222 
223 static void nohz_full_kick_func(struct irq_work *work)
224 {
225         /* Empty, the tick restart happens on tick_nohz_irq_exit() */
226 }
227 
228 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
229         .func = nohz_full_kick_func,
230 };
231 
232 /*
233  * Kick this CPU if it's full dynticks in order to force it to
234  * re-evaluate its dependency on the tick and restart it if necessary.
235  * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
236  * is NMI safe.
237  */
238 static void tick_nohz_full_kick(void)
239 {
240         if (!tick_nohz_full_cpu(smp_processor_id()))
241                 return;
242 
243         irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
244 }
245 
246 /*
247  * Kick the CPU if it's full dynticks in order to force it to
248  * re-evaluate its dependency on the tick and restart it if necessary.
249  */
250 void tick_nohz_full_kick_cpu(int cpu)
251 {
252         if (!tick_nohz_full_cpu(cpu))
253                 return;
254 
255         irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
256 }
257 
258 /*
259  * Kick all full dynticks CPUs in order to force these to re-evaluate
260  * their dependency on the tick and restart it if necessary.
261  */
262 static void tick_nohz_full_kick_all(void)
263 {
264         int cpu;
265 
266         if (!tick_nohz_full_running)
267                 return;
268 
269         preempt_disable();
270         for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
271                 tick_nohz_full_kick_cpu(cpu);
272         preempt_enable();
273 }
274 
275 static void tick_nohz_dep_set_all(atomic_t *dep,
276                                   enum tick_dep_bits bit)
277 {
278         int prev;
279 
280         prev = atomic_fetch_or(BIT(bit), dep);
281         if (!prev)
282                 tick_nohz_full_kick_all();
283 }
284 
285 /*
286  * Set a global tick dependency. Used by perf events that rely on freq and
287  * by unstable clock.
288  */
289 void tick_nohz_dep_set(enum tick_dep_bits bit)
290 {
291         tick_nohz_dep_set_all(&tick_dep_mask, bit);
292 }
293 
294 void tick_nohz_dep_clear(enum tick_dep_bits bit)
295 {
296         atomic_andnot(BIT(bit), &tick_dep_mask);
297 }
298 
299 /*
300  * Set per-CPU tick dependency. Used by scheduler and perf events in order to
301  * manage events throttling.
302  */
303 void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
304 {
305         int prev;
306         struct tick_sched *ts;
307 
308         ts = per_cpu_ptr(&tick_cpu_sched, cpu);
309 
310         prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
311         if (!prev) {
312                 preempt_disable();
313                 /* Perf needs local kick that is NMI safe */
314                 if (cpu == smp_processor_id()) {
315                         tick_nohz_full_kick();
316                 } else {
317                         /* Remote irq work not NMI-safe */
318                         if (!WARN_ON_ONCE(in_nmi()))
319                                 tick_nohz_full_kick_cpu(cpu);
320                 }
321                 preempt_enable();
322         }
323 }
324 
325 void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
326 {
327         struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
328 
329         atomic_andnot(BIT(bit), &ts->tick_dep_mask);
330 }
331 
332 /*
333  * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
334  * per task timers.
335  */
336 void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
337 {
338         /*
339          * We could optimize this with just kicking the target running the task
340          * if that noise matters for nohz full users.
341          */
342         tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
343 }
344 
345 void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
346 {
347         atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
348 }
349 
350 /*
351  * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
352  * per process timers.
353  */
354 void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
355 {
356         tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
357 }
358 
359 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
360 {
361         atomic_andnot(BIT(bit), &sig->tick_dep_mask);
362 }
363 
364 /*
365  * Re-evaluate the need for the tick as we switch the current task.
366  * It might need the tick due to per task/process properties:
367  * perf events, posix CPU timers, ...
