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/module.h>
 
 
 
 
 23
 24#include <asm/irq_regs.h>
 25
 26#include "tick-internal.h"
 27
 28/*
 29 * Per cpu nohz control structure
 30 */
 31static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 32
 33/*
 34 * The time, when the last jiffy update happened. Protected by xtime_lock.
 35 */
 36static ktime_t last_jiffies_update;
 37
 38struct tick_sched *tick_get_tick_sched(int cpu)
 39{
 40	return &per_cpu(tick_cpu_sched, cpu);
 41}
 42
 
 
 
 
 
 
 43/*
 44 * Must be called with interrupts disabled !
 45 */
 46static void tick_do_update_jiffies64(ktime_t now)
 47{
 48	unsigned long ticks = 0;
 49	ktime_t delta;
 50
 51	/*
 52	 * Do a quick check without holding xtime_lock:
 
 53	 */
 54	delta = ktime_sub(now, last_jiffies_update);
 55	if (delta.tv64 < tick_period.tv64)
 56		return;
 57
 58	/* Reevalute with xtime_lock held */
 59	write_seqlock(&xtime_lock);
 
 60
 61	delta = ktime_sub(now, last_jiffies_update);
 62	if (delta.tv64 >= tick_period.tv64) {
 63
 64		delta = ktime_sub(delta, tick_period);
 65		last_jiffies_update = ktime_add(last_jiffies_update,
 66						tick_period);
 
 67
 68		/* Slow path for long timeouts */
 69		if (unlikely(delta.tv64 >= tick_period.tv64)) {
 70			s64 incr = ktime_to_ns(tick_period);
 71
 72			ticks = ktime_divns(delta, incr);
 73
 74			last_jiffies_update = ktime_add_ns(last_jiffies_update,
 75							   incr * ticks);
 
 
 76		}
 77		do_timer(++ticks);
 78
 79		/* Keep the tick_next_period variable up to date */
 80		tick_next_period = ktime_add(last_jiffies_update, tick_period);
 
 
 
 
 81	}
 82	write_sequnlock(&xtime_lock);
 
 
 83}
 84
 85/*
 86 * Initialize and return retrieve the jiffies update.
 87 */
 88static ktime_t tick_init_jiffy_update(void)
 89{
 90	ktime_t period;
 91
 92	write_seqlock(&xtime_lock);
 
 93	/* Did we start the jiffies update yet ? */
 94	if (last_jiffies_update.tv64 == 0)
 95		last_jiffies_update = tick_next_period;
 96	period = last_jiffies_update;
 97	write_sequnlock(&xtime_lock);
 
 98	return period;
 99}
100
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
101/*
102 * NOHZ - aka dynamic tick functionality
103 */
104#ifdef CONFIG_NO_HZ
105/*
106 * NO HZ enabled ?
107 */
108static int tick_nohz_enabled __read_mostly  = 1;
109
110/*
111 * Enable / Disable tickless mode
112 */
113static int __init setup_tick_nohz(char *str)
114{
115	if (!strcmp(str, "off"))
116		tick_nohz_enabled = 0;
117	else if (!strcmp(str, "on"))
118		tick_nohz_enabled = 1;
119	else
120		return 0;
121	return 1;
122}
123
124__setup("nohz=", setup_tick_nohz);
125
 
 
 
 
 
 
 
 
 
 
 
 
 
