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Linux/kernel/time/tick-sched.c

  1 /*
  2  *  linux/kernel/time/tick-sched.c
  3  *
  4  *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
  5  *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
  6  *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
  7  *
  8  *  No idle tick implementation for low and high resolution timers
  9  *
 10  *  Started by: Thomas Gleixner and Ingo Molnar
 11  *
 12  *  Distribute under GPLv2.
 13  */
 14 #include <linux/cpu.h>
 15 #include <linux/err.h>
 16 #include <linux/hrtimer.h>
 17 #include <linux/interrupt.h>
 18 #include <linux/kernel_stat.h>
 19 #include <linux/percpu.h>
 20 #include <linux/profile.h>
 21 #include <linux/sched.h>
 22 #include <linux/module.h>
 23 #include <linux/irq_work.h>
 24 #include <linux/posix-timers.h>
 25 #include <linux/perf_event.h>
 26 #include <linux/context_tracking.h>
 27 
 28 #include <asm/irq_regs.h>
 29 
 30 #include "tick-internal.h"
 31 
 32 #include <trace/events/timer.h>
 33 
 34 /*
 35  * Per cpu nohz control structure
 36  */
 37 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 38 
 39 /*
 40  * The time, when the last jiffy update happened. Protected by jiffies_lock.
 41  */
 42 static ktime_t last_jiffies_update;
 43 
 44 struct tick_sched *tick_get_tick_sched(int cpu)
 45 {
 46         return &per_cpu(tick_cpu_sched, cpu);
 47 }
 48 
 49 /*
 50  * Must be called with interrupts disabled !
 51  */
 52 static void tick_do_update_jiffies64(ktime_t now)
 53 {
 54         unsigned long ticks = 0;
 55         ktime_t delta;
 56 
 57         /*
 58          * Do a quick check without holding jiffies_lock:
 59          */
 60         delta = ktime_sub(now, last_jiffies_update);
 61         if (delta.tv64 < tick_period.tv64)
 62                 return;
 63 
 64         /* Reevalute with jiffies_lock held */
 65         write_seqlock(&jiffies_lock);
 66 
 67         delta = ktime_sub(now, last_jiffies_update);
 68         if (delta.tv64 >= tick_period.tv64) {
 69 
 70                 delta = ktime_sub(delta, tick_period);
 71                 last_jiffies_update = ktime_add(last_jiffies_update,
 72                                                 tick_period);
 73 
 74                 /* Slow path for long timeouts */
 75                 if (unlikely(delta.tv64 >= tick_period.tv64)) {
 76                         s64 incr = ktime_to_ns(tick_period);
 77 
 78                         ticks = ktime_divns(delta, incr);
 79 
 80                         last_jiffies_update = ktime_add_ns(last_jiffies_update,
 81                                                            incr * ticks);
 82                 }
 83                 do_timer(++ticks);
 84 
 85                 /* Keep the tick_next_period variable up to date */
 86                 tick_next_period = ktime_add(last_jiffies_update, tick_period);
 87         } else {
 88                 write_sequnlock(&jiffies_lock);
 89                 return;
 90         }
 91         write_sequnlock(&jiffies_lock);
 92         update_wall_time();
 93 }
 94 
 95 /*
 96  * Initialize and return retrieve the jiffies update.
 97  */
 98 static ktime_t tick_init_jiffy_update(void)
 99 {
100         ktime_t period;
101 
102         write_seqlock(&jiffies_lock);
103         /* Did we start the jiffies update yet ? */
104         if (last_jiffies_update.tv64 == 0)
105                 last_jiffies_update = tick_next_period;
106         period = last_jiffies_update;
107         write_sequnlock(&jiffies_lock);
108         return period;
109 }
110 
111 
112 static void tick_sched_do_timer(ktime_t now)
113 {
114         int cpu = smp_processor_id();
115 
116 #ifdef CONFIG_NO_HZ_COMMON
117         /*
118          * Check if the do_timer duty was dropped. We don't care about
119          * concurrency: This happens only when the cpu in charge went
120          * into a long sleep. If two cpus happen to assign themself to
121          * this duty, then the jiffies update is still serialized by
122          * jiffies_lock.
