Merge branch 'x86/apic' into x86/platform

[linux-2.6/linux-mips.git] / kernel / time / timekeeping.c

/*
 *  linux/kernel/time/timekeeping.c
 *
 *  Kernel timekeeping code and accessor functions
 *
 *  This code was moved from linux/kernel/timer.c.
 *  Please see that file for copyright and history logs.
 *
 */

#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/sysdev.h>
#include <linux/clocksource.h>
#include <linux/jiffies.h>
#include <linux/time.h>
#include <linux/tick.h>
#include <linux/stop_machine.h>

/* Structure holding internal timekeeping values. */
struct timekeeper {
        /* Current clocksource used for timekeeping. */
        struct clocksource *clock;
        /* The shift value of the current clocksource. */
        int     shift;

        /* Number of clock cycles in one NTP interval. */
        cycle_t cycle_interval;
        /* Number of clock shifted nano seconds in one NTP interval. */
        u64     xtime_interval;
        /* shifted nano seconds left over when rounding cycle_interval */
        s64     xtime_remainder;
        /* Raw nano seconds accumulated per NTP interval. */
        u32     raw_interval;

        /* Clock shifted nano seconds remainder not stored in xtime.tv_nsec. */
        u64     xtime_nsec;
        /* Difference between accumulated time and NTP time in ntp
         * shifted nano seconds. */
        s64     ntp_error;
        /* Shift conversion between clock shifted nano seconds and
         * ntp shifted nano seconds. */
        int     ntp_error_shift;
        /* NTP adjusted clock multiplier */
        u32     mult;
};

static struct timekeeper timekeeper;

/**
 * timekeeper_setup_internals - Set up internals to use clocksource clock.
 *
 * @clock:              Pointer to clocksource.
 *
 * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
 * pair and interval request.
 *
 * Unless you're the timekeeping code, you should not be using this!
 */
static void timekeeper_setup_internals(struct clocksource *clock)
{
        cycle_t interval;
        u64 tmp, ntpinterval;

        timekeeper.clock = clock;
        clock->cycle_last = clock->read(clock);

        /* Do the ns -> cycle conversion first, using original mult */
        tmp = NTP_INTERVAL_LENGTH;
        tmp <<= clock->shift;
        ntpinterval = tmp;
        tmp += clock->mult/2;
        do_div(tmp, clock->mult);
        if (tmp == 0)
                tmp = 1;

        interval = (cycle_t) tmp;
        timekeeper.cycle_interval = interval;

        /* Go back from cycles -> shifted ns */
        timekeeper.xtime_interval = (u64) interval * clock->mult;
        timekeeper.xtime_remainder = ntpinterval - timekeeper.xtime_interval;
        timekeeper.raw_interval =
                ((u64) interval * clock->mult) >> clock->shift;

        timekeeper.xtime_nsec = 0;
        timekeeper.shift = clock->shift;

        timekeeper.ntp_error = 0;
        timekeeper.ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;

        /*
         * The timekeeper keeps its own mult values for the currently
         * active clocksource. These value will be adjusted via NTP
         * to counteract clock drifting.
         */
        timekeeper.mult = clock->mult;
}

/* Timekeeper helper functions. */
static inline s64 timekeeping_get_ns(void)
{
        cycle_t cycle_now, cycle_delta;
        struct clocksource *clock;

        /* read clocksource: */
        clock = timekeeper.clock;
        cycle_now = clock->read(clock);

        /* calculate the delta since the last update_wall_time: */
        cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

        /* return delta convert to nanoseconds using ntp adjusted mult. */
        return clocksource_cyc2ns(cycle_delta, timekeeper.mult,
                                  timekeeper.shift);
}

static inline s64 timekeeping_get_ns_raw(void)
{
        cycle_t cycle_now, cycle_delta;
        struct clocksource *clock;

        /* read clocksource: */
        clock = timekeeper.clock;
        cycle_now = clock->read(clock);

        /* calculate the delta since the last update_wall_time: */
        cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

        /* return delta convert to nanoseconds using ntp adjusted mult. */
        return clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
}

/*
 * This read-write spinlock protects us from races in SMP while
 * playing with xtime.
 */
__cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);


