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Linux/kernel/time/tick-sched.c

  1 /*
  2  *  linux/kernel/time/tick-sched.c
  3  *
  4  *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
  5  *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
  6  *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
  7  *
  8  *  No idle tick implementation for low and high resolution timers
  9  *
 10  *  Started by: Thomas Gleixner and Ingo Molnar
 11  *
 12  *  Distribute under GPLv2.
 13  */
 14 #include <linux/cpu.h>
 15 #include <linux/err.h>
 16 #include <linux/hrtimer.h>
 17 #include <linux/interrupt.h>
 18 #include <linux/kernel_stat.h>
 19 #include <linux/percpu.h>
 20 #include <linux/profile.h>
 21 #include <linux/sched.h>
 22 #include <linux/module.h>
 23 #include <linux/irq_work.h>
 24 #include <linux/posix-timers.h>
 25 #include <linux/perf_event.h>
 26 #include <linux/context_tracking.h>
 27 
 28 #include <asm/irq_regs.h>
 29 
 30 #include "tick-internal.h"
 31 
 32 #include <trace/events/timer.h>
 33 
 34 /*
 35  * Per cpu nohz control structure
 36  */
 37 DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 38 
 39 /*
 40  * The time, when the last jiffy update happened. Protected by jiffies_lock.
 41  */
 42 static ktime_t last_jiffies_update;
 43 
 44 struct tick_sched *tick_get_tick_sched(int cpu)
 45 {
 46         return &per_cpu(tick_cpu_sched, cpu);
 47 }
 48 
 49 /*
 50  * Must be called with interrupts disabled !
 51  */
 52 static void tick_do_update_jiffies64(ktime_t now)
 53 {
 54         unsigned long ticks = 0;
 55         ktime_t delta;
 56 
 57         /*
 58          * Do a quick check without holding jiffies_lock:
 59          */
 60         delta = ktime_sub(now, last_jiffies_update);
 61         if (delta.tv64 < tick_period.tv64)
 62                 return;
 63 
 64         /* Reevalute with jiffies_lock held */
 65         write_seqlock(&jiffies_lock);
 66 
 67         delta = ktime_sub(now, last_jiffies_update);
 68         if (delta.tv64 >= tick_period.tv64) {
 69 
 70                 delta = ktime_sub(delta, tick_period);
 71                 last_jiffies_update = ktime_add(last_jiffies_update,
 72                                                 tick_period);
 73 
 74                 /* Slow path for long timeouts */
 75                 if (unlikely(delta.tv64 >= tick_period.tv64)) {
 76                         s64 incr = ktime_to_ns(tick_period);
 77 
 78                         ticks = ktime_divns(delta, incr);
 79 
 80                         last_jiffies_update = ktime_add_ns(last_jiffies_update,
 81                                                            incr * ticks);
 82                 }
 83                 do_timer(++ticks);
 84 
 85                 /* Keep the tick_next_period variable up to date */
 86                 tick_next_period = ktime_add(last_jiffies_update, tick_period);
 87         } else {
 88                 write_sequnlock(&jiffies_lock);
 89                 return;
 90         }
 91         write_sequnlock(&jiffies_lock);
 92         update_wall_time();
 93 }
 94 
 95 /*
 96  * Initialize and return retrieve the jiffies update.
 97  */
 98 static ktime_t tick_init_jiffy_update(void)
 99 {
100         ktime_t period;
101 
102         write_seqlock(&jiffies_lock);
103         /* Did we start the jiffies update yet ? */
104         if (last_jiffies_update.tv64 == 0)
105                 last_jiffies_update = tick_next_period;
106         period = last_jiffies_update;
107         write_sequnlock(&jiffies_lock);
108         return period;
109 }
110 
111 
112 static void tick_sched_do_timer(ktime_t now)
113 {
114         int cpu = smp_processor_id();
115 
116 #ifdef CONFIG_NO_HZ_COMMON
117         /*
118          * Check if the do_timer duty was dropped. We don't care about
119          * concurrency: This happens only when the cpu in charge went
120          * into a long sleep. If two cpus happen to assign themself to
121          * this duty, then the jiffies update is still serialized by
122          * jiffies_lock.
123          */
124         if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
125             && !tick_nohz_full_cpu(cpu))
126                 tick_do_timer_cpu = cpu;
127 #endif
128 
129         /* Check, if the jiffies need an update */
130         if (tick_do_timer_cpu == cpu)
131                 tick_do_update_jiffies64(now);
132 }
133 
134 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
135 {
136 #ifdef CONFIG_NO_HZ_COMMON
137         /*
138          * When we are idle and the tick is stopped, we have to touch
139          * the watchdog as we might not schedule for a really long
140          * time. This happens on complete idle SMP systems while
141          * waiting on the login prompt. We also increment the "start of
142          * idle" jiffy stamp so the idle accounting adjustment we do
143          * when we go busy again does not account too much ticks.
