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;
51 /* Reevalute with xtime_lock held */
52 write_seqlock(&xtime_lock
);
54 delta
= ktime_sub(now
, last_jiffies_update
);
55 if (delta
.tv64
>= tick_period
.tv64
) {
57 delta
= ktime_sub(delta
, tick_period
);
58 last_jiffies_update
= ktime_add(last_jiffies_update
,
61 /* Slow path for long timeouts */
62 if (unlikely(delta
.tv64
>= tick_period
.tv64
)) {
63 s64 incr
= ktime_to_ns(tick_period
);
65 ticks
= ktime_divns(delta
, incr
);
67 last_jiffies_update
= ktime_add_ns(last_jiffies_update
,
72 write_sequnlock(&xtime_lock
);
76 * Initialize and return retrieve the jiffies update.
78 static ktime_t
tick_init_jiffy_update(void)
82 write_seqlock(&xtime_lock
);
83 /* Did we start the jiffies update yet ? */
84 if (last_jiffies_update
.tv64
== 0)
85 last_jiffies_update
= tick_next_period
;
86 period
= last_jiffies_update
;
87 write_sequnlock(&xtime_lock
);
92 * NOHZ - aka dynamic tick functionality
98 static int tick_nohz_enabled __read_mostly
= 1;
101 * Enable / Disable tickless mode
103 static int __init
setup_tick_nohz(char *str
)
105 if (!strcmp(str
, "off"))
106 tick_nohz_enabled
= 0;
107 else if (!strcmp(str
, "on"))
108 tick_nohz_enabled
= 1;
114 __setup("nohz=", setup_tick_nohz
);
117 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
119 * Called from interrupt entry when the CPU was idle
121 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
122 * must be updated. Otherwise an interrupt handler could use a stale jiffy
123 * value. We do this unconditionally on any cpu, as we don't know whether the
124 * cpu, which has the update task assigned is in a long sleep.
126 void tick_nohz_update_jiffies(void)
128 int cpu
= smp_processor_id();
129 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
133 if (!ts
->tick_stopped
)
136 touch_softlockup_watchdog();
138 cpu_clear(cpu
, nohz_cpu_mask
);
140 ts
->idle_waketime
= now
;
142 local_irq_save(flags
);
143 tick_do_update_jiffies64(now
);
144 local_irq_restore(flags
);
147 void tick_nohz_stop_idle(int cpu
)
149 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
151 if (ts
->idle_active
) {
154 delta
= ktime_sub(now
, ts
->idle_entrytime
);
155 ts
->idle_lastupdate
= now
;
156 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
161 static ktime_t
tick_nohz_start_idle(struct tick_sched
*ts
)
166 if (ts
->idle_active
) {
167 delta
= ktime_sub(now
, ts
->idle_entrytime
);
168 ts
->idle_lastupdate
= now
;
169 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
171 ts
->idle_entrytime
= now
;
176 u64
get_cpu_idle_time_us(int cpu
, u64
*last_update_time
)
178 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
180 *last_update_time
= ktime_to_us(ts
->idle_lastupdate
);
181 return ktime_to_us(ts
->idle_sleeptime
);
185 * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
187 * When the next event is more than a tick into the future, stop the idle tick
188 * Called either from the idle loop or from irq_exit() when an idle period was
189 * just interrupted by an interrupt which did not cause a reschedule.