123          */
124         if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
125             && !tick_nohz_full_cpu(cpu))
126                 tick_do_timer_cpu = cpu;
127 #endif
128 
129         /* Check, if the jiffies need an update */
130         if (tick_do_timer_cpu == cpu)
131                 tick_do_update_jiffies64(now);
132 }
133 
134 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
135 {
136 #ifdef CONFIG_NO_HZ_COMMON
137         /*
138          * When we are idle and the tick is stopped, we have to touch
139          * the watchdog as we might not schedule for a really long
140          * time. This happens on complete idle SMP systems while
141          * waiting on the login prompt. We also increment the "start of
142          * idle" jiffy stamp so the idle accounting adjustment we do
143          * when we go busy again does not account too much ticks.
144          */
145         if (ts->tick_stopped) {
146                 touch_softlockup_watchdog();
147                 if (is_idle_task(current))
148                         ts->idle_jiffies++;
149         }
150 #endif
151         update_process_times(user_mode(regs));
152         profile_tick(CPU_PROFILING);
153 }
154 
155 #ifdef CONFIG_NO_HZ_FULL
156 cpumask_var_t tick_nohz_full_mask;
157 cpumask_var_t housekeeping_mask;
158 bool tick_nohz_full_running;
159 
160 static bool can_stop_full_tick(void)
161 {
162         WARN_ON_ONCE(!irqs_disabled());
163 
164         if (!sched_can_stop_tick()) {
165                 trace_tick_stop(0, "more than 1 task in runqueue\n");
166                 return false;
167         }
168 
169         if (!posix_cpu_timers_can_stop_tick(current)) {
170                 trace_tick_stop(0, "posix timers running\n");
171                 return false;
172         }
173 
174         if (!perf_event_can_stop_tick()) {
175                 trace_tick_stop(0, "perf events running\n");
176                 return false;
177         }
178 
179         /* sched_clock_tick() needs us? */
180 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
181         /*
182          * TODO: kick full dynticks CPUs when
183          * sched_clock_stable is set.
184          */
185         if (!sched_clock_stable()) {
186                 trace_tick_stop(0, "unstable sched clock\n");
187                 /*
188                  * Don't allow the user to think they can get
189                  * full NO_HZ with this machine.
190                  */
191                 WARN_ONCE(tick_nohz_full_running,
192                           "NO_HZ FULL will not work with unstable sched clock");
193                 return false;
194         }
195 #endif
196 
197         return true;
198 }
199 
200 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
201 
202 /*
203  * Re-evaluate the need for the tick on the current CPU
204  * and restart it if necessary.
205  */
206 void __tick_nohz_full_check(void)
207 {
208         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
209 
210         if (tick_nohz_full_cpu(smp_processor_id())) {
211                 if (ts->tick_stopped && !is_idle_task(current)) {
212                         if (!can_stop_full_tick())
213                                 tick_nohz_restart_sched_tick(ts, ktime_get());
214                 }
215         }
216 }
217 
218 static void nohz_full_kick_work_func(struct irq_work *work)
219 {
220         __tick_nohz_full_check();
221 }
222 
223 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
224         .func = nohz_full_kick_work_func,
225 };
226 
227 /*
228  * Kick this CPU if it's full dynticks in order to force it to
229  * re-evaluate its dependency on the tick and restart it if necessary.
230  * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
231  * is NMI safe.
232  */
233 void tick_nohz_full_kick(void)
234 {
235         if (!tick_nohz_full_cpu(smp_processor_id()))
236                 return;
237 
238         irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
239 }
240 
241 /*
242  * Kick the CPU if it's full dynticks in order to force it to
243  * re-evaluate its dependency on the tick and restart it if necessary.
244  */
245 void tick_nohz_full_kick_cpu(int cpu)
246 {
247         if (!tick_nohz_full_cpu(cpu))
248                 return;
249 
250         irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
251 }
252 
253 static void nohz_full_kick_ipi(void *info)
254 {
255         __tick_nohz_full_check();
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 void tick_nohz_full_kick_all(void)
263 {
264         if (!tick_nohz_full_running)
265                 return;
266 
267         preempt_disable();
268         smp_call_function_many(tick_nohz_full_mask,
269                                nohz_full_kick_ipi, NULL, false);
270         tick_nohz_full_kick();
271         preempt_enable();
272 }
273 
274 /*
275  * Re-evaluate the need for the tick as we switch the current task.
276  * It might need the tick due to per task/process properties:
277  * perf events, posix cpu timers, ...
