/*
 * 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);
}