patch-2.6.6-vs1.9.0

[linux-2.6.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.
 *  2003-09-03  Interactivity tuning by Con Kolivas.
 */

#include <linux/mm.h>
#include <linux/module.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/suspend.h>
#include <linux/blkdev.h>
#include <linux/delay.h>
#include <linux/smp.h>
#include <linux/timer.h>
#include <linux/rcupdate.h>
#include <linux/cpu.h>
#include <linux/percpu.h>
#include <linux/kthread.h>
#include <linux/vserver/sched.h>
#include <linux/vinline.h>

#ifdef CONFIG_NUMA
#define cpu_to_node_mask(cpu) node_to_cpumask(cpu_to_node(cpu))
#else
#define cpu_to_node_mask(cpu) (cpu_online_map)
#endif

/*
 * 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))
#define AVG_TIMESLICE   (MIN_TIMESLICE + ((MAX_TIMESLICE - MIN_TIMESLICE) *\
                        (MAX_PRIO-1-NICE_TO_PRIO(0))/(MAX_USER_PRIO - 1)))

/*
 * Some helpers for converting nanosecond timing to jiffy resolution
 */
#define NS_TO_JIFFIES(TIME)     ((TIME) / (1000000000 / HZ))
#define JIFFIES_TO_NS(TIME)     ((TIME) * (1000000000 / HZ))

/*
 * These are the 'tuning knobs' of the scheduler:
 *
 * Minimum timeslice is 10 msecs, default timeslice is 100 msecs,
 * maximum timeslice is 200 msecs. Timeslices get refilled after
 * they expire.
 */
#define MIN_TIMESLICE           ( 10 * HZ / 1000)
#define MAX_TIMESLICE           (200 * HZ / 1000)
#define ON_RUNQUEUE_WEIGHT       30
#define CHILD_PENALTY            95
#define PARENT_PENALTY          100
#define EXIT_WEIGHT               3
#define PRIO_BONUS_RATIO         25
#define MAX_BONUS               (MAX_USER_PRIO * PRIO_BONUS_RATIO / 100)
#define INTERACTIVE_DELTA         2
#define MAX_SLEEP_AVG           (AVG_TIMESLICE * MAX_BONUS)
#define STARVATION_LIMIT        (MAX_SLEEP_AVG)
#define NS_MAX_SLEEP_AVG        (JIFFIES_TO_NS(MAX_SLEEP_AVG))
#define NODE_THRESHOLD          125
#define CREDIT_LIMIT            100

/*
 * 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 CURRENT_BONUS(p) \
        (NS_TO_JIFFIES((p)->sleep_avg) * MAX_BONUS / \
                MAX_SLEEP_AVG)

#ifdef CONFIG_SMP
#define TIMESLICE_GRANULARITY(p)        (MIN_TIMESLICE * \
                (1 << (((MAX_BONUS - CURRENT_BONUS(p)) ? : 1) - 1)) * \
                        num_online_cpus())
#else
#define TIMESLICE_GRANULARITY(p)        (MIN_TIMESLICE * \
                (1 << (((MAX_BONUS - CURRENT_BONUS(p)) ? : 1) - 1)))
#endif

#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))

#define INTERACTIVE_SLEEP(p) \
        (JIFFIES_TO_NS(MAX_SLEEP_AVG * \
                (MAX_BONUS / 2 + DELTA((p)) + 1) / MAX_BONUS - 1))

#define HIGH_CREDIT(p) \
        ((p)->interactive_credit > CREDIT_LIMIT)

#define LOW_CREDIT(p) \
        ((p)->interactive_credit < -CREDIT_LIMIT)

#define TASK_PREEMPTS_CURR(p, rq) \
        ((p)->prio < (rq)->curr->prio)

/*
 * 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 long nr_switches;
        unsigned long nr_running, expired_timestamp, nr_uninterruptible,
                timestamp_last_tick;
        task_t *curr, *idle;
        struct mm_struct *prev_mm;
        prio_array_t *active, *expired, arrays[2];
        int best_expired_prio, prev_cpu_load[NR_CPUS];
#ifdef CONFIG_NUMA
        atomic_t *node_nr_running;
        int prev_node_load[MAX_NUMNODES];
#endif
        task_t *migration_thread;
        struct list_head migration_queue;
        struct list_head hold_queue;
        int idle_tokens;

        atomic_t nr_iowait;
};

static DEFINE_PER_CPU(struct runqueue, runqueues);

#define cpu_rq(cpu)             (&per_cpu(runqueues, (cpu)))
#define this_rq()               (&__get_cpu_var(runqueues))
#define task_rq(p)              cpu_rq(task_cpu(p))
#define cpu_curr(cpu)           (cpu_rq(cpu)->curr)

extern unsigned long __scheduling_functions_start_here;
extern unsigned long __scheduling_functions_end_here;
const unsigned long scheduling_functions_start_here =
                        (unsigned long)&__scheduling_functions_start_here;
const unsigned long scheduling_functions_end_here =
                        (unsigned long)&__scheduling_functions_end_here;

/*
 * 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

#ifdef CONFIG_NUMA

/*
 * Keep track of running tasks.
 */

static atomic_t node_nr_running[MAX_NUMNODES] ____cacheline_maxaligned_in_smp =
        {[0 ...MAX_NUMNODES-1] = ATOMIC_INIT(0)};

static inline void nr_running_init(struct runqueue *rq)
{
        rq->node_nr_running = &node_nr_running[0];
}

static inline void nr_running_inc(runqueue_t *rq)
{
        atomic_inc(rq->node_nr_running);
        rq->nr_running++;
}

static inline void nr_running_dec(runqueue_t *rq)
{
        atomic_dec(rq->node_nr_running);
        rq->nr_running--;
}

__init void node_nr_running_init(void)
{
        int i;

        for (i = 0; i < NR_CPUS; i++) {
                if (cpu_possible(i))
                        cpu_rq(i)->node_nr_running =
                                &node_nr_running[cpu_to_node(i)];
        }
}

#else /* !CONFIG_NUMA */

# define nr_running_init(rq)    do { } while (0)
# define nr_running_inc(rq)     do { (rq)->nr_running++; } while (0)
# define nr_running_dec(rq)     do { (rq)->nr_running--; } while (0)

