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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 nohz_full_kick_work_func(struct irq_work *work)
201 {
202         /* Empty, the tick restart happens on tick_nohz_irq_exit() */
203 }
204 
205 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
206         .func = nohz_full_kick_work_func,
207 };
208 
209 /*
210  * Kick this CPU if it's full dynticks in order to force it to
211  * re-evaluate its dependency on the tick and restart it if necessary.
212  * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
213  * is NMI safe.
214  */
215 void tick_nohz_full_kick(void)
216 {
217         if (!tick_nohz_full_cpu(smp_processor_id()))
218                 return;
219 
220         irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
221 }
222 
223 /*
224  * Kick the CPU if it's full dynticks in order to force it to
225  * re-evaluate its dependency on the tick and restart it if necessary.
226  */
227 void tick_nohz_full_kick_cpu(int cpu)
228 {
229         if (!tick_nohz_full_cpu(cpu))
230                 return;
231 
232         irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
233 }
234 
235 static void nohz_full_kick_ipi(void *info)
236 {
237         /* Empty, the tick restart happens on tick_nohz_irq_exit() */
238 }
239 
240 /*
241  * Kick all full dynticks CPUs in order to force these to re-evaluate
242  * their dependency on the tick and restart it if necessary.
243  */
244 void tick_nohz_full_kick_all(void)
245 {
246         if (!tick_nohz_full_running)
247                 return;
248 
249         preempt_disable();
250         smp_call_function_many(tick_nohz_full_mask,
251                                nohz_full_kick_ipi, NULL, false);
252         tick_nohz_full_kick();
253         preempt_enable();
254 }
255 
256 /*
257  * Re-evaluate the need for the tick as we switch the current task.
258  * It might need the tick due to per task/process properties:
259  * perf events, posix cpu timers, ...
260  */
261 void __tick_nohz_task_switch(void)
262 {
263         unsigned long flags;
264 
265         local_irq_save(flags);
266 
267         if (!tick_nohz_full_cpu(smp_processor_id()))
268                 goto out;
269 
270         if (tick_nohz_tick_stopped() && !can_stop_full_tick())
271                 tick_nohz_full_kick();
272 
273 out:
274         local_irq_restore(flags);
275 }
276 
277 /* Parse the boot-time nohz CPU list from the kernel parameters. */
278 static int __init tick_nohz_full_setup(char *str)
279 {
280         alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
281         if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
282                 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
283                 free_bootmem_cpumask_var(tick_nohz_full_mask);
284                 return 1;
285         }
286         tick_nohz_full_running = true;
287 
288         return 1;
289 }
290 __setup("nohz_full=", tick_nohz_full_setup);
291 
292 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
293                                        unsigned long action,
294                                        void *hcpu)
295 {
296         unsigned int cpu = (unsigned long)hcpu;
297 
298         switch (action & ~CPU_TASKS_FROZEN) {
299         case CPU_DOWN_PREPARE:
300                 /*
301                  * The boot CPU handles housekeeping duty (unbound timers,
302                  * workqueues, timekeeping, ...) on behalf of full dynticks
303                  * CPUs. It must remain online when nohz full is enabled.
