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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 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 int 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 /**
420  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
421  *
422  * Called from interrupt entry when the CPU was idle
423  *
424  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
425  * must be updated. Otherwise an interrupt handler could use a stale jiffy
426  * value. We do this unconditionally on any cpu, as we don't know whether the
427  * cpu, which has the update task assigned is in a long sleep.
428  */
429 static void tick_nohz_update_jiffies(ktime_t now)
430 {
431         unsigned long flags;
432 
433         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
434 
435         local_irq_save(flags);
436         tick_do_update_jiffies64(now);
437         local_irq_restore(flags);
438 
439         touch_softlockup_watchdog();
440 }
441 
442 /*
443  * Updates the per cpu time idle statistics counters
444  */
445 static void
446 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
447 {
448         ktime_t delta;
449 
450         if (ts->idle_active) {
451                 delta = ktime_sub(now, ts->idle_entrytime);
452                 if (nr_iowait_cpu(cpu) > 0)
453                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
454                 else
455                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
456                 ts->idle_entrytime = now;
457         }
458 
459         if (last_update_time)
460                 *last_update_time = ktime_to_us(now);
461 
462 }
463 
464 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
465 {
466         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
467         ts->idle_active = 0;
468 
469         sched_clock_idle_wakeup_event(0);
470 }
471 
472 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
473 {
474         ktime_t now = ktime_get();
475 
476         ts->idle_entrytime = now;
477         ts->idle_active = 1;
478         sched_clock_idle_sleep_event();
479         return now;
480 }
481 
482 /**
483  * get_cpu_idle_time_us - get the total idle time of a cpu
484  * @cpu: CPU number to query
485  * @last_update_time: variable to store update time in. Do not update
486  * counters if NULL.
487  *
488  * Return the cummulative idle time (since boot) for a given
489  * CPU, in microseconds.
490  *
491  * This time is measured via accounting rather than sampling,
492  * and is as accurate as ktime_get() is.
493  *
494  * This function returns -1 if NOHZ is not enabled.
495  */
496 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
497 {
498         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
499         ktime_t now, idle;
500 
501         if (!tick_nohz_active)
502                 return -1;
503 
504         now = ktime_get();
505         if (last_update_time) {
506                 update_ts_time_stats(cpu, ts, now, last_update_time);
507                 idle = ts->idle_sleeptime;
508         } else {
509                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
510                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
511 
512                         idle = ktime_add(ts->idle_sleeptime, delta);
513                 } else {
514                         idle = ts->idle_sleeptime;
515                 }
516         }
517 
518         return ktime_to_us(idle);
519 
520 }
521 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
522 
523 /**
524  * get_cpu_iowait_time_us - get the total iowait time of a cpu
525  * @cpu: CPU number to query
526  * @last_update_time: variable to store update time in. Do not update
527  * counters if NULL.
528  *
529  * Return the cummulative iowait time (since boot) for a given
530  * CPU, in microseconds.
531  *
532  * This time is measured via accounting rather than sampling,
533  * and is as accurate as ktime_get() is.
534  *
535  * This function returns -1 if NOHZ is not enabled.
