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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 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 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 ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
569                                          ktime_t now, int cpu)
570 {
571         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
572         ktime_t last_update, expires, ret = { .tv64 = 0 };
573         unsigned long rcu_delta_jiffies;
574         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
575         u64 time_delta;
576 
577         time_delta = timekeeping_max_deferment();
578 
579         /* Read jiffies and the time when jiffies were updated last */
580         do {
581                 seq = read_seqbegin(&jiffies_lock);
582                 last_update = last_jiffies_update;
583                 last_jiffies = jiffies;
584         } while (read_seqretry(&jiffies_lock, seq));
585 
586         if (rcu_needs_cpu(&rcu_delta_jiffies) ||
587             arch_needs_cpu() || irq_work_needs_cpu()) {
588                 next_jiffies = last_jiffies + 1;
589                 delta_jiffies = 1;
590         } else {
591                 /* Get the next timer wheel timer */
592                 next_jiffies = get_next_timer_interrupt(last_jiffies);
593                 delta_jiffies = next_jiffies - last_jiffies;
594                 if (rcu_delta_jiffies < delta_jiffies) {
595                         next_jiffies = last_jiffies + rcu_delta_jiffies;
596                         delta_jiffies = rcu_delta_jiffies;
597                 }
598         }
599 
600         /*
601          * Do not stop the tick, if we are only one off (or less)
602          * or if the cpu is required for RCU:
603          */
604         if (!ts->tick_stopped && delta_jiffies <= 1)
605                 goto out;
606 
607         /* Schedule the tick, if we are at least one jiffie off */
608         if ((long)delta_jiffies >= 1) {
609 
610                 /*
611                  * If this cpu is the one which updates jiffies, then
612                  * give up the assignment and let it be taken by the
613                  * cpu which runs the tick timer next, which might be
614                  * this cpu as well. If we don't drop this here the
615                  * jiffies might be stale and do_timer() never
616                  * invoked. Keep track of the fact that it was the one
617                  * which had the do_timer() duty last. If this cpu is
618                  * the one which had the do_timer() duty last, we
619                  * limit the sleep time to the timekeeping
620                  * max_deferement value which we retrieved
621                  * above. Otherwise we can sleep as long as we want.
622                  */
623                 if (cpu == tick_do_timer_cpu) {
624                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
625                         ts->do_timer_last = 1;
626                 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
627                         time_delta = KTIME_MAX;
628                         ts->do_timer_last = 0;
629                 } else if (!ts->do_timer_last) {
630                         time_delta = KTIME_MAX;
631                 }
632 
633 #ifdef CONFIG_NO_HZ_FULL
634                 if (!ts->inidle) {
635                         time_delta = min(time_delta,
636                                          scheduler_tick_max_deferment());
637                 }
638 #endif
639 
640                 /*
641                  * calculate the expiry time for the next timer wheel
642                  * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
643                  * that there is no timer pending or at least extremely
644                  * far into the future (12 days for HZ=1000). In this
645                  * case we set the expiry to the end of time.
646                  */
647                 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
648                         /*
649                          * Calculate the time delta for the next timer event.
650                          * If the time delta exceeds the maximum time delta
651                          * permitted by the current clocksource then adjust
652                          * the time delta accordingly to ensure the
653                          * clocksource does not wrap.
654                          */
655                         time_delta = min_t(u64, time_delta,
656                                            tick_period.tv64 * delta_jiffies);
657                 }
658 
659                 if (time_delta < KTIME_MAX)
660                         expires = ktime_add_ns(last_update, time_delta);
661                 else
662                         expires.tv64 = KTIME_MAX;
663 
664                 /* Skip reprogram of event if its not changed */
665                 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
666                         goto out;
667 
668                 ret = expires;
669 
670                 /*
671                  * nohz_stop_sched_tick can be called several times before
672                  * the nohz_restart_sched_tick is called. This happens when
673                  * interrupts arrive which do not cause a reschedule. In the
674                  * first call we save the current tick time, so we can restart
675                  * the scheduler tick in nohz_restart_sched_tick.
