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 * For licencing details see kernel-base/COPYING
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 cpu_clear(cpu
, nohz_cpu_mask
);
139 local_irq_save(flags
);
140 tick_do_update_jiffies64(now
);
141 local_irq_restore(flags
);
145 * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
147 * When the next event is more than a tick into the future, stop the idle tick
148 * Called either from the idle loop or from irq_exit() when an idle period was
149 * just interrupted by an interrupt which did not cause a reschedule.
151 void tick_nohz_stop_sched_tick(void)
153 unsigned long seq
, last_jiffies
, next_jiffies
, delta_jiffies
, flags
;
154 struct tick_sched
*ts
;
155 ktime_t last_update
, expires
, now
, delta
;
158 local_irq_save(flags
);
160 cpu
= smp_processor_id();
161 ts
= &per_cpu(tick_cpu_sched
, cpu
);
163 if (unlikely(ts
->nohz_mode
== NOHZ_MODE_INACTIVE
))
169 cpu
= smp_processor_id();
170 if (unlikely(local_softirq_pending()))
171 printk(KERN_ERR
"NOHZ: local_softirq_pending %02x\n",
172 local_softirq_pending());
176 * When called from irq_exit we need to account the idle sleep time
179 if (ts
->tick_stopped
) {
180 delta
= ktime_sub(now
, ts
->idle_entrytime
);
181 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
184 ts
->idle_entrytime
= now
;
187 /* Read jiffies and the time when jiffies were updated last */
189 seq
= read_seqbegin(&xtime_lock
);
190 last_update
= last_jiffies_update
;
191 last_jiffies
= jiffies
;
192 } while (read_seqretry(&xtime_lock
, seq
));
194 /* Get the next timer wheel timer */
195 next_jiffies
= get_next_timer_interrupt(last_jiffies
);
196 delta_jiffies
= next_jiffies
- last_jiffies
;
198 if (rcu_needs_cpu(cpu
))
201 * Do not stop the tick, if we are only one off
202 * or if the cpu is required for rcu
204 if (!ts
->tick_stopped
&& delta_jiffies
== 1)
207 /* Schedule the tick, if we are at least one jiffie off */
208 if ((long)delta_jiffies
>= 1) {
210 if (delta_jiffies
> 1)
211 cpu_set(cpu
, nohz_cpu_mask
);
213 * nohz_stop_sched_tick can be called several times before
214 * the nohz_restart_sched_tick is called. This happens when
215 * interrupts arrive which do not cause a reschedule. In the
216 * first call we save the current tick time, so we can restart
217 * the scheduler tick in nohz_restart_sched_tick.
219 if (!ts
->tick_stopped
) {
220 ts
->idle_tick
= ts
->sched_timer
.expires
;
221 ts
->tick_stopped
= 1;
222 ts
->idle_jiffies
= last_jiffies
;
226 * If this cpu is the one which updates jiffies, then
227 * give up the assignment and let it be taken by the
228 * cpu which runs the tick timer next, which might be
229 * this cpu as well. If we don't drop this here the
230 * jiffies might be stale and do_timer() never
233 if (cpu
== tick_do_timer_cpu
)
234 tick_do_timer_cpu
= -1;
237 * calculate the expiry time for the next timer wheel
240 expires
= ktime_add_ns(last_update
, tick_period
.tv64
*
242 ts
->idle_expires
= expires
;
245 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
246 hrtimer_start(&ts
->sched_timer
, expires
,
248 /* Check, if the timer was already in the past */
249 if (hrtimer_active(&ts
->sched_timer
))
251 } else if(!tick_program_event(expires
, 0))
254 * We are past the event already. So we crossed a
255 * jiffie boundary. Update jiffies and raise the
258 tick_do_update_jiffies64(ktime_get());
259 cpu_clear(cpu
, nohz_cpu_mask
);
261 raise_softirq_irqoff(TIMER_SOFTIRQ
);
263 ts
->next_jiffies
= next_jiffies
;
264 ts
->last_jiffies
= last_jiffies
;
266 local_irq_restore(flags
);
270 * nohz_restart_sched_tick - restart the idle tick from the idle task
272 * Restart the idle tick when the CPU is woken up from idle
274 void tick_nohz_restart_sched_tick(void)
276 int cpu
= smp_processor_id();
277 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
281 if (!ts
->tick_stopped
)
284 /* Update jiffies first */
288 tick_do_update_jiffies64(now
);
289 cpu_clear(cpu
, nohz_cpu_mask
);
291 /* Account the idle time */
292 delta
= ktime_sub(now
, ts
->idle_entrytime
);
293 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
296 * We stopped the tick in idle. Update process times would miss the
297 * time we slept as update_process_times does only a 1 tick
298 * accounting. Enforce that this is accounted to idle !