368  */
369 void __tick_nohz_task_switch(void)
370 {
371         unsigned long flags;
372         struct tick_sched *ts;
373 
374         local_irq_save(flags);
375 
376         if (!tick_nohz_full_cpu(smp_processor_id()))
377                 goto out;
378 
379         ts = this_cpu_ptr(&tick_cpu_sched);
380 
381         if (ts->tick_stopped) {
382                 if (atomic_read(&current->tick_dep_mask) ||
383                     atomic_read(&current->signal->tick_dep_mask))
384                         tick_nohz_full_kick();
385         }
386 out:
387         local_irq_restore(flags);
388 }
389 
390 /* Get the boot-time nohz CPU list from the kernel parameters. */
391 void __init tick_nohz_full_setup(cpumask_var_t cpumask)
392 {
393         alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
394         cpumask_copy(tick_nohz_full_mask, cpumask);
395         tick_nohz_full_running = true;
396 }
397 
398 static int tick_nohz_cpu_down(unsigned int cpu)
399 {
400         /*
401          * The boot CPU handles housekeeping duty (unbound timers,
402          * workqueues, timekeeping, ...) on behalf of full dynticks
403          * CPUs. It must remain online when nohz full is enabled.
404          */
405         if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
406                 return -EBUSY;
407         return 0;
408 }
409 
410 void __init tick_nohz_init(void)
411 {
412         int cpu, ret;
413 
414         if (!tick_nohz_full_running)
415                 return;
416 
417         /*
418          * Full dynticks uses irq work to drive the tick rescheduling on safe
419          * locking contexts. But then we need irq work to raise its own
420          * interrupts to avoid circular dependency on the tick
421          */
422         if (!arch_irq_work_has_interrupt()) {
423                 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
424                 cpumask_clear(tick_nohz_full_mask);
425                 tick_nohz_full_running = false;
426                 return;
427         }
428 
429         cpu = smp_processor_id();
430 
431         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
432                 pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
433                         cpu);
434                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
435         }
436 
437         for_each_cpu(cpu, tick_nohz_full_mask)
438                 context_tracking_cpu_set(cpu);
439 
440         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
441                                         "kernel/nohz:predown", NULL,
442                                         tick_nohz_cpu_down);
443         WARN_ON(ret < 0);
444         pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
445                 cpumask_pr_args(tick_nohz_full_mask));
446 }
447 #endif
448 
449 /*
450  * NOHZ - aka dynamic tick functionality
451  */
452 #ifdef CONFIG_NO_HZ_COMMON
453 /*
454  * NO HZ enabled ?
455  */
456 bool tick_nohz_enabled __read_mostly  = true;
457 unsigned long tick_nohz_active  __read_mostly;
458 /*
459  * Enable / Disable tickless mode
460  */
461 static int __init setup_tick_nohz(char *str)
462 {
463         return (kstrtobool(str, &tick_nohz_enabled) == 0);
464 }
465 
466 __setup("nohz=", setup_tick_nohz);
467 
468 bool tick_nohz_tick_stopped(void)
469 {
470         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
471 
472         return ts->tick_stopped;
473 }
474 
475 bool tick_nohz_tick_stopped_cpu(int cpu)
476 {
477         struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
478 
479         return ts->tick_stopped;
480 }
481 
482 /**
483  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
484  *
485  * Called from interrupt entry when the CPU was idle
486  *
487  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
488  * must be updated. Otherwise an interrupt handler could use a stale jiffy
489  * value. We do this unconditionally on any CPU, as we don't know whether the
490  * CPU, which has the update task assigned is in a long sleep.
491  */
492 static void tick_nohz_update_jiffies(ktime_t now)
493 {
494         unsigned long flags;
495 
496         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
497 
498         local_irq_save(flags);
499         tick_do_update_jiffies64(now);
500         local_irq_restore(flags);
501 
502         touch_softlockup_watchdog_sched();
503 }
504 
505 /*
506  * Updates the per-CPU time idle statistics counters
507  */
508 static void
509 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
510 {
511         ktime_t delta;
512 
513         if (ts->idle_active) {
514                 delta = ktime_sub(now, ts->idle_entrytime);
515                 if (nr_iowait_cpu(cpu) > 0)
516                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
517                 else
518                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
519                 ts->idle_entrytime = now;
520         }
521 
522         if (last_update_time)
523                 *last_update_time = ktime_to_us(now);
524 
525 }
526 
527 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
528 {
529         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
530         ts->idle_active = 0;
531 
532         sched_clock_idle_wakeup_event();
533 }
534 
535 static void tick_nohz_start_idle(struct tick_sched *ts)
536 {
537         ts->idle_entrytime = ktime_get();
538         ts->idle_active = 1;
539         sched_clock_idle_sleep_event();
540 }
541 
542 /**
543  * get_cpu_idle_time_us - get the total idle time of a CPU
544  * @cpu: CPU number to query
545  * @last_update_time: variable to store update time in. Do not update
546  * counters if NULL.