676                  */
677                 if (!ts->tick_stopped) {
678                         nohz_balance_enter_idle(cpu);
679                         calc_load_enter_idle();
680 
681                         ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
682                         ts->tick_stopped = 1;
683                         trace_tick_stop(1, " ");
684                 }
685 
686                 /*
687                  * If the expiration time == KTIME_MAX, then
688                  * in this case we simply stop the tick timer.
689                  */
690                  if (unlikely(expires.tv64 == KTIME_MAX)) {
691                         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
692                                 hrtimer_cancel(&ts->sched_timer);
693                         goto out;
694                 }
695 
696                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
697                         hrtimer_start(&ts->sched_timer, expires,
698                                       HRTIMER_MODE_ABS_PINNED);
699                         /* Check, if the timer was already in the past */
700                         if (hrtimer_active(&ts->sched_timer))
701                                 goto out;
702                 } else if (!tick_program_event(expires, 0))
703                                 goto out;
704                 /*
705                  * We are past the event already. So we crossed a
706                  * jiffie boundary. Update jiffies and raise the
707                  * softirq.
708                  */
709                 tick_do_update_jiffies64(ktime_get());
710         }
711         raise_softirq_irqoff(TIMER_SOFTIRQ);
712 out:
713         ts->next_jiffies = next_jiffies;
714         ts->last_jiffies = last_jiffies;
715         ts->sleep_length = ktime_sub(dev->next_event, now);
716 
717         return ret;
718 }
719 
720 static void tick_nohz_full_stop_tick(struct tick_sched *ts)
721 {
722 #ifdef CONFIG_NO_HZ_FULL
723         int cpu = smp_processor_id();
724 
725         if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
726                 return;
727 
728         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
729                 return;
730 
731         if (!can_stop_full_tick())
732                 return;
733 
734         tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
735 #endif
736 }
737 
738 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
739 {
740         /*
741          * If this cpu is offline and it is the one which updates
742          * jiffies, then give up the assignment and let it be taken by
743          * the cpu which runs the tick timer next. If we don't drop
744          * this here the jiffies might be stale and do_timer() never
745          * invoked.
746          */
747         if (unlikely(!cpu_online(cpu))) {
748                 if (cpu == tick_do_timer_cpu)
749                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
750                 return false;
751         }
752 
753         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
754                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
755                 return false;
756         }
757 
758         if (need_resched())
759                 return false;
760 
761         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
762                 static int ratelimit;
763 
764                 if (ratelimit < 10 &&
765                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
766                         pr_warn("NOHZ: local_softirq_pending %02x\n",
767                                 (unsigned int) local_softirq_pending());
768                         ratelimit++;
769                 }
770                 return false;
771         }
772 
773         if (tick_nohz_full_enabled()) {
774                 /*
775                  * Keep the tick alive to guarantee timekeeping progression
776                  * if there are full dynticks CPUs around
777                  */
778                 if (tick_do_timer_cpu == cpu)
779                         return false;
780                 /*
781                  * Boot safety: make sure the timekeeping duty has been
782                  * assigned before entering dyntick-idle mode,
783                  */
784                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
785                         return false;
786         }
787 
788         return true;
789 }
790 
791 static void __tick_nohz_idle_enter(struct tick_sched *ts)
792 {
793         ktime_t now, expires;
794         int cpu = smp_processor_id();
795 
796         now = tick_nohz_start_idle(ts);
797 
798         if (can_stop_idle_tick(cpu, ts)) {
799                 int was_stopped = ts->tick_stopped;
800 
801                 ts->idle_calls++;
802 
803                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
804                 if (expires.tv64 > 0LL) {
805                         ts->idle_sleeps++;
806                         ts->idle_expires = expires;
807                 }
808 
809                 if (!was_stopped && ts->tick_stopped)
810                         ts->idle_jiffies = ts->last_jiffies;
811         }
812 }
813 
814 /**
815  * tick_nohz_idle_enter - stop the idle tick from the idle task
816  *
817  * When the next event is more than a tick into the future, stop the idle tick
818  * Called when we start the idle loop.
819  *
820  * The arch is responsible of calling:
821  *
822  * - rcu_idle_enter() after its last use of RCU before the CPU is put
823  *  to sleep.
