Import 2.1.116pre2

[davej-history.git] / kernel / sched.c

/*
 *  linux/kernel/sched.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  1996-04-21  Modified by Ulrich Windl to make NTP work
 *  1996-12-23  Modified by Dave Grothe to fix bugs in semaphores and
 *              make semaphores SMP safe
 *  1997-01-28  Modified by Finn Arne Gangstad to make timers scale better.
 */

/*
 * 'sched.c' is the main kernel file. It contains scheduling primitives
 * (sleep_on, wakeup, schedule etc) as well as a number of simple system
 * call functions (type getpid()), which just extract a field from
 * current-task
 */

#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/kernel.h>
#include <linux/kernel_stat.h>
#include <linux/fdreg.h>
#include <linux/errno.h>
#include <linux/time.h>
#include <linux/ptrace.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/tqueue.h>
#include <linux/resource.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/init.h>

#include <asm/system.h>
#include <asm/io.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/mmu_context.h>
#include <asm/spinlock.h>

#include <linux/timex.h>

/*
 * kernel variables
 */

unsigned securebits = SECUREBITS_DEFAULT; /* systemwide security settings */

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_ERROR;    /* clock synchronization status */
int time_status = STA_UNSYNC;   /* clock status bits */
long time_offset = 0;           /* 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 = MAXPHASE;  /* maximum error (us) */
long time_esterror = MAXPHASE;  /* estimated error (us) */
long time_phase = 0;            /* phase offset (scaled us) */
long time_freq = ((1000000 + HZ/2) % HZ - HZ/2) << SHIFT_USEC;  /* frequency offset (scaled ppm) */
long time_adj = 0;              /* tick adjust (scaled 1 / HZ) */
long time_reftime = 0;          /* time at last adjustment (s) */

long time_adjust = 0;
long time_adjust_step = 0;

unsigned long event = 0;

extern int do_setitimer(int, struct itimerval *, struct itimerval *);
unsigned int * prof_buffer = NULL;
unsigned long prof_len = 0;
unsigned long prof_shift = 0;

extern void mem_use(void);

unsigned long volatile jiffies=0;

/*
 *      Init task must be ok at boot for the ix86 as we will check its signals
 *      via the SMP irq return path.
 */
 
struct task_struct * task[NR_TASKS] = {&init_task, };

struct kernel_stat kstat = { 0 };

void scheduling_functions_start_here(void) { }

static inline void reschedule_idle(struct task_struct * p)
{

        /*
         * For SMP, we try to see if the CPU the task used
         * to run on is idle..
         */
#if 0
        /*
         * Disable this for now. Ingo has some interesting
         * code that looks too complex, and I have some ideas,
         * but in the meantime.. One problem is that "wakeup()"
         * can be (and is) called before we've even initialized
         * SMP completely, so..
         */
#ifdef __SMP__
        int want_cpu = p->processor;

        /*
         * Don't even try to find another CPU for us if the task
         * ran on this one before..
         */
        if (want_cpu != smp_processor_id()) {
                struct task_struct **idle = task;
                int i = smp_num_cpus;

                do {
                        struct task_struct *tsk = *idle;
                        idle++;
                        /* Something like this.. */
                        if (tsk->has_cpu && tsk->processor == want_cpu) {
                                tsk->need_resched = 1;
                                smp_send_reschedule(want_cpu);
                                return;
                        }
                } while (--i > 0);
        }
#endif
#endif
        if (p->policy != SCHED_OTHER || p->counter > current->counter + 3)
                current->need_resched = 1;      
}

/*
 * Careful!
 *
 * This has to add the process to the _beginning_ of the
 * run-queue, not the end. See the comment about "This is
 * subtle" in the scheduler proper..
 */
static inline void add_to_runqueue(struct task_struct * p)
{
        struct task_struct *next = init_task.next_run;

        p->prev_run = &init_task;
        init_task.next_run = p;
        p->next_run = next;
        next->prev_run = p;
}

static inline void del_from_runqueue(struct task_struct * p)
{
        struct task_struct *next = p->next_run;
        struct task_struct *prev = p->prev_run;

        nr_running--;
        next->prev_run = prev;
        prev->next_run = next;
        p->next_run = NULL;
        p->prev_run = NULL;
}

static inline void move_last_runqueue(struct task_struct * p)
{
        struct task_struct *next = p->next_run;
        struct task_struct *prev = p->prev_run;

