kernel/sched/clock.c - third_party/linux - Git at Google

 /*
  * sched_clock() for unstable CPU clocks
  *
  *  Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra
  *
  *  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>
  *
  *
  * What this file implements:
  *
  * cpu_clock(i) provides a fast (execution time) high resolution
  * clock with bounded drift between CPUs. The value of cpu_clock(i)
  * is monotonic for constant i. The timestamp returned is in nanoseconds.
  *
  * ######################### BIG FAT WARNING ##########################
  * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
  * # go backwards !!                                                  #
  * ####################################################################
  *
  * There is no strict promise about the base, although it tends to start
  * at 0 on boot (but people really shouldn't rely on that).
  *
  * cpu_clock(i)       -- can be used from any context, including NMI.
  * local_clock()      -- is cpu_clock() on the current CPU.
  *
  * sched_clock_cpu(i)
  *
  * How it is implemented:
  *
  * The implementation either uses sched_clock() when
  * !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
  * sched_clock() is assumed to provide these properties (mostly it means
  * the architecture provides a globally synchronized highres time source).
  *
  * Otherwise it tries to create a semi stable clock from a mixture of other
  * clocks, including:
  *
  *  - GTOD (clock monotomic)
  *  - sched_clock()
  *  - explicit idle events
  *
  * We use GTOD as base and use sched_clock() deltas to improve resolution. The
  * deltas are filtered to provide monotonicity 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).
  *
  */
 #include "sched.h"

 /*
  * Scheduler clock - returns current time in nanosec units.
  * This is default implementation.
  * Architectures and sub-architectures can override this.
  */
 unsigned long long __weak sched_clock(void)
 {
 	return (unsigned long long)(jiffies - INITIAL_JIFFIES)
 					* (NSEC_PER_SEC / HZ);
 }
 EXPORT_SYMBOL_GPL(sched_clock);

 __read_mostly int sched_clock_running;

 void sched_clock_init(void)
 {
 	sched_clock_running = 1;
 }

 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
 /*
  * We must start with !__sched_clock_stable because the unstable -> stable
  * transition is accurate, while the stable -> unstable transition is not.
  *
  * Similarly we start with __sched_clock_stable_early, thereby assuming we
  * will become stable, such that there's only a single 1 -> 0 transition.
  */
 static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);
 static int __sched_clock_stable_early = 1;

 /*
  * We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset
  */
 __read_mostly u64 __sched_clock_offset;
 static __read_mostly u64 __gtod_offset;

 struct sched_clock_data {
 	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 this_cpu_ptr(&sched_clock_data);
 }

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

 int sched_clock_stable(void)
 {
 	return static_branch_likely(&__sched_clock_stable);
 }

 static void __scd_stamp(struct sched_clock_data *scd)
 {
 	scd->tick_gtod = ktime_get_ns();
 	scd->tick_raw = sched_clock();
 }

 static void __set_sched_clock_stable(void)
 {
 	struct sched_clock_data *scd;

 	/*
 	 * Since we're still unstable and the tick is already running, we have
 	 * to disable IRQs in order to get a consistent scd->tick* reading.
 	 */
 	local_irq_disable();
 	scd = this_scd();
 	/*
 	 * Attempt to make the (initial) unstable->stable transition continuous.
 	 */
 	__sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw);
 	local_irq_enable();

 	printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n",
 			scd->tick_gtod, __gtod_offset,
 			scd->tick_raw,  __sched_clock_offset);

 	static_branch_enable(&__sched_clock_stable);
 	tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
 }

 /*
  * If we ever get here, we're screwed, because we found out -- typically after
  * the fact -- that TSC wasn't good. This means all our clocksources (including
  * ktime) could have reported wrong values.
  *
  * What we do here is an attempt to fix up and continue sort of where we left
  * off in a coherent manner.
  *
  * The only way to fully avoid random clock jumps is to boot with:
  * "tsc=unstable".
  */
 static void __sched_clock_work(struct work_struct *work)
 {
 	struct sched_clock_data *scd;
 	int cpu;

 	/* take a current timestamp and set 'now' */
 	preempt_disable();
 	scd = this_scd();
 	__scd_stamp(scd);
 	scd->clock = scd->tick_gtod + __gtod_offset;
 	preempt_enable();

