/* * 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. * local_clock()      -- is cpu_clock() on the current cpu. * * sched_clock_cpu(i) * * 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). * */#include <linux/spinlock.h>#include <linux/hardirq.h>#include <linux/export.h>#include <linux/percpu.h>#include <linux/ktime.h>#include <linux/sched.h>#include <linux/static_key.h>#include <linux/workqueue.h>#include <linux/compiler.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; #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCKstatic struct static_key __sched_clock_stable = STATIC_KEY_INIT;static int __sched_clock_stable_early; int sched_clock_stable(void){	return static_key_false(&__sched_clock_stable);} static void __set_sched_clock_stable(void){	if (!sched_clock_stable())		static_key_slow_inc(&__sched_clock_stable);} void set_sched_clock_stable(void){	__sched_clock_stable_early = 1; 	smp_mb(); /* matches sched_clock_init() */ 	if (!sched_clock_running)		return; 	__set_sched_clock_stable();} static void __clear_sched_clock_stable(struct work_struct *work){	/* XXX worry about clock continuity */	if (sched_clock_stable())		static_key_slow_dec(&__sched_clock_stable);} static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable); void clear_sched_clock_stable(void){	__sched_clock_stable_early = 0; 	smp_mb(); /* matches sched_clock_init() */ 	if (!sched_clock_running)		return; 	schedule_work(&sched_clock_work);} 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; 	/*	 * 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();	else		__clear_sched_clock_stable(NULL);} /* * 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 != 64again:	/*	 * 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; 	if (sched_clock_stable())		return sched_clock(); 	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;} 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){	if (!sched_clock_stable())		return sched_clock_cpu(cpu); 	return sched_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){	if (!sched_clock_stable())		return sched_clock_cpu(raw_smp_processor_id()); 	return sched_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();} u64 local_clock(void){	return sched_clock();} #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ EXPORT_SYMBOL_GPL(cpu_clock);EXPORT_SYMBOL_GPL(local_clock);