        /* remove from list */
        next->prev_run = prev;
        prev->next_run = next;
        /* add back to list */
        p->next_run = &init_task;
        prev = init_task.prev_run;
        init_task.prev_run = p;
        p->prev_run = prev;
        prev->next_run = p;
}

static inline void move_first_runqueue(struct task_struct * p)
{
        struct task_struct *next = p->next_run;
        struct task_struct *prev = p->prev_run;

        /* remove from list */
        next->prev_run = prev;
        prev->next_run = next;
        /* add back to list */
        p->prev_run = &init_task;
        next = init_task.next_run;
        init_task.next_run = p;
        p->next_run = next;
        next->prev_run = p;
}

/*
 * The tasklist_lock protects the linked list of processes.
 *
 * The scheduler lock is protecting against multiple entry
 * into the scheduling code, and doesn't need to worry
 * about interrupts (because interrupts cannot call the
 * scheduler).
 *
 * The run-queue lock locks the parts that actually access
 * and change the run-queues, and have to be interrupt-safe.
 */
spinlock_t scheduler_lock = SPIN_LOCK_UNLOCKED; /* should be acquired first */
spinlock_t runqueue_lock = SPIN_LOCK_UNLOCKED;  /* second */
rwlock_t tasklist_lock = RW_LOCK_UNLOCKED;      /* third */

/*
 * Wake up a process. Put it on the run-queue if it's not
 * already there.  The "current" process is always on the
 * run-queue (except when the actual re-schedule is in
 * progress), and as such you're allowed to do the simpler
 * "current->state = TASK_RUNNING" to mark yourself runnable
 * without the overhead of this.
 */
inline void wake_up_process(struct task_struct * p)
{
        unsigned long flags;

        spin_lock_irqsave(&runqueue_lock, flags);
        p->state = TASK_RUNNING;
        if (!p->next_run) {
                add_to_runqueue(p);
                reschedule_idle(p);
                nr_running++;
        }
        spin_unlock_irqrestore(&runqueue_lock, flags);
}

static void process_timeout(unsigned long __data)
{
        struct task_struct * p = (struct task_struct *) __data;

        p->timeout = 0;
        wake_up_process(p);
}

/*
 * This is the function that decides how desirable a process is..
 * You can weigh different processes against each other depending
 * on what CPU they've run on lately etc to try to handle cache
 * and TLB miss penalties.
 *
 * Return values:
 *       -1000: never select this
 *           0: out of time, recalculate counters (but it might still be
 *              selected)
 *         +ve: "goodness" value (the larger, the better)
 *       +1000: realtime process, select this.
 */
static inline int goodness(struct task_struct * p, struct task_struct * prev, int this_cpu)
{
        int policy = p->policy;
        int weight;

        if (policy & SCHED_YIELD) {
                p->policy = policy & ~SCHED_YIELD;
                return 0;
        }

        /*
         * Realtime process, select the first one on the
         * runqueue (taking priorities within processes
         * into account).
         */
        if (policy != SCHED_OTHER)
                return 1000 + p->rt_priority;

        /*
         * Give the process a first-approximation goodness value
         * according to the number of clock-ticks it has left.
         *
         * Don't do any other calculations if the time slice is
         * over..
         */
        weight = p->counter;
        if (weight) {
                        
#ifdef __SMP__
                /* Give a largish advantage to the same processor...   */
                /* (this is equivalent to penalizing other processors) */
                if (p->processor == this_cpu)
                        weight += PROC_CHANGE_PENALTY;
#endif

                /* .. and a slight advantage to the current thread */
                if (p->mm == prev->mm)
                        weight += 1;
                weight += p->priority;
        }

        return weight;
}

/*
 * 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 timer_list *vec[TVN_SIZE];
};

struct timer_vec_root {
        int index;
        struct timer_list *vec[TVR_SIZE];
};

static struct timer_vec tv5 = { 0 };
static struct timer_vec tv4 = { 0 };
static struct timer_vec tv3 = { 0 };
static struct timer_vec tv2 = { 0 };
static struct timer_vec_root tv1 = { 0 };

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

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

static unsigned long timer_jiffies = 0;

static inline void insert_timer(struct timer_list *timer,
                                struct timer_list **vec, int idx)
{
        if ((timer->next = vec[idx]))
                vec[idx]->prev = timer;
        vec[idx] = timer;
        timer->prev = (struct timer_list *)&vec[idx];
}