 
126/**
127 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
128 *
129 * Called from interrupt entry when the CPU was idle
130 *
131 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
132 * must be updated. Otherwise an interrupt handler could use a stale jiffy
133 * value. We do this unconditionally on any cpu, as we don't know whether the
134 * cpu, which has the update task assigned is in a long sleep.
135 */
136static void tick_nohz_update_jiffies(ktime_t now)
137{
138	int cpu = smp_processor_id();
139	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
140	unsigned long flags;
141
142	ts->idle_waketime = now;
143
144	local_irq_save(flags);
145	tick_do_update_jiffies64(now);
146	local_irq_restore(flags);
147
148	calc_load_exit_idle();
149	touch_softlockup_watchdog();
150}
151
152/*
153 * Updates the per cpu time idle statistics counters
154 */
155static void
156update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
157{
158	ktime_t delta;
159
160	if (ts->idle_active) {
161		delta = ktime_sub(now, ts->idle_entrytime);
162		if (nr_iowait_cpu(cpu) > 0)
163			ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
164		else
165			ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
166		ts->idle_entrytime = now;
167	}
168
169	if (last_update_time)
170		*last_update_time = ktime_to_us(now);
171
172}
173
174static void tick_nohz_stop_idle(int cpu, ktime_t now)
175{
176	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
177
178	update_ts_time_stats(cpu, ts, now, NULL);
179	ts->idle_active = 0;
180
181	sched_clock_idle_wakeup_event(0);
182}
183
184static ktime_t tick_nohz_start_idle(int cpu, struct tick_sched *ts)
185{
186	ktime_t now = ktime_get();
187
188	ts->idle_entrytime = now;
189	ts->idle_active = 1;
190	sched_clock_idle_sleep_event();
191	return now;
192}
193
194/**
195 * get_cpu_idle_time_us - get the total idle time of a cpu
196 * @cpu: CPU number to query
197 * @last_update_time: variable to store update time in. Do not update
198 * counters if NULL.
199 *
200 * Return the cummulative idle time (since boot) for a given
201 * CPU, in microseconds.
202 *
203 * This time is measured via accounting rather than sampling,
204 * and is as accurate as ktime_get() is.
205 *
206 * This function returns -1 if NOHZ is not enabled.
207 */
208u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
209{
210	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
211	ktime_t now, idle;
212
213	if (!tick_nohz_enabled)
214		return -1;
215
216	now = ktime_get();
217	if (last_update_time) {
218		update_ts_time_stats(cpu, ts, now, last_update_time);
219		idle = ts->idle_sleeptime;
220	} else {
221		if (ts->idle_active && !nr_iowait_cpu(cpu)) {
222			ktime_t delta = ktime_sub(now, ts->idle_entrytime);
223
224			idle = ktime_add(ts->idle_sleeptime, delta);
225		} else {
226			idle = ts->idle_sleeptime;
227		}
228	}
229
230	return ktime_to_us(idle);
231
232}
233EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
234
235/**
236 * get_cpu_iowait_time_us - get the total iowait time of a cpu
237 * @cpu: CPU number to query
238 * @last_update_time: variable to store update time in. Do not update
239 * counters if NULL.
240 *
241 * Return the cummulative iowait time (since boot) for a given
242 * CPU, in microseconds.
243 *
244 * This time is measured via accounting rather than sampling,
245 * and is as accurate as ktime_get() is.
246 *
247 * This function returns -1 if NOHZ is not enabled.
248 */
249u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
250{
251	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
252	ktime_t now, iowait;
253
254	if (!tick_nohz_enabled)
255		return -1;
256
257	now = ktime_get();
258	if (last_update_time) {
259		update_ts_time_stats(cpu, ts, now, last_update_time);
260		iowait = ts->iowait_sleeptime;
261	} else {
262		if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
263			ktime_t delta = ktime_sub(now, ts->idle_entrytime);
264
265			iowait = ktime_add(ts->iowait_sleeptime, delta);
266		} else {
267			iowait = ts->iowait_sleeptime;
268		}
269	}
270
271	return ktime_to_us(iowait);
272}
273EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
274
275static void tick_nohz_stop_sched_tick(struct tick_sched *ts)
276{
277	unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
278	unsigned long rcu_delta_jiffies;
279	ktime_t last_update, expires, now;
280	struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
281	u64 time_delta;
282	int cpu;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
283
284	cpu = smp_processor_id();
285	ts = &per_cpu(tick_cpu_sched, cpu);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
286
287	now = tick_nohz_start_idle(cpu, ts);
 
 
 
