[PATCH] raid5 BIO_UPTODATE set

[linux-2.6/history.git] / kernel / sched.c

/*
 *  kernel/sched.c
 *
 *  Kernel scheduler and related syscalls
 *
 *  Copyright (C) 1991-2002  Linus Torvalds
 *
 *  1996-12-23  Modified by Dave Grothe to fix bugs in semaphores and
 *              make semaphores SMP safe
 *  1998-11-19  Implemented schedule_timeout() and related stuff
 *              by Andrea Arcangeli
 *  2002-01-04  New ultra-scalable O(1) scheduler by Ingo Molnar:
 *              hybrid priority-list and round-robin design with
 *              an array-switch method of distributing timeslices
 *              and per-CPU runqueues.  Cleanups and useful suggestions
 *              by Davide Libenzi, preemptible kernel bits by Robert Love.
 */

#include <linux/mm.h>
#include <linux/nmi.h>
#include <linux/init.h>
#include <asm/uaccess.h>
#include <linux/highmem.h>
#include <linux/smp_lock.h>
#include <asm/mmu_context.h>
#include <linux/interrupt.h>
#include <linux/completion.h>
#include <linux/kernel_stat.h>
#include <linux/security.h>
#include <linux/notifier.h>
#include <linux/delay.h>
#include <linux/timer.h>

/*
 * Convert user-nice values [ -20 ... 0 ... 19 ]
 * to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
 * and back.
 */
#define NICE_TO_PRIO(nice)      (MAX_RT_PRIO + (nice) + 20)
#define PRIO_TO_NICE(prio)      ((prio) - MAX_RT_PRIO - 20)
#define TASK_NICE(p)            PRIO_TO_NICE((p)->static_prio)

/*
 * 'User priority' is the nice value converted to something we
 * can work with better when scaling various scheduler parameters,
 * it's a [ 0 ... 39 ] range.
 */
#define USER_PRIO(p)            ((p)-MAX_RT_PRIO)
#define TASK_USER_PRIO(p)       USER_PRIO((p)->static_prio)
#define MAX_USER_PRIO           (USER_PRIO(MAX_PRIO))

/*
 * These are the 'tuning knobs' of the scheduler:
 *
 * Minimum timeslice is 10 msecs, default timeslice is 150 msecs,
 * maximum timeslice is 300 msecs. Timeslices get refilled after
 * they expire.
 */
#define MIN_TIMESLICE           ( 10 * HZ / 1000)
#define MAX_TIMESLICE           (300 * HZ / 1000)
#define CHILD_PENALTY           95
#define PARENT_PENALTY          100
#define EXIT_WEIGHT             3
#define PRIO_BONUS_RATIO        25
#define INTERACTIVE_DELTA       2
#define MAX_SLEEP_AVG           (2*HZ)
#define STARVATION_LIMIT        (2*HZ)

/*
 * If a task is 'interactive' then we reinsert it in the active
 * array after it has expired its current timeslice. (it will not
 * continue to run immediately, it will still roundrobin with
 * other interactive tasks.)
 *
 * This part scales the interactivity limit depending on niceness.
 *
 * We scale it linearly, offset by the INTERACTIVE_DELTA delta.
 * Here are a few examples of different nice levels:
 *
 *  TASK_INTERACTIVE(-20): [1,1,1,1,1,1,1,1,1,0,0]
 *  TASK_INTERACTIVE(-10): [1,1,1,1,1,1,1,0,0,0,0]
 *  TASK_INTERACTIVE(  0): [1,1,1,1,0,0,0,0,0,0,0]
 *  TASK_INTERACTIVE( 10): [1,1,0,0,0,0,0,0,0,0,0]
 *  TASK_INTERACTIVE( 19): [0,0,0,0,0,0,0,0,0,0,0]
 *
 * (the X axis represents the possible -5 ... 0 ... +5 dynamic
 *  priority range a task can explore, a value of '1' means the
 *  task is rated interactive.)
 *
 * Ie. nice +19 tasks can never get 'interactive' enough to be
 * reinserted into the active array. And only heavily CPU-hog nice -20
 * tasks will be expired. Default nice 0 tasks are somewhere between,
 * it takes some effort for them to get interactive, but it's not
 * too hard.
 */

#define SCALE(v1,v1_max,v2_max) \
        (v1) * (v2_max) / (v1_max)

#define DELTA(p) \
        (SCALE(TASK_NICE(p), 40, MAX_USER_PRIO*PRIO_BONUS_RATIO/100) + \
                INTERACTIVE_DELTA)

#define TASK_INTERACTIVE(p) \
        ((p)->prio <= (p)->static_prio - DELTA(p))

/*
 * BASE_TIMESLICE scales user-nice values [ -20 ... 19 ]
 * to time slice values.
 *
 * The higher a thread's priority, the bigger timeslices
 * it gets during one round of execution. But even the lowest
 * priority thread gets MIN_TIMESLICE worth of execution time.
 *
 * task_timeslice() is the interface that is used by the scheduler.
 */

#define BASE_TIMESLICE(p) (MIN_TIMESLICE + \
        ((MAX_TIMESLICE - MIN_TIMESLICE) * (MAX_PRIO-1-(p)->static_prio)/(MAX_USER_PRIO - 1)))

static inline unsigned int task_timeslice(task_t *p)
{
        return BASE_TIMESLICE(p);
}

/*
 * These are the runqueue data structures:
 */

#define BITMAP_SIZE ((((MAX_PRIO+1+7)/8)+sizeof(long)-1)/sizeof(long))

typedef struct runqueue runqueue_t;

struct prio_array {
        int nr_active;
        unsigned long bitmap[BITMAP_SIZE];
        struct list_head queue[MAX_PRIO];
};

/*
 * This is the main, per-CPU runqueue data structure.
 *
 * Locking rule: those places that want to lock multiple runqueues
 * (such as the load balancing or the thread migration code), lock
 * acquire operations must be ordered by ascending &runqueue.
 */
struct runqueue {
        spinlock_t lock;
        unsigned long nr_running, nr_switches, expired_timestamp,
                        nr_uninterruptible;
        task_t *curr, *idle;
        prio_array_t *active, *expired, arrays[2];
        int prev_nr_running[NR_CPUS];

        task_t *migration_thread;
        struct list_head migration_queue;

} ____cacheline_aligned;

static struct runqueue runqueues[NR_CPUS] __cacheline_aligned;

#define cpu_rq(cpu)             (runqueues + (cpu))
#define this_rq()               cpu_rq(smp_processor_id())
#define task_rq(p)              cpu_rq(task_cpu(p))
#define cpu_curr(cpu)           (cpu_rq(cpu)->curr)
#define rt_task(p)              ((p)->prio < MAX_RT_PRIO)

/*
 * Default context-switch locking:
 */
#ifndef prepare_arch_switch
# define prepare_arch_switch(rq, next)  do { } while(0)
# define finish_arch_switch(rq, next)   spin_unlock_irq(&(rq)->lock)
# define task_running(rq, p)            ((rq)->curr == (p))
#endif

/*
 * task_rq_lock - lock the runqueue a given task resides on and disable
 * interrupts.  Note the ordering: we can safely lookup the task_rq without
 * explicitly disabling preemption.
 */
static inline runqueue_t *task_rq_lock(task_t *p, unsigned long *flags)
{
        struct runqueue *rq;

repeat_lock_task:
        local_irq_save(*flags);
        rq = task_rq(p);
        spin_lock(&rq->lock);
        if (unlikely(rq != task_rq(p))) {
                spin_unlock_irqrestore(&rq->lock, *flags);
                goto repeat_lock_task;
        }
        return rq;
}

static inline void task_rq_unlock(runqueue_t *rq, unsigned long *flags)
{
        spin_unlock_irqrestore(&rq->lock, *flags);
}