 	/* clone to all CPUs */
 	for_each_possible_cpu(cpu)
 		per_cpu(sched_clock_data, cpu) = *scd;

 	printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n");
 	printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
 			scd->tick_gtod, __gtod_offset,
 			scd->tick_raw,  __sched_clock_offset);

 	static_branch_disable(&__sched_clock_stable);
 }

 static DECLARE_WORK(sched_clock_work, __sched_clock_work);

 static void __clear_sched_clock_stable(void)
 {
 	if (!sched_clock_stable())
 		return;

 	tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
 	schedule_work(&sched_clock_work);
 }

 void clear_sched_clock_stable(void)
 {
 	__sched_clock_stable_early = 0;

 	smp_mb(); /* matches sched_clock_init_late() */

 	if (sched_clock_running == 2)
 		__clear_sched_clock_stable();
 }

 /*
  * We run this as late_initcall() such that it runs after all built-in drivers,
  * notably: acpi_processor and intel_idle, which can mark the TSC as unstable.
  */
 static int __init sched_clock_init_late(void)
 {
 	sched_clock_running = 2;
 	/*
 	 * Ensure that it is impossible to not do a static_key update.
 	 *
 	 * Either {set,clear}_sched_clock_stable() must see sched_clock_running
 	 * and do the update, or we must see their __sched_clock_stable_early
 	 * and do the update, or both.
 	 */
 	smp_mb(); /* matches {set,clear}_sched_clock_stable() */

 	if (__sched_clock_stable_early)
 		__set_sched_clock_stable();

 	return 0;
 }
 late_initcall(sched_clock_init_late);

 /*
  * 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 sched_clock_local(struct sched_clock_data *scd)
 {
 	u64 now, clock, old_clock, min_clock, max_clock, gtod;
 	s64 delta;

 again:
 	now = sched_clock();
 	delta = now - scd->tick_raw;
 	if (unlikely(delta < 0))
 		delta = 0;

 	old_clock = scd->clock;

 	/*
 	 * scd->clock = clamp(scd->tick_gtod + delta,
 	 *		      max(scd->tick_gtod, scd->clock),
 	 *		      scd->tick_gtod + TICK_NSEC);
 	 */

 	gtod = scd->tick_gtod + __gtod_offset;
 	clock = gtod + delta;
 	min_clock = wrap_max(gtod, old_clock);
 	max_clock = wrap_max(old_clock, gtod + TICK_NSEC);

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

 	if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
 		goto again;

 	return clock;
 }

 static u64 sched_clock_remote(struct sched_clock_data *scd)
 {
 	struct sched_clock_data *my_scd = this_scd();
 	u64 this_clock, remote_clock;
 	u64 *ptr, old_val, val;

 #if BITS_PER_LONG != 64
 again:
 	/*
 	 * Careful here: The local and the remote clock values need to
 	 * be read out atomic as we need to compare the values and
 	 * then update either the local or the remote side. So the
 	 * cmpxchg64 below only protects one readout.
 	 *
 	 * We must reread via sched_clock_local() in the retry case on
 	 * 32-bit kernels as an NMI could use sched_clock_local() via the
 	 * tracer and hit between the readout of
 	 * the low 32-bit and the high 32-bit portion.
 	 */
 	this_clock = sched_clock_local(my_scd);
 	/*
 	 * We must enforce atomic readout on 32-bit, otherwise the
 	 * update on the remote CPU can hit inbetween the readout of
 	 * the low 32-bit and the high 32-bit portion.
 	 */
 	remote_clock = cmpxchg64(&scd->clock, 0, 0);
 #else
 	/*
 	 * On 64-bit kernels the read of [my]scd->clock is atomic versus the
 	 * update, so we can avoid the above 32-bit dance.
 	 */
 	sched_clock_local(my_scd);
 again:
 	this_clock = my_scd->clock;
 	remote_clock = scd->clock;
 #endif

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

 	if (cmpxchg64(ptr, old_val, val) != old_val)
 		goto again;

 	return val;
 }

 /*
  * Similar to cpu_clock(), but requires local IRQs to be disabled.
  *
  * See cpu_clock().
  */
 u64 sched_clock_cpu(int cpu)
 {
 	struct sched_clock_data *scd;
 	u64 clock;

 	if (sched_clock_stable())
 		return sched_clock() + __sched_clock_offset;

