kernel/time/tick-sched.c - kernel/msm-4.19 - Gitiles

 /*
  *  linux/kernel/time/tick-sched.c
  *
  *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
  *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
  *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
  *
  *  No idle tick implementation for low and high resolution timers
  *
  *  Started by: Thomas Gleixner and Ingo Molnar
  *
  *  Distribute under GPLv2.
  */
 #include <linux/cpu.h>
 #include <linux/err.h>
 #include <linux/hrtimer.h>
 #include <linux/interrupt.h>
 #include <linux/kernel_stat.h>
 #include <linux/percpu.h>
 #include <linux/profile.h>
 #include <linux/sched.h>
 #include <linux/tick.h>

 #include <asm/irq_regs.h>

 #include "tick-internal.h"

 /*
  * Per cpu nohz control structure
  */
 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);

 /*
  * The time, when the last jiffy update happened. Protected by xtime_lock.
  */
 static ktime_t last_jiffies_update;

 struct tick_sched *tick_get_tick_sched(int cpu)
 {
 	return &per_cpu(tick_cpu_sched, cpu);
 }

 /*
  * Must be called with interrupts disabled !
  */
 static void tick_do_update_jiffies64(ktime_t now)
 {
 	unsigned long ticks = 0;
 	ktime_t delta;

 	/*
 	 * Do a quick check without holding xtime_lock:
 	 */
 	delta = ktime_sub(now, last_jiffies_update);
 	if (delta.tv64 < tick_period.tv64)
 		return;

 	/* Reevalute with xtime_lock held */
 	write_seqlock(&xtime_lock);

 	delta = ktime_sub(now, last_jiffies_update);
 	if (delta.tv64 >= tick_period.tv64) {

 		delta = ktime_sub(delta, tick_period);
 		last_jiffies_update = ktime_add(last_jiffies_update,
 						tick_period);

 		/* Slow path for long timeouts */
 		if (unlikely(delta.tv64 >= tick_period.tv64)) {
 			s64 incr = ktime_to_ns(tick_period);

 			ticks = ktime_divns(delta, incr);

 			last_jiffies_update = ktime_add_ns(last_jiffies_update,
 							   incr * ticks);
 		}
 		do_timer(++ticks);
 	}
 	write_sequnlock(&xtime_lock);
 }

 /*
  * Initialize and return retrieve the jiffies update.
  */
 static ktime_t tick_init_jiffy_update(void)
 {
 	ktime_t period;

 	write_seqlock(&xtime_lock);
 	/* Did we start the jiffies update yet ? */
 	if (last_jiffies_update.tv64 == 0)
 		last_jiffies_update = tick_next_period;
 	period = last_jiffies_update;
 	write_sequnlock(&xtime_lock);
 	return period;
 }

 /*
  * NOHZ - aka dynamic tick functionality
  */
 #ifdef CONFIG_NO_HZ
 /*
  * NO HZ enabled ?
  */
 static int tick_nohz_enabled __read_mostly  = 1;

 /*
  * Enable / Disable tickless mode
  */
 static int __init setup_tick_nohz(char *str)
 {
 	if (!strcmp(str, "off"))
 		tick_nohz_enabled = 0;
 	else if (!strcmp(str, "on"))
 		tick_nohz_enabled = 1;
 	else
 		return 0;
 	return 1;
 }

 __setup("nohz=", setup_tick_nohz);

 /**
  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
  *
  * Called from interrupt entry when the CPU was idle
  *
  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
  * must be updated. Otherwise an interrupt handler could use a stale jiffy
  * value. We do this unconditionally on any cpu, as we don't know whether the
  * cpu, which has the update task assigned is in a long sleep.
  */
 void tick_nohz_update_jiffies(void)
 {
 	int cpu = smp_processor_id();
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 	unsigned long flags;
 	ktime_t now;

 	if (!ts->tick_stopped)
 		return;

 	cpu_clear(cpu, nohz_cpu_mask);
 	now = ktime_get();
 	ts->idle_waketime = now;

 	local_irq_save(flags);
 	tick_do_update_jiffies64(now);
 	local_irq_restore(flags);

 	touch_softlockup_watchdog();
 }

 void tick_nohz_stop_idle(int cpu)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

 	if (ts->idle_active) {
 		ktime_t now, delta;
 		now = ktime_get();
 		delta = ktime_sub(now, ts->idle_entrytime);
 		ts->idle_lastupdate = now;
 		ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
 		ts->idle_active = 0;
 	}
 }

 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
 {
 	ktime_t now, delta;

 	now = ktime_get();
 	if (ts->idle_active) {
 		delta = ktime_sub(now, ts->idle_entrytime);
 		ts->idle_lastupdate = now;
 		ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
 	}
 	ts->idle_entrytime = now;
 	ts->idle_active = 1;
 	return now;
 }

 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

 	*last_update_time = ktime_to_us(ts->idle_lastupdate);
 	return ktime_to_us(ts->idle_sleeptime);
 }