/*
 * rq_lock - lock a given runqueue and disable interrupts.
 */
static inline runqueue_t *this_rq_lock(void)
{
        runqueue_t *rq;

        local_irq_disable();
        rq = this_rq();
        spin_lock(&rq->lock);

        return rq;
}

static inline void rq_unlock(runqueue_t *rq)
{
        spin_unlock_irq(&rq->lock);
}

/*
 * Adding/removing a task to/from a priority array:
 */
static inline void dequeue_task(struct task_struct *p, prio_array_t *array)
{
        array->nr_active--;
        list_del(&p->run_list);
        if (list_empty(array->queue + p->prio))
                __clear_bit(p->prio, array->bitmap);
}

static inline void enqueue_task(struct task_struct *p, prio_array_t *array)
{
        list_add_tail(&p->run_list, array->queue + p->prio);
        __set_bit(p->prio, array->bitmap);
        array->nr_active++;
        p->array = array;
}

/*
 * effective_prio - return the priority that is based on the static
 * priority but is modified by bonuses/penalties.
 *
 * We scale the actual sleep average [0 .... MAX_SLEEP_AVG]
 * into the -5 ... 0 ... +5 bonus/penalty range.
 *
 * We use 25% of the full 0...39 priority range so that:
 *
 * 1) nice +19 interactive tasks do not preempt nice 0 CPU hogs.
 * 2) nice -20 CPU hogs do not get preempted by nice 0 tasks.
 *
 * Both properties are important to certain workloads.
 */
static inline int effective_prio(task_t *p)
{
        int bonus, prio;

        bonus = MAX_USER_PRIO*PRIO_BONUS_RATIO*p->sleep_avg/MAX_SLEEP_AVG/100 -
                        MAX_USER_PRIO*PRIO_BONUS_RATIO/100/2;

        prio = p->static_prio - bonus;
        if (prio < MAX_RT_PRIO)
                prio = MAX_RT_PRIO;
        if (prio > MAX_PRIO-1)
                prio = MAX_PRIO-1;
        return prio;
}

/*
 * activate_task - move a task to the runqueue.

 * Also update all the scheduling statistics stuff. (sleep average
 * calculation, priority modifiers, etc.)
 */
static inline void activate_task(task_t *p, runqueue_t *rq)
{
        unsigned long sleep_time = jiffies - p->sleep_timestamp;
        prio_array_t *array = rq->active;

        if (!rt_task(p) && sleep_time) {
                /*
                 * This code gives a bonus to interactive tasks. We update
                 * an 'average sleep time' value here, based on
                 * sleep_timestamp. The more time a task spends sleeping,
                 * the higher the average gets - and the higher the priority
                 * boost gets as well.
                 */
                p->sleep_avg += sleep_time;
                if (p->sleep_avg > MAX_SLEEP_AVG)
                        p->sleep_avg = MAX_SLEEP_AVG;
                p->prio = effective_prio(p);
        }
        enqueue_task(p, array);
        rq->nr_running++;
}

/*
 * deactivate_task - remove a task from the runqueue.
 */
static inline void deactivate_task(struct task_struct *p, runqueue_t *rq)
{
        rq->nr_running--;
        if (p->state == TASK_UNINTERRUPTIBLE)
                rq->nr_uninterruptible++;
        dequeue_task(p, p->array);
        p->array = NULL;
}

/*
 * resched_task - mark a task 'to be rescheduled now'.
 *
 * On UP this means the setting of the need_resched flag, on SMP it
 * might also involve a cross-CPU call to trigger the scheduler on
 * the target CPU.
 */
static inline void resched_task(task_t *p)
{
#ifdef CONFIG_SMP
        int need_resched, nrpolling;

        preempt_disable();
        /* minimise the chance of sending an interrupt to poll_idle() */
        nrpolling = test_tsk_thread_flag(p,TIF_POLLING_NRFLAG);
        need_resched = test_and_set_tsk_thread_flag(p,TIF_NEED_RESCHED);
        nrpolling |= test_tsk_thread_flag(p,TIF_POLLING_NRFLAG);

        if (!need_resched && !nrpolling && (task_cpu(p) != smp_processor_id()))
                smp_send_reschedule(task_cpu(p));
        preempt_enable();
#else
        set_tsk_need_resched(p);
#endif
}

#ifdef CONFIG_SMP

/*
 * wait_task_inactive - wait for a thread to unschedule.
 *
 * The caller must ensure that the task *will* unschedule sometime soon,
 * else this function might spin for a *long* time.
 */
void wait_task_inactive(task_t * p)
{
        unsigned long flags;
        runqueue_t *rq;

repeat:
        preempt_disable();
        rq = task_rq(p);
        if (unlikely(task_running(rq, p))) {
                cpu_relax();
                /*
                 * enable/disable preemption just to make this
                 * a preemption point - we are busy-waiting
                 * anyway.
                 */
                preempt_enable();
                goto repeat;
        }
        rq = task_rq_lock(p, &flags);
        if (unlikely(task_running(rq, p))) {
                task_rq_unlock(rq, &flags);
                preempt_enable();
                goto repeat;
        }
        task_rq_unlock(rq, &flags);
        preempt_enable();
}
#endif

/*
 * kick_if_running - kick the remote CPU if the task is running currently.
 *
 * This code is used by the signal code to signal tasks
 * which are in user-mode, as quickly as possible.
 *
 * (Note that we do this lockless - if the task does anything
 * while the message is in flight then it will notice the
 * sigpending condition anyway.)
 */
void kick_if_running(task_t * p)
{
        if ((task_running(task_rq(p), p)) && (task_cpu(p) != smp_processor_id()))
                resched_task(p);
}

/***
 * try_to_wake_up - wake up a thread
 * @p: the to-be-woken-up thread
 * @sync: do a synchronous wakeup?
 *
 * Put it on the run-queue if it's not already there. The "current"
 * thread 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.
 *
 * returns failure only if the task is already active.
 */
static int try_to_wake_up(task_t * p, int sync)
{
        unsigned long flags;
        int success = 0;
        long old_state;
        runqueue_t *rq;

repeat_lock_task:
        rq = task_rq_lock(p, &flags);
        old_state = p->state;
        if (!p->array) {
                /*
                 * Fast-migrate the task if it's not running or runnable
                 * currently. Do not violate hard affinity.
                 */
                if (unlikely(sync && !task_running(rq, p) &&
                        (task_cpu(p) != smp_processor_id()) &&
                        (p->cpus_allowed & (1UL << smp_processor_id())))) {

