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Linux/kernel/time/tick-sched.c

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  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/tick.h>
 23 #include <linux/module.h>
 24 
 25 #include <asm/irq_regs.h>
 26 
 27 #include "tick-internal.h"
 28 
 29 /*
 30  * Per cpu nohz control structure
 31  */
 32 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 33 
 34 /*
 35  * The time, when the last jiffy update happened. Protected by xtime_lock.
 36  */
 37 static ktime_t last_jiffies_update;
 38 
 39 struct tick_sched *tick_get_tick_sched(int cpu)
 40 {
 41         return &per_cpu(tick_cpu_sched, cpu);
 42 }
 43 
 44 /*
 45  * Must be called with interrupts disabled !
 46  */
 47 static void tick_do_update_jiffies64(ktime_t now)
 48 {
 49         unsigned long ticks = 0;
 50         ktime_t delta;
 51 
 52         /*
 53          * Do a quick check without holding xtime_lock:
 54          */
 55         delta = ktime_sub(now, last_jiffies_update);
 56         if (delta.tv64 < tick_period.tv64)
 57                 return;
 58 
 59         /* Reevalute with xtime_lock held */
 60         write_seqlock(&xtime_lock);
 61 
 62         delta = ktime_sub(now, last_jiffies_update);
 63         if (delta.tv64 >= tick_period.tv64) {
 64 
 65                 delta = ktime_sub(delta, tick_period);
 66                 last_jiffies_update = ktime_add(last_jiffies_update,
 67                                                 tick_period);
 68 
 69                 /* Slow path for long timeouts */
 70                 if (unlikely(delta.tv64 >= tick_period.tv64)) {
 71                         s64 incr = ktime_to_ns(tick_period);
 72 
 73                         ticks = ktime_divns(delta, incr);
 74 
 75                         last_jiffies_update = ktime_add_ns(last_jiffies_update,
 76                                                            incr * ticks);
 77                 }
 78                 do_timer(++ticks);
 79 
 80                 /* Keep the tick_next_period variable up to date */
 81                 tick_next_period = ktime_add(last_jiffies_update, tick_period);
 82         }
 83         write_sequnlock(&xtime_lock);
 84 }
 85 
 86 /*
 87  * Initialize and return retrieve the jiffies update.
 88  */
 89 static ktime_t tick_init_jiffy_update(void)
 90 {
 91         ktime_t period;
 92 
 93         write_seqlock(&xtime_lock);
 94         /* Did we start the jiffies update yet ? */
 95         if (last_jiffies_update.tv64 == 0)
 96                 last_jiffies_update = tick_next_period;
 97         period = last_jiffies_update;
 98         write_sequnlock(&xtime_lock);
 99         return period;
100 }
101 
102 /*
103  * NOHZ - aka dynamic tick functionality
104  */
105 #ifdef CONFIG_NO_HZ
106 /*
107  * NO HZ enabled ?
108  */
109 static int tick_nohz_enabled __read_mostly  = 1;
110 
111 /*
112  * Enable / Disable tickless mode
113  */
114 static int __init setup_tick_nohz(char *str)
115 {
116         if (!strcmp(str, "off"))
117                 tick_nohz_enabled = 0;
118         else if (!strcmp(str, "on"))
119                 tick_nohz_enabled = 1;
120         else
121                 return 0;
122         return 1;
123 }
124 
125 __setup("nohz=", setup_tick_nohz);
126 
127 /**
128  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
129  *
130  * Called from interrupt entry when the CPU was idle
131  *
132  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
133  * must be updated. Otherwise an interrupt handler could use a stale jiffy
134  * value. We do this unconditionally on any cpu, as we don't know whether the
135  * cpu, which has the update task assigned is in a long sleep.