191 void tick_nohz_stop_sched_tick(void)
193 unsigned long seq
, last_jiffies
, next_jiffies
, delta_jiffies
, flags
;
194 unsigned long rt_jiffies
;
195 struct tick_sched
*ts
;
196 ktime_t last_update
, expires
, now
;
197 struct clock_event_device
*dev
= __get_cpu_var(tick_cpu_device
).evtdev
;
200 local_irq_save(flags
);
202 cpu
= smp_processor_id();
203 ts
= &per_cpu(tick_cpu_sched
, cpu
);
204 now
= tick_nohz_start_idle(ts
);
207 * If this cpu is offline and it is the one which updates
208 * jiffies, then give up the assignment and let it be taken by
209 * the cpu which runs the tick timer next. If we don't drop
210 * this here the jiffies might be stale and do_timer() never
213 if (unlikely(!cpu_online(cpu
))) {
214 if (cpu
== tick_do_timer_cpu
)
215 tick_do_timer_cpu
= -1;
218 if (unlikely(ts
->nohz_mode
== NOHZ_MODE_INACTIVE
))
224 if (unlikely(local_softirq_pending())) {
225 static int ratelimit
;
227 if (ratelimit
< 10) {
228 printk(KERN_ERR
"NOHZ: local_softirq_pending %02x\n",
229 local_softirq_pending());
235 /* Read jiffies and the time when jiffies were updated last */
237 seq
= read_seqbegin(&xtime_lock
);
238 last_update
= last_jiffies_update
;
239 last_jiffies
= jiffies
;
240 } while (read_seqretry(&xtime_lock
, seq
));
242 /* Get the next timer wheel timer */
243 next_jiffies
= get_next_timer_interrupt(last_jiffies
);
244 delta_jiffies
= next_jiffies
- last_jiffies
;
246 rt_jiffies
= rt_needs_cpu(cpu
);
247 if (rt_jiffies
&& rt_jiffies
< delta_jiffies
)
248 delta_jiffies
= rt_jiffies
;
250 if (rcu_needs_cpu(cpu
))
253 * Do not stop the tick, if we are only one off
254 * or if the cpu is required for rcu
256 if (!ts
->tick_stopped
&& delta_jiffies
== 1)
259 /* Schedule the tick, if we are at least one jiffie off */
260 if ((long)delta_jiffies
>= 1) {
262 if (delta_jiffies
> 1)
263 cpu_set(cpu
, nohz_cpu_mask
);
265 * nohz_stop_sched_tick can be called several times before
266 * the nohz_restart_sched_tick is called. This happens when
267 * interrupts arrive which do not cause a reschedule. In the
268 * first call we save the current tick time, so we can restart
269 * the scheduler tick in nohz_restart_sched_tick.
271 if (!ts
->tick_stopped
) {
272 if (select_nohz_load_balancer(1)) {
274 * sched tick not stopped!
276 cpu_clear(cpu
, nohz_cpu_mask
);
280 ts
->idle_tick
= ts
->sched_timer
.expires
;
281 ts
->tick_stopped
= 1;
282 ts
->idle_jiffies
= last_jiffies
;
287 * If this cpu is the one which updates jiffies, then
288 * give up the assignment and let it be taken by the
289 * cpu which runs the tick timer next, which might be
290 * this cpu as well. If we don't drop this here the
291 * jiffies might be stale and do_timer() never
294 if (cpu
== tick_do_timer_cpu
)
295 tick_do_timer_cpu
= -1;
300 * delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that
301 * there is no timer pending or at least extremly far
302 * into the future (12 days for HZ=1000). In this case
303 * we simply stop the tick timer:
305 if (unlikely(delta_jiffies
>= NEXT_TIMER_MAX_DELTA
)) {
306 ts
->idle_expires
.tv64
= KTIME_MAX
;
307 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
)
308 hrtimer_cancel(&ts
->sched_timer
);
313 * calculate the expiry time for the next timer wheel
316 expires
= ktime_add_ns(last_update
, tick_period
.tv64
*
318 ts
->idle_expires
= expires
;
320 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
321 hrtimer_start(&ts
->sched_timer
, expires
,
323 /* Check, if the timer was already in the past */
324 if (hrtimer_active(&ts
->sched_timer
))
326 } else if (!tick_program_event(expires
, 0))
329 * We are past the event already. So we crossed a
330 * jiffie boundary. Update jiffies and raise the
333 tick_do_update_jiffies64(ktime_get());
334 cpu_clear(cpu
, nohz_cpu_mask
);
336 raise_softirq_irqoff(TIMER_SOFTIRQ
);
338 ts
->next_jiffies
= next_jiffies
;
339 ts
->last_jiffies
= last_jiffies
;
340 ts
->sleep_length
= ktime_sub(dev
->next_event
, now
);
342 local_irq_restore(flags
);
346 * tick_nohz_get_sleep_length - return the length of the current sleep
348 * Called from power state control code with interrupts disabled
350 ktime_t
tick_nohz_get_sleep_length(void)
352 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
354 return ts
->sleep_length
;
358 * tick_nohz_restart_sched_tick - restart the idle tick from the idle task
360 * Restart the idle tick when the CPU is woken up from idle
362 void tick_nohz_restart_sched_tick(void)
364 int cpu
= smp_processor_id();
365 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
370 tick_nohz_stop_idle(cpu
);
372 if (!ts
->tick_stopped
) {
379 /* Update jiffies first */
380 select_nohz_load_balancer(0);
382 tick_do_update_jiffies64(now
);
383 cpu_clear(cpu
, nohz_cpu_mask
);
386 * We stopped the tick in idle. Update process times would miss the
387 * time we slept as update_process_times does only a 1 tick
388 * accounting. Enforce that this is accounted to idle !
