2 * linux/kernel/time/tick-sched.c
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
8 * No idle tick implementation for low and high resolution timers
10 * Started by: Thomas Gleixner and Ingo Molnar
12 * Distribute under GPLv2.
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>
24 #include <asm/irq_regs.h>
26 #include "tick-internal.h"
29 * Per cpu nohz control structure
31 static DEFINE_PER_CPU(struct tick_sched
, tick_cpu_sched
);
34 * The time, when the last jiffy update happened. Protected by xtime_lock.
36 static ktime_t last_jiffies_update
;
38 struct tick_sched
*tick_get_tick_sched(int cpu
)
40 return &per_cpu(tick_cpu_sched
, cpu
);
44 * Must be called with interrupts disabled !
46 static void tick_do_update_jiffies64(ktime_t now
)
48 unsigned long ticks
= 0;
52 * Do a quick check without holding xtime_lock:
54 delta
= ktime_sub(now
, last_jiffies_update
);
55 if (delta
.tv64
< tick_period
.tv64
)
58 /* Reevalute with xtime_lock held */
59 write_seqlock(&xtime_lock
);
61 delta
= ktime_sub(now
, last_jiffies_update
);
62 if (delta
.tv64
>= tick_period
.tv64
) {
64 delta
= ktime_sub(delta
, tick_period
);
65 last_jiffies_update
= ktime_add(last_jiffies_update
,
68 /* Slow path for long timeouts */
69 if (unlikely(delta
.tv64
>= tick_period
.tv64
)) {
70 s64 incr
= ktime_to_ns(tick_period
);
72 ticks
= ktime_divns(delta
, incr
);
74 last_jiffies_update
= ktime_add_ns(last_jiffies_update
,
79 write_sequnlock(&xtime_lock
);
83 * Initialize and return retrieve the jiffies update.
85 static ktime_t
tick_init_jiffy_update(void)
89 write_seqlock(&xtime_lock
);
90 /* Did we start the jiffies update yet ? */
91 if (last_jiffies_update
.tv64
== 0)
92 last_jiffies_update
= tick_next_period
;
93 period
= last_jiffies_update
;
94 write_sequnlock(&xtime_lock
);
99 * NOHZ - aka dynamic tick functionality
105 static int tick_nohz_enabled __read_mostly
= 1;
108 * Enable / Disable tickless mode
110 static int __init
setup_tick_nohz(char *str
)
112 if (!strcmp(str
, "off"))
113 tick_nohz_enabled
= 0;
114 else if (!strcmp(str
, "on"))
115 tick_nohz_enabled
= 1;
121 __setup("nohz=", setup_tick_nohz
);
124 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
126 * Called from interrupt entry when the CPU was idle
128 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
129 * must be updated. Otherwise an interrupt handler could use a stale jiffy
130 * value. We do this unconditionally on any cpu, as we don't know whether the
131 * cpu, which has the update task assigned is in a long sleep.
133 void tick_nohz_update_jiffies(void)
135 int cpu
= smp_processor_id();
136 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
140 if (!ts
->tick_stopped
)
143 cpu_clear(cpu
, nohz_cpu_mask
);
145 ts
->idle_waketime
= now
;
147 local_irq_save(flags
);
148 tick_do_update_jiffies64(now
);
149 local_irq_restore(flags
);
151 touch_softlockup_watchdog();
154 void tick_nohz_stop_idle(int cpu
)
156 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
158 if (ts
->idle_active
) {
161 delta
= ktime_sub(now
, ts
->idle_entrytime
);
162 ts
->idle_lastupdate
= now
;
163 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
168 static ktime_t
tick_nohz_start_idle(struct tick_sched
*ts
)
173 if (ts
->idle_active
) {
174 delta
= ktime_sub(now
, ts
->idle_entrytime
);
175 ts
->idle_lastupdate
= now
;
176 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
178 ts
->idle_entrytime
= now
;
183 u64
get_cpu_idle_time_us(int cpu
, u64
*last_update_time
)
185 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
187 *last_update_time
= ktime_to_us(ts
->idle_lastupdate
);
188 return ktime_to_us(ts
->idle_sleeptime
);
192 * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
194 * When the next event is more than a tick into the future, stop the idle tick
195 * Called either from the idle loop or from irq_exit() when an idle period was
196 * just interrupted by an interrupt which did not cause a reschedule.