#endif /* CONFIG_NUMA */

/*
 * 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 int effective_prio(task_t *p)
{
        int bonus, prio;

        if (rt_task(p))
                return p->prio;

        bonus = CURRENT_BONUS(p) - MAX_BONUS / 2;

        prio = p->static_prio - bonus;
        if (__vx_task_flags(p, VXF_SCHED_PRIO, 0))
                prio += effective_vavavoom(p, MAX_USER_PRIO);

        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.
 */
static inline void __activate_task(task_t *p, runqueue_t *rq)
{
        enqueue_task(p, rq->active);
        nr_running_inc(rq);
}

static void recalc_task_prio(task_t *p, unsigned long long now)
{
        unsigned long long __sleep_time = now - p->timestamp;
        unsigned long sleep_time;

        if (__sleep_time > NS_MAX_SLEEP_AVG)
                sleep_time = NS_MAX_SLEEP_AVG;
        else
                sleep_time = (unsigned long)__sleep_time;

        if (likely(sleep_time > 0)) {
                /*
                 * User tasks that sleep a long time are categorised as
                 * idle and will get just interactive status to stay active &
                 * prevent them suddenly becoming cpu hogs and starving
                 * other processes.
                 */
                if (p->mm && p->activated != -1 &&
                        sleep_time > INTERACTIVE_SLEEP(p)) {
                                p->sleep_avg = JIFFIES_TO_NS(MAX_SLEEP_AVG -
                                                AVG_TIMESLICE);
                                if (!HIGH_CREDIT(p))
                                        p->interactive_credit++;
                } else {
                        /*
                         * The lower the sleep avg a task has the more
                         * rapidly it will rise with sleep time.
                         */
                        sleep_time *= (MAX_BONUS - CURRENT_BONUS(p)) ? : 1;

                        /*
                         * Tasks with low interactive_credit are limited to
                         * one timeslice worth of sleep avg bonus.
                         */
                        if (LOW_CREDIT(p) &&
                            sleep_time > JIFFIES_TO_NS(task_timeslice(p)))
                                sleep_time = JIFFIES_TO_NS(task_timeslice(p));

                        /*
                         * Non high_credit tasks waking from uninterruptible
                         * sleep are limited in their sleep_avg rise as they
                         * are likely to be cpu hogs waiting on I/O
                         */
                        if (p->activated == -1 && !HIGH_CREDIT(p) && p->mm) {
                                if (p->sleep_avg >= INTERACTIVE_SLEEP(p))
                                        sleep_time = 0;
                                else if (p->sleep_avg + sleep_time >=
                                                INTERACTIVE_SLEEP(p)) {
                                        p->sleep_avg = INTERACTIVE_SLEEP(p);
                                        sleep_time = 0;
                                }
                        }

                        /*
                         * This code gives a bonus to interactive tasks.
                         *
                         * The boost works by updating the 'average sleep time'
                         * value here, based on ->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 > NS_MAX_SLEEP_AVG) {
                                p->sleep_avg = NS_MAX_SLEEP_AVG;
                                if (!HIGH_CREDIT(p))
                                        p->interactive_credit++;
                        }
                }
        }

        p->prio = effective_prio(p);
}

/*
 * activate_task - move a task to the runqueue and do priority recalculation
 *
 * 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 long now = sched_clock();

        recalc_task_prio(p, now);

        /*
         * This checks to make sure it's not an uninterruptible task
         * that is now waking up.
         */
        if (!p->activated) {
                /*
                 * Tasks which were woken up by interrupts (ie. hw events)
                 * are most likely of interactive nature. So we give them
                 * the credit of extending their sleep time to the period
                 * of time they spend on the runqueue, waiting for execution
                 * on a CPU, first time around:
                 */
                if (in_interrupt())
                        p->activated = 2;
                else {
                        /*
                         * Normal first-time wakeups get a credit too for
                         * on-runqueue time, but it will be weighted down:
                         */
                        p->activated = 1;
                }
        }
        p->timestamp = now;

        __activate_task(p, rq);
}

/*
 * deactivate_task - remove a task from the runqueue.
 */
static inline void deactivate_task(struct task_struct *p, runqueue_t *rq)
{
        nr_running_dec(rq);
        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
}

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

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

/*
 * The task's runqueue lock must be held, and the new mask must be valid.
 * Returns true if you have to wait for migration thread.
 */
static int __set_cpus_allowed(task_t *p, cpumask_t new_mask,
                                migration_req_t *req)
{
        runqueue_t *rq = task_rq(p);

        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 (cpu_isset(task_cpu(p), new_mask))
                return 0;

        /*
         * 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, any_online_cpu(p->cpus_allowed));
                return 0;
        }

        init_completion(&req->done);
        req->task = p;
        list_add(&req->list, &rq->migration_queue);
        return 1;
}

/*
 * 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. This function can't
 * be called with interrupts off, or it may introduce deadlock with
 * smp_call_function() if an IPI is sent by the same process we are
 * waiting to become inactive.
 */
void wait_task_inactive(task_t * p)
{
        unsigned long flags;
        runqueue_t *rq;
        int preempted;

repeat:
        rq = task_rq_lock(p, &flags);
        /* Must be off runqueue entirely, not preempted. */
        if (unlikely(p->array)) {
                /* If it's preempted, we yield.  It could be a while. */
                preempted = !task_running(rq, p);
                task_rq_unlock(rq, &flags);
                cpu_relax();
                if (preempted)
                        yield();
                goto repeat;
        }
        task_rq_unlock(rq, &flags);
}

/***
 * kick_process - kick a running thread to enter/exit the kernel
 * @p: the to-be-kicked thread
 *
 * Cause a process which is running on another CPU to enter
 * kernel-mode, without any delay. (to get signals handled.)
 */
void kick_process(task_t *p)
{
        int cpu;

        preempt_disable();
        cpu = task_cpu(p);
        if ((cpu != smp_processor_id()) && task_curr(p))
                smp_send_reschedule(cpu);
        preempt_enable();
}

EXPORT_SYMBOL_GPL(kick_process);