144          */
145         if (ts->tick_stopped) {
146                 touch_softlockup_watchdog();
147                 if (is_idle_task(current))
148                         ts->idle_jiffies++;
149         }
150 #endif
151         update_process_times(user_mode(regs));
152         profile_tick(CPU_PROFILING);
153 }
154 
155 #ifdef CONFIG_NO_HZ_FULL
156 cpumask_var_t tick_nohz_full_mask;
157 bool tick_nohz_full_running;
158 
159 static bool can_stop_full_tick(void)
160 {
161         WARN_ON_ONCE(!irqs_disabled());
162 
163         if (!sched_can_stop_tick()) {
164                 trace_tick_stop(0, "more than 1 task in runqueue\n");
165                 return false;
166         }
167 
168         if (!posix_cpu_timers_can_stop_tick(current)) {
169                 trace_tick_stop(0, "posix timers running\n");
170                 return false;
171         }
172 
173         if (!perf_event_can_stop_tick()) {
174                 trace_tick_stop(0, "perf events running\n");
175                 return false;
176         }
177 
178         /* sched_clock_tick() needs us? */
179 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
180         /*
181          * TODO: kick full dynticks CPUs when
182          * sched_clock_stable is set.
183          */
184         if (!sched_clock_stable()) {
185                 trace_tick_stop(0, "unstable sched clock\n");
186                 /*
187                  * Don't allow the user to think they can get
188                  * full NO_HZ with this machine.
189                  */
190                 WARN_ONCE(tick_nohz_full_running,
191                           "NO_HZ FULL will not work with unstable sched clock");
192                 return false;
193         }
194 #endif
195 
196         return true;
197 }
198 
199 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
200 
201 /*
202  * Re-evaluate the need for the tick on the current CPU
203  * and restart it if necessary.
204  */
205 void __tick_nohz_full_check(void)
206 {
207         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
208 
209         if (tick_nohz_full_cpu(smp_processor_id())) {
210                 if (ts->tick_stopped && !is_idle_task(current)) {
211                         if (!can_stop_full_tick())
212                                 tick_nohz_restart_sched_tick(ts, ktime_get());
213                 }
214         }
215 }
216 
217 static void nohz_full_kick_work_func(struct irq_work *work)
218 {
219         __tick_nohz_full_check();
220 }
221 
222 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
223         .func = nohz_full_kick_work_func,
224 };
225 
226 /*
227  * Kick the current CPU if it's full dynticks in order to force it to
228  * re-evaluate its dependency on the tick and restart it if necessary.
229  */
230 void tick_nohz_full_kick(void)
231 {
232         if (tick_nohz_full_cpu(smp_processor_id()))
233                 irq_work_queue(&__get_cpu_var(nohz_full_kick_work));
234 }
235 
236 static void nohz_full_kick_ipi(void *info)
237 {
238         __tick_nohz_full_check();
239 }
240 
241 /*
242  * Kick all full dynticks CPUs in order to force these to re-evaluate
243  * their dependency on the tick and restart it if necessary.
244  */
245 void tick_nohz_full_kick_all(void)
246 {
247         if (!tick_nohz_full_running)
248                 return;
249 
250         preempt_disable();
251         smp_call_function_many(tick_nohz_full_mask,
252                                nohz_full_kick_ipi, NULL, false);
253         tick_nohz_full_kick();
254         preempt_enable();
255 }
256 
257 /*
258  * Re-evaluate the need for the tick as we switch the current task.
259  * It might need the tick due to per task/process properties:
260  * perf events, posix cpu timers, ...
