- Alan Cox: synch. PA-RISC arch and bitops cleanups

[davej-history.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
 */

#include <linux/config.h>
#include <linux/mm.h>
#include <linux/timex.h>
#include <linux/delay.h>
#include <linux/smp_lock.h>
#include <linux/interrupt.h>
#include <linux/kernel_stat.h>

#include <asm/uaccess.h>

/*
 * Timekeeping variables
 */

long tick = (1000000 + HZ/2) / HZ;      /* timer interrupt period */

/* The current time */
volatile struct timeval xtime __attribute__ ((aligned (16)));

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

DECLARE_TASK_QUEUE(tq_timer);
DECLARE_TASK_QUEUE(tq_immediate);
DECLARE_TASK_QUEUE(tq_scheduler);

/*
 * 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 = ((1000000 + HZ/2) % HZ - HZ/2) << SHIFT_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_adjust_step;

unsigned long event;

extern int do_setitimer(int, struct itimerval *, struct itimerval *);

unsigned long volatile jiffies;

unsigned int * prof_buffer;
unsigned long prof_len;
unsigned long prof_shift;

/*
 * Event timer code
 */
#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)

struct timer_vec {
        int index;
        struct list_head vec[TVN_SIZE];
};

struct timer_vec_root {
        int index;
        struct list_head vec[TVR_SIZE];
};

static struct timer_vec tv5;
static struct timer_vec tv4;
static struct timer_vec tv3;
static struct timer_vec tv2;
static struct timer_vec_root tv1;

static struct timer_vec * const tvecs[] = {
        (struct timer_vec *)&tv1, &tv2, &tv3, &tv4, &tv5
};

#define NOOF_TVECS (sizeof(tvecs) / sizeof(tvecs[0]))

void init_timervecs (void)
{
        int i;

        for (i = 0; i < TVN_SIZE; i++) {
                INIT_LIST_HEAD(tv5.vec + i);
                INIT_LIST_HEAD(tv4.vec + i);
                INIT_LIST_HEAD(tv3.vec + i);
                INIT_LIST_HEAD(tv2.vec + i);
        }
        for (i = 0; i < TVR_SIZE; i++)
                INIT_LIST_HEAD(tv1.vec + i);
}

static unsigned long timer_jiffies;

static inline void internal_add_timer(struct timer_list *timer)
{
        /*
         * must be cli-ed when calling this
         */
        unsigned long expires = timer->expires;
        unsigned long idx = expires - timer_jiffies;
        struct list_head * vec;

        if (idx < TVR_SIZE) {
                int i = expires & TVR_MASK;
                vec = tv1.vec + i;
        } else if (idx < 1 << (TVR_BITS + TVN_BITS)) {
                int i = (expires >> TVR_BITS) & TVN_MASK;
                vec = tv2.vec + i;
        } else if (idx < 1 << (TVR_BITS + 2 * TVN_BITS)) {
                int i = (expires >> (TVR_BITS + TVN_BITS)) & TVN_MASK;
                vec =  tv3.vec + i;
        } else if (idx < 1 << (TVR_BITS + 3 * TVN_BITS)) {
                int i = (expires >> (TVR_BITS + 2 * TVN_BITS)) & TVN_MASK;
                vec = 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 = tv1.vec + tv1.index;
        } else if (idx <= 0xffffffffUL) {
                int i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK;
                vec = tv5.vec + i;
        } else {
                /* Can only get here on architectures with 64-bit jiffies */
                INIT_LIST_HEAD(&timer->list);
                return;
        }
        /*
         * Timers are FIFO!
         */
        list_add(&timer->list, vec->prev);
}

/* Initialize both explicitly - let's try to have them in the same cache line */
spinlock_t timerlist_lock = SPIN_LOCK_UNLOCKED;

#ifdef CONFIG_SMP
volatile struct timer_list * volatile running_timer;
#define timer_enter(t) do { running_timer = t; mb(); } while (0)
#define timer_exit() do { running_timer = NULL; } while (0)
#define timer_is_running(t) (running_timer == t)
#define timer_synchronize(t) while (timer_is_running(t)) barrier()
#else
#define timer_enter(t)          do { } while (0)
#define timer_exit()            do { } while (0)
#endif

void add_timer(struct timer_list *timer)
{
        unsigned long flags;

        spin_lock_irqsave(&timerlist_lock, flags);
        if (timer_pending(timer))
                goto bug;
        internal_add_timer(timer);
        spin_unlock_irqrestore(&timerlist_lock, flags);
        return;
bug:
        spin_unlock_irqrestore(&timerlist_lock, flags);
        printk("bug: kernel timer added twice at %p.\n",
                        __builtin_return_address(0));
}

