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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         }
 88         write_sequnlock(&jiffies_lock);
 89         update_wall_time();
 90 }
 91 
 92 /*
 93  * Initialize and return retrieve the jiffies update.
 94  */
 95 static ktime_t tick_init_jiffy_update(void)
 96 {
 97         ktime_t period;
 98 
 99         write_seqlock(&jiffies_lock);
100         /* Did we start the jiffies update yet ? */
101         if (last_jiffies_update.tv64 == 0)
102                 last_jiffies_update = tick_next_period;
103         period = last_jiffies_update;
104         write_sequnlock(&jiffies_lock);
105         return period;
106 }
107 
108 
109 static void tick_sched_do_timer(ktime_t now)
110 {
111         int cpu = smp_processor_id();
112 
113 #ifdef CONFIG_NO_HZ_COMMON
114         /*
115          * Check if the do_timer duty was dropped. We don't care about
116          * concurrency: This happens only when the cpu in charge went
117          * into a long sleep. If two cpus happen to assign themself to
118          * this duty, then the jiffies update is still serialized by
119          * jiffies_lock.
120          */
121         if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
122             && !tick_nohz_full_cpu(cpu))
123                 tick_do_timer_cpu = cpu;
124 #endif
125 
126         /* Check, if the jiffies need an update */
127         if (tick_do_timer_cpu == cpu)
128                 tick_do_update_jiffies64(now);
129 }
130 
131 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
132 {
133 #ifdef CONFIG_NO_HZ_COMMON
134         /*
135          * When we are idle and the tick is stopped, we have to touch
136          * the watchdog as we might not schedule for a really long
137          * time. This happens on complete idle SMP systems while
138          * waiting on the login prompt. We also increment the "start of
139          * idle" jiffy stamp so the idle accounting adjustment we do
140          * when we go busy again does not account too much ticks.
141          */
142         if (ts->tick_stopped) {
143                 touch_softlockup_watchdog();
144                 if (is_idle_task(current))
145                         ts->idle_jiffies++;
146         }
147 #endif
148         update_process_times(user_mode(regs));
149         profile_tick(CPU_PROFILING);
150 }
151 
152 #ifdef CONFIG_NO_HZ_FULL
153 cpumask_var_t tick_nohz_full_mask;
154 bool tick_nohz_full_running;
155 
156 static bool can_stop_full_tick(void)
157 {
158         WARN_ON_ONCE(!irqs_disabled());
159 
160         if (!sched_can_stop_tick()) {
161                 trace_tick_stop(0, "more than 1 task in runqueue\n");
162                 return false;
163         }
164 
165         if (!posix_cpu_timers_can_stop_tick(current)) {
166                 trace_tick_stop(0, "posix timers running\n");
167                 return false;
168         }
169 
170         if (!perf_event_can_stop_tick()) {
171                 trace_tick_stop(0, "perf events running\n");
172                 return false;
173         }
174 
175         /* sched_clock_tick() needs us? */
176 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
177         /*
178          * TODO: kick full dynticks CPUs when
179          * sched_clock_stable is set.
180          */
181         if (!sched_clock_stable()) {
182                 trace_tick_stop(0, "unstable sched clock\n");
183                 /*
184                  * Don't allow the user to think they can get
185                  * full NO_HZ with this machine.
186                  */
187                 WARN_ONCE(tick_nohz_full_running,
188                           "NO_HZ FULL will not work with unstable sched clock");
189                 return false;
190         }
191 #endif
192 
193         return true;
194 }
195 
196 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
197 
198 /*
199  * Re-evaluate the need for the tick on the current CPU
200  * and restart it if necessary.