278  */
279 void __tick_nohz_task_switch(struct task_struct *tsk)
280 {
281         unsigned long flags;
282 
283         local_irq_save(flags);
284 
285         if (!tick_nohz_full_cpu(smp_processor_id()))
286                 goto out;
287 
288         if (tick_nohz_tick_stopped() && !can_stop_full_tick())
289                 tick_nohz_full_kick();
290 
291 out:
292         local_irq_restore(flags);
293 }
294 
295 /* Parse the boot-time nohz CPU list from the kernel parameters. */
296 static int __init tick_nohz_full_setup(char *str)
297 {
298         alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
299         if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
300                 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
301                 free_bootmem_cpumask_var(tick_nohz_full_mask);
302                 return 1;
303         }
304         tick_nohz_full_running = true;
305 
306         return 1;
307 }
308 __setup("nohz_full=", tick_nohz_full_setup);
309 
310 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
311                                                  unsigned long action,
312                                                  void *hcpu)
313 {
314         unsigned int cpu = (unsigned long)hcpu;
315 
316         switch (action & ~CPU_TASKS_FROZEN) {
317         case CPU_DOWN_PREPARE:
318                 /*
319                  * If we handle the timekeeping duty for full dynticks CPUs,
320                  * we can't safely shutdown that CPU.
321                  */
322                 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
323                         return NOTIFY_BAD;
324                 break;
325         }
326         return NOTIFY_OK;
327 }
328 
329 static int tick_nohz_init_all(void)
330 {
331         int err = -1;
332 
333 #ifdef CONFIG_NO_HZ_FULL_ALL
334         if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
335                 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
336                 return err;
337         }
338         err = 0;
339         cpumask_setall(tick_nohz_full_mask);
340         tick_nohz_full_running = true;
341 #endif
342         return err;
343 }
344 
345 void __init tick_nohz_init(void)
346 {
347         int cpu;
348 
349         if (!tick_nohz_full_running) {
350                 if (tick_nohz_init_all() < 0)
351                         return;
352         }
353 
354         if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
355                 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
356                 cpumask_clear(tick_nohz_full_mask);
357                 tick_nohz_full_running = false;
358                 return;
359         }
360 
361         /*
362          * Full dynticks uses irq work to drive the tick rescheduling on safe
363          * locking contexts. But then we need irq work to raise its own
364          * interrupts to avoid circular dependency on the tick
365          */
366         if (!arch_irq_work_has_interrupt()) {
367                 pr_warning("NO_HZ: Can't run full dynticks because arch doesn't "
368                            "support irq work self-IPIs\n");
369                 cpumask_clear(tick_nohz_full_mask);
370                 cpumask_copy(housekeeping_mask, cpu_possible_mask);
371                 tick_nohz_full_running = false;
372                 return;
373         }
374 
375         cpu = smp_processor_id();
376 
377         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
378                 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
379                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
380         }
381 
382         cpumask_andnot(housekeeping_mask,
383                        cpu_possible_mask, tick_nohz_full_mask);
384 
385         for_each_cpu(cpu, tick_nohz_full_mask)
386                 context_tracking_cpu_set(cpu);
387 
388         cpu_notifier(tick_nohz_cpu_down_callback, 0);
389         pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
390                 cpumask_pr_args(tick_nohz_full_mask));
391 }
392 #endif
393 
394 /*
395  * NOHZ - aka dynamic tick functionality
396  */
397 #ifdef CONFIG_NO_HZ_COMMON
398 /*
399  * NO HZ enabled ?
400  */
401 static int tick_nohz_enabled __read_mostly  = 1;
402 unsigned long tick_nohz_active  __read_mostly;
403 /*
404  * Enable / Disable tickless mode
405  */
406 static int __init setup_tick_nohz(char *str)
407 {
408         if (!strcmp(str, "off"))
409                 tick_nohz_enabled = 0;
410         else if (!strcmp(str, "on"))
411                 tick_nohz_enabled = 1;
412         else
413                 return 0;
414         return 1;
415 }
416 
417 __setup("nohz=", setup_tick_nohz);
418 
419 int tick_nohz_tick_stopped(void)
420 {
421         return __this_cpu_read(tick_cpu_sched.tick_stopped);
422 }
423 
424 /**
425  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
426  *
427  * Called from interrupt entry when the CPU was idle
428  *
429  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
430  * must be updated. Otherwise an interrupt handler could use a stale jiffy
431  * value. We do this unconditionally on any cpu, as we don't know whether the
432  * cpu, which has the update task assigned is in a long sleep.