261  */
262 void __tick_nohz_task_switch(struct task_struct *tsk)
263 {
264         unsigned long flags;
265 
266         local_irq_save(flags);
267 
268         if (!tick_nohz_full_cpu(smp_processor_id()))
269                 goto out;
270 
271         if (tick_nohz_tick_stopped() && !can_stop_full_tick())
272                 tick_nohz_full_kick();
273 
274 out:
275         local_irq_restore(flags);
276 }
277 
278 /* Parse the boot-time nohz CPU list from the kernel parameters. */
279 static int __init tick_nohz_full_setup(char *str)
280 {
281         int cpu;
282 
283         alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
284         if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
285                 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
286                 return 1;
287         }
288 
289         cpu = smp_processor_id();
290         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
291                 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
292                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
293         }
294         tick_nohz_full_running = true;
295 
296         return 1;
297 }
298 __setup("nohz_full=", tick_nohz_full_setup);
299 
300 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
301                                                  unsigned long action,
302                                                  void *hcpu)
303 {
304         unsigned int cpu = (unsigned long)hcpu;
305 
306         switch (action & ~CPU_TASKS_FROZEN) {
307         case CPU_DOWN_PREPARE:
308                 /*
309                  * If we handle the timekeeping duty for full dynticks CPUs,
310                  * we can't safely shutdown that CPU.
311                  */
312                 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
313                         return NOTIFY_BAD;
314                 break;
315         }
316         return NOTIFY_OK;
317 }
318 
319 /*
320  * Worst case string length in chunks of CPU range seems 2 steps
321  * separations: 0,2,4,6,...
322  * This is NR_CPUS + sizeof('\0')
323  */
324 static char __initdata nohz_full_buf[NR_CPUS + 1];
325 
326 static int tick_nohz_init_all(void)
327 {
328         int err = -1;
329 
330 #ifdef CONFIG_NO_HZ_FULL_ALL
331         if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
332                 pr_err("NO_HZ: Can't allocate full dynticks cpumask\n");
333                 return err;
334         }
335         err = 0;
336         cpumask_setall(tick_nohz_full_mask);
337         cpumask_clear_cpu(smp_processor_id(), tick_nohz_full_mask);
338         tick_nohz_full_running = true;
339 #endif
340         return err;
341 }
342 
343 void __init tick_nohz_init(void)
344 {
345         int cpu;
346 
347         if (!tick_nohz_full_running) {
348                 if (tick_nohz_init_all() < 0)
349                         return;
350         }
351 
352         for_each_cpu(cpu, tick_nohz_full_mask)
353                 context_tracking_cpu_set(cpu);
354 
355         cpu_notifier(tick_nohz_cpu_down_callback, 0);
356         cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), tick_nohz_full_mask);
357         pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
358 }
359 #endif
360 
361 /*
362  * NOHZ - aka dynamic tick functionality
363  */
364 #ifdef CONFIG_NO_HZ_COMMON
365 /*
366  * NO HZ enabled ?
367  */
368 static int tick_nohz_enabled __read_mostly  = 1;
369 int tick_nohz_active  __read_mostly;
370 /*
371  * Enable / Disable tickless mode
372  */
373 static int __init setup_tick_nohz(char *str)
374 {
375         if (!strcmp(str, "off"))
376                 tick_nohz_enabled = 0;
377         else if (!strcmp(str, "on"))
378                 tick_nohz_enabled = 1;
379         else
380                 return 0;
381         return 1;
382 }
383 
384 __setup("nohz=", setup_tick_nohz);
385 
386 /**
387  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
388  *
389  * Called from interrupt entry when the CPU was idle
390  *
391  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
392  * must be updated. Otherwise an interrupt handler could use a stale jiffy
393  * value. We do this unconditionally on any cpu, as we don't know whether the
394  * cpu, which has the update task assigned is in a long sleep.
395  */
396 static void tick_nohz_update_jiffies(ktime_t now)
397 {
398         unsigned long flags;
399 
400         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
401 
402         local_irq_save(flags);
403         tick_do_update_jiffies64(now);
404         local_irq_restore(flags);
405 
406         touch_softlockup_watchdog();
407 }
408 
409 /*
410  * Updates the per cpu time idle statistics counters
411  */
412 static void
413 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
414 {
415         ktime_t delta;
416 
417         if (ts->idle_active) {
418                 delta = ktime_sub(now, ts->idle_entrytime);
419                 if (nr_iowait_cpu(cpu) > 0)
420                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
421                 else
422                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
423                 ts->idle_entrytime = now;
424         }
425 
426         if (last_update_time)
427                 *last_update_time = ktime_to_us(now);
428 
429 }
430 
431 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
432 {
433         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
434         ts->idle_active = 0;
435 
436         sched_clock_idle_wakeup_event(0);
437 }
438 
439 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
440 {
441         ktime_t now = ktime_get();
442 
443         ts->idle_entrytime = now;
444         ts->idle_active = 1;
445         sched_clock_idle_sleep_event();
446         return now;
447 }
448 
449 /**
450  * get_cpu_idle_time_us - get the total idle time of a cpu
451  * @cpu: CPU number to query
452  * @last_update_time: variable to store update time in. Do not update
453  * counters if NULL.