304                  */
305                 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
306                         return NOTIFY_BAD;
307                 break;
308         }
309         return NOTIFY_OK;
310 }
311 
312 static int tick_nohz_init_all(void)
313 {
314         int err = -1;
315 
316 #ifdef CONFIG_NO_HZ_FULL_ALL
317         if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
318                 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
319                 return err;
320         }
321         err = 0;
322         cpumask_setall(tick_nohz_full_mask);
323         tick_nohz_full_running = true;
324 #endif
325         return err;
326 }
327 
328 void __init tick_nohz_init(void)
329 {
330         int cpu;
331 
332         if (!tick_nohz_full_running) {
333                 if (tick_nohz_init_all() < 0)
334                         return;
335         }
336 
337         if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
338                 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
339                 cpumask_clear(tick_nohz_full_mask);
340                 tick_nohz_full_running = false;
341                 return;
342         }
343 
344         /*
345          * Full dynticks uses irq work to drive the tick rescheduling on safe
346          * locking contexts. But then we need irq work to raise its own
347          * interrupts to avoid circular dependency on the tick
348          */
349         if (!arch_irq_work_has_interrupt()) {
350                 pr_warning("NO_HZ: Can't run full dynticks because arch doesn't "
351                            "support irq work self-IPIs\n");
352                 cpumask_clear(tick_nohz_full_mask);
353                 cpumask_copy(housekeeping_mask, cpu_possible_mask);
354                 tick_nohz_full_running = false;
355                 return;
356         }
357 
358         cpu = smp_processor_id();
359 
360         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
361                 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
362                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
363         }
364 
365         cpumask_andnot(housekeeping_mask,
366                        cpu_possible_mask, tick_nohz_full_mask);
367 
368         for_each_cpu(cpu, tick_nohz_full_mask)
369                 context_tracking_cpu_set(cpu);
370 
371         cpu_notifier(tick_nohz_cpu_down_callback, 0);
372         pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
373                 cpumask_pr_args(tick_nohz_full_mask));
374 
375         /*
376          * We need at least one CPU to handle housekeeping work such
377          * as timekeeping, unbound timers, workqueues, ...
378          */
379         WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
380 }
381 #endif
382 
383 /*
384  * NOHZ - aka dynamic tick functionality
385  */
386 #ifdef CONFIG_NO_HZ_COMMON
387 /*
388  * NO HZ enabled ?
389  */
390 static int tick_nohz_enabled __read_mostly  = 1;
391 unsigned long tick_nohz_active  __read_mostly;
392 /*
393  * Enable / Disable tickless mode
394  */
395 static int __init setup_tick_nohz(char *str)
396 {
397         if (!strcmp(str, "off"))
398                 tick_nohz_enabled = 0;
399         else if (!strcmp(str, "on"))
400                 tick_nohz_enabled = 1;
401         else
402                 return 0;
403         return 1;
404 }
405 
406 __setup("nohz=", setup_tick_nohz);
407 
408 int tick_nohz_tick_stopped(void)
409 {
410         return __this_cpu_read(tick_cpu_sched.tick_stopped);
411 }
412 
413 /**
414  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
415  *
416  * Called from interrupt entry when the CPU was idle
417  *
418  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
419  * must be updated. Otherwise an interrupt handler could use a stale jiffy
420  * value. We do this unconditionally on any cpu, as we don't know whether the
421  * cpu, which has the update task assigned is in a long sleep.
422  */
423 static void tick_nohz_update_jiffies(ktime_t now)
424 {
425         unsigned long flags;
426 
427         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
428 
429         local_irq_save(flags);
430         tick_do_update_jiffies64(now);
431         local_irq_restore(flags);
432 
433         touch_softlockup_watchdog();
434 }
435 
436 /*
437  * Updates the per cpu time idle statistics counters
438  */
439 static void
440 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
441 {
442         ktime_t delta;
443 
444         if (ts->idle_active) {
445                 delta = ktime_sub(now, ts->idle_entrytime);
446                 if (nr_iowait_cpu(cpu) > 0)
447                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
448                 else
449                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
450                 ts->idle_entrytime = now;
451         }
452 
453         if (last_update_time)
454                 *last_update_time = ktime_to_us(now);
455 
456 }
457 
458 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
459 {
460         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
461         ts->idle_active = 0;
462 
463         sched_clock_idle_wakeup_event(0);
464 }
465 
466 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
467 {
468         ktime_t now = ktime_get();
469 
470         ts->idle_entrytime = now;
471         ts->idle_active = 1;
472         sched_clock_idle_sleep_event();
473         return now;
474 }
475 
476 /**
477  * get_cpu_idle_time_us - get the total idle time of a cpu
478  * @cpu: CPU number to query
479  * @last_update_time: variable to store update time in. Do not update
480  * counters if NULL.
481  *
482  * Return the cummulative idle time (since boot) for a given
483  * CPU, in microseconds.
484  *
485  * This time is measured via accounting rather than sampling,
486  * and is as accurate as ktime_get() is.