 /**
  * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
  *
  * When the next event is more than a tick into the future, stop the idle tick
  * Called either from the idle loop or from irq_exit() when an idle period was
  * just interrupted by an interrupt which did not cause a reschedule.
  */
 void tick_nohz_stop_sched_tick(int inidle)
 {
 	unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
 	struct tick_sched *ts;
 	ktime_t last_update, expires, now;
 	struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
 	int cpu;

 	local_irq_save(flags);

 	cpu = smp_processor_id();
 	ts = &per_cpu(tick_cpu_sched, cpu);
 	now = tick_nohz_start_idle(ts);

 	/*
 	 * If this cpu is offline and it is the one which updates
 	 * jiffies, then give up the assignment and let it be taken by
 	 * the cpu which runs the tick timer next. If we don't drop
 	 * this here the jiffies might be stale and do_timer() never
 	 * invoked.
 	 */
 	if (unlikely(!cpu_online(cpu))) {
 		if (cpu == tick_do_timer_cpu)
 			tick_do_timer_cpu = -1;
 	}

 	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
 		goto end;

 	if (!inidle && !ts->inidle)
 		goto end;

 	ts->inidle = 1;

 	if (need_resched())
 		goto end;

 	if (unlikely(local_softirq_pending())) {
 		static int ratelimit;

 		if (ratelimit < 10) {
 			printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
 			       local_softirq_pending());
 			ratelimit++;
 		}
 		goto end;
 	}

 	ts->idle_calls++;
 	/* Read jiffies and the time when jiffies were updated last */
 	do {
 		seq = read_seqbegin(&xtime_lock);
 		last_update = last_jiffies_update;
 		last_jiffies = jiffies;
 	} while (read_seqretry(&xtime_lock, seq));

 	/* Get the next timer wheel timer */
 	next_jiffies = get_next_timer_interrupt(last_jiffies);
 	delta_jiffies = next_jiffies - last_jiffies;

 	if (rcu_needs_cpu(cpu))
 		delta_jiffies = 1;
 	/*
 	 * Do not stop the tick, if we are only one off
 	 * or if the cpu is required for rcu
 	 */
 	if (!ts->tick_stopped && delta_jiffies == 1)
 		goto out;

 	/* Schedule the tick, if we are at least one jiffie off */
 	if ((long)delta_jiffies >= 1) {

 		if (delta_jiffies > 1)
 			cpu_set(cpu, nohz_cpu_mask);
 		/*
 		 * nohz_stop_sched_tick can be called several times before
 		 * the nohz_restart_sched_tick is called. This happens when
 		 * interrupts arrive which do not cause a reschedule. In the
 		 * first call we save the current tick time, so we can restart
 		 * the scheduler tick in nohz_restart_sched_tick.
 		 */
 		if (!ts->tick_stopped) {
 			if (select_nohz_load_balancer(1)) {
 				/*
 				 * sched tick not stopped!
 				 */
 				cpu_clear(cpu, nohz_cpu_mask);
 				goto out;
 			}

 			ts->idle_tick = ts->sched_timer.expires;
 			ts->tick_stopped = 1;
 			ts->idle_jiffies = last_jiffies;
 			rcu_enter_nohz();
 			sched_clock_tick_stop(cpu);
 		}

 		/*
 		 * If this cpu is the one which updates jiffies, then
 		 * give up the assignment and let it be taken by the
 		 * cpu which runs the tick timer next, which might be
 		 * this cpu as well. If we don't drop this here the
 		 * jiffies might be stale and do_timer() never
 		 * invoked.
 		 */
 		if (cpu == tick_do_timer_cpu)
 			tick_do_timer_cpu = -1;

 		ts->idle_sleeps++;

 		/*
 		 * delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that
 		 * there is no timer pending or at least extremly far
 		 * into the future (12 days for HZ=1000). In this case
 		 * we simply stop the tick timer:
 		 */
 		if (unlikely(delta_jiffies >= NEXT_TIMER_MAX_DELTA)) {
 			ts->idle_expires.tv64 = KTIME_MAX;
 			if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
 				hrtimer_cancel(&ts->sched_timer);
 			goto out;
 		}

 		/*
 		 * calculate the expiry time for the next timer wheel
 		 * timer
 		 */
 		expires = ktime_add_ns(last_update, tick_period.tv64 *
 				       delta_jiffies);
 		ts->idle_expires = expires;

 		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
 			hrtimer_start(&ts->sched_timer, expires,
 				      HRTIMER_MODE_ABS);
 			/* Check, if the timer was already in the past */
 			if (hrtimer_active(&ts->sched_timer))
 				goto out;
 		} else if (!tick_program_event(expires, 0))
 				goto out;
 		/*
 		 * We are past the event already. So we crossed a
 		 * jiffie boundary. Update jiffies and raise the
 		 * softirq.
 		 */
 		tick_do_update_jiffies64(ktime_get());
 		cpu_clear(cpu, nohz_cpu_mask);
 	}
 	raise_softirq_irqoff(TIMER_SOFTIRQ);
 out:
 	ts->next_jiffies = next_jiffies;
 	ts->last_jiffies = last_jiffies;
 	ts->sleep_length = ktime_sub(dev->next_event, now);
 end:
 	local_irq_restore(flags);
 }