288
289	/*
290	 * If this cpu is offline and it is the one which updates
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
291	 * jiffies, then give up the assignment and let it be taken by
292	 * the cpu which runs the tick timer next. If we don't drop
293	 * this here the jiffies might be stale and do_timer() never
294	 * invoked.
295	 */
296	if (unlikely(!cpu_online(cpu))) {
297		if (cpu == tick_do_timer_cpu)
298			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
 
 
 
 
 
 
299	}
300
301	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
302		return;
303
304	if (need_resched())
305		return;
306
307	if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
308		static int ratelimit;
309
310		if (ratelimit < 10) {
311			printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
312			       (unsigned int) local_softirq_pending());
 
313			ratelimit++;
314		}
315		return;
316	}
317
318	ts->idle_calls++;
319	/* Read jiffies and the time when jiffies were updated last */
320	do {
321		seq = read_seqbegin(&xtime_lock);
322		last_update = last_jiffies_update;
323		last_jiffies = jiffies;
324		time_delta = timekeeping_max_deferment();
325	} while (read_seqretry(&xtime_lock, seq));
326
327	if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || printk_needs_cpu(cpu) ||
328	    arch_needs_cpu(cpu)) {
329		next_jiffies = last_jiffies + 1;
330		delta_jiffies = 1;
331	} else {
332		/* Get the next timer wheel timer */
333		next_jiffies = get_next_timer_interrupt(last_jiffies);
334		delta_jiffies = next_jiffies - last_jiffies;
335		if (rcu_delta_jiffies < delta_jiffies) {
336			next_jiffies = last_jiffies + rcu_delta_jiffies;
337			delta_jiffies = rcu_delta_jiffies;
338		}
339	}
340	/*
341	 * Do not stop the tick, if we are only one off
342	 * or if the cpu is required for rcu
343	 */
344	if (!ts->tick_stopped && delta_jiffies == 1)
345		goto out;
346
347	/* Schedule the tick, if we are at least one jiffie off */
348	if ((long)delta_jiffies >= 1) {
349
350		/*
351		 * If this cpu is the one which updates jiffies, then
352		 * give up the assignment and let it be taken by the
353		 * cpu which runs the tick timer next, which might be
354		 * this cpu as well. If we don't drop this here the
355		 * jiffies might be stale and do_timer() never
356		 * invoked. Keep track of the fact that it was the one
357		 * which had the do_timer() duty last. If this cpu is
358		 * the one which had the do_timer() duty last, we
359		 * limit the sleep time to the timekeeping
360		 * max_deferement value which we retrieved
361		 * above. Otherwise we can sleep as long as we want.
362		 */
363		if (cpu == tick_do_timer_cpu) {
364			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
365			ts->do_timer_last = 1;
366		} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
367			time_delta = KTIME_MAX;
368			ts->do_timer_last = 0;
369		} else if (!ts->do_timer_last) {
370			time_delta = KTIME_MAX;
371		}
372
373		/*
374		 * calculate the expiry time for the next timer wheel
375		 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
376		 * that there is no timer pending or at least extremely
377		 * far into the future (12 days for HZ=1000). In this
378		 * case we set the expiry to the end of time.
379		 */
380		if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
381			/*
382			 * Calculate the time delta for the next timer event.
383			 * If the time delta exceeds the maximum time delta
384			 * permitted by the current clocksource then adjust
385			 * the time delta accordingly to ensure the
386			 * clocksource does not wrap.
387			 */
388			time_delta = min_t(u64, time_delta,
389					   tick_period.tv64 * delta_jiffies);
390		}
391
392		if (time_delta < KTIME_MAX)
393			expires = ktime_add_ns(last_update, time_delta);
394		else
395			expires.tv64 = KTIME_MAX;
396
397		/* Skip reprogram of event if its not changed */
398		if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
399			goto out;
400
401		/*
402		 * nohz_stop_sched_tick can be called several times before
403		 * the nohz_restart_sched_tick is called. This happens when
404		 * interrupts arrive which do not cause a reschedule. In the
405		 * first call we save the current tick time, so we can restart
406		 * the scheduler tick in nohz_restart_sched_tick.
407		 */
408		if (!ts->tick_stopped) {
409			select_nohz_load_balancer(1);
410			calc_load_enter_idle();
411
412			ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
413			ts->tick_stopped = 1;
414			ts->idle_jiffies = last_jiffies;
415		}
 