                        set_task_cpu(p, smp_processor_id());
                        task_rq_unlock(rq, &flags);
                        goto repeat_lock_task;
                }
                if (old_state == TASK_UNINTERRUPTIBLE)
                        rq->nr_uninterruptible--;
                activate_task(p, rq);

                if (p->prio < rq->curr->prio)
                        resched_task(rq->curr);
                success = 1;
        }
        p->state = TASK_RUNNING;
        task_rq_unlock(rq, &flags);

        return success;
}

int wake_up_process(task_t * p)
{
        return try_to_wake_up(p, 0);
}

/*
 * wake_up_forked_process - wake up a freshly forked process.
 *
 * This function will do some initial scheduler statistics housekeeping
 * that must be done for every newly created process.
 */
void wake_up_forked_process(task_t * p)
{
        runqueue_t *rq = this_rq_lock();

        p->state = TASK_RUNNING;
        if (!rt_task(p)) {
                /*
                 * We decrease the sleep average of forking parents
                 * and children as well, to keep max-interactive tasks
                 * from forking tasks that are max-interactive.
                 */
                current->sleep_avg = current->sleep_avg * PARENT_PENALTY / 100;
                p->sleep_avg = p->sleep_avg * CHILD_PENALTY / 100;
                p->prio = effective_prio(p);
        }
        set_task_cpu(p, smp_processor_id());
        activate_task(p, rq);

        rq_unlock(rq);
}

/*
 * Potentially available exiting-child timeslices are
 * retrieved here - this way the parent does not get
 * penalized for creating too many threads.
 *
 * (this cannot be used to 'generate' timeslices
 * artificially, because any timeslice recovered here
 * was given away by the parent in the first place.)
 */
void sched_exit(task_t * p)
{
        unsigned long flags;

        local_irq_save(flags);
        if (p->first_time_slice) {
                p->parent->time_slice += p->time_slice;
                if (unlikely(p->parent->time_slice > MAX_TIMESLICE))
                        p->parent->time_slice = MAX_TIMESLICE;
        }
        local_irq_restore(flags);
        /*
         * If the child was a (relative-) CPU hog then decrease
         * the sleep_avg of the parent as well.
         */
        if (p->sleep_avg < p->parent->sleep_avg)
                p->parent->sleep_avg = (p->parent->sleep_avg * EXIT_WEIGHT +
                        p->sleep_avg) / (EXIT_WEIGHT + 1);
}

/**
 * schedule_tail - first thing a freshly forked thread must call.
 * @prev: the thread we just switched away from.
 */
#if CONFIG_SMP || CONFIG_PREEMPT
asmlinkage void schedule_tail(task_t *prev)
{
        finish_arch_switch(this_rq(), prev);
}
#endif

/*
 * context_switch - switch to the new MM and the new
 * thread's register state.
 */
static inline task_t * context_switch(task_t *prev, task_t *next)
{
        struct mm_struct *mm = next->mm;
        struct mm_struct *oldmm = prev->active_mm;

        if (unlikely(!mm)) {
                next->active_mm = oldmm;
                atomic_inc(&oldmm->mm_count);
                enter_lazy_tlb(oldmm, next, smp_processor_id());
        } else
                switch_mm(oldmm, mm, next, smp_processor_id());

        if (unlikely(!prev->mm)) {
                prev->active_mm = NULL;
                mmdrop(oldmm);
        }

        /* Here we just switch the register state and the stack. */
        switch_to(prev, next, prev);

        return prev;
}

/*
 * nr_running, nr_uninterruptible and nr_context_switches:
 *
 * externally visible scheduler statistics: current number of runnable
 * threads, current number of uninterruptible-sleeping threads, total
 * number of context switches performed since bootup.
 */
unsigned long nr_running(void)
{
        unsigned long i, sum = 0;

        for (i = 0; i < NR_CPUS; i++)
                sum += cpu_rq(i)->nr_running;

        return sum;
}

unsigned long nr_uninterruptible(void)
{
        unsigned long i, sum = 0;

        for (i = 0; i < NR_CPUS; i++)
                sum += cpu_rq(i)->nr_uninterruptible;

        return sum;
}

unsigned long nr_context_switches(void)
{
        unsigned long i, sum = 0;

        for (i = 0; i < NR_CPUS; i++)
                sum += cpu_rq(i)->nr_switches;

        return sum;
}

/*
 * double_rq_lock - safely lock two runqueues
 *
 * Note this does not disable interrupts like task_rq_lock,
 * you need to do so manually before calling.
 */
static inline void double_rq_lock(runqueue_t *rq1, runqueue_t *rq2)
{
        if (rq1 == rq2)
                spin_lock(&rq1->lock);
        else {
                if (rq1 < rq2) {
                        spin_lock(&rq1->lock);
                        spin_lock(&rq2->lock);
                } else {
                        spin_lock(&rq2->lock);
                        spin_lock(&rq1->lock);
                }
        }
}

/*
 * double_rq_unlock - safely unlock two runqueues
 *
 * Note this does not restore interrupts like task_rq_unlock,
 * you need to do so manually after calling.
 */
static inline void double_rq_unlock(runqueue_t *rq1, runqueue_t *rq2)
{
        spin_unlock(&rq1->lock);
        if (rq1 != rq2)
                spin_unlock(&rq2->lock);
}

#if CONFIG_SMP

/*
 * double_lock_balance - lock the busiest runqueue
 *
 * this_rq is locked already. Recalculate nr_running if we have to
 * drop the runqueue lock.
 */
static inline unsigned int double_lock_balance(runqueue_t *this_rq,
        runqueue_t *busiest, int this_cpu, int idle, unsigned int nr_running)
{
        if (unlikely(!spin_trylock(&busiest->lock))) {
                if (busiest < this_rq) {
                        spin_unlock(&this_rq->lock);
                        spin_lock(&busiest->lock);
                        spin_lock(&this_rq->lock);
                        /* Need to recalculate nr_running */
                        if (idle || (this_rq->nr_running > this_rq->prev_nr_running[this_cpu]))
                                nr_running = this_rq->nr_running;
                        else
                                nr_running = this_rq->prev_nr_running[this_cpu];
                } else
                        spin_lock(&busiest->lock);
        }
        return nr_running;
}

/*
 * find_busiest_queue - find the busiest runqueue.
 */
static inline runqueue_t *find_busiest_queue(runqueue_t *this_rq, int this_cpu, int idle, int *imbalance)
{
        int nr_running, load, max_load, i;
        runqueue_t *busiest, *rq_src;

        /*
         * We search all runqueues to find the most busy one.
         * We do this lockless to reduce cache-bouncing overhead,
         * we re-check the 'best' source CPU later on again, with
         * the lock held.
         *
         * We fend off statistical fluctuations in runqueue lengths by
         * saving the runqueue length during the previous load-balancing
         * operation and using the smaller one the current and saved lengths.
         * If a runqueue is long enough for a longer amount of time then
         * we recognize it and pull tasks from it.
         *
         * The 'current runqueue length' is a statistical maximum variable,
         * for that one we take the longer one - to avoid fluctuations in
         * the other direction. So for a load-balance to happen it needs
         * stable long runqueue on the target CPU and stable short runqueue
         * on the local runqueue.
         *
         * We make an exception if this CPU is about to become idle - in
         * that case we are less picky about moving a task across CPUs and
         * take what can be taken.
         */
        if (idle || (this_rq->nr_running > this_rq->prev_nr_running[this_cpu]))
                nr_running = this_rq->nr_running;
        else
                nr_running = this_rq->prev_nr_running[this_cpu];

        busiest = NULL;
        max_load = 1;
        for (i = 0; i < NR_CPUS; i++) {
                if (!cpu_online(i))
                        continue;

                rq_src = cpu_rq(i);
                if (idle || (rq_src->nr_running < this_rq->prev_nr_running[i]))
                        load = rq_src->nr_running;
                else
                        load = this_rq->prev_nr_running[i];
                this_rq->prev_nr_running[i] = rq_src->nr_running;

                if ((load > max_load) && (rq_src != this_rq)) {
                        busiest = rq_src;
                        max_load = load;
                }
        }

        if (likely(!busiest))
                goto out;

        *imbalance = (max_load - nr_running) / 2;

        /* It needs an at least ~25% imbalance to trigger balancing. */
        if (!idle && (*imbalance < (max_load + 3)/4)) {
                busiest = NULL;
                goto out;
        }

        nr_running = double_lock_balance(this_rq, busiest, this_cpu, idle, nr_running);
        /*
         * Make sure nothing changed since we checked the
         * runqueue length.
         */
        if (busiest->nr_running <= nr_running + 1) {
                spin_unlock(&busiest->lock);
                busiest = NULL;
        }
out:
        return busiest;
}