300 ticks
= jiffies
- ts
->idle_jiffies
;
302 * We might be one off. Do not randomly account a huge number of ticks!
304 if (ticks
&& ticks
< LONG_MAX
) {
305 add_preempt_count(HARDIRQ_OFFSET
);
306 account_system_time(current
, HARDIRQ_OFFSET
,
307 jiffies_to_cputime(ticks
));
308 sub_preempt_count(HARDIRQ_OFFSET
);
312 * Cancel the scheduled timer and restore the tick
314 ts
->tick_stopped
= 0;
315 hrtimer_cancel(&ts
->sched_timer
);
316 ts
->sched_timer
.expires
= ts
->idle_tick
;
319 /* Forward the time to expire in the future */
320 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
322 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
323 hrtimer_start(&ts
->sched_timer
,
324 ts
->sched_timer
.expires
,
326 /* Check, if the timer was already in the past */
327 if (hrtimer_active(&ts
->sched_timer
))
330 if (!tick_program_event(ts
->sched_timer
.expires
, 0))
333 /* Update jiffies and reread time */
334 tick_do_update_jiffies64(now
);
340 static int tick_nohz_reprogram(struct tick_sched
*ts
, ktime_t now
)
342 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
343 return tick_program_event(ts
->sched_timer
.expires
, 0);
347 * The nohz low res interrupt handler
349 static void tick_nohz_handler(struct clock_event_device
*dev
)
351 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
352 struct pt_regs
*regs
= get_irq_regs();
353 int cpu
= smp_processor_id();
354 ktime_t now
= ktime_get();
356 dev
->next_event
.tv64
= KTIME_MAX
;
359 * Check if the do_timer duty was dropped. We don't care about
360 * concurrency: This happens only when the cpu in charge went
361 * into a long sleep. If two cpus happen to assign themself to
362 * this duty, then the jiffies update is still serialized by
365 if (unlikely(tick_do_timer_cpu
== -1))
366 tick_do_timer_cpu
= cpu
;
368 /* Check, if the jiffies need an update */
369 if (tick_do_timer_cpu
== cpu
)
370 tick_do_update_jiffies64(now
);
373 * When we are idle and the tick is stopped, we have to touch
374 * the watchdog as we might not schedule for a really long
375 * time. This happens on complete idle SMP systems while
376 * waiting on the login prompt. We also increment the "start
377 * of idle" jiffy stamp so the idle accounting adjustment we
378 * do when we go busy again does not account too much ticks.
380 if (ts
->tick_stopped
) {
381 touch_softlockup_watchdog();
385 update_process_times(user_mode(regs
));
386 profile_tick(CPU_PROFILING
);
388 /* Do not restart, when we are in the idle loop */
389 if (ts
->tick_stopped
)
392 while (tick_nohz_reprogram(ts
, now
)) {
394 tick_do_update_jiffies64(now
);
399 * tick_nohz_switch_to_nohz - switch to nohz mode
401 static void tick_nohz_switch_to_nohz(void)
403 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
406 if (!tick_nohz_enabled
)
410 if (tick_switch_to_oneshot(tick_nohz_handler
)) {
415 ts
->nohz_mode
= NOHZ_MODE_LOWRES
;
418 * Recycle the hrtimer in ts, so we can share the
419 * hrtimer_forward with the highres code.
421 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
422 /* Get the next period */
423 next
= tick_init_jiffy_update();
426 ts
->sched_timer
.expires
= next
;
427 if (!tick_program_event(next
, 0))
429 next
= ktime_add(next
, tick_period
);
433 printk(KERN_INFO
"Switched to NOHz mode on CPU #%d\n",
439 static inline void tick_nohz_switch_to_nohz(void) { }
444 * High resolution timer specific code
446 #ifdef CONFIG_HIGH_RES_TIMERS
448 * We rearm the timer until we get disabled by the idle code
449 * Called with interrupts disabled and timer->base->cpu_base->lock held.