536  */
537 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
538 {
539         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
540         ktime_t now, iowait;
541 
542         if (!tick_nohz_active)
543                 return -1;
544 
545         now = ktime_get();
546         if (last_update_time) {
547                 update_ts_time_stats(cpu, ts, now, last_update_time);
548                 iowait = ts->iowait_sleeptime;
549         } else {
550                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
551                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
552 
553                         iowait = ktime_add(ts->iowait_sleeptime, delta);
554                 } else {
555                         iowait = ts->iowait_sleeptime;
556                 }
557         }
558 
559         return ktime_to_us(iowait);
560 }
561 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
562 
563 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
564                                          ktime_t now, int cpu)
565 {
566         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
567         ktime_t last_update, expires, ret = { .tv64 = 0 };
568         unsigned long rcu_delta_jiffies;
569         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
570         u64 time_delta;
571 
572         time_delta = timekeeping_max_deferment();
573 
574         /* Read jiffies and the time when jiffies were updated last */
575         do {
576                 seq = read_seqbegin(&jiffies_lock);
577                 last_update = last_jiffies_update;
578                 last_jiffies = jiffies;
579         } while (read_seqretry(&jiffies_lock, seq));
580 
581         if (rcu_needs_cpu(&rcu_delta_jiffies) ||
582             arch_needs_cpu() || irq_work_needs_cpu()) {
583                 next_jiffies = last_jiffies + 1;
584                 delta_jiffies = 1;
585         } else {
586                 /* Get the next timer wheel timer */
587                 next_jiffies = get_next_timer_interrupt(last_jiffies);
588                 delta_jiffies = next_jiffies - last_jiffies;
589                 if (rcu_delta_jiffies < delta_jiffies) {
590                         next_jiffies = last_jiffies + rcu_delta_jiffies;
591                         delta_jiffies = rcu_delta_jiffies;
592                 }
593         }
594 
595         /*
596          * Do not stop the tick, if we are only one off (or less)
597          * or if the cpu is required for RCU:
598          */
599         if (!ts->tick_stopped && delta_jiffies <= 1)
600                 goto out;
601 
602         /* Schedule the tick, if we are at least one jiffie off */
603         if ((long)delta_jiffies >= 1) {
604 
605                 /*
606                  * If this cpu is the one which updates jiffies, then
607                  * give up the assignment and let it be taken by the
608                  * cpu which runs the tick timer next, which might be
609                  * this cpu as well. If we don't drop this here the
610                  * jiffies might be stale and do_timer() never
611                  * invoked. Keep track of the fact that it was the one
612                  * which had the do_timer() duty last. If this cpu is
613                  * the one which had the do_timer() duty last, we
614                  * limit the sleep time to the timekeeping
615                  * max_deferement value which we retrieved
616                  * above. Otherwise we can sleep as long as we want.
617                  */
618                 if (cpu == tick_do_timer_cpu) {
619                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
620                         ts->do_timer_last = 1;
621                 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
622                         time_delta = KTIME_MAX;
623                         ts->do_timer_last = 0;
624                 } else if (!ts->do_timer_last) {
625                         time_delta = KTIME_MAX;
626                 }
627 
628 #ifdef CONFIG_NO_HZ_FULL
629                 if (!ts->inidle) {
630                         time_delta = min(time_delta,
631                                          scheduler_tick_max_deferment());
632                 }
633 #endif
634 
635                 /*
636                  * calculate the expiry time for the next timer wheel
637                  * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
638                  * that there is no timer pending or at least extremely
639                  * far into the future (12 days for HZ=1000). In this
640                  * case we set the expiry to the end of time.
641                  */
642                 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
643                         /*
644                          * Calculate the time delta for the next timer event.
645                          * If the time delta exceeds the maximum time delta
646                          * permitted by the current clocksource then adjust
647                          * the time delta accordingly to ensure the
648                          * clocksource does not wrap.
649                          */
650                         time_delta = min_t(u64, time_delta,
651                                            tick_period.tv64 * delta_jiffies);
652                 }
653 
654                 if (time_delta < KTIME_MAX)
655                         expires = ktime_add_ns(last_update, time_delta);
656                 else
657                         expires.tv64 = KTIME_MAX;
658 
659                 /* Skip reprogram of event if its not changed */
660                 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
661                         goto out;
662 
663                 ret = expires;
664 
665                 /*
666                  * nohz_stop_sched_tick can be called several times before
667                  * the nohz_restart_sched_tick is called. This happens when
668                  * interrupts arrive which do not cause a reschedule. In the
669                  * first call we save the current tick time, so we can restart
670                  * the scheduler tick in nohz_restart_sched_tick.
671                  */
672                 if (!ts->tick_stopped) {
673                         nohz_balance_enter_idle(cpu);
674                         calc_load_enter_idle();
675 
676                         ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
677                         ts->tick_stopped = 1;
678                         trace_tick_stop(1, " ");
679                 }
680 
681                 /*
682                  * If the expiration time == KTIME_MAX, then
683                  * in this case we simply stop the tick timer.