/*
 * The current time
 * wall_to_monotonic is what we need to add to xtime (or xtime corrected
 * for sub jiffie times) to get to monotonic time.  Monotonic is pegged
 * at zero at system boot time, so wall_to_monotonic will be negative,
 * however, we will ALWAYS keep the tv_nsec part positive so we can use
 * the usual normalization.
 *
 * wall_to_monotonic is moved after resume from suspend for the monotonic
 * time not to jump. We need to add total_sleep_time to wall_to_monotonic
 * to get the real boot based time offset.
 *
 * - wall_to_monotonic is no longer the boot time, getboottime must be
 * used instead.
 */
static struct timespec xtime __attribute__ ((aligned (16)));
static struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
static struct timespec total_sleep_time;

/*
 * The raw monotonic time for the CLOCK_MONOTONIC_RAW posix clock.
 */
static struct timespec raw_time;

/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;

/* must hold xtime_lock */
void timekeeping_leap_insert(int leapsecond)
{
        xtime.tv_sec += leapsecond;
        wall_to_monotonic.tv_sec -= leapsecond;
        update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
                        timekeeper.mult);
}

/**
 * timekeeping_forward_now - update clock to the current time
 *
 * Forward the current clock to update its state since the last call to
 * update_wall_time(). This is useful before significant clock changes,
 * as it avoids having to deal with this time offset explicitly.
 */
static void timekeeping_forward_now(void)
{
        cycle_t cycle_now, cycle_delta;
        struct clocksource *clock;
        s64 nsec;

        clock = timekeeper.clock;
        cycle_now = clock->read(clock);
        cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
        clock->cycle_last = cycle_now;

        nsec = clocksource_cyc2ns(cycle_delta, timekeeper.mult,
                                  timekeeper.shift);

        /* If arch requires, add in gettimeoffset() */
        nsec += arch_gettimeoffset();

        timespec_add_ns(&xtime, nsec);

        nsec = clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
        timespec_add_ns(&raw_time, nsec);
}

/**
 * getnstimeofday - Returns the time of day in a timespec
 * @ts:         pointer to the timespec to be set
 *
 * Returns the time of day in a timespec.
 */
void getnstimeofday(struct timespec *ts)
{
        unsigned long seq;
        s64 nsecs;

        WARN_ON(timekeeping_suspended);

        do {
                seq = read_seqbegin(&xtime_lock);

                *ts = xtime;
                nsecs = timekeeping_get_ns();

                /* If arch requires, add in gettimeoffset() */
                nsecs += arch_gettimeoffset();

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

        timespec_add_ns(ts, nsecs);
}

EXPORT_SYMBOL(getnstimeofday);

ktime_t ktime_get(void)
{
        unsigned int seq;
        s64 secs, nsecs;

        WARN_ON(timekeeping_suspended);

        do {
                seq = read_seqbegin(&xtime_lock);
                secs = xtime.tv_sec + wall_to_monotonic.tv_sec;
                nsecs = xtime.tv_nsec + wall_to_monotonic.tv_nsec;
                nsecs += timekeeping_get_ns();

        } while (read_seqretry(&xtime_lock, seq));
        /*
         * Use ktime_set/ktime_add_ns to create a proper ktime on
         * 32-bit architectures without CONFIG_KTIME_SCALAR.
         */
        return ktime_add_ns(ktime_set(secs, 0), nsecs);
}
EXPORT_SYMBOL_GPL(ktime_get);

/**
 * 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 int seq;
        s64 nsecs;

        WARN_ON(timekeeping_suspended);

        do {
                seq = read_seqbegin(&xtime_lock);
                *ts = xtime;
                tomono = wall_to_monotonic;
                nsecs = timekeeping_get_ns();

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

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

#ifdef CONFIG_NTP_PPS

/**
 * getnstime_raw_and_real - get day and raw monotonic time in timespec format
 * @ts_raw:     pointer to the timespec to be set to raw monotonic time
 * @ts_real:    pointer to the timespec to be set to the time of day
 *
 * This function reads both the time of day and raw monotonic time at the
 * same time atomically and stores the resulting timestamps in timespec
 * format.
 */
void getnstime_raw_and_real(struct timespec *ts_raw, struct timespec *ts_real)
{
        unsigned long seq;
        s64 nsecs_raw, nsecs_real;

        WARN_ON_ONCE(timekeeping_suspended);

        do {
                u32 arch_offset;

                seq = read_seqbegin(&xtime_lock);

                *ts_raw = raw_time;
                *ts_real = xtime;

                nsecs_raw = timekeeping_get_ns_raw();
                nsecs_real = timekeeping_get_ns();

                /* If arch requires, add in gettimeoffset() */
                arch_offset = arch_gettimeoffset();
                nsecs_raw += arch_offset;
                nsecs_real += arch_offset;