 /**
  * tick_nohz_get_sleep_length - return the length of the current sleep
  *
  * Called from power state control code with interrupts disabled
  */
 ktime_t tick_nohz_get_sleep_length(void)
 {
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

 	return ts->sleep_length;
 }

 /**
  * tick_nohz_restart_sched_tick - restart the idle tick from the idle task
  *
  * Restart the idle tick when the CPU is woken up from idle
  */
 void tick_nohz_restart_sched_tick(void)
 {
 	int cpu = smp_processor_id();
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 	unsigned long ticks;
 	ktime_t now;

 	local_irq_disable();
 	tick_nohz_stop_idle(cpu);

 	if (!ts->inidle || !ts->tick_stopped) {
 		ts->inidle = 0;
 		local_irq_enable();
 		return;
 	}

 	ts->inidle = 0;

 	rcu_exit_nohz();

 	/* Update jiffies first */
 	select_nohz_load_balancer(0);
 	now = ktime_get();
 	tick_do_update_jiffies64(now);
 	sched_clock_tick_start(cpu);
 	cpu_clear(cpu, nohz_cpu_mask);

 	/*
 	 * We stopped the tick in idle. Update process times would miss the
 	 * time we slept as update_process_times does only a 1 tick
 	 * accounting. Enforce that this is accounted to idle !
 	 */
 	ticks = jiffies - ts->idle_jiffies;
 	/*
 	 * We might be one off. Do not randomly account a huge number of ticks!
 	 */
 	if (ticks && ticks < LONG_MAX) {
 		add_preempt_count(HARDIRQ_OFFSET);
 		account_system_time(current, HARDIRQ_OFFSET,
 				    jiffies_to_cputime(ticks));
 		sub_preempt_count(HARDIRQ_OFFSET);
 	}

 	touch_softlockup_watchdog();
 	/*
 	 * Cancel the scheduled timer and restore the tick
 	 */
 	ts->tick_stopped  = 0;
 	ts->idle_exittime = now;
 	hrtimer_cancel(&ts->sched_timer);
 	ts->sched_timer.expires = ts->idle_tick;

 	while (1) {
 		/* Forward the time to expire in the future */
 		hrtimer_forward(&ts->sched_timer, now, tick_period);

 		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
 			hrtimer_start(&ts->sched_timer,
 				      ts->sched_timer.expires,
 				      HRTIMER_MODE_ABS);
 			/* Check, if the timer was already in the past */
 			if (hrtimer_active(&ts->sched_timer))
 				break;
 		} else {
 			if (!tick_program_event(ts->sched_timer.expires, 0))
 				break;
 		}
 		/* Update jiffies and reread time */
 		tick_do_update_jiffies64(now);
 		now = ktime_get();
 	}
 	local_irq_enable();
 }

 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
 {
 	hrtimer_forward(&ts->sched_timer, now, tick_period);
 	return tick_program_event(ts->sched_timer.expires, 0);
 }

 /*
  * The nohz low res interrupt handler
  */
 static void tick_nohz_handler(struct clock_event_device *dev)
 {
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 	struct pt_regs *regs = get_irq_regs();
 	int cpu = smp_processor_id();
 	ktime_t now = ktime_get();

 	dev->next_event.tv64 = KTIME_MAX;

 	/*
 	 * Check if the do_timer duty was dropped. We don't care about
 	 * concurrency: This happens only when the cpu in charge went
 	 * into a long sleep. If two cpus happen to assign themself to
 	 * this duty, then the jiffies update is still serialized by
 	 * xtime_lock.
 	 */
 	if (unlikely(tick_do_timer_cpu == -1))
 		tick_do_timer_cpu = cpu;

 	/* Check, if the jiffies need an update */
 	if (tick_do_timer_cpu == cpu)
 		tick_do_update_jiffies64(now);

 	/*
 	 * When we are idle and the tick is stopped, we have to touch
 	 * the watchdog as we might not schedule for a really long
 	 * time. This happens on complete idle SMP systems while
 	 * waiting on the login prompt. We also increment the "start
 	 * of idle" jiffy stamp so the idle accounting adjustment we
 	 * do when we go busy again does not account too much ticks.
 	 */
 	if (ts->tick_stopped) {
 		touch_softlockup_watchdog();
 		ts->idle_jiffies++;
 	}

 	update_process_times(user_mode(regs));
 	profile_tick(CPU_PROFILING);

 	/* Do not restart, when we are in the idle loop */
 	if (ts->tick_stopped)
 		return;

 	while (tick_nohz_reprogram(ts, now)) {
 		now = ktime_get();
 		tick_do_update_jiffies64(now);
 	}
 }

