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

 /*
  * 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>
  *
  *
  * What:
  *
  * 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.
  * sched_clock_cpu(i) -- must be used with local IRQs disabled (implied by NMI)
  * local_clock()      -- is cpu_clock() on the current cpu.
  *
  * How:
  *
  * 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).
  *
  *
  * Notes:
  *
  * The !IRQ-safetly of sched_clock() and sched_clock_cpu() comes from things
  * like cpufreq interrupts that can change the base clock (TSC) multiplier
  * and cause funny jumps in time -- although the filtering provided by
  * sched_clock_cpu() should mitigate serious artifacts we cannot rely on it
  * in general since for !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK we fully rely on
  * sched_clock().
  */
 #include <linux/spinlock.h>
 #include <linux/hardirq.h>
 #include <linux/export.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);
 }
 EXPORT_SYMBOL_GPL(sched_clock);

 __read_mostly int sched_clock_running;

 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
 __read_mostly int sched_clock_stable;

 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 &__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->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 sched_clock_local(struct sched_clock_data *scd)
 {
 	u64 now, clock, old_clock, min_clock, max_clock;
 	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);
 	 */

 	clock = scd->tick_gtod + delta;
 	min_clock = wrap_max(scd->tick_gtod, old_clock);
 	max_clock = wrap_max(old_clock, scd->tick_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
 	 * 32bit as an NMI could use sched_clock_local() via the
 	 * tracer and hit between the readout of
 	 * the low32bit and the high 32bit portion.
 	 */
 	this_clock = sched_clock_local(my_scd);
 	/*
 	 * We must enforce atomic readout on 32bit, otherwise the
 	 * update on the remote cpu can hit inbetween the readout of
 	 * the low32bit and the high 32bit portion.
 	 */
 	remote_clock = cmpxchg64(&scd->clock, 0, 0);
 #else
 	/*
 	 * On 64bit the read of [my]scd->clock is atomic versus the
 	 * update, so we can avoid the above 32bit 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;

 	WARN_ON_ONCE(!irqs_disabled());

 	if (sched_clock_stable)
 		return sched_clock();

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

 	scd = cpu_sdc(cpu);

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

 	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();

 	scd->tick_raw = now;
 	scd->tick_gtod = now_gtod;
 	sched_clock_local(scd);
 }

 /*
  * 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);

 /*
  * As outlined at the top, provides a fast, high resolution, nanosecond
  * time source that is monotonic per cpu argument and has bounded drift
  * between cpus.
  *
  * ######################### BIG FAT WARNING ##########################
  * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
  * # go backwards !!                                                  #
  * ####################################################################
  */
 u64 cpu_clock(int cpu)
 {
 	u64 clock;
 	unsigned long flags;

 	local_irq_save(flags);
 	clock = sched_clock_cpu(cpu);
 	local_irq_restore(flags);

 	return clock;
 }

 /*
  * Similar to cpu_clock() for the current cpu. Time will only be observed
  * to be monotonic if care is taken to only compare timestampt taken on the
  * same CPU.
  *
  * See cpu_clock().
  */
 u64 local_clock(void)
 {
 	u64 clock;
 	unsigned long flags;

 	local_irq_save(flags);
 	clock = sched_clock_cpu(smp_processor_id());
 	local_irq_restore(flags);

 	return clock;
 }

 #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();
 }

 u64 cpu_clock(int cpu)
 {
 	return sched_clock_cpu(cpu);
 }

 u64 local_clock(void)
 {
 	return sched_clock_cpu(0);
 }

 #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

 EXPORT_SYMBOL_GPL(cpu_clock);
 EXPORT_SYMBOL_GPL(local_clock);
	/*
	* 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>
	*
	*
	* What:
	*
	* 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.
	* sched_clock_cpu(i) -- must be used with local IRQs disabled (implied by NMI)
	* local_clock() -- is cpu_clock() on the current cpu.
	*
	* How:
	*
	* 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).
	*
	*
	* Notes:
	*
	* The !IRQ-safetly of sched_clock() and sched_clock_cpu() comes from things
	* like cpufreq interrupts that can change the base clock (TSC) multiplier
	* and cause funny jumps in time -- although the filtering provided by
	* sched_clock_cpu() should mitigate serious artifacts we cannot rely on it
	* in general since for !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK we fully rely on
	* sched_clock().
	*/
	#include <linux/spinlock.h>
	#include <linux/hardirq.h>
	#include <linux/export.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);
	}
	EXPORT_SYMBOL_GPL(sched_clock);

	__read_mostly int sched_clock_running;

	#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
	__read_mostly int sched_clock_stable;

	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 &__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->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 sched_clock_local(struct sched_clock_data *scd)
	{
	u64 now, clock, old_clock, min_clock, max_clock;
	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);
	*/

	clock = scd->tick_gtod + delta;
	min_clock = wrap_max(scd->tick_gtod, old_clock);
	max_clock = wrap_max(old_clock, scd->tick_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
	* 32bit as an NMI could use sched_clock_local() via the
	* tracer and hit between the readout of
	* the low32bit and the high 32bit portion.
	*/
	this_clock = sched_clock_local(my_scd);
	/*
	* We must enforce atomic readout on 32bit, otherwise the
	* update on the remote cpu can hit inbetween the readout of
	* the low32bit and the high 32bit portion.
	*/
	remote_clock = cmpxchg64(&scd->clock, 0, 0);
	#else
	/*
	* On 64bit the read of [my]scd->clock is atomic versus the
	* update, so we can avoid the above 32bit 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;

	WARN_ON_ONCE(!irqs_disabled());

	if (sched_clock_stable)
	return sched_clock();

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

	scd = cpu_sdc(cpu);

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

	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();

	scd->tick_raw = now;
	scd->tick_gtod = now_gtod;
	sched_clock_local(scd);
	}

	/*
	* 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);

	/*
	* As outlined at the top, provides a fast, high resolution, nanosecond
	* time source that is monotonic per cpu argument and has bounded drift
	* between cpus.
	*
	* ######################### BIG FAT WARNING ##########################
	* # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
	* # go backwards !! #
	* ####################################################################
	*/
	u64 cpu_clock(int cpu)
	{
	u64 clock;
	unsigned long flags;

	local_irq_save(flags);
	clock = sched_clock_cpu(cpu);
	local_irq_restore(flags);

	return clock;
	}

	/*
	* Similar to cpu_clock() for the current cpu. Time will only be observed
	* to be monotonic if care is taken to only compare timestampt taken on the
	* same CPU.
	*
	* See cpu_clock().
	*/
	u64 local_clock(void)
	{
	u64 clock;
	unsigned long flags;

	local_irq_save(flags);
	clock = sched_clock_cpu(smp_processor_id());
	local_irq_restore(flags);

	return clock;
	}

	#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();
	}

	u64 cpu_clock(int cpu)
	{
	return sched_clock_cpu(cpu);
	}

	u64 local_clock(void)
	{
	return sched_clock_cpu(0);
	}

	#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

	EXPORT_SYMBOL_GPL(cpu_clock);
	EXPORT_SYMBOL_GPL(local_clock);