547  *
548  * Return the cumulative idle time (since boot) for a given
549  * CPU, in microseconds.
550  *
551  * This time is measured via accounting rather than sampling,
552  * and is as accurate as ktime_get() is.
553  *
554  * This function returns -1 if NOHZ is not enabled.
555  */
556 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
557 {
558         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
559         ktime_t now, idle;
560 
561         if (!tick_nohz_active)
562                 return -1;
563 
564         now = ktime_get();
565         if (last_update_time) {
566                 update_ts_time_stats(cpu, ts, now, last_update_time);
567                 idle = ts->idle_sleeptime;
568         } else {
569                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
570                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
571 
572                         idle = ktime_add(ts->idle_sleeptime, delta);
573                 } else {
574                         idle = ts->idle_sleeptime;
575                 }
576         }
577 
578         return ktime_to_us(idle);
579 
580 }
581 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
582 
583 /**
584  * get_cpu_iowait_time_us - get the total iowait time of a CPU
585  * @cpu: CPU number to query
586  * @last_update_time: variable to store update time in. Do not update
587  * counters if NULL.
588  *
589  * Return the cumulative iowait time (since boot) for a given
590  * CPU, in microseconds.
591  *
592  * This time is measured via accounting rather than sampling,
593  * and is as accurate as ktime_get() is.
594  *
595  * This function returns -1 if NOHZ is not enabled.
596  */
597 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
598 {
599         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
600         ktime_t now, iowait;
601 
602         if (!tick_nohz_active)
603                 return -1;
604 
605         now = ktime_get();
606         if (last_update_time) {
607                 update_ts_time_stats(cpu, ts, now, last_update_time);
608                 iowait = ts->iowait_sleeptime;
609         } else {
610                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
611                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
612 
613                         iowait = ktime_add(ts->iowait_sleeptime, delta);
614                 } else {
615                         iowait = ts->iowait_sleeptime;
616                 }
617         }
618 
619         return ktime_to_us(iowait);
620 }
621 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
622 
623 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
624 {
625         hrtimer_cancel(&ts->sched_timer);
626         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
627 
628         /* Forward the time to expire in the future */
629         hrtimer_forward(&ts->sched_timer, now, tick_period);
630 
631         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
632                 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
633         else
634                 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
635 
636         /*
637          * Reset to make sure next tick stop doesn't get fooled by past
638          * cached clock deadline.
639          */
640         ts->next_tick = 0;
641 }
642 
643 static inline bool local_timer_softirq_pending(void)
644 {
645         return local_softirq_pending() & BIT(TIMER_SOFTIRQ);
646 }
647 
648 static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
649 {
650         u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
651         unsigned long seq, basejiff;
652 
653         /* Read jiffies and the time when jiffies were updated last */
654         do {
655                 seq = read_seqbegin(&jiffies_lock);
656                 basemono = last_jiffies_update;
657                 basejiff = jiffies;
658         } while (read_seqretry(&jiffies_lock, seq));
659         ts->last_jiffies = basejiff;
660         ts->timer_expires_base = basemono;
661 
662         /*
663          * Keep the periodic tick, when RCU, architecture or irq_work
664          * requests it.
665          * Aside of that check whether the local timer softirq is
666          * pending. If so its a bad idea to call get_next_timer_interrupt()
667          * because there is an already expired timer, so it will request
668          * immeditate expiry, which rearms the hardware timer with a
669          * minimal delta which brings us back to this place
670          * immediately. Lather, rinse and repeat...
671          */
672         if (rcu_needs_cpu(basemono, &next_rcu) || arch_needs_cpu() ||
673             irq_work_needs_cpu() || local_timer_softirq_pending()) {
674                 next_tick = basemono + TICK_NSEC;
675         } else {
676                 /*
677                  * Get the next pending timer. If high resolution
678                  * timers are enabled this only takes the timer wheel
679                  * timers into account. If high resolution timers are
680                  * disabled this also looks at the next expiring
681                  * hrtimer.