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

 	preempt_disable_notrace();
 	scd = cpu_sdc(cpu);

 	if (cpu != smp_processor_id())
 		clock = sched_clock_remote(scd);
 	else
 		clock = sched_clock_local(scd);
 	preempt_enable_notrace();

 	return clock;
 }
 EXPORT_SYMBOL_GPL(sched_clock_cpu);

 void sched_clock_tick(void)
 {
 	struct sched_clock_data *scd;

 	if (sched_clock_stable())
 		return;

 	if (unlikely(!sched_clock_running))
 		return;

 	lockdep_assert_irqs_disabled();

 	scd = this_scd();
 	__scd_stamp(scd);
 	sched_clock_local(scd);
 }

 void sched_clock_tick_stable(void)
 {
 	u64 gtod, clock;

 	if (!sched_clock_stable())
 		return;

 	/*
 	 * Called under watchdog_lock.
 	 *
 	 * The watchdog just found this TSC to (still) be stable, so now is a
 	 * good moment to update our __gtod_offset. Because once we find the
 	 * TSC to be unstable, any computation will be computing crap.
 	 */
 	local_irq_disable();
 	gtod = ktime_get_ns();
 	clock = sched_clock();
 	__gtod_offset = (clock + __sched_clock_offset) - gtod;
 	local_irq_enable();
 }

 /*
  * 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; resync with ktime.
  */
 void sched_clock_idle_wakeup_event(void)
 {
 	unsigned long flags;

 	if (sched_clock_stable())
 		return;

 	if (unlikely(timekeeping_suspended))
 		return;

 	local_irq_save(flags);
 	sched_clock_tick();
 	local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

 #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

 u64 sched_clock_cpu(int cpu)
 {
 	if (unlikely(!sched_clock_running))
 		return 0;

 	return sched_clock();
 }

 #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

 /*
  * Running clock - returns the time that has elapsed while a guest has been
  * running.
  * On a guest this value should be local_clock minus the time the guest was
  * suspended by the hypervisor (for any reason).
  * On bare metal this function should return the same as local_clock.
  * Architectures and sub-architectures can override this.
  */
 u64 __weak running_clock(void)
 {
 	return local_clock();
 }
	/*
	* sched_clock() for unstable CPU clocks
	*
	* Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra
	*
	* 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>
	*
	*
	* What this file implements:
	*
	* cpu_clock(i) provides a fast (execution time) high resolution
	* clock with bounded drift between CPUs. The value of cpu_clock(i)
	* is monotonic for constant i. The timestamp returned is in nanoseconds.
	*
	* ######################### BIG FAT WARNING ##########################
	* # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
	* # go backwards !! #
	* ####################################################################
	*
	* There is no strict promise about the base, although it tends to start
	* at 0 on boot (but people really shouldn't rely on that).
	*
	* cpu_clock(i) -- can be used from any context, including NMI.
	* local_clock() -- is cpu_clock() on the current CPU.
	*
	* sched_clock_cpu(i)
	*
	* How it is implemented:
	*
	* The implementation either uses sched_clock() when
	* !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
	* sched_clock() is assumed to provide these properties (mostly it means
	* the architecture provides a globally synchronized highres time source).
	*
	* Otherwise it tries to create a semi stable clock from a mixture of other
	* clocks, including:
	*
	* - GTOD (clock monotomic)
	* - sched_clock()
	* - explicit idle events
	*
	* We use GTOD as base and use sched_clock() deltas to improve resolution. The
	* deltas are filtered to provide monotonicity 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).
	*
	*/
	#include "sched.h"

	/*
	* Scheduler clock - returns current time in nanosec units.
	* This is default implementation.
	* Architectures and sub-architectures can override this.
	*/
	unsigned long long __weak sched_clock(void)
	{
	return (unsigned long long)(jiffies - INITIAL_JIFFIES)
	* (NSEC_PER_SEC / HZ);
	}
	EXPORT_SYMBOL_GPL(sched_clock);