433  */
434 static void tick_nohz_update_jiffies(ktime_t now)
435 {
436         unsigned long flags;
437 
438         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
439 
440         local_irq_save(flags);
441         tick_do_update_jiffies64(now);
442         local_irq_restore(flags);
443 
444         touch_softlockup_watchdog();
445 }
446 
447 /*
448  * Updates the per cpu time idle statistics counters
449  */
450 static void
451 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
452 {
453         ktime_t delta;
454 
455         if (ts->idle_active) {
456                 delta = ktime_sub(now, ts->idle_entrytime);
457                 if (nr_iowait_cpu(cpu) > 0)
458                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
459                 else
460                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
461                 ts->idle_entrytime = now;
462         }
463 
464         if (last_update_time)
465                 *last_update_time = ktime_to_us(now);
466 
467 }
468 
469 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
470 {
471         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
472         ts->idle_active = 0;
473 
474         sched_clock_idle_wakeup_event(0);
475 }
476 
477 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
478 {
479         ktime_t now = ktime_get();
480 
481         ts->idle_entrytime = now;
482         ts->idle_active = 1;
483         sched_clock_idle_sleep_event();
484         return now;
485 }
486 
487 /**
488  * get_cpu_idle_time_us - get the total idle time of a cpu
489  * @cpu: CPU number to query
490  * @last_update_time: variable to store update time in. Do not update
491  * counters if NULL.
492  *
493  * Return the cummulative idle time (since boot) for a given
494  * CPU, in microseconds.
495  *
496  * This time is measured via accounting rather than sampling,
497  * and is as accurate as ktime_get() is.
498  *
499  * This function returns -1 if NOHZ is not enabled.
500  */
501 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
502 {
503         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
504         ktime_t now, idle;
505 
506         if (!tick_nohz_active)
507                 return -1;
508 
509         now = ktime_get();
510         if (last_update_time) {
511                 update_ts_time_stats(cpu, ts, now, last_update_time);
512                 idle = ts->idle_sleeptime;
513         } else {
514                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
515                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
516 
517                         idle = ktime_add(ts->idle_sleeptime, delta);
518                 } else {
519                         idle = ts->idle_sleeptime;
520                 }
521         }
522 
523         return ktime_to_us(idle);
524 
525 }
526 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
527 
528 /**
529  * get_cpu_iowait_time_us - get the total iowait time of a cpu
530  * @cpu: CPU number to query
531  * @last_update_time: variable to store update time in. Do not update
532  * counters if NULL.
533  *
534  * Return the cummulative iowait time (since boot) for a given
535  * CPU, in microseconds.
536  *
537  * This time is measured via accounting rather than sampling,
538  * and is as accurate as ktime_get() is.
539  *
540  * This function returns -1 if NOHZ is not enabled.
541  */
542 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
543 {
544         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
545         ktime_t now, iowait;
546 
547         if (!tick_nohz_active)
548                 return -1;
549 
550         now = ktime_get();
551         if (last_update_time) {
552                 update_ts_time_stats(cpu, ts, now, last_update_time);
553                 iowait = ts->iowait_sleeptime;
554         } else {
555                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
556                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
557 
558                         iowait = ktime_add(ts->iowait_sleeptime, delta);
559                 } else {
560                         iowait = ts->iowait_sleeptime;
561                 }
562         }
563 
564         return ktime_to_us(iowait);
565 }
566 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
567 
568 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
569 {
570         hrtimer_cancel(&ts->sched_timer);
571         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
572 
573         /* Forward the time to expire in the future */
574         hrtimer_forward(&ts->sched_timer, now, tick_period);
575 
576         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
577                 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
578         else
579                 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
580 }
581 
582 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
583                                          ktime_t now, int cpu)
584 {
585         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
586         u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
587         unsigned long seq, basejiff;
588         ktime_t tick;
589 
590         /* Read jiffies and the time when jiffies were updated last */
591         do {
592                 seq = read_seqbegin(&jiffies_lock);
593                 basemono = last_jiffies_update.tv64;
594                 basejiff = jiffies;
595         } while (read_seqretry(&jiffies_lock, seq));
596         ts->last_jiffies = basejiff;
597 
598         if (rcu_needs_cpu(basemono, &next_rcu) ||
599             arch_needs_cpu() || irq_work_needs_cpu()) {
600                 next_tick = basemono + TICK_NSEC;
601         } else {
602                 /*
603                  * Get the next pending timer. If high resolution
604                  * timers are enabled this only takes the timer wheel
605                  * timers into account. If high resolution timers are
606                  * disabled this also looks at the next expiring
607                  * hrtimer.