682                  */
683                 next_tmr = get_next_timer_interrupt(basejiff, basemono);
684                 ts->next_timer = next_tmr;
685                 /* Take the next rcu event into account */
686                 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
687         }
688 
689         /*
690          * If the tick is due in the next period, keep it ticking or
691          * force prod the timer.
692          */
693         delta = next_tick - basemono;
694         if (delta <= (u64)TICK_NSEC) {
695                 /*
696                  * Tell the timer code that the base is not idle, i.e. undo
697                  * the effect of get_next_timer_interrupt():
698                  */
699                 timer_clear_idle();
700                 /*
701                  * We've not stopped the tick yet, and there's a timer in the
702                  * next period, so no point in stopping it either, bail.
703                  */
704                 if (!ts->tick_stopped) {
705                         ts->timer_expires = 0;
706                         goto out;
707                 }
708         }
709 
710         /*
711          * If this CPU is the one which had the do_timer() duty last, we limit
712          * the sleep time to the timekeeping max_deferment value.
713          * Otherwise we can sleep as long as we want.
714          */
715         delta = timekeeping_max_deferment();
716         if (cpu != tick_do_timer_cpu &&
717             (tick_do_timer_cpu != TICK_DO_TIMER_NONE || !ts->do_timer_last))
718                 delta = KTIME_MAX;
719 
720         /* Calculate the next expiry time */
721         if (delta < (KTIME_MAX - basemono))
722                 expires = basemono + delta;
723         else
724                 expires = KTIME_MAX;
725 
726         ts->timer_expires = min_t(u64, expires, next_tick);
727 
728 out:
729         return ts->timer_expires;
730 }
731 
732 static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
733 {
734         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
735         u64 basemono = ts->timer_expires_base;
736         u64 expires = ts->timer_expires;
737         ktime_t tick = expires;
738 
739         /* Make sure we won't be trying to stop it twice in a row. */
740         ts->timer_expires_base = 0;
741 
742         /*
743          * If this CPU is the one which updates jiffies, then give up
744          * the assignment and let it be taken by the CPU which runs
745          * the tick timer next, which might be this CPU as well. If we
746          * don't drop this here the jiffies might be stale and
747          * do_timer() never invoked. Keep track of the fact that it
748          * was the one which had the do_timer() duty last.
749          */
750         if (cpu == tick_do_timer_cpu) {
751                 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
752                 ts->do_timer_last = 1;
753         } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
754                 ts->do_timer_last = 0;
755         }
756 
757         /* Skip reprogram of event if its not changed */
758         if (ts->tick_stopped && (expires == ts->next_tick)) {
759                 /* Sanity check: make sure clockevent is actually programmed */
760                 if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer))
761                         return;
762 
763                 WARN_ON_ONCE(1);
764                 printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n",
765                             basemono, ts->next_tick, dev->next_event,
766                             hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer));
767         }
768 
769         /*
770          * nohz_stop_sched_tick can be called several times before
771          * the nohz_restart_sched_tick is called. This happens when
772          * interrupts arrive which do not cause a reschedule. In the
773          * first call we save the current tick time, so we can restart
774          * the scheduler tick in nohz_restart_sched_tick.
775          */
776         if (!ts->tick_stopped) {
777                 calc_load_nohz_start();
778                 cpu_load_update_nohz_start();
779                 quiet_vmstat();
780 
781                 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
782                 ts->tick_stopped = 1;
783                 trace_tick_stop(1, TICK_DEP_MASK_NONE);
784         }
785 
786         ts->next_tick = tick;
787 
788         /*
789          * If the expiration time == KTIME_MAX, then we simply stop
790          * the tick timer.