#endif

/***
 * try_to_wake_up - wake up a thread
 * @p: the to-be-woken-up thread
 * @state: the mask of task states that can be woken
 * @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, unsigned int state, 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 (old_state & 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()) &&
                                        cpu_isset(smp_processor_id(),
                                                        p->cpus_allowed) &&
                                        !cpu_is_offline(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--;
                                /*
                                 * Tasks on involuntary sleep don't earn
                                 * sleep_avg beyond just interactive state.
                                 */
                                p->activated = -1;
                        }
                        if (sync && (task_cpu(p) == smp_processor_id()))
                                __activate_task(p, rq);
                        else {
                                activate_task(p, rq);
                                if (TASK_PREEMPTS_CURR(p, rq))
                                        resched_task(rq->curr);
                        }
                        success = 1;
                }
                p->state = TASK_RUNNING;
        }
        task_rq_unlock(rq, &flags);

        return success;
}
int fastcall wake_up_process(task_t * p)
{
        return try_to_wake_up(p, TASK_STOPPED |
                                 TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE, 0);
}

EXPORT_SYMBOL(wake_up_process);

int fastcall wake_up_state(task_t *p, unsigned int state)
{
        return try_to_wake_up(p, state, 0);
}

/*
 * Perform scheduler related setup for a newly forked process p.
 * p is forked by current.
 */
void fastcall sched_fork(task_t *p)
{
        /*
         * We mark the process as running here, but have not actually
         * inserted it onto the runqueue yet. This guarantees that
         * nobody will actually run it, and a signal or other external
         * event cannot wake it up and insert it on the runqueue either.
         */
        p->state = TASK_RUNNING;
        INIT_LIST_HEAD(&p->run_list);
        p->array = NULL;
        spin_lock_init(&p->switch_lock);
#ifdef CONFIG_PREEMPT
        /*
         * During context-switch we hold precisely one spinlock, which
         * schedule_tail drops. (in the common case it's this_rq()->lock,
         * but it also can be p->switch_lock.) So we compensate with a count
         * of 1. Also, we want to start with kernel preemption disabled.
         */
        p->thread_info->preempt_count = 1;
#endif
        /*
         * Share the timeslice between parent and child, thus the
         * total amount of pending timeslices in the system doesn't change,
         * resulting in more scheduling fairness.
         */
        local_irq_disable();
        p->time_slice = (current->time_slice + 1) >> 1;
        /*
         * The remainder of the first timeslice might be recovered by
         * the parent if the child exits early enough.
         */
        p->first_time_slice = 1;
        current->time_slice >>= 1;
        p->timestamp = sched_clock();
        if (!current->time_slice) {
                /*
                 * This case is rare, it happens when the parent has only
                 * a single jiffy left from its timeslice. Taking the
                 * runqueue lock is not a problem.
                 */
                current->time_slice = 1;
                preempt_disable();
                scheduler_tick(0, 0);
                local_irq_enable();
                preempt_enable();
        } else
                local_irq_enable();
}

/*
 * 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 fastcall wake_up_forked_process(task_t * p)
{
        unsigned long flags;
        runqueue_t *rq = task_rq_lock(current, &flags);

        BUG_ON(p->state != TASK_RUNNING);

        /*
         * 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 = JIFFIES_TO_NS(CURRENT_BONUS(current) *
                PARENT_PENALTY / 100 * MAX_SLEEP_AVG / MAX_BONUS);

        p->sleep_avg = JIFFIES_TO_NS(CURRENT_BONUS(p) *
                CHILD_PENALTY / 100 * MAX_SLEEP_AVG / MAX_BONUS);

        p->interactive_credit = 0;

        p->prio = effective_prio(p);
        set_task_cpu(p, smp_processor_id());

        if (unlikely(!current->array))
                __activate_task(p, rq);
        else {
                p->prio = current->prio;
                list_add_tail(&p->run_list, &current->run_list);
                p->array = current->array;
                p->array->nr_active++;
                nr_running_inc(rq);
        }
        task_rq_unlock(rq, &flags);
}

/*
 * 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 fastcall sched_exit(task_t * p)
{
        unsigned long flags;
        runqueue_t *rq;

        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.
         */
        rq = task_rq_lock(p->parent, &flags);
        if (p->sleep_avg < p->parent->sleep_avg)
                p->parent->sleep_avg = p->parent->sleep_avg /
                (EXIT_WEIGHT + 1) * EXIT_WEIGHT + p->sleep_avg /
                (EXIT_WEIGHT + 1);
        task_rq_unlock(rq, &flags);
}

/**
 * finish_task_switch - clean up after a task-switch
 * @prev: the thread we just switched away from.
 *
 * We enter this with the runqueue still locked, and finish_arch_switch()
 * will unlock it along with doing any other architecture-specific cleanup
 * actions.
 *
 * Note that we may have delayed dropping an mm in context_switch(). If
 * so, we finish that here outside of the runqueue lock.  (Doing it
 * with the lock held can cause deadlocks; see schedule() for
 * details.)
 */
static inline void finish_task_switch(task_t *prev)
{
        runqueue_t *rq = this_rq();
        struct mm_struct *mm = rq->prev_mm;
        unsigned long prev_task_flags;

        rq->prev_mm = NULL;

        /*
         * A task struct has one reference for the use as "current".
         * If a task dies, then it sets TASK_ZOMBIE in tsk->state and calls
         * schedule one last time. The schedule call will never return,
         * and the scheduled task must drop that reference.
         * The test for TASK_ZOMBIE must occur while the runqueue locks are
         * still held, otherwise prev could be scheduled on another cpu, die
         * there before we look at prev->state, and then the reference would
         * be dropped twice.
         *              Manfred Spraul <manfred@colorfullife.com>
         */
        prev_task_flags = prev->flags;
        finish_arch_switch(rq, prev);
        if (mm)
                mmdrop(mm);
        if (unlikely(prev_task_flags & PF_DEAD))
                put_task_struct(prev);
}

/**
 * schedule_tail - first thing a freshly forked thread must call.
 * @prev: the thread we just switched away from.
 */
asmlinkage void schedule_tail(task_t *prev)
{
        finish_task_switch(prev);

        if (current->set_child_tid)
                put_user(current->pid, current->set_child_tid);
}

/*
 * context_switch - switch to the new MM and the new
 * thread's register state.
 */
static inline
task_t * context_switch(runqueue_t *rq, 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);
        } else
                switch_mm(oldmm, mm, next);

        if (unlikely(!prev->mm)) {
                prev->active_mm = NULL;
                WARN_ON(rq->prev_mm);
                rq->prev_mm = 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_each_cpu(i)
                sum += cpu_rq(i)->nr_uninterruptible;

        return sum;
}

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

        for_each_cpu(i)
                sum += cpu_rq(i)->nr_switches;

        return sum;
}

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

        for_each_cpu(i)
                sum += atomic_read(&cpu_rq(i)->nr_iowait);

