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 "tick-internal.h"
27 * Per cpu nohz control structure
29 static DEFINE_PER_CPU(struct tick_sched
, tick_cpu_sched
);
32 * The time, when the last jiffy update happened. Protected by xtime_lock.
34 static ktime_t last_jiffies_update
;
36 struct tick_sched
*tick_get_tick_sched(int cpu
)
38 return &per_cpu(tick_cpu_sched
, cpu
);
42 * Must be called with interrupts disabled !
44 static void tick_do_update_jiffies64(ktime_t now
)
46 unsigned long ticks
= 0;
49 /* Reevalute with xtime_lock held */
50 write_seqlock(&xtime_lock
);
52 delta
= ktime_sub(now
, last_jiffies_update
);
53 if (delta
.tv64
>= tick_period
.tv64
) {
55 delta
= ktime_sub(delta
, tick_period
);
56 last_jiffies_update
= ktime_add(last_jiffies_update
,
59 /* Slow path for long timeouts */
60 if (unlikely(delta
.tv64
>= tick_period
.tv64
)) {
61 s64 incr
= ktime_to_ns(tick_period
);
63 ticks
= ktime_divns(delta
, incr
);
65 last_jiffies_update
= ktime_add_ns(last_jiffies_update
,
70 write_sequnlock(&xtime_lock
);
74 * Initialize and return retrieve the jiffies update.
76 static ktime_t
tick_init_jiffy_update(void)
80 write_seqlock(&xtime_lock
);
81 /* Did we start the jiffies update yet ? */
82 if (last_jiffies_update
.tv64
== 0)
83 last_jiffies_update
= tick_next_period
;
84 period
= last_jiffies_update
;
85 write_sequnlock(&xtime_lock
);
90 * NOHZ - aka dynamic tick functionality
96 static int tick_nohz_enabled __read_mostly
= 1;
99 * Enable / Disable tickless mode
101 static int __init
setup_tick_nohz(char *str
)
103 if (!strcmp(str
, "off"))
104 tick_nohz_enabled
= 0;
105 else if (!strcmp(str
, "on"))
106 tick_nohz_enabled
= 1;
112 __setup("nohz=", setup_tick_nohz
);
115 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
117 * Called from interrupt entry when the CPU was idle
119 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
120 * must be updated. Otherwise an interrupt handler could use a stale jiffy
121 * value. We do this unconditionally on any cpu, as we don't know whether the
122 * cpu, which has the update task assigned is in a long sleep.
124 void tick_nohz_update_jiffies(void)
126 int cpu
= smp_processor_id();
127 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
131 if (!ts
->tick_stopped
)
134 cpu_clear(cpu
, nohz_cpu_mask
);
137 local_irq_save(flags
);
138 tick_do_update_jiffies64(now
);
139 local_irq_restore(flags
);
143 * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
145 * When the next event is more than a tick into the future, stop the idle tick
146 * Called either from the idle loop or from irq_exit() when an idle period was
147 * just interrupted by an interrupt which did not cause a reschedule.
149 void tick_nohz_stop_sched_tick(void)
151 unsigned long seq
, last_jiffies
, next_jiffies
, delta_jiffies
, flags
;
152 struct tick_sched
*ts
;
153 ktime_t last_update
, expires
, now
, delta
;
156 local_irq_save(flags
);
158 cpu
= smp_processor_id();
159 ts
= &per_cpu(tick_cpu_sched
, cpu
);
161 if (unlikely(ts
->nohz_mode
== NOHZ_MODE_INACTIVE
))
167 cpu
= smp_processor_id();
168 if (unlikely(local_softirq_pending()))
169 printk(KERN_ERR
"NOHZ: local_softirq_pending %02x\n",
170 local_softirq_pending());
174 * When called from irq_exit we need to account the idle sleep time
177 if (ts
->tick_stopped
) {
178 delta
= ktime_sub(now
, ts
->idle_entrytime
);
179 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
182 ts
->idle_entrytime
= now
;
185 /* Read jiffies and the time when jiffies were updated last */
187 seq
= read_seqbegin(&xtime_lock
);
188 last_update
= last_jiffies_update
;
189 last_jiffies
= jiffies
;
190 } while (read_seqretry(&xtime_lock
, seq
));
192 /* Get the next timer wheel timer */
193 next_jiffies
= get_next_timer_interrupt(last_jiffies
);
194 delta_jiffies
= next_jiffies
- last_jiffies
;
196 if (rcu_needs_cpu(cpu
))
199 * Do not stop the tick, if we are only one off
200 * or if the cpu is required for rcu
202 if (!ts
->tick_stopped
&& delta_jiffies
== 1)
205 /* Schedule the tick, if we are at least one jiffie off */
206 if ((long)delta_jiffies
>= 1) {
208 if (delta_jiffies
> 1)
209 cpu_set(cpu
, nohz_cpu_mask
);
211 * nohz_stop_sched_tick can be called several times before
212 * the nohz_restart_sched_tick is called. This happens when
213 * interrupts arrive which do not cause a reschedule. In the
214 * first call we save the current tick time, so we can restart
215 * the scheduler tick in nohz_restart_sched_tick.