791          */
792         if (unlikely(expires == KTIME_MAX)) {
793                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
794                         hrtimer_cancel(&ts->sched_timer);
795                 return;
796         }
797 
798         if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
799                 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
800         } else {
801                 hrtimer_set_expires(&ts->sched_timer, tick);
802                 tick_program_event(tick, 1);
803         }
804 }
805 
806 static void tick_nohz_retain_tick(struct tick_sched *ts)
807 {
808         ts->timer_expires_base = 0;
809 }
810 
811 #ifdef CONFIG_NO_HZ_FULL
812 static void tick_nohz_stop_sched_tick(struct tick_sched *ts, int cpu)
813 {
814         if (tick_nohz_next_event(ts, cpu))
815                 tick_nohz_stop_tick(ts, cpu);
816         else
817                 tick_nohz_retain_tick(ts);
818 }
819 #endif /* CONFIG_NO_HZ_FULL */
820 
821 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
822 {
823         /* Update jiffies first */
824         tick_do_update_jiffies64(now);
825         cpu_load_update_nohz_stop();
826 
827         /*
828          * Clear the timer idle flag, so we avoid IPIs on remote queueing and
829          * the clock forward checks in the enqueue path:
830          */
831         timer_clear_idle();
832 
833         calc_load_nohz_stop();
834         touch_softlockup_watchdog_sched();
835         /*
836          * Cancel the scheduled timer and restore the tick
837          */
838         ts->tick_stopped  = 0;
839         ts->idle_exittime = now;
840 
841         tick_nohz_restart(ts, now);
842 }
843 
844 static void tick_nohz_full_update_tick(struct tick_sched *ts)
845 {
846 #ifdef CONFIG_NO_HZ_FULL
847         int cpu = smp_processor_id();
848 
849         if (!tick_nohz_full_cpu(cpu))
850                 return;
851 
852         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
853                 return;
854 
855         if (can_stop_full_tick(cpu, ts))
856                 tick_nohz_stop_sched_tick(ts, cpu);
857         else if (ts->tick_stopped)
858                 tick_nohz_restart_sched_tick(ts, ktime_get());
859 #endif
860 }
861 
862 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
863 {
864         /*
865          * If this CPU is offline and it is the one which updates
866          * jiffies, then give up the assignment and let it be taken by
867          * the CPU which runs the tick timer next. If we don't drop
868          * this here the jiffies might be stale and do_timer() never
869          * invoked.
870          */
871         if (unlikely(!cpu_online(cpu))) {
872                 if (cpu == tick_do_timer_cpu)
873                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
874                 /*
875                  * Make sure the CPU doesn't get fooled by obsolete tick
876                  * deadline if it comes back online later.
877                  */
878                 ts->next_tick = 0;
879                 return false;
880         }
881 
882         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
883                 return false;
884 
885         if (need_resched())
886                 return false;
887 
888         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
889                 static int ratelimit;
890 
891                 if (ratelimit < 10 &&
892                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
893                         pr_warn("NOHZ: local_softirq_pending %02x\n",
894                                 (unsigned int) local_softirq_pending());
895                         ratelimit++;
896                 }
897                 return false;
898         }
899 
900         if (tick_nohz_full_enabled()) {
901                 /*
902                  * Keep the tick alive to guarantee timekeeping progression
903                  * if there are full dynticks CPUs around
904                  */
905                 if (tick_do_timer_cpu == cpu)
906                         return false;
907                 /*
908                  * Boot safety: make sure the timekeeping duty has been
909                  * assigned before entering dyntick-idle mode,
910                  */
911                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
912                         return false;
913         }
914 
915         return true;
916 }
917 
918 static void __tick_nohz_idle_stop_tick(struct tick_sched *ts)
919 {
920         ktime_t expires;
921         int cpu = smp_processor_id();
922 
923         /*
924          * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the
925          * tick timer expiration time is known already.
926          */
927         if (ts->timer_expires_base)
928                 expires = ts->timer_expires;
929         else if (can_stop_idle_tick(cpu, ts))
930                 expires = tick_nohz_next_event(ts, cpu);
931         else
932                 return;
933 
934         ts->idle_calls++;
935 
936         if (expires > 0LL) {
937                 int was_stopped = ts->tick_stopped;
938 
939                 tick_nohz_stop_tick(ts, cpu);
940 
941                 ts->idle_sleeps++;
942                 ts->idle_expires = expires;
943 
944                 if (!was_stopped && ts->tick_stopped) {
945                         ts->idle_jiffies = ts->last_jiffies;
946                         nohz_balance_enter_idle(cpu);
947                 }
948         } else {
949                 tick_nohz_retain_tick(ts);
950         }
951 }
952 
953 /**
954  * tick_nohz_idle_stop_tick - stop the idle tick from the idle task
955  *
956  * When the next event is more than a tick into the future, stop the idle tick
957  */
958 void tick_nohz_idle_stop_tick(void)
959 {
960         __tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched));
961 }
962 
963 void tick_nohz_idle_retain_tick(void)
964 {
965         tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched));
966         /*
967          * Undo the effect of get_next_timer_interrupt() called from
968          * tick_nohz_next_event().