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;

        if (idx < TVR_SIZE) {
                int i = expires & TVR_MASK;
                insert_timer(timer, tv1.vec, i);
        } else if (idx < 1 << (TVR_BITS + TVN_BITS)) {
                int i = (expires >> TVR_BITS) & TVN_MASK;
                insert_timer(timer, tv2.vec, i);
        } else if (idx < 1 << (TVR_BITS + 2 * TVN_BITS)) {
                int i = (expires >> (TVR_BITS + TVN_BITS)) & TVN_MASK;
                insert_timer(timer, tv3.vec, i);
        } else if (idx < 1 << (TVR_BITS + 3 * TVN_BITS)) {
                int i = (expires >> (TVR_BITS + 2 * TVN_BITS)) & TVN_MASK;
                insert_timer(timer, tv4.vec, i);
        } else if (expires < timer_jiffies) {
                /* can happen if you add a timer with expires == jiffies,
                 * or you set a timer to go off in the past
                 */
                insert_timer(timer, tv1.vec, tv1.index);
        } else if (idx < 0xffffffffUL) {
                int i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK;
                insert_timer(timer, tv5.vec, i);
        } else {
                /* Can only get here on architectures with 64-bit jiffies */
                timer->next = timer->prev = timer;
        }
}

spinlock_t timerlist_lock = SPIN_LOCK_UNLOCKED;

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

        spin_lock_irqsave(&timerlist_lock, flags);
        internal_add_timer(timer);
        spin_unlock_irqrestore(&timerlist_lock, flags);
}

static inline int detach_timer(struct timer_list *timer)
{
        struct timer_list *prev = timer->prev;
        if (prev) {
                struct timer_list *next = timer->next;
                prev->next = next;
                if (next)
                        next->prev = prev;
                return 1;
        }
        return 0;
}

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

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

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

        spin_lock_irqsave(&timerlist_lock, flags);
        ret = detach_timer(timer);
        timer->next = timer->prev = 0;
        spin_unlock_irqrestore(&timerlist_lock, flags);

        /* Make sure the timer isn't running in parallell.. */
        synchronize_bh();
        return ret;
}

#ifdef __SMP__

#define idle_task (task[cpu_number_map[this_cpu]])
#define can_schedule(p) (!(p)->has_cpu)

#else

#define idle_task (&init_task)
#define can_schedule(p) (1)

#endif

/*
 *  'schedule()' is the scheduler function. It's a very simple and nice
 * scheduler: it's not perfect, but certainly works for most things.
 *
 * The goto is "interesting".
 *
 *   NOTE!!  Task 0 is the 'idle' task, which gets called when no other
 * tasks can run. It can not be killed, and it cannot sleep. The 'state'
 * information in task[0] is never used.
 */
asmlinkage void schedule(void)
{
        struct task_struct * prev, * next;
        unsigned long timeout;
        int this_cpu;

        prev = current;
        this_cpu = prev->processor;
        if (in_interrupt())
                goto scheduling_in_interrupt;
        release_kernel_lock(prev, this_cpu);

        __check_locks(1);

        /* Do "administrative" work here while we don't hold any locks */
        if (bh_active & bh_mask)
                do_bottom_half();
        run_task_queue(&tq_scheduler);

        spin_lock(&scheduler_lock);
        spin_lock_irq(&runqueue_lock);

        /* move an exhausted RR process to be last.. */
        prev->need_resched = 0;
        if (!prev->counter && prev->policy == SCHED_RR) {
                prev->counter = prev->priority;
                move_last_runqueue(prev);
        }
        timeout = 0;
        switch (prev->state) {
                case TASK_INTERRUPTIBLE:
                        if (signal_pending(prev))
                                goto makerunnable;
                        timeout = prev->timeout;
                        if (timeout && (timeout <= jiffies)) {
                                prev->timeout = 0;
                                timeout = 0;
                makerunnable:
                                prev->state = TASK_RUNNING;
                                break;
                        }
                default:
                        del_from_runqueue(prev);
                case TASK_RUNNING:
        }
        {
                struct task_struct * p = init_task.next_run;
                /*
                 * This is subtle.
                 * Note how we can enable interrupts here, even
                 * though interrupts can add processes to the run-
                 * queue. This is because any new processes will
                 * be added to the front of the queue, so "p" above
                 * is a safe starting point.
                 * run-queue deletion and re-ordering is protected by
                 * the scheduler lock
                 */
                spin_unlock_irq(&runqueue_lock);
#ifdef __SMP__
                prev->has_cpu = 0;
#endif
        
/*
 * Note! there may appear new tasks on the run-queue during this, as
 * interrupts are enabled. However, they will be put on front of the
 * list, so our list starting at "p" is essentially fixed.
 */
/* this is the scheduler proper: */
                {
                        int c = -1000;
                        next = idle_task;
                        while (p != &init_task) {
                                if (can_schedule(p)) {
                                        int weight = goodness(p, prev, this_cpu);
                                        if (weight > c)
                                                c = weight, next = p;
                                }
                                p = p->next_run;
                        }