824  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
825  */
826 void tick_nohz_idle_enter(void)
827 {
828         struct tick_sched *ts;
829 
830         WARN_ON_ONCE(irqs_disabled());
831 
832         /*
833          * Update the idle state in the scheduler domain hierarchy
834          * when tick_nohz_stop_sched_tick() is called from the idle loop.
835          * State will be updated to busy during the first busy tick after
836          * exiting idle.
837          */
838         set_cpu_sd_state_idle();
839 
840         local_irq_disable();
841 
842         ts = this_cpu_ptr(&tick_cpu_sched);
843         ts->inidle = 1;
844         __tick_nohz_idle_enter(ts);
845 
846         local_irq_enable();
847 }
848 
849 /**
850  * tick_nohz_irq_exit - update next tick event from interrupt exit
851  *
852  * When an interrupt fires while we are idle and it doesn't cause
853  * a reschedule, it may still add, modify or delete a timer, enqueue
854  * an RCU callback, etc...
855  * So we need to re-calculate and reprogram the next tick event.
856  */
857 void tick_nohz_irq_exit(void)
858 {
859         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
860 
861         if (ts->inidle)
862                 __tick_nohz_idle_enter(ts);
863         else
864                 tick_nohz_full_stop_tick(ts);
865 }
866 
867 /**
868  * tick_nohz_get_sleep_length - return the length of the current sleep
869  *
870  * Called from power state control code with interrupts disabled
871  */
872 ktime_t tick_nohz_get_sleep_length(void)
873 {
874         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
875 
876         return ts->sleep_length;
877 }
878 
879 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
880 {
881         hrtimer_cancel(&ts->sched_timer);
882         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
883 
884         while (1) {
885                 /* Forward the time to expire in the future */
886                 hrtimer_forward(&ts->sched_timer, now, tick_period);
887 
888                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
889                         hrtimer_start_expires(&ts->sched_timer,
890                                               HRTIMER_MODE_ABS_PINNED);
891                         /* Check, if the timer was already in the past */
892                         if (hrtimer_active(&ts->sched_timer))
893                                 break;
894                 } else {
895                         if (!tick_program_event(
896                                 hrtimer_get_expires(&ts->sched_timer), 0))
897                                 break;
898                 }
899                 /* Reread time and update jiffies */
900                 now = ktime_get();
901                 tick_do_update_jiffies64(now);
902         }
903 }
904 
905 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
906 {
907         /* Update jiffies first */
908         tick_do_update_jiffies64(now);
909         update_cpu_load_nohz();
910 
911         calc_load_exit_idle();
912         touch_softlockup_watchdog();
913         /*
914          * Cancel the scheduled timer and restore the tick
915          */
916         ts->tick_stopped  = 0;
917         ts->idle_exittime = now;
918 
919         tick_nohz_restart(ts, now);
920 }
921 
922 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
923 {
924 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
925         unsigned long ticks;
926 
927         if (vtime_accounting_enabled())
928                 return;
929         /*
930          * We stopped the tick in idle. Update process times would miss the
931          * time we slept as update_process_times does only a 1 tick
932          * accounting. Enforce that this is accounted to idle !
933          */
934         ticks = jiffies - ts->idle_jiffies;
935         /*
936          * We might be one off. Do not randomly account a huge number of ticks!
937          */
938         if (ticks && ticks < LONG_MAX)
939                 account_idle_ticks(ticks);
940 #endif
941 }
942 
943 /**
944  * tick_nohz_idle_exit - restart the idle tick from the idle task
945  *
946  * Restart the idle tick when the CPU is woken up from idle
947  * This also exit the RCU extended quiescent state. The CPU
948  * can use RCU again after this function is called.