 
 
 
 
 
416
417		ts->idle_sleeps++;
418
419		/* Mark expires */
 
 
 
 
 
420		ts->idle_expires = expires;
421
422		/*
423		 * If the expiration time == KTIME_MAX, then
424		 * in this case we simply stop the tick timer.
425		 */
426		 if (unlikely(expires.tv64 == KTIME_MAX)) {
427			if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
428				hrtimer_cancel(&ts->sched_timer);
429			goto out;
430		}
431
432		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
433			hrtimer_start(&ts->sched_timer, expires,
434				      HRTIMER_MODE_ABS_PINNED);
435			/* Check, if the timer was already in the past */
436			if (hrtimer_active(&ts->sched_timer))
437				goto out;
438		} else if (!tick_program_event(expires, 0))
439				goto out;
440		/*
441		 * We are past the event already. So we crossed a
442		 * jiffie boundary. Update jiffies and raise the
443		 * softirq.
444		 */
445		tick_do_update_jiffies64(ktime_get());
446	}
447	raise_softirq_irqoff(TIMER_SOFTIRQ);
448out:
449	ts->next_jiffies = next_jiffies;
450	ts->last_jiffies = last_jiffies;
451	ts->sleep_length = ktime_sub(dev->next_event, now);
452}
453
454/**
455 * tick_nohz_idle_enter - stop the idle tick from the idle task
456 *
457 * When the next event is more than a tick into the future, stop the idle tick
458 * Called when we start the idle loop.
459 *
460 * The arch is responsible of calling:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
461 *
462 * - rcu_idle_enter() after its last use of RCU before the CPU is put
463 *  to sleep.
464 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
465 */
466void tick_nohz_idle_enter(void)
467{
468	struct tick_sched *ts;
469
470	WARN_ON_ONCE(irqs_disabled());
471
472	/*
473 	 * Update the idle state in the scheduler domain hierarchy
474 	 * when tick_nohz_stop_sched_tick() is called from the idle loop.
475 	 * State will be updated to busy during the first busy tick after
476 	 * exiting idle.
477 	 */
478	set_cpu_sd_state_idle();
479
480	local_irq_disable();
481
482	ts = &__get_cpu_var(tick_cpu_sched);
483	/*
484	 * set ts->inidle unconditionally. even if the system did not
485	 * switch to nohz mode the cpu frequency governers rely on the
486	 * update of the idle time accounting in tick_nohz_start_idle().
487	 */
488	ts->inidle = 1;
489	tick_nohz_stop_sched_tick(ts);
490
491	local_irq_enable();
492}
493
494/**
495 * tick_nohz_irq_exit - update next tick event from interrupt exit
496 *
497 * When an interrupt fires while we are idle and it doesn't cause
498 * a reschedule, it may still add, modify or delete a timer, enqueue
499 * an RCU callback, etc...
500 * So we need to re-calculate and reprogram the next tick event.
501 */
502void tick_nohz_irq_exit(void)
503{
504	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
505
506	if (!ts->inidle)
507		return;
508
509	tick_nohz_stop_sched_tick(ts);
 
 
 
510}
511
512/**
513 * tick_nohz_get_sleep_length - return the length of the current sleep
514 *
515 * Called from power state control code with interrupts disabled
516 */
517ktime_t tick_nohz_get_sleep_length(void)
518{
519	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
520
521	return ts->sleep_length;
 
 
 
 
522}
523
524static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
 
 
 
 
 
 
 