                        /* Do we need to re-calculate counters? */
                        if (!c) {
                                struct task_struct *p;
                                read_lock(&tasklist_lock);
                                for_each_task(p)
                                        p->counter = (p->counter >> 1) + p->priority;
                                read_unlock(&tasklist_lock);
                        }
                }
        }

#ifdef __SMP__
        next->has_cpu = 1;
        next->processor = this_cpu;
#endif

        if (prev != next) {
                struct timer_list timer;

                kstat.context_swtch++;
                if (timeout) {
                        init_timer(&timer);
                        timer.expires = timeout;
                        timer.data = (unsigned long) prev;
                        timer.function = process_timeout;
                        add_timer(&timer);
                }
                get_mmu_context(next);
                switch_to(prev,next);

                if (timeout)
                        del_timer(&timer);
        }

        spin_unlock(&scheduler_lock);

        /*
         * At this point "prev" is "current", as we just
         * switched into it (from an even more "previous"
         * prev)
         */
        reacquire_kernel_lock(prev);
        return;

scheduling_in_interrupt:
        printk("Scheduling in interrupt\n");
        *(int *)0 = 0;
}


rwlock_t waitqueue_lock = RW_LOCK_UNLOCKED;

/*
 * wake_up doesn't wake up stopped processes - they have to be awakened
 * with signals or similar.
 *
 * Note that we only need a read lock for the wait queue (and thus do not
 * have to protect against interrupts), as the actual removal from the
 * queue is handled by the process itself.
 */
void __wake_up(struct wait_queue **q, unsigned int mode)
{
        struct wait_queue *next;

        read_lock(&waitqueue_lock);
        if (q && (next = *q)) {
                struct wait_queue *head;

                head = WAIT_QUEUE_HEAD(q);
                while (next != head) {
                        struct task_struct *p = next->task;
                        next = next->next;
                        if (p->state & mode)
                                wake_up_process(p);
                }
        }
        read_unlock(&waitqueue_lock);
}

/*
 * Semaphores are implemented using a two-way counter:
 * The "count" variable is decremented for each process
 * that tries to sleep, while the "waking" variable is
 * incremented when the "up()" code goes to wake up waiting
 * processes.
 *
 * Notably, the inline "up()" and "down()" functions can
 * efficiently test if they need to do any extra work (up
 * needs to do something only if count was negative before
 * the increment operation.
 *
 * waking_non_zero() (from asm/semaphore.h) must execute
 * atomically.
 *
 * When __up() is called, the count was negative before
 * incrementing it, and we need to wake up somebody.
 *
 * This routine adds one to the count of processes that need to
 * wake up and exit.  ALL waiting processes actually wake up but
 * only the one that gets to the "waking" field first will gate
 * through and acquire the semaphore.  The others will go back
 * to sleep.
 *
 * Note that these functions are only called when there is
 * contention on the lock, and as such all this is the
 * "non-critical" part of the whole semaphore business. The
 * critical part is the inline stuff in <asm/semaphore.h>
 * where we want to avoid any extra jumps and calls.
 */
void __up(struct semaphore *sem)
{
        wake_one_more(sem);
        wake_up(&sem->wait);
}

/*
 * Perform the "down" function.  Return zero for semaphore acquired,
 * return negative for signalled out of the function.
 *
 * If called from __down, the return is ignored and the wait loop is
 * not interruptible.  This means that a task waiting on a semaphore
 * using "down()" cannot be killed until someone does an "up()" on
 * the semaphore.
 *
 * If called from __down_interruptible, the return value gets checked
 * upon return.  If the return value is negative then the task continues
 * with the negative value in the return register (it can be tested by
 * the caller).
 *
 * Either form may be used in conjunction with "up()".
 *
 */
static inline int __do_down(struct semaphore * sem, int task_state)
{
        struct task_struct *tsk = current;
        struct wait_queue wait = { tsk, NULL };
        int               ret = 0;

        tsk->state = task_state;
        add_wait_queue(&sem->wait, &wait);