487  *
488  * This function returns -1 if NOHZ is not enabled.
489  */
490 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
491 {
492         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
493         ktime_t now, idle;
494 
495         if (!tick_nohz_active)
496                 return -1;
497 
498         now = ktime_get();
499         if (last_update_time) {
500                 update_ts_time_stats(cpu, ts, now, last_update_time);
501                 idle = ts->idle_sleeptime;
502         } else {
503                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
504                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
505 
506                         idle = ktime_add(ts->idle_sleeptime, delta);
507                 } else {
508                         idle = ts->idle_sleeptime;
509                 }
510         }
511 
512         return ktime_to_us(idle);
513 
514 }
515 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
516 
517 /**
518  * get_cpu_iowait_time_us - get the total iowait time of a cpu
519  * @cpu: CPU number to query
520  * @last_update_time: variable to store update time in. Do not update
521  * counters if NULL.
522  *
523  * Return the cummulative iowait time (since boot) for a given
524  * CPU, in microseconds.
525  *
526  * This time is measured via accounting rather than sampling,
527  * and is as accurate as ktime_get() is.
528  *
529  * This function returns -1 if NOHZ is not enabled.
530  */
531 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
532 {
533         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
534         ktime_t now, iowait;
535 
536         if (!tick_nohz_active)
537                 return -1;
538 
539         now = ktime_get();
540         if (last_update_time) {
541                 update_ts_time_stats(cpu, ts, now, last_update_time);
542                 iowait = ts->iowait_sleeptime;
543         } else {
544                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
545                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
546 
547                         iowait = ktime_add(ts->iowait_sleeptime, delta);
548                 } else {
549                         iowait = ts->iowait_sleeptime;
550                 }
551         }
552 
553         return ktime_to_us(iowait);
554 }
555 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
556 
557 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
558 {
559         hrtimer_cancel(&ts->sched_timer);
560         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
561 
562         /* Forward the time to expire in the future */
563         hrtimer_forward(&ts->sched_timer, now, tick_period);
564 
565         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
566                 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
567         else
568                 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
569 }
570 
571 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
572                                          ktime_t now, int cpu)
573 {
574         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
575         u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
576         unsigned long seq, basejiff;
577         ktime_t tick;
578 
579         /* Read jiffies and the time when jiffies were updated last */
580         do {
581                 seq = read_seqbegin(&jiffies_lock);
582                 basemono = last_jiffies_update.tv64;
583                 basejiff = jiffies;
584         } while (read_seqretry(&jiffies_lock, seq));
585         ts->last_jiffies = basejiff;
586 
587         if (rcu_needs_cpu(basemono, &next_rcu) ||
588             arch_needs_cpu() || irq_work_needs_cpu()) {
589                 next_tick = basemono + TICK_NSEC;
590         } else {
591                 /*
592                  * Get the next pending timer. If high resolution
593                  * timers are enabled this only takes the timer wheel
594                  * timers into account. If high resolution timers are
595                  * disabled this also looks at the next expiring
596                  * hrtimer.
597                  */
598                 next_tmr = get_next_timer_interrupt(basejiff, basemono);
599                 ts->next_timer = next_tmr;
600                 /* Take the next rcu event into account */
601                 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
602         }
603 
604         /*
605          * If the tick is due in the next period, keep it ticking or
606          * restart it proper.
607          */
608         delta = next_tick - basemono;
609         if (delta <= (u64)TICK_NSEC) {
610                 tick.tv64 = 0;
611                 if (!ts->tick_stopped)
612                         goto out;
613                 if (delta == 0) {
614                         /* Tick is stopped, but required now. Enforce it */
615                         tick_nohz_restart(ts, now);
616                         goto out;
617                 }
618         }
619 
620         /*
621          * If this cpu is the one which updates jiffies, then give up
622          * the assignment and let it be taken by the cpu which runs
623          * the tick timer next, which might be this cpu as well. If we
624          * don't drop this here the jiffies might be stale and
625          * do_timer() never invoked. Keep track of the fact that it
626          * was the one which had the do_timer() duty last. If this cpu
627          * is the one which had the do_timer() duty last, we limit the
628          * sleep time to the timekeeping max_deferement value.