198 void tick_nohz_stop_sched_tick(int inidle
)
200 unsigned long seq
, last_jiffies
, next_jiffies
, delta_jiffies
, flags
;
201 struct tick_sched
*ts
;
202 ktime_t last_update
, expires
, now
;
203 struct clock_event_device
*dev
= __get_cpu_var(tick_cpu_device
).evtdev
;
206 local_irq_save(flags
);
208 cpu
= smp_processor_id();
209 ts
= &per_cpu(tick_cpu_sched
, cpu
);
210 now
= tick_nohz_start_idle(ts
);
213 * If this cpu is offline and it is the one which updates
214 * jiffies, then give up the assignment and let it be taken by
215 * the cpu which runs the tick timer next. If we don't drop
216 * this here the jiffies might be stale and do_timer() never
219 if (unlikely(!cpu_online(cpu
))) {
220 if (cpu
== tick_do_timer_cpu
)
221 tick_do_timer_cpu
= -1;
224 if (unlikely(ts
->nohz_mode
== NOHZ_MODE_INACTIVE
))
227 if (!inidle
&& !ts
->inidle
)
235 if (unlikely(local_softirq_pending())) {
236 static int ratelimit
;
238 if (ratelimit
< 10) {
239 printk(KERN_ERR
"NOHZ: local_softirq_pending %02x\n",
240 local_softirq_pending());
247 /* Read jiffies and the time when jiffies were updated last */
249 seq
= read_seqbegin(&xtime_lock
);
250 last_update
= last_jiffies_update
;
251 last_jiffies
= jiffies
;
252 } while (read_seqretry(&xtime_lock
, seq
));
254 /* Get the next timer wheel timer */
255 next_jiffies
= get_next_timer_interrupt(last_jiffies
);
256 delta_jiffies
= next_jiffies
- last_jiffies
;
258 if (rcu_needs_cpu(cpu
))
261 * Do not stop the tick, if we are only one off
262 * or if the cpu is required for rcu
264 if (!ts
->tick_stopped
&& delta_jiffies
== 1)
267 /* Schedule the tick, if we are at least one jiffie off */
268 if ((long)delta_jiffies
>= 1) {
270 if (delta_jiffies
> 1)
271 cpu_set(cpu
, nohz_cpu_mask
);
273 * nohz_stop_sched_tick can be called several times before
274 * the nohz_restart_sched_tick is called. This happens when
275 * interrupts arrive which do not cause a reschedule. In the
276 * first call we save the current tick time, so we can restart
277 * the scheduler tick in nohz_restart_sched_tick.
279 if (!ts
->tick_stopped
) {
280 if (select_nohz_load_balancer(1)) {
282 * sched tick not stopped!
284 cpu_clear(cpu
, nohz_cpu_mask
);
288 ts
->idle_tick
= ts
->sched_timer
.expires
;
289 ts
->tick_stopped
= 1;
290 ts
->idle_jiffies
= last_jiffies
;
292 sched_clock_tick_stop(cpu
);
296 * If this cpu is the one which updates jiffies, then
297 * give up the assignment and let it be taken by the
298 * cpu which runs the tick timer next, which might be
299 * this cpu as well. If we don't drop this here the
300 * jiffies might be stale and do_timer() never
303 if (cpu
== tick_do_timer_cpu
)
304 tick_do_timer_cpu
= -1;
309 * delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that
310 * there is no timer pending or at least extremly far
311 * into the future (12 days for HZ=1000). In this case
312 * we simply stop the tick timer:
314 if (unlikely(delta_jiffies
>= NEXT_TIMER_MAX_DELTA
)) {
315 ts
->idle_expires
.tv64
= KTIME_MAX
;
316 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
317 hrtimer_cancel(&ts
->sched_timer
);
322 * calculate the expiry time for the next timer wheel
325 expires
= ktime_add_ns(last_update
, tick_period
.tv64
*
327 ts
->idle_expires
= expires
;
329 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
330 hrtimer_start(&ts
->sched_timer
, expires
,
332 /* Check, if the timer was already in the past */
333 if (hrtimer_active(&ts
->sched_timer
))
335 } else if (!tick_program_event(expires
, 0))
338 * We are past the event already. So we crossed a
339 * jiffie boundary. Update jiffies and raise the
342 tick_do_update_jiffies64(ktime_get());
343 cpu_clear(cpu
, nohz_cpu_mask
);
345 raise_softirq_irqoff(TIMER_SOFTIRQ
);
347 ts
->next_jiffies
= next_jiffies
;
348 ts
->last_jiffies
= last_jiffies
;
349 ts
->sleep_length
= ktime_sub(dev
->next_event
, now
);
351 local_irq_restore(flags
);
355 * tick_nohz_get_sleep_length - return the length of the current sleep
357 * Called from power state control code with interrupts disabled
359 ktime_t
tick_nohz_get_sleep_length(void)
361 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
363 return ts
->sleep_length
;
367 * tick_nohz_restart_sched_tick - restart the idle tick from the idle task
369 * Restart the idle tick when the CPU is woken up from idle
371 void tick_nohz_restart_sched_tick(void)
373 int cpu
= smp_processor_id();
374 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
379 tick_nohz_stop_idle(cpu
);
381 if (!ts
->inidle
|| !ts
->tick_stopped
) {
391 /* Update jiffies first */
392 select_nohz_load_balancer(0);
394 tick_do_update_jiffies64(now
);
395 sched_clock_tick_start(cpu
);
396 cpu_clear(cpu
, nohz_cpu_mask
);
399 * We stopped the tick in idle. Update process times would miss the
400 * time we slept as update_process_times does only a 1 tick
401 * accounting. Enforce that this is accounted to idle !