 /**
  * tick_nohz_switch_to_nohz - switch to nohz mode
  */
 static void tick_nohz_switch_to_nohz(void)
 {
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 	ktime_t next;

 	if (!tick_nohz_enabled)
 		return;

 	local_irq_disable();
 	if (tick_switch_to_oneshot(tick_nohz_handler)) {
 		local_irq_enable();
 		return;
 	}

 	ts->nohz_mode = NOHZ_MODE_LOWRES;

 	/*
 	 * Recycle the hrtimer in ts, so we can share the
 	 * hrtimer_forward with the highres code.
 	 */
 	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
 	/* Get the next period */
 	next = tick_init_jiffy_update();

 	for (;;) {
 		ts->sched_timer.expires = next;
 		if (!tick_program_event(next, 0))
 			break;
 		next = ktime_add(next, tick_period);
 	}
 	local_irq_enable();

 	printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
 	       smp_processor_id());
 }

 #else

 static inline void tick_nohz_switch_to_nohz(void) { }

 #endif /* NO_HZ */

 /*
  * High resolution timer specific code
  */
 #ifdef CONFIG_HIGH_RES_TIMERS
 /*
  * We rearm the timer until we get disabled by the idle code.
  * Called with interrupts disabled and timer->base->cpu_base->lock held.
  */
 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
 {
 	struct tick_sched *ts =
 		container_of(timer, struct tick_sched, sched_timer);
 	struct pt_regs *regs = get_irq_regs();
 	ktime_t now = ktime_get();
 	int cpu = smp_processor_id();

 #ifdef CONFIG_NO_HZ
 	/*
 	 * Check if the do_timer duty was dropped. We don't care about
 	 * concurrency: This happens only when the cpu in charge went
 	 * into a long sleep. If two cpus happen to assign themself to
 	 * this duty, then the jiffies update is still serialized by
 	 * xtime_lock.
 	 */
 	if (unlikely(tick_do_timer_cpu == -1))
 		tick_do_timer_cpu = cpu;
 #endif

 	/* Check, if the jiffies need an update */
 	if (tick_do_timer_cpu == cpu)
 		tick_do_update_jiffies64(now);

 	/*
 	 * Do not call, when we are not in irq context and have
 	 * no valid regs pointer
 	 */
 	if (regs) {
 		/*
 		 * When we are idle and the tick is stopped, we have to touch
 		 * the watchdog as we might not schedule for a really long
 		 * time. This happens on complete idle SMP systems while
 		 * waiting on the login prompt. We also increment the "start of
 		 * idle" jiffy stamp so the idle accounting adjustment we do
 		 * when we go busy again does not account too much ticks.
 		 */
 		if (ts->tick_stopped) {
 			touch_softlockup_watchdog();
 			ts->idle_jiffies++;
 		}
 		update_process_times(user_mode(regs));
 		profile_tick(CPU_PROFILING);
 	}

 	/* Do not restart, when we are in the idle loop */
 	if (ts->tick_stopped)
 		return HRTIMER_NORESTART;

 	hrtimer_forward(timer, now, tick_period);

 	return HRTIMER_RESTART;
 }

 /**
  * tick_setup_sched_timer - setup the tick emulation timer
  */
 void tick_setup_sched_timer(void)
 {
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 	ktime_t now = ktime_get();
 	u64 offset;

 	/*
 	 * Emulate tick processing via per-CPU hrtimers:
 	 */
 	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
 	ts->sched_timer.function = tick_sched_timer;
 	ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;

 	/* Get the next period (per cpu) */
 	ts->sched_timer.expires = tick_init_jiffy_update();
 	offset = ktime_to_ns(tick_period) >> 1;
 	do_div(offset, num_possible_cpus());
 	offset *= smp_processor_id();
 	ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset);

 	for (;;) {
 		hrtimer_forward(&ts->sched_timer, now, tick_period);
 		hrtimer_start(&ts->sched_timer, ts->sched_timer.expires,
 			      HRTIMER_MODE_ABS);
 		/* Check, if the timer was already in the past */
 		if (hrtimer_active(&ts->sched_timer))
 			break;
 		now = ktime_get();
 	}

 #ifdef CONFIG_NO_HZ
 	if (tick_nohz_enabled)
 		ts->nohz_mode = NOHZ_MODE_HIGHRES;
 #endif
 }

 void tick_cancel_sched_timer(int cpu)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

 	if (ts->sched_timer.base)
 		hrtimer_cancel(&ts->sched_timer);

 	ts->nohz_mode = NOHZ_MODE_INACTIVE;
 }
 #endif /* HIGH_RES_TIMERS */

 /**
  * Async notification about clocksource changes
  */
 void tick_clock_notify(void)
 {
 	int cpu;

 	for_each_possible_cpu(cpu)
 		set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
 }