629          * Otherwise we can sleep as long as we want.
630          */
631         delta = timekeeping_max_deferment();
632         if (cpu == tick_do_timer_cpu) {
633                 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
634                 ts->do_timer_last = 1;
635         } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
636                 delta = KTIME_MAX;
637                 ts->do_timer_last = 0;
638         } else if (!ts->do_timer_last) {
639                 delta = KTIME_MAX;
640         }
641 
642 #ifdef CONFIG_NO_HZ_FULL
643         /* Limit the tick delta to the maximum scheduler deferment */
644         if (!ts->inidle)
645                 delta = min(delta, scheduler_tick_max_deferment());
646 #endif
647 
648         /* Calculate the next expiry time */
649         if (delta < (KTIME_MAX - basemono))
650                 expires = basemono + delta;
651         else
652                 expires = KTIME_MAX;
653 
654         expires = min_t(u64, expires, next_tick);
655         tick.tv64 = expires;
656 
657         /* Skip reprogram of event if its not changed */
658         if (ts->tick_stopped && (expires == dev->next_event.tv64))
659                 goto out;
660 
661         /*
662          * nohz_stop_sched_tick can be called several times before
663          * the nohz_restart_sched_tick is called. This happens when
664          * interrupts arrive which do not cause a reschedule. In the
665          * first call we save the current tick time, so we can restart
666          * the scheduler tick in nohz_restart_sched_tick.
667          */
668         if (!ts->tick_stopped) {
669                 nohz_balance_enter_idle(cpu);
670                 calc_load_enter_idle();
671 
672                 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
673                 ts->tick_stopped = 1;
674                 trace_tick_stop(1, " ");
675         }
676 
677         /*
678          * If the expiration time == KTIME_MAX, then we simply stop
679          * the tick timer.
680          */
681         if (unlikely(expires == KTIME_MAX)) {
682                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
683                         hrtimer_cancel(&ts->sched_timer);
684                 goto out;
685         }
686 
687         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
688                 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
689         else
690                 tick_program_event(tick, 1);
691 out:
692         /* Update the estimated sleep length */
693         ts->sleep_length = ktime_sub(dev->next_event, now);
694         return tick;
695 }
696 
697 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
698 {
699         /* Update jiffies first */
700         tick_do_update_jiffies64(now);
701         update_cpu_load_nohz();
702 
703         calc_load_exit_idle();
704         touch_softlockup_watchdog();
705         /*
706          * Cancel the scheduled timer and restore the tick
707          */
708         ts->tick_stopped  = 0;
709         ts->idle_exittime = now;
710 
711         tick_nohz_restart(ts, now);
712 }
713 
714 static void tick_nohz_full_update_tick(struct tick_sched *ts)
715 {
716 #ifdef CONFIG_NO_HZ_FULL
717         int cpu = smp_processor_id();
718 
719         if (!tick_nohz_full_cpu(cpu))
720                 return;
721 
722         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
723                 return;
724 
725         if (can_stop_full_tick())
726                 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
727         else if (ts->tick_stopped)
728                 tick_nohz_restart_sched_tick(ts, ktime_get());
729 #endif
730 }
731 
732 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
733 {
734         /*
735          * If this cpu is offline and it is the one which updates
736          * jiffies, then give up the assignment and let it be taken by
737          * the cpu which runs the tick timer next. If we don't drop
738          * this here the jiffies might be stale and do_timer() never
739          * invoked.
