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[pohmelfs.git] / kernel / hrtimer.c

/*
 *  linux/kernel/hrtimer.c
 *
 *  Copyright(C) 2005, Thomas Gleixner <tglx@linutronix.de>
 *  Copyright(C) 2005, Red Hat, Inc., Ingo Molnar
 *
 *  High-resolution kernel timers
 *
 *  In contrast to the low-resolution timeout API implemented in
 *  kernel/timer.c, hrtimers provide finer resolution and accuracy
 *  depending on system configuration and capabilities.
 *
 *  These timers are currently used for:
 *   - itimers
 *   - POSIX timers
 *   - nanosleep
 *   - precise in-kernel timing
 *
 *  Started by: Thomas Gleixner and Ingo Molnar
 *
 *  Credits:
 *      based on kernel/timer.c
 *
 *      Help, testing, suggestions, bugfixes, improvements were
 *      provided by:
 *
 *      George Anzinger, Andrew Morton, Steven Rostedt, Roman Zippel
 *      et. al.
 *
 *  For licencing details see kernel-base/COPYING
 */

#include <linux/cpu.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/hrtimer.h>
#include <linux/notifier.h>
#include <linux/syscalls.h>
#include <linux/interrupt.h>

#include <asm/uaccess.h>

/**
 * ktime_get - get the monotonic time in ktime_t format
 *
 * returns the time in ktime_t format
 */
static ktime_t ktime_get(void)
{
        struct timespec now;

        ktime_get_ts(&now);

        return timespec_to_ktime(now);
}

/**
 * ktime_get_real - get the real (wall-) time in ktime_t format
 *
 * returns the time in ktime_t format
 */
static ktime_t ktime_get_real(void)
{
        struct timespec now;

        getnstimeofday(&now);

        return timespec_to_ktime(now);
}

EXPORT_SYMBOL_GPL(ktime_get_real);

/*
 * The timer bases:
 *
 * Note: If we want to add new timer bases, we have to skip the two
 * clock ids captured by the cpu-timers. We do this by holding empty
 * entries rather than doing math adjustment of the clock ids.
 * This ensures that we capture erroneous accesses to these clock ids
 * rather than moving them into the range of valid clock id's.
 */

#define MAX_HRTIMER_BASES 2

static DEFINE_PER_CPU(struct hrtimer_base, hrtimer_bases[MAX_HRTIMER_BASES]) =
{
        {
                .index = CLOCK_REALTIME,
                .get_time = &ktime_get_real,
                .resolution = KTIME_REALTIME_RES,
        },
        {
                .index = CLOCK_MONOTONIC,
                .get_time = &ktime_get,
                .resolution = KTIME_MONOTONIC_RES,
        },
};

/**
 * ktime_get_ts - get the monotonic clock in timespec format
 * @ts:         pointer to timespec variable
 *
 * The function calculates the monotonic clock from the realtime
 * clock and the wall_to_monotonic offset and stores the result
 * in normalized timespec format in the variable pointed to by @ts.
 */
void ktime_get_ts(struct timespec *ts)
{
        struct timespec tomono;
        unsigned long seq;

        do {
                seq = read_seqbegin(&xtime_lock);
                getnstimeofday(ts);
                tomono = wall_to_monotonic;

        } while (read_seqretry(&xtime_lock, seq));

        set_normalized_timespec(ts, ts->tv_sec + tomono.tv_sec,
                                ts->tv_nsec + tomono.tv_nsec);
}
EXPORT_SYMBOL_GPL(ktime_get_ts);

/*
 * Get the coarse grained time at the softirq based on xtime and
 * wall_to_monotonic.
 */
static void hrtimer_get_softirq_time(struct hrtimer_base *base)
{
        ktime_t xtim, tomono;
        struct timespec xts;
        unsigned long seq;

        do {
                seq = read_seqbegin(&xtime_lock);
#ifdef CONFIG_NO_HZ
                getnstimeofday(&xts);
#else
                xts = xtime;
#endif
        } while (read_seqretry(&xtime_lock, seq));

        xtim = timespec_to_ktime(xts);
        tomono = timespec_to_ktime(wall_to_monotonic);
        base[CLOCK_REALTIME].softirq_time = xtim;
        base[CLOCK_MONOTONIC].softirq_time = ktime_add(xtim, tomono);
}