217 if (!ts
->tick_stopped
) {
218 ts
->idle_tick
= ts
->sched_timer
.expires
;
219 ts
->tick_stopped
= 1;
220 ts
->idle_jiffies
= last_jiffies
;
223 * calculate the expiry time for the next timer wheel
226 expires
= ktime_add_ns(last_update
, tick_period
.tv64
*
228 ts
->idle_expires
= expires
;
231 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
232 hrtimer_start(&ts
->sched_timer
, expires
,
234 /* Check, if the timer was already in the past */
235 if (hrtimer_active(&ts
->sched_timer
))
237 } else if(!tick_program_event(expires
, 0))
240 * We are past the event already. So we crossed a
241 * jiffie boundary. Update jiffies and raise the
244 tick_do_update_jiffies64(ktime_get());
245 cpu_clear(cpu
, nohz_cpu_mask
);
247 raise_softirq_irqoff(TIMER_SOFTIRQ
);
249 ts
->next_jiffies
= next_jiffies
;
250 ts
->last_jiffies
= last_jiffies
;
252 local_irq_restore(flags
);
256 * nohz_restart_sched_tick - restart the idle tick from the idle task
258 * Restart the idle tick when the CPU is woken up from idle
260 void tick_nohz_restart_sched_tick(void)
262 int cpu
= smp_processor_id();
263 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
267 if (!ts
->tick_stopped
)
270 /* Update jiffies first */
274 tick_do_update_jiffies64(now
);
275 cpu_clear(cpu
, nohz_cpu_mask
);
277 /* Account the idle time */
278 delta
= ktime_sub(now
, ts
->idle_entrytime
);
279 ts
->idle_sleeptime
= ktime_add(ts
->idle_sleeptime
, delta
);
282 * We stopped the tick in idle. Update process times would miss the
283 * time we slept as update_process_times does only a 1 tick
284 * accounting. Enforce that this is accounted to idle !
286 ticks
= jiffies
- ts
->idle_jiffies
;
288 * We might be one off. Do not randomly account a huge number of ticks!
290 if (ticks
&& ticks
< LONG_MAX
) {
291 add_preempt_count(HARDIRQ_OFFSET
);
292 account_system_time(current
, HARDIRQ_OFFSET
,
293 jiffies_to_cputime(ticks
));
294 sub_preempt_count(HARDIRQ_OFFSET
);
298 * Cancel the scheduled timer and restore the tick
300 ts
->tick_stopped
= 0;
301 hrtimer_cancel(&ts
->sched_timer
);
302 ts
->sched_timer
.expires
= ts
->idle_tick
;
305 /* Forward the time to expire in the future */
306 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
308 if (ts
->nohz_mode
== NOHZ_MODE_HIGHRES
) {
309 hrtimer_start(&ts
->sched_timer
,
310 ts
->sched_timer
.expires
,
312 /* Check, if the timer was already in the past */
313 if (hrtimer_active(&ts
->sched_timer
))
316 if (!tick_program_event(ts
->sched_timer
.expires
, 0))
319 /* Update jiffies and reread time */
320 tick_do_update_jiffies64(now
);
326 static int tick_nohz_reprogram(struct tick_sched
*ts
, ktime_t now
)
328 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
329 return tick_program_event(ts
->sched_timer
.expires
, 0);
333 * The nohz low res interrupt handler
335 static void tick_nohz_handler(struct clock_event_device
*dev
)
337 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
338 struct pt_regs
*regs
= get_irq_regs();
339 ktime_t now
= ktime_get();
341 dev
->next_event
.tv64
= KTIME_MAX
;
343 /* Check, if the jiffies need an update */
344 tick_do_update_jiffies64(now
);
347 * When we are idle and the tick is stopped, we have to touch
348 * the watchdog as we might not schedule for a really long
349 * time. This happens on complete idle SMP systems while
350 * waiting on the login prompt. We also increment the "start
351 * of idle" jiffy stamp so the idle accounting adjustment we
352 * do when we go busy again does not account too much ticks.
354 if (ts
->tick_stopped
) {
355 touch_softlockup_watchdog();
359 update_process_times(user_mode(regs
));
360 profile_tick(CPU_PROFILING
);
362 /* Do not restart, when we are in the idle loop */
363 if (ts
->tick_stopped
)
366 while (tick_nohz_reprogram(ts
, now
)) {
368 tick_do_update_jiffies64(now
);
373 * tick_nohz_switch_to_nohz - switch to nohz mode
375 static void tick_nohz_switch_to_nohz(void)
377 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
380 if (!tick_nohz_enabled
)
384 if (tick_switch_to_oneshot(tick_nohz_handler
)) {
389 ts
->nohz_mode
= NOHZ_MODE_LOWRES
;
392 * Recycle the hrtimer in ts, so we can share the
393 * hrtimer_forward with the highres code.