        /*
         * Ok, we're set up.  sem->count is known to be less than zero
         * so we must wait.
         *
         * We can let go the lock for purposes of waiting.
         * We re-acquire it after awaking so as to protect
         * all semaphore operations.
         *
         * If "up()" is called before we call waking_non_zero() then
         * we will catch it right away.  If it is called later then
         * we will have to go through a wakeup cycle to catch it.
         *
         * Multiple waiters contend for the semaphore lock to see
         * who gets to gate through and who has to wait some more.
         */
        for (;;) {
                if (waking_non_zero(sem))       /* are we waking up?  */
                        break;                  /* yes, exit loop */

                if (task_state == TASK_INTERRUPTIBLE && signal_pending(tsk)) {
                        ret = -EINTR;                   /* interrupted */
                        atomic_inc(&sem->count);        /* give up on down operation */
                        break;
                }

                schedule();
                tsk->state = task_state;
        }

        tsk->state = TASK_RUNNING;
        remove_wait_queue(&sem->wait, &wait);
        return ret;
}

void __down(struct semaphore * sem)
{
        __do_down(sem,TASK_UNINTERRUPTIBLE);
}

int __down_interruptible(struct semaphore * sem)
{
        return __do_down(sem,TASK_INTERRUPTIBLE);
}


static void FASTCALL(__sleep_on(struct wait_queue **p, int state));
static void __sleep_on(struct wait_queue **p, int state)
{
        unsigned long flags;
        struct wait_queue wait;

        current->state = state;
        wait.task = current;
        write_lock_irqsave(&waitqueue_lock, flags);
        __add_wait_queue(p, &wait);
        write_unlock(&waitqueue_lock);
        schedule();
        write_lock_irq(&waitqueue_lock);
        __remove_wait_queue(p, &wait);
        write_unlock_irqrestore(&waitqueue_lock, flags);
}

void interruptible_sleep_on(struct wait_queue **p)
{
        __sleep_on(p,TASK_INTERRUPTIBLE);
}

void sleep_on(struct wait_queue **p)
{
        __sleep_on(p,TASK_UNINTERRUPTIBLE);
}

void scheduling_functions_end_here(void) { }

static inline void cascade_timers(struct timer_vec *tv)
{
        /* cascade all the timers from tv up one level */
        struct timer_list *timer;
        timer = tv->vec[tv->index];
        /*
         * We are removing _all_ timers from the list, so we don't  have to
         * detach them individually, just clear the list afterwards.
         */
        while (timer) {
                struct timer_list *tmp = timer;
                timer = timer->next;
                internal_add_timer(tmp);
        }
        tv->vec[tv->index] = NULL;
        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 timer_list *timer;
                if (!tv1.index) {
                        int n = 1;
                        do {
                                cascade_timers(tvecs[n]);
                        } while (tvecs[n]->index == 1 && ++n < NOOF_TVECS);
                }
                while ((timer = tv1.vec[tv1.index])) {
                        void (*fn)(unsigned long) = timer->function;
                        unsigned long data = timer->data;
                        detach_timer(timer);
                        timer->next = timer->prev = NULL;
                        spin_unlock_irq(&timerlist_lock);
                        fn(data);
                        spin_lock_irq(&timerlist_lock);
                }
                ++timer_jiffies; 
                tv1.index = (tv1.index + 1) & TVR_MASK;
        }
        spin_unlock_irq(&timerlist_lock);
}


static inline void run_old_timers(void)
{
        struct timer_struct *tp;
        unsigned long mask;

        for (mask = 1, tp = timer_table+0 ; mask ; tp++,mask += mask) {
                if (mask > timer_active)
                        break;
                if (!(mask & timer_active))
                        continue;
                if (tp->expires > jiffies)
                        continue;
                timer_active &= ~mask;
                tp->fn();
                sti();
        }
}

spinlock_t tqueue_lock;

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

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

unsigned long timer_active = 0;
struct timer_struct timer_table[32];

/*
 * 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] = { 0,0,0 };

/*
 * 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->pid &&
                    (p->state == TASK_RUNNING ||
                     p->state == TASK_UNINTERRUPTIBLE ||
                     p->state == TASK_SWAPPING))
                        nr += FIXED_1;
        }
        read_unlock(&tasklist_lock);
        return nr;
}

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);
        }
}

/*
 * 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 > MAXPHASE )
        time_maxerror = MAXPHASE;

    /*
     * 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("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("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_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) != 128. Add 25% to get 125; => only 3% error */
    if (time_adj < 0)
        time_adj -= -time_adj >> 2;
    else
        time_adj += time_adj >> 2;
#endif
}