403 ticks
= jiffies
- ts
->idle_jiffies
;
405 * We might be one off. Do not randomly account a huge number of ticks!
407 if (ticks
&& ticks
< LONG_MAX
) {
408 add_preempt_count(HARDIRQ_OFFSET
);
409 account_system_time(current
, HARDIRQ_OFFSET
,
410 jiffies_to_cputime(ticks
));
411 sub_preempt_count(HARDIRQ_OFFSET
);
414 touch_softlockup_watchdog();
416 * Cancel the scheduled timer and restore the tick
418 ts
->tick_stopped
= 0;
419 ts
->idle_exittime
= now
;
420 hrtimer_cancel(&ts
->sched_timer
);
421 ts
->sched_timer
.expires
= ts
->idle_tick
;
424 /* Forward the time to expire in the future */
425 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
427 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
428 hrtimer_start(&ts
->sched_timer
,
429 ts
->sched_timer
.expires
,
431 /* Check, if the timer was already in the past */
432 if (hrtimer_active(&ts
->sched_timer
))
435 if (!tick_program_event(ts
->sched_timer
.expires
, 0))
438 /* Update jiffies and reread time */
439 tick_do_update_jiffies64(now
);
445 static int tick_nohz_reprogram(struct tick_sched
*ts
, ktime_t now
)
447 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
448 return tick_program_event(ts
->sched_timer
.expires
, 0);
452 * The nohz low res interrupt handler
454 static void tick_nohz_handler(struct clock_event_device
*dev
)
456 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
457 struct pt_regs
*regs
= get_irq_regs();
458 int cpu
= smp_processor_id();
459 ktime_t now
= ktime_get();
461 dev
->next_event
.tv64
= KTIME_MAX
;
464 * Check if the do_timer duty was dropped. We don't care about
465 * concurrency: This happens only when the cpu in charge went
466 * into a long sleep. If two cpus happen to assign themself to
467 * this duty, then the jiffies update is still serialized by
470 if (unlikely(tick_do_timer_cpu
== -1))
471 tick_do_timer_cpu
= cpu
;
473 /* Check, if the jiffies need an update */
474 if (tick_do_timer_cpu
== cpu
)
475 tick_do_update_jiffies64(now
);
478 * When we are idle and the tick is stopped, we have to touch
479 * the watchdog as we might not schedule for a really long
480 * time. This happens on complete idle SMP systems while
481 * waiting on the login prompt. We also increment the "start
482 * of idle" jiffy stamp so the idle accounting adjustment we
483 * do when we go busy again does not account too much ticks.
485 if (ts
->tick_stopped
) {
486 touch_softlockup_watchdog();
490 update_process_times(user_mode(regs
));
491 profile_tick(CPU_PROFILING
);
493 /* Do not restart, when we are in the idle loop */
494 if (ts
->tick_stopped
)
497 while (tick_nohz_reprogram(ts
, now
)) {
499 tick_do_update_jiffies64(now
);
504 * tick_nohz_switch_to_nohz - switch to nohz mode
506 static void tick_nohz_switch_to_nohz(void)
508 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
511 if (!tick_nohz_enabled
)
515 if (tick_switch_to_oneshot(tick_nohz_handler
)) {
520 ts
->nohz_mode
= NOHZ_MODE_LOWRES
;
523 * Recycle the hrtimer in ts, so we can share the
524 * hrtimer_forward with the highres code.