454  *
455  * Return the cummulative idle time (since boot) for a given
456  * CPU, in microseconds.
457  *
458  * This time is measured via accounting rather than sampling,
459  * and is as accurate as ktime_get() is.
460  *
461  * This function returns -1 if NOHZ is not enabled.
462  */
463 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
464 {
465         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
466         ktime_t now, idle;
467 
468         if (!tick_nohz_active)
469                 return -1;
470 
471         now = ktime_get();
472         if (last_update_time) {
473                 update_ts_time_stats(cpu, ts, now, last_update_time);
474                 idle = ts->idle_sleeptime;
475         } else {
476                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
477                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
478 
479                         idle = ktime_add(ts->idle_sleeptime, delta);
480                 } else {
481                         idle = ts->idle_sleeptime;
482                 }
483         }
484 
485         return ktime_to_us(idle);
486 
487 }
488 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
489 
490 /**
491  * get_cpu_iowait_time_us - get the total iowait time of a cpu
492  * @cpu: CPU number to query
493  * @last_update_time: variable to store update time in. Do not update
494  * counters if NULL.
495  *
496  * Return the cummulative iowait time (since boot) for a given
497  * CPU, in microseconds.
498  *
499  * This time is measured via accounting rather than sampling,
500  * and is as accurate as ktime_get() is.
501  *
502  * This function returns -1 if NOHZ is not enabled.
503  */
504 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
505 {
506         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
507         ktime_t now, iowait;
508 
509         if (!tick_nohz_active)
510                 return -1;
511 
512         now = ktime_get();
513         if (last_update_time) {
514                 update_ts_time_stats(cpu, ts, now, last_update_time);
515                 iowait = ts->iowait_sleeptime;
516         } else {
517                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
518                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
519 
520                         iowait = ktime_add(ts->iowait_sleeptime, delta);
521                 } else {
522                         iowait = ts->iowait_sleeptime;
523                 }
524         }
525 
526         return ktime_to_us(iowait);
527 }
528 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
529 
530 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
531                                          ktime_t now, int cpu)
532 {
533         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
534         ktime_t last_update, expires, ret = { .tv64 = 0 };
535         unsigned long rcu_delta_jiffies;
536         struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
537         u64 time_delta;
538 
539         time_delta = timekeeping_max_deferment();
540 
541         /* Read jiffies and the time when jiffies were updated last */
542         do {
543                 seq = read_seqbegin(&jiffies_lock);
544                 last_update = last_jiffies_update;
545                 last_jiffies = jiffies;
546         } while (read_seqretry(&jiffies_lock, seq));
547 
548         if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
549             arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
550                 next_jiffies = last_jiffies + 1;
551                 delta_jiffies = 1;
552         } else {
553                 /* Get the next timer wheel timer */
554                 next_jiffies = get_next_timer_interrupt(last_jiffies);
555                 delta_jiffies = next_jiffies - last_jiffies;
556                 if (rcu_delta_jiffies < delta_jiffies) {
557                         next_jiffies = last_jiffies + rcu_delta_jiffies;
558                         delta_jiffies = rcu_delta_jiffies;
559                 }
560         }
561 
562         /*
563          * Do not stop the tick, if we are only one off (or less)
564          * or if the cpu is required for RCU:
565          */
566         if (!ts->tick_stopped && delta_jiffies <= 1)
567                 goto out;
568 
569         /* Schedule the tick, if we are at least one jiffie off */
570         if ((long)delta_jiffies >= 1) {
571 
572                 /*
573                  * If this cpu is the one which updates jiffies, then
574                  * give up the assignment and let it be taken by the
575                  * cpu which runs the tick timer next, which might be
576                  * this cpu as well. If we don't drop this here the
577                  * jiffies might be stale and do_timer() never
578                  * invoked. Keep track of the fact that it was the one
579                  * which had the do_timer() duty last. If this cpu is
580                  * the one which had the do_timer() duty last, we
581                  * limit the sleep time to the timekeeping
582                  * max_deferement value which we retrieved
583                  * above. Otherwise we can sleep as long as we want.
584                  */
585                 if (cpu == tick_do_timer_cpu) {
586                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
587                         ts->do_timer_last = 1;
588                 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
589                         time_delta = KTIME_MAX;
590                         ts->do_timer_last = 0;
591                 } else if (!ts->do_timer_last) {
592                         time_delta = KTIME_MAX;
593                 }
594 
595 #ifdef CONFIG_NO_HZ_FULL
596                 if (!ts->inidle) {
597                         time_delta = min(time_delta,
598                                          scheduler_tick_max_deferment());
599                 }
600 #endif
601 
602                 /*
603                  * calculate the expiry time for the next timer wheel
604                  * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
605                  * that there is no timer pending or at least extremely
606                  * far into the future (12 days for HZ=1000). In this
607                  * case we set the expiry to the end of time.