/* in the NTP reference this is called "hardclock()" */
static void update_wall_time_one_tick(void)
{
        /*
         * 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 += tick + time_adjust_step - ltemp;
        }
        else if (time_phase >= FINEUSEC) {
                long ltemp = time_phase >> SHIFT_SCALE;
                time_phase -= ltemp << SHIFT_SCALE;
                xtime.tv_usec += tick + time_adjust_step + ltemp;
        } else
                xtime.tv_usec += tick + time_adjust_step;

        if (time_adjust) {
            /* We are doing an adjtime thing. 
             *
             * Modify the value of the tick for next time.
             * Note that a positive delta means we want the clock
             * to run fast. This means that the tick should be bigger
             *
             * Limit the amount of the step for *next* tick to be
             * in the range -tickadj .. +tickadj
             */
             if (time_adjust > tickadj)
                time_adjust_step = tickadj;
             else if (time_adjust < -tickadj)
                time_adjust_step = -tickadj;
             else
                time_adjust_step = time_adjust;
             
            /* Reduce by this step the amount of time left  */
            time_adjust -= time_adjust_step;
        }
        else
            time_adjust_step = 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_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)
{
        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) {
                if (it_virt <= ticks) {
                        it_virt = ticks + p->it_virt_incr;
                        send_sig(SIGVTALRM, p, 1);
                }
                p->it_virt_value = it_virt - ticks;
        }
}

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

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

void update_one_process(struct task_struct *p,
        unsigned long ticks, 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, ticks);
}       

static void update_process_times(unsigned long ticks, unsigned long system)
{
/*
 * SMP does this on a per-CPU basis elsewhere
 */
#ifndef  __SMP__
        struct task_struct * p = current;
        unsigned long user = ticks - system;
        if (p->pid) {
                p->counter -= ticks;
                if (p->counter < 0) {
                        p->counter = 0;
                        p->need_resched = 1;
                }
                if (p->priority < DEF_PRIORITY)
                        kstat.cpu_nice += user;
                else
                        kstat.cpu_user += user;
                kstat.cpu_system += system;
        }
        update_one_process(p, ticks, user, system, 0);
#endif
}

volatile unsigned long lost_ticks = 0;
static unsigned long lost_ticks_system = 0;

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

        save_flags(flags);
        cli();

        ticks = lost_ticks;
        lost_ticks = 0;

        if (ticks) {
                unsigned long system;
                system = xchg(&lost_ticks_system, 0);

                calc_load(ticks);
                update_wall_time(ticks);
                restore_flags(flags);
                
                update_process_times(ticks, system);

        } else
                restore_flags(flags);
}

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

void do_timer(struct pt_regs * regs)
{
        (*(unsigned long *)&jiffies)++;
        lost_ticks++;
        mark_bh(TIMER_BH);
        if (!user_mode(regs))
                lost_ticks_system++;
        if (tq_timer)
                mark_bh(TQUEUE_BH);
}

#ifndef __alpha__

/*
 * For backwards compatibility?  This can be done in libc so Alpha
 * and all newer ports shouldn't need it.
 */
asmlinkage unsigned int 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;
}

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

/*
 * 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 int sys_getppid(void)
{
        int pid;
        struct task_struct * me = current;
        struct task_struct * parent;

        parent = me->p_opptr;
        for (;;) {
                pid = parent->pid;
#if __SMP__
{
                struct task_struct *old = parent;
                mb();
                parent = me->p_opptr;
                if (old != parent)
                        continue;
}
#endif
                break;
        }
        return pid;
}

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

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

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

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

/*
 * This has been replaced by sys_setpriority.  Maybe it should be
 * moved into the arch dependent tree for those ports that require
 * it for backward compatibility?
 */

asmlinkage int sys_nice(int increment)
{
        unsigned long newprio;
        int increase = 0;

        /*
         *      Setpriority might change our priority at the same moment.
         *      We don't have to worry. Conceptually one call occurs first
         *      and we have a single winner.
         */
         
        newprio = increment;
        if (increment < 0) {
                if (!capable(CAP_SYS_NICE))
                        return -EPERM;
                newprio = -increment;
                increase = 1;
        }

        if (newprio > 40)
                newprio = 40;
        /*
         * do a "normalization" of the priority (traditionally
         * Unix nice values are -20 to 20; Linux doesn't really
         * use that kind of thing, but uses the length of the
         * timeslice instead (default 150 ms). The rounding is
         * why we want to avoid negative values.
         */
        newprio = (newprio * DEF_PRIORITY + 10) / 20;
        increment = newprio;
        if (increase)
                increment = -increment;
        /*
         *      Current->priority can change between this point
         *      and the assignment. We are assigning not doing add/subs
         *      so thats ok. Conceptually a process might just instantaneously
         *      read the value we stomp over. I don't think that is an issue
         *      unless posix makes it one. If so we can loop on changes
         *      to current->priority.
         */
        newprio = current->priority - increment;
        if ((signed) newprio < 1)
                newprio = 1;
        if (newprio > DEF_PRIORITY*2)
                newprio = DEF_PRIORITY*2;
        current->priority = newprio;
        return 0;
}