740          */
741         if (unlikely(!cpu_online(cpu))) {
742                 if (cpu == tick_do_timer_cpu)
743                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
744                 return false;
745         }
746 
747         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
748                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
749                 return false;
750         }
751 
752         if (need_resched())
753                 return false;
754 
755         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
756                 static int ratelimit;
757 
758                 if (ratelimit < 10 &&
759                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
760                         pr_warn("NOHZ: local_softirq_pending %02x\n",
761                                 (unsigned int) local_softirq_pending());
762                         ratelimit++;
763                 }
764                 return false;
765         }
766 
767         if (tick_nohz_full_enabled()) {
768                 /*
769                  * Keep the tick alive to guarantee timekeeping progression
770                  * if there are full dynticks CPUs around
771                  */
772                 if (tick_do_timer_cpu == cpu)
773                         return false;
774                 /*
775                  * Boot safety: make sure the timekeeping duty has been
776                  * assigned before entering dyntick-idle mode,
777                  */
778                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
779                         return false;
780         }
781 
782         return true;
783 }
784 
785 static void __tick_nohz_idle_enter(struct tick_sched *ts)
786 {
787         ktime_t now, expires;
788         int cpu = smp_processor_id();
789 
790         now = tick_nohz_start_idle(ts);
791 
792         if (can_stop_idle_tick(cpu, ts)) {
793                 int was_stopped = ts->tick_stopped;
794 
795                 ts->idle_calls++;
796 
797                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
798                 if (expires.tv64 > 0LL) {
799                         ts->idle_sleeps++;
800                         ts->idle_expires = expires;
801                 }
802 
803                 if (!was_stopped && ts->tick_stopped)
804                         ts->idle_jiffies = ts->last_jiffies;
805         }
806 }
807 
808 /**
809  * tick_nohz_idle_enter - stop the idle tick from the idle task
810  *
811  * When the next event is more than a tick into the future, stop the idle tick
812  * Called when we start the idle loop.
813  *
814  * The arch is responsible of calling:
815  *
816  * - rcu_idle_enter() after its last use of RCU before the CPU is put
817  *  to sleep.
818  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
819  */
820 void tick_nohz_idle_enter(void)
821 {
822         struct tick_sched *ts;
823 
824         WARN_ON_ONCE(irqs_disabled());
825 
826         /*
827          * Update the idle state in the scheduler domain hierarchy
828          * when tick_nohz_stop_sched_tick() is called from the idle loop.
829          * State will be updated to busy during the first busy tick after
830          * exiting idle.
831          */
832         set_cpu_sd_state_idle();
833 
834         local_irq_disable();
835 
836         ts = this_cpu_ptr(&tick_cpu_sched);
837         ts->inidle = 1;
838         __tick_nohz_idle_enter(ts);
839 
840         local_irq_enable();
841 }
842 
843 /**
844  * tick_nohz_irq_exit - update next tick event from interrupt exit
845  *
846  * When an interrupt fires while we are idle and it doesn't cause
847  * a reschedule, it may still add, modify or delete a timer, enqueue
848  * an RCU callback, etc...
849  * So we need to re-calculate and reprogram the next tick event.
850  */
851 void tick_nohz_irq_exit(void)
852 {
853         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
854 
855         if (ts->inidle)
856                 __tick_nohz_idle_enter(ts);
857         else
858                 tick_nohz_full_update_tick(ts);
859 }
860 
861 /**
862  * tick_nohz_get_sleep_length - return the length of the current sleep
863  *
864  * Called from power state control code with interrupts disabled
865  */
866 ktime_t tick_nohz_get_sleep_length(void)
867 {
868         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
869 
870         return ts->sleep_length;
871 }
872 
873 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
874 {
875 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
876         unsigned long ticks;
877 
878         if (vtime_accounting_enabled())
879                 return;
880         /*
881          * We stopped the tick in idle. Update process times would miss the
882          * time we slept as update_process_times does only a 1 tick
883          * accounting. Enforce that this is accounted to idle !
884          */
885         ticks = jiffies - ts->idle_jiffies;
886         /*
887          * We might be one off. Do not randomly account a huge number of ticks!
888          */
889         if (ticks && ticks < LONG_MAX)
890                 account_idle_ticks(ticks);
891 #endif
892 }
893 
894 /**
895  * tick_nohz_idle_exit - restart the idle tick from the idle task
896  *
897  * Restart the idle tick when the CPU is woken up from idle
898  * This also exit the RCU extended quiescent state. The CPU
899  * can use RCU again after this function is called.