        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);
}

#ifdef CONFIG_NUMA
/*
 * If dest_cpu is allowed for this process, migrate the task to it.
 * This is accomplished by forcing the cpu_allowed mask to only
 * allow dest_cpu, which will force the cpu onto dest_cpu.  Then
 * the cpu_allowed mask is restored.
 */
static void sched_migrate_task(task_t *p, int dest_cpu)
{
        runqueue_t *rq;
        migration_req_t req;
        unsigned long flags;
        cpumask_t old_mask, new_mask = cpumask_of_cpu(dest_cpu);

        lock_cpu_hotplug();
        rq = task_rq_lock(p, &flags);
        old_mask = p->cpus_allowed;
        if (!cpu_isset(dest_cpu, old_mask) || !cpu_online(dest_cpu))
                goto out;

        /* force the process onto the specified CPU */
        if (__set_cpus_allowed(p, new_mask, &req)) {
                /* Need to wait for migration thread. */
                task_rq_unlock(rq, &flags);
                wake_up_process(rq->migration_thread);
                wait_for_completion(&req.done);

                /* If we raced with sys_sched_setaffinity, don't
                 * restore mask. */
                rq = task_rq_lock(p, &flags);
                if (likely(cpus_equal(p->cpus_allowed, new_mask))) {
                        /* Restore old mask: won't need migration
                         * thread, since current cpu is allowed. */
                        BUG_ON(__set_cpus_allowed(p, old_mask, NULL));
                }
        }
out:
        task_rq_unlock(rq, &flags);
        unlock_cpu_hotplug();
}

/*
 * Find the least loaded CPU.  Slightly favor the current CPU by
 * setting its runqueue length as the minimum to start.
 */
static int sched_best_cpu(struct task_struct *p)
{
        int i, minload, load, best_cpu, node = 0;
        cpumask_t cpumask;

        best_cpu = task_cpu(p);
        if (cpu_rq(best_cpu)->nr_running <= 2)
                return best_cpu;

        minload = 10000000;
        for_each_node_with_cpus(i) {
                /*
                 * Node load is always divided by nr_cpus_node to normalise
                 * load values in case cpu count differs from node to node.
                 * We first multiply node_nr_running by 10 to get a little
                 * better resolution.
                 */
                load = 10 * atomic_read(&node_nr_running[i]) / nr_cpus_node(i);
                if (load < minload) {
                        minload = load;
                        node = i;
                }
        }

        minload = 10000000;
        cpumask = node_to_cpumask(node);
        for (i = 0; i < NR_CPUS; ++i) {
                if (!cpu_isset(i, cpumask))
                        continue;
                if (cpu_rq(i)->nr_running < minload) {
                        best_cpu = i;
                        minload = cpu_rq(i)->nr_running;
                }
        }
        return best_cpu;
}

void sched_balance_exec(void)
{
        int new_cpu;

        if (numnodes > 1) {
                new_cpu = sched_best_cpu(current);
                if (new_cpu != smp_processor_id())
                        sched_migrate_task(current, new_cpu);
        }
}

/*
 * Find the busiest node. All previous node loads contribute with a
 * geometrically deccaying weight to the load measure:
 *      load_{t} = load_{t-1}/2 + nr_node_running_{t}
 * This way sudden load peaks are flattened out a bit.
 * Node load is divided by nr_cpus_node() in order to compare nodes
 * of different cpu count but also [first] multiplied by 10 to
 * provide better resolution.
 */
static int find_busiest_node(int this_node)
{
        int i, node = -1, load, this_load, maxload;

        if (!nr_cpus_node(this_node))
                return node;
        this_load = maxload = (this_rq()->prev_node_load[this_node] >> 1)
                + (10 * atomic_read(&node_nr_running[this_node])
                / nr_cpus_node(this_node));
        this_rq()->prev_node_load[this_node] = this_load;
        for_each_node_with_cpus(i) {
                if (i == this_node)
                        continue;
                load = (this_rq()->prev_node_load[i] >> 1)
                        + (10 * atomic_read(&node_nr_running[i])
                        / nr_cpus_node(i));
                this_rq()->prev_node_load[i] = load;
                if (load > maxload && (100*load > NODE_THRESHOLD*this_load)) {
                        maxload = load;
                        node = i;
                }
        }
        return node;
}

#endif /* CONFIG_NUMA */

#ifdef 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_cpu_load[this_cpu]))
                                nr_running = this_rq->nr_running;
                        else
                                nr_running = this_rq->prev_cpu_load[this_cpu];
                } else
                        spin_lock(&busiest->lock);
        }
        return nr_running;
}

/*
 * find_busiest_queue - find the busiest runqueue among the cpus in cpumask.
 */
static inline
runqueue_t *find_busiest_queue(runqueue_t *this_rq, int this_cpu, int idle,
                               int *imbalance, cpumask_t cpumask)
{
        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 (as seen by the balancing CPU) during
         * the previous load-balancing operation and using the smaller one
         * of 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_cpu_load[this_cpu]))
                nr_running = this_rq->nr_running;
        else
                nr_running = this_rq->prev_cpu_load[this_cpu];

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

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

        /* It needs an at least ~25% imbalance to trigger balancing. */
        if (!idle && ((*imbalance)*4 < max_load)) {
                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) {
                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);
        nr_running_dec(src_rq);
        set_task_cpu(p, this_cpu);
        nr_running_inc(this_rq);
        enqueue_task(p, this_rq->active);
        p->timestamp = sched_clock() -
                                (src_rq->timestamp_last_tick - p->timestamp);
        /*
         * Note that idle threads have a prio of MAX_PRIO, for this test
         * to be always true for them.
         */
        if (TASK_PREEMPTS_CURR(p, this_rq))
                set_need_resched();
}

/*
 * can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
 */
static inline
int can_migrate_task(task_t *tsk, runqueue_t *rq, int this_cpu, int idle)
{
        unsigned long delta = rq->timestamp_last_tick - tsk->timestamp;

        /*
         * 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.
         */
        if (task_running(rq, tsk))
                return 0;
        if (!cpu_isset(this_cpu, tsk->cpus_allowed))
                return 0;
        if (!idle && (delta <= JIFFIES_TO_NS(cache_decay_ticks)))
                return 0;
        return 1;
}