526 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
527 /* Get the next period */
528 next
= tick_init_jiffy_update();
531 ts
->sched_timer
.expires
= next
;
532 if (!tick_program_event(next
, 0))
534 next
= ktime_add(next
, tick_period
);
538 printk(KERN_INFO
"Switched to NOHz mode on CPU #%d\n",
544 static inline void tick_nohz_switch_to_nohz(void) { }
549 * High resolution timer specific code
551 #ifdef CONFIG_HIGH_RES_TIMERS
553 * We rearm the timer until we get disabled by the idle code.
554 * Called with interrupts disabled and timer->base->cpu_base->lock held.
556 static enum hrtimer_restart
tick_sched_timer(struct hrtimer
*timer
)
558 struct tick_sched
*ts
=
559 container_of(timer
, struct tick_sched
, sched_timer
);
560 struct pt_regs
*regs
= get_irq_regs();
561 ktime_t now
= ktime_get();
562 int cpu
= smp_processor_id();
566 * Check if the do_timer duty was dropped. We don't care about
567 * concurrency: This happens only when the cpu in charge went
568 * into a long sleep. If two cpus happen to assign themself to
569 * this duty, then the jiffies update is still serialized by
572 if (unlikely(tick_do_timer_cpu
== -1))
573 tick_do_timer_cpu
= cpu
;
576 /* Check, if the jiffies need an update */
577 if (tick_do_timer_cpu
== cpu
)
578 tick_do_update_jiffies64(now
);
581 * Do not call, when we are not in irq context and have
582 * no valid regs pointer
586 * When we are idle and the tick is stopped, we have to touch
587 * the watchdog as we might not schedule for a really long
588 * time. This happens on complete idle SMP systems while
589 * waiting on the login prompt. We also increment the "start of
590 * idle" jiffy stamp so the idle accounting adjustment we do
591 * when we go busy again does not account too much ticks.
593 if (ts
->tick_stopped
) {
594 touch_softlockup_watchdog();
597 update_process_times(user_mode(regs
));
598 profile_tick(CPU_PROFILING
);
601 /* Do not restart, when we are in the idle loop */
602 if (ts
->tick_stopped
)
603 return HRTIMER_NORESTART
;
605 hrtimer_forward(timer
, now
, tick_period
);
607 return HRTIMER_RESTART
;
611 * tick_setup_sched_timer - setup the tick emulation timer
613 void tick_setup_sched_timer(void)
615 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
616 ktime_t now
= ktime_get();
620 * Emulate tick processing via per-CPU hrtimers:
622 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
623 ts
->sched_timer
.function
= tick_sched_timer
;
624 ts
->sched_timer
.cb_mode
= HRTIMER_CB_IRQSAFE_NO_SOFTIRQ
;
626 /* Get the next period (per cpu) */
627 ts
->sched_timer
.expires
= tick_init_jiffy_update();
628 offset
= ktime_to_ns(tick_period
) >> 1;
629 do_div(offset
, num_possible_cpus());
630 offset
*= smp_processor_id();
631 ts
->sched_timer
.expires
= ktime_add_ns(ts
->sched_timer
.expires
, offset
);
634 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
635 hrtimer_start(&ts
->sched_timer
, ts
->sched_timer
.expires
,
637 /* Check, if the timer was already in the past */
638 if (hrtimer_active(&ts
->sched_timer
))
644 if (tick_nohz_enabled
)
645 ts
->nohz_mode
= NOHZ_MODE_HIGHRES
;
649 void tick_cancel_sched_timer(int cpu
)
651 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
653 if (ts
->sched_timer
.base
)
654 hrtimer_cancel(&ts
->sched_timer
);
656 ts
->nohz_mode
= NOHZ_MODE_INACTIVE
;
658 #endif /* HIGH_RES_TIMERS */
661 * Async notification about clocksource changes
663 void tick_clock_notify(void)
667 for_each_possible_cpu(cpu
)
668 set_bit(0, &per_cpu(tick_cpu_sched
, cpu
).check_clocks
);
672 * Async notification about clock event changes
674 void tick_oneshot_notify(void)
676 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
678 set_bit(0, &ts
->check_clocks
);
682 * Check, if a change happened, which makes oneshot possible.
684 * Called cyclic from the hrtimer softirq (driven by the timer
685 * softirq) allow_nohz signals, that we can switch into low-res nohz
686 * mode, because high resolution timers are disabled (either compile
689 int tick_check_oneshot_change(int allow_nohz
)
691 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
693 if (!test_and_clear_bit(0, &ts
->check_clocks
))
696 if (ts
->nohz_mode
!= NOHZ_MODE_INACTIVE
)
699 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
705 tick_nohz_switch_to_nohz();