#endif

static inline struct task_struct *find_process_by_pid(pid_t pid)
{
        struct task_struct *tsk = current;

        if (pid)
                tsk = find_task_by_pid(pid);
        return tsk;
}

static int setscheduler(pid_t pid, int policy, 
                        struct sched_param *param)
{
        struct sched_param lp;
        struct task_struct *p;
        int retval;

        retval = -EINVAL;
        if (!param || pid < 0)
                goto out_nounlock;

        retval = -EFAULT;
        if (copy_from_user(&lp, param, sizeof(struct sched_param)))
                goto out_nounlock;

        /*
         * We play safe to avoid deadlocks.
         */
        spin_lock(&scheduler_lock);
        spin_lock_irq(&runqueue_lock);
        read_lock(&tasklist_lock);

        p = find_process_by_pid(pid);

        retval = -ESRCH;
        if (!p)
                goto out_unlock;
                        
        if (policy < 0)
                policy = p->policy;
        else {
                retval = -EINVAL;
                if (policy != SCHED_FIFO && policy != SCHED_RR &&
                                policy != SCHED_OTHER)
                        goto out_unlock;
        }
        
        /*
         * Valid priorities for SCHED_FIFO and SCHED_RR are 1..99, valid
         * priority for SCHED_OTHER is 0.
         */
        retval = -EINVAL;
        if (lp.sched_priority < 0 || lp.sched_priority > 99)
                goto out_unlock;
        if ((policy == SCHED_OTHER) != (lp.sched_priority == 0))
                goto out_unlock;

        retval = -EPERM;
        if ((policy == SCHED_FIFO || policy == SCHED_RR) && 
            !capable(CAP_SYS_NICE))
                goto out_unlock;
        if ((current->euid != p->euid) && (current->euid != p->uid) &&
            !capable(CAP_SYS_NICE))
                goto out_unlock;

        retval = 0;
        p->policy = policy;
        p->rt_priority = lp.sched_priority;
        if (p->next_run)
                move_first_runqueue(p);

        current->need_resched = 1;

out_unlock:
        read_unlock(&tasklist_lock);
        spin_unlock_irq(&runqueue_lock);
        spin_unlock(&scheduler_lock);

out_nounlock:
        return retval;
}

asmlinkage int sys_sched_setscheduler(pid_t pid, int policy, 
                                      struct sched_param *param)
{
        return setscheduler(pid, policy, param);
}

asmlinkage int sys_sched_setparam(pid_t pid, struct sched_param *param)
{
        return setscheduler(pid, -1, param);
}

asmlinkage int sys_sched_getscheduler(pid_t pid)
{
        struct task_struct *p;
        int retval;

        retval = -EINVAL;
        if (pid < 0)
                goto out_nounlock;

        read_lock(&tasklist_lock);

        retval = -ESRCH;
        p = find_process_by_pid(pid);
        if (!p)
                goto out_unlock;
                        
        retval = p->policy;

out_unlock:
        read_unlock(&tasklist_lock);

out_nounlock:
        return retval;
}

asmlinkage int sys_sched_getparam(pid_t pid, struct sched_param *param)
{
        struct task_struct *p;
        struct sched_param lp;
        int retval;

        retval = -EINVAL;
        if (!param || pid < 0)
                goto out_nounlock;

        read_lock(&tasklist_lock);
        p = find_process_by_pid(pid);
        retval = -ESRCH;
        if (!p)
                goto out_unlock;
        lp.sched_priority = p->rt_priority;
        read_unlock(&tasklist_lock);

        /*
         * This one might sleep, we cannot do it with a spinlock held ...
         */
        retval = copy_to_user(param, &lp, sizeof(*param)) ? -EFAULT : 0;

out_nounlock:
        return retval;

out_unlock:
        read_unlock(&tasklist_lock);
        return retval;
}

asmlinkage int sys_sched_yield(void)
{
        spin_lock(&scheduler_lock);
        spin_lock_irq(&runqueue_lock);
        current->policy |= SCHED_YIELD;
        current->need_resched = 1;
        move_last_runqueue(current);
        spin_unlock_irq(&runqueue_lock);
        spin_unlock(&scheduler_lock);
        return 0;
}

asmlinkage int sys_sched_get_priority_max(int policy)
{
        int ret = -EINVAL;

        switch (policy) {
        case SCHED_FIFO:
        case SCHED_RR:
                ret = 99;
                break;
        case SCHED_OTHER:
                ret = 0;
                break;
        }
        return ret;
}