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

        timespec_add_ns(ts_raw, nsecs_raw);
        timespec_add_ns(ts_real, nsecs_real);
}
EXPORT_SYMBOL(getnstime_raw_and_real);

#endif /* CONFIG_NTP_PPS */

/**
 * do_gettimeofday - Returns the time of day in a timeval
 * @tv:         pointer to the timeval to be set
 *
 * NOTE: Users should be converted to using getnstimeofday()
 */
void do_gettimeofday(struct timeval *tv)
{
        struct timespec now;

        getnstimeofday(&now);
        tv->tv_sec = now.tv_sec;
        tv->tv_usec = now.tv_nsec/1000;
}

EXPORT_SYMBOL(do_gettimeofday);
/**
 * do_settimeofday - Sets the time of day
 * @tv:         pointer to the timespec variable containing the new time
 *
 * Sets the time of day to the new time and update NTP and notify hrtimers
 */
int do_settimeofday(struct timespec *tv)
{
        struct timespec ts_delta;
        unsigned long flags;

        if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
                return -EINVAL;

        write_seqlock_irqsave(&xtime_lock, flags);

        timekeeping_forward_now();

        ts_delta.tv_sec = tv->tv_sec - xtime.tv_sec;
        ts_delta.tv_nsec = tv->tv_nsec - xtime.tv_nsec;
        wall_to_monotonic = timespec_sub(wall_to_monotonic, ts_delta);

        xtime = *tv;

        timekeeper.ntp_error = 0;
        ntp_clear();

        update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
                                timekeeper.mult);

        write_sequnlock_irqrestore(&xtime_lock, flags);

        /* signal hrtimers about time change */
        clock_was_set();

        return 0;
}

EXPORT_SYMBOL(do_settimeofday);

/**
 * change_clocksource - Swaps clocksources if a new one is available
 *
 * Accumulates current time interval and initializes new clocksource
 */
static int change_clocksource(void *data)
{
        struct clocksource *new, *old;

        new = (struct clocksource *) data;

        timekeeping_forward_now();
        if (!new->enable || new->enable(new) == 0) {
                old = timekeeper.clock;
                timekeeper_setup_internals(new);
                if (old->disable)
                        old->disable(old);
        }
        return 0;
}

/**
 * timekeeping_notify - Install a new clock source
 * @clock:              pointer to the clock source
 *
 * This function is called from clocksource.c after a new, better clock
 * source has been registered. The caller holds the clocksource_mutex.
 */
void timekeeping_notify(struct clocksource *clock)
{
        if (timekeeper.clock == clock)
                return;
        stop_machine(change_clocksource, clock, NULL);
        tick_clock_notify();
}

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

        getnstimeofday(&now);

        return timespec_to_ktime(now);
}
EXPORT_SYMBOL_GPL(ktime_get_real);

/**
 * getrawmonotonic - Returns the raw monotonic time in a timespec
 * @ts:         pointer to the timespec to be set
 *
 * Returns the raw monotonic time (completely un-modified by ntp)
 */
void getrawmonotonic(struct timespec *ts)
{
        unsigned long seq;
        s64 nsecs;

        do {
                seq = read_seqbegin(&xtime_lock);
                nsecs = timekeeping_get_ns_raw();
                *ts = raw_time;

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

        timespec_add_ns(ts, nsecs);
}
EXPORT_SYMBOL(getrawmonotonic);


/**
 * timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
 */
int timekeeping_valid_for_hres(void)
{
        unsigned long seq;
        int ret;

        do {
                seq = read_seqbegin(&xtime_lock);

                ret = timekeeper.clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

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

        return ret;
}

/**
 * timekeeping_max_deferment - Returns max time the clocksource can be deferred
 *
 * Caller must observe xtime_lock via read_seqbegin/read_seqretry to
 * ensure that the clocksource does not change!
 */
u64 timekeeping_max_deferment(void)
{
        return timekeeper.clock->max_idle_ns;
}

/**
 * read_persistent_clock -  Return time from the persistent clock.
 *
 * Weak dummy function for arches that do not yet support it.
 * Reads the time from the battery backed persistent clock.
 * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
 *
 *  XXX - Do be sure to remove it once all arches implement it.
 */
void __attribute__((weak)) read_persistent_clock(struct timespec *ts)
{
        ts->tv_sec = 0;
        ts->tv_nsec = 0;
}