/*
 * pull_task - move a task from a remote runqueue to the local runqueue.
 * Both runqueues must be locked.
 */
static inline void pull_task(runqueue_t *src_rq, prio_array_t *src_array, task_t *p, runqueue_t *this_rq, int this_cpu)
{
        dequeue_task(p, src_array);
        src_rq->nr_running--;
        set_task_cpu(p, this_cpu);
        this_rq->nr_running++;
        enqueue_task(p, this_rq->active);
        /*
         * Note that idle threads have a prio of MAX_PRIO, for this test
         * to be always true for them.
         */
        if (p->prio < this_rq->curr->prio)
                set_need_resched();
}

/*
 * Current runqueue is empty, or rebalance tick: if there is an
 * inbalance (current runqueue is too short) then pull from
 * busiest runqueue(s).
 *
 * We call this with the current runqueue locked,
 * irqs disabled.
 */
static void load_balance(runqueue_t *this_rq, int idle)
{
        int imbalance, idx, this_cpu = smp_processor_id();
        runqueue_t *busiest;
        prio_array_t *array;
        struct list_head *head, *curr;
        task_t *tmp;

        busiest = find_busiest_queue(this_rq, this_cpu, idle, &imbalance);
        if (!busiest)
                goto out;

        /*
         * We first consider expired tasks. Those will likely not be
         * executed in the near future, and they are most likely to
         * be cache-cold, thus switching CPUs has the least effect
         * on them.
         */
        if (busiest->expired->nr_active)
                array = busiest->expired;
        else
                array = busiest->active;

new_array:
        /* Start searching at priority 0: */
        idx = 0;
skip_bitmap:
        if (!idx)
                idx = sched_find_first_bit(array->bitmap);
        else
                idx = find_next_bit(array->bitmap, MAX_PRIO, idx);
        if (idx == MAX_PRIO) {
                if (array == busiest->expired) {
                        array = busiest->active;
                        goto new_array;
                }
                goto out_unlock;
        }

        head = array->queue + idx;
        curr = head->prev;
skip_queue:
        tmp = list_entry(curr, task_t, run_list);

        /*
         * We do not migrate tasks that are:
         * 1) running (obviously), or
         * 2) cannot be migrated to this CPU due to cpus_allowed, or
         * 3) are cache-hot on their current CPU.
         */

#define CAN_MIGRATE_TASK(p,rq,this_cpu)                                 \
        ((jiffies - (p)->sleep_timestamp > cache_decay_ticks) &&        \
                !task_running(rq, p) &&                                 \
                        ((p)->cpus_allowed & (1UL << (this_cpu))))

        curr = curr->prev;

        if (!CAN_MIGRATE_TASK(tmp, busiest, this_cpu)) {
                if (curr != head)
                        goto skip_queue;
                idx++;
                goto skip_bitmap;
        }
        pull_task(busiest, array, tmp, this_rq, this_cpu);
        if (!idle && --imbalance) {
                if (curr != head)
                        goto skip_queue;
                idx++;
                goto skip_bitmap;
        }
out_unlock:
        spin_unlock(&busiest->lock);
out:
        ;
}

/*
 * One of the idle_cpu_tick() and busy_cpu_tick() functions will
 * get called every timer tick, on every CPU. Our balancing action
 * frequency and balancing agressivity depends on whether the CPU is
 * idle or not.
 *
 * busy-rebalance every 250 msecs. idle-rebalance every 1 msec. (or on
 * systems with HZ=100, every 10 msecs.)
 */
#define BUSY_REBALANCE_TICK (HZ/4 ?: 1)
#define IDLE_REBALANCE_TICK (HZ/1000 ?: 1)

static inline void idle_tick(runqueue_t *rq)
{
        if (jiffies % IDLE_REBALANCE_TICK)
                return;
        spin_lock(&rq->lock);
        load_balance(rq, 1);
        spin_unlock(&rq->lock);
}

#endif

/*
 * We place interactive tasks back into the active array, if possible.
 *
 * To guarantee that this does not starve expired tasks we ignore the
 * interactivity of a task if the first expired task had to wait more
 * than a 'reasonable' amount of time. This deadline timeout is
 * load-dependent, as the frequency of array switched decreases with
 * increasing number of running tasks:
 */
#define EXPIRED_STARVING(rq) \
                ((rq)->expired_timestamp && \
                (jiffies - (rq)->expired_timestamp >= \
                        STARVATION_LIMIT * ((rq)->nr_running) + 1))

/*
 * This function gets called by the timer code, with HZ frequency.
 * We call it with interrupts disabled.
 */
void scheduler_tick(int user_ticks, int sys_ticks)
{
        int cpu = smp_processor_id();
        runqueue_t *rq = this_rq();
        task_t *p = current;

        run_local_timers();
        if (p == rq->idle) {
                /* note: this timer irq context must be accounted for as well */
                if (irq_count() - HARDIRQ_OFFSET >= SOFTIRQ_OFFSET)
                        kstat.per_cpu_system[cpu] += sys_ticks;
#if CONFIG_SMP
                idle_tick(rq);
#endif
                return;
        }
        if (TASK_NICE(p) > 0)
                kstat.per_cpu_nice[cpu] += user_ticks;
        else
                kstat.per_cpu_user[cpu] += user_ticks;
        kstat.per_cpu_system[cpu] += sys_ticks;

        /* Task might have expired already, but not scheduled off yet */
        if (p->array != rq->active) {
                set_tsk_need_resched(p);
                return;
        }
        spin_lock(&rq->lock);
        if (unlikely(rt_task(p))) {
                /*
                 * RR tasks need a special form of timeslice management.
                 * FIFO tasks have no timeslices.
                 */
                if ((p->policy == SCHED_RR) && !--p->time_slice) {
                        p->time_slice = task_timeslice(p);
                        p->first_time_slice = 0;
                        set_tsk_need_resched(p);

                        /* put it at the end of the queue: */
                        dequeue_task(p, rq->active);
                        enqueue_task(p, rq->active);
                }
                goto out;
        }
        /*
         * The task was running during this tick - update the
         * time slice counter and the sleep average. Note: we
         * do not update a thread's priority until it either
         * goes to sleep or uses up its timeslice. This makes
         * it possible for interactive tasks to use up their
         * timeslices at their highest priority levels.
         */
        if (p->sleep_avg)
                p->sleep_avg--;
        if (!--p->time_slice) {
                dequeue_task(p, rq->active);
                set_tsk_need_resched(p);
                p->prio = effective_prio(p);
                p->time_slice = task_timeslice(p);
                p->first_time_slice = 0;

                if (!TASK_INTERACTIVE(p) || EXPIRED_STARVING(rq)) {
                        if (!rq->expired_timestamp)
                                rq->expired_timestamp = jiffies;
                        enqueue_task(p, rq->expired);
                } else
                        enqueue_task(p, rq->active);
        }
out:
#if CONFIG_SMP
        if (!(jiffies % BUSY_REBALANCE_TICK))
                load_balance(rq, 0);
#endif
        spin_unlock(&rq->lock);
}

void scheduling_functions_start_here(void) { }

/*
 * schedule() is the main scheduler function.
 */
asmlinkage void schedule(void)
{
        task_t *prev, *next;
        runqueue_t *rq;
        prio_array_t *array;
        struct list_head *queue;
        int idx;

