/*
   *  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/module.h>

  #include <linux/irq_work.h>

  #include <linux/posix-timers.h>
  #include <linux/perf_event.h>

  #include <linux/context_tracking.h>

  #include <asm/irq_regs.h>

  #include "tick-internal.h"

  #include <trace/events/timer.h>

  /*
   * Per cpu nohz control structure
   */

  DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);

  
  /*

   * The time, when the last jiffy update happened. Protected by jiffies_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 jiffies_lock:

  	 */
  	delta = ktime_sub(now, last_jiffies_update);
  	if (delta.tv64 < tick_period.tv64)
  		return;

  	/* Reevalute with jiffies_lock held */
  	write_seqlock(&jiffies_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);

  
  		/* Keep the tick_next_period variable up to date */
  		tick_next_period = ktime_add(last_jiffies_update, tick_period);

  	} else {
  		write_sequnlock(&jiffies_lock);
  		return;

  	}

  	write_sequnlock(&jiffies_lock);

  	update_wall_time();

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

  	write_seqlock(&jiffies_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(&jiffies_lock);

  	return period;
  }

  
  static void tick_sched_do_timer(ktime_t now)
  {
  	int cpu = smp_processor_id();

  #ifdef CONFIG_NO_HZ_COMMON

  	/*
  	 * 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

  	 * jiffies_lock.

  	 */

  	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)

  	    && !tick_nohz_full_cpu(cpu))

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

  static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
  {

  #ifdef CONFIG_NO_HZ_COMMON

  	/*
  	 * 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();
  		if (is_idle_task(current))
  			ts->idle_jiffies++;
  	}

  #endif

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

  #ifdef CONFIG_NO_HZ_FULL

  cpumask_var_t tick_nohz_full_mask;

  cpumask_var_t housekeeping_mask;

  bool tick_nohz_full_running;

  static bool can_stop_full_tick(void)
  {
  	WARN_ON_ONCE(!irqs_disabled());

  	if (!sched_can_stop_tick()) {
  		trace_tick_stop(0, "more than 1 task in runqueue
  ");

  		return false;

  	}

  	if (!posix_cpu_timers_can_stop_tick(current)) {
  		trace_tick_stop(0, "posix timers running
  ");

  		return false;

  	}

  	if (!perf_event_can_stop_tick()) {
  		trace_tick_stop(0, "perf events running
  ");

  		return false;

  	}

  
  	/* sched_clock_tick() needs us? */
  #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
  	/*
  	 * TODO: kick full dynticks CPUs when
  	 * sched_clock_stable is set.
  	 */

  	if (!sched_clock_stable()) {

  		trace_tick_stop(0, "unstable sched clock
  ");

  		/*
  		 * Don't allow the user to think they can get
  		 * full NO_HZ with this machine.
  		 */

  		WARN_ONCE(tick_nohz_full_running,

  			  "NO_HZ FULL will not work with unstable sched clock");

  		return false;

  	}

  #endif
  
  	return true;
  }
  
  static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);

  /*
   * Re-evaluate the need for the tick on the current CPU
   * and restart it if necessary.
   */

  void __tick_nohz_full_check(void)

  {

  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

  
  	if (tick_nohz_full_cpu(smp_processor_id())) {
  		if (ts->tick_stopped && !is_idle_task(current)) {
  			if (!can_stop_full_tick())
  				tick_nohz_restart_sched_tick(ts, ktime_get());
  		}
  	}

  }
  
  static void nohz_full_kick_work_func(struct irq_work *work)
  {

  	__tick_nohz_full_check();

  }
  
  static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
  	.func = nohz_full_kick_work_func,
  };
  
  /*

   * Kick this CPU if it's full dynticks in order to force it to
   * re-evaluate its dependency on the tick and restart it if necessary.
   * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
   * is NMI safe.
   */
  void tick_nohz_full_kick(void)
  {
  	if (!tick_nohz_full_cpu(smp_processor_id()))
  		return;

  	irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));

  }
  
  /*

   * Kick the CPU if it's full dynticks in order to force it to

   * re-evaluate its dependency on the tick and restart it if necessary.
   */

  void tick_nohz_full_kick_cpu(int cpu)

  {

  	if (!tick_nohz_full_cpu(cpu))
  		return;
  
  	irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);