608                  */
609                 next_tmr = get_next_timer_interrupt(basejiff, basemono);
610                 ts->next_timer = next_tmr;
611                 /* Take the next rcu event into account */
612                 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
613         }
614 
615         /*
616          * If the tick is due in the next period, keep it ticking or
617          * restart it proper.
618          */
619         delta = next_tick - basemono;
620         if (delta <= (u64)TICK_NSEC) {
621                 tick.tv64 = 0;
622                 if (!ts->tick_stopped)
623                         goto out;
624                 if (delta == 0) {
625                         /* Tick is stopped, but required now. Enforce it */
626                         tick_nohz_restart(ts, now);
627                         goto out;
628                 }
629         }
630 
631         /*
632          * If this cpu is the one which updates jiffies, then give up
633          * the assignment and let it be taken by the cpu which runs
634          * the tick timer next, which might be this cpu as well. If we
635          * don't drop this here the jiffies might be stale and
636          * do_timer() never invoked. Keep track of the fact that it
637          * was the one which had the do_timer() duty last. If this cpu
638          * is the one which had the do_timer() duty last, we limit the
639          * sleep time to the timekeeping max_deferement value.
640          * Otherwise we can sleep as long as we want.
641          */
642         delta = timekeeping_max_deferment();
643         if (cpu == tick_do_timer_cpu) {
644                 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
645                 ts->do_timer_last = 1;
646         } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
647                 delta = KTIME_MAX;
648                 ts->do_timer_last = 0;
649         } else if (!ts->do_timer_last) {
650                 delta = KTIME_MAX;
651         }
652 
653 #ifdef CONFIG_NO_HZ_FULL
654         /* Limit the tick delta to the maximum scheduler deferment */
655         if (!ts->inidle)
656                 delta = min(delta, scheduler_tick_max_deferment());
657 #endif
658 
659         /* Calculate the next expiry time */
660         if (delta < (KTIME_MAX - basemono))
661                 expires = basemono + delta;
662         else
663                 expires = KTIME_MAX;
664 
665         expires = min_t(u64, expires, next_tick);
666         tick.tv64 = expires;
667 
668         /* Skip reprogram of event if its not changed */
669         if (ts->tick_stopped && (expires == dev->next_event.tv64))
670                 goto out;
671 
672         /*
673          * nohz_stop_sched_tick can be called several times before
674          * the nohz_restart_sched_tick is called. This happens when
675          * interrupts arrive which do not cause a reschedule. In the
676          * first call we save the current tick time, so we can restart
677          * the scheduler tick in nohz_restart_sched_tick.
678          */
679         if (!ts->tick_stopped) {
680                 nohz_balance_enter_idle(cpu);
681                 calc_load_enter_idle();
682 
683                 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
684                 ts->tick_stopped = 1;
685                 trace_tick_stop(1, " ");
686         }
687 
688         /*
689          * If the expiration time == KTIME_MAX, then we simply stop
690          * the tick timer.
691          */
692         if (unlikely(expires == KTIME_MAX)) {
693                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
694                         hrtimer_cancel(&ts->sched_timer);
695                 goto out;
696         }
697 
698         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
699                 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
700         else
701                 tick_program_event(tick, 1);
702 out:
703         /* Update the estimated sleep length */
704         ts->sleep_length = ktime_sub(dev->next_event, now);
705         return tick;
706 }
707 
708 static void tick_nohz_full_stop_tick(struct tick_sched *ts)
709 {
710 #ifdef CONFIG_NO_HZ_FULL
711         int cpu = smp_processor_id();
712 
713         if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
714                 return;
715 
716         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
717                 return;
718 
719         if (!can_stop_full_tick())
720                 return;
721 
722         tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
723 #endif
724 }
725 
726 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
727 {
728         /*
729          * If this cpu is offline and it is the one which updates
730          * jiffies, then give up the assignment and let it be taken by
731          * the cpu which runs the tick timer next. If we don't drop
732          * this here the jiffies might be stale and do_timer() never
733          * invoked.