/*
 * Functions and macros which are different for UP/SMP systems are kept in a
 * single place
 */
#ifdef CONFIG_SMP

#define set_curr_timer(b, t)            do { (b)->curr_timer = (t); } while (0)

/*
 * We are using hashed locking: holding per_cpu(hrtimer_bases)[n].lock
 * means that all timers which are tied to this base via timer->base are
 * locked, and the base itself is locked too.
 *
 * So __run_timers/migrate_timers can safely modify all timers which could
 * be found on the lists/queues.
 *
 * When the timer's base is locked, and the timer removed from list, it is
 * possible to set timer->base = NULL and drop the lock: the timer remains
 * locked.
 */
static struct hrtimer_base *lock_hrtimer_base(const struct hrtimer *timer,
                                              unsigned long *flags)
{
        struct hrtimer_base *base;

        for (;;) {
                base = timer->base;
                if (likely(base != NULL)) {
                        spin_lock_irqsave(&base->lock, *flags);
                        if (likely(base == timer->base))
                                return base;
                        /* The timer has migrated to another CPU: */
                        spin_unlock_irqrestore(&base->lock, *flags);
                }
                cpu_relax();
        }
}

/*
 * Switch the timer base to the current CPU when possible.
 */
static inline struct hrtimer_base *
switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_base *base)
{
        struct hrtimer_base *new_base;

        new_base = &__get_cpu_var(hrtimer_bases)[base->index];

        if (base != new_base) {
                /*
                 * We are trying to schedule the timer on the local CPU.
                 * However we can't change timer's base while it is running,
                 * so we keep it on the same CPU. No hassle vs. reprogramming
                 * the event source in the high resolution case. The softirq
                 * code will take care of this when the timer function has
                 * completed. There is no conflict as we hold the lock until
                 * the timer is enqueued.
                 */
                if (unlikely(base->curr_timer == timer))
                        return base;

                /* See the comment in lock_timer_base() */
                timer->base = NULL;
                spin_unlock(&base->lock);
                spin_lock(&new_base->lock);
                timer->base = new_base;
        }
        return new_base;
}

#else /* CONFIG_SMP */

#define set_curr_timer(b, t)            do { } while (0)

static inline struct hrtimer_base *
lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
{
        struct hrtimer_base *base = timer->base;

        spin_lock_irqsave(&base->lock, *flags);

        return base;
}

#define switch_hrtimer_base(t, b)       (b)

#endif  /* !CONFIG_SMP */

/*
 * Functions for the union type storage format of ktime_t which are
 * too large for inlining:
 */
#if BITS_PER_LONG < 64
# ifndef CONFIG_KTIME_SCALAR
/**
 * ktime_add_ns - Add a scalar nanoseconds value to a ktime_t variable
 * @kt:         addend
 * @nsec:       the scalar nsec value to add
 *
 * Returns the sum of kt and nsec in ktime_t format
 */
ktime_t ktime_add_ns(const ktime_t kt, u64 nsec)
{
        ktime_t tmp;

        if (likely(nsec < NSEC_PER_SEC)) {
                tmp.tv64 = nsec;
        } else {
                unsigned long rem = do_div(nsec, NSEC_PER_SEC);

                tmp = ktime_set((long)nsec, rem);
        }

        return ktime_add(kt, tmp);
}

#else /* CONFIG_KTIME_SCALAR */

# endif /* !CONFIG_KTIME_SCALAR */

/*
 * Divide a ktime value by a nanosecond value
 */
static unsigned long ktime_divns(const ktime_t kt, s64 div)
{
        u64 dclc, inc, dns;
        int sft = 0;

        dclc = dns = ktime_to_ns(kt);
        inc = div;
        /* Make sure the divisor is less than 2^32: */
        while (div >> 32) {
                sft++;
                div >>= 1;
        }
        dclc >>= sft;
        do_div(dclc, (unsigned long) div);

        return (unsigned long) dclc;
}

#else /* BITS_PER_LONG < 64 */
# define ktime_divns(kt, div)           (unsigned long)((kt).tv64 / (div))
#endif /* BITS_PER_LONG >= 64 */