        /*
         * Test if we are atomic.  Since do_exit() needs to call into
         * schedule() atomically, we ignore that path for now.
         * Otherwise, whine if we are scheduling when we should not be.
         */
        if (likely(current->state != TASK_ZOMBIE)) {
                if (unlikely(in_atomic())) {
                        printk(KERN_ERR "bad: scheduling while atomic!\n");
                        dump_stack();
                }
        }

#if CONFIG_DEBUG_HIGHMEM
        check_highmem_ptes();
#endif
need_resched:
        preempt_disable();
        prev = current;
        rq = this_rq();

        release_kernel_lock(prev);
        prev->sleep_timestamp = jiffies;
        spin_lock_irq(&rq->lock);

        /*
         * if entering off of a kernel preemption go straight
         * to picking the next task.
         */
        if (unlikely(preempt_count() & PREEMPT_ACTIVE))
                goto pick_next_task;

        switch (prev->state) {
        case TASK_INTERRUPTIBLE:
                if (unlikely(signal_pending(prev))) {
                        prev->state = TASK_RUNNING;
                        break;
                }
        default:
                deactivate_task(prev, rq);
        case TASK_RUNNING:
                ;
        }
pick_next_task:
        if (unlikely(!rq->nr_running)) {
#if CONFIG_SMP
                load_balance(rq, 1);
                if (rq->nr_running)
                        goto pick_next_task;
#endif
                next = rq->idle;
                rq->expired_timestamp = 0;
                goto switch_tasks;
        }

        array = rq->active;
        if (unlikely(!array->nr_active)) {
                /*
                 * Switch the active and expired arrays.
                 */
                rq->active = rq->expired;
                rq->expired = array;
                array = rq->active;
                rq->expired_timestamp = 0;
        }

        idx = sched_find_first_bit(array->bitmap);
        queue = array->queue + idx;
        next = list_entry(queue->next, task_t, run_list);

switch_tasks:
        prefetch(next);
        clear_tsk_need_resched(prev);

        if (likely(prev != next)) {
                rq->nr_switches++;
                rq->curr = next;
        
                prepare_arch_switch(rq, next);
                prev = context_switch(prev, next);
                barrier();
                rq = this_rq();
                finish_arch_switch(rq, prev);
        } else
                spin_unlock_irq(&rq->lock);

        reacquire_kernel_lock(current);
        preempt_enable_no_resched();
        if (test_thread_flag(TIF_NEED_RESCHED))
                goto need_resched;
}

#ifdef CONFIG_PREEMPT
/*
 * this is is the entry point to schedule() from in-kernel preemption
 * off of preempt_enable.  Kernel preemptions off return from interrupt
 * occur there and call schedule directly.
 */
asmlinkage void preempt_schedule(void)
{
        struct thread_info *ti = current_thread_info();

        /*
         * If there is a non-zero preempt_count or interrupts are disabled,
         * we do not want to preempt the current task.  Just return..
         */
        if (unlikely(ti->preempt_count || irqs_disabled()))
                return;

need_resched:
        ti->preempt_count = PREEMPT_ACTIVE;
        schedule();
        ti->preempt_count = 0;

        /* we could miss a preemption opportunity between schedule and now */
        barrier();
        if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
                goto need_resched;
}
#endif /* CONFIG_PREEMPT */

int default_wake_function(wait_queue_t *curr, unsigned mode, int sync)
{
        task_t *p = curr->task;
        return ((p->state & mode) && try_to_wake_up(p, sync));
}

/*
 * The core wakeup function.  Non-exclusive wakeups (nr_exclusive == 0) just
 * wake everything up.  If it's an exclusive wakeup (nr_exclusive == small +ve
 * number) then we wake all the non-exclusive tasks and one exclusive task.
 *
 * There are circumstances in which we can try to wake a task which has already
 * started to run but is not in state TASK_RUNNING.  try_to_wake_up() returns
 * zero in this (rare) case, and we handle it by continuing to scan the queue.
 */
static void __wake_up_common(wait_queue_head_t *q, unsigned int mode, int nr_exclusive, int sync)
{
        struct list_head *tmp, *next;

        list_for_each_safe(tmp, next, &q->task_list) {
                wait_queue_t *curr;
                unsigned flags;
                curr = list_entry(tmp, wait_queue_t, task_list);
                flags = curr->flags;
                if (curr->func(curr, mode, sync) &&
                    (flags & WQ_FLAG_EXCLUSIVE) &&
                    !--nr_exclusive)
                        break;
        }
}

/**
 * __wake_up - wake up threads blocked on a waitqueue.
 * @q: the waitqueue
 * @mode: which threads
 * @nr_exclusive: how many wake-one or wake-many threads to wake up
 */
void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
{
        unsigned long flags;

        if (unlikely(!q))
                return;

        spin_lock_irqsave(&q->lock, flags);
        __wake_up_common(q, mode, nr_exclusive, 0);
        spin_unlock_irqrestore(&q->lock, flags);
}

/*
 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
 */
void __wake_up_locked(wait_queue_head_t *q, unsigned int mode)
{
        __wake_up_common(q, mode, 1, 0);
}

#if CONFIG_SMP

/**
 * __wake_up - sync- wake up threads blocked on a waitqueue.
 * @q: the waitqueue
 * @mode: which threads
 * @nr_exclusive: how many wake-one or wake-many threads to wake up
 *
 * The sync wakeup differs that the waker knows that it will schedule
 * away soon, so while the target thread will be woken up, it will not
 * be migrated to another CPU - ie. the two threads are 'synchronized'
 * with each other. This can prevent needless bouncing between CPUs.
 */
void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
{
        unsigned long flags;

        if (unlikely(!q))
                return;

        spin_lock_irqsave(&q->lock, flags);
        if (likely(nr_exclusive))
                __wake_up_common(q, mode, nr_exclusive, 1);
        else
                __wake_up_common(q, mode, nr_exclusive, 0);
        spin_unlock_irqrestore(&q->lock, flags);
}

#endif
 
void complete(struct completion *x)
{
        unsigned long flags;

        spin_lock_irqsave(&x->wait.lock, flags);
        x->done++;
        __wake_up_common(&x->wait, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1, 0);
        spin_unlock_irqrestore(&x->wait.lock, flags);
}

void wait_for_completion(struct completion *x)
{
        might_sleep();
        spin_lock_irq(&x->wait.lock);
        if (!x->done) {
                DECLARE_WAITQUEUE(wait, current);

                wait.flags |= WQ_FLAG_EXCLUSIVE;
                __add_wait_queue_tail(&x->wait, &wait);
                do {
                        __set_current_state(TASK_UNINTERRUPTIBLE);
                        spin_unlock_irq(&x->wait.lock);
                        schedule();
                        spin_lock_irq(&x->wait.lock);
                } while (!x->done);
                __remove_wait_queue(&x->wait, &wait);
        }
        x->done--;
        spin_unlock_irq(&x->wait.lock);
}

#define SLEEP_ON_VAR                            \
        unsigned long flags;                    \
        wait_queue_t wait;                      \
        init_waitqueue_entry(&wait, current);

#define SLEEP_ON_HEAD                                   \
        spin_lock_irqsave(&q->lock,flags);              \
        __add_wait_queue(q, &wait);                     \
        spin_unlock(&q->lock);

#define SLEEP_ON_TAIL                                           \
        spin_lock_irq(&q->lock);                                \
        __remove_wait_queue(q, &wait);                          \
        spin_unlock_irqrestore(&q->lock, flags);

void interruptible_sleep_on(wait_queue_head_t *q)
{
        SLEEP_ON_VAR

        current->state = TASK_INTERRUPTIBLE;

        SLEEP_ON_HEAD
        schedule();
        SLEEP_ON_TAIL
}

long interruptible_sleep_on_timeout(wait_queue_head_t *q, long timeout)
{
        SLEEP_ON_VAR

        current->state = TASK_INTERRUPTIBLE;

