/*
 * 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>
 *
 * Create a semi stable clock from a mixture of other events, including:
 *  - gtod
 *  - 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.
 *
 * 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 2 jiffies difference).
 */
#include <linux/sched.h>
#include <linux/percpu.h>
#include <linux/spinlock.h>
#include <linux/ktime.h>
#include <linux/module.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 * (NSEC_PER_SEC / HZ);
}

static __read_mostly int sched_clock_running;

#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;

        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->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
                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 __update_sched_clock(struct sched_clock_data *scd, u64 now)
{
        s64 delta = now - scd->tick_raw;
        u64 clock, min_clock, max_clock;

        WARN_ON_ONCE(!irqs_disabled());

        if (unlikely(delta < 0))
                delta = 0;

        /*
         * 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, scd->clock);
        max_clock = wrap_max(scd->clock, scd->tick_gtod + TICK_NSEC);

        clock = wrap_max(clock, min_clock);
        clock = wrap_min(clock, max_clock);

        scd->clock = clock;

        return scd->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, this_clock, remote_clock;

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

        WARN_ON_ONCE(!irqs_disabled());
        now = sched_clock();

        if (cpu != raw_smp_processor_id()) {
                struct sched_clock_data *my_scd = this_scd();

                lock_double_clock(scd, my_scd);

                this_clock = __update_sched_clock(my_scd, now);
                remote_clock = scd->clock;

                /*
                 * 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)) {
                        clock = this_clock;
                        scd->clock = clock;
                } else {
                        /*
                         * Should be rare, but possible:
                         */
                        clock = remote_clock;
                        my_scd->clock = remote_clock;
                }

                __raw_spin_unlock(&my_scd->lock);
        } else {
                __raw_spin_lock(&scd->lock);
                clock = __update_sched_clock(scd, now);
        }

        __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_gtod = ktime_to_ns(ktime_get());
        now = sched_clock();

        __raw_spin_lock(&scd->lock);
        scd->tick_raw = now;
        scd->tick_gtod = now_gtod;
        __update_sched_clock(scd, now);
        __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)
{
        if (timekeeping_suspended)
                return;

        sched_clock_tick();
        touch_softlockup_watchdog();
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

#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();
}

#endif

unsigned long long cpu_clock(int cpu)
{
        unsigned long long clock;
        unsigned long flags;

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

        return clock;
}
EXPORT_SYMBOL_GPL(cpu_clock);