static inline int detach_timer (struct timer_list *timer)
{
        if (!timer_pending(timer))
                return 0;
        list_del(&timer->list);
        return 1;
}

int mod_timer(struct timer_list *timer, unsigned long expires)
{
        int ret;
        unsigned long flags;

        spin_lock_irqsave(&timerlist_lock, flags);
        timer->expires = expires;
        ret = detach_timer(timer);
        internal_add_timer(timer);
        spin_unlock_irqrestore(&timerlist_lock, flags);
        return ret;
}

int del_timer(struct timer_list * timer)
{
        int ret;
        unsigned long flags;

        spin_lock_irqsave(&timerlist_lock, flags);
        ret = detach_timer(timer);
        timer->list.next = timer->list.prev = NULL;
        spin_unlock_irqrestore(&timerlist_lock, flags);
        return ret;
}

#ifdef CONFIG_SMP
void sync_timers(void)
{
        spin_unlock_wait(&global_bh_lock);
}

/*
 * SMP specific function to delete periodic timer.
 * Caller must disable by some means restarting the timer
 * for new. Upon exit the timer is not queued and handler is not running
 * on any CPU. It returns number of times, which timer was deleted
 * (for reference counting).
 */

int del_timer_sync(struct timer_list * timer)
{
        int ret = 0;

        for (;;) {
                unsigned long flags;
                int running;

                spin_lock_irqsave(&timerlist_lock, flags);
                ret += detach_timer(timer);
                timer->list.next = timer->list.prev = 0;
                running = timer_is_running(timer);
                spin_unlock_irqrestore(&timerlist_lock, flags);

                if (!running)
                        break;

                timer_synchronize(timer);
        }

        return ret;
}
#endif


static inline void cascade_timers(struct timer_vec *tv)
{
        /* cascade all the timers from tv up one level */
        struct list_head *head, *curr, *next;

        head = tv->vec + tv->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, list);
                next = curr->next;
                list_del(curr); // not needed
                internal_add_timer(tmp);
                curr = next;
        }
        INIT_LIST_HEAD(head);
        tv->index = (tv->index + 1) & TVN_MASK;
}

static inline void run_timer_list(void)
{
        spin_lock_irq(&timerlist_lock);
        while ((long)(jiffies - timer_jiffies) >= 0) {
                struct list_head *head, *curr;
                if (!tv1.index) {
                        int n = 1;
                        do {
                                cascade_timers(tvecs[n]);
                        } while (tvecs[n]->index == 1 && ++n < NOOF_TVECS);
                }
repeat:
                head = tv1.vec + tv1.index;
                curr = head->next;
                if (curr != head) {
                        struct timer_list *timer;
                        void (*fn)(unsigned long);
                        unsigned long data;

                        timer = list_entry(curr, struct timer_list, list);
                        fn = timer->function;
                        data= timer->data;

                        detach_timer(timer);
                        timer->list.next = timer->list.prev = NULL;
                        timer_enter(timer);
                        spin_unlock_irq(&timerlist_lock);
                        fn(data);
                        spin_lock_irq(&timerlist_lock);
                        timer_exit();
                        goto repeat;
                }
                ++timer_jiffies; 
                tv1.index = (tv1.index + 1) & TVR_MASK;
        }
        spin_unlock_irq(&timerlist_lock);
}

spinlock_t tqueue_lock = SPIN_LOCK_UNLOCKED;

void tqueue_bh(void)
{
        run_task_queue(&tq_timer);
}

void immediate_bh(void)
{
        run_task_queue(&tq_immediate);
}

/*
 * 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--;
            time_state = TIME_OOP;
            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++;
            time_state = TIME_WAIT;
            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
}

/* in the NTP reference this is called "hardclock()" */
static void update_wall_time_one_tick(void)
{
        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;
        }
        xtime.tv_usec += tick + time_adjust_step;
        /*
         * Advance the phase, once it gets to one microsecond, then
         * advance the tick more.
         */
        time_phase += time_adj;
        if (time_phase <= -FINEUSEC) {
                long ltemp = -time_phase >> SHIFT_SCALE;
                time_phase += ltemp << SHIFT_SCALE;
                xtime.tv_usec -= ltemp;
        }
        else if (time_phase >= FINEUSEC) {
                long ltemp = time_phase >> SHIFT_SCALE;
                time_phase -= ltemp << SHIFT_SCALE;
                xtime.tv_usec += ltemp;
        }
}