136  */
137 static void tick_nohz_update_jiffies(ktime_t now)
138 {
139         int cpu = smp_processor_id();
140         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
141         unsigned long flags;
142 
143         cpumask_clear_cpu(cpu, nohz_cpu_mask);
144         ts->idle_waketime = now;
145 
146         local_irq_save(flags);
147         tick_do_update_jiffies64(now);
148         local_irq_restore(flags);
149 
150         touch_softlockup_watchdog();
151 }
152 
153 static void tick_nohz_stop_idle(int cpu, ktime_t now)
154 {
155         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
156         ktime_t delta;
157 
158         delta = ktime_sub(now, ts->idle_entrytime);
159         ts->idle_lastupdate = now;
160         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
161         ts->idle_active = 0;
162 
163         sched_clock_idle_wakeup_event(0);
164 }
165 
166 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
167 {
168         ktime_t now, delta;
169 
170         now = ktime_get();
171         if (ts->idle_active) {
172                 delta = ktime_sub(now, ts->idle_entrytime);
173                 ts->idle_lastupdate = now;
174                 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
175         }
176         ts->idle_entrytime = now;
177         ts->idle_active = 1;
178         sched_clock_idle_sleep_event();
179         return now;
180 }
181 
182 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
183 {
184         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
185 
186         if (!tick_nohz_enabled)
187                 return -1;
188 
189         if (ts->idle_active)
190                 *last_update_time = ktime_to_us(ts->idle_lastupdate);
191         else
192                 *last_update_time = ktime_to_us(ktime_get());
193 
194         return ktime_to_us(ts->idle_sleeptime);
195 }
196 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
197 
198 /**
199  * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
200  *
201  * When the next event is more than a tick into the future, stop the idle tick
202  * Called either from the idle loop or from irq_exit() when an idle period was
203  * just interrupted by an interrupt which did not cause a reschedule.
204  */
205 void tick_nohz_stop_sched_tick(int inidle)
206 {
207         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
208         struct tick_sched *ts;
209         ktime_t last_update, expires, now;
210         struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
211         u64 time_delta;
212         int cpu;
213 
214         local_irq_save(flags);
215 
216         cpu = smp_processor_id();
217         ts = &per_cpu(tick_cpu_sched, cpu);
218 
219         /*
220          * Call to tick_nohz_start_idle stops the last_update_time from being
221          * updated. Thus, it must not be called in the event we are called from
222          * irq_exit() with the prior state different than idle.
223          */
224         if (!inidle && !ts->inidle)
225                 goto end;
226 
227         /*
228          * Set ts->inidle unconditionally. Even if the system did not
229          * switch to NOHZ mode the cpu frequency governers rely on the
230          * update of the idle time accounting in tick_nohz_start_idle().
231          */
232         ts->inidle = 1;
233 
234         now = tick_nohz_start_idle(ts);
235 
236         /*
237          * If this cpu is offline and it is the one which updates
238          * jiffies, then give up the assignment and let it be taken by
239          * the cpu which runs the tick timer next. If we don't drop
240          * this here the jiffies might be stale and do_timer() never
241          * invoked.
242          */
243         if (unlikely(!cpu_online(cpu))) {
244                 if (cpu == tick_do_timer_cpu)
245                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
246         }
247 
248         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
249                 goto end;
250 
251         if (need_resched())
252                 goto end;
253 
254         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
255                 static int ratelimit;
256 
257                 if (ratelimit < 10) {
258                         printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
259                                local_softirq_pending());
260                         ratelimit++;
261                 }
262                 goto end;
263         }
264 
265         ts->idle_calls++;
266         /* Read jiffies and the time when jiffies were updated last */
267         do {
268                 seq = read_seqbegin(&xtime_lock);
269                 last_update = last_jiffies_update;
270                 last_jiffies = jiffies;
271 
272                 /*
273                  * On SMP we really should only care for the CPU which
274                  * has the do_timer duty assigned. All other CPUs can
275                  * sleep as long as they want.