 /*
  * Async notification about clock event changes
  */
 void tick_oneshot_notify(void)
 {
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

 	set_bit(0, &ts->check_clocks);
 }

 /**
  * Check, if a change happened, which makes oneshot possible.
  *
  * Called cyclic from the hrtimer softirq (driven by the timer
  * softirq) allow_nohz signals, that we can switch into low-res nohz
  * mode, because high resolution timers are disabled (either compile
  * or runtime).
  */
 int tick_check_oneshot_change(int allow_nohz)
 {
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

 	if (!test_and_clear_bit(0, &ts->check_clocks))
 		return 0;

 	if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
 		return 0;

 	if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
 		return 0;

 	if (!allow_nohz)
 		return 1;

 	tick_nohz_switch_to_nohz();
 	return 0;
 }
	/*
	* linux/kernel/time/tick-sched.c
	*
	* Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
	* Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
	* Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner
	*
	* No idle tick implementation for low and high resolution timers
	*
	* Started by: Thomas Gleixner and Ingo Molnar
	*
	* Distribute under GPLv2.
	*/
	#include <linux/cpu.h>
	#include <linux/err.h>
	#include <linux/hrtimer.h>
	#include <linux/interrupt.h>
	#include <linux/kernel_stat.h>
	#include <linux/percpu.h>
	#include <linux/profile.h>
	#include <linux/sched.h>
	#include <linux/tick.h>

	#include <asm/irq_regs.h>

	#include "tick-internal.h"

	/*
	* Per cpu nohz control structure
	*/
	static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);

	/*
	* The time, when the last jiffy update happened. Protected by xtime_lock.
	*/
	static ktime_t last_jiffies_update;

	struct tick_sched *tick_get_tick_sched(int cpu)
	{
	return &per_cpu(tick_cpu_sched, cpu);
	}

	/*
	* Must be called with interrupts disabled !
	*/
	static void tick_do_update_jiffies64(ktime_t now)
	{
	unsigned long ticks = 0;
	ktime_t delta;

	/*
	* Do a quick check without holding xtime_lock:
	*/
	delta = ktime_sub(now, last_jiffies_update);
	if (delta.tv64 < tick_period.tv64)
	return;

	/* Reevalute with xtime_lock held */
	write_seqlock(&xtime_lock);

	delta = ktime_sub(now, last_jiffies_update);
	if (delta.tv64 >= tick_period.tv64) {

	delta = ktime_sub(delta, tick_period);
	last_jiffies_update = ktime_add(last_jiffies_update,
	tick_period);

	/* Slow path for long timeouts */
	if (unlikely(delta.tv64 >= tick_period.tv64)) {
	s64 incr = ktime_to_ns(tick_period);

	ticks = ktime_divns(delta, incr);

	last_jiffies_update = ktime_add_ns(last_jiffies_update,
	incr * ticks);
	}
	do_timer(++ticks);
	}
	write_sequnlock(&xtime_lock);
	}

	/*
	* Initialize and return retrieve the jiffies update.
	*/
	static ktime_t tick_init_jiffy_update(void)
	{
	ktime_t period;

	write_seqlock(&xtime_lock);
	/* Did we start the jiffies update yet ? */
	if (last_jiffies_update.tv64 == 0)
	last_jiffies_update = tick_next_period;
	period = last_jiffies_update;
	write_sequnlock(&xtime_lock);
	return period;
	}

	/*
	* NOHZ - aka dynamic tick functionality
	*/
	#ifdef CONFIG_NO_HZ
	/*
	* NO HZ enabled ?
	*/
	static int tick_nohz_enabled __read_mostly = 1;

	/*
	* Enable / Disable tickless mode
	*/
	static int __init setup_tick_nohz(char *str)
	{
	if (!strcmp(str, "off"))
	tick_nohz_enabled = 0;
	else if (!strcmp(str, "on"))
	tick_nohz_enabled = 1;
	else
	return 0;
	return 1;
	}

	__setup("nohz=", setup_tick_nohz);

	/**
	* tick_nohz_update_jiffies - update jiffies when idle was interrupted
	*
	* Called from interrupt entry when the CPU was idle
	*
	* In case the sched_tick was stopped on this CPU, we have to check if jiffies
	* must be updated. Otherwise an interrupt handler could use a stale jiffy
	* value. We do this unconditionally on any cpu, as we don't know whether the
	* cpu, which has the update task assigned is in a long sleep.
	*/
	void tick_nohz_update_jiffies(void)
	{
	int cpu = smp_processor_id();
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
	unsigned long flags;
	ktime_t now;

	if (!ts->tick_stopped)
	return;

	cpu_clear(cpu, nohz_cpu_mask);
	now = ktime_get();
	ts->idle_waketime = now;

	local_irq_save(flags);
	tick_do_update_jiffies64(now);
	local_irq_restore(flags);

	touch_softlockup_watchdog();
	}

	void tick_nohz_stop_idle(int cpu)
	{
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

	if (ts->idle_active) {
	ktime_t now, delta;
	now = ktime_get();
	delta = ktime_sub(now, ts->idle_entrytime);
	ts->idle_lastupdate = now;
	ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
	ts->idle_active = 0;
	}
	}

	static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
	{
	ktime_t now, delta;

	now = ktime_get();
	if (ts->idle_active) {
	delta = ktime_sub(now, ts->idle_entrytime);
	ts->idle_lastupdate = now;
	ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
	}
	ts->idle_entrytime = now;
	ts->idle_active = 1;
	return now;
	}

	u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
	{
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