/*
 * 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, cpumask_t cpumask)
{
        int imbalance, idx, this_cpu = smp_processor_id();
        runqueue_t *busiest;
        prio_array_t *array;
        struct list_head *head, *curr;
        task_t *tmp;

        if (cpu_is_offline(this_cpu))
                goto out;

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

        /*
         * We only want to steal a number of tasks equal to 1/2 the imbalance,
         * otherwise we'll just shift the imbalance to the new queue:
         */
        imbalance /= 2;

        /*
         * 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);

        curr = curr->prev;

        if (!can_migrate_task(tmp, busiest, this_cpu, idle)) {
                if (curr != head)
                        goto skip_queue;
                idx++;
                goto skip_bitmap;
        }
        pull_task(busiest, array, tmp, this_rq, this_cpu);

        /* Only migrate one task if we are idle */
        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 200 msecs. idle-rebalance every 1 msec. (or on
 * systems with HZ=100, every 10 msecs.)
 *
 * On NUMA, do a node-rebalance every 400 msecs.
 */
#define IDLE_REBALANCE_TICK (HZ/1000 ?: 1)
#define BUSY_REBALANCE_TICK (HZ/5 ?: 1)
#define IDLE_NODE_REBALANCE_TICK (IDLE_REBALANCE_TICK * 5)
#define BUSY_NODE_REBALANCE_TICK (BUSY_REBALANCE_TICK * 2)

#ifdef CONFIG_NUMA
static void balance_node(runqueue_t *this_rq, int idle, int this_cpu)
{
        int node = find_busiest_node(cpu_to_node(this_cpu));

        if (node >= 0) {
                cpumask_t cpumask = node_to_cpumask(node);
                cpu_set(this_cpu, cpumask);
                spin_lock(&this_rq->lock);
                load_balance(this_rq, idle, cpumask);
                spin_unlock(&this_rq->lock);
        }
}
#endif

static void rebalance_tick(runqueue_t *this_rq, int idle)
{
#ifdef CONFIG_NUMA
        int this_cpu = smp_processor_id();
#endif
        unsigned long j = jiffies;

        /*
         * First do inter-node rebalancing, then intra-node rebalancing,
         * if both events happen in the same tick. The inter-node
         * rebalancing does not necessarily have to create a perfect
         * balance within the node, since we load-balance the most loaded
         * node with the current CPU. (ie. other CPUs in the local node
         * are not balanced.)
         */
        if (idle) {
#ifdef CONFIG_NUMA
                if (!(j % IDLE_NODE_REBALANCE_TICK))
                        balance_node(this_rq, idle, this_cpu);
#endif
                if (!(j % IDLE_REBALANCE_TICK)) {
                        spin_lock(&this_rq->lock);
                        load_balance(this_rq, idle, cpu_to_node_mask(this_cpu));
                        spin_unlock(&this_rq->lock);
                }
                return;
        }
#ifdef CONFIG_NUMA
        if (!(j % BUSY_NODE_REBALANCE_TICK))
                balance_node(this_rq, idle, this_cpu);
#endif
        if (!(j % BUSY_REBALANCE_TICK)) {
                spin_lock(&this_rq->lock);
                load_balance(this_rq, idle, cpu_to_node_mask(this_cpu));
                spin_unlock(&this_rq->lock);
        }
}
#else
/*
 * on UP we do not need to balance between CPUs:
 */
static inline void rebalance_tick(runqueue_t *this_rq, int idle)
{
}
#endif

DEFINE_PER_CPU(struct kernel_stat, kstat);

EXPORT_PER_CPU_SYMBOL(kstat);

/*
 * 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. We also ignore the interactivity
 * if a better static_prio task has expired:
 */
#define EXPIRED_STARVING(rq) \
        ((STARVATION_LIMIT && ((rq)->expired_timestamp && \
                (jiffies - (rq)->expired_timestamp >= \
                        STARVATION_LIMIT * ((rq)->nr_running) + 1))) || \
                        ((rq)->curr->static_prio > (rq)->best_expired_prio))

/*
 * This function gets called by the timer code, with HZ frequency.
 * We call it with interrupts disabled.
 *
 * It also gets called by the fork code, when changing the parent's
 * timeslices.
 */
void scheduler_tick(int user_ticks, int sys_ticks)
{
        int cpu = smp_processor_id();
        struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
        runqueue_t *rq = this_rq();
        task_t *p = current;

        rq->timestamp_last_tick = sched_clock();

        if (rcu_pending(cpu))
                rcu_check_callbacks(cpu, user_ticks);

        /* note: this timer irq context must be accounted for as well */
        if (hardirq_count() - HARDIRQ_OFFSET) {
                cpustat->irq += sys_ticks;
                sys_ticks = 0;
        } else if (softirq_count()) {
                cpustat->softirq += sys_ticks;
                sys_ticks = 0;
        }

        if (p == rq->idle) {
                if (!--rq->idle_tokens && !list_empty(&rq->hold_queue))
                        set_need_resched();     

                if (atomic_read(&rq->nr_iowait) > 0)
                        cpustat->iowait += sys_ticks;
                else
                        cpustat->idle += sys_ticks;
                rebalance_tick(rq, 1);
                return;
        }
        if (TASK_NICE(p) > 0)
                cpustat->nice += user_ticks;
        else
                cpustat->user += user_ticks;
        cpustat->system += sys_ticks;

        /* Task might have expired already, but not scheduled off yet */
        if (p->array != rq->active) {
                set_tsk_need_resched(p);
                goto out;
        }
        spin_lock(&rq->lock);
        /*
         * The task was running during this tick - update the
         * time slice counter. 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 (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_unlock;
        }
        if (vx_need_resched(p)) {
                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 (!rq->expired_timestamp)
                        rq->expired_timestamp = jiffies;
                if (!TASK_INTERACTIVE(p) || EXPIRED_STARVING(rq)) {
                        enqueue_task(p, rq->expired);
                        if (p->static_prio < rq->best_expired_prio)
                                rq->best_expired_prio = p->static_prio;
                } else
                        enqueue_task(p, rq->active);
        } else {
                /*
                 * Prevent a too long timeslice allowing a task to monopolize
                 * the CPU. We do this by splitting up the timeslice into
                 * smaller pieces.
                 *
                 * Note: this does not mean the task's timeslices expire or
                 * get lost in any way, they just might be preempted by
                 * another task of equal priority. (one with higher
                 * priority would have preempted this task already.) We
                 * requeue this task to the end of the list on this priority
                 * level, which is in essence a round-robin of tasks with
                 * equal priority.
                 *
                 * This only applies to tasks in the interactive
                 * delta range with at least TIMESLICE_GRANULARITY to requeue.
                 */
                if (TASK_INTERACTIVE(p) && !((task_timeslice(p) -
                        p->time_slice) % TIMESLICE_GRANULARITY(p)) &&
                        (p->time_slice >= TIMESLICE_GRANULARITY(p)) &&
                        (p->array == rq->active)) {