  }
  
  static void nohz_full_kick_ipi(void *info)
  {

  	__tick_nohz_full_check();

  }
  
  /*
   * Kick all full dynticks CPUs in order to force these to re-evaluate
   * their dependency on the tick and restart it if necessary.
   */
  void tick_nohz_full_kick_all(void)
  {

  	if (!tick_nohz_full_running)

  		return;
  
  	preempt_disable();

  	smp_call_function_many(tick_nohz_full_mask,

  			       nohz_full_kick_ipi, NULL, false);

  	tick_nohz_full_kick();

  	preempt_enable();
  }

  /*
   * Re-evaluate the need for the tick as we switch the current task.
   * It might need the tick due to per task/process properties:
   * perf events, posix cpu timers, ...
   */

  void __tick_nohz_task_switch(struct task_struct *tsk)

  {
  	unsigned long flags;

  	local_irq_save(flags);

  	if (!tick_nohz_full_cpu(smp_processor_id()))
  		goto out;

  	if (tick_nohz_tick_stopped() && !can_stop_full_tick())
  		tick_nohz_full_kick();

  out:

  	local_irq_restore(flags);
  }

  /* Parse the boot-time nohz CPU list from the kernel parameters. */

  static int __init tick_nohz_full_setup(char *str)

  {

  	alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
  	if (cpulist_parse(str, tick_nohz_full_mask) < 0) {

  		pr_warning("NOHZ: Incorrect nohz_full cpumask
  ");

  		free_bootmem_cpumask_var(tick_nohz_full_mask);

  		return 1;
  	}

  	tick_nohz_full_running = true;

  	return 1;
  }

  __setup("nohz_full=", tick_nohz_full_setup);

  static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,

  						 unsigned long action,
  						 void *hcpu)
  {
  	unsigned int cpu = (unsigned long)hcpu;
  
  	switch (action & ~CPU_TASKS_FROZEN) {
  	case CPU_DOWN_PREPARE:
  		/*
  		 * If we handle the timekeeping duty for full dynticks CPUs,
  		 * we can't safely shutdown that CPU.
  		 */

  		if (tick_nohz_full_running && tick_do_timer_cpu == cpu)

  			return NOTIFY_BAD;

  		break;
  	}
  	return NOTIFY_OK;
  }

  /*
   * Worst case string length in chunks of CPU range seems 2 steps
   * separations: 0,2,4,6,...
   * This is NR_CPUS + sizeof('\0')
   */

  static char __initdata nohz_full_buf[NR_CPUS + 1];

  static int tick_nohz_init_all(void)
  {
  	int err = -1;
  
  #ifdef CONFIG_NO_HZ_FULL_ALL

  	if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {

  		WARN(1, "NO_HZ: Can't allocate full dynticks cpumask
  ");

  		return err;
  	}

  	err = 0;

  	cpumask_setall(tick_nohz_full_mask);

  	tick_nohz_full_running = true;

  #endif
  	return err;
  }

  void __init tick_nohz_init(void)

  {

  	int cpu;

  	if (!tick_nohz_full_running) {

  		if (tick_nohz_init_all() < 0)
  			return;
  	}

  	if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
  		WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask
  ");
  		cpumask_clear(tick_nohz_full_mask);
  		tick_nohz_full_running = false;
  		return;
  	}

  	/*
  	 * Full dynticks uses irq work to drive the tick rescheduling on safe
  	 * locking contexts. But then we need irq work to raise its own
  	 * interrupts to avoid circular dependency on the tick
  	 */
  	if (!arch_irq_work_has_interrupt()) {
  		pr_warning("NO_HZ: Can't run full dynticks because arch doesn't "
  			   "support irq work self-IPIs
  ");
  		cpumask_clear(tick_nohz_full_mask);
  		cpumask_copy(housekeeping_mask, cpu_possible_mask);
  		tick_nohz_full_running = false;
  		return;
  	}

  	cpu = smp_processor_id();
  
  	if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
  		pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping
  ", cpu);
  		cpumask_clear_cpu(cpu, tick_nohz_full_mask);
  	}
  
  	cpumask_andnot(housekeeping_mask,
  		       cpu_possible_mask, tick_nohz_full_mask);

  	for_each_cpu(cpu, tick_nohz_full_mask)

  		context_tracking_cpu_set(cpu);

  	cpu_notifier(tick_nohz_cpu_down_callback, 0);

  	cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), tick_nohz_full_mask);

  	pr_info("NO_HZ: Full dynticks CPUs: %s.
  ", nohz_full_buf);