276                  */
277                 if (cpu == tick_do_timer_cpu ||
278                     tick_do_timer_cpu == TICK_DO_TIMER_NONE)
279                         time_delta = timekeeping_max_deferment();
280                 else
281                         time_delta = KTIME_MAX;
282         } while (read_seqretry(&xtime_lock, seq));
283 
284         if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
285             arch_needs_cpu(cpu)) {
286                 next_jiffies = last_jiffies + 1;
287                 delta_jiffies = 1;
288         } else {
289                 /* Get the next timer wheel timer */
290                 next_jiffies = get_next_timer_interrupt(last_jiffies);
291                 delta_jiffies = next_jiffies - last_jiffies;
292         }
293         /*
294          * Do not stop the tick, if we are only one off
295          * or if the cpu is required for rcu
296          */
297         if (!ts->tick_stopped && delta_jiffies == 1)
298                 goto out;
299 
300         /* Schedule the tick, if we are at least one jiffie off */
301         if ((long)delta_jiffies >= 1) {
302 
303                 /*
304                  * calculate the expiry time for the next timer wheel
305                  * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
306                  * that there is no timer pending or at least extremely
307                  * far into the future (12 days for HZ=1000). In this
308                  * case we set the expiry to the end of time.
309                  */
310                 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
311                         /*
312                          * Calculate the time delta for the next timer event.
313                          * If the time delta exceeds the maximum time delta
314                          * permitted by the current clocksource then adjust
315                          * the time delta accordingly to ensure the
316                          * clocksource does not wrap.
317                          */
318                         time_delta = min_t(u64, time_delta,
319                                            tick_period.tv64 * delta_jiffies);
320                         expires = ktime_add_ns(last_update, time_delta);
321                 } else {
322                         expires.tv64 = KTIME_MAX;
323                 }
324 
325                 /*
326                  * If this cpu is the one which updates jiffies, then
327                  * give up the assignment and let it be taken by the
328                  * cpu which runs the tick timer next, which might be
329                  * this cpu as well. If we don't drop this here the
330                  * jiffies might be stale and do_timer() never
331                  * invoked.
332                  */
333                 if (cpu == tick_do_timer_cpu)
334                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
335 
336                 if (delta_jiffies > 1)
337                         cpumask_set_cpu(cpu, nohz_cpu_mask);
338 
339                 /* Skip reprogram of event if its not changed */
340                 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
341                         goto out;
342 
343                 /*
344                  * nohz_stop_sched_tick can be called several times before
345                  * the nohz_restart_sched_tick is called. This happens when
346                  * interrupts arrive which do not cause a reschedule. In the
347                  * first call we save the current tick time, so we can restart
348                  * the scheduler tick in nohz_restart_sched_tick.
349                  */
350                 if (!ts->tick_stopped) {
351                         if (select_nohz_load_balancer(1)) {
352                                 /*
353                                  * sched tick not stopped!
354                                  */
355                                 cpumask_clear_cpu(cpu, nohz_cpu_mask);
356                                 goto out;
357                         }
358 
359                         ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
360                         ts->tick_stopped = 1;
361                         ts->idle_jiffies = last_jiffies;
362                         rcu_enter_nohz();
363                 }
364 
365                 ts->idle_sleeps++;
366 
367                 /* Mark expires */
368                 ts->idle_expires = expires;
369 
370                 /*
371                  * If the expiration time == KTIME_MAX, then
372                  * in this case we simply stop the tick timer.
373                  */
374                  if (unlikely(expires.tv64 == KTIME_MAX)) {
375                         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
376                                 hrtimer_cancel(&ts->sched_timer);
377                         goto out;
378                 }
379 
380                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
381                         hrtimer_start(&ts->sched_timer, expires,
382                                       HRTIMER_MODE_ABS_PINNED);
383                         /* Check, if the timer was already in the past */
384                         if (hrtimer_active(&ts->sched_timer))
385                                 goto out;
386                 } else if (!tick_program_event(expires, 0))
387                                 goto out;
388                 /*
389                  * We are past the event already. So we crossed a
390                  * jiffie boundary. Update jiffies and raise the
391                  * softirq.
