[linux-flexiantxendom0-3.2.10.git] / kernel / timer.c

/*
 *  linux/kernel/timer.c
 *
 *  Kernel internal timers, kernel timekeeping, basic process system calls
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  1997-01-28  Modified by Finn Arne Gangstad to make timers scale better.
 *
 *  1997-09-10  Updated NTP code according to technical memorandum Jan '96
 *              "A Kernel Model for Precision Timekeeping" by Dave Mills
 *  1998-12-24  Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
 *              serialize accesses to xtime/lost_ticks).
 *                              Copyright (C) 1998  Andrea Arcangeli
 *  1999-03-10  Improved NTP compatibility by Ulrich Windl
 *  2002-05-31  Move sys_sysinfo here and make its locking sane, Robert Love
 *  2000-10-05  Implemented scalable SMP per-CPU timer handling.
 *                              Copyright (C) 2000, 2001, 2002  Ingo Molnar
 *              Designed by David S. Miller, Alexey Kuznetsov and Ingo Molnar
 */

#include <linux/kernel_stat.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/notifier.h>
#include <linux/thread_info.h>
#include <linux/time.h>
#include <linux/jiffies.h>
#include <linux/cpu.h>

#include <asm/uaccess.h>
#include <asm/unistd.h>
#include <asm/div64.h>
#include <asm/timex.h>

/*
 * per-CPU timer vector definitions:
 */
#define TVN_BITS 6
#define TVR_BITS 8
#define TVN_SIZE (1 << TVN_BITS)
#define TVR_SIZE (1 << TVR_BITS)
#define TVN_MASK (TVN_SIZE - 1)
#define TVR_MASK (TVR_SIZE - 1)

typedef struct tvec_s {
        struct list_head vec[TVN_SIZE];
} tvec_t;

typedef struct tvec_root_s {
        struct list_head vec[TVR_SIZE];
} tvec_root_t;

struct tvec_t_base_s {
        spinlock_t lock;
        unsigned long timer_jiffies;
        struct timer_list *running_timer;
        tvec_root_t tv1;
        tvec_t tv2;
        tvec_t tv3;
        tvec_t tv4;
        tvec_t tv5;
} ____cacheline_aligned_in_smp;

typedef struct tvec_t_base_s tvec_base_t;

static inline void set_running_timer(tvec_base_t *base,
                                        struct timer_list *timer)
{
#ifdef CONFIG_SMP
        base->running_timer = timer;
#endif
}

/* Fake initialization */
static DEFINE_PER_CPU(tvec_base_t, tvec_bases) = { SPIN_LOCK_UNLOCKED };

static void check_timer_failed(struct timer_list *timer)
{
        static int whine_count;
        if (whine_count < 16) {
                whine_count++;
                printk("Uninitialised timer!\n");
                printk("This is just a warning.  Your computer is OK\n");
                printk("function=0x%p, data=0x%lx\n",
                        timer->function, timer->data);
                dump_stack();
        }
        /*
         * Now fix it up
         */
        spin_lock_init(&timer->lock);
        timer->magic = TIMER_MAGIC;
}

static inline void check_timer(struct timer_list *timer)
{
        if (timer->magic != TIMER_MAGIC)
                check_timer_failed(timer);
}


static void internal_add_timer(tvec_base_t *base, struct timer_list *timer)
{
        unsigned long expires = timer->expires;
        unsigned long idx = expires - base->timer_jiffies;
        struct list_head *vec;

        if (idx < TVR_SIZE) {
                int i = expires & TVR_MASK;
                vec = base->tv1.vec + i;
        } else if (idx < 1 << (TVR_BITS + TVN_BITS)) {
                int i = (expires >> TVR_BITS) & TVN_MASK;
                vec = base->tv2.vec + i;
        } else if (idx < 1 << (TVR_BITS + 2 * TVN_BITS)) {
                int i = (expires >> (TVR_BITS + TVN_BITS)) & TVN_MASK;
                vec = base->tv3.vec + i;
        } else if (idx < 1 << (TVR_BITS + 3 * TVN_BITS)) {
                int i = (expires >> (TVR_BITS + 2 * TVN_BITS)) & TVN_MASK;
                vec = base->tv4.vec + i;
        } else if ((signed long) idx < 0) {
                /*
                 * Can happen if you add a timer with expires == jiffies,
                 * or you set a timer to go off in the past
                 */
                vec = base->tv1.vec + (base->timer_jiffies & TVR_MASK);
        } else {
                int i;
                /* If the timeout is larger than 0xffffffff on 64-bit
                 * architectures then we use the maximum timeout:
                 */
                if (idx > 0xffffffffUL) {
                        idx = 0xffffffffUL;
                        expires = idx + base->timer_jiffies;
                }
                i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK;
                vec = base->tv5.vec + i;
        }
        /*
         * Timers are FIFO:
         */
        list_add_tail(&timer->entry, vec);
}

int __mod_timer(struct timer_list *timer, unsigned long expires)
{
        tvec_base_t *old_base, *new_base;
        unsigned long flags;
        int ret = 0;

        BUG_ON(!timer->function);

        check_timer(timer);

        spin_lock_irqsave(&timer->lock, flags);
        new_base = &__get_cpu_var(tvec_bases);
repeat:
        old_base = timer->base;

        /*
         * Prevent deadlocks via ordering by old_base < new_base.
         */
        if (old_base && (new_base != old_base)) {
                if (old_base < new_base) {
                        spin_lock(&new_base->lock);
                        spin_lock(&old_base->lock);
                } else {
                        spin_lock(&old_base->lock);
                        spin_lock(&new_base->lock);
                }
                /*
                 * The timer base might have been cancelled while we were
                 * trying to take the lock(s):
                 */
                if (timer->base != old_base) {
                        spin_unlock(&new_base->lock);
                        spin_unlock(&old_base->lock);
                        goto repeat;
                }
        } else {
                spin_lock(&new_base->lock);
                if (timer->base != old_base) {
                        spin_unlock(&new_base->lock);
                        goto repeat;
                }
        }