/*
 * Counterpart to lock_timer_base above:
 */
static inline
void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
{
        spin_unlock_irqrestore(&timer->base->lock, *flags);
}

/**
 * hrtimer_forward - forward the timer expiry
 * @timer:      hrtimer to forward
 * @now:        forward past this time
 * @interval:   the interval to forward
 *
 * Forward the timer expiry so it will expire in the future.
 * Returns the number of overruns.
 */
unsigned long
hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval)
{
        unsigned long orun = 1;
        ktime_t delta;

        delta = ktime_sub(now, timer->expires);

        if (delta.tv64 < 0)
                return 0;

        if (interval.tv64 < timer->base->resolution.tv64)
                interval.tv64 = timer->base->resolution.tv64;

        if (unlikely(delta.tv64 >= interval.tv64)) {
                s64 incr = ktime_to_ns(interval);

                orun = ktime_divns(delta, incr);
                timer->expires = ktime_add_ns(timer->expires, incr * orun);
                if (timer->expires.tv64 > now.tv64)
                        return orun;
                /*
                 * This (and the ktime_add() below) is the
                 * correction for exact:
                 */
                orun++;
        }
        timer->expires = ktime_add(timer->expires, interval);

        return orun;
}

/*
 * enqueue_hrtimer - internal function to (re)start a timer
 *
 * The timer is inserted in expiry order. Insertion into the
 * red black tree is O(log(n)). Must hold the base lock.
 */
static void enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
{
        struct rb_node **link = &base->active.rb_node;
        struct rb_node *parent = NULL;
        struct hrtimer *entry;

        /*
         * Find the right place in the rbtree:
         */
        while (*link) {
                parent = *link;
                entry = rb_entry(parent, struct hrtimer, node);
                /*
                 * We dont care about collisions. Nodes with
                 * the same expiry time stay together.
                 */
                if (timer->expires.tv64 < entry->expires.tv64)
                        link = &(*link)->rb_left;
                else
                        link = &(*link)->rb_right;
        }

        /*
         * Insert the timer to the rbtree and check whether it
         * replaces the first pending timer
         */
        rb_link_node(&timer->node, parent, link);
        rb_insert_color(&timer->node, &base->active);

        if (!base->first || timer->expires.tv64 <
            rb_entry(base->first, struct hrtimer, node)->expires.tv64)
                base->first = &timer->node;
}

/*
 * __remove_hrtimer - internal function to remove a timer
 *
 * Caller must hold the base lock.
 */
static void __remove_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
{
        /*
         * Remove the timer from the rbtree and replace the
         * first entry pointer if necessary.
         */
        if (base->first == &timer->node)
                base->first = rb_next(&timer->node);
        rb_erase(&timer->node, &base->active);
        rb_set_parent(&timer->node, &timer->node);
}

/*
 * remove hrtimer, called with base lock held
 */
static inline int
remove_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
{
        if (hrtimer_active(timer)) {
                __remove_hrtimer(timer, base);
                return 1;
        }
        return 0;
}

/**
 * hrtimer_start - (re)start an relative timer on the current CPU
 * @timer:      the timer to be added
 * @tim:        expiry time
 * @mode:       expiry mode: absolute (HRTIMER_ABS) or relative (HRTIMER_REL)
 *
 * Returns:
 *  0 on success
 *  1 when the timer was active
 */
int
hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
{
        struct hrtimer_base *base, *new_base;
        unsigned long flags;
        int ret;

        base = lock_hrtimer_base(timer, &flags);

        /* Remove an active timer from the queue: */
        ret = remove_hrtimer(timer, base);

        /* Switch the timer base, if necessary: */
        new_base = switch_hrtimer_base(timer, base);

        if (mode == HRTIMER_REL) {
                tim = ktime_add(tim, new_base->get_time());
                /*
                 * CONFIG_TIME_LOW_RES is a temporary way for architectures
                 * to signal that they simply return xtime in
                 * do_gettimeoffset(). In this case we want to round up by
                 * resolution when starting a relative timer, to avoid short
                 * timeouts. This will go away with the GTOD framework.
                 */
#ifdef CONFIG_TIME_LOW_RES
                tim = ktime_add(tim, base->resolution);
#endif
        }
        timer->expires = tim;

        enqueue_hrtimer(timer, new_base);

        unlock_hrtimer_base(timer, &flags);

        return ret;
}
EXPORT_SYMBOL_GPL(hrtimer_start);