900  */
901 void tick_nohz_idle_exit(void)
902 {
903         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
904         ktime_t now;
905 
906         local_irq_disable();
907 
908         WARN_ON_ONCE(!ts->inidle);
909 
910         ts->inidle = 0;
911 
912         if (ts->idle_active || ts->tick_stopped)
913                 now = ktime_get();
914 
915         if (ts->idle_active)
916                 tick_nohz_stop_idle(ts, now);
917 
918         if (ts->tick_stopped) {
919                 tick_nohz_restart_sched_tick(ts, now);
920                 tick_nohz_account_idle_ticks(ts);
921         }
922 
923         local_irq_enable();
924 }
925 
926 /*
927  * The nohz low res interrupt handler
928  */
929 static void tick_nohz_handler(struct clock_event_device *dev)
930 {
931         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
932         struct pt_regs *regs = get_irq_regs();
933         ktime_t now = ktime_get();
934 
935         dev->next_event.tv64 = KTIME_MAX;
936 
937         tick_sched_do_timer(now);
938         tick_sched_handle(ts, regs);
939 
940         /* No need to reprogram if we are running tickless  */
941         if (unlikely(ts->tick_stopped))
942                 return;
943 
944         hrtimer_forward(&ts->sched_timer, now, tick_period);
945         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
946 }
947 
948 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
949 {
950         if (!tick_nohz_enabled)
951                 return;
952         ts->nohz_mode = mode;
953         /* One update is enough */
954         if (!test_and_set_bit(0, &tick_nohz_active))
955                 timers_update_migration(true);
956 }
957 
958 /**
959  * tick_nohz_switch_to_nohz - switch to nohz mode
960  */
961 static void tick_nohz_switch_to_nohz(void)
962 {
963         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
964         ktime_t next;
965 
966         if (!tick_nohz_enabled)
967                 return;
968 
969         if (tick_switch_to_oneshot(tick_nohz_handler))
970                 return;
971 
972         /*
973          * Recycle the hrtimer in ts, so we can share the
974          * hrtimer_forward with the highres code.
975          */
976         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
977         /* Get the next period */
978         next = tick_init_jiffy_update();
979 
980         hrtimer_forward_now(&ts->sched_timer, tick_period);
981         hrtimer_set_expires(&ts->sched_timer, next);
982         tick_program_event(next, 1);
983         tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
984 }
985 
986 /*
987  * When NOHZ is enabled and the tick is stopped, we need to kick the
988  * tick timer from irq_enter() so that the jiffies update is kept
989  * alive during long running softirqs. That's ugly as hell, but
990  * correctness is key even if we need to fix the offending softirq in
991  * the first place.
992  *
993  * Note, this is different to tick_nohz_restart. We just kick the
994  * timer and do not touch the other magic bits which need to be done
995  * when idle is left.
996  */
997 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
998 {
999 #if 0
1000         /* Switch back to 2.6.27 behaviour */
1001         ktime_t delta;
1002 
1003         /*
1004          * Do not touch the tick device, when the next expiry is either
1005          * already reached or less/equal than the tick period.
1006          */
1007         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1008         if (delta.tv64 <= tick_period.tv64)
1009                 return;
1010 
1011         tick_nohz_restart(ts, now);
1012 #endif
1013 }
1014 
1015 static inline void tick_nohz_irq_enter(void)
1016 {
1017         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1018         ktime_t now;
1019 
1020         if (!ts->idle_active && !ts->tick_stopped)
1021                 return;
1022         now = ktime_get();
1023         if (ts->idle_active)
1024                 tick_nohz_stop_idle(ts, now);
1025         if (ts->tick_stopped) {
1026                 tick_nohz_update_jiffies(now);
1027                 tick_nohz_kick_tick(ts, now);
1028         }
1029 }
1030 
1031 #else
1032 
1033 static inline void tick_nohz_switch_to_nohz(void) { }
1034 static inline void tick_nohz_irq_enter(void) { }
1035 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1036 
1037 #endif /* CONFIG_NO_HZ_COMMON */
1038 
1039 /*
1040  * Called from irq_enter to notify about the possible interruption of idle()
1041  */
1042 void tick_irq_enter(void)
1043 {
1044         tick_check_oneshot_broadcast_this_cpu();
1045         tick_nohz_irq_enter();
1046 }
1047 
1048 /*
1049  * High resolution timer specific code
1050  */
1051 #ifdef CONFIG_HIGH_RES_TIMERS
1052 /*
1053  * We rearm the timer until we get disabled by the idle code.