  }

  #endif

  /*
   * NOHZ - aka dynamic tick functionality
   */

  #ifdef CONFIG_NO_HZ_COMMON

  /*
   * NO HZ enabled ?
   */

  static int tick_nohz_enabled __read_mostly  = 1;
  int tick_nohz_active  __read_mostly;

  /*
   * 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.
   */

  static void tick_nohz_update_jiffies(ktime_t now)

  {

  	unsigned long flags;

  	__this_cpu_write(tick_cpu_sched.idle_waketime, now);

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

  
  	touch_softlockup_watchdog();

  }

  /*
   * Updates the per cpu time idle statistics counters
   */

  static void

  update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)

  {

  	ktime_t delta;

  	if (ts->idle_active) {
  		delta = ktime_sub(now, ts->idle_entrytime);

  		if (nr_iowait_cpu(cpu) > 0)

  			ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);

  		else
  			ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);

  		ts->idle_entrytime = now;

  	}

  	if (last_update_time)

  		*last_update_time = ktime_to_us(now);

  }

  static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)

  {

  	update_ts_time_stats(smp_processor_id(), ts, now, NULL);

  	ts->idle_active = 0;

  	sched_clock_idle_wakeup_event(0);

  }

  static ktime_t tick_nohz_start_idle(struct tick_sched *ts)

  {

  	ktime_t now = ktime_get();

  	ts->idle_entrytime = now;
  	ts->idle_active = 1;

  	sched_clock_idle_sleep_event();

  	return now;
  }

  /**
   * get_cpu_idle_time_us - get the total idle time of a cpu
   * @cpu: CPU number to query

   * @last_update_time: variable to store update time in. Do not update
   * counters if NULL.

   *
   * Return the cummulative idle time (since boot) for a given

   * CPU, in microseconds.

   *
   * This time is measured via accounting rather than sampling,
   * and is as accurate as ktime_get() is.
   *
   * This function returns -1 if NOHZ is not enabled.
   */

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

  	ktime_t now, idle;

  	if (!tick_nohz_active)

  		return -1;

  	now = ktime_get();
  	if (last_update_time) {
  		update_ts_time_stats(cpu, ts, now, last_update_time);
  		idle = ts->idle_sleeptime;
  	} else {
  		if (ts->idle_active && !nr_iowait_cpu(cpu)) {
  			ktime_t delta = ktime_sub(now, ts->idle_entrytime);
  
  			idle = ktime_add(ts->idle_sleeptime, delta);
  		} else {
  			idle = ts->idle_sleeptime;
  		}
  	}
  
  	return ktime_to_us(idle);

  }

  EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);

  /**

   * get_cpu_iowait_time_us - get the total iowait time of a cpu
   * @cpu: CPU number to query

   * @last_update_time: variable to store update time in. Do not update
   * counters if NULL.

   *
   * Return the cummulative iowait time (since boot) for a given
   * CPU, in microseconds.
   *
   * This time is measured via accounting rather than sampling,
   * and is as accurate as ktime_get() is.
   *
   * This function returns -1 if NOHZ is not enabled.
   */
  u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
  {
  	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

  	ktime_t now, iowait;

  	if (!tick_nohz_active)

  		return -1;

  	now = ktime_get();
  	if (last_update_time) {
  		update_ts_time_stats(cpu, ts, now, last_update_time);
  		iowait = ts->iowait_sleeptime;
  	} else {
  		if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
  			ktime_t delta = ktime_sub(now, ts->idle_entrytime);

  			iowait = ktime_add(ts->iowait_sleeptime, delta);
  		} else {
  			iowait = ts->iowait_sleeptime;
  		}
  	}

  	return ktime_to_us(iowait);

  }
  EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);

  static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
  					 ktime_t now, int cpu)

  {

  	unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;

  	ktime_t last_update, expires, ret = { .tv64 = 0 };

  	unsigned long rcu_delta_jiffies;

  	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);

  	u64 time_delta;

  	time_delta = timekeeping_max_deferment();

  	/* Read jiffies and the time when jiffies were updated last */
  	do {

  		seq = read_seqbegin(&jiffies_lock);

  		last_update = last_jiffies_update;
  		last_jiffies = jiffies;

  	} while (read_seqretry(&jiffies_lock, seq));

  	if (rcu_needs_cpu(&rcu_delta_jiffies) ||

  	    arch_needs_cpu() || irq_work_needs_cpu()) {

  		next_jiffies = last_jiffies + 1;

  		delta_jiffies = 1;

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

  		if (rcu_delta_jiffies < delta_jiffies) {
  			next_jiffies = last_jiffies + rcu_delta_jiffies;
  			delta_jiffies = rcu_delta_jiffies;
  		}

  	}

  	/*

  	 * Do not stop the tick, if we are only one off (or less)
  	 * 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 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. Keep track of the fact that it was the one
  		 * which had the do_timer() duty last. If this cpu is
  		 * the one which had the do_timer() duty last, we
  		 * limit the sleep time to the timekeeping
  		 * max_deferement value which we retrieved
  		 * above. Otherwise we can sleep as long as we want.