        SLEEP_ON_HEAD
        timeout = schedule_timeout(timeout);
        SLEEP_ON_TAIL

        return timeout;
}

void sleep_on(wait_queue_head_t *q)
{
        SLEEP_ON_VAR
        
        current->state = TASK_UNINTERRUPTIBLE;

        SLEEP_ON_HEAD
        schedule();
        SLEEP_ON_TAIL
}

long sleep_on_timeout(wait_queue_head_t *q, long timeout)
{
        SLEEP_ON_VAR
        
        current->state = TASK_UNINTERRUPTIBLE;

        SLEEP_ON_HEAD
        timeout = schedule_timeout(timeout);
        SLEEP_ON_TAIL

        return timeout;
}

void scheduling_functions_end_here(void) { }

void set_user_nice(task_t *p, long nice)
{
        unsigned long flags;
        prio_array_t *array;
        runqueue_t *rq;

        if (TASK_NICE(p) == nice || nice < -20 || nice > 19)
                return;
        /*
         * We have to be careful, if called from sys_setpriority(),
         * the task might be in the middle of scheduling on another CPU.
         */
        rq = task_rq_lock(p, &flags);
        if (rt_task(p)) {
                p->static_prio = NICE_TO_PRIO(nice);
                goto out_unlock;
        }
        array = p->array;
        if (array)
                dequeue_task(p, array);
        p->static_prio = NICE_TO_PRIO(nice);
        p->prio = NICE_TO_PRIO(nice);
        if (array) {
                enqueue_task(p, array);
                /*
                 * If the task is running and lowered its priority,
                 * or increased its priority then reschedule its CPU:
                 */
                if ((NICE_TO_PRIO(nice) < p->static_prio) ||
                                                        task_running(rq, p))
                        resched_task(rq->curr);
        }
out_unlock:
        task_rq_unlock(rq, &flags);
}

#ifndef __alpha__

/*
 * sys_nice - change the priority of the current process.
 * @increment: priority increment
 *
 * sys_setpriority is a more generic, but much slower function that
 * does similar things.
 */
asmlinkage long sys_nice(int increment)
{
        int retval;
        long nice;

        /*
         *      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.
         */
        if (increment < 0) {
                if (!capable(CAP_SYS_NICE))
                        return -EPERM;
                if (increment < -40)
                        increment = -40;
        }
        if (increment > 40)
                increment = 40;

        nice = PRIO_TO_NICE(current->static_prio) + increment;
        if (nice < -20)
                nice = -20;
        if (nice > 19)
                nice = 19;

        retval = security_ops->task_setnice(current, nice);
        if (retval)
                return retval;

        set_user_nice(current, nice);
        return 0;
}

#endif

/**
 * task_prio - return the priority value of a given task.
 * @p: the task in question.
 *
 * This is the priority value as seen by users in /proc.
 * RT tasks are offset by -200. Normal tasks are centered
 * around 0, value goes from -16 to +15.
 */
int task_prio(task_t *p)
{
        return p->prio - MAX_USER_RT_PRIO;
}

/**
 * task_nice - return the nice value of a given task.
 * @p: the task in question.
 */
int task_nice(task_t *p)
{
        return TASK_NICE(p);
}

/**
 * task_curr - is this task currently executing on a CPU?
 * @p: the task in question.
 */
int task_curr(task_t *p)
{
        return cpu_curr(task_cpu(p)) == p;
}

/**
 * idle_cpu - is a given cpu idle currently?
 * @cpu: the processor in question.
 */
int idle_cpu(int cpu)
{
        return cpu_curr(cpu) == cpu_rq(cpu)->idle;
}

/**
 * find_process_by_pid - find a process with a matching PID value.
 * @pid: the pid in question.
 */
static inline task_t *find_process_by_pid(pid_t pid)
{
        return pid ? find_task_by_pid(pid) : current;
}

/*
 * setscheduler - change the scheduling policy and/or RT priority of a thread.
 */
static int setscheduler(pid_t pid, int policy, struct sched_param *param)
{
        struct sched_param lp;
        int retval = -EINVAL;
        prio_array_t *array;
        unsigned long flags;
        runqueue_t *rq;
        task_t *p;

        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.
         */
        read_lock_irq(&tasklist_lock);

        p = find_process_by_pid(pid);

        retval = -ESRCH;
        if (!p)
                goto out_unlock_tasklist;

        /*
         * To be able to change p->policy safely, the apropriate
         * runqueue lock must be held.
         */
        rq = task_rq_lock(p, &flags);

        if (policy < 0)
                policy = p->policy;
        else {
                retval = -EINVAL;
                if (policy != SCHED_FIFO && policy != SCHED_RR &&
                                policy != SCHED_NORMAL)
                        goto out_unlock;
        }

        /*
         * Valid priorities for SCHED_FIFO and SCHED_RR are
         * 1..MAX_USER_RT_PRIO-1, valid priority for SCHED_NORMAL is 0.
         */
        retval = -EINVAL;
        if (lp.sched_priority < 0 || lp.sched_priority > MAX_USER_RT_PRIO-1)
                goto out_unlock;
        if ((policy == SCHED_NORMAL) != (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 = security_ops->task_setscheduler(p, policy, &lp);
        if (retval)
                goto out_unlock;

        array = p->array;
        if (array)
                deactivate_task(p, task_rq(p));
        retval = 0;
        p->policy = policy;
        p->rt_priority = lp.sched_priority;
        if (policy != SCHED_NORMAL)
                p->prio = MAX_USER_RT_PRIO-1 - p->rt_priority;
        else
                p->prio = p->static_prio;
        if (array)
                activate_task(p, task_rq(p));

out_unlock:
        task_rq_unlock(rq, &flags);
out_unlock_tasklist:
        read_unlock_irq(&tasklist_lock);

out_nounlock:
        return retval;
}

/**
 * sys_sched_setscheduler - set/change the scheduler policy and RT priority
 * @pid: the pid in question.
 * @policy: new policy
 * @param: structure containing the new RT priority.
 */
asmlinkage long sys_sched_setscheduler(pid_t pid, int policy,
                                      struct sched_param *param)
{
        return setscheduler(pid, policy, param);
}

/**
 * sys_sched_setparam - set/change the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the new RT priority.
 */
asmlinkage long sys_sched_setparam(pid_t pid, struct sched_param *param)
{
        return setscheduler(pid, -1, param);
}

/**
 * sys_sched_getscheduler - get the policy (scheduling class) of a thread
 * @pid: the pid in question.
 */
asmlinkage long sys_sched_getscheduler(pid_t pid)
{
        int retval = -EINVAL;
        task_t *p;

        if (pid < 0)
                goto out_nounlock;

        retval = -ESRCH;
        read_lock(&tasklist_lock);
        p = find_process_by_pid(pid);
        if (p) {
                retval = security_ops->task_getscheduler(p);
                if (!retval)
                        retval = p->policy;
        }
        read_unlock(&tasklist_lock);

out_nounlock:
        return retval;
}

/**
 * sys_sched_getscheduler - get the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the RT priority.
 */
asmlinkage long sys_sched_getparam(pid_t pid, struct sched_param *param)
{
        struct sched_param lp;
        int retval = -EINVAL;
        task_t *p;

        if (!param || pid < 0)
                goto out_nounlock;

        read_lock(&tasklist_lock);
        p = find_process_by_pid(pid);
        retval = -ESRCH;
        if (!p)
                goto out_unlock;

        retval = security_ops->task_getscheduler(p);
        if (retval)
                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;
}