201  */
202 void __tick_nohz_full_check(void)
203 {
204         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
205 
206         if (tick_nohz_full_cpu(smp_processor_id())) {
207                 if (ts->tick_stopped && !is_idle_task(current)) {
208                         if (!can_stop_full_tick())
209                                 tick_nohz_restart_sched_tick(ts, ktime_get());
210                 }
211         }
212 }
213 
214 static void nohz_full_kick_work_func(struct irq_work *work)
215 {
216         __tick_nohz_full_check();
217 }
218 
219 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
220         .func = nohz_full_kick_work_func,
221 };
222 
223 /*
224  * Kick the current 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(void)
228 {
229         if (tick_nohz_full_cpu(smp_processor_id()))
230                 irq_work_queue(&__get_cpu_var(nohz_full_kick_work));
231 }
232 
233 static void nohz_full_kick_ipi(void *info)
234 {
235         __tick_nohz_full_check();
236 }
237 
238 /*
239  * Kick all full dynticks CPUs in order to force these to re-evaluate
240  * their dependency on the tick and restart it if necessary.
241  */
242 void tick_nohz_full_kick_all(void)
243 {
244         if (!tick_nohz_full_running)
245                 return;
246 
247         preempt_disable();
248         smp_call_function_many(tick_nohz_full_mask,
249                                nohz_full_kick_ipi, NULL, false);
250         tick_nohz_full_kick();
251         preempt_enable();
252 }
253 
254 /*
255  * Re-evaluate the need for the tick as we switch the current task.
256  * It might need the tick due to per task/process properties:
257  * perf events, posix cpu timers, ...
258  */
259 void __tick_nohz_task_switch(struct task_struct *tsk)
260 {
261         unsigned long flags;
262 
263         local_irq_save(flags);
264 
265         if (!tick_nohz_full_cpu(smp_processor_id()))
266                 goto out;
267 
268         if (tick_nohz_tick_stopped() && !can_stop_full_tick())
269                 tick_nohz_full_kick();
270 
271 out:
272         local_irq_restore(flags);
273 }
274 
275 /* Parse the boot-time nohz CPU list from the kernel parameters. */
276 static int __init tick_nohz_full_setup(char *str)
277 {
278         int cpu;
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                 return 1;
284         }
285 
286         cpu = smp_processor_id();
287         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
288                 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
289                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
290         }
291         tick_nohz_full_running = true;
292 
293         return 1;
294 }
295 __setup("nohz_full=", tick_nohz_full_setup);
296 
297 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
298                                                  unsigned long action,
299                                                  void *hcpu)
300 {
301         unsigned int cpu = (unsigned long)hcpu;
302 
303         switch (action & ~CPU_TASKS_FROZEN) {
304         case CPU_DOWN_PREPARE:
305                 /*
306                  * If we handle the timekeeping duty for full dynticks CPUs,
307                  * we can't safely shutdown that CPU.
308                  */
309                 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
310                         return NOTIFY_BAD;
311                 break;
312         }
313         return NOTIFY_OK;
314 }
315 
316 /*
317  * Worst case string length in chunks of CPU range seems 2 steps
318  * separations: 0,2,4,6,...
319  * This is NR_CPUS + sizeof('\0')
320  */
321 static char __initdata nohz_full_buf[NR_CPUS + 1];
322 
323 static int tick_nohz_init_all(void)
324 {
325         int err = -1;
326 
327 #ifdef CONFIG_NO_HZ_FULL_ALL
328         if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
329                 pr_err("NO_HZ: Can't allocate full dynticks cpumask\n");
330                 return err;
331         }
332         err = 0;
333         cpumask_setall(tick_nohz_full_mask);
334         cpumask_clear_cpu(smp_processor_id(), tick_nohz_full_mask);
335         tick_nohz_full_running = true;
336 #endif
337         return err;
338 }
339 
340 void __init tick_nohz_init(void)
341 {
342         int cpu;
343 
344         if (!tick_nohz_full_running) {
345                 if (tick_nohz_init_all() < 0)
346                         return;
347         }
348 
349         for_each_cpu(cpu, tick_nohz_full_mask)
350                 context_tracking_cpu_set(cpu);
351 
352         cpu_notifier(tick_nohz_cpu_down_callback, 0);
353         cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), tick_nohz_full_mask);
354         pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
355 }
356 #endif
357 
358 /*
359  * NOHZ - aka dynamic tick functionality
360  */
361 #ifdef CONFIG_NO_HZ_COMMON
362 /*
363  * NO HZ enabled ?