390 ticks
= jiffies
- ts
->idle_jiffies
;
392 * We might be one off. Do not randomly account a huge number of ticks!
394 if (ticks
&& ticks
< LONG_MAX
) {
395 add_preempt_count(HARDIRQ_OFFSET
);
396 account_system_time(current
, HARDIRQ_OFFSET
,
397 jiffies_to_cputime(ticks
));
398 sub_preempt_count(HARDIRQ_OFFSET
);
402 * Cancel the scheduled timer and restore the tick
404 ts
->tick_stopped
= 0;
405 ts
->idle_exittime
= now
;
406 hrtimer_cancel(&ts
->sched_timer
);
407 ts
->sched_timer
.expires
= ts
->idle_tick
;
410 /* Forward the time to expire in the future */
411 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
413 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
414 hrtimer_start(&ts
->sched_timer
,
415 ts
->sched_timer
.expires
,
417 /* Check, if the timer was already in the past */
418 if (hrtimer_active(&ts
->sched_timer
))
421 if (!tick_program_event(ts
->sched_timer
.expires
, 0))
424 /* Update jiffies and reread time */
425 tick_do_update_jiffies64(now
);
431 static int tick_nohz_reprogram(struct tick_sched
*ts
, ktime_t now
)
433 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
434 return tick_program_event(ts
->sched_timer
.expires
, 0);
438 * The nohz low res interrupt handler
440 static void tick_nohz_handler(struct clock_event_device
*dev
)
442 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
443 struct pt_regs
*regs
= get_irq_regs();
444 int cpu
= smp_processor_id();
445 ktime_t now
= ktime_get();
447 dev
->next_event
.tv64
= KTIME_MAX
;
450 * Check if the do_timer duty was dropped. We don't care about
451 * concurrency: This happens only when the cpu in charge went
452 * into a long sleep. If two cpus happen to assign themself to
453 * this duty, then the jiffies update is still serialized by
456 if (unlikely(tick_do_timer_cpu
== -1))
457 tick_do_timer_cpu
= cpu
;
459 /* Check, if the jiffies need an update */
460 if (tick_do_timer_cpu
== cpu
)
461 tick_do_update_jiffies64(now
);
464 * When we are idle and the tick is stopped, we have to touch
465 * the watchdog as we might not schedule for a really long
466 * time. This happens on complete idle SMP systems while
467 * waiting on the login prompt. We also increment the "start
468 * of idle" jiffy stamp so the idle accounting adjustment we
469 * do when we go busy again does not account too much ticks.
471 if (ts
->tick_stopped
) {
472 touch_softlockup_watchdog();
476 update_process_times(user_mode(regs
));
477 profile_tick(CPU_PROFILING
);
479 /* Do not restart, when we are in the idle loop */
480 if (ts
->tick_stopped
)
483 while (tick_nohz_reprogram(ts
, now
)) {
485 tick_do_update_jiffies64(now
);
490 * tick_nohz_switch_to_nohz - switch to nohz mode
492 static void tick_nohz_switch_to_nohz(void)
494 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
497 if (!tick_nohz_enabled
)
501 if (tick_switch_to_oneshot(tick_nohz_handler
)) {
506 ts
->nohz_mode
= NOHZ_MODE_LOWRES
;
509 * Recycle the hrtimer in ts, so we can share the
510 * hrtimer_forward with the highres code.
512 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
513 /* Get the next period */
514 next
= tick_init_jiffy_update();
517 ts
->sched_timer
.expires
= next
;
518 if (!tick_program_event(next
, 0))
520 next
= ktime_add(next
, tick_period
);
524 printk(KERN_INFO
"Switched to NOHz mode on CPU #%d\n",
530 static inline void tick_nohz_switch_to_nohz(void) { }
535 * High resolution timer specific code
537 #ifdef CONFIG_HIGH_RES_TIMERS
539 * We rearm the timer until we get disabled by the idle code.