1054  * Called with interrupts disabled.
1055  */
1056 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1057 {
1058         struct tick_sched *ts =
1059                 container_of(timer, struct tick_sched, sched_timer);
1060         struct pt_regs *regs = get_irq_regs();
1061         ktime_t now = ktime_get();
1062 
1063         tick_sched_do_timer(now);
1064 
1065         /*
1066          * Do not call, when we are not in irq context and have
1067          * no valid regs pointer
1068          */
1069         if (regs)
1070                 tick_sched_handle(ts, regs);
1071 
1072         /* No need to reprogram if we are in idle or full dynticks mode */
1073         if (unlikely(ts->tick_stopped))
1074                 return HRTIMER_NORESTART;
1075 
1076         hrtimer_forward(timer, now, tick_period);
1077 
1078         return HRTIMER_RESTART;
1079 }
1080 
1081 static int sched_skew_tick;
1082 
1083 static int __init skew_tick(char *str)
1084 {
1085         get_option(&str, &sched_skew_tick);
1086 
1087         return 0;
1088 }
1089 early_param("skew_tick", skew_tick);
1090 
1091 /**
1092  * tick_setup_sched_timer - setup the tick emulation timer
1093  */
1094 void tick_setup_sched_timer(void)
1095 {
1096         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1097         ktime_t now = ktime_get();
1098 
1099         /*
1100          * Emulate tick processing via per-CPU hrtimers:
1101          */
1102         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1103         ts->sched_timer.function = tick_sched_timer;
1104 
1105         /* Get the next period (per cpu) */
1106         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1107 
1108         /* Offset the tick to avert jiffies_lock contention. */
1109         if (sched_skew_tick) {
1110                 u64 offset = ktime_to_ns(tick_period) >> 1;
1111                 do_div(offset, num_possible_cpus());
1112                 offset *= smp_processor_id();
1113                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1114         }
1115 
1116         hrtimer_forward(&ts->sched_timer, now, tick_period);
1117         hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1118         tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1119 }
1120 #endif /* HIGH_RES_TIMERS */
1121 
1122 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1123 void tick_cancel_sched_timer(int cpu)
1124 {
1125         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1126 
1127 # ifdef CONFIG_HIGH_RES_TIMERS
1128         if (ts->sched_timer.base)
1129                 hrtimer_cancel(&ts->sched_timer);
1130 # endif
1131 
1132         memset(ts, 0, sizeof(*ts));
1133 }
1134 #endif
1135 
1136 /**
1137  * Async notification about clocksource changes
1138  */
1139 void tick_clock_notify(void)
1140 {
1141         int cpu;
1142 
1143         for_each_possible_cpu(cpu)
1144                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1145 }
1146 
1147 /*
1148  * Async notification about clock event changes
1149  */
1150 void tick_oneshot_notify(void)
1151 {
1152         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1153 
1154         set_bit(0, &ts->check_clocks);
1155 }
1156 
1157 /**
1158  * Check, if a change happened, which makes oneshot possible.
1159  *
1160  * Called cyclic from the hrtimer softirq (driven by the timer
1161  * softirq) allow_nohz signals, that we can switch into low-res nohz
1162  * mode, because high resolution timers are disabled (either compile
1163  * or runtime). Called with interrupts disabled.
1164  */
1165 int tick_check_oneshot_change(int allow_nohz)
1166 {
1167         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1168 
1169         if (!test_and_clear_bit(0, &ts->check_clocks))
1170                 return 0;
1171 
1172         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1173                 return 0;
1174 
1175         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1176                 return 0;
1177 
1178         if (!allow_nohz)
1179                 return 1;
1180 
1181         tick_nohz_switch_to_nohz();
1182         return 0;
1183 }
1184 

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