/**
 * read_boot_clock -  Return time of the system start.
 *
 * Weak dummy function for arches that do not yet support it.
 * Function to read the exact time the system has been started.
 * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
 *
 *  XXX - Do be sure to remove it once all arches implement it.
 */
void __attribute__((weak)) read_boot_clock(struct timespec *ts)
{
        ts->tv_sec = 0;
        ts->tv_nsec = 0;
}

/*
 * timekeeping_init - Initializes the clocksource and common timekeeping values
 */
void __init timekeeping_init(void)
{
        struct clocksource *clock;
        unsigned long flags;
        struct timespec now, boot;

        read_persistent_clock(&now);
        read_boot_clock(&boot);

        write_seqlock_irqsave(&xtime_lock, flags);

        ntp_init();

        clock = clocksource_default_clock();
        if (clock->enable)
                clock->enable(clock);
        timekeeper_setup_internals(clock);

        xtime.tv_sec = now.tv_sec;
        xtime.tv_nsec = now.tv_nsec;
        raw_time.tv_sec = 0;
        raw_time.tv_nsec = 0;
        if (boot.tv_sec == 0 && boot.tv_nsec == 0) {
                boot.tv_sec = xtime.tv_sec;
                boot.tv_nsec = xtime.tv_nsec;
        }
        set_normalized_timespec(&wall_to_monotonic,
                                -boot.tv_sec, -boot.tv_nsec);
        total_sleep_time.tv_sec = 0;
        total_sleep_time.tv_nsec = 0;
        write_sequnlock_irqrestore(&xtime_lock, flags);
}

/* time in seconds when suspend began */
static struct timespec timekeeping_suspend_time;

/**
 * timekeeping_resume - Resumes the generic timekeeping subsystem.
 * @dev:        unused
 *
 * This is for the generic clocksource timekeeping.
 * xtime/wall_to_monotonic/jiffies/etc are
 * still managed by arch specific suspend/resume code.
 */
static int timekeeping_resume(struct sys_device *dev)
{
        unsigned long flags;
        struct timespec ts;

        read_persistent_clock(&ts);

        clocksource_resume();

        write_seqlock_irqsave(&xtime_lock, flags);

        if (timespec_compare(&ts, &timekeeping_suspend_time) > 0) {
                ts = timespec_sub(ts, timekeeping_suspend_time);
                xtime = timespec_add(xtime, ts);
                wall_to_monotonic = timespec_sub(wall_to_monotonic, ts);
                total_sleep_time = timespec_add(total_sleep_time, ts);
        }
        /* re-base the last cycle value */
        timekeeper.clock->cycle_last = timekeeper.clock->read(timekeeper.clock);
        timekeeper.ntp_error = 0;
        timekeeping_suspended = 0;
        write_sequnlock_irqrestore(&xtime_lock, flags);

        touch_softlockup_watchdog();

        clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);

        /* Resume hrtimers */
        hres_timers_resume();

        return 0;
}

static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
{
        unsigned long flags;

        read_persistent_clock(&timekeeping_suspend_time);

        write_seqlock_irqsave(&xtime_lock, flags);
        timekeeping_forward_now();
        timekeeping_suspended = 1;
        write_sequnlock_irqrestore(&xtime_lock, flags);

        clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
        clocksource_suspend();

        return 0;
}

/* sysfs resume/suspend bits for timekeeping */
static struct sysdev_class timekeeping_sysclass = {
        .name           = "timekeeping",
        .resume         = timekeeping_resume,
        .suspend        = timekeeping_suspend,
};

static struct sys_device device_timer = {
        .id             = 0,
        .cls            = &timekeeping_sysclass,
};

static int __init timekeeping_init_device(void)
{
        int error = sysdev_class_register(&timekeeping_sysclass);
        if (!error)
                error = sysdev_register(&device_timer);
        return error;
}

device_initcall(timekeeping_init_device);

/*
 * If the error is already larger, we look ahead even further
 * to compensate for late or lost adjustments.
 */
static __always_inline int timekeeping_bigadjust(s64 error, s64 *interval,
                                                 s64 *offset)
{
        s64 tick_error, i;
        u32 look_ahead, adj;
        s32 error2, mult;

        /*
         * Use the current error value to determine how much to look ahead.
         * The larger the error the slower we adjust for it to avoid problems
         * with losing too many ticks, otherwise we would overadjust and
         * produce an even larger error.  The smaller the adjustment the
         * faster we try to adjust for it, as lost ticks can do less harm
         * here.  This is tuned so that an error of about 1 msec is adjusted
         * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
         */
        error2 = timekeeper.ntp_error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
        error2 = abs(error2);
        for (look_ahead = 0; error2 > 0; look_ahead++)
                error2 >>= 2;