949  */
950 void tick_nohz_idle_exit(void)
951 {
952         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
953         ktime_t now;
954 
955         local_irq_disable();
956 
957         WARN_ON_ONCE(!ts->inidle);
958 
959         ts->inidle = 0;
960 
961         if (ts->idle_active || ts->tick_stopped)
962                 now = ktime_get();
963 
964         if (ts->idle_active)
965                 tick_nohz_stop_idle(ts, now);
966 
967         if (ts->tick_stopped) {
968                 tick_nohz_restart_sched_tick(ts, now);
969                 tick_nohz_account_idle_ticks(ts);
970         }
971 
972         local_irq_enable();
973 }
974 
975 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
976 {
977         hrtimer_forward(&ts->sched_timer, now, tick_period);
978         return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
979 }
980 
981 /*
982  * The nohz low res interrupt handler
983  */
984 static void tick_nohz_handler(struct clock_event_device *dev)
985 {
986         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
987         struct pt_regs *regs = get_irq_regs();
988         ktime_t now = ktime_get();
989 
990         dev->next_event.tv64 = KTIME_MAX;
991 
992         tick_sched_do_timer(now);
993         tick_sched_handle(ts, regs);
994 
995         /* No need to reprogram if we are running tickless  */
996         if (unlikely(ts->tick_stopped))
997                 return;
998 
999         while (tick_nohz_reprogram(ts, now)) {
1000                 now = ktime_get();
1001                 tick_do_update_jiffies64(now);
1002         }
1003 }
1004 
1005 /**
1006  * tick_nohz_switch_to_nohz - switch to nohz mode
1007  */
1008 static void tick_nohz_switch_to_nohz(void)
1009 {
1010         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1011         ktime_t next;
1012 
1013         if (!tick_nohz_enabled)
1014                 return;
1015 
1016         local_irq_disable();
1017         if (tick_switch_to_oneshot(tick_nohz_handler)) {
1018                 local_irq_enable();
1019                 return;
1020         }
1021         tick_nohz_active = 1;
1022         ts->nohz_mode = NOHZ_MODE_LOWRES;
1023 
1024         /*
1025          * Recycle the hrtimer in ts, so we can share the
1026          * hrtimer_forward with the highres code.
1027          */
1028         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1029         /* Get the next period */
1030         next = tick_init_jiffy_update();
1031 
1032         for (;;) {
1033                 hrtimer_set_expires(&ts->sched_timer, next);
1034                 if (!tick_program_event(next, 0))
1035                         break;
1036                 next = ktime_add(next, tick_period);
1037         }
1038         local_irq_enable();
1039 }
1040 
1041 /*
1042  * When NOHZ is enabled and the tick is stopped, we need to kick the
1043  * tick timer from irq_enter() so that the jiffies update is kept
1044  * alive during long running softirqs. That's ugly as hell, but
1045  * correctness is key even if we need to fix the offending softirq in
1046  * the first place.
1047  *
1048  * Note, this is different to tick_nohz_restart. We just kick the
1049  * timer and do not touch the other magic bits which need to be done
1050  * when idle is left.
1051  */
1052 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1053 {
1054 #if 0
1055         /* Switch back to 2.6.27 behaviour */
1056         ktime_t delta;
1057 
1058         /*
1059          * Do not touch the tick device, when the next expiry is either
1060          * already reached or less/equal than the tick period.
1061          */
1062         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1063         if (delta.tv64 <= tick_period.tv64)
1064                 return;
1065 
1066         tick_nohz_restart(ts, now);
1067 #endif
1068 }
1069 
1070 static inline void tick_nohz_irq_enter(void)
1071 {
1072         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1073         ktime_t now;
1074 
1075         if (!ts->idle_active && !ts->tick_stopped)
1076                 return;
1077         now = ktime_get();
1078         if (ts->idle_active)
1079                 tick_nohz_stop_idle(ts, now);
1080         if (ts->tick_stopped) {
1081                 tick_nohz_update_jiffies(now);
1082                 tick_nohz_kick_tick(ts, now);
1083         }
1084 }
1085 
1086 #else
1087 
1088 static inline void tick_nohz_switch_to_nohz(void) { }
1089 static inline void tick_nohz_irq_enter(void) { }
1090 
1091 #endif /* CONFIG_NO_HZ_COMMON */
1092 
1093 /*
1094  * Called from irq_enter to notify about the possible interruption of idle()
1095  */
1096 void tick_irq_enter(void)
1097 {
1098         tick_check_oneshot_broadcast_this_cpu();
1099         tick_nohz_irq_enter();
1100 }
1101 
1102 /*
1103  * High resolution timer specific code
1104  */
1105 #ifdef CONFIG_HIGH_RES_TIMERS
1106 /*
1107  * We rearm the timer until we get disabled by the idle code.
1108  * Called with interrupts disabled.
