/* * 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 != 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	 * 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();}