/*
   * sched_clock for unstable cpu clocks
   *
   *  Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   *

   *  Updates and enhancements:
   *    Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
   *

   * Based on code by:
   *   Ingo Molnar <mingo@redhat.com>
   *   Guillaume Chazarain <guichaz@gmail.com>
   *
   * Create a semi stable clock from a mixture of other events, including:
   *  - gtod
   *  - jiffies
   *  - sched_clock()
   *  - explicit idle events
   *
   * We use gtod as base and the unstable clock deltas. The deltas are filtered,
   * making it monotonic and keeping it within an expected window.  This window
   * is set up using jiffies.
   *
   * Furthermore, explicit sleep and wakeup hooks allow us to account for time
   * that is otherwise invisible (TSC gets stopped).
   *
   * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
   * consistent between cpus (never more than 1 jiffies difference).
   */
  #include <linux/sched.h>
  #include <linux/percpu.h>
  #include <linux/spinlock.h>
  #include <linux/ktime.h>
  #include <linux/module.h>
  
  
  #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

  #define MULTI_SHIFT 15
  /* Max is double, Min is 1/2 */
  #define MAX_MULTI (2LL << MULTI_SHIFT)
  #define MIN_MULTI (1LL << (MULTI_SHIFT-1))

  struct sched_clock_data {
  	/*
  	 * Raw spinlock - this is a special case: this might be called
  	 * from within instrumentation code so we dont want to do any
  	 * instrumentation ourselves.
  	 */
  	raw_spinlock_t		lock;

  	unsigned long		tick_jiffies;

  	u64			prev_raw;
  	u64			tick_raw;
  	u64			tick_gtod;
  	u64			clock;

  	s64			multi;

  #ifdef CONFIG_NO_HZ
  	int			check_max;
  #endif

  };
  
  static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
  
  static inline struct sched_clock_data *this_scd(void)
  {
  	return &__get_cpu_var(sched_clock_data);
  }
  
  static inline struct sched_clock_data *cpu_sdc(int cpu)
  {
  	return &per_cpu(sched_clock_data, cpu);
  }

  static __read_mostly int sched_clock_running;

  void sched_clock_init(void)
  {
  	u64 ktime_now = ktime_to_ns(ktime_get());

  	unsigned long now_jiffies = jiffies;

  	int cpu;
  
  	for_each_possible_cpu(cpu) {
  		struct sched_clock_data *scd = cpu_sdc(cpu);
  
  		scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;

  		scd->tick_jiffies = now_jiffies;

  		scd->prev_raw = 0;
  		scd->tick_raw = 0;

  		scd->tick_gtod = ktime_now;
  		scd->clock = ktime_now;

  		scd->multi = 1 << MULTI_SHIFT;

  #ifdef CONFIG_NO_HZ
  		scd->check_max = 1;
  #endif

  	}

  
  	sched_clock_running = 1;

  }

  #ifdef CONFIG_NO_HZ
  /*
   * The dynamic ticks makes the delta jiffies inaccurate. This
   * prevents us from checking the maximum time update.
   * Disable the maximum check during stopped ticks.
   */
  void sched_clock_tick_stop(int cpu)
  {
  	struct sched_clock_data *scd = cpu_sdc(cpu);
  
  	scd->check_max = 0;
  }
  
  void sched_clock_tick_start(int cpu)
  {
  	struct sched_clock_data *scd = cpu_sdc(cpu);
  
  	scd->check_max = 1;
  }
  
  static int check_max(struct sched_clock_data *scd)
  {
  	return scd->check_max;
  }
  #else
  static int check_max(struct sched_clock_data *scd)
  {
  	return 1;
  }
  #endif /* CONFIG_NO_HZ */

  /*
   * update the percpu scd from the raw @now value
   *
   *  - filter out backward motion
   *  - use jiffies to generate a min,max window to clip the raw values
   */

  static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *time)

  {
  	unsigned long now_jiffies = jiffies;

  	long delta_jiffies = now_jiffies - scd->tick_jiffies;

  	u64 clock = scd->clock;
  	u64 min_clock, max_clock;
  	s64 delta = now - scd->prev_raw;
  
  	WARN_ON_ONCE(!irqs_disabled());

  	/*
  	 * At schedule tick the clock can be just under the gtod. We don't
  	 * want to push it too prematurely.
  	 */
  	min_clock = scd->tick_gtod + (delta_jiffies * TICK_NSEC);
  	if (min_clock > TICK_NSEC)
  		min_clock -= TICK_NSEC / 2;

  
  	if (unlikely(delta < 0)) {
  		clock++;
  		goto out;
  	}

  	/*
  	 * The clock must stay within a jiffie of the gtod.
  	 * But since we may be at the start of a jiffy or the end of one
  	 * we add another jiffy buffer.
  	 */
  	max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;

  	delta *= scd->multi;
  	delta >>= MULTI_SHIFT;

  	if (unlikely(clock + delta > max_clock) && check_max(scd)) {

  		if (clock < max_clock)
  			clock = max_clock;
  		else
  			clock++;
  	} else {
  		clock += delta;
  	}
  
   out:
  	if (unlikely(clock < min_clock))
  		clock = min_clock;

  	if (time)
  		*time = clock;
  	else {
  		scd->prev_raw = now;
  		scd->clock = clock;
  	}