        /*
         * Now calculate the error in (1 << look_ahead) ticks, but first
         * remove the single look ahead already included in the error.
         */
        tick_error = tick_length >> (timekeeper.ntp_error_shift + 1);
        tick_error -= timekeeper.xtime_interval >> 1;
        error = ((error - tick_error) >> look_ahead) + tick_error;

        /* Finally calculate the adjustment shift value.  */
        i = *interval;
        mult = 1;
        if (error < 0) {
                error = -error;
                *interval = -*interval;
                *offset = -*offset;
                mult = -1;
        }
        for (adj = 0; error > i; adj++)
                error >>= 1;

        *interval <<= adj;
        *offset <<= adj;
        return mult << adj;
}

/*
 * Adjust the multiplier to reduce the error value,
 * this is optimized for the most common adjustments of -1,0,1,
 * for other values we can do a bit more work.
 */
static void timekeeping_adjust(s64 offset)
{
        s64 error, interval = timekeeper.cycle_interval;
        int adj;

        error = timekeeper.ntp_error >> (timekeeper.ntp_error_shift - 1);
        if (error > interval) {
                error >>= 2;
                if (likely(error <= interval))
                        adj = 1;
                else
                        adj = timekeeping_bigadjust(error, &interval, &offset);
        } else if (error < -interval) {
                error >>= 2;
                if (likely(error >= -interval)) {
                        adj = -1;
                        interval = -interval;
                        offset = -offset;
                } else
                        adj = timekeeping_bigadjust(error, &interval, &offset);
        } else
                return;

        timekeeper.mult += adj;
        timekeeper.xtime_interval += interval;
        timekeeper.xtime_nsec -= offset;
        timekeeper.ntp_error -= (interval - offset) <<
                                timekeeper.ntp_error_shift;
}


/**
 * logarithmic_accumulation - shifted accumulation of cycles
 *
 * This functions accumulates a shifted interval of cycles into
 * into a shifted interval nanoseconds. Allows for O(log) accumulation
 * loop.
 *
 * Returns the unconsumed cycles.
 */
static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
{
        u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift;
        u64 raw_nsecs;

        /* If the offset is smaller then a shifted interval, do nothing */
        if (offset < timekeeper.cycle_interval<<shift)
                return offset;

        /* Accumulate one shifted interval */
        offset -= timekeeper.cycle_interval << shift;
        timekeeper.clock->cycle_last += timekeeper.cycle_interval << shift;

        timekeeper.xtime_nsec += timekeeper.xtime_interval << shift;
        while (timekeeper.xtime_nsec >= nsecps) {
                timekeeper.xtime_nsec -= nsecps;
                xtime.tv_sec++;
                second_overflow();
        }

        /* Accumulate raw time */
        raw_nsecs = timekeeper.raw_interval << shift;
        raw_nsecs += raw_time.tv_nsec;
        if (raw_nsecs >= NSEC_PER_SEC) {
                u64 raw_secs = raw_nsecs;
                raw_nsecs = do_div(raw_secs, NSEC_PER_SEC);
                raw_time.tv_sec += raw_secs;
        }
        raw_time.tv_nsec = raw_nsecs;

        /* Accumulate error between NTP and clock interval */
        timekeeper.ntp_error += tick_length << shift;
        timekeeper.ntp_error -=
            (timekeeper.xtime_interval + timekeeper.xtime_remainder) <<
                                (timekeeper.ntp_error_shift + shift);

        return offset;
}


/**
 * update_wall_time - Uses the current clocksource to increment the wall time
 *
 * Called from the timer interrupt, must hold a write on xtime_lock.
 */
void update_wall_time(void)
{
        struct clocksource *clock;
        cycle_t offset;
        int shift = 0, maxshift;

        /* Make sure we're fully resumed: */
        if (unlikely(timekeeping_suspended))
                return;

        clock = timekeeper.clock;

#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
        offset = timekeeper.cycle_interval;
#else
        offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
#endif
        timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;