  		 */

  		if (cpu == tick_do_timer_cpu) {

  			tick_do_timer_cpu = TICK_DO_TIMER_NONE;

  			ts->do_timer_last = 1;
  		} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
  			time_delta = KTIME_MAX;
  			ts->do_timer_last = 0;
  		} else if (!ts->do_timer_last) {
  			time_delta = KTIME_MAX;
  		}

  #ifdef CONFIG_NO_HZ_FULL
  		if (!ts->inidle) {
  			time_delta = min(time_delta,
  					 scheduler_tick_max_deferment());
  		}
  #endif

  		/*

  		 * calculate the expiry time for the next timer wheel
  		 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
  		 * that there is no timer pending or at least extremely
  		 * far into the future (12 days for HZ=1000). In this
  		 * case we set the expiry to the end of time.
  		 */
  		if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
  			/*
  			 * Calculate the time delta for the next timer event.
  			 * If the time delta exceeds the maximum time delta
  			 * permitted by the current clocksource then adjust
  			 * the time delta accordingly to ensure the
  			 * clocksource does not wrap.
  			 */
  			time_delta = min_t(u64, time_delta,
  					   tick_period.tv64 * delta_jiffies);

  		}

  		if (time_delta < KTIME_MAX)
  			expires = ktime_add_ns(last_update, time_delta);
  		else
  			expires.tv64 = KTIME_MAX;

  		/* Skip reprogram of event if its not changed */
  		if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
  			goto out;

  		ret = expires;

  		/*
  		 * 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) {

  			nohz_balance_enter_idle(cpu);

  			calc_load_enter_idle();

  			ts->last_tick = hrtimer_get_expires(&ts->sched_timer);

  			ts->tick_stopped = 1;

  			trace_tick_stop(1, " ");

  		}

  		/*

  		 * If the expiration time == KTIME_MAX, then
  		 * in this case we simply stop the tick timer.

  		 */

  		 if (unlikely(expires.tv64 == KTIME_MAX)) {

  			if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
  				hrtimer_cancel(&ts->sched_timer);
  			goto out;
  		}

  		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
  			hrtimer_start(&ts->sched_timer, expires,

  				      HRTIMER_MODE_ABS_PINNED);

  			/* 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());

  	}
  	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);

  
  	return ret;

  }

  static void tick_nohz_full_stop_tick(struct tick_sched *ts)
  {
  #ifdef CONFIG_NO_HZ_FULL

  	int cpu = smp_processor_id();

  	if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
  		return;

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

  	if (!can_stop_full_tick())
  		return;

  	tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);

  #endif
  }

  static bool can_stop_idle_tick(int cpu, struct tick_sched *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 = TICK_DO_TIMER_NONE;

  		return false;

  	}

  	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
  		ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };

  		return false;

  	}

  
  	if (need_resched())
  		return false;
  
  	if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
  		static int ratelimit;

  		if (ratelimit < 10 &&
  		    (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {

  			pr_warn("NOHZ: local_softirq_pending %02x
  ",
  				(unsigned int) local_softirq_pending());

  			ratelimit++;
  		}
  		return false;
  	}

  	if (tick_nohz_full_enabled()) {

  		/*
  		 * Keep the tick alive to guarantee timekeeping progression
  		 * if there are full dynticks CPUs around
  		 */
  		if (tick_do_timer_cpu == cpu)
  			return false;
  		/*
  		 * Boot safety: make sure the timekeeping duty has been
  		 * assigned before entering dyntick-idle mode,
  		 */
  		if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
  			return false;
  	}

  	return true;
  }

  static void __tick_nohz_idle_enter(struct tick_sched *ts)
  {

  	ktime_t now, expires;

  	int cpu = smp_processor_id();

  	now = tick_nohz_start_idle(ts);

  	if (can_stop_idle_tick(cpu, ts)) {
  		int was_stopped = ts->tick_stopped;
  
  		ts->idle_calls++;

  
  		expires = tick_nohz_stop_sched_tick(ts, now, cpu);
  		if (expires.tv64 > 0LL) {
  			ts->idle_sleeps++;
  			ts->idle_expires = expires;
  		}

  
  		if (!was_stopped && ts->tick_stopped)
  			ts->idle_jiffies = ts->last_jiffies;
  	}

  }
  
  /**
   * tick_nohz_idle_enter - 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 when we start the idle loop.