/**
 * hrtimer_try_to_cancel - try to deactivate a timer
 * @timer:      hrtimer to stop
 *
 * Returns:
 *  0 when the timer was not active
 *  1 when the timer was active
 * -1 when the timer is currently excuting the callback function and
 *    cannot be stopped
 */
int hrtimer_try_to_cancel(struct hrtimer *timer)
{
        struct hrtimer_base *base;
        unsigned long flags;
        int ret = -1;

        base = lock_hrtimer_base(timer, &flags);

        if (base->curr_timer != timer)
                ret = remove_hrtimer(timer, base);

        unlock_hrtimer_base(timer, &flags);

        return ret;

}
EXPORT_SYMBOL_GPL(hrtimer_try_to_cancel);

/**
 * hrtimer_cancel - cancel a timer and wait for the handler to finish.
 * @timer:      the timer to be cancelled
 *
 * Returns:
 *  0 when the timer was not active
 *  1 when the timer was active
 */
int hrtimer_cancel(struct hrtimer *timer)
{
        for (;;) {
                int ret = hrtimer_try_to_cancel(timer);

                if (ret >= 0)
                        return ret;
                cpu_relax();
        }
}
EXPORT_SYMBOL_GPL(hrtimer_cancel);

/**
 * hrtimer_get_remaining - get remaining time for the timer
 * @timer:      the timer to read
 */
ktime_t hrtimer_get_remaining(const struct hrtimer *timer)
{
        struct hrtimer_base *base;
        unsigned long flags;
        ktime_t rem;

        base = lock_hrtimer_base(timer, &flags);
        rem = ktime_sub(timer->expires, timer->base->get_time());
        unlock_hrtimer_base(timer, &flags);

        return rem;
}
EXPORT_SYMBOL_GPL(hrtimer_get_remaining);

#ifdef CONFIG_NO_IDLE_HZ
/**
 * hrtimer_get_next_event - get the time until next expiry event
 *
 * Returns the delta to the next expiry event or KTIME_MAX if no timer
 * is pending.
 */
ktime_t hrtimer_get_next_event(void)
{
        struct hrtimer_base *base = __get_cpu_var(hrtimer_bases);
        ktime_t delta, mindelta = { .tv64 = KTIME_MAX };
        unsigned long flags;
        int i;

        for (i = 0; i < MAX_HRTIMER_BASES; i++, base++) {
                struct hrtimer *timer;

                spin_lock_irqsave(&base->lock, flags);
                if (!base->first) {
                        spin_unlock_irqrestore(&base->lock, flags);
                        continue;
                }
                timer = rb_entry(base->first, struct hrtimer, node);
                delta.tv64 = timer->expires.tv64;
                spin_unlock_irqrestore(&base->lock, flags);
                delta = ktime_sub(delta, base->get_time());
                if (delta.tv64 < mindelta.tv64)
                        mindelta.tv64 = delta.tv64;
        }
        if (mindelta.tv64 < 0)
                mindelta.tv64 = 0;
        return mindelta;
}
#endif

/**
 * hrtimer_init - initialize a timer to the given clock
 * @timer:      the timer to be initialized
 * @clock_id:   the clock to be used
 * @mode:       timer mode abs/rel
 */
void hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
                  enum hrtimer_mode mode)
{
        struct hrtimer_base *bases;

        memset(timer, 0, sizeof(struct hrtimer));

        bases = __raw_get_cpu_var(hrtimer_bases);

        if (clock_id == CLOCK_REALTIME && mode != HRTIMER_ABS)
                clock_id = CLOCK_MONOTONIC;

        timer->base = &bases[clock_id];
        rb_set_parent(&timer->node, &timer->node);
}
EXPORT_SYMBOL_GPL(hrtimer_init);