734          */
735         if (unlikely(!cpu_online(cpu))) {
736                 if (cpu == tick_do_timer_cpu)
737                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
738                 return false;
739         }
740 
741         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
742                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
743                 return false;
744         }
745 
746         if (need_resched())
747                 return false;
748 
749         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
750                 static int ratelimit;
751 
752                 if (ratelimit < 10 &&
753                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
754                         pr_warn("NOHZ: local_softirq_pending %02x\n",
755                                 (unsigned int) local_softirq_pending());
756                         ratelimit++;
757                 }
758                 return false;
759         }
760 
761         if (tick_nohz_full_enabled()) {
762                 /*
763                  * Keep the tick alive to guarantee timekeeping progression
764                  * if there are full dynticks CPUs around
765                  */
766                 if (tick_do_timer_cpu == cpu)
767                         return false;
768                 /*
769                  * Boot safety: make sure the timekeeping duty has been
770                  * assigned before entering dyntick-idle mode,
771                  */
772                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
773                         return false;
774         }
775 
776         return true;
777 }
778 
779 static void __tick_nohz_idle_enter(struct tick_sched *ts)
780 {
781         ktime_t now, expires;
782         int cpu = smp_processor_id();
783 
784         now = tick_nohz_start_idle(ts);
785 
786         if (can_stop_idle_tick(cpu, ts)) {
787                 int was_stopped = ts->tick_stopped;
788 
789                 ts->idle_calls++;
790 
791                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
792                 if (expires.tv64 > 0LL) {
793                         ts->idle_sleeps++;
794                         ts->idle_expires = expires;
795                 }
796 
797                 if (!was_stopped && ts->tick_stopped)
798                         ts->idle_jiffies = ts->last_jiffies;
799         }
800 }
801 
802 /**
803  * tick_nohz_idle_enter - stop the idle tick from the idle task
804  *
805  * When the next event is more than a tick into the future, stop the idle tick
806  * Called when we start the idle loop.
807  *
808  * The arch is responsible of calling:
809  *
810  * - rcu_idle_enter() after its last use of RCU before the CPU is put
811  *  to sleep.
812  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
813  */
814 void tick_nohz_idle_enter(void)
815 {
816         struct tick_sched *ts;
817 
818         WARN_ON_ONCE(irqs_disabled());
819 
820         /*
821          * Update the idle state in the scheduler domain hierarchy
822          * when tick_nohz_stop_sched_tick() is called from the idle loop.
823          * State will be updated to busy during the first busy tick after
824          * exiting idle.
825          */
826         set_cpu_sd_state_idle();
827 
828         local_irq_disable();
829 
830         ts = this_cpu_ptr(&tick_cpu_sched);
831         ts->inidle = 1;
832         __tick_nohz_idle_enter(ts);
833 
834         local_irq_enable();
835 }
836 
837 /**
838  * tick_nohz_irq_exit - update next tick event from interrupt exit
839  *
840  * When an interrupt fires while we are idle and it doesn't cause
841  * a reschedule, it may still add, modify or delete a timer, enqueue
842  * an RCU callback, etc...
843  * So we need to re-calculate and reprogram the next tick event.
844  */
845 void tick_nohz_irq_exit(void)
846 {
847         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
848 
849         if (ts->inidle)
850                 __tick_nohz_idle_enter(ts);
851         else
852                 tick_nohz_full_stop_tick(ts);
853 }
854 
855 /**
856  * tick_nohz_get_sleep_length - return the length of the current sleep
857  *
858  * Called from power state control code with interrupts disabled
859  */
860 ktime_t tick_nohz_get_sleep_length(void)
861 {
862         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
863 
864         return ts->sleep_length;
865 }
866 
867 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
868 {
869         /* Update jiffies first */
870         tick_do_update_jiffies64(now);
871         update_cpu_load_nohz();
872 
873         calc_load_exit_idle();
874         touch_softlockup_watchdog();
875         /*
876          * Cancel the scheduled timer and restore the tick
877          */
878         ts->tick_stopped  = 0;
879         ts->idle_exittime = now;
880 
881         tick_nohz_restart(ts, now);
882 }
883 
884 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
885 {
886 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
887         unsigned long ticks;
888 
889         if (vtime_accounting_enabled())
890                 return;
891         /*
892          * We stopped the tick in idle. Update process times would miss the
893          * time we slept as update_process_times does only a 1 tick
894          * accounting. Enforce that this is accounted to idle !