451 static enum hrtimer_restart
tick_sched_timer(struct hrtimer
*timer
)
453 struct tick_sched
*ts
=
454 container_of(timer
, struct tick_sched
, sched_timer
);
455 struct hrtimer_cpu_base
*base
= timer
->base
->cpu_base
;
456 struct pt_regs
*regs
= get_irq_regs();
457 ktime_t now
= ktime_get();
458 int cpu
= smp_processor_id();
462 * Check if the do_timer duty was dropped. We don't care about
463 * concurrency: This happens only when the cpu in charge went
464 * into a long sleep. If two cpus happen to assign themself to
465 * this duty, then the jiffies update is still serialized by
468 if (unlikely(tick_do_timer_cpu
== -1))
469 tick_do_timer_cpu
= cpu
;
472 /* Check, if the jiffies need an update */
473 if (tick_do_timer_cpu
== cpu
)
474 tick_do_update_jiffies64(now
);
477 * Do not call, when we are not in irq context and have
478 * no valid regs pointer
482 * When we are idle and the tick is stopped, we have to touch
483 * the watchdog as we might not schedule for a really long
484 * time. This happens on complete idle SMP systems while
485 * waiting on the login prompt. We also increment the "start of
486 * idle" jiffy stamp so the idle accounting adjustment we do
487 * when we go busy again does not account too much ticks.
489 if (ts
->tick_stopped
) {
490 touch_softlockup_watchdog();
494 * update_process_times() might take tasklist_lock, hence
495 * drop the base lock. sched-tick hrtimers are per-CPU and
496 * never accessible by userspace APIs, so this is safe to do.
498 spin_unlock(&base
->lock
);
499 update_process_times(user_mode(regs
));
500 profile_tick(CPU_PROFILING
);
501 spin_lock(&base
->lock
);
504 /* Do not restart, when we are in the idle loop */
505 if (ts
->tick_stopped
)
506 return HRTIMER_NORESTART
;
508 hrtimer_forward(timer
, now
, tick_period
);
510 return HRTIMER_RESTART
;
514 * tick_setup_sched_timer - setup the tick emulation timer
516 void tick_setup_sched_timer(void)
518 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
519 ktime_t now
= ktime_get();
522 * Emulate tick processing via per-CPU hrtimers:
524 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
525 ts
->sched_timer
.function
= tick_sched_timer
;
526 ts
->sched_timer
.cb_mode
= HRTIMER_CB_IRQSAFE_NO_SOFTIRQ
;
528 /* Get the next period */
529 ts
->sched_timer
.expires
= tick_init_jiffy_update();
532 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
533 hrtimer_start(&ts
->sched_timer
, ts
->sched_timer
.expires
,
535 /* Check, if the timer was already in the past */
536 if (hrtimer_active(&ts
->sched_timer
))
542 if (tick_nohz_enabled
)
543 ts
->nohz_mode
= NOHZ_MODE_HIGHRES
;
547 void tick_cancel_sched_timer(int cpu
)
549 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
551 if (ts
->sched_timer
.base
)
552 hrtimer_cancel(&ts
->sched_timer
);
553 ts
->tick_stopped
= 0;
554 ts
->nohz_mode
= NOHZ_MODE_INACTIVE
;
556 #endif /* HIGH_RES_TIMERS */
559 * Async notification about clocksource changes
561 void tick_clock_notify(void)
565 for_each_possible_cpu(cpu
)
566 set_bit(0, &per_cpu(tick_cpu_sched
, cpu
).check_clocks
);
570 * Async notification about clock event changes
572 void tick_oneshot_notify(void)
574 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
576 set_bit(0, &ts
->check_clocks
);
580 * Check, if a change happened, which makes oneshot possible.
582 * Called cyclic from the hrtimer softirq (driven by the timer
583 * softirq) allow_nohz signals, that we can switch into low-res nohz
584 * mode, because high resolution timers are disabled (either compile
587 int tick_check_oneshot_change(int allow_nohz
)
589 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
591 if (!test_and_clear_bit(0, &ts
->check_clocks
))
594 if (ts
->nohz_mode
!= NOHZ_MODE_INACTIVE
)
597 if (!timekeeping_is_continuous() || !tick_is_oneshot_available())
603 tick_nohz_switch_to_nohz();