        /*
         * Delete the previous timeout (if there was any), and install
         * the new one:
         */
        if (old_base) {
                list_del(&timer->entry);
                ret = 1;
        }
        timer->expires = expires;
        internal_add_timer(new_base, timer);
        timer->base = new_base;

        if (old_base && (new_base != old_base))
                spin_unlock(&old_base->lock);
        spin_unlock(&new_base->lock);
        spin_unlock_irqrestore(&timer->lock, flags);

        return ret;
}

EXPORT_SYMBOL(__mod_timer);

/***
 * add_timer_on - start a timer on a particular CPU
 * @timer: the timer to be added
 * @cpu: the CPU to start it on
 *
 * This is not very scalable on SMP. Double adds are not possible.
 */
void add_timer_on(struct timer_list *timer, int cpu)
{
        tvec_base_t *base = &per_cpu(tvec_bases, cpu);
        unsigned long flags;
  
        BUG_ON(timer_pending(timer) || !timer->function);

        check_timer(timer);

        spin_lock_irqsave(&base->lock, flags);
        internal_add_timer(base, timer);
        timer->base = base;
        spin_unlock_irqrestore(&base->lock, flags);
}

/***
 * mod_timer - modify a timer's timeout
 * @timer: the timer to be modified
 *
 * mod_timer is a more efficient way to update the expire field of an
 * active timer (if the timer is inactive it will be activated)
 *
 * mod_timer(timer, expires) is equivalent to:
 *
 *     del_timer(timer); timer->expires = expires; add_timer(timer);
 *
 * Note that if there are multiple unserialized concurrent users of the
 * same timer, then mod_timer() is the only safe way to modify the timeout,
 * since add_timer() cannot modify an already running timer.
 *
 * The function returns whether it has modified a pending timer or not.
 * (ie. mod_timer() of an inactive timer returns 0, mod_timer() of an
 * active timer returns 1.)
 */
int mod_timer(struct timer_list *timer, unsigned long expires)
{
        BUG_ON(!timer->function);

        check_timer(timer);

        /*
         * This is a common optimization triggered by the
         * networking code - if the timer is re-modified
         * to be the same thing then just return:
         */
        if (timer->expires == expires && timer_pending(timer))
                return 1;

        return __mod_timer(timer, expires);
}

EXPORT_SYMBOL(mod_timer);

/***
 * del_timer - deactive a timer.
 * @timer: the timer to be deactivated
 *
 * del_timer() deactivates a timer - this works on both active and inactive
 * timers.
 *
 * The function returns whether it has deactivated a pending timer or not.
 * (ie. del_timer() of an inactive timer returns 0, del_timer() of an
 * active timer returns 1.)
 */
int del_timer(struct timer_list *timer)
{
        unsigned long flags;
        tvec_base_t *base;

        check_timer(timer);

repeat:
        base = timer->base;
        if (!base)
                return 0;
        spin_lock_irqsave(&base->lock, flags);
        if (base != timer->base) {
                spin_unlock_irqrestore(&base->lock, flags);
                goto repeat;
        }
        list_del(&timer->entry);
        timer->base = NULL;
        spin_unlock_irqrestore(&base->lock, flags);

        return 1;
}

EXPORT_SYMBOL(del_timer);

#ifdef CONFIG_SMP
/***
 * del_timer_sync - deactivate a timer and wait for the handler to finish.
 * @timer: the timer to be deactivated
 *
 * This function only differs from del_timer() on SMP: besides deactivating
 * the timer it also makes sure the handler has finished executing on other
 * CPUs.
 *
 * Synchronization rules: callers must prevent restarting of the timer,
 * otherwise this function is meaningless. It must not be called from
 * interrupt contexts. The caller must not hold locks which would prevent
 * completion of the timer's handler.  Upon exit the timer is not queued and
 * the handler is not running on any CPU.
 *
 * The function returns whether it has deactivated a pending timer or not.
 *
 * del_timer_sync() is slow and complicated because it copes with timer
 * handlers which re-arm the timer (periodic timers).  If the timer handler
 * is known to not do this (a single shot timer) then use
 * del_singleshot_timer_sync() instead.
 */
int del_timer_sync(struct timer_list *timer)
{
        tvec_base_t *base;
        int i, ret = 0;

        check_timer(timer);

del_again:
        ret += del_timer(timer);

        for_each_online_cpu(i) {
                base = &per_cpu(tvec_bases, i);
                if (base->running_timer == timer) {
                        while (base->running_timer == timer) {
                                cpu_relax();
                                preempt_check_resched();
                        }
                        break;
                }
        }
        smp_rmb();
        if (timer_pending(timer))
                goto del_again;

        return ret;
}
EXPORT_SYMBOL(del_timer_sync);