395 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
396 /* Get the next period */
397 next
= tick_init_jiffy_update();
400 ts
->sched_timer
.expires
= next
;
401 if (!tick_program_event(next
, 0))
403 next
= ktime_add(next
, tick_period
);
407 printk(KERN_INFO
"Switched to NOHz mode on CPU #%d\n",
413 static inline void tick_nohz_switch_to_nohz(void) { }
418 * High resolution timer specific code
420 #ifdef CONFIG_HIGH_RES_TIMERS
422 * We rearm the timer until we get disabled by the idle code
423 * Called with interrupts disabled and timer->base->cpu_base->lock held.
425 static enum hrtimer_restart
tick_sched_timer(struct hrtimer
*timer
)
427 struct tick_sched
*ts
=
428 container_of(timer
, struct tick_sched
, sched_timer
);
429 struct hrtimer_cpu_base
*base
= timer
->base
->cpu_base
;
430 struct pt_regs
*regs
= get_irq_regs();
431 ktime_t now
= ktime_get();
433 /* Check, if the jiffies need an update */
434 tick_do_update_jiffies64(now
);
437 * Do not call, when we are not in irq context and have
438 * no valid regs pointer
442 * When we are idle and the tick is stopped, we have to touch
443 * the watchdog as we might not schedule for a really long
444 * time. This happens on complete idle SMP systems while
445 * waiting on the login prompt. We also increment the "start of
446 * idle" jiffy stamp so the idle accounting adjustment we do
447 * when we go busy again does not account too much ticks.
449 if (ts
->tick_stopped
) {
450 touch_softlockup_watchdog();
454 * update_process_times() might take tasklist_lock, hence
455 * drop the base lock. sched-tick hrtimers are per-CPU and
456 * never accessible by userspace APIs, so this is safe to do.
458 spin_unlock(&base
->lock
);
459 update_process_times(user_mode(regs
));
460 profile_tick(CPU_PROFILING
);
461 spin_lock(&base
->lock
);
464 /* Do not restart, when we are in the idle loop */
465 if (ts
->tick_stopped
)
466 return HRTIMER_NORESTART
;
468 hrtimer_forward(timer
, now
, tick_period
);
470 return HRTIMER_RESTART
;
474 * tick_setup_sched_timer - setup the tick emulation timer
476 void tick_setup_sched_timer(void)
478 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
479 ktime_t now
= ktime_get();
482 * Emulate tick processing via per-CPU hrtimers:
484 hrtimer_init(&ts
->sched_timer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
485 ts
->sched_timer
.function
= tick_sched_timer
;
486 ts
->sched_timer
.cb_mode
= HRTIMER_CB_IRQSAFE_NO_SOFTIRQ
;
488 /* Get the next period */
489 ts
->sched_timer
.expires
= tick_init_jiffy_update();
492 hrtimer_forward(&ts
->sched_timer
, now
, tick_period
);
493 hrtimer_start(&ts
->sched_timer
, ts
->sched_timer
.expires
,
495 /* Check, if the timer was already in the past */
496 if (hrtimer_active(&ts
->sched_timer
))
502 if (tick_nohz_enabled
)
503 ts
->nohz_mode
= NOHZ_MODE_HIGHRES
;
507 void tick_cancel_sched_timer(int cpu
)
509 struct tick_sched
*ts
= &per_cpu(tick_cpu_sched
, cpu
);
511 if (ts
->sched_timer
.base
)
512 hrtimer_cancel(&ts
->sched_timer
);
513 ts
->tick_stopped
= 0;
514 ts
->nohz_mode
= NOHZ_MODE_INACTIVE
;
516 #endif /* HIGH_RES_TIMERS */
519 * Async notification about clocksource changes
521 void tick_clock_notify(void)
525 for_each_possible_cpu(cpu
)
526 set_bit(0, &per_cpu(tick_cpu_sched
, cpu
).check_clocks
);
530 * Async notification about clock event changes
532 void tick_oneshot_notify(void)
534 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
536 set_bit(0, &ts
->check_clocks
);
540 * Check, if a change happened, which makes oneshot possible.
542 * Called cyclic from the hrtimer softirq (driven by the timer
543 * softirq) allow_nohz signals, that we can switch into low-res nohz
544 * mode, because high resolution timers are disabled (either compile
547 int tick_check_oneshot_change(int allow_nohz
)
549 struct tick_sched
*ts
= &__get_cpu_var(tick_cpu_sched
);
551 if (!test_and_clear_bit(0, &ts
->check_clocks
))
554 if (ts
->nohz_mode
!= NOHZ_MODE_INACTIVE
)
557 if (!timekeeping_is_continuous() || !tick_is_oneshot_available())
563 tick_nohz_switch_to_nohz();