684                  */
685                  if (unlikely(expires.tv64 == KTIME_MAX)) {
686                         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
687                                 hrtimer_cancel(&ts->sched_timer);
688                         goto out;
689                 }
690 
691                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
692                         hrtimer_start(&ts->sched_timer, expires,
693                                       HRTIMER_MODE_ABS_PINNED);
694                         /* Check, if the timer was already in the past */
695                         if (hrtimer_active(&ts->sched_timer))
696                                 goto out;
697                 } else if (!tick_program_event(expires, 0))
698                                 goto out;
699                 /*
700                  * We are past the event already. So we crossed a
701                  * jiffie boundary. Update jiffies and raise the
702                  * softirq.
703                  */
704                 tick_do_update_jiffies64(ktime_get());
705         }
706         raise_softirq_irqoff(TIMER_SOFTIRQ);
707 out:
708         ts->next_jiffies = next_jiffies;
709         ts->last_jiffies = last_jiffies;
710         ts->sleep_length = ktime_sub(dev->next_event, now);
711 
712         return ret;
713 }
714 
715 static void tick_nohz_full_stop_tick(struct tick_sched *ts)
716 {
717 #ifdef CONFIG_NO_HZ_FULL
718         int cpu = smp_processor_id();
719 
720         if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
721                 return;
722 
723         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
724                 return;
725 
726         if (!can_stop_full_tick())
727                 return;
728 
729         tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
730 #endif
731 }
732 
733 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
734 {
735         /*
736          * If this cpu is offline and it is the one which updates
737          * jiffies, then give up the assignment and let it be taken by
738          * the cpu which runs the tick timer next. If we don't drop
739          * this here the jiffies might be stale and do_timer() never
740          * invoked.
741          */
742         if (unlikely(!cpu_online(cpu))) {
743                 if (cpu == tick_do_timer_cpu)
744                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
745                 return false;
746         }
747 
748         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
749                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
750                 return false;
751         }
752 
753         if (need_resched())
754                 return false;
755 
756         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
757                 static int ratelimit;
758 
759                 if (ratelimit < 10 &&
760                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
761                         pr_warn("NOHZ: local_softirq_pending %02x\n",
762                                 (unsigned int) local_softirq_pending());
763                         ratelimit++;
764                 }
765                 return false;
766         }
767 
768         if (tick_nohz_full_enabled()) {
769                 /*
770                  * Keep the tick alive to guarantee timekeeping progression
771                  * if there are full dynticks CPUs around
772                  */
773                 if (tick_do_timer_cpu == cpu)
774                         return false;
775                 /*
776                  * Boot safety: make sure the timekeeping duty has been
777                  * assigned before entering dyntick-idle mode,
778                  */
779                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
780                         return false;
781         }
782 
783         return true;
784 }
785 
786 static void __tick_nohz_idle_enter(struct tick_sched *ts)
787 {
788         ktime_t now, expires;
789         int cpu = smp_processor_id();
790 
791         now = tick_nohz_start_idle(ts);
792 
793         if (can_stop_idle_tick(cpu, ts)) {
794                 int was_stopped = ts->tick_stopped;
795 
796                 ts->idle_calls++;
797 
798                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
799                 if (expires.tv64 > 0LL) {
800                         ts->idle_sleeps++;
801                         ts->idle_expires = expires;
802                 }
803 
804                 if (!was_stopped && ts->tick_stopped)
805                         ts->idle_jiffies = ts->last_jiffies;
806         }
807 }
808 
809 /**
810  * tick_nohz_idle_enter - stop the idle tick from the idle task
811  *
812  * When the next event is more than a tick into the future, stop the idle tick
813  * Called when we start the idle loop.
814  *
815  * The arch is responsible of calling:
816  *
817  * - rcu_idle_enter() after its last use of RCU before the CPU is put
818  *  to sleep.
819  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
820  */
821 void tick_nohz_idle_enter(void)
822 {
823         struct tick_sched *ts;
824 
825         WARN_ON_ONCE(irqs_disabled());
826 
827         /*
828          * Update the idle state in the scheduler domain hierarchy
829          * when tick_nohz_stop_sched_tick() is called from the idle loop.
830          * State will be updated to busy during the first busy tick after
831          * exiting idle.