	__read_mostly int sched_clock_running;

	void sched_clock_init(void)
	{
	sched_clock_running = 1;
	}

	#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
	/*
	* We must start with !__sched_clock_stable because the unstable -> stable
	* transition is accurate, while the stable -> unstable transition is not.
	*
	* Similarly we start with __sched_clock_stable_early, thereby assuming we
	* will become stable, such that there's only a single 1 -> 0 transition.
	*/
	static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);
	static int __sched_clock_stable_early = 1;

	/*
	* We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset
	*/
	__read_mostly u64 __sched_clock_offset;
	static __read_mostly u64 __gtod_offset;

	struct sched_clock_data {
	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 this_cpu_ptr(&sched_clock_data);
	}

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

	int sched_clock_stable(void)
	{
	return static_branch_likely(&__sched_clock_stable);
	}

	static void __scd_stamp(struct sched_clock_data *scd)
	{
	scd->tick_gtod = ktime_get_ns();
	scd->tick_raw = sched_clock();
	}

	static void __set_sched_clock_stable(void)
	{
	struct sched_clock_data *scd;

	/*
	* Since we're still unstable and the tick is already running, we have
	* to disable IRQs in order to get a consistent scd->tick* reading.
	*/
	local_irq_disable();
	scd = this_scd();
	/*
	* Attempt to make the (initial) unstable->stable transition continuous.
	*/
	__sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw);
	local_irq_enable();

	printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n",
	scd->tick_gtod, __gtod_offset,
	scd->tick_raw, __sched_clock_offset);

	static_branch_enable(&__sched_clock_stable);
	tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
	}

	/*
	* If we ever get here, we're screwed, because we found out -- typically after
	* the fact -- that TSC wasn't good. This means all our clocksources (including
	* ktime) could have reported wrong values.
	*
	* What we do here is an attempt to fix up and continue sort of where we left
	* off in a coherent manner.
	*
	* The only way to fully avoid random clock jumps is to boot with:
	* "tsc=unstable".
	*/
	static void __sched_clock_work(struct work_struct *work)
	{
	struct sched_clock_data *scd;
	int cpu;

	/* take a current timestamp and set 'now' */
	preempt_disable();
	scd = this_scd();
	__scd_stamp(scd);
	scd->clock = scd->tick_gtod + __gtod_offset;
	preempt_enable();

	/* clone to all CPUs */
	for_each_possible_cpu(cpu)
	per_cpu(sched_clock_data, cpu) = *scd;

	printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n");
	printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
	scd->tick_gtod, __gtod_offset,
	scd->tick_raw, __sched_clock_offset);

	static_branch_disable(&__sched_clock_stable);
	}

	static DECLARE_WORK(sched_clock_work, __sched_clock_work);

	static void __clear_sched_clock_stable(void)
	{
	if (!sched_clock_stable())
	return;

	tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
	schedule_work(&sched_clock_work);
	}

	void clear_sched_clock_stable(void)
	{
	__sched_clock_stable_early = 0;

	smp_mb(); /* matches sched_clock_init_late() */

	if (sched_clock_running == 2)
	__clear_sched_clock_stable();
	}

	/*
	* We run this as late_initcall() such that it runs after all built-in drivers,
	* notably: acpi_processor and intel_idle, which can mark the TSC as unstable.
	*/
	static int __init sched_clock_init_late(void)
	{
	sched_clock_running = 2;
	/*
	* Ensure that it is impossible to not do a static_key update.
	*
	* Either {set,clear}_sched_clock_stable() must see sched_clock_running
	* and do the update, or we must see their __sched_clock_stable_early
	* and do the update, or both.
	*/
	smp_mb(); /* matches {set,clear}_sched_clock_stable() */

	if (__sched_clock_stable_early)
	__set_sched_clock_stable();

	return 0;
	}
	late_initcall(sched_clock_init_late);

	/*
	* 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 sched_clock_local(struct sched_clock_data *scd)
	{
	u64 now, clock, old_clock, min_clock, max_clock, gtod;
	s64 delta;

	again:
	now = sched_clock();
	delta = now - scd->tick_raw;
	if (unlikely(delta < 0))
	delta = 0;

	old_clock = scd->clock;