   *

   * The arch is responsible of calling:

   *
   * - rcu_idle_enter() after its last use of RCU before the CPU is put
   *  to sleep.
   * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.

   */

  void tick_nohz_idle_enter(void)

  {
  	struct tick_sched *ts;

  	WARN_ON_ONCE(irqs_disabled());

  	/*
   	 * Update the idle state in the scheduler domain hierarchy
   	 * when tick_nohz_stop_sched_tick() is called from the idle loop.
   	 * State will be updated to busy during the first busy tick after
   	 * exiting idle.
   	 */
  	set_cpu_sd_state_idle();

  	local_irq_disable();

  	ts = this_cpu_ptr(&tick_cpu_sched);

  	ts->inidle = 1;

  	__tick_nohz_idle_enter(ts);

  
  	local_irq_enable();

  }
  
  /**
   * tick_nohz_irq_exit - update next tick event from interrupt exit
   *
   * When an interrupt fires while we are idle and it doesn't cause
   * a reschedule, it may still add, modify or delete a timer, enqueue
   * an RCU callback, etc...
   * So we need to re-calculate and reprogram the next tick event.
   */
  void tick_nohz_irq_exit(void)
  {

  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

  	if (ts->inidle)

  		__tick_nohz_idle_enter(ts);

  	else

  		tick_nohz_full_stop_tick(ts);

  }
  
  /**

   * 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 = this_cpu_ptr(&tick_cpu_sched);

  
  	return ts->sleep_length;
  }

  static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
  {
  	hrtimer_cancel(&ts->sched_timer);

  	hrtimer_set_expires(&ts->sched_timer, ts->last_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_expires(&ts->sched_timer,

  					      HRTIMER_MODE_ABS_PINNED);

  			/* Check, if the timer was already in the past */
  			if (hrtimer_active(&ts->sched_timer))
  				break;
  		} else {

  			if (!tick_program_event(
  				hrtimer_get_expires(&ts->sched_timer), 0))

  				break;
  		}

  		/* Reread time and update jiffies */

  		now = ktime_get();

  		tick_do_update_jiffies64(now);

  	}
  }

  static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)

  {

  	/* Update jiffies first */

  	tick_do_update_jiffies64(now);

  	update_cpu_load_nohz();

  	calc_load_exit_idle();

  	touch_softlockup_watchdog();
  	/*
  	 * Cancel the scheduled timer and restore the tick
  	 */
  	ts->tick_stopped  = 0;
  	ts->idle_exittime = now;
  
  	tick_nohz_restart(ts, now);
  }
  
  static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
  {

  #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE

  	unsigned long ticks;

  
  	if (vtime_accounting_enabled())
  		return;

  	/*
  	 * 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)
  		account_idle_ticks(ticks);
  #endif

  }

  /**

   * tick_nohz_idle_exit - restart the idle tick from the idle task

   *
   * Restart the idle tick when the CPU is woken up from idle

   * This also exit the RCU extended quiescent state. The CPU
   * can use RCU again after this function is called.

   */

  void tick_nohz_idle_exit(void)

  {

  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

  	ktime_t now;

  	local_irq_disable();

  	WARN_ON_ONCE(!ts->inidle);
  
  	ts->inidle = 0;
  
  	if (ts->idle_active || ts->tick_stopped)

  		now = ktime_get();
  
  	if (ts->idle_active)

  		tick_nohz_stop_idle(ts, now);

  	if (ts->tick_stopped) {

  		tick_nohz_restart_sched_tick(ts, now);

  		tick_nohz_account_idle_ticks(ts);

  	}

  	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(hrtimer_get_expires(&ts->sched_timer), 0);

  }
  
  /*
   * The nohz low res interrupt handler
   */
  static void tick_nohz_handler(struct clock_event_device *dev)
  {

  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

  	struct pt_regs *regs = get_irq_regs();
  	ktime_t now = ktime_get();
  
  	dev->next_event.tv64 = KTIME_MAX;

  	tick_sched_do_timer(now);

  	tick_sched_handle(ts, regs);