969          */
970         timer_clear_idle();
971 }
972 
973 /**
974  * tick_nohz_idle_enter - prepare for entering idle on the current CPU
975  *
976  * Called when we start the idle loop.
977  */
978 void tick_nohz_idle_enter(void)
979 {
980         struct tick_sched *ts;
981 
982         lockdep_assert_irqs_enabled();
983 
984         local_irq_disable();
985 
986         ts = this_cpu_ptr(&tick_cpu_sched);
987 
988         WARN_ON_ONCE(ts->timer_expires_base);
989 
990         ts->inidle = 1;
991         tick_nohz_start_idle(ts);
992 
993         local_irq_enable();
994 }
995 
996 /**
997  * tick_nohz_irq_exit - update next tick event from interrupt exit
998  *
999  * When an interrupt fires while we are idle and it doesn't cause
1000  * a reschedule, it may still add, modify or delete a timer, enqueue
1001  * an RCU callback, etc...
1002  * So we need to re-calculate and reprogram the next tick event.
1003  */
1004 void tick_nohz_irq_exit(void)
1005 {
1006         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1007 
1008         if (ts->inidle)
1009                 tick_nohz_start_idle(ts);
1010         else
1011                 tick_nohz_full_update_tick(ts);
1012 }
1013 
1014 /**
1015  * tick_nohz_idle_got_tick - Check whether or not the tick handler has run
1016  */
1017 bool tick_nohz_idle_got_tick(void)
1018 {
1019         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1020 
1021         if (ts->got_idle_tick) {
1022                 ts->got_idle_tick = 0;
1023                 return true;
1024         }
1025         return false;
1026 }
1027 
1028 /**
1029  * tick_nohz_get_sleep_length - return the expected length of the current sleep
1030  * @delta_next: duration until the next event if the tick cannot be stopped
1031  *
1032  * Called from power state control code with interrupts disabled
1033  */
1034 ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
1035 {
1036         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
1037         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1038         int cpu = smp_processor_id();
1039         /*
1040          * The idle entry time is expected to be a sufficient approximation of
1041          * the current time at this point.
1042          */
1043         ktime_t now = ts->idle_entrytime;
1044         ktime_t next_event;
1045 
1046         WARN_ON_ONCE(!ts->inidle);
1047 
1048         *delta_next = ktime_sub(dev->next_event, now);
1049 
1050         if (!can_stop_idle_tick(cpu, ts))
1051                 return *delta_next;
1052 
1053         next_event = tick_nohz_next_event(ts, cpu);
1054         if (!next_event)
1055                 return *delta_next;
1056 
1057         /*
1058          * If the next highres timer to expire is earlier than next_event, the
1059          * idle governor needs to know that.
1060          */
1061         next_event = min_t(u64, next_event,
1062                            hrtimer_next_event_without(&ts->sched_timer));
1063 
1064         return ktime_sub(next_event, now);
1065 }
1066 
1067 /**
1068  * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
1069  * for a particular CPU.
1070  *
1071  * Called from the schedutil frequency scaling governor in scheduler context.
1072  */
1073 unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
1074 {
1075         struct tick_sched *ts = tick_get_tick_sched(cpu);
1076 
1077         return ts->idle_calls;
1078 }
1079 
1080 /**
1081  * tick_nohz_get_idle_calls - return the current idle calls counter value
1082  *
1083  * Called from the schedutil frequency scaling governor in scheduler context.
1084  */
1085 unsigned long tick_nohz_get_idle_calls(void)
1086 {
1087         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1088 
1089         return ts->idle_calls;
1090 }
1091 
1092 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
1093 {
1094 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1095         unsigned long ticks;
1096 
1097         if (vtime_accounting_cpu_enabled())
1098                 return;
1099         /*
1100          * We stopped the tick in idle. Update process times would miss the
1101          * time we slept as update_process_times does only a 1 tick
1102          * accounting. Enforce that this is accounted to idle !
1103          */
1104         ticks = jiffies - ts->idle_jiffies;
1105         /*
1106          * We might be one off. Do not randomly account a huge number of ticks!