	*last_update_time = ktime_to_us(ts->idle_lastupdate);
	return ktime_to_us(ts->idle_sleeptime);
	}

	/**
	* tick_nohz_stop_sched_tick - stop the idle tick from the idle task
	*
	* When the next event is more than a tick into the future, stop the idle tick
	* Called either from the idle loop or from irq_exit() when an idle period was
	* just interrupted by an interrupt which did not cause a reschedule.
	*/
	void tick_nohz_stop_sched_tick(int inidle)
	{
	unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
	struct tick_sched *ts;
	ktime_t last_update, expires, now;
	struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
	int cpu;

	local_irq_save(flags);

	cpu = smp_processor_id();
	ts = &per_cpu(tick_cpu_sched, cpu);
	now = tick_nohz_start_idle(ts);

	/*
	* If this cpu is offline and it is the one which updates
	* jiffies, then give up the assignment and let it be taken by
	* the cpu which runs the tick timer next. If we don't drop
	* this here the jiffies might be stale and do_timer() never
	* invoked.
	*/
	if (unlikely(!cpu_online(cpu))) {
	if (cpu == tick_do_timer_cpu)
	tick_do_timer_cpu = -1;
	}

	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
	goto end;

	if (!inidle && !ts->inidle)
	goto end;

	ts->inidle = 1;

	if (need_resched())
	goto end;

	if (unlikely(local_softirq_pending())) {
	static int ratelimit;

	if (ratelimit < 10) {
	printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
	local_softirq_pending());
	ratelimit++;
	}
	goto end;
	}

	ts->idle_calls++;
	/* Read jiffies and the time when jiffies were updated last */
	do {
	seq = read_seqbegin(&xtime_lock);
	last_update = last_jiffies_update;
	last_jiffies = jiffies;
	} while (read_seqretry(&xtime_lock, seq));

	/* Get the next timer wheel timer */
	next_jiffies = get_next_timer_interrupt(last_jiffies);
	delta_jiffies = next_jiffies - last_jiffies;

	if (rcu_needs_cpu(cpu))
	delta_jiffies = 1;
	/*
	* Do not stop the tick, if we are only one off
	* or if the cpu is required for rcu
	*/
	if (!ts->tick_stopped && delta_jiffies == 1)
	goto out;

	/* Schedule the tick, if we are at least one jiffie off */
	if ((long)delta_jiffies >= 1) {

	if (delta_jiffies > 1)
	cpu_set(cpu, nohz_cpu_mask);
	/*
	* nohz_stop_sched_tick can be called several times before
	* the nohz_restart_sched_tick is called. This happens when
	* interrupts arrive which do not cause a reschedule. In the
	* first call we save the current tick time, so we can restart
	* the scheduler tick in nohz_restart_sched_tick.
	*/
	if (!ts->tick_stopped) {
	if (select_nohz_load_balancer(1)) {
	/*
	* sched tick not stopped!
	*/
	cpu_clear(cpu, nohz_cpu_mask);
	goto out;
	}

	ts->idle_tick = ts->sched_timer.expires;
	ts->tick_stopped = 1;
	ts->idle_jiffies = last_jiffies;
	rcu_enter_nohz();
	sched_clock_tick_stop(cpu);
	}

	/*
	* If this cpu is the one which updates jiffies, then
	* give up the assignment and let it be taken by the
	* cpu which runs the tick timer next, which might be
	* this cpu as well. If we don't drop this here the
	* jiffies might be stale and do_timer() never
	* invoked.
	*/
	if (cpu == tick_do_timer_cpu)
	tick_do_timer_cpu = -1;

	ts->idle_sleeps++;

	/*
	* delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that
	* there is no timer pending or at least extremly far
	* into the future (12 days for HZ=1000). In this case
	* we simply stop the tick timer:
	*/
	if (unlikely(delta_jiffies >= NEXT_TIMER_MAX_DELTA)) {
	ts->idle_expires.tv64 = KTIME_MAX;
	if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
	hrtimer_cancel(&ts->sched_timer);
	goto out;
	}

	/*
	* calculate the expiry time for the next timer wheel
	* timer
	*/
	expires = ktime_add_ns(last_update, tick_period.tv64 *
	delta_jiffies);
	ts->idle_expires = expires;

	if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
	hrtimer_start(&ts->sched_timer, expires,
	HRTIMER_MODE_ABS);
	/* Check, if the timer was already in the past */
	if (hrtimer_active(&ts->sched_timer))
	goto out;
	} else if (!tick_program_event(expires, 0))
	goto out;
	/*
	* We are past the event already. So we crossed a
	* jiffie boundary. Update jiffies and raise the
	* softirq.
	*/
	tick_do_update_jiffies64(ktime_get());
	cpu_clear(cpu, nohz_cpu_mask);
	}
	raise_softirq_irqoff(TIMER_SOFTIRQ);
	out:
	ts->next_jiffies = next_jiffies;
	ts->last_jiffies = last_jiffies;
	ts->sleep_length = ktime_sub(dev->next_event, now);
	end:
	local_irq_restore(flags);
	}

