/*
   * tracing clocks
   *
   *  Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   *
   * Implements 3 trace clock variants, with differing scalability/precision
   * tradeoffs:
   *
   *  -   local: CPU-local trace clock
   *  -  medium: scalable global clock with some jitter
   *  -  global: globally monotonic, serialized clock
   *
   * Tracer plugins will chose a default from these clocks.
   */
  #include <linux/spinlock.h>

  #include <linux/irqflags.h>

  #include <linux/hardirq.h>
  #include <linux/module.h>
  #include <linux/percpu.h>
  #include <linux/sched.h>

  #include <linux/sched/clock.h>

  #include <linux/ktime.h>

  #include <linux/trace_clock.h>

  
  /*
   * trace_clock_local(): the simplest and least coherent tracing clock.
   *
   * Useful for tracing that does not cross to other CPUs nor
   * does it go through idle events.
   */
  u64 notrace trace_clock_local(void)
  {

  	u64 clock;

  	/*
  	 * sched_clock() is an architecture implemented, fast, scalable,
  	 * lockless clock. It is not guaranteed to be coherent across
  	 * CPUs, nor across CPU idle events.
  	 */

  	preempt_disable_notrace();

  	clock = sched_clock();

  	preempt_enable_notrace();

  
  	return clock;

  }

  EXPORT_SYMBOL_GPL(trace_clock_local);

  
  /*

   * trace_clock(): 'between' trace clock. Not completely serialized,

   * but not completely incorrect when crossing CPUs either.
   *
   * This is based on cpu_clock(), which will allow at most ~1 jiffy of
   * jitter between CPUs. So it's a pretty scalable clock, but there
   * can be offsets in the trace data.
   */
  u64 notrace trace_clock(void)
  {

  	return local_clock();

  }

  EXPORT_SYMBOL_GPL(trace_clock);

  /*
   * trace_jiffy_clock(): Simply use jiffies as a clock counter.

   * Note that this use of jiffies_64 is not completely safe on
   * 32-bit systems. But the window is tiny, and the effect if
   * we are affected is that we will have an obviously bogus
   * timestamp on a trace event - i.e. not life threatening.

   */
  u64 notrace trace_clock_jiffies(void)
  {

  	return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);

  }

  EXPORT_SYMBOL_GPL(trace_clock_jiffies);

  
  /*
   * trace_clock_global(): special globally coherent trace clock
   *
   * It has higher overhead than the other trace clocks but is still
   * an order of magnitude faster than GTOD derived hardware clocks.
   *
   * Used by plugins that need globally coherent timestamps.
   */

  /* keep prev_time and lock in the same cacheline. */
  static struct {
  	u64 prev_time;

  	arch_spinlock_t lock;

  } trace_clock_struct ____cacheline_aligned_in_smp =
  	{

  		.lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,

  	};

  
  u64 notrace trace_clock_global(void)
  {
  	unsigned long flags;
  	int this_cpu;
  	u64 now;

  	local_irq_save(flags);

  
  	this_cpu = raw_smp_processor_id();

  	now = sched_clock_cpu(this_cpu);

  	/*
  	 * If in an NMI context then dont risk lockups and return the
  	 * cpu_clock() time:
  	 */
  	if (unlikely(in_nmi()))
  		goto out;

  	arch_spin_lock(&trace_clock_struct.lock);

  
  	/*
  	 * TODO: if this happens often then maybe we should reset

  	 * my_scd->clock to prev_time+1, to make sure

  	 * we start ticking with the local clock from now on?
  	 */

  	if ((s64)(now - trace_clock_struct.prev_time) < 0)
  		now = trace_clock_struct.prev_time + 1;

  	trace_clock_struct.prev_time = now;

  	arch_spin_unlock(&trace_clock_struct.lock);

  
   out:

  	local_irq_restore(flags);

  
  	return now;
  }

  EXPORT_SYMBOL_GPL(trace_clock_global);

  
  static atomic64_t trace_counter;
  
  /*
   * trace_clock_counter(): simply an atomic counter.
   * Use the trace_counter "counter" for cases where you do not care
   * about timings, but are interested in strict ordering.
   */
  u64 notrace trace_clock_counter(void)
  {
  	return atomic64_add_return(1, &trace_counter);
  }