/* * sched_clock for unstable cpu clocks * * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> * * Based on code by: * Ingo Molnar <mingo@redhat.com> * Guillaume Chazarain <guichaz@gmail.com> * * Create a semi stable clock from a mixture of other events, including: * - gtod * - jiffies * - sched_clock() * - explicit idle events * * We use gtod as base and the unstable clock deltas. The deltas are filtered, * making it monotonic and keeping it within an expected window. This window * is set up using jiffies. * * Furthermore, explicit sleep and wakeup hooks allow us to account for time * that is otherwise invisible (TSC gets stopped). * * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat * consistent between cpus (never more than 1 jiffies difference). */ #include <linux/sched.h> #include <linux/percpu.h> #include <linux/spinlock.h> #include <linux/ktime.h> #include <linux/module.h> #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK struct sched_clock_data { /* * Raw spinlock - this is a special case: this might be called * from within instrumentation code so we dont want to do any * instrumentation ourselves. */ raw_spinlock_t lock; unsigned long prev_jiffies; u64 prev_raw; 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); } static __read_mostly int sched_clock_running; void sched_clock_init(void) { u64 ktime_now = ktime_to_ns(ktime_get()); unsigned long now_jiffies = jiffies; int cpu; for_each_possible_cpu(cpu) { struct sched_clock_data *scd = cpu_sdc(cpu); scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED; scd->prev_jiffies = now_jiffies; scd->prev_raw = 0; scd->tick_raw = 0; scd->tick_gtod = ktime_now; scd->clock = ktime_now; } sched_clock_running = 1; } /* * update the percpu scd from the raw @now value * * - filter out backward motion * - use jiffies to generate a min,max window to clip the raw values */ static void __update_sched_clock(struct sched_clock_data *scd, u64 now) { unsigned long now_jiffies = jiffies; long delta_jiffies = now_jiffies - scd->prev_jiffies; u64 clock = scd->clock; u64 min_clock, max_clock; s64 delta = now - scd->prev_raw; WARN_ON_ONCE(!irqs_disabled()); min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC; if (unlikely(delta < 0)) { clock++; goto out; } max_clock = min_clock + TICK_NSEC; if (unlikely(clock + delta > max_clock)) { if (clock < max_clock) clock = max_clock; else clock++; } else { clock += delta; } out: if (unlikely(clock < min_clock)) clock = min_clock; scd->prev_raw = now; scd->prev_jiffies = now_jiffies; scd->clock = clock; } static void lock_double_clock(struct sched_clock_data *data1, struct sched_clock_data *data2) { if (data1 < data2) { __raw_spin_lock(&data1->lock); __raw_spin_lock(&data2->lock); } else { __raw_spin_lock(&data2->lock); __raw_spin_lock(&data1->lock); } } u64 sched_clock_cpu(int cpu) { struct sched_clock_data *scd = cpu_sdc(cpu); u64 now, clock; if (unlikely(!sched_clock_running)) return 0ull; WARN_ON_ONCE(!irqs_disabled()); now = sched_clock(); if (cpu != raw_smp_processor_id()) { /* * in order to update a remote cpu's clock based on our * unstable raw time rebase it against: * tick_raw (offset between raw counters) * tick_gotd (tick offset between cpus) */ struct sched_clock_data *my_scd = this_scd(); lock_double_clock(scd, my_scd); now -= my_scd->tick_raw; now += scd->tick_raw; now -= my_scd->tick_gtod; now += scd->tick_gtod; __raw_spin_unlock(&my_scd->lock); } else { __raw_spin_lock(&scd->lock); } __update_sched_clock(scd, now); clock = scd->clock; __raw_spin_unlock(&scd->lock); return clock; } void sched_clock_tick(void) { struct sched_clock_data *scd = this_scd(); u64 now, now_gtod; if (unlikely(!sched_clock_running)) return; WARN_ON_ONCE(!irqs_disabled()); now = sched_clock(); now_gtod = ktime_to_ns(ktime_get()); __raw_spin_lock(&scd->lock); __update_sched_clock(scd, now); /* * update tick_gtod after __update_sched_clock() because that will * already observe 1 new jiffy; adding a new tick_gtod to that would * increase the clock 2 jiffies. */ scd->tick_raw = now; scd->tick_gtod = now_gtod; __raw_spin_unlock(&scd->lock); } /* * 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) { struct sched_clock_data *scd = this_scd(); u64 now = sched_clock(); /* * Override the previous timestamp and ignore all * sched_clock() deltas that occured while we idled, * and use the PM-provided delta_ns to advance the * rq clock: */ __raw_spin_lock(&scd->lock); scd->prev_raw = now; scd->clock += delta_ns; __raw_spin_unlock(&scd->lock); touch_softlockup_watchdog(); } EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); #endif /* * 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 * (NSEC_PER_SEC / HZ); }