540 * Called with interrupts disabled and timer->base->cpu_base->lock held.
542 static enum hrtimer_restart
tick_sched_timer(struct hrtimer
*timer
)
544 struct tick_sched
*ts
=
545 container_of(timer
, struct tick_sched
, sched_timer
);
546 struct pt_regs
*regs
= get_irq_regs();
547 ktime_t now
= ktime_get();
548 int cpu
= smp_processor_id();
552 * Check if the do_timer duty was dropped. We don't care about
553 * concurrency: This happens only when the cpu in charge went
554 * into a long sleep. If two cpus happen to assign themself to
555 * this duty, then the jiffies update is still serialized by
558 if (unlikely(tick_do_timer_cpu
== -1))
559 tick_do_timer_cpu
= cpu
;
562 /* Check, if the jiffies need an update */
563 if (tick_do_timer_cpu
== cpu
)
564 tick_do_update_jiffies64(now
);
567 * Do not call, when we are not in irq context and have
568 * no valid regs pointer
572 * When we are idle and the tick is stopped, we have to touch
573 * the watchdog as we might not schedule for a really long
574 * time. This happens on complete idle SMP systems while
575 * waiting on the login prompt. We also increment the "start of
576 * idle" jiffy stamp so the idle accounting adjustment we do
577 * when we go busy again does not account too much ticks.
579 if (ts
->tick_stopped
) {
580 touch_softlockup_watchdog();
583 update_process_times(user_mode(regs
));
584 profile_tick(CPU_PROFILING
);
587 /* Do not restart, when we are in the idle loop */
588 if (ts
->tick_stopped
)
589 return HRTIMER_NORESTART
;
591 hrtimer_forward(timer
, now
, tick_period
);
593 return HRTIMER_RESTART
;
597 * tick_setup_sched_timer - setup the tick emulation timer
599 void tick_setup_sched_timer(void)
601 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
602 ktime_t now
= ktime_get();
606 * Emulate tick processing via per-CPU hrtimers:
608 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
609 ts
->sched_timer
.function
= tick_sched_timer
;
610 ts
->sched_timer
.cb_mode
= HRTIMER_CB_IRQSAFE_NO_SOFTIRQ
;
612 /* Get the next period (per cpu) */
613 ts
->sched_timer
.expires
= tick_init_jiffy_update();
614 offset
= ktime_to_ns(tick_period
) >> 1;
615 do_div(offset
, num_possible_cpus());
616 offset
*= smp_processor_id();
617 ts
->sched_timer
.expires
= ktime_add_ns(ts
->sched_timer
.expires
, offset
);
620 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
621 hrtimer_start(&ts
->sched_timer
, ts
->sched_timer
.expires
,
623 /* Check, if the timer was already in the past */
624 if (hrtimer_active(&ts
->sched_timer
))
630 if (tick_nohz_enabled
)
631 ts
->nohz_mode
= NOHZ_MODE_HIGHRES
;
635 void tick_cancel_sched_timer(int cpu
)
637 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
639 if (ts
->sched_timer
.base
)
640 hrtimer_cancel(&ts
->sched_timer
);
642 ts
->nohz_mode
= NOHZ_MODE_INACTIVE
;
644 #endif /* HIGH_RES_TIMERS */
647 * Async notification about clocksource changes
649 void tick_clock_notify(void)
653 for_each_possible_cpu(cpu
)
654 set_bit(0, &per_cpu(tick_cpu_sched
, cpu
).check_clocks
);
658 * Async notification about clock event changes
660 void tick_oneshot_notify(void)
662 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
664 set_bit(0, &ts
->check_clocks
);
668 * Check, if a change happened, which makes oneshot possible.
670 * Called cyclic from the hrtimer softirq (driven by the timer
671 * softirq) allow_nohz signals, that we can switch into low-res nohz
672 * mode, because high resolution timers are disabled (either compile
675 int tick_check_oneshot_change(int allow_nohz
)
677 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
679 if (!test_and_clear_bit(0, &ts
->check_clocks
))
682 if (ts
->nohz_mode
!= NOHZ_MODE_INACTIVE
)
685 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
691 tick_nohz_switch_to_nohz();