608                  */
609                 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
610                         /*
611                          * Calculate the time delta for the next timer event.
612                          * If the time delta exceeds the maximum time delta
613                          * permitted by the current clocksource then adjust
614                          * the time delta accordingly to ensure the
615                          * clocksource does not wrap.
616                          */
617                         time_delta = min_t(u64, time_delta,
618                                            tick_period.tv64 * delta_jiffies);
619                 }
620 
621                 if (time_delta < KTIME_MAX)
622                         expires = ktime_add_ns(last_update, time_delta);
623                 else
624                         expires.tv64 = KTIME_MAX;
625 
626                 /* Skip reprogram of event if its not changed */
627                 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
628                         goto out;
629 
630                 ret = expires;
631 
632                 /*
633                  * nohz_stop_sched_tick can be called several times before
634                  * the nohz_restart_sched_tick is called. This happens when
635                  * interrupts arrive which do not cause a reschedule. In the
636                  * first call we save the current tick time, so we can restart
637                  * the scheduler tick in nohz_restart_sched_tick.
638                  */
639                 if (!ts->tick_stopped) {
640                         nohz_balance_enter_idle(cpu);
641                         calc_load_enter_idle();
642 
643                         ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
644                         ts->tick_stopped = 1;
645                         trace_tick_stop(1, " ");
646                 }
647 
648                 /*
649                  * If the expiration time == KTIME_MAX, then
650                  * in this case we simply stop the tick timer.
651                  */
652                  if (unlikely(expires.tv64 == KTIME_MAX)) {
653                         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
654                                 hrtimer_cancel(&ts->sched_timer);
655                         goto out;
656                 }
657 
658                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
659                         hrtimer_start(&ts->sched_timer, expires,
660                                       HRTIMER_MODE_ABS_PINNED);
661                         /* Check, if the timer was already in the past */
662                         if (hrtimer_active(&ts->sched_timer))
663                                 goto out;
664                 } else if (!tick_program_event(expires, 0))
665                                 goto out;
666                 /*
667                  * We are past the event already. So we crossed a
668                  * jiffie boundary. Update jiffies and raise the
669                  * softirq.
670                  */
671                 tick_do_update_jiffies64(ktime_get());
672         }
673         raise_softirq_irqoff(TIMER_SOFTIRQ);
674 out:
675         ts->next_jiffies = next_jiffies;
676         ts->last_jiffies = last_jiffies;
677         ts->sleep_length = ktime_sub(dev->next_event, now);
678 
679         return ret;
680 }
681 
682 static void tick_nohz_full_stop_tick(struct tick_sched *ts)
683 {
684 #ifdef CONFIG_NO_HZ_FULL
685         int cpu = smp_processor_id();
686 
687         if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
688                 return;
689 
690         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
691                 return;
692 
693         if (!can_stop_full_tick())
694                 return;
695 
696         tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
697 #endif
698 }
699 
700 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
701 {
702         /*
703          * If this cpu is offline and it is the one which updates
704          * jiffies, then give up the assignment and let it be taken by
705          * the cpu which runs the tick timer next. If we don't drop
706          * this here the jiffies might be stale and do_timer() never
707          * invoked.
708          */
709         if (unlikely(!cpu_online(cpu))) {
710                 if (cpu == tick_do_timer_cpu)
711                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
712                 return false;
713         }
714 
715         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
716                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
717                 return false;
718         }
719 
720         if (need_resched())
721                 return false;
722 
723         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
724                 static int ratelimit;
725 
726                 if (ratelimit < 10 &&
727                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
728                         pr_warn("NOHZ: local_softirq_pending %02x\n",
729                                 (unsigned int) local_softirq_pending());
730                         ratelimit++;
731                 }
732                 return false;
733         }
734 
735         if (tick_nohz_full_enabled()) {
736                 /*
737                  * Keep the tick alive to guarantee timekeeping progression
738                  * if there are full dynticks CPUs around
739                  */
740                 if (tick_do_timer_cpu == cpu)
741                         return false;
742                 /*
743                  * Boot safety: make sure the timekeeping duty has been
744                  * assigned before entering dyntick-idle mode,
745                  */
746                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
747                         return false;
748         }
749 
750         return true;
751 }
752 
753 static void __tick_nohz_idle_enter(struct tick_sched *ts)
754 {
755         ktime_t now, expires;
756         int cpu = smp_processor_id();
757 
758         now = tick_nohz_start_idle(ts);
759 
760         if (can_stop_idle_tick(cpu, ts)) {
761                 int was_stopped = ts->tick_stopped;
762 
763                 ts->idle_calls++;
764 
765                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
766                 if (expires.tv64 > 0LL) {
767                         ts->idle_sleeps++;
768                         ts->idle_expires = expires;
769                 }
770 
771                 if (!was_stopped && ts->tick_stopped)
772                         ts->idle_jiffies = ts->last_jiffies;
773         }
774 }
775 
776 /**
777  * tick_nohz_idle_enter - stop the idle tick from the idle task
778  *
779  * When the next event is more than a tick into the future, stop the idle tick
780  * Called when we start the idle loop.