1109  */
1110 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1111 {
1112         struct tick_sched *ts =
1113                 container_of(timer, struct tick_sched, sched_timer);
1114         struct pt_regs *regs = get_irq_regs();
1115         ktime_t now = ktime_get();
1116 
1117         tick_sched_do_timer(now);
1118 
1119         /*
1120          * Do not call, when we are not in irq context and have
1121          * no valid regs pointer
1122          */
1123         if (regs)
1124                 tick_sched_handle(ts, regs);
1125 
1126         /* No need to reprogram if we are in idle or full dynticks mode */
1127         if (unlikely(ts->tick_stopped))
1128                 return HRTIMER_NORESTART;
1129 
1130         hrtimer_forward(timer, now, tick_period);
1131 
1132         return HRTIMER_RESTART;
1133 }
1134 
1135 static int sched_skew_tick;
1136 
1137 static int __init skew_tick(char *str)
1138 {
1139         get_option(&str, &sched_skew_tick);
1140 
1141         return 0;
1142 }
1143 early_param("skew_tick", skew_tick);
1144 
1145 /**
1146  * tick_setup_sched_timer - setup the tick emulation timer
1147  */
1148 void tick_setup_sched_timer(void)
1149 {
1150         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1151         ktime_t now = ktime_get();
1152 
1153         /*
1154          * Emulate tick processing via per-CPU hrtimers:
1155          */
1156         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1157         ts->sched_timer.function = tick_sched_timer;
1158 
1159         /* Get the next period (per cpu) */
1160         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1161 
1162         /* Offset the tick to avert jiffies_lock contention. */
1163         if (sched_skew_tick) {
1164                 u64 offset = ktime_to_ns(tick_period) >> 1;
1165                 do_div(offset, num_possible_cpus());
1166                 offset *= smp_processor_id();
1167                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1168         }
1169 
1170         for (;;) {
1171                 hrtimer_forward(&ts->sched_timer, now, tick_period);
1172                 hrtimer_start_expires(&ts->sched_timer,
1173                                       HRTIMER_MODE_ABS_PINNED);
1174                 /* Check, if the timer was already in the past */
1175                 if (hrtimer_active(&ts->sched_timer))
1176                         break;
1177                 now = ktime_get();
1178         }
1179 
1180 #ifdef CONFIG_NO_HZ_COMMON
1181         if (tick_nohz_enabled) {
1182                 ts->nohz_mode = NOHZ_MODE_HIGHRES;
1183                 tick_nohz_active = 1;
1184         }
1185 #endif
1186 }
1187 #endif /* HIGH_RES_TIMERS */
1188 
1189 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1190 void tick_cancel_sched_timer(int cpu)
1191 {
1192         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1193 
1194 # ifdef CONFIG_HIGH_RES_TIMERS
1195         if (ts->sched_timer.base)
1196                 hrtimer_cancel(&ts->sched_timer);
1197 # endif
1198 
1199         memset(ts, 0, sizeof(*ts));
1200 }
1201 #endif
1202 
1203 /**
1204  * Async notification about clocksource changes
1205  */
1206 void tick_clock_notify(void)
1207 {
1208         int cpu;
1209 
1210         for_each_possible_cpu(cpu)
1211                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1212 }
1213 
1214 /*
1215  * Async notification about clock event changes
1216  */
1217 void tick_oneshot_notify(void)
1218 {
1219         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1220 
1221         set_bit(0, &ts->check_clocks);
1222 }
1223 
1224 /**
1225  * Check, if a change happened, which makes oneshot possible.
1226  *
1227  * Called cyclic from the hrtimer softirq (driven by the timer
1228  * softirq) allow_nohz signals, that we can switch into low-res nohz
1229  * mode, because high resolution timers are disabled (either compile
1230  * or runtime).
1231  */
1232 int tick_check_oneshot_change(int allow_nohz)
1233 {
1234         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1235 
1236         if (!test_and_clear_bit(0, &ts->check_clocks))
1237                 return 0;
1238 
1239         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1240                 return 0;
1241 
1242         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1243                 return 0;
1244 
1245         if (!allow_nohz)
1246                 return 1;
1247 
1248         tick_nohz_switch_to_nohz();
1249         return 0;
1250 }
1251 

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