/**
 * sys_sched_setaffinity - set the cpu affinity of a process
 * @pid: pid of the process
 * @len: length in bytes of the bitmask pointed to by user_mask_ptr
 * @user_mask_ptr: user-space pointer to the new cpu mask
 */
asmlinkage int sys_sched_setaffinity(pid_t pid, unsigned int len,
                                      unsigned long *user_mask_ptr)
{
        unsigned long new_mask;
        int retval;
        task_t *p;

        if (len < sizeof(new_mask))
                return -EINVAL;

        if (copy_from_user(&new_mask, user_mask_ptr, sizeof(new_mask)))
                return -EFAULT;

        new_mask &= cpu_online_map;
        if (!new_mask)
                return -EINVAL;

        read_lock(&tasklist_lock);

        p = find_process_by_pid(pid);
        if (!p) {
                read_unlock(&tasklist_lock);
                return -ESRCH;
        }

        /*
         * It is not safe to call set_cpus_allowed with the
         * tasklist_lock held.  We will bump the task_struct's
         * usage count and then drop tasklist_lock.
         */
        get_task_struct(p);
        read_unlock(&tasklist_lock);

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

        retval = 0;
        set_cpus_allowed(p, new_mask);

out_unlock:
        put_task_struct(p);
        return retval;
}

/**
 * sys_sched_getaffinity - get the cpu affinity of a process
 * @pid: pid of the process
 * @len: length in bytes of the bitmask pointed to by user_mask_ptr
 * @user_mask_ptr: user-space pointer to hold the current cpu mask
 */
asmlinkage int sys_sched_getaffinity(pid_t pid, unsigned int len,
                                      unsigned long *user_mask_ptr)
{
        unsigned int real_len;
        unsigned long mask;
        int retval;
        task_t *p;

        real_len = sizeof(mask);
        if (len < real_len)
                return -EINVAL;

        read_lock(&tasklist_lock);

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

        retval = 0;
        mask = p->cpus_allowed & cpu_online_map;

out_unlock:
        read_unlock(&tasklist_lock);
        if (retval)
                return retval;
        if (copy_to_user(user_mask_ptr, &mask, real_len))
                return -EFAULT;
        return real_len;
}

/**
 * sys_sched_yield - yield the current processor to other threads.
 *
 * this function yields the current CPU by moving the calling thread
 * to the expired array. If there are no other threads running on this
 * CPU then this function will return.
 */
asmlinkage long sys_sched_yield(void)
{
        runqueue_t *rq = this_rq_lock();
        prio_array_t *array = current->array;

        /*
         * We implement yielding by moving the task into the expired
         * queue.
         *
         * (special rule: RT tasks will just roundrobin in the active
         *  array.)
         */
        if (likely(!rt_task(current))) {
                dequeue_task(current, array);
                enqueue_task(current, rq->expired);
        } else {
                list_del(&current->run_list);
                list_add_tail(&current->run_list, array->queue + current->prio);
        }
        /*
         * Since we are going to call schedule() anyway, there's
         * no need to preempt:
         */
        _raw_spin_unlock(&rq->lock);
        preempt_enable_no_resched();

        schedule();

        return 0;
}

void __cond_resched(void)
{
        set_current_state(TASK_RUNNING);
        schedule();
}

/**
 * yield - yield the current processor to other threads.
 *
 * this is a shortcut for kernel-space yielding - it marks the
 * thread runnable and calls sys_sched_yield().
 */
void yield(void)
{
        set_current_state(TASK_RUNNING);
        sys_sched_yield();
}

/**
 * sys_sched_get_priority_max - return maximum RT priority.
 * @policy: scheduling class.
 *
 * this syscall returns the maximum rt_priority that can be used
 * by a given scheduling class.
 */
asmlinkage long sys_sched_get_priority_max(int policy)
{
        int ret = -EINVAL;

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

/**
 * sys_sched_get_priority_mix - return minimum RT priority.
 * @policy: scheduling class.
 *
 * this syscall returns the minimum rt_priority that can be used
 * by a given scheduling class.
 */
asmlinkage long sys_sched_get_priority_min(int policy)
{
        int ret = -EINVAL;

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

/**
 * sys_sched_rr_get_interval - return the default timeslice of a process.
 * @pid: pid of the process.
 * @interval: userspace pointer to the timeslice value.
 *
 * this syscall writes the default timeslice value of a given process
 * into the user-space timespec buffer. A value of '0' means infinity.
 */
asmlinkage long sys_sched_rr_get_interval(pid_t pid, struct timespec *interval)
{
        int retval = -EINVAL;
        struct timespec t;
        task_t *p;

        if (pid < 0)
                goto out_nounlock;

        retval = -ESRCH;
        read_lock(&tasklist_lock);
        p = find_process_by_pid(pid);
        if (!p)
                goto out_unlock;

        retval = security_ops->task_getscheduler(p);
        if (retval)
                goto out_unlock;

        jiffies_to_timespec(p->policy & SCHED_FIFO ?
                                0 : task_timeslice(p), &t);
        read_unlock(&tasklist_lock);
        retval = copy_to_user(interval, &t, sizeof(t)) ? -EFAULT : 0;
out_nounlock:
        return retval;
out_unlock:
        read_unlock(&tasklist_lock);
        return retval;
}

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

        printk("%-13.13s ", p->comm);
        state = p->state ? __ffs(p->state) + 1 : 0;
        if (((unsigned) state) < sizeof(stat_nam)/sizeof(char *))
                printk(stat_nam[state]);
        else
                printk(" ");
#if (BITS_PER_LONG == 32)
        if (p == current)
                printk(" current  ");
        else
                printk(" %08lX ", thread_saved_pc(p));
#else
        if (p == current)
                printk("   current task   ");
        else
                printk(" %016lx ", thread_saved_pc(p));
#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->parent->pid);
        if ((relative = eldest_child(p)))
                printk("%5d ", relative->pid);
        else
                printk("      ");
        if ((relative = younger_sibling(p)))
                printk("%7d", relative->pid);
        else
                printk("       ");
        if ((relative = older_sibling(p)))
                printk(" %5d", relative->pid);
        else
                printk("      ");
        if (!p->mm)
                printk(" (L-TLB)\n");
        else
                printk(" (NOTLB)\n");

        {
                extern void show_trace_task(task_t *tsk);
                show_trace_task(p);
        }
}

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)
{
        task_t *g, *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);
        do_each_thread(g, p) {
                /*
                 * reset the NMI-timeout, listing all files on a slow
                 * console might take alot of time:
                 */
                touch_nmi_watchdog();
                show_task(p);
        } while_each_thread(g, p);

        read_unlock(&tasklist_lock);
}

void __init init_idle(task_t *idle, int cpu)
{
        runqueue_t *idle_rq = cpu_rq(cpu), *rq = cpu_rq(task_cpu(idle));
        unsigned long flags;

        local_irq_save(flags);
        double_rq_lock(idle_rq, rq);

        idle_rq->curr = idle_rq->idle = idle;
        deactivate_task(idle, rq);
        idle->array = NULL;
        idle->prio = MAX_PRIO;
        idle->state = TASK_RUNNING;
        set_task_cpu(idle, cpu);
        double_rq_unlock(idle_rq, rq);
        set_tsk_need_resched(idle);
        local_irq_restore(flags);

        /* Set the preempt count _outside_ the spinlocks! */
#if CONFIG_PREEMPT
        idle->thread_info->preempt_count = (idle->lock_depth >= 0);
#else
        idle->thread_info->preempt_count = 0;
#endif
}