781  *
782  * The arch is responsible of calling:
783  *
784  * - rcu_idle_enter() after its last use of RCU before the CPU is put
785  *  to sleep.
786  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
787  */
788 void tick_nohz_idle_enter(void)
789 {
790         struct tick_sched *ts;
791 
792         WARN_ON_ONCE(irqs_disabled());
793 
794         /*
795          * Update the idle state in the scheduler domain hierarchy
796          * when tick_nohz_stop_sched_tick() is called from the idle loop.
797          * State will be updated to busy during the first busy tick after
798          * exiting idle.
799          */
800         set_cpu_sd_state_idle();
801 
802         local_irq_disable();
803 
804         ts = &__get_cpu_var(tick_cpu_sched);
805         ts->inidle = 1;
806         __tick_nohz_idle_enter(ts);
807 
808         local_irq_enable();
809 }
810 EXPORT_SYMBOL_GPL(tick_nohz_idle_enter);
811 
812 /**
813  * tick_nohz_irq_exit - update next tick event from interrupt exit
814  *
815  * When an interrupt fires while we are idle and it doesn't cause
816  * a reschedule, it may still add, modify or delete a timer, enqueue
817  * an RCU callback, etc...
818  * So we need to re-calculate and reprogram the next tick event.
819  */
820 void tick_nohz_irq_exit(void)
821 {
822         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
823 
824         if (ts->inidle)
825                 __tick_nohz_idle_enter(ts);
826         else
827                 tick_nohz_full_stop_tick(ts);
828 }
829 
830 /**
831  * tick_nohz_get_sleep_length - return the length of the current sleep
832  *
833  * Called from power state control code with interrupts disabled
834  */
835 ktime_t tick_nohz_get_sleep_length(void)
836 {
837         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
838 
839         return ts->sleep_length;
840 }
841 
842 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
843 {
844         hrtimer_cancel(&ts->sched_timer);
845         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
846 
847         while (1) {
848                 /* Forward the time to expire in the future */
849                 hrtimer_forward(&ts->sched_timer, now, tick_period);
850 
851                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
852                         hrtimer_start_expires(&ts->sched_timer,
853                                               HRTIMER_MODE_ABS_PINNED);
854                         /* Check, if the timer was already in the past */
855                         if (hrtimer_active(&ts->sched_timer))
856                                 break;
857                 } else {
858                         if (!tick_program_event(
859                                 hrtimer_get_expires(&ts->sched_timer), 0))
860                                 break;
861                 }
862                 /* Reread time and update jiffies */
863                 now = ktime_get();
864                 tick_do_update_jiffies64(now);
865         }
866 }
867 
868 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
869 {
870         /* Update jiffies first */
871         tick_do_update_jiffies64(now);
872         update_cpu_load_nohz();
873 
874         calc_load_exit_idle();
875         touch_softlockup_watchdog();
876         /*
877          * Cancel the scheduled timer and restore the tick
878          */
879         ts->tick_stopped  = 0;
880         ts->idle_exittime = now;
881 
882         tick_nohz_restart(ts, now);
883 }
884 
885 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
886 {
887 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
888         unsigned long ticks;
889 
890         if (vtime_accounting_enabled())
891                 return;
892         /*
893          * We stopped the tick in idle. Update process times would miss the
894          * time we slept as update_process_times does only a 1 tick
895          * accounting. Enforce that this is accounted to idle !
896          */
897         ticks = jiffies - ts->idle_jiffies;
898         /*
899          * We might be one off. Do not randomly account a huge number of ticks!