832          */
833         set_cpu_sd_state_idle();
834 
835         local_irq_disable();
836 
837         ts = this_cpu_ptr(&tick_cpu_sched);
838         ts->inidle = 1;
839         __tick_nohz_idle_enter(ts);
840 
841         local_irq_enable();
842 }
843 
844 /**
845  * tick_nohz_irq_exit - update next tick event from interrupt exit
846  *
847  * When an interrupt fires while we are idle and it doesn't cause
848  * a reschedule, it may still add, modify or delete a timer, enqueue
849  * an RCU callback, etc...
850  * So we need to re-calculate and reprogram the next tick event.
851  */
852 void tick_nohz_irq_exit(void)
853 {
854         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
855 
856         if (ts->inidle)
857                 __tick_nohz_idle_enter(ts);
858         else
859                 tick_nohz_full_stop_tick(ts);
860 }
861 
862 /**
863  * tick_nohz_get_sleep_length - return the length of the current sleep
864  *
865  * Called from power state control code with interrupts disabled
866  */
867 ktime_t tick_nohz_get_sleep_length(void)
868 {
869         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
870 
871         return ts->sleep_length;
872 }
873 
874 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
875 {
876         hrtimer_cancel(&ts->sched_timer);
877         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
878 
879         while (1) {
880                 /* Forward the time to expire in the future */
881                 hrtimer_forward(&ts->sched_timer, now, tick_period);
882 
883                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
884                         hrtimer_start_expires(&ts->sched_timer,
885                                               HRTIMER_MODE_ABS_PINNED);
886                         /* Check, if the timer was already in the past */
887                         if (hrtimer_active(&ts->sched_timer))
888                                 break;
889                 } else {
890                         if (!tick_program_event(
891                                 hrtimer_get_expires(&ts->sched_timer), 0))
892                                 break;
893                 }
894                 /* Reread time and update jiffies */
895                 now = ktime_get();
896                 tick_do_update_jiffies64(now);
897         }
898 }
899 
900 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
901 {
902         /* Update jiffies first */
903         tick_do_update_jiffies64(now);
904         update_cpu_load_nohz();
905 
906         calc_load_exit_idle();
907         touch_softlockup_watchdog();
908         /*
909          * Cancel the scheduled timer and restore the tick
910          */
911         ts->tick_stopped  = 0;
912         ts->idle_exittime = now;
913 
914         tick_nohz_restart(ts, now);
915 }
916 
917 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
918 {
919 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
920         unsigned long ticks;
921 
922         if (vtime_accounting_enabled())
923                 return;
924         /*
925          * We stopped the tick in idle. Update process times would miss the
926          * time we slept as update_process_times does only a 1 tick
927          * accounting. Enforce that this is accounted to idle !
928          */
929         ticks = jiffies - ts->idle_jiffies;
930         /*
931          * We might be one off. Do not randomly account a huge number of ticks!
932          */
933         if (ticks && ticks < LONG_MAX)
934                 account_idle_ticks(ticks);
935 #endif
936 }
937 
938 /**
939  * tick_nohz_idle_exit - restart the idle tick from the idle task
940  *
941  * Restart the idle tick when the CPU is woken up from idle
942  * This also exit the RCU extended quiescent state. The CPU
943  * can use RCU again after this function is called.