/***
 * del_singleshot_timer_sync - deactivate a non-recursive timer
 * @timer: the timer to be deactivated
 *
 * This function is an optimization of del_timer_sync for the case where the
 * caller can guarantee the timer does not reschedule itself in its timer
 * function.
 *
 * Synchronization rules: callers must prevent restarting of the timer,
 * otherwise this function is meaningless. It must not be called from
 * interrupt contexts. The caller must not hold locks which wold prevent
 * completion of the timer's handler.  Upon exit the timer is not queued and
 * the handler is not running on any CPU.
 *
 * The function returns whether it has deactivated a pending timer or not.
 */
int del_singleshot_timer_sync(struct timer_list *timer)
{
        int ret = del_timer(timer);

        if (!ret) {
                ret = del_timer_sync(timer);
                BUG_ON(ret);
        }

        return ret;
}
EXPORT_SYMBOL(del_singleshot_timer_sync);
#endif

static int cascade(tvec_base_t *base, tvec_t *tv, int index)
{
        /* cascade all the timers from tv up one level */
        struct list_head *head, *curr;

        head = tv->vec + index;
        curr = head->next;
        /*
         * We are removing _all_ timers from the list, so we don't  have to
         * detach them individually, just clear the list afterwards.
         */
        while (curr != head) {
                struct timer_list *tmp;

                tmp = list_entry(curr, struct timer_list, entry);
                BUG_ON(tmp->base != base);
                curr = curr->next;
                internal_add_timer(base, tmp);
        }
        INIT_LIST_HEAD(head);

        return index;
}

/***
 * __run_timers - run all expired timers (if any) on this CPU.
 * @base: the timer vector to be processed.
 *
 * This function cascades all vectors and executes all expired timer
 * vectors.
 */
#define INDEX(N) (base->timer_jiffies >> (TVR_BITS + N * TVN_BITS)) & TVN_MASK

static inline void __run_timers(tvec_base_t *base)
{
        struct timer_list *timer;

        spin_lock_irq(&base->lock);
        while (time_after_eq(jiffies, base->timer_jiffies)) {
                struct list_head work_list = LIST_HEAD_INIT(work_list);
                struct list_head *head = &work_list;
                int index = base->timer_jiffies & TVR_MASK;
 
                /*
                 * Cascade timers:
                 */
                if (!index &&
                        (!cascade(base, &base->tv2, INDEX(0))) &&
                                (!cascade(base, &base->tv3, INDEX(1))) &&
                                        !cascade(base, &base->tv4, INDEX(2)))
                        cascade(base, &base->tv5, INDEX(3));
                ++base->timer_jiffies; 
                list_splice_init(base->tv1.vec + index, &work_list);
repeat:
                if (!list_empty(head)) {
                        void (*fn)(unsigned long);
                        unsigned long data;

                        timer = list_entry(head->next,struct timer_list,entry);
                        fn = timer->function;
                        data = timer->data;

                        list_del(&timer->entry);
                        set_running_timer(base, timer);
                        smp_wmb();
                        timer->base = NULL;
                        spin_unlock_irq(&base->lock);
                        fn(data);
                        spin_lock_irq(&base->lock);
                        goto repeat;
                }
        }
        set_running_timer(base, NULL);
        spin_unlock_irq(&base->lock);
}

#ifdef CONFIG_NO_IDLE_HZ
/*
 * Find out when the next timer event is due to happen. This
 * is used on S/390 to stop all activity when a cpus is idle.
 * This functions needs to be called disabled.
 */
unsigned long next_timer_interrupt(void)
{
        tvec_base_t *base;
        struct list_head *list;
        struct timer_list *nte;
        unsigned long expires;
        tvec_t *varray[4];
        int i, j;

        base = &__get_cpu_var(tvec_bases);
        spin_lock(&base->lock);
        expires = base->timer_jiffies + (LONG_MAX >> 1);
        list = 0;

        /* Look for timer events in tv1. */
        j = base->timer_jiffies & TVR_MASK;
        do {
                list_for_each_entry(nte, base->tv1.vec + j, entry) {
                        expires = nte->expires;
                        if (j < (base->timer_jiffies & TVR_MASK))
                                list = base->tv2.vec + (INDEX(0));
                        goto found;
                }
                j = (j + 1) & TVR_MASK;
        } while (j != (base->timer_jiffies & TVR_MASK));

        /* Check tv2-tv5. */
        varray[0] = &base->tv2;
        varray[1] = &base->tv3;
        varray[2] = &base->tv4;
        varray[3] = &base->tv5;
        for (i = 0; i < 4; i++) {
                j = INDEX(i);
                do {
                        if (list_empty(varray[i]->vec + j)) {
                                j = (j + 1) & TVN_MASK;
                                continue;
                        }
                        list_for_each_entry(nte, varray[i]->vec + j, entry)
                                if (time_before(nte->expires, expires))
                                        expires = nte->expires;
                        if (j < (INDEX(i)) && i < 3)
                                list = varray[i + 1]->vec + (INDEX(i + 1));
                        goto found;
                } while (j != (INDEX(i)));
        }
found:
        if (list) {
                /*
                 * The search wrapped. We need to look at the next list
                 * from next tv element that would cascade into tv element
                 * where we found the timer element.
                 */
                list_for_each_entry(nte, list, entry) {
                        if (time_before(nte->expires, expires))
                                expires = nte->expires;
                }
        }
        spin_unlock(&base->lock);
        return expires;
}
#endif

/******************************************************************/

/*
 * Timekeeping variables
 */
unsigned long tick_usec = TICK_USEC;            /* USER_HZ period (usec) */
unsigned long tick_nsec = TICK_NSEC;            /* ACTHZ period (nsec) */

/* 
 * 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 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.
 */
struct timespec xtime __attribute__ ((aligned (16)));
struct timespec wall_to_monotonic __attribute__ ((aligned (16)));

EXPORT_SYMBOL(xtime);

/* Don't completely fail for HZ > 500.  */
int tickadj = 500/HZ ? : 1;             /* microsecs */