	/*
	* scd->clock = clamp(scd->tick_gtod + delta,
	* max(scd->tick_gtod, scd->clock),
	* scd->tick_gtod + TICK_NSEC);
	*/

	gtod = scd->tick_gtod + __gtod_offset;
	clock = gtod + delta;
	min_clock = wrap_max(gtod, old_clock);
	max_clock = wrap_max(old_clock, gtod + TICK_NSEC);

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

	if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
	goto again;

	return clock;
	}

	static u64 sched_clock_remote(struct sched_clock_data *scd)
	{
	struct sched_clock_data *my_scd = this_scd();
	u64 this_clock, remote_clock;
	u64 *ptr, old_val, val;

	#if BITS_PER_LONG != 64
	again:
	/*
	* Careful here: The local and the remote clock values need to
	* be read out atomic as we need to compare the values and
	* then update either the local or the remote side. So the
	* cmpxchg64 below only protects one readout.
	*
	* We must reread via sched_clock_local() in the retry case on
	* 32-bit kernels as an NMI could use sched_clock_local() via the
	* tracer and hit between the readout of
	* the low 32-bit and the high 32-bit portion.
	*/
	this_clock = sched_clock_local(my_scd);
	/*
	* We must enforce atomic readout on 32-bit, otherwise the
	* update on the remote CPU can hit inbetween the readout of
	* the low 32-bit and the high 32-bit portion.
	*/
	remote_clock = cmpxchg64(&scd->clock, 0, 0);
	#else
	/*
	* On 64-bit kernels the read of [my]scd->clock is atomic versus the
	* update, so we can avoid the above 32-bit dance.
	*/
	sched_clock_local(my_scd);
	again:
	this_clock = my_scd->clock;
	remote_clock = scd->clock;
	#endif

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

	if (cmpxchg64(ptr, old_val, val) != old_val)
	goto again;

	return val;
	}

	/*
	* Similar to cpu_clock(), but requires local IRQs to be disabled.
	*
	* See cpu_clock().
	*/
	u64 sched_clock_cpu(int cpu)
	{
	struct sched_clock_data *scd;
	u64 clock;

	if (sched_clock_stable())
	return sched_clock() + __sched_clock_offset;

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

	preempt_disable_notrace();
	scd = cpu_sdc(cpu);

	if (cpu != smp_processor_id())
	clock = sched_clock_remote(scd);
	else
	clock = sched_clock_local(scd);
	preempt_enable_notrace();

	return clock;
	}
	EXPORT_SYMBOL_GPL(sched_clock_cpu);

	void sched_clock_tick(void)
	{
	struct sched_clock_data *scd;

	if (sched_clock_stable())
	return;

	if (unlikely(!sched_clock_running))
	return;

	lockdep_assert_irqs_disabled();

	scd = this_scd();
	__scd_stamp(scd);
	sched_clock_local(scd);
	}

	void sched_clock_tick_stable(void)
	{
	u64 gtod, clock;

	if (!sched_clock_stable())
	return;

	/*
	* Called under watchdog_lock.
	*
	* The watchdog just found this TSC to (still) be stable, so now is a
	* good moment to update our __gtod_offset. Because once we find the
	* TSC to be unstable, any computation will be computing crap.
	*/
	local_irq_disable();
	gtod = ktime_get_ns();
	clock = sched_clock();
	__gtod_offset = (clock + __sched_clock_offset) - gtod;
	local_irq_enable();
	}

	/*
	* 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; resync with ktime.
	*/
	void sched_clock_idle_wakeup_event(void)
	{
	unsigned long flags;

	if (sched_clock_stable())
	return;

	if (unlikely(timekeeping_suspended))
	return;

	local_irq_save(flags);
	sched_clock_tick();
	local_irq_restore(flags);
	}
	EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

	#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

	u64 sched_clock_cpu(int cpu)
	{
	if (unlikely(!sched_clock_running))
	return 0;

	return sched_clock();
	}

	#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

	/*
	* Running clock - returns the time that has elapsed while a guest has been
	* running.
	* On a guest this value should be local_clock minus the time the guest was
	* suspended by the hypervisor (for any reason).
	* On bare metal this function should return the same as local_clock.
	* Architectures and sub-architectures can override this.
	*/
	u64 __weak running_clock(void)
	{
	return local_clock();
	}