364  */
365 static int tick_nohz_enabled __read_mostly  = 1;
366 int tick_nohz_active  __read_mostly;
367 /*
368  * Enable / Disable tickless mode
369  */
370 static int __init setup_tick_nohz(char *str)
371 {
372         if (!strcmp(str, "off"))
373                 tick_nohz_enabled = 0;
374         else if (!strcmp(str, "on"))
375                 tick_nohz_enabled = 1;
376         else
377                 return 0;
378         return 1;
379 }
380 
381 __setup("nohz=", setup_tick_nohz);
382 
383 /**
384  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
385  *
386  * Called from interrupt entry when the CPU was idle
387  *
388  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
389  * must be updated. Otherwise an interrupt handler could use a stale jiffy
390  * value. We do this unconditionally on any cpu, as we don't know whether the
391  * cpu, which has the update task assigned is in a long sleep.
392  */
393 static void tick_nohz_update_jiffies(ktime_t now)
394 {
395         unsigned long flags;
396 
397         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
398 
399         local_irq_save(flags);
400         tick_do_update_jiffies64(now);
401         local_irq_restore(flags);
402 
403         touch_softlockup_watchdog();
404 }
405 
406 /*
407  * Updates the per cpu time idle statistics counters
408  */
409 static void
410 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
411 {
412         ktime_t delta;
413 
414         if (ts->idle_active) {
415                 delta = ktime_sub(now, ts->idle_entrytime);
416                 if (nr_iowait_cpu(cpu) > 0)
417                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
418                 else
419                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
420                 ts->idle_entrytime = now;
421         }
422 
423         if (last_update_time)
424                 *last_update_time = ktime_to_us(now);
425 
426 }
427 
428 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
429 {
430         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
431         ts->idle_active = 0;
432 
433         sched_clock_idle_wakeup_event(0);
434 }
435 
436 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
437 {
438         ktime_t now = ktime_get();
439 
440         ts->idle_entrytime = now;
441         ts->idle_active = 1;
442         sched_clock_idle_sleep_event();
443         return now;
444 }
445 
446 /**
447  * get_cpu_idle_time_us - get the total idle time of a cpu
448  * @cpu: CPU number to query
449  * @last_update_time: variable to store update time in. Do not update
450  * counters if NULL.
451  *
452  * Return the cummulative idle time (since boot) for a given
453  * CPU, in microseconds.
454  *
455  * This time is measured via accounting rather than sampling,
456  * and is as accurate as ktime_get() is.
457  *
458  * This function returns -1 if NOHZ is not enabled.
459  */
460 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
461 {
462         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
463         ktime_t now, idle;
464 
465         if (!tick_nohz_active)
466                 return -1;
467 
468         now = ktime_get();
469         if (last_update_time) {
470                 update_ts_time_stats(cpu, ts, now, last_update_time);
471                 idle = ts->idle_sleeptime;
472         } else {
473                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
474                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
475 
476                         idle = ktime_add(ts->idle_sleeptime, delta);
477                 } else {
478                         idle = ts->idle_sleeptime;
479                 }
480         }
481 
482         return ktime_to_us(idle);
483 
484 }
485 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
486 
487 /**
488  * get_cpu_iowait_time_us - get the total iowait 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 iowait 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_iowait_time_us(int cpu, u64 *last_update_time)
502 {
503         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
504         ktime_t now, iowait;
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                 iowait = ts->iowait_sleeptime;
513         } else {
514                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
515                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
516 
517                         iowait = ktime_add(ts->iowait_sleeptime, delta);
518                 } else {
519                         iowait = ts->iowait_sleeptime;
520                 }
521         }
522 
523         return ktime_to_us(iowait);
524 }
525 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
526 
527 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
528                                          ktime_t now, int cpu)
529 {
530         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
531         ktime_t last_update, expires, ret = { .tv64 = 0 };
532         unsigned long rcu_delta_jiffies;
533         struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
534         u64 time_delta;
535 
536         time_delta = timekeeping_max_deferment();
537 
538         /* Read jiffies and the time when jiffies were updated last */
539         do {