895          */
896         ticks = jiffies - ts->idle_jiffies;
897         /*
898          * We might be one off. Do not randomly account a huge number of ticks!
899          */
900         if (ticks && ticks < LONG_MAX)
901                 account_idle_ticks(ticks);
902 #endif
903 }
904 
905 /**
906  * tick_nohz_idle_exit - restart the idle tick from the idle task
907  *
908  * Restart the idle tick when the CPU is woken up from idle
909  * This also exit the RCU extended quiescent state. The CPU
910  * can use RCU again after this function is called.
911  */
912 void tick_nohz_idle_exit(void)
913 {
914         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
915         ktime_t now;
916 
917         local_irq_disable();
918 
919         WARN_ON_ONCE(!ts->inidle);
920 
921         ts->inidle = 0;
922 
923         if (ts->idle_active || ts->tick_stopped)
924                 now = ktime_get();
925 
926         if (ts->idle_active)
927                 tick_nohz_stop_idle(ts, now);
928 
929         if (ts->tick_stopped) {
930                 tick_nohz_restart_sched_tick(ts, now);
931                 tick_nohz_account_idle_ticks(ts);
932         }
933 
934         local_irq_enable();
935 }
936 
937 /*
938  * The nohz low res interrupt handler
939  */
940 static void tick_nohz_handler(struct clock_event_device *dev)
941 {
942         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
943         struct pt_regs *regs = get_irq_regs();
944         ktime_t now = ktime_get();
945 
946         dev->next_event.tv64 = KTIME_MAX;
947 
948         tick_sched_do_timer(now);
949         tick_sched_handle(ts, regs);
950 
951         /* No need to reprogram if we are running tickless  */
952         if (unlikely(ts->tick_stopped))
953                 return;
954 
955         hrtimer_forward(&ts->sched_timer, now, tick_period);
956         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
957 }
958 
959 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
960 {
961         if (!tick_nohz_enabled)
962                 return;
963         ts->nohz_mode = mode;
964         /* One update is enough */
965         if (!test_and_set_bit(0, &tick_nohz_active))
966                 timers_update_migration(true);
967 }
968 
969 /**
970  * tick_nohz_switch_to_nohz - switch to nohz mode
971  */
972 static void tick_nohz_switch_to_nohz(void)
973 {
974         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
975         ktime_t next;
976 
977         if (!tick_nohz_enabled)
978                 return;
979 
980         if (tick_switch_to_oneshot(tick_nohz_handler))
981                 return;
982 
983         /*
984          * Recycle the hrtimer in ts, so we can share the
985          * hrtimer_forward with the highres code.
986          */
987         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
988         /* Get the next period */
989         next = tick_init_jiffy_update();
990 
991         hrtimer_forward_now(&ts->sched_timer, tick_period);
992         hrtimer_set_expires(&ts->sched_timer, next);
993         tick_program_event(next, 1);
994         tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
995 }
996 
997 /*
998  * When NOHZ is enabled and the tick is stopped, we need to kick the
999  * tick timer from irq_enter() so that the jiffies update is kept
1000  * alive during long running softirqs. That's ugly as hell, but
1001  * correctness is key even if we need to fix the offending softirq in
1002  * the first place.
1003  *
1004  * Note, this is different to tick_nohz_restart. We just kick the
1005  * timer and do not touch the other magic bits which need to be done
1006  * when idle is left.
1007  */
1008 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1009 {
1010 #if 0
1011         /* Switch back to 2.6.27 behaviour */
1012         ktime_t delta;
1013 
1014         /*
1015          * Do not touch the tick device, when the next expiry is either
1016          * already reached or less/equal than the tick period.
1017          */
1018         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1019         if (delta.tv64 <= tick_period.tv64)
1020                 return;
1021 
1022         tick_nohz_restart(ts, now);
1023 #endif
1024 }
1025 
1026 static inline void tick_nohz_irq_enter(void)
1027 {
1028         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1029         ktime_t now;
1030 
1031         if (!ts->idle_active && !ts->tick_stopped)
1032                 return;
1033         now = ktime_get();
1034         if (ts->idle_active)
1035                 tick_nohz_stop_idle(ts, now);
1036         if (ts->tick_stopped) {
1037                 tick_nohz_update_jiffies(now);
1038                 tick_nohz_kick_tick(ts, now);
1039         }
1040 }
1041 
1042 #else
1043 
1044 static inline void tick_nohz_switch_to_nohz(void) { }
1045 static inline void tick_nohz_irq_enter(void) { }
1046 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1047 
1048 #endif /* CONFIG_NO_HZ_COMMON */
1049 
1050 /*
1051  * Called from irq_enter to notify about the possible interruption of idle()
1052  */
1053 void tick_irq_enter(void)
1054 {
1055         tick_check_oneshot_broadcast_this_cpu();
1056         tick_nohz_irq_enter();
1057 }
1058 
1059 /*
1060  * High resolution timer specific code
1061  */
1062 #ifdef CONFIG_HIGH_RES_TIMERS
1063 /*
1064  * We rearm the timer until we get disabled by the idle code.