1107          */
1108         if (ticks && ticks < LONG_MAX)
1109                 account_idle_ticks(ticks);
1110 #endif
1111 }
1112 
1113 static void __tick_nohz_idle_restart_tick(struct tick_sched *ts, ktime_t now)
1114 {
1115         tick_nohz_restart_sched_tick(ts, now);
1116         tick_nohz_account_idle_ticks(ts);
1117 }
1118 
1119 void tick_nohz_idle_restart_tick(void)
1120 {
1121         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1122 
1123         if (ts->tick_stopped)
1124                 __tick_nohz_idle_restart_tick(ts, ktime_get());
1125 }
1126 
1127 /**
1128  * tick_nohz_idle_exit - restart the idle tick from the idle task
1129  *
1130  * Restart the idle tick when the CPU is woken up from idle
1131  * This also exit the RCU extended quiescent state. The CPU
1132  * can use RCU again after this function is called.
1133  */
1134 void tick_nohz_idle_exit(void)
1135 {
1136         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1137         bool idle_active, tick_stopped;
1138         ktime_t now;
1139 
1140         local_irq_disable();
1141 
1142         WARN_ON_ONCE(!ts->inidle);
1143         WARN_ON_ONCE(ts->timer_expires_base);
1144 
1145         ts->inidle = 0;
1146         idle_active = ts->idle_active;
1147         tick_stopped = ts->tick_stopped;
1148 
1149         if (idle_active || tick_stopped)
1150                 now = ktime_get();
1151 
1152         if (idle_active)
1153                 tick_nohz_stop_idle(ts, now);
1154 
1155         if (tick_stopped)
1156                 __tick_nohz_idle_restart_tick(ts, now);
1157 
1158         local_irq_enable();
1159 }
1160 
1161 /*
1162  * The nohz low res interrupt handler
1163  */
1164 static void tick_nohz_handler(struct clock_event_device *dev)
1165 {
1166         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1167         struct pt_regs *regs = get_irq_regs();
1168         ktime_t now = ktime_get();
1169 
1170         dev->next_event = KTIME_MAX;
1171 
1172         tick_sched_do_timer(ts, now);
1173         tick_sched_handle(ts, regs);
1174 
1175         /* No need to reprogram if we are running tickless  */
1176         if (unlikely(ts->tick_stopped))
1177                 return;
1178 
1179         hrtimer_forward(&ts->sched_timer, now, tick_period);
1180         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1181 }
1182 
1183 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1184 {
1185         if (!tick_nohz_enabled)
1186                 return;
1187         ts->nohz_mode = mode;
1188         /* One update is enough */
1189         if (!test_and_set_bit(0, &tick_nohz_active))
1190                 timers_update_nohz();
1191 }
1192 
1193 /**
1194  * tick_nohz_switch_to_nohz - switch to nohz mode
1195  */
1196 static void tick_nohz_switch_to_nohz(void)
1197 {
1198         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1199         ktime_t next;
1200 
1201         if (!tick_nohz_enabled)
1202                 return;
1203 
1204         if (tick_switch_to_oneshot(tick_nohz_handler))
1205                 return;
1206 
1207         /*
1208          * Recycle the hrtimer in ts, so we can share the
1209          * hrtimer_forward with the highres code.
1210          */
1211         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1212         /* Get the next period */
1213         next = tick_init_jiffy_update();
1214 
1215         hrtimer_set_expires(&ts->sched_timer, next);
1216         hrtimer_forward_now(&ts->sched_timer, tick_period);
1217         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1218         tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1219 }
1220 
1221 static inline void tick_nohz_irq_enter(void)
1222 {
1223         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1224         ktime_t now;
1225 
1226         if (!ts->idle_active && !ts->tick_stopped)
1227                 return;
1228         now = ktime_get();
1229         if (ts->idle_active)
1230                 tick_nohz_stop_idle(ts, now);
1231         if (ts->tick_stopped)
1232                 tick_nohz_update_jiffies(now);
1233 }
1234 
1235 #else
1236 
1237 static inline void tick_nohz_switch_to_nohz(void) { }
1238 static inline void tick_nohz_irq_enter(void) { }
1239 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1240 
1241 #endif /* CONFIG_NO_HZ_COMMON */
1242 
1243 /*
1244  * Called from irq_enter to notify about the possible interruption of idle()
1245  */
1246 void tick_irq_enter(void)
1247 {
1248         tick_check_oneshot_broadcast_this_cpu();
1249         tick_nohz_irq_enter();
1250 }
1251 
1252 /*
1253  * High resolution timer specific code
1254  */
1255 #ifdef CONFIG_HIGH_RES_TIMERS
1256 /*
1257  * We rearm the timer until we get disabled by the idle code.