525{
526	hrtimer_cancel(&ts->sched_timer);
527	hrtimer_set_expires(&ts->sched_timer, ts->idle_tick);
528
529	while (1) {
530		/* Forward the time to expire in the future */
531		hrtimer_forward(&ts->sched_timer, now, tick_period);
532
533		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
534			hrtimer_start_expires(&ts->sched_timer,
535					      HRTIMER_MODE_ABS_PINNED);
536			/* Check, if the timer was already in the past */
537			if (hrtimer_active(&ts->sched_timer))
538				break;
539		} else {
540			if (!tick_program_event(
541				hrtimer_get_expires(&ts->sched_timer), 0))
542				break;
543		}
544		/* Reread time and update jiffies */
545		now = ktime_get();
546		tick_do_update_jiffies64(now);
547	}
548}
549
550/**
551 * tick_nohz_idle_exit - restart the idle tick from the idle task
 
552 *
553 * Restart the idle tick when the CPU is woken up from idle
554 * This also exit the RCU extended quiescent state. The CPU
555 * can use RCU again after this function is called.
556 */
557void tick_nohz_idle_exit(void)
558{
 
 
559	int cpu = smp_processor_id();
560	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
561#ifndef CONFIG_VIRT_CPU_ACCOUNTING
562	unsigned long ticks;
563#endif
564	ktime_t now;
565
566	local_irq_disable();
567
568	WARN_ON_ONCE(!ts->inidle);
569
570	ts->inidle = 0;
571
572	if (ts->idle_active || ts->tick_stopped)
573		now = ktime_get();
574
575	if (ts->idle_active)
576		tick_nohz_stop_idle(cpu, now);
 
577
578	if (!ts->tick_stopped) {
579		local_irq_enable();
580		return;
581	}
 
 
582
583	/* Update jiffies first */
584	select_nohz_load_balancer(0);
585	tick_do_update_jiffies64(now);
586	update_cpu_load_nohz();
 
 
 
 
 
 
 
 
 
 
 
587
588#ifndef CONFIG_VIRT_CPU_ACCOUNTING
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
589	/*
590	 * We stopped the tick in idle. Update process times would miss the
591	 * time we slept as update_process_times does only a 1 tick
592	 * accounting. Enforce that this is accounted to idle !
593	 */
594	ticks = jiffies - ts->idle_jiffies;
595	/*
596	 * We might be one off. Do not randomly account a huge number of ticks!
597	 */
598	if (ticks && ticks < LONG_MAX)
599		account_idle_ticks(ticks);
600#endif
 
601
602	calc_load_exit_idle();
603	touch_softlockup_watchdog();
604	/*
605	 * Cancel the scheduled timer and restore the tick
606	 */
607	ts->tick_stopped  = 0;
608	ts->idle_exittime = now;
609
610	tick_nohz_restart(ts, now);
 
 
611
612	local_irq_enable();
 
613}
614
615static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
 
 
 
 
 
 
 
616{
617	hrtimer_forward(&ts->sched_timer, now, tick_period);
618	return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
619}
620
621/*
622 * The nohz low res interrupt handler
623 */
624static void tick_nohz_handler(struct clock_event_device *dev)
625{
626	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
627	struct pt_regs *regs = get_irq_regs();
628	int cpu = smp_processor_id();
629	ktime_t now = ktime_get();
630
631	dev->next_event.tv64 = KTIME_MAX;
632
633	/*
634	 * Check if the do_timer duty was dropped. We don't care about
635	 * concurrency: This happens only when the cpu in charge went
636	 * into a long sleep. If two cpus happen to assign themself to
637	 * this duty, then the jiffies update is still serialized by
638	 * xtime_lock.
639	 */
640	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
641		tick_do_timer_cpu = cpu;
642
643	/* Check, if the jiffies need an update */
644	if (tick_do_timer_cpu == cpu)
645		tick_do_update_jiffies64(now);
646
647	/*
648	 * When we are idle and the tick is stopped, we have to touch
649	 * the watchdog as we might not schedule for a really long
650	 * time. This happens on complete idle SMP systems while
651	 * waiting on the login prompt. We also increment the "start
652	 * of idle" jiffy stamp so the idle accounting adjustment we
653	 * do when we go busy again does not account too much ticks.
654	 */
655	if (ts->tick_stopped) {
656		touch_softlockup_watchdog();
657		ts->idle_jiffies++;
658	}
659
660	update_process_times(user_mode(regs));
661	profile_tick(CPU_PROFILING);
 