	/**
	* tick_nohz_get_sleep_length - return the length of the current sleep
	*
	* Called from power state control code with interrupts disabled
	*/
	ktime_t tick_nohz_get_sleep_length(void)
	{
	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

	return ts->sleep_length;
	}

	/**
	* tick_nohz_restart_sched_tick - restart the idle tick from the idle task
	*
	* Restart the idle tick when the CPU is woken up from idle
	*/
	void tick_nohz_restart_sched_tick(void)
	{
	int cpu = smp_processor_id();
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
	unsigned long ticks;
	ktime_t now;

	local_irq_disable();
	tick_nohz_stop_idle(cpu);

	if (!ts->inidle \|\| !ts->tick_stopped) {
	ts->inidle = 0;
	local_irq_enable();
	return;
	}

	ts->inidle = 0;

	rcu_exit_nohz();

	/* Update jiffies first */
	select_nohz_load_balancer(0);
	now = ktime_get();
	tick_do_update_jiffies64(now);
	sched_clock_tick_start(cpu);
	cpu_clear(cpu, nohz_cpu_mask);

	/*
	* We stopped the tick in idle. Update process times would miss the
	* time we slept as update_process_times does only a 1 tick
	* accounting. Enforce that this is accounted to idle !
	*/
	ticks = jiffies - ts->idle_jiffies;
	/*
	* We might be one off. Do not randomly account a huge number of ticks!
	*/
	if (ticks && ticks < LONG_MAX) {
	add_preempt_count(HARDIRQ_OFFSET);
	account_system_time(current, HARDIRQ_OFFSET,
	jiffies_to_cputime(ticks));
	sub_preempt_count(HARDIRQ_OFFSET);
	}

	touch_softlockup_watchdog();
	/*
	* Cancel the scheduled timer and restore the tick
	*/
	ts->tick_stopped = 0;
	ts->idle_exittime = now;
	hrtimer_cancel(&ts->sched_timer);
	ts->sched_timer.expires = ts->idle_tick;

	while (1) {
	/* Forward the time to expire in the future */
	hrtimer_forward(&ts->sched_timer, now, tick_period);

	if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
	hrtimer_start(&ts->sched_timer,
	ts->sched_timer.expires,
	HRTIMER_MODE_ABS);
	/* Check, if the timer was already in the past */
	if (hrtimer_active(&ts->sched_timer))
	break;
	} else {
	if (!tick_program_event(ts->sched_timer.expires, 0))
	break;
	}
	/* Update jiffies and reread time */
	tick_do_update_jiffies64(now);
	now = ktime_get();
	}
	local_irq_enable();
	}

	static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
	{
	hrtimer_forward(&ts->sched_timer, now, tick_period);
	return tick_program_event(ts->sched_timer.expires, 0);
	}

	/*
	* The nohz low res interrupt handler
	*/
	static void tick_nohz_handler(struct clock_event_device *dev)
	{
	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
	struct pt_regs *regs = get_irq_regs();
	int cpu = smp_processor_id();
	ktime_t now = ktime_get();

	dev->next_event.tv64 = KTIME_MAX;

	/*
	* Check if the do_timer duty was dropped. We don't care about
	* concurrency: This happens only when the cpu in charge went
	* into a long sleep. If two cpus happen to assign themself to
	* this duty, then the jiffies update is still serialized by
	* xtime_lock.
	*/
	if (unlikely(tick_do_timer_cpu == -1))
	tick_do_timer_cpu = cpu;

	/* Check, if the jiffies need an update */
	if (tick_do_timer_cpu == cpu)
	tick_do_update_jiffies64(now);

	/*
	* When we are idle and the tick is stopped, we have to touch
	* the watchdog as we might not schedule for a really long
	* time. This happens on complete idle SMP systems while
	* waiting on the login prompt. We also increment the "start
	* of idle" jiffy stamp so the idle accounting adjustment we
	* do when we go busy again does not account too much ticks.
	*/
	if (ts->tick_stopped) {
	touch_softlockup_watchdog();
	ts->idle_jiffies++;
	}

	update_process_times(user_mode(regs));
	profile_tick(CPU_PROFILING);

	/* Do not restart, when we are in the idle loop */
	if (ts->tick_stopped)
	return;

	while (tick_nohz_reprogram(ts, now)) {
	now = ktime_get();
	tick_do_update_jiffies64(now);
	}
	}

	/**
	* tick_nohz_switch_to_nohz - switch to nohz mode
	*/
	static void tick_nohz_switch_to_nohz(void)
	{
	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
	ktime_t next;

	if (!tick_nohz_enabled)
	return;

	local_irq_disable();
	if (tick_switch_to_oneshot(tick_nohz_handler)) {
	local_irq_enable();
	return;
	}

	ts->nohz_mode = NOHZ_MODE_LOWRES;