/*
 * phase-lock loop variables
 */
/* TIME_ERROR prevents overwriting the CMOS clock */
int time_state = TIME_OK;               /* clock synchronization status */
int time_status = STA_UNSYNC;           /* clock status bits            */
long time_offset;                       /* time adjustment (us)         */
long time_constant = 2;                 /* pll time constant            */
long time_tolerance = MAXFREQ;          /* frequency tolerance (ppm)    */
long time_precision = 1;                /* clock precision (us)         */
long time_maxerror = NTP_PHASE_LIMIT;   /* maximum error (us)           */
long time_esterror = NTP_PHASE_LIMIT;   /* estimated error (us)         */
long time_phase;                        /* phase offset (scaled us)     */
long time_freq = (((NSEC_PER_SEC + HZ/2) % HZ - HZ/2) << SHIFT_USEC) / NSEC_PER_USEC;
                                        /* frequency offset (scaled ppm)*/
long time_adj;                          /* tick adjust (scaled 1 / HZ)  */
long time_reftime;                      /* time at last adjustment (s)  */
long time_adjust;
long time_next_adjust;

/*
 * this routine handles the overflow of the microsecond field
 *
 * The tricky bits of code to handle the accurate clock support
 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
 * They were originally developed for SUN and DEC kernels.
 * All the kudos should go to Dave for this stuff.
 *
 */
static void second_overflow(void)
{
    long ltemp;

    /* Bump the maxerror field */
    time_maxerror += time_tolerance >> SHIFT_USEC;
    if ( time_maxerror > NTP_PHASE_LIMIT ) {
        time_maxerror = NTP_PHASE_LIMIT;
        time_status |= STA_UNSYNC;
    }

    /*
     * Leap second processing. If in leap-insert state at
     * the end of the day, the system clock is set back one
     * second; if in leap-delete state, the system clock is
     * set ahead one second. The microtime() routine or
     * external clock driver will insure that reported time
     * is always monotonic. The ugly divides should be
     * replaced.
     */
    switch (time_state) {

    case TIME_OK:
        if (time_status & STA_INS)
            time_state = TIME_INS;
        else if (time_status & STA_DEL)
            time_state = TIME_DEL;
        break;

    case TIME_INS:
        if (xtime.tv_sec % 86400 == 0) {
            xtime.tv_sec--;
            wall_to_monotonic.tv_sec++;
            time_interpolator_update(-NSEC_PER_SEC);
            time_state = TIME_OOP;
            clock_was_set();
            printk(KERN_NOTICE "Clock: inserting leap second 23:59:60 UTC\n");
        }
        break;

    case TIME_DEL:
        if ((xtime.tv_sec + 1) % 86400 == 0) {
            xtime.tv_sec++;
            wall_to_monotonic.tv_sec--;
            time_interpolator_update(NSEC_PER_SEC);
            time_state = TIME_WAIT;
            clock_was_set();
            printk(KERN_NOTICE "Clock: deleting leap second 23:59:59 UTC\n");
        }
        break;

    case TIME_OOP:
        time_state = TIME_WAIT;
        break;

    case TIME_WAIT:
        if (!(time_status & (STA_INS | STA_DEL)))
            time_state = TIME_OK;
    }

    /*
     * Compute the phase adjustment for the next second. In
     * PLL mode, the offset is reduced by a fixed factor
     * times the time constant. In FLL mode the offset is
     * used directly. In either mode, the maximum phase
     * adjustment for each second is clamped so as to spread
     * the adjustment over not more than the number of
     * seconds between updates.
     */
    if (time_offset < 0) {
        ltemp = -time_offset;
        if (!(time_status & STA_FLL))
            ltemp >>= SHIFT_KG + time_constant;
        if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
            ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE;
        time_offset += ltemp;
        time_adj = -ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
    } else {
        ltemp = time_offset;
        if (!(time_status & STA_FLL))
            ltemp >>= SHIFT_KG + time_constant;
        if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
            ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE;
        time_offset -= ltemp;
        time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
    }

    /*
     * Compute the frequency estimate and additional phase
     * adjustment due to frequency error for the next
     * second. When the PPS signal is engaged, gnaw on the
     * watchdog counter and update the frequency computed by
     * the pll and the PPS signal.
     */
    pps_valid++;
    if (pps_valid == PPS_VALID) {       /* PPS signal lost */
        pps_jitter = MAXTIME;
        pps_stabil = MAXFREQ;
        time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
                         STA_PPSWANDER | STA_PPSERROR);
    }
    ltemp = time_freq + pps_freq;
    if (ltemp < 0)
        time_adj -= -ltemp >>
            (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);
    else
        time_adj += ltemp >>
            (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE);

#if HZ == 100
    /* Compensate for (HZ==100) != (1 << SHIFT_HZ).
     * Add 25% and 3.125% to get 128.125; => only 0.125% error (p. 14)
     */
    if (time_adj < 0)
        time_adj -= (-time_adj >> 2) + (-time_adj >> 5);
    else
        time_adj += (time_adj >> 2) + (time_adj >> 5);
#endif
#if HZ == 1000
    /* Compensate for (HZ==1000) != (1 << SHIFT_HZ).
     * Add 1.5625% and 0.78125% to get 1023.4375; => only 0.05% error (p. 14)
     */
    if (time_adj < 0)
        time_adj -= (-time_adj >> 6) + (-time_adj >> 7);
    else
        time_adj += (time_adj >> 6) + (time_adj >> 7);
#endif
}

/* in the NTP reference this is called "hardclock()" */
static void update_wall_time_one_tick(void)
{
        long time_adjust_step, delta_nsec;

        if ( (time_adjust_step = time_adjust) != 0 ) {
            /* We are doing an adjtime thing. 
             *
             * Prepare time_adjust_step to be within bounds.
             * Note that a positive time_adjust means we want the clock
             * to run faster.
             *
             * Limit the amount of the step to be in the range
             * -tickadj .. +tickadj
             */
             if (time_adjust > tickadj)
                time_adjust_step = tickadj;
             else if (time_adjust < -tickadj)
                time_adjust_step = -tickadj;