662
663	while (tick_nohz_reprogram(ts, now)) {
664		now = ktime_get();
665		tick_do_update_jiffies64(now);
666	}
 
 
 
 
667}
668
669/**
670 * tick_nohz_switch_to_nohz - switch to nohz mode
671 */
672static void tick_nohz_switch_to_nohz(void)
673{
674	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
675	ktime_t next;
676
677	if (!tick_nohz_enabled)
678		return;
679
680	local_irq_disable();
681	if (tick_switch_to_oneshot(tick_nohz_handler)) {
682		local_irq_enable();
683		return;
684	}
685
686	ts->nohz_mode = NOHZ_MODE_LOWRES;
687
688	/*
689	 * Recycle the hrtimer in ts, so we can share the
690	 * hrtimer_forward with the highres code.
691	 */
692	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
693	/* Get the next period */
694	next = tick_init_jiffy_update();
695
696	for (;;) {
697		hrtimer_set_expires(&ts->sched_timer, next);
698		if (!tick_program_event(next, 0))
699			break;
700		next = ktime_add(next, tick_period);
701	}
702	local_irq_enable();
703}
704
705/*
706 * When NOHZ is enabled and the tick is stopped, we need to kick the
707 * tick timer from irq_enter() so that the jiffies update is kept
708 * alive during long running softirqs. That's ugly as hell, but
709 * correctness is key even if we need to fix the offending softirq in
710 * the first place.
711 *
712 * Note, this is different to tick_nohz_restart. We just kick the
713 * timer and do not touch the other magic bits which need to be done
714 * when idle is left.
715 */
716static void tick_nohz_kick_tick(int cpu, ktime_t now)
717{
718#if 0
719	/* Switch back to 2.6.27 behaviour */
720
721	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
722	ktime_t delta;
723
724	/*
725	 * Do not touch the tick device, when the next expiry is either
726	 * already reached or less/equal than the tick period.
727	 */
728	delta =	ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
729	if (delta.tv64 <= tick_period.tv64)
730		return;
731
732	tick_nohz_restart(ts, now);
733#endif
734}
735
736static inline void tick_check_nohz(int cpu)
737{
738	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
739	ktime_t now;
740
741	if (!ts->idle_active && !ts->tick_stopped)
742		return;
743	now = ktime_get();
744	if (ts->idle_active)
745		tick_nohz_stop_idle(cpu, now);
746	if (ts->tick_stopped) {
747		tick_nohz_update_jiffies(now);
748		tick_nohz_kick_tick(cpu, now);
749	}
750}
751
752#else
753
754static inline void tick_nohz_switch_to_nohz(void) { }
755static inline void tick_check_nohz(int cpu) { }
 