        /*
         * With NO_HZ we may have to accumulate many cycle_intervals
         * (think "ticks") worth of time at once. To do this efficiently,
         * we calculate the largest doubling multiple of cycle_intervals
         * that is smaller then the offset. We then accumulate that
         * chunk in one go, and then try to consume the next smaller
         * doubled multiple.
         */
        shift = ilog2(offset) - ilog2(timekeeper.cycle_interval);
        shift = max(0, shift);
        /* Bound shift to one less then what overflows tick_length */
        maxshift = (8*sizeof(tick_length) - (ilog2(tick_length)+1)) - 1;
        shift = min(shift, maxshift);
        while (offset >= timekeeper.cycle_interval) {
                offset = logarithmic_accumulation(offset, shift);
                if(offset < timekeeper.cycle_interval<<shift)
                        shift--;
        }

        /* correct the clock when NTP error is too big */
        timekeeping_adjust(offset);

        /*
         * Since in the loop above, we accumulate any amount of time
         * in xtime_nsec over a second into xtime.tv_sec, its possible for
         * xtime_nsec to be fairly small after the loop. Further, if we're
         * slightly speeding the clocksource up in timekeeping_adjust(),
         * its possible the required corrective factor to xtime_nsec could
         * cause it to underflow.
         *
         * Now, we cannot simply roll the accumulated second back, since
         * the NTP subsystem has been notified via second_overflow. So
         * instead we push xtime_nsec forward by the amount we underflowed,
         * and add that amount into the error.
         *
         * We'll correct this error next time through this function, when
         * xtime_nsec is not as small.
         */
        if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
                s64 neg = -(s64)timekeeper.xtime_nsec;
                timekeeper.xtime_nsec = 0;
                timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
        }


        /*
         * Store full nanoseconds into xtime after rounding it up and
         * add the remainder to the error difference.
         */
        xtime.tv_nsec = ((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;
        timekeeper.xtime_nsec -= (s64) xtime.tv_nsec << timekeeper.shift;
        timekeeper.ntp_error += timekeeper.xtime_nsec <<
                                timekeeper.ntp_error_shift;

        /*
         * Finally, make sure that after the rounding
         * xtime.tv_nsec isn't larger then NSEC_PER_SEC
         */
        if (unlikely(xtime.tv_nsec >= NSEC_PER_SEC)) {
                xtime.tv_nsec -= NSEC_PER_SEC;
                xtime.tv_sec++;
                second_overflow();
        }

        /* check to see if there is a new clocksource to use */
        update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
                                timekeeper.mult);
}

/**
 * getboottime - Return the real time of system boot.
 * @ts:         pointer to the timespec to be set
 *
 * Returns the time of day in a timespec.
 *
 * This is based on the wall_to_monotonic offset and the total suspend
 * time. Calls to settimeofday will affect the value returned (which
 * basically means that however wrong your real time clock is at boot time,
 * you get the right time here).
 */
void getboottime(struct timespec *ts)
{
        struct timespec boottime = {
                .tv_sec = wall_to_monotonic.tv_sec + total_sleep_time.tv_sec,
                .tv_nsec = wall_to_monotonic.tv_nsec + total_sleep_time.tv_nsec
        };

        set_normalized_timespec(ts, -boottime.tv_sec, -boottime.tv_nsec);
}
EXPORT_SYMBOL_GPL(getboottime);

/**
 * monotonic_to_bootbased - Convert the monotonic time to boot based.
 * @ts:         pointer to the timespec to be converted
 */
void monotonic_to_bootbased(struct timespec *ts)
{
        *ts = timespec_add(*ts, total_sleep_time);
}
EXPORT_SYMBOL_GPL(monotonic_to_bootbased);

unsigned long get_seconds(void)
{
        return xtime.tv_sec;
}
EXPORT_SYMBOL(get_seconds);

struct timespec __current_kernel_time(void)
{
        return xtime;
}

struct timespec __get_wall_to_monotonic(void)
{
        return wall_to_monotonic;
}

struct timespec current_kernel_time(void)
{
        struct timespec now;
        unsigned long seq;

        do {
                seq = read_seqbegin(&xtime_lock);

                now = xtime;
        } while (read_seqretry(&xtime_lock, seq));

        return now;
}
EXPORT_SYMBOL(current_kernel_time);

struct timespec get_monotonic_coarse(void)
{
        struct timespec now, mono;
        unsigned long seq;

        do {
                seq = read_seqbegin(&xtime_lock);

                now = xtime;
                mono = wall_to_monotonic;
        } while (read_seqretry(&xtime_lock, seq));

        set_normalized_timespec(&now, now.tv_sec + mono.tv_sec,
                                now.tv_nsec + mono.tv_nsec);
        return now;
}