900          */
901         if (ticks && ticks < LONG_MAX)
902                 account_idle_ticks(ticks);
903 #endif
904 }
905 
906 /**
907  * tick_nohz_idle_exit - restart the idle tick from the idle task
908  *
909  * Restart the idle tick when the CPU is woken up from idle
910  * This also exit the RCU extended quiescent state. The CPU
911  * can use RCU again after this function is called.
912  */
913 void tick_nohz_idle_exit(void)
914 {
915         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
916         ktime_t now;
917 
918         local_irq_disable();
919 
920         WARN_ON_ONCE(!ts->inidle);
921 
922         ts->inidle = 0;
923 
924         if (ts->idle_active || ts->tick_stopped)
925                 now = ktime_get();
926 
927         if (ts->idle_active)
928                 tick_nohz_stop_idle(ts, now);
929 
930         if (ts->tick_stopped) {
931                 tick_nohz_restart_sched_tick(ts, now);
932                 tick_nohz_account_idle_ticks(ts);
933         }
934 
935         local_irq_enable();
936 }
937 EXPORT_SYMBOL_GPL(tick_nohz_idle_exit);
938 
939 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
940 {
941         hrtimer_forward(&ts->sched_timer, now, tick_period);
942         return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
943 }
944 
945 /*
946  * The nohz low res interrupt handler
947  */
948 static void tick_nohz_handler(struct clock_event_device *dev)
949 {
950         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
951         struct pt_regs *regs = get_irq_regs();
952         ktime_t now = ktime_get();
953 
954         dev->next_event.tv64 = KTIME_MAX;
955 
956         tick_sched_do_timer(now);
957         tick_sched_handle(ts, regs);
958 
959         while (tick_nohz_reprogram(ts, now)) {
960                 now = ktime_get();
961                 tick_do_update_jiffies64(now);
962         }
963 }
964 
965 /**
966  * tick_nohz_switch_to_nohz - switch to nohz mode
967  */
968 static void tick_nohz_switch_to_nohz(void)
969 {
970         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
971         ktime_t next;
972 
973         if (!tick_nohz_enabled)
974                 return;
975 
976         local_irq_disable();
977         if (tick_switch_to_oneshot(tick_nohz_handler)) {
978                 local_irq_enable();
979                 return;
980         }
981         tick_nohz_active = 1;
982         ts->nohz_mode = NOHZ_MODE_LOWRES;
983 
984         /*
985          * Recycle the hrtimer in ts, so we can share the
986          * hrtimer_forward with the highres code.
987          */
988         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
989         /* Get the next period */
990         next = tick_init_jiffy_update();
991 
992         for (;;) {
993                 hrtimer_set_expires(&ts->sched_timer, next);
994                 if (!tick_program_event(next, 0))
995                         break;
996                 next = ktime_add(next, tick_period);
997         }
998         local_irq_enable();
999 }
1000 
1001 /*
1002  * When NOHZ is enabled and the tick is stopped, we need to kick the
1003  * tick timer from irq_enter() so that the jiffies update is kept
1004  * alive during long running softirqs. That's ugly as hell, but
1005  * correctness is key even if we need to fix the offending softirq in
1006  * the first place.
1007  *
1008  * Note, this is different to tick_nohz_restart. We just kick the
1009  * timer and do not touch the other magic bits which need to be done
1010  * when idle is left.
1011  */
1012 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1013 {
1014 #if 0
1015         /* Switch back to 2.6.27 behaviour */
1016         ktime_t delta;
1017 
1018         /*
1019          * Do not touch the tick device, when the next expiry is either
1020          * already reached or less/equal than the tick period.
1021          */
1022         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1023         if (delta.tv64 <= tick_period.tv64)
1024                 return;
1025 
1026         tick_nohz_restart(ts, now);
1027 #endif
1028 }
1029 
1030 static inline void tick_nohz_irq_enter(void)
1031 {
1032         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1033         ktime_t now;
1034 
1035         if (!ts->idle_active && !ts->tick_stopped)
1036                 return;
1037         now = ktime_get();
1038         if (ts->idle_active)
1039                 tick_nohz_stop_idle(ts, now);
1040         if (ts->tick_stopped) {
1041                 tick_nohz_update_jiffies(now);
1042                 tick_nohz_kick_tick(ts, now);
1043         }
1044 }
1045 
1046 #else
1047 
1048 static inline void tick_nohz_switch_to_nohz(void) { }
1049 static inline void tick_nohz_irq_enter(void) { }
1050 
1051 #endif /* CONFIG_NO_HZ_COMMON */
1052 
1053 /*
1054  * Called from irq_enter to notify about the possible interruption of idle()
1055  */
1056 void tick_irq_enter(void)
1057 {
1058         tick_check_oneshot_broadcast_this_cpu();
1059         tick_nohz_irq_enter();
1060 }
1061 
1062 /*
1063  * High resolution timer specific code
1064  */
1065 #ifdef CONFIG_HIGH_RES_TIMERS
1066 /*
1067  * We rearm the timer until we get disabled by the idle code.