540                 seq = read_seqbegin(&jiffies_lock);
541                 last_update = last_jiffies_update;
542                 last_jiffies = jiffies;
543         } while (read_seqretry(&jiffies_lock, seq));
544 
545         if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
546             arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
547                 next_jiffies = last_jiffies + 1;
548                 delta_jiffies = 1;
549         } else {
550                 /* Get the next timer wheel timer */
551                 next_jiffies = get_next_timer_interrupt(last_jiffies);
552                 delta_jiffies = next_jiffies - last_jiffies;
553                 if (rcu_delta_jiffies < delta_jiffies) {
554                         next_jiffies = last_jiffies + rcu_delta_jiffies;
555                         delta_jiffies = rcu_delta_jiffies;
556                 }
557         }
558 
559         /*
560          * Do not stop the tick, if we are only one off (or less)
561          * or if the cpu is required for RCU:
562          */
563         if (!ts->tick_stopped && delta_jiffies <= 1)
564                 goto out;
565 
566         /* Schedule the tick, if we are at least one jiffie off */
567         if ((long)delta_jiffies >= 1) {
568 
569                 /*
570                  * If this cpu is the one which updates jiffies, then
571                  * give up the assignment and let it be taken by the
572                  * cpu which runs the tick timer next, which might be
573                  * this cpu as well. If we don't drop this here the
574                  * jiffies might be stale and do_timer() never
575                  * invoked. Keep track of the fact that it was the one
576                  * which had the do_timer() duty last. If this cpu is
577                  * the one which had the do_timer() duty last, we
578                  * limit the sleep time to the timekeeping
579                  * max_deferement value which we retrieved
580                  * above. Otherwise we can sleep as long as we want.
581                  */
582                 if (cpu == tick_do_timer_cpu) {
583                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
584                         ts->do_timer_last = 1;
585                 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
586                         time_delta = KTIME_MAX;
587                         ts->do_timer_last = 0;
588                 } else if (!ts->do_timer_last) {
589                         time_delta = KTIME_MAX;
590                 }
591 
592 #ifdef CONFIG_NO_HZ_FULL
593                 if (!ts->inidle) {
594                         time_delta = min(time_delta,
595                                          scheduler_tick_max_deferment());
596                 }
597 #endif
598 
599                 /*
600                  * calculate the expiry time for the next timer wheel
601                  * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
602                  * that there is no timer pending or at least extremely
603                  * far into the future (12 days for HZ=1000). In this
604                  * case we set the expiry to the end of time.
605                  */
606                 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
607                         /*
608                          * Calculate the time delta for the next timer event.
609                          * If the time delta exceeds the maximum time delta
610                          * permitted by the current clocksource then adjust
611                          * the time delta accordingly to ensure the
612                          * clocksource does not wrap.
613                          */
614                         time_delta = min_t(u64, time_delta,
615                                            tick_period.tv64 * delta_jiffies);
616                 }
617 
618                 if (time_delta < KTIME_MAX)
619                         expires = ktime_add_ns(last_update, time_delta);
620                 else
621                         expires.tv64 = KTIME_MAX;
622 
623                 /* Skip reprogram of event if its not changed */
624                 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
625                         goto out;
626 
627                 ret = expires;
628 
629                 /*
630                  * nohz_stop_sched_tick can be called several times before
631                  * the nohz_restart_sched_tick is called. This happens when
632                  * interrupts arrive which do not cause a reschedule. In the
633                  * first call we save the current tick time, so we can restart
634                  * the scheduler tick in nohz_restart_sched_tick.
635                  */
636                 if (!ts->tick_stopped) {
637                         nohz_balance_enter_idle(cpu);
638                         calc_load_enter_idle();
639 
640                         ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
641                         ts->tick_stopped = 1;
642                         trace_tick_stop(1, " ");
643                 }
644 
645                 /*
646                  * If the expiration time == KTIME_MAX, then
647                  * in this case we simply stop the tick timer.