  	/* No need to reprogram if we are running tickless  */
  	if (unlikely(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 = this_cpu_ptr(&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;
  	}

  	tick_nohz_active = 1;

  	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 (;;) {

  		hrtimer_set_expires(&ts->sched_timer, next);

  		if (!tick_program_event(next, 0))
  			break;
  		next = ktime_add(next, tick_period);
  	}
  	local_irq_enable();

  }

  /*
   * When NOHZ is enabled and the tick is stopped, we need to kick the
   * tick timer from irq_enter() so that the jiffies update is kept
   * alive during long running softirqs. That's ugly as hell, but
   * correctness is key even if we need to fix the offending softirq in
   * the first place.
   *
   * Note, this is different to tick_nohz_restart. We just kick the
   * timer and do not touch the other magic bits which need to be done
   * when idle is left.
   */

  static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)

  {

  #if 0
  	/* Switch back to 2.6.27 behaviour */

  	ktime_t delta;

  	/*
  	 * Do not touch the tick device, when the next expiry is either
  	 * already reached or less/equal than the tick period.
  	 */

  	delta =	ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);

  	if (delta.tv64 <= tick_period.tv64)
  		return;
  
  	tick_nohz_restart(ts, now);

  #endif

  }

  static inline void tick_nohz_irq_enter(void)

  {

  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

  	ktime_t now;
  
  	if (!ts->idle_active && !ts->tick_stopped)
  		return;
  	now = ktime_get();
  	if (ts->idle_active)

  		tick_nohz_stop_idle(ts, now);

  	if (ts->tick_stopped) {
  		tick_nohz_update_jiffies(now);

  		tick_nohz_kick_tick(ts, now);

  	}
  }

  #else
  
  static inline void tick_nohz_switch_to_nohz(void) { }

  static inline void tick_nohz_irq_enter(void) { }

  #endif /* CONFIG_NO_HZ_COMMON */

  
  /*

   * Called from irq_enter to notify about the possible interruption of idle()
   */

  void tick_irq_enter(void)

  {

  	tick_check_oneshot_broadcast_this_cpu();

  	tick_nohz_irq_enter();

  }
  
  /*

   * 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.

   */
  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();

  	tick_sched_do_timer(now);

  
  	/*
  	 * Do not call, when we are not in irq context and have
  	 * no valid regs pointer
  	 */

  	if (regs)
  		tick_sched_handle(ts, regs);

  	/* No need to reprogram if we are in idle or full dynticks mode */
  	if (unlikely(ts->tick_stopped))
  		return HRTIMER_NORESTART;

  	hrtimer_forward(timer, now, tick_period);
  
  	return HRTIMER_RESTART;
  }

  static int sched_skew_tick;

  static int __init skew_tick(char *str)
  {
  	get_option(&str, &sched_skew_tick);
  
  	return 0;
  }
  early_param("skew_tick", skew_tick);

  /**
   * tick_setup_sched_timer - setup the tick emulation timer
   */
  void tick_setup_sched_timer(void)
  {

  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

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

  	/* Get the next period (per cpu) */

  	hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());

  	/* Offset the tick to avert jiffies_lock contention. */

  	if (sched_skew_tick) {
  		u64 offset = ktime_to_ns(tick_period) >> 1;
  		do_div(offset, num_possible_cpus());
  		offset *= smp_processor_id();
  		hrtimer_add_expires_ns(&ts->sched_timer, offset);
  	}

  	for (;;) {
  		hrtimer_forward(&ts->sched_timer, now, tick_period);

  		hrtimer_start_expires(&ts->sched_timer,
  				      HRTIMER_MODE_ABS_PINNED);

  		/* Check, if the timer was already in the past */
  		if (hrtimer_active(&ts->sched_timer))
  			break;
  		now = ktime_get();
  	}

  #ifdef CONFIG_NO_HZ_COMMON

  	if (tick_nohz_enabled) {

  		ts->nohz_mode = NOHZ_MODE_HIGHRES;

  		tick_nohz_active = 1;
  	}

  #endif
  }

  #endif /* HIGH_RES_TIMERS */

  #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS

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

  # ifdef CONFIG_HIGH_RES_TIMERS

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

  # endif

  	memset(ts, 0, sizeof(*ts));

  }

  #endif

  
  /**
   * 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 = this_cpu_ptr(&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 = this_cpu_ptr(&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;
  }