/*
   * 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

   *  - 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.

   *
   * 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 2 jiffies difference).

   */

  #include <linux/spinlock.h>

  #include <linux/hardirq.h>

  #include <linux/module.h>

  #include <linux/percpu.h>
  #include <linux/ktime.h>
  #include <linux/sched.h>

  /*
   * 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 - INITIAL_JIFFIES)
  					* (NSEC_PER_SEC / HZ);

  }

  static __read_mostly int sched_clock_running;

  #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

  __read_mostly int sched_clock_stable;

  
  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;

  	u64			tick_raw;
  	u64			tick_gtod;
  	u64			clock;
  };
  
  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);
  }
  
  void sched_clock_init(void)
  {
  	u64 ktime_now = ktime_to_ns(ktime_get());

  	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_raw = 0;

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

  
  	sched_clock_running = 1;

  }
  
  /*

   * min, max except they take wrapping into account

   */
  
  static inline u64 wrap_min(u64 x, u64 y)
  {
  	return (s64)(x - y) < 0 ? x : y;
  }
  
  static inline u64 wrap_max(u64 x, u64 y)
  {
  	return (s64)(x - y) > 0 ? x : y;
  }
  
  /*

   * update the percpu scd from the raw @now value
   *
   *  - filter out backward motion

   *  - use the GTOD tick value to create a window to filter crazy TSC values

   */

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

  {

  	s64 delta = now - scd->tick_raw;

  	u64 clock, min_clock, max_clock;

  	if (unlikely(delta < 0))
  		delta = 0;

  	/*
  	 * scd->clock = clamp(scd->tick_gtod + delta,

  	 *		      max(scd->tick_gtod, scd->clock),
  	 *		      scd->tick_gtod + TICK_NSEC);

  	 */

  	clock = scd->tick_gtod + delta;
  	min_clock = wrap_max(scd->tick_gtod, scd->clock);

  	max_clock = wrap_max(scd->clock, scd->tick_gtod + TICK_NSEC);

  	clock = wrap_max(clock, min_clock);
  	clock = wrap_min(clock, max_clock);

  	scd->clock = clock;

  	return scd->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)
  {

  	u64 now, clock, this_clock, remote_clock;

  	struct sched_clock_data *scd;

  	if (sched_clock_stable)
  		return sched_clock();

  	scd = cpu_sdc(cpu);

  	/*
  	 * Normally this is not called in NMI context - but if it is,
  	 * trying to do any locking here is totally lethal.
  	 */
  	if (unlikely(in_nmi()))
  		return scd->clock;

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

  	WARN_ON_ONCE(!irqs_disabled());
  	now = sched_clock();
  
  	if (cpu != raw_smp_processor_id()) {

  		struct sched_clock_data *my_scd = this_scd();
  
  		lock_double_clock(scd, my_scd);

  		this_clock = __update_sched_clock(my_scd, now);
  		remote_clock = scd->clock;
  
  		/*
  		 * Use the opportunity that we have both locks
  		 * taken to couple the two clocks: we take the
  		 * larger time as the latest time for both
  		 * runqueues. (this creates monotonic movement)
  		 */

  		if (likely((s64)(remote_clock - this_clock) < 0)) {

  			clock = this_clock;
  			scd->clock = clock;
  		} else {
  			/*
  			 * Should be rare, but possible:
  			 */
  			clock = remote_clock;
  			my_scd->clock = remote_clock;
  		}

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

  		clock = __update_sched_clock(scd, now);

  	}

  	__raw_spin_unlock(&scd->lock);

  	return clock;
  }
  
  void sched_clock_tick(void)
  {

  	struct sched_clock_data *scd;

  	u64 now, now_gtod;

  	if (sched_clock_stable)
  		return;

  	if (unlikely(!sched_clock_running))
  		return;

  	WARN_ON_ONCE(!irqs_disabled());

  	scd = this_scd();

  	now_gtod = ktime_to_ns(ktime_get());

  	now = sched_clock();

  
  	__raw_spin_lock(&scd->lock);

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

  	__update_sched_clock(scd, now);

  	__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)
  {

  	if (timekeeping_suspended)
  		return;

  	sched_clock_tick();

  	touch_softlockup_watchdog();
  }
  EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

  #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
  
  void sched_clock_init(void)
  {
  	sched_clock_running = 1;
  }
  
  u64 sched_clock_cpu(int cpu)
  {
  	if (unlikely(!sched_clock_running))
  		return 0;
  
  	return sched_clock();
  }

  #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

  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);