/**
 * hrtimer_get_res - get the timer resolution for a clock
 * @which_clock: which clock to query
 * @tp:          pointer to timespec variable to store the resolution
 *
 * Store the resolution of the clock selected by @which_clock in the
 * variable pointed to by @tp.
 */
int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
{
        struct hrtimer_base *bases;

        bases = __raw_get_cpu_var(hrtimer_bases);
        *tp = ktime_to_timespec(bases[which_clock].resolution);

        return 0;
}
EXPORT_SYMBOL_GPL(hrtimer_get_res);

/*
 * Expire the per base hrtimer-queue:
 */
static inline void run_hrtimer_queue(struct hrtimer_base *base)
{
        struct rb_node *node;

        if (!base->first)
                return;

        if (base->get_softirq_time)
                base->softirq_time = base->get_softirq_time();

        spin_lock_irq(&base->lock);

        while ((node = base->first)) {
                struct hrtimer *timer;
                int (*fn)(struct hrtimer *);
                int restart;

                timer = rb_entry(node, struct hrtimer, node);
                if (base->softirq_time.tv64 <= timer->expires.tv64)
                        break;

                fn = timer->function;
                set_curr_timer(base, timer);
                __remove_hrtimer(timer, base);
                spin_unlock_irq(&base->lock);

                restart = fn(timer);

                spin_lock_irq(&base->lock);

                if (restart != HRTIMER_NORESTART) {
                        BUG_ON(hrtimer_active(timer));
                        enqueue_hrtimer(timer, base);
                }
        }
        set_curr_timer(base, NULL);
        spin_unlock_irq(&base->lock);
}

/*
 * Called from timer softirq every jiffy, expire hrtimers:
 */
void hrtimer_run_queues(void)
{
        struct hrtimer_base *base = __get_cpu_var(hrtimer_bases);
        int i;

        hrtimer_get_softirq_time(base);

        for (i = 0; i < MAX_HRTIMER_BASES; i++)
                run_hrtimer_queue(&base[i]);
}

/*
 * Sleep related functions:
 */
static int hrtimer_wakeup(struct hrtimer *timer)
{
        struct hrtimer_sleeper *t =
                container_of(timer, struct hrtimer_sleeper, timer);
        struct task_struct *task = t->task;

        t->task = NULL;
        if (task)
                wake_up_process(task);

        return HRTIMER_NORESTART;
}

void hrtimer_init_sleeper(struct hrtimer_sleeper *sl, struct task_struct *task)
{
        sl->timer.function = hrtimer_wakeup;
        sl->task = task;
}

static int __sched do_nanosleep(struct hrtimer_sleeper *t, enum hrtimer_mode mode)
{
        hrtimer_init_sleeper(t, current);

        do {
                set_current_state(TASK_INTERRUPTIBLE);
                hrtimer_start(&t->timer, t->timer.expires, mode);

                schedule();

                hrtimer_cancel(&t->timer);
                mode = HRTIMER_ABS;

        } while (t->task && !signal_pending(current));

        return t->task == NULL;
}

long __sched hrtimer_nanosleep_restart(struct restart_block *restart)
{
        struct hrtimer_sleeper t;
        struct timespec __user *rmtp;
        struct timespec tu;
        ktime_t time;

        restart->fn = do_no_restart_syscall;

        hrtimer_init(&t.timer, restart->arg0, HRTIMER_ABS);
        t.timer.expires.tv64 = ((u64)restart->arg3 << 32) | (u64) restart->arg2;

        if (do_nanosleep(&t, HRTIMER_ABS))
                return 0;

        rmtp = (struct timespec __user *) restart->arg1;
        if (rmtp) {
                time = ktime_sub(t.timer.expires, t.timer.base->get_time());
                if (time.tv64 <= 0)
                        return 0;
                tu = ktime_to_timespec(time);
                if (copy_to_user(rmtp, &tu, sizeof(tu)))
                        return -EFAULT;
        }

        restart->fn = hrtimer_nanosleep_restart;