756
757#endif /* NO_HZ */
758
759/*
760 * Called from irq_enter to notify about the possible interruption of idle()
761 */
762void tick_check_idle(int cpu)
763{
764	tick_check_oneshot_broadcast(cpu);
765	tick_check_nohz(cpu);
766}
767
768/*
769 * High resolution timer specific code
770 */
771#ifdef CONFIG_HIGH_RES_TIMERS
772/*
773 * We rearm the timer until we get disabled by the idle code.
774 * Called with interrupts disabled and timer->base->cpu_base->lock held.
775 */
776static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
777{
778	struct tick_sched *ts =
779		container_of(timer, struct tick_sched, sched_timer);
780	struct pt_regs *regs = get_irq_regs();
781	ktime_t now = ktime_get();
782	int cpu = smp_processor_id();
783
784#ifdef CONFIG_NO_HZ
785	/*
786	 * Check if the do_timer duty was dropped. We don't care about
787	 * concurrency: This happens only when the cpu in charge went
788	 * into a long sleep. If two cpus happen to assign themself to
789	 * this duty, then the jiffies update is still serialized by
790	 * xtime_lock.
791	 */
792	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
793		tick_do_timer_cpu = cpu;
794#endif
795
796	/* Check, if the jiffies need an update */
797	if (tick_do_timer_cpu == cpu)
798		tick_do_update_jiffies64(now);
799
800	/*
801	 * Do not call, when we are not in irq context and have
802	 * no valid regs pointer
803	 */
804	if (regs) {
805		/*
806		 * When we are idle and the tick is stopped, we have to touch
807		 * the watchdog as we might not schedule for a really long
808		 * time. This happens on complete idle SMP systems while
809		 * waiting on the login prompt. We also increment the "start of
810		 * idle" jiffy stamp so the idle accounting adjustment we do
811		 * when we go busy again does not account too much ticks.
812		 */
813		if (ts->tick_stopped) {
814			touch_softlockup_watchdog();
815			ts->idle_jiffies++;
816		}
817		update_process_times(user_mode(regs));
818		profile_tick(CPU_PROFILING);
819	}
820
821	hrtimer_forward(timer, now, tick_period);
822
823	return HRTIMER_RESTART;
824}
825
826static int sched_skew_tick;
827
828static int __init skew_tick(char *str)
829{
830	get_option(&str, &sched_skew_tick);
831
832	return 0;
833}
834early_param("skew_tick", skew_tick);
835
836/**
837 * tick_setup_sched_timer - setup the tick emulation timer
838 */
839void tick_setup_sched_timer(void)
840{
841	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
842	ktime_t now = ktime_get();
843
844	/*
845	 * Emulate tick processing via per-CPU hrtimers:
846	 */
847	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
848	ts->sched_timer.function = tick_sched_timer;
849
850	/* Get the next period (per cpu) */
851	hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
852
853	/* Offset the tick to avert xtime_lock contention. */
854	if (sched_skew_tick) {
855		u64 offset = ktime_to_ns(tick_period) >> 1;
856		do_div(offset, num_possible_cpus());
857		offset *= smp_processor_id();
858		hrtimer_add_expires_ns(&ts->sched_timer, offset);
859	}
860
861	for (;;) {
862		hrtimer_forward(&ts->sched_timer, now, tick_period);
863		hrtimer_start_expires(&ts->sched_timer,
864				      HRTIMER_MODE_ABS_PINNED);
865		/* Check, if the timer was already in the past */
866		if (hrtimer_active(&ts->sched_timer))
867			break;
868		now = ktime_get();
869	}
870
871#ifdef CONFIG_NO_HZ
872	if (tick_nohz_enabled)
873		ts->nohz_mode = NOHZ_MODE_HIGHRES;
874#endif
875}
876#endif /* HIGH_RES_TIMERS */
877
878#if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS
879void tick_cancel_sched_timer(int cpu)
880{
881	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
882
883# ifdef CONFIG_HIGH_RES_TIMERS
884	if (ts->sched_timer.base)
885		hrtimer_cancel(&ts->sched_timer);
886# endif
887
888	ts->nohz_mode = NOHZ_MODE_INACTIVE;
889}
890#endif
891
892/**
893 * Async notification about clocksource changes
894 */
895void tick_clock_notify(void)
896{
897	int cpu;
898
899	for_each_possible_cpu(cpu)
900		set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
901}
902
903/*
904 * Async notification about clock event changes
905 */
906void tick_oneshot_notify(void)
907{
908	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
909
910	set_bit(0, &ts->check_clocks);
911}
912
913/**
914 * Check, if a change happened, which makes oneshot possible.
915 *
916 * Called cyclic from the hrtimer softirq (driven by the timer
917 * softirq) allow_nohz signals, that we can switch into low-res nohz
918 * mode, because high resolution timers are disabled (either compile
919 * or runtime).
920 */
921int tick_check_oneshot_change(int allow_nohz)
922{
923	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
924
925	if (!test_and_clear_bit(0, &ts->check_clocks))
926		return 0;
927
928	if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
929		return 0;
930
931	if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
932		return 0;
933
934	if (!allow_nohz)
935		return 1;
936
937	tick_nohz_switch_to_nohz();
938	return 0;
939}