648                  */
649                  if (unlikely(expires.tv64 == KTIME_MAX)) {
650                         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
651                                 hrtimer_cancel(&ts->sched_timer);
652                         goto out;
653                 }
654 
655                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
656                         hrtimer_start(&ts->sched_timer, expires,
657                                       HRTIMER_MODE_ABS_PINNED);
658                         /* Check, if the timer was already in the past */
659                         if (hrtimer_active(&ts->sched_timer))
660                                 goto out;
661                 } else if (!tick_program_event(expires, 0))
662                                 goto out;
663                 /*
664                  * We are past the event already. So we crossed a
665                  * jiffie boundary. Update jiffies and raise the
666                  * softirq.
667                  */
668                 tick_do_update_jiffies64(ktime_get());
669         }
670         raise_softirq_irqoff(TIMER_SOFTIRQ);
671 out:
672         ts->next_jiffies = next_jiffies;
673         ts->last_jiffies = last_jiffies;
674         ts->sleep_length = ktime_sub(dev->next_event, now);
675 
676         return ret;
677 }
678 
679 static void tick_nohz_full_stop_tick(struct tick_sched *ts)
680 {
681 #ifdef CONFIG_NO_HZ_FULL
682         int cpu = smp_processor_id();
683 
684         if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
685                 return;
686 
687         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
688                 return;
689 
690         if (!can_stop_full_tick())
691                 return;
692 
693         tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
694 #endif
695 }
696 
697 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
698 {
699         /*
700          * If this cpu is offline and it is the one which updates
701          * jiffies, then give up the assignment and let it be taken by
702          * the cpu which runs the tick timer next. If we don't drop
703          * this here the jiffies might be stale and do_timer() never
704          * invoked.
705          */
706         if (unlikely(!cpu_online(cpu))) {
707                 if (cpu == tick_do_timer_cpu)
708                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
709                 return false;
710         }
711 
712         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
713                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
714                 return false;
715         }
716 
717         if (need_resched())
718                 return false;
719 
720         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
721                 static int ratelimit;
722 
723                 if (ratelimit < 10 &&
724                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
725                         pr_warn("NOHZ: local_softirq_pending %02x\n",
726                                 (unsigned int) local_softirq_pending());
727                         ratelimit++;
728                 }
729                 return false;
730         }
731 
732         if (tick_nohz_full_enabled()) {
733                 /*
734                  * Keep the tick alive to guarantee timekeeping progression
735                  * if there are full dynticks CPUs around
736                  */
737                 if (tick_do_timer_cpu == cpu)
738                         return false;
739                 /*
740                  * Boot safety: make sure the timekeeping duty has been
741                  * assigned before entering dyntick-idle mode,
742                  */
743                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
744                         return false;
745         }
746 
747         return true;
748 }
749 
750 static void __tick_nohz_idle_enter(struct tick_sched *ts)
751 {
752         ktime_t now, expires;
753         int cpu = smp_processor_id();
754 
755         now = tick_nohz_start_idle(ts);
756 
757         if (can_stop_idle_tick(cpu, ts)) {
758                 int was_stopped = ts->tick_stopped;
759 
760                 ts->idle_calls++;
761 
762                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
763                 if (expires.tv64 > 0LL) {
764                         ts->idle_sleeps++;
765                         ts->idle_expires = expires;
766                 }
767 
768                 if (!was_stopped && ts->tick_stopped)
769                         ts->idle_jiffies = ts->last_jiffies;
770         }
771 }
772 
773 /**
774  * tick_nohz_idle_enter - stop the idle tick from the idle task
775  *
776  * When the next event is more than a tick into the future, stop the idle tick
777  * Called when we start the idle loop.
778  *
779  * The arch is responsible of calling:
780  *
781  * - rcu_idle_enter() after its last use of RCU before the CPU is put
782  *  to sleep.
783  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
784  */
785 void tick_nohz_idle_enter(void)
786 {
787         struct tick_sched *ts;
788 
789         WARN_ON_ONCE(irqs_disabled());
790 
791         /*
792          * Update the idle state in the scheduler domain hierarchy
793          * when tick_nohz_stop_sched_tick() is called from the idle loop.