asmlinkage int sys_sched_get_priority_min(int policy)
{
        int ret = -EINVAL;

        switch (policy) {
        case SCHED_FIFO:
        case SCHED_RR:
                ret = 1;
                break;
        case SCHED_OTHER:
                ret = 0;
        }
        return ret;
}

asmlinkage int sys_sched_rr_get_interval(pid_t pid, struct timespec *interval)
{
        struct timespec t;

        t.tv_sec = 0;
        t.tv_nsec = 150000;
        if (copy_to_user(interval, &t, sizeof(struct timespec)))
                return -EFAULT;
        return 0;
}

asmlinkage int 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) + jiffies;

        current->timeout = expire;
        current->state = TASK_INTERRUPTIBLE;
        schedule();

        if (expire > jiffies) {
                if (rmtp) {
                        jiffies_to_timespec(expire - jiffies -
                                            (expire > jiffies + 1), &t);
                        if (copy_to_user(rmtp, &t, sizeof(struct timespec)))
                                return -EFAULT;
                }
                return -EINTR;
        }
        return 0;
}

static void show_task(int nr,struct task_struct * p)
{
        unsigned long free = 0;
        static const char * stat_nam[] = { "R", "S", "D", "Z", "T", "W" };

        printk("%-8s %3d ", p->comm, (p == current) ? -nr : nr);
        if (((unsigned) p->state) < sizeof(stat_nam)/sizeof(char *))
                printk(stat_nam[p->state]);
        else
                printk(" ");
#if (BITS_PER_LONG == 32)
        if (p == current)
                printk(" current  ");
        else
                printk(" %08lX ", thread_saved_pc(&p->tss));
#else
        if (p == current)
                printk("   current task   ");
        else
                printk(" %016lx ", thread_saved_pc(&p->tss));
#endif
        {
                unsigned long * n = (unsigned long *) (p+1);
                while (!*n)
                        n++;
                free = (unsigned long) n - (unsigned long)(p+1);
        }
        printk("%5lu %5d %6d ", free, p->pid, p->p_pptr->pid);
        if (p->p_cptr)
                printk("%5d ", p->p_cptr->pid);
        else
                printk("      ");
        if (p->p_ysptr)
                printk("%7d", p->p_ysptr->pid);
        else
                printk("       ");
        if (p->p_osptr)
                printk(" %5d\n", p->p_osptr->pid);
        else
                printk("\n");

        {
                struct signal_queue *q;
                char s[sizeof(sigset_t)*2+1], b[sizeof(sigset_t)*2+1]; 

                render_sigset_t(&p->signal, s);
                render_sigset_t(&p->blocked, b);
                printk("   sig: %d %s %s :", signal_pending(p), s, b);
                for (q = p->sigqueue; q ; q = q->next)
                        printk(" %d", q->info.si_signo);
                printk(" X\n");
        }
}

char * render_sigset_t(sigset_t *set, char *buffer)
{
        int i = _NSIG, x;
        do {
                i -= 4, x = 0;
                if (sigismember(set, i+1)) x |= 1;
                if (sigismember(set, i+2)) x |= 2;
                if (sigismember(set, i+3)) x |= 4;
                if (sigismember(set, i+4)) x |= 8;
                *buffer++ = (x < 10 ? '0' : 'a' - 10) + x;
        } while (i >= 4);
        *buffer = 0;
        return buffer;
}

void show_state(void)
{
        struct task_struct *p;

#if (BITS_PER_LONG == 32)
        printk("\n"
               "                         free                        sibling\n");
        printk("  task             PC    stack   pid father child younger older\n");
#else
        printk("\n"
               "                                 free                        sibling\n");
        printk("  task                 PC        stack   pid father child younger older\n");
#endif
        read_lock(&tasklist_lock);
        for_each_task(p)
                show_task((p->tarray_ptr - &task[0]),p);
        read_unlock(&tasklist_lock);
}

__initfunc(void sched_init(void))
{
        /*
         *      We have to do a little magic to get the first
         *      process right in SMP mode.
         */
        int cpu=hard_smp_processor_id();
        int nr = NR_TASKS;

        init_task.processor=cpu;

        /* Init task array free list and pidhash table. */
        while(--nr > 0)
                add_free_taskslot(&task[nr]);

        for(nr = 0; nr < PIDHASH_SZ; nr++)
                pidhash[nr] = NULL;

        init_bh(TIMER_BH, timer_bh);
        init_bh(TQUEUE_BH, tqueue_bh);
        init_bh(IMMEDIATE_BH, immediate_bh);
}