                        dequeue_task(p, rq->active);
                        set_tsk_need_resched(p);
                        p->prio = effective_prio(p);
                        enqueue_task(p, rq->active);
                }
        }
out_unlock:
        spin_unlock(&rq->lock);
out:
        rebalance_tick(rq, 0);
}

/*
 * schedule() is the main scheduler function.
 */
asmlinkage void __sched schedule(void)
{
        long *switch_count;
        task_t *prev, *next;
        runqueue_t *rq;
        prio_array_t *array;
        struct list_head *queue;
        unsigned long long now;
        unsigned long run_time;
#ifdef  CONFIG_VSERVER_HARDCPU          
        struct vx_info *vxi;
        int maxidle = -HZ;
#endif
        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_DEAD | TASK_ZOMBIE)))) {
                if (unlikely(in_atomic())) {
                        printk(KERN_ERR "bad: scheduling while atomic!\n");
                        dump_stack();
                }
        }

need_resched:
        preempt_disable();
        prev = current;
        rq = this_rq();

        release_kernel_lock(prev);
        now = sched_clock();
        if (likely(now - prev->timestamp < NS_MAX_SLEEP_AVG))
                run_time = now - prev->timestamp;
        else
                run_time = NS_MAX_SLEEP_AVG;

        /*
         * Tasks with interactive credits get charged less run_time
         * at high sleep_avg to delay them losing their interactive
         * status
         */
        if (HIGH_CREDIT(prev))
                run_time /= (CURRENT_BONUS(prev) ? : 1);

        spin_lock_irq(&rq->lock);

        /*
         * if entering off of a kernel preemption go straight
         * to picking the next task.
         */
        switch_count = &prev->nivcsw;
        if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
                switch_count = &prev->nvcsw;
                if (unlikely((prev->state & TASK_INTERRUPTIBLE) &&
                                unlikely(signal_pending(prev))))
                        prev->state = TASK_RUNNING;
                else
                        deactivate_task(prev, rq);
        }

#ifdef  CONFIG_VSERVER_HARDCPU          
        if (!list_empty(&rq->hold_queue)) {
                struct list_head *l, *n;
                int ret;

                vxi = NULL;
                list_for_each_safe(l, n, &rq->hold_queue) {
                        next = list_entry(l, task_t, run_list);
                        if (vxi == next->vx_info)
                                continue;

                        vxi = next->vx_info;
                        ret = vx_tokens_recalc(vxi);
                        // tokens = vx_tokens_avail(next);

                        if (ret > 0) {
                                list_del(&next->run_list);
                                next->state &= ~TASK_ONHOLD;
                                recalc_task_prio(next, now);
                                __activate_task(next, rq);
                                // printk("··· unhold %p\n", next);
                                break;
                        }
                        if ((ret < 0) && (maxidle < ret))
                                maxidle = ret;
                }       
        }
        rq->idle_tokens = -maxidle;

pick_next:
#endif
        if (unlikely(!rq->nr_running)) {
#ifdef CONFIG_SMP
                load_balance(rq, 1, cpu_to_node_mask(smp_processor_id()));
#endif
                if (!rq->nr_running) {
                        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;
                rq->best_expired_prio = MAX_PRIO;
        }

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

#ifdef  CONFIG_VSERVER_HARDCPU          
        vxi = next->vx_info;
        if (vxi && __vx_flags(vxi->vx_flags,
                VXF_SCHED_PAUSE|VXF_SCHED_HARD, 0)) {
                int ret = vx_tokens_recalc(vxi);

                if (unlikely(ret <= 0)) {
                        if (ret && (rq->idle_tokens > -ret))
                                rq->idle_tokens = -ret;
                        deactivate_task(next, rq);
                        list_add_tail(&next->run_list, &rq->hold_queue);
                        next->state |= TASK_ONHOLD;                     
                        goto pick_next;
                }
        }
#endif

        if (!rt_task(next) && next->activated > 0) {
                unsigned long long delta = now - next->timestamp;

                if (next->activated == 1)
                        delta = delta * (ON_RUNQUEUE_WEIGHT * 128 / 100) / 128;

                array = next->array;
                dequeue_task(next, array);
                recalc_task_prio(next, next->timestamp + delta);
                enqueue_task(next, array);
        }
        next->activated = 0;
switch_tasks:
        prefetch(next);
        clear_tsk_need_resched(prev);
        RCU_qsctr(task_cpu(prev))++;

        prev->sleep_avg -= run_time;
        if ((long)prev->sleep_avg <= 0) {
                prev->sleep_avg = 0;
                if (!(HIGH_CREDIT(prev) || LOW_CREDIT(prev)))
                        prev->interactive_credit--;
        }
        prev->timestamp = now;

        if (likely(prev != next)) {
                next->timestamp = now;
                rq->nr_switches++;
                rq->curr = next;
                ++*switch_count;

                prepare_arch_switch(rq, next);
                prev = context_switch(rq, prev, next);
                barrier();

                finish_task_switch(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;
}

EXPORT_SYMBOL(schedule);

#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 __sched 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;
}

EXPORT_SYMBOL(preempt_schedule);
#endif /* CONFIG_PREEMPT */

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

EXPORT_SYMBOL(default_wake_function);

/*
 * 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 fastcall __wake_up(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
{
        unsigned long flags;

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

EXPORT_SYMBOL(__wake_up);