794          * State will be updated to busy during the first busy tick after
795          * exiting idle.
796          */
797         set_cpu_sd_state_idle();
798 
799         local_irq_disable();
800 
801         ts = &__get_cpu_var(tick_cpu_sched);
802         ts->inidle = 1;
803         __tick_nohz_idle_enter(ts);
804 
805         local_irq_enable();
806 }
807 EXPORT_SYMBOL_GPL(tick_nohz_idle_enter);
808 
809 /**
810  * tick_nohz_irq_exit - update next tick event from interrupt exit
811  *
812  * When an interrupt fires while we are idle and it doesn't cause
813  * a reschedule, it may still add, modify or delete a timer, enqueue
814  * an RCU callback, etc...
815  * So we need to re-calculate and reprogram the next tick event.
816  */
817 void tick_nohz_irq_exit(void)
818 {
819         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
820 
821         if (ts->inidle)
822                 __tick_nohz_idle_enter(ts);
823         else
824                 tick_nohz_full_stop_tick(ts);
825 }
826 
827 /**
828  * tick_nohz_get_sleep_length - return the length of the current sleep
829  *
830  * Called from power state control code with interrupts disabled
831  */
832 ktime_t tick_nohz_get_sleep_length(void)
833 {
834         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
835 
836         return ts->sleep_length;
837 }
838 
839 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
840 {
841         hrtimer_cancel(&ts->sched_timer);
842         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
843 
844         while (1) {
845                 /* Forward the time to expire in the future */
846                 hrtimer_forward(&ts->sched_timer, now, tick_period);
847 
848                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
849                         hrtimer_start_expires(&ts->sched_timer,
850                                               HRTIMER_MODE_ABS_PINNED);
851                         /* Check, if the timer was already in the past */
852                         if (hrtimer_active(&ts->sched_timer))
853                                 break;
854                 } else {
855                         if (!tick_program_event(
856                                 hrtimer_get_expires(&ts->sched_timer), 0))
857                                 break;
858                 }
859                 /* Reread time and update jiffies */
860                 now = ktime_get();
861                 tick_do_update_jiffies64(now);
862         }
863 }
864 
865 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
866 {
867         /* Update jiffies first */
868         tick_do_update_jiffies64(now);
869         update_cpu_load_nohz();
870 
871         calc_load_exit_idle();
872         touch_softlockup_watchdog();
873         /*
874          * Cancel the scheduled timer and restore the tick
875          */
876         ts->tick_stopped  = 0;
877         ts->idle_exittime = now;
878 
879         tick_nohz_restart(ts, now);
880 }
881 
882 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
883 {
884 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
885         unsigned long ticks;
886 
887         if (vtime_accounting_enabled())
888                 return;
889         /*
890          * We stopped the tick in idle. Update process times would miss the
891          * time we slept as update_process_times does only a 1 tick
892          * accounting. Enforce that this is accounted to idle !
893          */
894         ticks = jiffies - ts->idle_jiffies;
895         /*
896          * We might be one off. Do not randomly account a huge number of ticks!
897          */
898         if (ticks && ticks < LONG_MAX)
899                 account_idle_ticks(ticks);
900 #endif
901 }
902 
903 /**
904  * tick_nohz_idle_exit - restart the idle tick from the idle task
905  *
906  * Restart the idle tick when the CPU is woken up from idle
907  * This also exit the RCU extended quiescent state. The CPU
908  * can use RCU again after this function is called.