1065  * Called with interrupts disabled.
1066  */
1067 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1068 {
1069         struct tick_sched *ts =
1070                 container_of(timer, struct tick_sched, sched_timer);
1071         struct pt_regs *regs = get_irq_regs();
1072         ktime_t now = ktime_get();
1073 
1074         tick_sched_do_timer(now);
1075 
1076         /*
1077          * Do not call, when we are not in irq context and have
1078          * no valid regs pointer
1079          */
1080         if (regs)
1081                 tick_sched_handle(ts, regs);
1082 
1083         /* No need to reprogram if we are in idle or full dynticks mode */
1084         if (unlikely(ts->tick_stopped))
1085                 return HRTIMER_NORESTART;
1086 
1087         hrtimer_forward(timer, now, tick_period);
1088 
1089         return HRTIMER_RESTART;
1090 }
1091 
1092 static int sched_skew_tick;
1093 
1094 static int __init skew_tick(char *str)
1095 {
1096         get_option(&str, &sched_skew_tick);
1097 
1098         return 0;
1099 }
1100 early_param("skew_tick", skew_tick);
1101 
1102 /**
1103  * tick_setup_sched_timer - setup the tick emulation timer
1104  */
1105 void tick_setup_sched_timer(void)
1106 {
1107         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1108         ktime_t now = ktime_get();
1109 
1110         /*
1111          * Emulate tick processing via per-CPU hrtimers:
1112          */
1113         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1114         ts->sched_timer.function = tick_sched_timer;
1115 
1116         /* Get the next period (per cpu) */
1117         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1118 
1119         /* Offset the tick to avert jiffies_lock contention. */
1120         if (sched_skew_tick) {
1121                 u64 offset = ktime_to_ns(tick_period) >> 1;
1122                 do_div(offset, num_possible_cpus());
1123                 offset *= smp_processor_id();
1124                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1125         }
1126 
1127         hrtimer_forward(&ts->sched_timer, now, tick_period);
1128         hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1129         tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1130 }
1131 #endif /* HIGH_RES_TIMERS */
1132 
1133 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1134 void tick_cancel_sched_timer(int cpu)
1135 {
1136         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1137 
1138 # ifdef CONFIG_HIGH_RES_TIMERS
1139         if (ts->sched_timer.base)
1140                 hrtimer_cancel(&ts->sched_timer);
1141 # endif
1142 
1143         memset(ts, 0, sizeof(*ts));
1144 }
1145 #endif
1146 
1147 /**
1148  * Async notification about clocksource changes
1149  */
1150 void tick_clock_notify(void)
1151 {
1152         int cpu;
1153 
1154         for_each_possible_cpu(cpu)
1155                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1156 }
1157 
1158 /*
1159  * Async notification about clock event changes
1160  */
1161 void tick_oneshot_notify(void)
1162 {
1163         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1164 
1165         set_bit(0, &ts->check_clocks);
1166 }
1167 
1168 /**
1169  * Check, if a change happened, which makes oneshot possible.
1170  *
1171  * Called cyclic from the hrtimer softirq (driven by the timer
1172  * softirq) allow_nohz signals, that we can switch into low-res nohz
1173  * mode, because high resolution timers are disabled (either compile
1174  * or runtime). Called with interrupts disabled.
1175  */
1176 int tick_check_oneshot_change(int allow_nohz)
1177 {
1178         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1179 
1180         if (!test_and_clear_bit(0, &ts->check_clocks))
1181                 return 0;
1182 
1183         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1184                 return 0;
1185 
1186         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1187                 return 0;
1188 
1189         if (!allow_nohz)
1190                 return 1;
1191 
1192         tick_nohz_switch_to_nohz();
1193         return 0;
1194 }
1195 

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