944  */
945 void tick_nohz_idle_exit(void)
946 {
947         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
948         ktime_t now;
949 
950         local_irq_disable();
951 
952         WARN_ON_ONCE(!ts->inidle);
953 
954         ts->inidle = 0;
955 
956         if (ts->idle_active || ts->tick_stopped)
957                 now = ktime_get();
958 
959         if (ts->idle_active)
960                 tick_nohz_stop_idle(ts, now);
961 
962         if (ts->tick_stopped) {
963                 tick_nohz_restart_sched_tick(ts, now);
964                 tick_nohz_account_idle_ticks(ts);
965         }
966 
967         local_irq_enable();
968 }
969 
970 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
971 {
972         hrtimer_forward(&ts->sched_timer, now, tick_period);
973         return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
974 }
975 
976 /*
977  * The nohz low res interrupt handler
978  */
979 static void tick_nohz_handler(struct clock_event_device *dev)
980 {
981         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
982         struct pt_regs *regs = get_irq_regs();
983         ktime_t now = ktime_get();
984 
985         dev->next_event.tv64 = KTIME_MAX;
986 
987         tick_sched_do_timer(now);
988         tick_sched_handle(ts, regs);
989 
990         /* No need to reprogram if we are running tickless  */
991         if (unlikely(ts->tick_stopped))
992                 return;
993 
994         while (tick_nohz_reprogram(ts, now)) {
995                 now = ktime_get();
996                 tick_do_update_jiffies64(now);
997         }
998 }
999 
1000 /**
1001  * tick_nohz_switch_to_nohz - switch to nohz mode
1002  */
1003 static void tick_nohz_switch_to_nohz(void)
1004 {
1005         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1006         ktime_t next;
1007 
1008         if (!tick_nohz_enabled)
1009                 return;
1010 
1011         local_irq_disable();
1012         if (tick_switch_to_oneshot(tick_nohz_handler)) {
1013                 local_irq_enable();
1014                 return;
1015         }
1016         tick_nohz_active = 1;
1017         ts->nohz_mode = NOHZ_MODE_LOWRES;
1018 
1019         /*
1020          * Recycle the hrtimer in ts, so we can share the
1021          * hrtimer_forward with the highres code.
1022          */
1023         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1024         /* Get the next period */
1025         next = tick_init_jiffy_update();
1026 
1027         for (;;) {
1028                 hrtimer_set_expires(&ts->sched_timer, next);
1029                 if (!tick_program_event(next, 0))
1030                         break;
1031                 next = ktime_add(next, tick_period);
1032         }
1033         local_irq_enable();
1034 }
1035 
1036 /*
1037  * When NOHZ is enabled and the tick is stopped, we need to kick the
1038  * tick timer from irq_enter() so that the jiffies update is kept
1039  * alive during long running softirqs. That's ugly as hell, but
1040  * correctness is key even if we need to fix the offending softirq in
1041  * the first place.
1042  *
1043  * Note, this is different to tick_nohz_restart. We just kick the
1044  * timer and do not touch the other magic bits which need to be done
1045  * when idle is left.
1046  */
1047 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1048 {
1049 #if 0
1050         /* Switch back to 2.6.27 behaviour */
1051         ktime_t delta;
1052 
1053         /*
1054          * Do not touch the tick device, when the next expiry is either
1055          * already reached or less/equal than the tick period.
1056          */
1057         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1058         if (delta.tv64 <= tick_period.tv64)
1059                 return;
1060 
1061         tick_nohz_restart(ts, now);
1062 #endif
1063 }
1064 
1065 static inline void tick_nohz_irq_enter(void)
1066 {
1067         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1068         ktime_t now;
1069 
1070         if (!ts->idle_active && !ts->tick_stopped)
1071                 return;
1072         now = ktime_get();
1073         if (ts->idle_active)
1074                 tick_nohz_stop_idle(ts, now);
1075         if (ts->tick_stopped) {
1076                 tick_nohz_update_jiffies(now);
1077                 tick_nohz_kick_tick(ts, now);
1078         }
1079 }
1080 
1081 #else
1082 
1083 static inline void tick_nohz_switch_to_nohz(void) { }
1084 static inline void tick_nohz_irq_enter(void) { }
1085 
1086 #endif /* CONFIG_NO_HZ_COMMON */
1087 
1088 /*
1089  * Called from irq_enter to notify about the possible interruption of idle()
1090  */
1091 void tick_irq_enter(void)
1092 {
1093         tick_check_oneshot_broadcast_this_cpu();
1094         tick_nohz_irq_enter();
1095 }
1096 
1097 /*
1098  * High resolution timer specific code
1099  */
1100 #ifdef CONFIG_HIGH_RES_TIMERS
1101 /*
1102  * We rearm the timer until we get disabled by the idle code.
1103  * Called with interrupts disabled.