            /* Reduce by this step the amount of time left  */
            time_adjust -= time_adjust_step;
        }
        delta_nsec = tick_nsec + time_adjust_step * 1000;
        /*
         * Advance the phase, once it gets to one microsecond, then
         * advance the tick more.
         */
        time_phase += time_adj;
        if (time_phase <= -FINENSEC) {
                long ltemp = -time_phase >> (SHIFT_SCALE - 10);
                time_phase += ltemp << (SHIFT_SCALE - 10);
                delta_nsec -= ltemp;
        }
        else if (time_phase >= FINENSEC) {
                long ltemp = time_phase >> (SHIFT_SCALE - 10);
                time_phase -= ltemp << (SHIFT_SCALE - 10);
                delta_nsec += ltemp;
        }
        xtime.tv_nsec += delta_nsec;
        time_interpolator_update(delta_nsec);

        /* Changes by adjtime() do not take effect till next tick. */
        if (time_next_adjust != 0) {
                time_adjust = time_next_adjust;
                time_next_adjust = 0;
        }
}

/*
 * Using a loop looks inefficient, but "ticks" is
 * usually just one (we shouldn't be losing ticks,
 * we're doing this this way mainly for interrupt
 * latency reasons, not because we think we'll
 * have lots of lost timer ticks
 */
static void update_wall_time(unsigned long ticks)
{
        do {
                ticks--;
                update_wall_time_one_tick();
        } while (ticks);

        if (xtime.tv_nsec >= 1000000000) {
            xtime.tv_nsec -= 1000000000;
            xtime.tv_sec++;
            second_overflow();
        }
}

static inline void do_process_times(struct task_struct *p,
        unsigned long user, unsigned long system)
{
        unsigned long psecs;

        psecs = (p->utime += user);
        psecs += (p->stime += system);
        if (psecs / HZ >= p->rlim[RLIMIT_CPU].rlim_cur) {
                /* Send SIGXCPU every second.. */
                if (!(psecs % HZ))
                        send_sig(SIGXCPU, p, 1);
                /* and SIGKILL when we go over max.. */
                if (psecs / HZ >= p->rlim[RLIMIT_CPU].rlim_max)
                        send_sig(SIGKILL, p, 1);
        }
}

static inline void do_it_virt(struct task_struct * p, unsigned long ticks)
{
        unsigned long it_virt = p->it_virt_value;

        if (it_virt) {
                it_virt -= ticks;
                if (!it_virt) {
                        it_virt = p->it_virt_incr;
                        send_sig(SIGVTALRM, p, 1);
                }
                p->it_virt_value = it_virt;
        }
}

static inline void do_it_prof(struct task_struct *p)
{
        unsigned long it_prof = p->it_prof_value;

        if (it_prof) {
                if (--it_prof == 0) {
                        it_prof = p->it_prof_incr;
                        send_sig(SIGPROF, p, 1);
                }
                p->it_prof_value = it_prof;
        }
}

static void update_one_process(struct task_struct *p, unsigned long user,
                        unsigned long system, int cpu)
{
        do_process_times(p, user, system);
        do_it_virt(p, user);
        do_it_prof(p);
}       

/*
 * Called from the timer interrupt handler to charge one tick to the current 
 * process.  user_tick is 1 if the tick is user time, 0 for system.
 */
void update_process_times(int user_tick)
{
        struct task_struct *p = current;
        int cpu = smp_processor_id(), system = user_tick ^ 1;

        update_one_process(p, user_tick, system, cpu);
        run_local_timers();
        scheduler_tick(user_tick, system);
}

/*
 * Nr of active tasks - counted in fixed-point numbers
 */
static unsigned long count_active_tasks(void)
{
        return (nr_running() + nr_uninterruptible()) * FIXED_1;
}

/*
 * Hmm.. Changed this, as the GNU make sources (load.c) seems to
 * imply that avenrun[] is the standard name for this kind of thing.
 * Nothing else seems to be standardized: the fractional size etc
 * all seem to differ on different machines.
 *
 * Requires xtime_lock to access.
 */
unsigned long avenrun[3];

/*
 * calc_load - given tick count, update the avenrun load estimates.
 * This is called while holding a write_lock on xtime_lock.
 */
static inline void calc_load(unsigned long ticks)
{
        unsigned long active_tasks; /* fixed-point */
        static int count = LOAD_FREQ;

        count -= ticks;
        if (count < 0) {
                count += LOAD_FREQ;
                active_tasks = count_active_tasks();
                CALC_LOAD(avenrun[0], EXP_1, active_tasks);
                CALC_LOAD(avenrun[1], EXP_5, active_tasks);
                CALC_LOAD(avenrun[2], EXP_15, active_tasks);
        }
}

/* jiffies at the most recent update of wall time */
unsigned long wall_jiffies = INITIAL_JIFFIES;

/*
 * This read-write spinlock protects us from races in SMP while
 * playing with xtime and avenrun.
 */
#ifndef ARCH_HAVE_XTIME_LOCK
seqlock_t xtime_lock __cacheline_aligned_in_smp = SEQLOCK_UNLOCKED;

EXPORT_SYMBOL(xtime_lock);
#endif

/*
 * This function runs timers and the timer-tq in bottom half context.
 */
static void run_timer_softirq(struct softirq_action *h)
{
        tvec_base_t *base = &__get_cpu_var(tvec_bases);

        if (time_after_eq(jiffies, base->timer_jiffies))
                __run_timers(base);
}

/*
 * Called by the local, per-CPU timer interrupt on SMP.
 */
void run_local_timers(void)
{
        raise_softirq(TIMER_SOFTIRQ);
}

/*
 * Called by the timer interrupt. xtime_lock must already be taken
 * by the timer IRQ!
 */
static inline void update_times(void)
{
        unsigned long ticks;

        ticks = jiffies - wall_jiffies;
        if (ticks) {
                wall_jiffies += ticks;
                update_wall_time(ticks);
        }
        calc_load(ticks);
}
  