909  */
910 void tick_nohz_idle_exit(void)
911 {
912         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
913         ktime_t now;
914 
915         local_irq_disable();
916 
917         WARN_ON_ONCE(!ts->inidle);
918 
919         ts->inidle = 0;
920 
921         if (ts->idle_active || ts->tick_stopped)
922                 now = ktime_get();
923 
924         if (ts->idle_active)
925                 tick_nohz_stop_idle(ts, now);
926 
927         if (ts->tick_stopped) {
928                 tick_nohz_restart_sched_tick(ts, now);
929                 tick_nohz_account_idle_ticks(ts);
930         }
931 
932         local_irq_enable();
933 }
934 EXPORT_SYMBOL_GPL(tick_nohz_idle_exit);
935 
936 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
937 {
938         hrtimer_forward(&ts->sched_timer, now, tick_period);
939         return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
940 }
941 
942 /*
943  * The nohz low res interrupt handler
944  */
945 static void tick_nohz_handler(struct clock_event_device *dev)
946 {
947         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
948         struct pt_regs *regs = get_irq_regs();
949         ktime_t now = ktime_get();
950 
951         dev->next_event.tv64 = KTIME_MAX;
952 
953         tick_sched_do_timer(now);
954         tick_sched_handle(ts, regs);
955 
956         while (tick_nohz_reprogram(ts, now)) {
957                 now = ktime_get();
958                 tick_do_update_jiffies64(now);
959         }
960 }
961 
962 /**
963  * tick_nohz_switch_to_nohz - switch to nohz mode
964  */
965 static void tick_nohz_switch_to_nohz(void)
966 {
967         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
968         ktime_t next;
969 
970         if (!tick_nohz_active)
971                 return;
972 
973         local_irq_disable();
974         if (tick_switch_to_oneshot(tick_nohz_handler)) {
975                 local_irq_enable();
976                 return;
977         }
978         tick_nohz_active = 1;
979         ts->nohz_mode = NOHZ_MODE_LOWRES;
980 
981         /*
982          * Recycle the hrtimer in ts, so we can share the
983          * hrtimer_forward with the highres code.
984          */
985         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
986         /* Get the next period */
987         next = tick_init_jiffy_update();
988 
989         for (;;) {
990                 hrtimer_set_expires(&ts->sched_timer, next);
991                 if (!tick_program_event(next, 0))
992                         break;
993                 next = ktime_add(next, tick_period);
994         }
995         local_irq_enable();
996 }
997 
998 /*
999  * When NOHZ is enabled and the tick is stopped, we need to kick the
1000  * tick timer from irq_enter() so that the jiffies update is kept
1001  * alive during long running softirqs. That's ugly as hell, but
1002  * correctness is key even if we need to fix the offending softirq in
1003  * the first place.
1004  *
1005  * Note, this is different to tick_nohz_restart. We just kick the
1006  * timer and do not touch the other magic bits which need to be done
1007  * when idle is left.
1008  */
1009 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1010 {
1011 #if 0
1012         /* Switch back to 2.6.27 behaviour */
1013         ktime_t delta;
1014 
1015         /*
1016          * Do not touch the tick device, when the next expiry is either
1017          * already reached or less/equal than the tick period.
1018          */
1019         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1020         if (delta.tv64 <= tick_period.tv64)
1021                 return;
1022 
1023         tick_nohz_restart(ts, now);
1024 #endif
1025 }
1026 
1027 static inline void tick_nohz_irq_enter(void)
1028 {
1029         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1030         ktime_t now;
1031 
1032         if (!ts->idle_active && !ts->tick_stopped)
1033                 return;
1034         now = ktime_get();
1035         if (ts->idle_active)
1036                 tick_nohz_stop_idle(ts, now);
1037         if (ts->tick_stopped) {
1038                 tick_nohz_update_jiffies(now);
1039                 tick_nohz_kick_tick(ts, now);
1040         }
1041 }
1042 
1043 #else
1044 
1045 static inline void tick_nohz_switch_to_nohz(void) { }
1046 static inline void tick_nohz_irq_enter(void) { }
1047 
1048 #endif /* CONFIG_NO_HZ_COMMON */
1049 
1050 /*
1051  * Called from irq_enter to notify about the possible interruption of idle()
1052  */
1053 void tick_irq_enter(void)
1054 {
1055         tick_check_oneshot_broadcast_this_cpu();
1056         tick_nohz_irq_enter();
1057 }
1058 
1059 /*
1060  * High resolution timer specific code
1061  */
1062 #ifdef CONFIG_HIGH_RES_TIMERS
1063 /*
1064  * We rearm the timer until we get disabled by the idle code.
1065  * Called with interrupts disabled.