/*
 * 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_usec >= 1000000) {
            xtime.tv_usec -= 1000000;
            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->times.tms_utime += user);
        psecs += (p->times.tms_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;
        }
}

void update_one_process(struct task_struct *p, unsigned long user,
                        unsigned long system, int cpu)
{
        p->per_cpu_utime[cpu] += user;
        p->per_cpu_stime[cpu] += system;
        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);
        if (p->pid) {
                if (--p->counter <= 0) {
                        p->counter = 0;
                        p->need_resched = 1;
                }
                if (p->nice > 0)
                        kstat.per_cpu_nice[cpu] += user_tick;
                else
                        kstat.per_cpu_user[cpu] += user_tick;
                kstat.per_cpu_system[cpu] += system;
        } else if (local_bh_count(cpu) || local_irq_count(cpu) > 1)
                kstat.per_cpu_system[cpu] += system;
}

/*
 * Nr of active tasks - counted in fixed-point numbers
 */
static unsigned long count_active_tasks(void)
{
        struct task_struct *p;
        unsigned long nr = 0;

        read_lock(&tasklist_lock);
        for_each_task(p) {
                if ((p->state == TASK_RUNNING ||
                     (p->state & TASK_UNINTERRUPTIBLE)))
                        nr += FIXED_1;
        }
        read_unlock(&tasklist_lock);
        return nr;
}

/*
 * 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.
 */
unsigned long avenrun[3];

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;

/*
 * This spinlock protect us from races in SMP while playing with xtime. -arca
 */
rwlock_t xtime_lock = RW_LOCK_UNLOCKED;

static inline void update_times(void)
{
        unsigned long ticks;

        /*
         * update_times() is run from the raw timer_bh handler so we
         * just know that the irqs are locally enabled and so we don't
         * need to save/restore the flags of the local CPU here. -arca
         */
        write_lock_irq(&xtime_lock);

        ticks = jiffies - wall_jiffies;
        if (ticks) {
                wall_jiffies += ticks;
                update_wall_time(ticks);
        }
        write_unlock_irq(&xtime_lock);
        calc_load(ticks);
}

void timer_bh(void)
{
        update_times();
        run_timer_list();
}

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

        update_process_times(user_mode(regs));
#endif
        mark_bh(TIMER_BH);
        if (tq_timer)
                mark_bh(TQUEUE_BH);
}

#if !defined(__alpha__) && !defined(__ia64__)

/*
 * 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 (it_old.it_value.tv_usec)
                oldalarm++;
        return oldalarm;
}

#endif

#ifndef __alpha__

/*
 * The Alpha uses getxpid, getxuid, and getxgid instead.  Maybe this
 * should be moved into arch/i386 instead?
 */
 
asmlinkage long sys_getpid(void)
{
        /* This is SMP safe - current->pid doesn't change */
        return current->tgid;
}

/*
 * This is not strictly SMP safe: p_opptr 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: we just can't necessarily trust the result
 * until we know that the parent pointer is valid.
 *
 * The "mb()" macro is a memory barrier - a synchronizing
 * event. It also makes sure that gcc doesn't optimize
 * away the necessary memory references.. The barrier doesn't
 * have to have all that strong semantics: on x86 we don't
 * really require a synchronizing instruction, for example.
 * The barrier is more important for code generation than
 * for any real memory ordering semantics (even if there is
 * a small window for a race, using the old pointer is
 * harmless for a while).
 */
asmlinkage long sys_getppid(void)
{
        int pid;
        struct task_struct * me = current;
        struct task_struct * parent;

        parent = me->p_opptr;
        for (;;) {
                pid = parent->pid;
#if CONFIG_SMP
{
                struct task_struct *old = parent;
                mb();
                parent = me->p_opptr;
                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

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

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

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


        if (t.tv_sec == 0 && t.tv_nsec <= 2000000L &&
            current->policy != SCHED_OTHER)
        {
                /*
                 * Short delay requests up to 2 ms will be handled with
                 * high precision by a busy wait for all real-time processes.
                 *
                 * Its important on SMP not to do this holding locks.
                 */
                udelay((t.tv_nsec + 999) / 1000);
                return 0;
        }

        expire = timespec_to_jiffies(&t) + (t.tv_sec || t.tv_nsec);

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

        if (expire) {
                if (rmtp) {
                        jiffies_to_timespec(expire, &t);
                        if (copy_to_user(rmtp, &t, sizeof(struct timespec)))
                                return -EFAULT;
                }
                return -EINTR;
        }
        return 0;
}