/*
 * The 64-bit jiffies value is not atomic - you MUST NOT read it
 * without sampling the sequence number in xtime_lock.
 * jiffies is defined in the linker script...
 */

void do_timer(struct pt_regs *regs)
{
        jiffies_64++;
#ifndef CONFIG_SMP
        /* SMP process accounting uses the local APIC timer */

        update_process_times(user_mode(regs));
#endif
        update_times();
}

#ifdef __ARCH_WANT_SYS_ALARM

/*
 * For backwards compatibility?  This can be done in libc so Alpha
 * and all newer ports shouldn't need it.
 */
asmlinkage unsigned long sys_alarm(unsigned int seconds)
{
        struct itimerval it_new, it_old;
        unsigned int oldalarm;

        it_new.it_interval.tv_sec = it_new.it_interval.tv_usec = 0;
        it_new.it_value.tv_sec = seconds;
        it_new.it_value.tv_usec = 0;
        do_setitimer(ITIMER_REAL, &it_new, &it_old);
        oldalarm = it_old.it_value.tv_sec;
        /* ehhh.. We can't return 0 if we have an alarm pending.. */
        /* And we'd better return too much than too little anyway */
        if ((!oldalarm && it_old.it_value.tv_usec) || it_old.it_value.tv_usec >= 500000)
                oldalarm++;
        return oldalarm;
}

#endif

#ifndef __alpha__

/*
 * The Alpha uses getxpid, getxuid, and getxgid instead.  Maybe this
 * should be moved into arch/i386 instead?
 */

/**
 * sys_getpid - return the thread group id of the current process
 *
 * Note, despite the name, this returns the tgid not the pid.  The tgid and
 * the pid are identical unless CLONE_THREAD was specified on clone() in
 * which case the tgid is the same in all threads of the same group.
 *
 * This is SMP safe as current->tgid does not change.
 */
asmlinkage long sys_getpid(void)
{
        return current->tgid;
}

/*
 * Accessing ->group_leader->real_parent is not SMP-safe, it could
 * change from under us. However, rather than getting any lock
 * we can use an optimistic algorithm: get the parent
 * pid, and go back and check that the parent is still
 * the same. If it has changed (which is extremely unlikely
 * indeed), we just try again..
 *
 * NOTE! This depends on the fact that even if we _do_
 * get an old value of "parent", we can happily dereference
 * the pointer (it was and remains a dereferencable kernel pointer
 * no matter what): we just can't necessarily trust the result
 * until we know that the parent pointer is valid.
 *
 * NOTE2: ->group_leader never changes from under us.
 */
asmlinkage long sys_getppid(void)
{
        int pid;
        struct task_struct *me = current;
        struct task_struct *parent;

        parent = me->group_leader->real_parent;
        for (;;) {
                pid = parent->tgid;
#ifdef CONFIG_SMP
{
                struct task_struct *old = parent;

                /*
                 * Make sure we read the pid before re-reading the
                 * parent pointer:
                 */
                rmb();
                parent = me->group_leader->real_parent;
                if (old != parent)
                        continue;
}
#endif
                break;
        }
        return pid;
}

asmlinkage long sys_getuid(void)
{
        /* Only we change this so SMP safe */
        return current->uid;
}

asmlinkage long sys_geteuid(void)
{
        /* Only we change this so SMP safe */
        return current->euid;
}

asmlinkage long sys_getgid(void)
{
        /* Only we change this so SMP safe */
        return current->gid;
}

asmlinkage long sys_getegid(void)
{
        /* Only we change this so SMP safe */
        return  current->egid;
}

#endif

static void process_timeout(unsigned long __data)
{
        wake_up_process((task_t *)__data);
}

/**
 * schedule_timeout - sleep until timeout
 * @timeout: timeout value in jiffies
 *
 * Make the current task sleep until @timeout jiffies have
 * elapsed. The routine will return immediately unless
 * the current task state has been set (see set_current_state()).
 *
 * You can set the task state as follows -
 *
 * %TASK_UNINTERRUPTIBLE - at least @timeout jiffies are guaranteed to
 * pass before the routine returns. The routine will return 0
 *
 * %TASK_INTERRUPTIBLE - the routine may return early if a signal is
 * delivered to the current task. In this case the remaining time
 * in jiffies will be returned, or 0 if the timer expired in time
 *
 * The current task state is guaranteed to be TASK_RUNNING when this
 * routine returns.
 *
 * Specifying a @timeout value of %MAX_SCHEDULE_TIMEOUT will schedule
 * the CPU away without a bound on the timeout. In this case the return
 * value will be %MAX_SCHEDULE_TIMEOUT.
 *
 * In all cases the return value is guaranteed to be non-negative.
 */
fastcall signed long __sched schedule_timeout(signed long timeout)
{
        struct timer_list timer;
        unsigned long expire;

        switch (timeout)
        {
        case MAX_SCHEDULE_TIMEOUT:
                /*
                 * These two special cases are useful to be comfortable
                 * in the caller. Nothing more. We could take
                 * MAX_SCHEDULE_TIMEOUT from one of the negative value
                 * but I' d like to return a valid offset (>=0) to allow
                 * the caller to do everything it want with the retval.
                 */
                schedule();
                goto out;
        default:
                /*
                 * Another bit of PARANOID. Note that the retval will be
                 * 0 since no piece of kernel is supposed to do a check
                 * for a negative retval of schedule_timeout() (since it
                 * should never happens anyway). You just have the printk()
                 * that will tell you if something is gone wrong and where.
                 */
                if (timeout < 0)
                {
                        printk(KERN_ERR "schedule_timeout: wrong timeout "
                               "value %lx from %p\n", timeout,
                               __builtin_return_address(0));
                        current->state = TASK_RUNNING;
                        goto out;
                }
        }

        expire = timeout + jiffies;

        init_timer(&timer);
        timer.expires = expire;
        timer.data = (unsigned long) current;
        timer.function = process_timeout;

        add_timer(&timer);
        schedule();
        del_singleshot_timer_sync(&timer);

        timeout = expire - jiffies;

 out:
        return timeout < 0 ? 0 : timeout;
}

EXPORT_SYMBOL(schedule_timeout);