1104  */
1105 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1106 {
1107         struct tick_sched *ts =
1108                 container_of(timer, struct tick_sched, sched_timer);
1109         struct pt_regs *regs = get_irq_regs();
1110         ktime_t now = ktime_get();
1111 
1112         tick_sched_do_timer(now);
1113 
1114         /*
1115          * Do not call, when we are not in irq context and have
1116          * no valid regs pointer
1117          */
1118         if (regs)
1119                 tick_sched_handle(ts, regs);
1120 
1121         /* No need to reprogram if we are in idle or full dynticks mode */
1122         if (unlikely(ts->tick_stopped))
1123                 return HRTIMER_NORESTART;
1124 
1125         hrtimer_forward(timer, now, tick_period);
1126 
1127         return HRTIMER_RESTART;
1128 }
1129 
1130 static int sched_skew_tick;
1131 
1132 static int __init skew_tick(char *str)
1133 {
1134         get_option(&str, &sched_skew_tick);
1135 
1136         return 0;
1137 }
1138 early_param("skew_tick", skew_tick);
1139 
1140 /**
1141  * tick_setup_sched_timer - setup the tick emulation timer
1142  */
1143 void tick_setup_sched_timer(void)
1144 {
1145         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1146         ktime_t now = ktime_get();
1147 
1148         /*
1149          * Emulate tick processing via per-CPU hrtimers:
1150          */
1151         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1152         ts->sched_timer.function = tick_sched_timer;
1153 
1154         /* Get the next period (per cpu) */
1155         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1156 
1157         /* Offset the tick to avert jiffies_lock contention. */
1158         if (sched_skew_tick) {
1159                 u64 offset = ktime_to_ns(tick_period) >> 1;
1160                 do_div(offset, num_possible_cpus());
1161                 offset *= smp_processor_id();
1162                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1163         }
1164 
1165         for (;;) {
1166                 hrtimer_forward(&ts->sched_timer, now, tick_period);
1167                 hrtimer_start_expires(&ts->sched_timer,
1168                                       HRTIMER_MODE_ABS_PINNED);
1169                 /* Check, if the timer was already in the past */
1170                 if (hrtimer_active(&ts->sched_timer))
1171                         break;
1172                 now = ktime_get();
1173         }
1174 
1175 #ifdef CONFIG_NO_HZ_COMMON
1176         if (tick_nohz_enabled) {
1177                 ts->nohz_mode = NOHZ_MODE_HIGHRES;
1178                 tick_nohz_active = 1;
1179         }
1180 #endif
1181 }
1182 #endif /* HIGH_RES_TIMERS */
1183 
1184 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1185 void tick_cancel_sched_timer(int cpu)
1186 {
1187         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1188 
1189 # ifdef CONFIG_HIGH_RES_TIMERS
1190         if (ts->sched_timer.base)
1191                 hrtimer_cancel(&ts->sched_timer);
1192 # endif
1193 
1194         memset(ts, 0, sizeof(*ts));
1195 }
1196 #endif
1197 
1198 /**
1199  * Async notification about clocksource changes
1200  */
1201 void tick_clock_notify(void)
1202 {
1203         int cpu;
1204 
1205         for_each_possible_cpu(cpu)
1206                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1207 }
1208 
1209 /*
1210  * Async notification about clock event changes
1211  */
1212 void tick_oneshot_notify(void)
1213 {
1214         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1215 
1216         set_bit(0, &ts->check_clocks);
1217 }
1218 
1219 /**
1220  * Check, if a change happened, which makes oneshot possible.
1221  *
1222  * Called cyclic from the hrtimer softirq (driven by the timer
1223  * softirq) allow_nohz signals, that we can switch into low-res nohz
1224  * mode, because high resolution timers are disabled (either compile
1225  * or runtime).
1226  */
1227 int tick_check_oneshot_change(int allow_nohz)
1228 {
1229         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1230 
1231         if (!test_and_clear_bit(0, &ts->check_clocks))
1232                 return 0;
1233 
1234         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1235                 return 0;
1236 
1237         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1238                 return 0;
1239 
1240         if (!allow_nohz)
1241                 return 1;
1242 
1243         tick_nohz_switch_to_nohz();
1244         return 0;
1245 }
1246 

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