392                  */
393                 tick_do_update_jiffies64(ktime_get());
394                 cpumask_clear_cpu(cpu, nohz_cpu_mask);
395         }
396         raise_softirq_irqoff(TIMER_SOFTIRQ);
397 out:
398         ts->next_jiffies = next_jiffies;
399         ts->last_jiffies = last_jiffies;
400         ts->sleep_length = ktime_sub(dev->next_event, now);
401 end:
402         local_irq_restore(flags);
403 }
404 
405 /**
406  * tick_nohz_get_sleep_length - return the length of the current sleep
407  *
408  * Called from power state control code with interrupts disabled
409  */
410 ktime_t tick_nohz_get_sleep_length(void)
411 {
412         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
413 
414         return ts->sleep_length;
415 }
416 
417 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
418 {
419         hrtimer_cancel(&ts->sched_timer);
420         hrtimer_set_expires(&ts->sched_timer, ts->idle_tick);
421 
422         while (1) {
423                 /* Forward the time to expire in the future */
424                 hrtimer_forward(&ts->sched_timer, now, tick_period);
425 
426                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
427                         hrtimer_start_expires(&ts->sched_timer,
428                                               HRTIMER_MODE_ABS_PINNED);
429                         /* Check, if the timer was already in the past */
430                         if (hrtimer_active(&ts->sched_timer))
431                                 break;
432                 } else {
433                         if (!tick_program_event(
434                                 hrtimer_get_expires(&ts->sched_timer), 0))
435                                 break;
436                 }
437                 /* Update jiffies and reread time */
438                 tick_do_update_jiffies64(now);
439                 now = ktime_get();
440         }
441 }
442 
443 /**
444  * tick_nohz_restart_sched_tick - restart the idle tick from the idle task
445  *
446  * Restart the idle tick when the CPU is woken up from idle
447  */
448 void tick_nohz_restart_sched_tick(void)
449 {
450         int cpu = smp_processor_id();
451         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
452 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
453         unsigned long ticks;
454 #endif
455         ktime_t now;
456 
457         local_irq_disable();
458         if (ts->idle_active || (ts->inidle && ts->tick_stopped))
459                 now = ktime_get();
460 
461         if (ts->idle_active)
462                 tick_nohz_stop_idle(cpu, now);
463 
464         if (!ts->inidle || !ts->tick_stopped) {
465                 ts->inidle = 0;
466                 local_irq_enable();
467                 return;
468         }
469 
470         ts->inidle = 0;
471 
472         rcu_exit_nohz();
473 
474         /* Update jiffies first */
475         select_nohz_load_balancer(0);
476         tick_do_update_jiffies64(now);
477         cpumask_clear_cpu(cpu, nohz_cpu_mask);
478 
479 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
480         /*
481          * We stopped the tick in idle. Update process times would miss the
482          * time we slept as update_process_times does only a 1 tick
483          * accounting. Enforce that this is accounted to idle !
484          */
485         ticks = jiffies - ts->idle_jiffies;
486         /*
487          * We might be one off. Do not randomly account a huge number of ticks!
488          */
489         if (ticks && ticks < LONG_MAX)
490                 account_idle_ticks(ticks);
491 #endif
492 
493         touch_softlockup_watchdog();
494         /*
495          * Cancel the scheduled timer and restore the tick
496          */
497         ts->tick_stopped  = 0;
498         ts->idle_exittime = now;
499 
500         tick_nohz_restart(ts, now);
501 
502         local_irq_enable();
503 }
504 
505 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
506 {
507         hrtimer_forward(&ts->sched_timer, now, tick_period);
508         return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
509 }
510 
511 /*
512  * The nohz low res interrupt handler
513  */
514 static void tick_nohz_handler(struct clock_event_device *dev)
515 {
516         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
517         struct pt_regs *regs = get_irq_regs();
518         int cpu = smp_processor_id();
519         ktime_t now = ktime_get();
520 
521         dev->next_event.tv64 = KTIME_MAX;
522 
523         /*
524          * Check if the do_timer duty was dropped. We don't care about
525          * concurrency: This happens only when the cpu in charge went
526          * into a long sleep. If two cpus happen to assign themself to
527          * this duty, then the jiffies update is still serialized by
528          * xtime_lock.
529          */
530         if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
531                 tick_do_timer_cpu = cpu;
532 
533         /* Check, if the jiffies need an update */
534         if (tick_do_timer_cpu == cpu)
535                 tick_do_update_jiffies64(now);
536 
537         /*
538          * When we are idle and the tick is stopped, we have to touch
539          * the watchdog as we might not schedule for a really long
540          * time. This happens on complete idle SMP systems while
541          * waiting on the login prompt. We also increment the "start
542          * of idle" jiffy stamp so the idle accounting adjustment we
543          * do when we go busy again does not account too much ticks.