1258  * Called with interrupts disabled.
1259  */
1260 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1261 {
1262         struct tick_sched *ts =
1263                 container_of(timer, struct tick_sched, sched_timer);
1264         struct pt_regs *regs = get_irq_regs();
1265         ktime_t now = ktime_get();
1266 
1267         tick_sched_do_timer(ts, now);
1268 
1269         /*
1270          * Do not call, when we are not in irq context and have
1271          * no valid regs pointer
1272          */
1273         if (regs)
1274                 tick_sched_handle(ts, regs);
1275         else
1276                 ts->next_tick = 0;
1277 
1278         /* No need to reprogram if we are in idle or full dynticks mode */
1279         if (unlikely(ts->tick_stopped))
1280                 return HRTIMER_NORESTART;
1281 
1282         hrtimer_forward(timer, now, tick_period);
1283 
1284         return HRTIMER_RESTART;
1285 }
1286 
1287 static int sched_skew_tick;
1288 
1289 static int __init skew_tick(char *str)
1290 {
1291         get_option(&str, &sched_skew_tick);
1292 
1293         return 0;
1294 }
1295 early_param("skew_tick", skew_tick);
1296 
1297 /**
1298  * tick_setup_sched_timer - setup the tick emulation timer
1299  */
1300 void tick_setup_sched_timer(void)
1301 {
1302         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1303         ktime_t now = ktime_get();
1304 
1305         /*
1306          * Emulate tick processing via per-CPU hrtimers:
1307          */
1308         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1309         ts->sched_timer.function = tick_sched_timer;
1310 
1311         /* Get the next period (per-CPU) */
1312         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1313 
1314         /* Offset the tick to avert jiffies_lock contention. */
1315         if (sched_skew_tick) {
1316                 u64 offset = ktime_to_ns(tick_period) >> 1;
1317                 do_div(offset, num_possible_cpus());
1318                 offset *= smp_processor_id();
1319                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1320         }
1321 
1322         hrtimer_forward(&ts->sched_timer, now, tick_period);
1323         hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1324         tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1325 }
1326 #endif /* HIGH_RES_TIMERS */
1327 
1328 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1329 void tick_cancel_sched_timer(int cpu)
1330 {
1331         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1332 
1333 # ifdef CONFIG_HIGH_RES_TIMERS
1334         if (ts->sched_timer.base)
1335                 hrtimer_cancel(&ts->sched_timer);
1336 # endif
1337 
1338         memset(ts, 0, sizeof(*ts));
1339 }
1340 #endif
1341 
1342 /**
1343  * Async notification about clocksource changes
1344  */
1345 void tick_clock_notify(void)
1346 {
1347         int cpu;
1348 
1349         for_each_possible_cpu(cpu)
1350                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1351 }
1352 
1353 /*
1354  * Async notification about clock event changes
1355  */
1356 void tick_oneshot_notify(void)
1357 {
1358         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1359 
1360         set_bit(0, &ts->check_clocks);
1361 }
1362 
1363 /**
1364  * Check, if a change happened, which makes oneshot possible.
1365  *
1366  * Called cyclic from the hrtimer softirq (driven by the timer
1367  * softirq) allow_nohz signals, that we can switch into low-res nohz
1368  * mode, because high resolution timers are disabled (either compile
1369  * or runtime). Called with interrupts disabled.
1370  */
1371 int tick_check_oneshot_change(int allow_nohz)
1372 {
1373         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1374 
1375         if (!test_and_clear_bit(0, &ts->check_clocks))
1376                 return 0;
1377 
1378         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1379                 return 0;
1380 
1381         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1382                 return 0;
1383 
1384         if (!allow_nohz)
1385                 return 1;
1386 
1387         tick_nohz_switch_to_nohz();
1388         return 0;
1389 }
1390 

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