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

/**
 * __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.
 *
 * On UP it can prevent extra preemption.
 */
void fastcall __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);
}
EXPORT_SYMBOL_GPL(__wake_up_sync);      /* For internal use only */

void fastcall 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);
}
EXPORT_SYMBOL(complete);

void fastcall complete_all(struct completion *x)
{
        unsigned long flags;

        spin_lock_irqsave(&x->wait.lock, flags);
        x->done += UINT_MAX/2;
        __wake_up_common(&x->wait, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE,
                         0, 0);
        spin_unlock_irqrestore(&x->wait.lock, flags);
}
EXPORT_SYMBOL(complete_all);

void fastcall __sched 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);
}
EXPORT_SYMBOL(wait_for_completion);

#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 fastcall __sched interruptible_sleep_on(wait_queue_head_t *q)
{
        SLEEP_ON_VAR

        current->state = TASK_INTERRUPTIBLE;

        SLEEP_ON_HEAD
        schedule();
        SLEEP_ON_TAIL
}

EXPORT_SYMBOL(interruptible_sleep_on);

long fastcall __sched 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;
}

EXPORT_SYMBOL(interruptible_sleep_on_timeout);

void fastcall __sched sleep_on(wait_queue_head_t *q)
{
        SLEEP_ON_VAR

        current->state = TASK_UNINTERRUPTIBLE;

        SLEEP_ON_HEAD
        schedule();
        SLEEP_ON_TAIL
}

EXPORT_SYMBOL(sleep_on);

long fastcall __sched 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;
}

EXPORT_SYMBOL(sleep_on_timeout);

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

        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);
        /*
         * The RT priorities are set via setscheduler(), but we still
         * allow the 'normal' nice value to be set - but as expected
         * it wont have any effect on scheduling until the task is
         * not SCHED_NORMAL:
         */
        if (rt_task(p)) {
                p->static_prio = NICE_TO_PRIO(nice);
                goto out_unlock;
        }
        array = p->array;
        if (array)
                dequeue_task(p, array);

        old_prio = p->prio;
        new_prio = NICE_TO_PRIO(nice);
        delta = new_prio - old_prio;
        p->static_prio = NICE_TO_PRIO(nice);
        p->prio += delta;

        if (array) {
                enqueue_task(p, array);
                /*
                 * If the task increased its priority or is running and
                 * lowered its priority, then reschedule its CPU:
                 */
                if (delta < 0 || (delta > 0 && task_running(rq, p)))
                        resched_task(rq->curr);
        }
out_unlock:
        task_rq_unlock(rq, &flags);
}

EXPORT_SYMBOL(set_user_nice);

#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_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_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);
}

EXPORT_SYMBOL(task_nice);

/**
 * 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;
}

EXPORT_SYMBOL_GPL(idle_cpu);

/**
 * 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;
}

/* Actually do priority change: must hold rq lock. */
static void __setscheduler(struct task_struct *p, int policy, int prio)
{
        BUG_ON(p->array);
        p->policy = policy;
        p->rt_priority = prio;
        if (policy != SCHED_NORMAL)
                p->prio = MAX_USER_RT_PRIO-1 - p->rt_priority;
        else
                p->prio = p->static_prio;
}

/*
 * setscheduler - change the scheduling policy and/or RT priority of a thread.
 */
static int setscheduler(pid_t pid, int policy, struct sched_param __user *param)
{
        struct sched_param lp;
        int retval = -EINVAL;
        int oldprio;
        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_task_setscheduler(p, policy, &lp);
        if (retval)
                goto out_unlock;

        array = p->array;
        if (array)
                deactivate_task(p, task_rq(p));
        retval = 0;
        oldprio = p->prio;
        __setscheduler(p, policy, lp.sched_priority);
        if (array) {
                __activate_task(p, task_rq(p));
                /*
                 * Reschedule if we are currently running on this runqueue and
                 * our priority decreased, or if we are not currently running on
                 * this runqueue and our priority is higher than the current's
                 */
                if (task_running(rq, p)) {
                        if (p->prio > oldprio)
                                resched_task(rq->curr);
                } else if (p->prio < rq->curr->prio)
                        resched_task(rq->curr);
        }

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 __user *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 __user *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_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 __user *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_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 long sys_sched_setaffinity(pid_t pid, unsigned int len,
                                      unsigned long __user *user_mask_ptr)
{
        cpumask_t 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;

        lock_cpu_hotplug();
        read_lock(&tasklist_lock);

        p = find_process_by_pid(pid);
        if (!p) {
                read_unlock(&tasklist_lock);
                unlock_cpu_hotplug();
                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 = set_cpus_allowed(p, new_mask);

out_unlock:
        put_task_struct(p);
        unlock_cpu_hotplug();
        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 long sys_sched_getaffinity(pid_t pid, unsigned int len,
                                      unsigned long __user *user_mask_ptr)
{
        unsigned int real_len;
        cpumask_t 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;
        cpus_and(mask, p->cpus_allowed, cpu_possible_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 __sched __cond_resched(void)
{
        set_current_state(TASK_RUNNING);
        schedule();
}

EXPORT_SYMBOL(__cond_resched);

/**
 * 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 __sched yield(void)
{
        set_current_state(TASK_RUNNING);
        sys_sched_yield();
}

EXPORT_SYMBOL(yield);

/*
 * This task is about to go to sleep on IO.  Increment rq->nr_iowait so
 * that process accounting knows that this is a task in IO wait state.
 *
 * But don't do that if it is a deliberate, throttling IO wait (this task
 * has set its backing_dev_info: the queue against which it should throttle)
 */
void __sched io_schedule(void)
{
        struct runqueue *rq = this_rq();

        atomic_inc(&rq->nr_iowait);
        schedule();
        atomic_dec(&rq->nr_iowait);
}

EXPORT_SYMBOL(io_schedule);

long __sched io_schedule_timeout(long timeout)
{
        struct runqueue *rq = this_rq();
        long ret;

        atomic_inc(&rq->nr_iowait);
        ret = schedule_timeout(timeout);
        atomic_dec(&rq->nr_iowait);
        return ret;
}

/**
 * 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_min - 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 __user *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_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 inline struct task_struct *eldest_child(struct task_struct *p)
{
        if (list_empty(&p->children)) return NULL;
        return list_entry(p->children.next,struct task_struct,sibling);
}

static inline struct task_struct *older_sibling(struct task_struct *p)
{
        if (p->sibling.prev==&p->parent->children) return NULL;
        return list_entry(p->sibling.prev,struct task_struct,sibling);
}

static inline struct task_struct *younger_sibling(struct task_struct *p)
{
        if (p->sibling.next==&p->parent->children) return NULL;
        return list_entry(p->sibling.next,struct task_struct,sibling);
}