544          */
545         if (ts->tick_stopped) {
546                 touch_softlockup_watchdog();
547                 ts->idle_jiffies++;
548         }
549 
550         update_process_times(user_mode(regs));
551         profile_tick(CPU_PROFILING);
552 
553         while (tick_nohz_reprogram(ts, now)) {
554                 now = ktime_get();
555                 tick_do_update_jiffies64(now);
556         }
557 }
558 
559 /**
560  * tick_nohz_switch_to_nohz - switch to nohz mode
561  */
562 static void tick_nohz_switch_to_nohz(void)
563 {
564         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
565         ktime_t next;
566 
567         if (!tick_nohz_enabled)
568                 return;
569 
570         local_irq_disable();
571         if (tick_switch_to_oneshot(tick_nohz_handler)) {
572                 local_irq_enable();
573                 return;
574         }
575 
576         ts->nohz_mode = NOHZ_MODE_LOWRES;
577 
578         /*
579          * Recycle the hrtimer in ts, so we can share the
580          * hrtimer_forward with the highres code.
581          */
582         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
583         /* Get the next period */
584         next = tick_init_jiffy_update();
585 
586         for (;;) {
587                 hrtimer_set_expires(&ts->sched_timer, next);
588                 if (!tick_program_event(next, 0))
589                         break;
590                 next = ktime_add(next, tick_period);
591         }
592         local_irq_enable();
593 
594         printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
595                smp_processor_id());
596 }
597 
598 /*
599  * When NOHZ is enabled and the tick is stopped, we need to kick the
600  * tick timer from irq_enter() so that the jiffies update is kept
601  * alive during long running softirqs. That's ugly as hell, but
602  * correctness is key even if we need to fix the offending softirq in
603  * the first place.
604  *
605  * Note, this is different to tick_nohz_restart. We just kick the
606  * timer and do not touch the other magic bits which need to be done
607  * when idle is left.
608  */
609 static void tick_nohz_kick_tick(int cpu, ktime_t now)
610 {
611 #if 0
612         /* Switch back to 2.6.27 behaviour */
613 
614         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
615         ktime_t delta;
616 
617         /*
618          * Do not touch the tick device, when the next expiry is either
619          * already reached or less/equal than the tick period.
620          */
621         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
622         if (delta.tv64 <= tick_period.tv64)
623                 return;
624 
625         tick_nohz_restart(ts, now);
626 #endif
627 }
628 
629 static inline void tick_check_nohz(int cpu)
630 {
631         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
632         ktime_t now;
633 
634         if (!ts->idle_active && !ts->tick_stopped)
635                 return;
636         now = ktime_get();
637         if (ts->idle_active)
638                 tick_nohz_stop_idle(cpu, now);
639         if (ts->tick_stopped) {
640                 tick_nohz_update_jiffies(now);
641                 tick_nohz_kick_tick(cpu, now);
642         }
643 }
644 
645 #else
646 
647 static inline void tick_nohz_switch_to_nohz(void) { }
648 static inline void tick_check_nohz(int cpu) { }
649 
650 #endif /* NO_HZ */
651 
652 /*
653  * Called from irq_enter to notify about the possible interruption of idle()
654  */
655 void tick_check_idle(int cpu)
656 {
657         tick_check_oneshot_broadcast(cpu);
658         tick_check_nohz(cpu);
659 }
660 
661 /*
662  * High resolution timer specific code
663  */
664 #ifdef CONFIG_HIGH_RES_TIMERS
665 /*
666  * We rearm the timer until we get disabled by the idle code.
667  * Called with interrupts disabled and timer->base->cpu_base->lock held.
668  */
669 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
670 {
671         struct tick_sched *ts =
672                 container_of(timer, struct tick_sched, sched_timer);
673         struct pt_regs *regs = get_irq_regs();
674         ktime_t now = ktime_get();
675         int cpu = smp_processor_id();
676 
677 #ifdef CONFIG_NO_HZ
678         /*
679          * Check if the do_timer duty was dropped. We don't care about
680          * concurrency: This happens only when the cpu in charge went
681          * into a long sleep. If two cpus happen to assign themself to
682          * this duty, then the jiffies update is still serialized by
683          * xtime_lock.