#if CONFIG_SMP
/*
 * This is how migration works:
 *
 * 1) we queue a migration_req_t structure in the source CPU's
 *    runqueue and wake up that CPU's migration thread.
 * 2) we down() the locked semaphore => thread blocks.
 * 3) migration thread wakes up (implicitly it forces the migrated
 *    thread off the CPU)
 * 4) it gets the migration request and checks whether the migrated
 *    task is still in the wrong runqueue.
 * 5) if it's in the wrong runqueue then the migration thread removes
 *    it and puts it into the right queue.
 * 6) migration thread up()s the semaphore.
 * 7) we wake up and the migration is done.
 */

typedef struct {
        struct list_head list;
        task_t *task;
        struct completion done;
} migration_req_t;

/*
 * Change a given task's CPU affinity. Migrate the thread to a
 * proper CPU and schedule it away if the CPU it's executing on
 * is removed from the allowed bitmask.
 *
 * NOTE: the caller must have a valid reference to the task, the
 * task must not exit() & deallocate itself prematurely.  The
 * call is not atomic; no spinlocks may be held.
 */
void set_cpus_allowed(task_t *p, unsigned long new_mask)
{
        unsigned long flags;
        migration_req_t req;
        runqueue_t *rq;

#if 0 /* FIXME: Grab cpu_lock, return error on this case. --RR */
        new_mask &= cpu_online_map;
        if (!new_mask)
                BUG();
#endif

        preempt_disable();
        rq = task_rq_lock(p, &flags);
        p->cpus_allowed = new_mask;
        /*
         * Can the task run on the task's current CPU? If not then
         * migrate the thread off to a proper CPU.
         */
        if (new_mask & (1UL << task_cpu(p))) {
                task_rq_unlock(rq, &flags);
                goto out;
        }
        /*
         * If the task is not on a runqueue (and not running), then
         * it is sufficient to simply update the task's cpu field.
         */
        if (!p->array && !task_running(rq, p)) {
                set_task_cpu(p, __ffs(p->cpus_allowed));
                task_rq_unlock(rq, &flags);
                goto out;
        }
        init_completion(&req.done);
        req.task = p;
        list_add(&req.list, &rq->migration_queue);
        task_rq_unlock(rq, &flags);
        wake_up_process(rq->migration_thread);

        wait_for_completion(&req.done);
out:
        preempt_enable();
}

/*
 * migration_thread - this is a highprio system thread that performs
 * thread migration by 'pulling' threads into the target runqueue.
 */
static int migration_thread(void * data)
{
        struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
        int cpu = (long) data;
        runqueue_t *rq;
        int ret;

        daemonize();
        sigfillset(&current->blocked);
        set_fs(KERNEL_DS);

        set_cpus_allowed(current, 1UL << cpu);

        /*
         * Migration can happen without a migration thread on the
         * target CPU because here we remove the thread from the
         * runqueue and the helper thread then moves this thread
         * to the target CPU - we'll wake up there.
         */
        if (smp_processor_id() != cpu)
        printk("migration_task %d on cpu=%d\n", cpu, smp_processor_id());
        ret = setscheduler(0, SCHED_FIFO, &param);

        rq = this_rq();
        rq->migration_thread = current;

        sprintf(current->comm, "migration_CPU%d", smp_processor_id());

        for (;;) {
                runqueue_t *rq_src, *rq_dest;
                struct list_head *head;
                int cpu_src, cpu_dest;
                migration_req_t *req;
                unsigned long flags;
                task_t *p;

                spin_lock_irqsave(&rq->lock, flags);
                head = &rq->migration_queue;
                current->state = TASK_INTERRUPTIBLE;
                if (list_empty(head)) {
                        spin_unlock_irqrestore(&rq->lock, flags);
                        schedule();
                        continue;
                }
                req = list_entry(head->next, migration_req_t, list);
                list_del_init(head->next);
                spin_unlock_irqrestore(&rq->lock, flags);

                p = req->task;
                cpu_dest = __ffs(p->cpus_allowed);
                rq_dest = cpu_rq(cpu_dest);
repeat:
                cpu_src = task_cpu(p);
                rq_src = cpu_rq(cpu_src);

                local_irq_save(flags);
                double_rq_lock(rq_src, rq_dest);
                if (task_cpu(p) != cpu_src) {
                        double_rq_unlock(rq_src, rq_dest);
                        local_irq_restore(flags);
                        goto repeat;
                }
                if (rq_src == rq) {
                        set_task_cpu(p, cpu_dest);
                        if (p->array) {
                                deactivate_task(p, rq_src);
                                activate_task(p, rq_dest);
                        }
                }
                double_rq_unlock(rq_src, rq_dest);
                local_irq_restore(flags);

                complete(&req->done);
        }
}

/*
 * migration_call - callback that gets triggered when a CPU is added.
 * Here we can start up the necessary migration thread for the new CPU.
 */
static int migration_call(struct notifier_block *nfb,
                          unsigned long action,
                          void *hcpu)
{
        switch (action) {
        case CPU_ONLINE:
                printk("Starting migration thread for cpu %li\n",
                       (long)hcpu);
                kernel_thread(migration_thread, hcpu, CLONE_KERNEL);
                while (!cpu_rq((long)hcpu)->migration_thread)
                        yield();
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block migration_notifier = { &migration_call, NULL, 0 };

__init int migration_init(void)
{
        /* Start one for boot CPU. */
        migration_call(&migration_notifier, CPU_ONLINE,
                       (void *)(long)smp_processor_id());
        register_cpu_notifier(&migration_notifier);
        return 0;
}

#endif

#if CONFIG_SMP || CONFIG_PREEMPT
/*
 * The 'big kernel lock'
 *
 * This spinlock is taken and released recursively by lock_kernel()
 * and unlock_kernel().  It is transparently dropped and reaquired
 * over schedule().  It is used to protect legacy code that hasn't
 * been migrated to a proper locking design yet.
 *
 * Don't use in new code.
 */
spinlock_t kernel_flag __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
#endif

extern void init_timers(void);

void __init sched_init(void)
{
        runqueue_t *rq;
        int i, j, k;

        for (i = 0; i < NR_CPUS; i++) {
                prio_array_t *array;

                rq = cpu_rq(i);
                rq->active = rq->arrays;
                rq->expired = rq->arrays + 1;
                spin_lock_init(&rq->lock);
                INIT_LIST_HEAD(&rq->migration_queue);

                for (j = 0; j < 2; j++) {
                        array = rq->arrays + j;
                        for (k = 0; k < MAX_PRIO; k++) {
                                INIT_LIST_HEAD(array->queue + k);
                                __clear_bit(k, array->bitmap);
                        }
                        // delimiter for bitsearch
                        __set_bit(MAX_PRIO, array->bitmap);
                }
        }
        /*
         * We have to do a little magic to get the first
         * thread right in SMP mode.
         */
        rq = this_rq();
        rq->curr = current;
        rq->idle = current;
        set_task_cpu(current, smp_processor_id());
        wake_up_process(current);

        init_timers();

        /*
         * The boot idle thread does lazy MMU switching as well:
         */
        atomic_inc(&init_mm.mm_count);
        enter_lazy_tlb(&init_mm, current, smp_processor_id());
}

#ifdef CONFIG_DEBUG_KERNEL
void __might_sleep(char *file, int line)
{
#if defined(in_atomic)
        static unsigned long prev_jiffy;        /* ratelimiting */

        if (in_atomic()) {
                if (time_before(jiffies, prev_jiffy + HZ))
                        return;
                prev_jiffy = jiffies;
                printk(KERN_ERR "Debug: sleeping function called from illegal"
                                " context at %s:%d\n", file, line);
                dump_stack();
        }
#endif
}
#endif