/* Thread ID - the internal kernel "pid" */
asmlinkage long sys_gettid(void)
{
        return current->pid;
}

static long __sched nanosleep_restart(struct restart_block *restart)
{
        unsigned long expire = restart->arg0, now = jiffies;
        struct timespec __user *rmtp = (struct timespec __user *) restart->arg1;
        long ret;

        /* Did it expire while we handled signals? */
        if (!time_after(expire, now))
                return 0;

        current->state = TASK_INTERRUPTIBLE;
        expire = schedule_timeout(expire - now);

        ret = 0;
        if (expire) {
                struct timespec t;
                jiffies_to_timespec(expire, &t);

                ret = -ERESTART_RESTARTBLOCK;
                if (rmtp && copy_to_user(rmtp, &t, sizeof(t)))
                        ret = -EFAULT;
                /* The 'restart' block is already filled in */
        }
        return ret;
}

asmlinkage long sys_nanosleep(struct timespec __user *rqtp, struct timespec __user *rmtp)
{
        struct timespec t;
        unsigned long expire;
        long ret;

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

        if ((t.tv_nsec >= 1000000000L) || (t.tv_nsec < 0) || (t.tv_sec < 0))
                return -EINVAL;

        expire = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec);
        current->state = TASK_INTERRUPTIBLE;
        expire = schedule_timeout(expire);

        ret = 0;
        if (expire) {
                struct restart_block *restart;
                jiffies_to_timespec(expire, &t);
                if (rmtp && copy_to_user(rmtp, &t, sizeof(t)))
                        return -EFAULT;

                restart = &current_thread_info()->restart_block;
                restart->fn = nanosleep_restart;
                restart->arg0 = jiffies + expire;
                restart->arg1 = (unsigned long) rmtp;
                ret = -ERESTART_RESTARTBLOCK;
        }
        return ret;
}

/*
 * sys_sysinfo - fill in sysinfo struct
 */ 
asmlinkage long sys_sysinfo(struct sysinfo __user *info)
{
        struct sysinfo val;
        unsigned long mem_total, sav_total;
        unsigned int mem_unit, bitcount;
        unsigned long seq;

        memset((char *)&val, 0, sizeof(struct sysinfo));

        do {
                struct timespec tp;
                seq = read_seqbegin(&xtime_lock);

                /*
                 * This is annoying.  The below is the same thing
                 * posix_get_clock_monotonic() does, but it wants to
                 * take the lock which we want to cover the loads stuff
                 * too.
                 */

                do_gettimeofday((struct timeval *)&tp);
                tp.tv_nsec *= NSEC_PER_USEC;
                tp.tv_sec += wall_to_monotonic.tv_sec;
                tp.tv_nsec += wall_to_monotonic.tv_nsec;
                if (tp.tv_nsec - NSEC_PER_SEC >= 0) {
                        tp.tv_nsec = tp.tv_nsec - NSEC_PER_SEC;
                        tp.tv_sec++;
                }
                val.uptime = tp.tv_sec + (tp.tv_nsec ? 1 : 0);

                val.loads[0] = avenrun[0] << (SI_LOAD_SHIFT - FSHIFT);
                val.loads[1] = avenrun[1] << (SI_LOAD_SHIFT - FSHIFT);
                val.loads[2] = avenrun[2] << (SI_LOAD_SHIFT - FSHIFT);

                val.procs = nr_threads;
        } while (read_seqretry(&xtime_lock, seq));

        si_meminfo(&val);
        si_swapinfo(&val);

        /*
         * If the sum of all the available memory (i.e. ram + swap)
         * is less than can be stored in a 32 bit unsigned long then
         * we can be binary compatible with 2.2.x kernels.  If not,
         * well, in that case 2.2.x was broken anyways...
         *
         *  -Erik Andersen <andersee@debian.org>
         */

        mem_total = val.totalram + val.totalswap;
        if (mem_total < val.totalram || mem_total < val.totalswap)
                goto out;
        bitcount = 0;
        mem_unit = val.mem_unit;
        while (mem_unit > 1) {
                bitcount++;
                mem_unit >>= 1;
                sav_total = mem_total;
                mem_total <<= 1;
                if (mem_total < sav_total)
                        goto out;
        }

        /*
         * If mem_total did not overflow, multiply all memory values by
         * val.mem_unit and set it to 1.  This leaves things compatible
         * with 2.2.x, and also retains compatibility with earlier 2.4.x
         * kernels...
         */

        val.mem_unit = 1;
        val.totalram <<= bitcount;
        val.freeram <<= bitcount;
        val.sharedram <<= bitcount;
        val.bufferram <<= bitcount;
        val.totalswap <<= bitcount;
        val.freeswap <<= bitcount;
        val.totalhigh <<= bitcount;
        val.freehigh <<= bitcount;

 out:
        if (copy_to_user(info, &val, sizeof(struct sysinfo)))
                return -EFAULT;

        return 0;
}

static void __devinit init_timers_cpu(int cpu)
{
        int j;
        tvec_base_t *base;
       