684          */
685         if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
686                 tick_do_timer_cpu = cpu;
687 #endif
688 
689         /* Check, if the jiffies need an update */
690         if (tick_do_timer_cpu == cpu)
691                 tick_do_update_jiffies64(now);
692 
693         /*
694          * Do not call, when we are not in irq context and have
695          * no valid regs pointer
696          */
697         if (regs) {
698                 /*
699                  * When we are idle and the tick is stopped, we have to touch
700                  * the watchdog as we might not schedule for a really long
701                  * time. This happens on complete idle SMP systems while
702                  * waiting on the login prompt. We also increment the "start of
703                  * idle" jiffy stamp so the idle accounting adjustment we do
704                  * when we go busy again does not account too much ticks.
705                  */
706                 if (ts->tick_stopped) {
707                         touch_softlockup_watchdog();
708                         ts->idle_jiffies++;
709                 }
710                 update_process_times(user_mode(regs));
711                 profile_tick(CPU_PROFILING);
712         }
713 
714         hrtimer_forward(timer, now, tick_period);
715 
716         return HRTIMER_RESTART;
717 }
718 
719 /**
720  * tick_setup_sched_timer - setup the tick emulation timer
721  */
722 void tick_setup_sched_timer(void)
723 {
724         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
725         ktime_t now = ktime_get();
726         u64 offset;
727 
728         /*
729          * Emulate tick processing via per-CPU hrtimers:
730          */
731         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
732         ts->sched_timer.function = tick_sched_timer;
733 
734         /* Get the next period (per cpu) */
735         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
736         offset = ktime_to_ns(tick_period) >> 1;
737         do_div(offset, num_possible_cpus());
738         offset *= smp_processor_id();
739         hrtimer_add_expires_ns(&ts->sched_timer, offset);
740 
741         for (;;) {
742                 hrtimer_forward(&ts->sched_timer, now, tick_period);
743                 hrtimer_start_expires(&ts->sched_timer,
744                                       HRTIMER_MODE_ABS_PINNED);
745                 /* Check, if the timer was already in the past */
746                 if (hrtimer_active(&ts->sched_timer))
747                         break;
748                 now = ktime_get();
749         }
750 
751 #ifdef CONFIG_NO_HZ
752         if (tick_nohz_enabled)
753                 ts->nohz_mode = NOHZ_MODE_HIGHRES;
754 #endif
755 }
756 #endif /* HIGH_RES_TIMERS */
757 
758 #if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS
759 void tick_cancel_sched_timer(int cpu)
760 {
761         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
762 
763 # ifdef CONFIG_HIGH_RES_TIMERS
764         if (ts->sched_timer.base)
765                 hrtimer_cancel(&ts->sched_timer);
766 # endif
767 
768         memset(ts, 0, sizeof(*ts));
769 }
770 #endif
771 
772 /**
773  * Async notification about clocksource changes
774  */
775 void tick_clock_notify(void)
776 {
777         int cpu;
778 
779         for_each_possible_cpu(cpu)
780                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
781 }
782 
783 /*
784  * Async notification about clock event changes
785  */
786 void tick_oneshot_notify(void)
787 {
788         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
789 
790         set_bit(0, &ts->check_clocks);
791 }
792 
793 /**
794  * Check, if a change happened, which makes oneshot possible.
795  *
796  * Called cyclic from the hrtimer softirq (driven by the timer
797  * softirq) allow_nohz signals, that we can switch into low-res nohz
798  * mode, because high resolution timers are disabled (either compile
799  * or runtime).
800  */
801 int tick_check_oneshot_change(int allow_nohz)
802 {
803         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
804 
805         if (!test_and_clear_bit(0, &ts->check_clocks))
806                 return 0;
807 
808         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
809                 return 0;
810 
811         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
812                 return 0;
813 
814         if (!allow_nohz)
815                 return 1;
816 
817         tick_nohz_switch_to_nohz();
818         return 0;
819 }
820 

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