1068  * Called with interrupts disabled.
1069  */
1070 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1071 {
1072         struct tick_sched *ts =
1073                 container_of(timer, struct tick_sched, sched_timer);
1074         struct pt_regs *regs = get_irq_regs();
1075         ktime_t now = ktime_get();
1076 
1077         tick_sched_do_timer(now);
1078 
1079         /*
1080          * Do not call, when we are not in irq context and have
1081          * no valid regs pointer
1082          */
1083         if (regs)
1084                 tick_sched_handle(ts, regs);
1085 
1086         hrtimer_forward(timer, now, tick_period);
1087 
1088         return HRTIMER_RESTART;
1089 }
1090 
1091 static int sched_skew_tick;
1092 
1093 static int __init skew_tick(char *str)
1094 {
1095         get_option(&str, &sched_skew_tick);
1096 
1097         return 0;
1098 }
1099 early_param("skew_tick", skew_tick);
1100 
1101 /**
1102  * tick_setup_sched_timer - setup the tick emulation timer
1103  */
1104 void tick_setup_sched_timer(void)
1105 {
1106         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1107         ktime_t now = ktime_get();
1108 
1109         /*
1110          * Emulate tick processing via per-CPU hrtimers:
1111          */
1112         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1113         ts->sched_timer.function = tick_sched_timer;
1114 
1115         /* Get the next period (per cpu) */
1116         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1117 
1118         /* Offset the tick to avert jiffies_lock contention. */
1119         if (sched_skew_tick) {
1120                 u64 offset = ktime_to_ns(tick_period) >> 1;
1121                 do_div(offset, num_possible_cpus());
1122                 offset *= smp_processor_id();
1123                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1124         }
1125 
1126         for (;;) {
1127                 hrtimer_forward(&ts->sched_timer, now, tick_period);
1128                 hrtimer_start_expires(&ts->sched_timer,
1129                                       HRTIMER_MODE_ABS_PINNED);
1130                 /* Check, if the timer was already in the past */
1131                 if (hrtimer_active(&ts->sched_timer))
1132                         break;
1133                 now = ktime_get();
1134         }
1135 
1136 #ifdef CONFIG_NO_HZ_COMMON
1137         if (tick_nohz_enabled) {
1138                 ts->nohz_mode = NOHZ_MODE_HIGHRES;
1139                 tick_nohz_active = 1;
1140         }
1141 #endif
1142 }
1143 #endif /* HIGH_RES_TIMERS */
1144 
1145 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1146 void tick_cancel_sched_timer(int cpu)
1147 {
1148         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1149 
1150 # ifdef CONFIG_HIGH_RES_TIMERS
1151         if (ts->sched_timer.base)
1152                 hrtimer_cancel(&ts->sched_timer);
1153 # endif
1154 
1155         memset(ts, 0, sizeof(*ts));
1156 }
1157 #endif
1158 
1159 /**
1160  * Async notification about clocksource changes
1161  */
1162 void tick_clock_notify(void)
1163 {
1164         int cpu;
1165 
1166         for_each_possible_cpu(cpu)
1167                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1168 }
1169 
1170 /*
1171  * Async notification about clock event changes
1172  */
1173 void tick_oneshot_notify(void)
1174 {
1175         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1176 
1177         set_bit(0, &ts->check_clocks);
1178 }
1179 
1180 /**
1181  * Check, if a change happened, which makes oneshot possible.
1182  *
1183  * Called cyclic from the hrtimer softirq (driven by the timer
1184  * softirq) allow_nohz signals, that we can switch into low-res nohz
1185  * mode, because high resolution timers are disabled (either compile
1186  * or runtime).
1187  */
1188 int tick_check_oneshot_change(int allow_nohz)
1189 {
1190         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1191 
1192         if (!test_and_clear_bit(0, &ts->check_clocks))
1193                 return 0;
1194 
1195         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1196                 return 0;
1197 
1198         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1199                 return 0;
1200 
1201         if (!allow_nohz)
1202                 return 1;
1203 
1204         tick_nohz_switch_to_nohz();
1205         return 0;
1206 }
1207 

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