	/*
	* Recycle the hrtimer in ts, so we can share the
	* hrtimer_forward with the highres code.
	*/
	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	/* Get the next period */
	next = tick_init_jiffy_update();

	for (;;) {
	ts->sched_timer.expires = next;
	if (!tick_program_event(next, 0))
	break;
	next = ktime_add(next, tick_period);
	}
	local_irq_enable();

	printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
	smp_processor_id());
	}

	#else

	static inline void tick_nohz_switch_to_nohz(void) { }

	#endif /* NO_HZ */

	/*
	* High resolution timer specific code
	*/
	#ifdef CONFIG_HIGH_RES_TIMERS
	/*
	* We rearm the timer until we get disabled by the idle code.
	* Called with interrupts disabled and timer->base->cpu_base->lock held.
	*/
	static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
	{
	struct tick_sched *ts =
	container_of(timer, struct tick_sched, sched_timer);
	struct pt_regs *regs = get_irq_regs();
	ktime_t now = ktime_get();
	int cpu = smp_processor_id();

	#ifdef CONFIG_NO_HZ
	/*
	* Check if the do_timer duty was dropped. We don't care about
	* concurrency: This happens only when the cpu in charge went
	* into a long sleep. If two cpus happen to assign themself to
	* this duty, then the jiffies update is still serialized by
	* xtime_lock.
	*/
	if (unlikely(tick_do_timer_cpu == -1))
	tick_do_timer_cpu = cpu;
	#endif

	/* Check, if the jiffies need an update */
	if (tick_do_timer_cpu == cpu)
	tick_do_update_jiffies64(now);

	/*
	* Do not call, when we are not in irq context and have
	* no valid regs pointer
	*/
	if (regs) {
	/*
	* When we are idle and the tick is stopped, we have to touch
	* the watchdog as we might not schedule for a really long
	* time. This happens on complete idle SMP systems while
	* waiting on the login prompt. We also increment the "start of
	* idle" jiffy stamp so the idle accounting adjustment we do
	* when we go busy again does not account too much ticks.
	*/
	if (ts->tick_stopped) {
	touch_softlockup_watchdog();
	ts->idle_jiffies++;
	}
	update_process_times(user_mode(regs));
	profile_tick(CPU_PROFILING);
	}

	/* Do not restart, when we are in the idle loop */
	if (ts->tick_stopped)
	return HRTIMER_NORESTART;

	hrtimer_forward(timer, now, tick_period);

	return HRTIMER_RESTART;
	}

	/**
	* tick_setup_sched_timer - setup the tick emulation timer
	*/
	void tick_setup_sched_timer(void)
	{
	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
	ktime_t now = ktime_get();
	u64 offset;

	/*
	* Emulate tick processing via per-CPU hrtimers:
	*/
	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	ts->sched_timer.function = tick_sched_timer;
	ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;

	/* Get the next period (per cpu) */
	ts->sched_timer.expires = tick_init_jiffy_update();
	offset = ktime_to_ns(tick_period) >> 1;
	do_div(offset, num_possible_cpus());
	offset *= smp_processor_id();
	ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset);

	for (;;) {
	hrtimer_forward(&ts->sched_timer, now, tick_period);
	hrtimer_start(&ts->sched_timer, ts->sched_timer.expires,
	HRTIMER_MODE_ABS);
	/* Check, if the timer was already in the past */
	if (hrtimer_active(&ts->sched_timer))
	break;
	now = ktime_get();
	}

	#ifdef CONFIG_NO_HZ
	if (tick_nohz_enabled)
	ts->nohz_mode = NOHZ_MODE_HIGHRES;
	#endif
	}

	void tick_cancel_sched_timer(int cpu)
	{
	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

	if (ts->sched_timer.base)
	hrtimer_cancel(&ts->sched_timer);

	ts->nohz_mode = NOHZ_MODE_INACTIVE;
	}
	#endif /* HIGH_RES_TIMERS */

	/**
	* Async notification about clocksource changes
	*/
	void tick_clock_notify(void)
	{
	int cpu;

	for_each_possible_cpu(cpu)
	set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
	}

	/*
	* Async notification about clock event changes
	*/
	void tick_oneshot_notify(void)
	{
	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

	set_bit(0, &ts->check_clocks);
	}

	/**
	* Check, if a change happened, which makes oneshot possible.
	*
	* Called cyclic from the hrtimer softirq (driven by the timer
	* softirq) allow_nohz signals, that we can switch into low-res nohz
	* mode, because high resolution timers are disabled (either compile
	* or runtime).
	*/
	int tick_check_oneshot_change(int allow_nohz)
	{
	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

	if (!test_and_clear_bit(0, &ts->check_clocks))
	return 0;

	if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
	return 0;

	if (!timekeeping_valid_for_hres() \|\| !tick_is_oneshot_available())
	return 0;

	if (!allow_nohz)
	return 1;

	tick_nohz_switch_to_nohz();
	return 0;
	}