        /* The other values in restart are already filled in */
        return -ERESTART_RESTARTBLOCK;
}

long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp,
                       const enum hrtimer_mode mode, const clockid_t clockid)
{
        struct restart_block *restart;
        struct hrtimer_sleeper t;
        struct timespec tu;
        ktime_t rem;

        hrtimer_init(&t.timer, clockid, mode);
        t.timer.expires = timespec_to_ktime(*rqtp);
        if (do_nanosleep(&t, mode))
                return 0;

        /* Absolute timers do not update the rmtp value and restart: */
        if (mode == HRTIMER_ABS)
                return -ERESTARTNOHAND;

        if (rmtp) {
                rem = ktime_sub(t.timer.expires, t.timer.base->get_time());
                if (rem.tv64 <= 0)
                        return 0;
                tu = ktime_to_timespec(rem);
                if (copy_to_user(rmtp, &tu, sizeof(tu)))
                        return -EFAULT;
        }

        restart = &current_thread_info()->restart_block;
        restart->fn = hrtimer_nanosleep_restart;
        restart->arg0 = (unsigned long) t.timer.base->index;
        restart->arg1 = (unsigned long) rmtp;
        restart->arg2 = t.timer.expires.tv64 & 0xFFFFFFFF;
        restart->arg3 = t.timer.expires.tv64 >> 32;

        return -ERESTART_RESTARTBLOCK;
}

asmlinkage long
sys_nanosleep(struct timespec __user *rqtp, struct timespec __user *rmtp)
{
        struct timespec tu;

        if (copy_from_user(&tu, rqtp, sizeof(tu)))
                return -EFAULT;

        if (!timespec_valid(&tu))
                return -EINVAL;

        return hrtimer_nanosleep(&tu, rmtp, HRTIMER_REL, CLOCK_MONOTONIC);
}

/*
 * Functions related to boot-time initialization:
 */
static void __devinit init_hrtimers_cpu(int cpu)
{
        struct hrtimer_base *base = per_cpu(hrtimer_bases, cpu);
        int i;

        for (i = 0; i < MAX_HRTIMER_BASES; i++, base++) {
                spin_lock_init(&base->lock);
                lockdep_set_class(&base->lock, &base->lock_key);
        }
}

#ifdef CONFIG_HOTPLUG_CPU

static void migrate_hrtimer_list(struct hrtimer_base *old_base,
                                struct hrtimer_base *new_base)
{
        struct hrtimer *timer;
        struct rb_node *node;

        while ((node = rb_first(&old_base->active))) {
                timer = rb_entry(node, struct hrtimer, node);
                __remove_hrtimer(timer, old_base);
                timer->base = new_base;
                enqueue_hrtimer(timer, new_base);
        }
}

static void migrate_hrtimers(int cpu)
{
        struct hrtimer_base *old_base, *new_base;
        int i;

        BUG_ON(cpu_online(cpu));
        old_base = per_cpu(hrtimer_bases, cpu);
        new_base = get_cpu_var(hrtimer_bases);

        local_irq_disable();

        for (i = 0; i < MAX_HRTIMER_BASES; i++) {

                spin_lock(&new_base->lock);
                spin_lock(&old_base->lock);

                BUG_ON(old_base->curr_timer);

                migrate_hrtimer_list(old_base, new_base);

                spin_unlock(&old_base->lock);
                spin_unlock(&new_base->lock);
                old_base++;
                new_base++;
        }

        local_irq_enable();
        put_cpu_var(hrtimer_bases);
}
#endif /* CONFIG_HOTPLUG_CPU */

static int __cpuinit hrtimer_cpu_notify(struct notifier_block *self,
                                        unsigned long action, void *hcpu)
{
        long cpu = (long)hcpu;

        switch (action) {

        case CPU_UP_PREPARE:
                init_hrtimers_cpu(cpu);
                break;

#ifdef CONFIG_HOTPLUG_CPU
        case CPU_DEAD:
                migrate_hrtimers(cpu);
                break;
#endif

        default:
                break;
        }

        return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata hrtimers_nb = {
        .notifier_call = hrtimer_cpu_notify,
};

void __init hrtimers_init(void)
{
        hrtimer_cpu_notify(&hrtimers_nb, (unsigned long)CPU_UP_PREPARE,
                          (void *)(long)smp_processor_id());
        register_cpu_notifier(&hrtimers_nb);
}