        base = &per_cpu(tvec_bases, cpu);
        spin_lock_init(&base->lock);
        for (j = 0; j < TVN_SIZE; j++) {
                INIT_LIST_HEAD(base->tv5.vec + j);
                INIT_LIST_HEAD(base->tv4.vec + j);
                INIT_LIST_HEAD(base->tv3.vec + j);
                INIT_LIST_HEAD(base->tv2.vec + j);
        }
        for (j = 0; j < TVR_SIZE; j++)
                INIT_LIST_HEAD(base->tv1.vec + j);

        base->timer_jiffies = jiffies;
}

#ifdef CONFIG_HOTPLUG_CPU
static int migrate_timer_list(tvec_base_t *new_base, struct list_head *head)
{
        struct timer_list *timer;

        while (!list_empty(head)) {
                timer = list_entry(head->next, struct timer_list, entry);
                /* We're locking backwards from __mod_timer order here,
                   beware deadlock. */
                if (!spin_trylock(&timer->lock))
                        return 0;
                list_del(&timer->entry);
                internal_add_timer(new_base, timer);
                timer->base = new_base;
                spin_unlock(&timer->lock);
        }
        return 1;
}

static void __devinit migrate_timers(int cpu)
{
        tvec_base_t *old_base;
        tvec_base_t *new_base;
        int i;

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

        local_irq_disable();
again:
        /* Prevent deadlocks via ordering by old_base < new_base. */
        if (old_base < new_base) {
                spin_lock(&new_base->lock);
                spin_lock(&old_base->lock);
        } else {
                spin_lock(&old_base->lock);
                spin_lock(&new_base->lock);
        }

        if (old_base->running_timer)
                BUG();
        for (i = 0; i < TVR_SIZE; i++)
                if (!migrate_timer_list(new_base, old_base->tv1.vec + i))
                        goto unlock_again;
        for (i = 0; i < TVN_SIZE; i++)
                if (!migrate_timer_list(new_base, old_base->tv2.vec + i)
                    || !migrate_timer_list(new_base, old_base->tv3.vec + i)
                    || !migrate_timer_list(new_base, old_base->tv4.vec + i)
                    || !migrate_timer_list(new_base, old_base->tv5.vec + i))
                        goto unlock_again;
        spin_unlock(&old_base->lock);
        spin_unlock(&new_base->lock);
        local_irq_enable();
        put_cpu_var(tvec_bases);
        return;

unlock_again:
        /* Avoid deadlock with __mod_timer, by backing off. */
        spin_unlock(&old_base->lock);
        spin_unlock(&new_base->lock);
        cpu_relax();
        goto again;
}
#endif /* CONFIG_HOTPLUG_CPU */

static int __devinit timer_cpu_notify(struct notifier_block *self, 
                                unsigned long action, void *hcpu)
{
        long cpu = (long)hcpu;
        switch(action) {
        case CPU_UP_PREPARE:
                init_timers_cpu(cpu);
                break;
#ifdef CONFIG_HOTPLUG_CPU
        case CPU_DEAD:
                migrate_timers(cpu);
                break;
#endif
        default:
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block __devinitdata timers_nb = {
        .notifier_call  = timer_cpu_notify,
};


void __init init_timers(void)
{
        timer_cpu_notify(&timers_nb, (unsigned long)CPU_UP_PREPARE,
                                (void *)(long)smp_processor_id());
        register_cpu_notifier(&timers_nb);
        open_softirq(TIMER_SOFTIRQ, run_timer_softirq, NULL);
}

#ifdef CONFIG_TIME_INTERPOLATION
volatile unsigned long last_nsec_offset;
#ifndef __HAVE_ARCH_CMPXCHG
spinlock_t last_nsec_offset_lock = SPIN_LOCK_UNLOCKED;
#endif

struct time_interpolator *time_interpolator;
static struct time_interpolator *time_interpolator_list;
static spinlock_t time_interpolator_lock = SPIN_LOCK_UNLOCKED;

static inline int
is_better_time_interpolator(struct time_interpolator *new)
{
        if (!time_interpolator)
                return 1;
        return new->frequency > 2*time_interpolator->frequency ||
            (unsigned long)new->drift < (unsigned long)time_interpolator->drift;
}

void
register_time_interpolator(struct time_interpolator *ti)
{
        spin_lock(&time_interpolator_lock);
        write_seqlock_irq(&xtime_lock);
        if (is_better_time_interpolator(ti))
                time_interpolator = ti;
        write_sequnlock_irq(&xtime_lock);

        ti->next = time_interpolator_list;
        time_interpolator_list = ti;
        spin_unlock(&time_interpolator_lock);
}

void
unregister_time_interpolator(struct time_interpolator *ti)
{
        struct time_interpolator *curr, **prev;

        spin_lock(&time_interpolator_lock);
        prev = &time_interpolator_list;
        for (curr = *prev; curr; curr = curr->next) {
                if (curr == ti) {
                        *prev = curr->next;
                        break;
                }
                prev = &curr->next;
        }

        write_seqlock_irq(&xtime_lock);
        if (ti == time_interpolator) {
                /* we lost the best time-interpolator: */
                time_interpolator = NULL;
                /* find the next-best interpolator */
                for (curr = time_interpolator_list; curr; curr = curr->next)
                        if (is_better_time_interpolator(curr))
                                time_interpolator = curr;
        }
        write_sequnlock_irq(&xtime_lock);
        spin_unlock(&time_interpolator_lock);
}
#endif /* CONFIG_TIME_INTERPOLATION */

/**
 * msleep - sleep safely even with waitqueue interruptions
 * @msecs: Time in milliseconds to sleep for
 */
void msleep(unsigned int msecs)
{
        unsigned long timeout = msecs_to_jiffies(msecs);

        while (timeout) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                timeout = schedule_timeout(timeout);
        }
}

EXPORT_SYMBOL(msleep);