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