  }
  
  static void lock_double_clock(struct sched_clock_data *data1,
  				struct sched_clock_data *data2)
  {
  	if (data1 < data2) {
  		__raw_spin_lock(&data1->lock);
  		__raw_spin_lock(&data2->lock);
  	} else {
  		__raw_spin_lock(&data2->lock);
  		__raw_spin_lock(&data1->lock);
  	}
  }
  
  u64 sched_clock_cpu(int cpu)
  {
  	struct sched_clock_data *scd = cpu_sdc(cpu);
  	u64 now, clock;

  	if (unlikely(!sched_clock_running))
  		return 0ull;

  	WARN_ON_ONCE(!irqs_disabled());
  	now = sched_clock();
  
  	if (cpu != raw_smp_processor_id()) {
  		/*
  		 * in order to update a remote cpu's clock based on our
  		 * unstable raw time rebase it against:
  		 *   tick_raw		(offset between raw counters)
  		 *   tick_gotd          (tick offset between cpus)
  		 */
  		struct sched_clock_data *my_scd = this_scd();
  
  		lock_double_clock(scd, my_scd);
  
  		now -= my_scd->tick_raw;
  		now += scd->tick_raw;

  		now += my_scd->tick_gtod;
  		now -= scd->tick_gtod;

  
  		__raw_spin_unlock(&my_scd->lock);

  
  		__update_sched_clock(scd, now, &clock);
  
  		__raw_spin_unlock(&scd->lock);

  	} else {
  		__raw_spin_lock(&scd->lock);

  		__update_sched_clock(scd, now, NULL);
  		clock = scd->clock;
  		__raw_spin_unlock(&scd->lock);

  	}

  	return clock;
  }
  
  void sched_clock_tick(void)
  {
  	struct sched_clock_data *scd = this_scd();

  	unsigned long now_jiffies = jiffies;

  	s64 mult, delta_gtod, delta_raw;

  	u64 now, now_gtod;

  	if (unlikely(!sched_clock_running))
  		return;

  	WARN_ON_ONCE(!irqs_disabled());

  	now_gtod = ktime_to_ns(ktime_get());

  	now = sched_clock();

  
  	__raw_spin_lock(&scd->lock);

  	__update_sched_clock(scd, now, NULL);

  	/*
  	 * update tick_gtod after __update_sched_clock() because that will
  	 * already observe 1 new jiffy; adding a new tick_gtod to that would
  	 * increase the clock 2 jiffies.
  	 */

  	delta_gtod = now_gtod - scd->tick_gtod;
  	delta_raw = now - scd->tick_raw;
  
  	if ((long)delta_raw > 0) {
  		mult = delta_gtod << MULTI_SHIFT;
  		do_div(mult, delta_raw);
  		scd->multi = mult;
  		if (scd->multi > MAX_MULTI)
  			scd->multi = MAX_MULTI;
  		else if (scd->multi < MIN_MULTI)
  			scd->multi = MIN_MULTI;
  	} else
  		scd->multi = 1 << MULTI_SHIFT;

  	scd->tick_raw = now;
  	scd->tick_gtod = now_gtod;

  	scd->tick_jiffies = now_jiffies;

  	__raw_spin_unlock(&scd->lock);
  }
  
  /*
   * We are going deep-idle (irqs are disabled):
   */
  void sched_clock_idle_sleep_event(void)
  {
  	sched_clock_cpu(smp_processor_id());
  }
  EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
  
  /*
   * We just idled delta nanoseconds (called with irqs disabled):
   */
  void sched_clock_idle_wakeup_event(u64 delta_ns)
  {
  	struct sched_clock_data *scd = this_scd();
  	u64 now = sched_clock();
  
  	/*
  	 * Override the previous timestamp and ignore all
  	 * sched_clock() deltas that occured while we idled,
  	 * and use the PM-provided delta_ns to advance the
  	 * rq clock:
  	 */
  	__raw_spin_lock(&scd->lock);
  	scd->prev_raw = now;
  	scd->clock += delta_ns;

  	scd->multi = 1 << MULTI_SHIFT;

  	__raw_spin_unlock(&scd->lock);
  
  	touch_softlockup_watchdog();
  }
  EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
  
  #endif
  
  /*
   * Scheduler clock - returns current time in nanosec units.
   * This is default implementation.
   * Architectures and sub-architectures can override this.
   */
  unsigned long long __attribute__((weak)) sched_clock(void)
  {
  	return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
  }

  
  unsigned long long cpu_clock(int cpu)
  {
  	unsigned long long clock;
  	unsigned long flags;

  	local_irq_save(flags);

  	clock = sched_clock_cpu(cpu);

  	local_irq_restore(flags);

  
  	return clock;
  }

  EXPORT_SYMBOL_GPL(cpu_clock);