1066  */
1067 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1068 {
1069         struct tick_sched *ts =
1070                 container_of(timer, struct tick_sched, sched_timer);
1071         struct pt_regs *regs = get_irq_regs();
1072         ktime_t now = ktime_get();
1073 
1074         tick_sched_do_timer(now);
1075 
1076         /*
1077          * Do not call, when we are not in irq context and have
1078          * no valid regs pointer
1079          */
1080         if (regs)
1081                 tick_sched_handle(ts, regs);
1082 
1083         hrtimer_forward(timer, now, tick_period);
1084 
1085         return HRTIMER_RESTART;
1086 }
1087 
1088 static int sched_skew_tick;
1089 
1090 static int __init skew_tick(char *str)
1091 {
1092         get_option(&str, &sched_skew_tick);
1093 
1094         return 0;
1095 }
1096 early_param("skew_tick", skew_tick);
1097 
1098 /**
1099  * tick_setup_sched_timer - setup the tick emulation timer
1100  */
1101 void tick_setup_sched_timer(void)
1102 {
1103         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1104         ktime_t now = ktime_get();
1105 
1106         /*
1107          * Emulate tick processing via per-CPU hrtimers:
1108          */
1109         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1110         ts->sched_timer.function = tick_sched_timer;
1111 
1112         /* Get the next period (per cpu) */
1113         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1114 
1115         /* Offset the tick to avert jiffies_lock contention. */
1116         if (sched_skew_tick) {
1117                 u64 offset = ktime_to_ns(tick_period) >> 1;
1118                 do_div(offset, num_possible_cpus());
1119                 offset *= smp_processor_id();
1120                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1121         }
1122 
1123         for (;;) {
1124                 hrtimer_forward(&ts->sched_timer, now, tick_period);
1125                 hrtimer_start_expires(&ts->sched_timer,
1126                                       HRTIMER_MODE_ABS_PINNED);
1127                 /* Check, if the timer was already in the past */
1128                 if (hrtimer_active(&ts->sched_timer))
1129                         break;
1130                 now = ktime_get();
1131         }
1132 
1133 #ifdef CONFIG_NO_HZ_COMMON
1134         if (tick_nohz_enabled) {
1135                 ts->nohz_mode = NOHZ_MODE_HIGHRES;
1136                 tick_nohz_active = 1;
1137         }
1138 #endif
1139 }
1140 #endif /* HIGH_RES_TIMERS */
1141 
1142 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1143 void tick_cancel_sched_timer(int cpu)
1144 {
1145         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1146 
1147 # ifdef CONFIG_HIGH_RES_TIMERS
1148         if (ts->sched_timer.base)
1149                 hrtimer_cancel(&ts->sched_timer);
1150 # endif
1151 
1152         memset(ts, 0, sizeof(*ts));
1153 }
1154 #endif
1155 
1156 /**
1157  * Async notification about clocksource changes
1158  */
1159 void tick_clock_notify(void)
1160 {
1161         int cpu;
1162 
1163         for_each_possible_cpu(cpu)
1164                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1165 }
1166 
1167 /*
1168  * Async notification about clock event changes
1169  */
1170 void tick_oneshot_notify(void)
1171 {
1172         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1173 
1174         set_bit(0, &ts->check_clocks);
1175 }
1176 
1177 /**
1178  * Check, if a change happened, which makes oneshot possible.
1179  *
1180  * Called cyclic from the hrtimer softirq (driven by the timer
1181  * softirq) allow_nohz signals, that we can switch into low-res nohz
1182  * mode, because high resolution timers are disabled (either compile
1183  * or runtime).
1184  */
1185 int tick_check_oneshot_change(int allow_nohz)
1186 {
1187         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1188 
1189         if (!test_and_clear_bit(0, &ts->check_clocks))
1190                 return 0;
1191 
1192         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1193                 return 0;
1194 
1195         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1196                 return 0;
1197 
1198         if (!allow_nohz)
1199                 return 1;
1200 
1201         tick_nohz_switch_to_nohz();
1202         return 0;
1203 }
1204 

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