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

        printk("%-13.13s ", p->comm);
        state = p->state ? __ffs(p->state) + 1 : 0;
        if (state < ARRAY_SIZE(stat_nam))
                printk(stat_nam[state]);
        else
                printk("?");
#if (BITS_PER_LONG == 32)
        if (state == TASK_RUNNING)
                printk(" running ");
        else
                printk(" %08lX ", thread_saved_pc(p));
#else
        if (state == TASK_RUNNING)
                printk("  running task   ");
        else
                printk(" %016lx ", thread_saved_pc(p));
#endif
#ifdef CONFIG_DEBUG_STACK_USAGE
        {
                unsigned long * n = (unsigned long *) (p->thread_info+1);
                while (!*n)
                        n++;
                free = (unsigned long) n - (unsigned long)(p->thread_info+1);
        }
#endif
        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");

        if (state != TASK_RUNNING)
                show_stack(p, NULL);
}

void show_state(void)
{
        task_t *g, *p;

#if (BITS_PER_LONG == 32)
        printk("\n"
               "                                               sibling\n");
        printk("  task             PC      pid father child younger older\n");
#else
        printk("\n"
               "                                                       sibling\n");
        printk("  task                 PC          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! */
#ifdef CONFIG_PREEMPT
        idle->thread_info->preempt_count = (idle->lock_depth >= 0);
#else
        idle->thread_info->preempt_count = 0;
#endif
}

/*
 * In a system that switches off the HZ timer idle_cpu_mask
 * indicates which cpus entered this state. This is used
 * in the rcu update to wait only for active cpus. For system
 * which do not switch off the HZ timer idle_cpu_mask should
 * always be CPU_MASK_NONE.
 */
cpumask_t idle_cpu_mask = CPU_MASK_NONE;

#ifdef 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.
 */

/*
 * 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.
 */
int set_cpus_allowed(task_t *p, cpumask_t new_mask)
{
        unsigned long flags;
        int ret = 0;
        migration_req_t req;
        runqueue_t *rq;

        rq = task_rq_lock(p, &flags);
        if (any_online_cpu(new_mask) == NR_CPUS) {
                ret = -EINVAL;
                goto out;
        }

        if (__set_cpus_allowed(p, new_mask, &req)) {
                /* Need help from migration thread: drop lock and wait. */
                task_rq_unlock(rq, &flags);
                wake_up_process(rq->migration_thread);
                wait_for_completion(&req.done);
                return 0;
        }
out:
        task_rq_unlock(rq, &flags);
        return ret;
}

EXPORT_SYMBOL_GPL(set_cpus_allowed);

/* Move (not current) task off this cpu, onto dest cpu. */
static void move_task_away(struct task_struct *p, int dest_cpu)
{
        runqueue_t *rq_dest;

        rq_dest = cpu_rq(dest_cpu);

        double_rq_lock(this_rq(), rq_dest);
        if (task_cpu(p) != smp_processor_id())
                goto out; /* Already moved */

        set_task_cpu(p, dest_cpu);
        if (p->array) {
                deactivate_task(p, this_rq());
                activate_task(p, rq_dest);
                if (p->prio < rq_dest->curr->prio)
                        resched_task(rq_dest->curr);
        }
        p->timestamp = rq_dest->timestamp_last_tick;

out:
        double_rq_unlock(this_rq(), rq_dest);
}

/*
 * migration_thread - this is a highprio system thread that performs
 * thread migration by bumping thread off CPU then 'pushing' onto
 * another runqueue.
 */
static int migration_thread(void * data)
{
        runqueue_t *rq;
        int cpu = (long)data;

        rq = cpu_rq(cpu);
        BUG_ON(rq->migration_thread != current);

        while (!kthread_should_stop()) {
                struct list_head *head;
                migration_req_t *req;

                if (current->flags & PF_FREEZE)
                        refrigerator(PF_FREEZE);

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

                move_task_away(req->task,
                               any_online_cpu(req->task->cpus_allowed));
                local_irq_enable();
                complete(&req->done);
        }
        return 0;
}

#ifdef CONFIG_HOTPLUG_CPU
/* migrate_all_tasks - function to migrate all the tasks from the
 * current cpu caller must have already scheduled this to the target
 * cpu via set_cpus_allowed.  Machine is stopped.  */
void migrate_all_tasks(void)
{
        struct task_struct *tsk, *t;
        int dest_cpu, src_cpu;
        unsigned int node;

        /* We're nailed to this CPU. */
        src_cpu = smp_processor_id();

        /* Not required, but here for neatness. */
        write_lock(&tasklist_lock);

        /* watch out for per node tasks, let's stay on this node */
        node = cpu_to_node(src_cpu);

        do_each_thread(t, tsk) {
                cpumask_t mask;
                if (tsk == current)
                        continue;

                if (task_cpu(tsk) != src_cpu)
                        continue;

                /* Figure out where this task should go (attempting to
                 * keep it on-node), and check if it can be migrated
                 * as-is.  NOTE that kernel threads bound to more than
                 * one online cpu will be migrated. */
                mask = node_to_cpumask(node);
                cpus_and(mask, mask, tsk->cpus_allowed);
                dest_cpu = any_online_cpu(mask);
                if (dest_cpu == NR_CPUS)
                        dest_cpu = any_online_cpu(tsk->cpus_allowed);
                if (dest_cpu == NR_CPUS) {
                        cpus_clear(tsk->cpus_allowed);
                        cpus_complement(tsk->cpus_allowed);
                        dest_cpu = any_online_cpu(tsk->cpus_allowed);

                        /* Don't tell them about moving exiting tasks
                           or kernel threads (both mm NULL), since
                           they never leave kernel. */
                        if (tsk->mm && printk_ratelimit())
                                printk(KERN_INFO "process %d (%s) no "
                                       "longer affine to cpu%d\n",
                                       tsk->pid, tsk->comm, src_cpu);
                }

                move_task_away(tsk, dest_cpu);
        } while_each_thread(t, tsk);

        write_unlock(&tasklist_lock);
}
#endif /* CONFIG_HOTPLUG_CPU */

/*
 * 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)
{
        int cpu = (long)hcpu;
        struct task_struct *p;
        struct runqueue *rq;
        unsigned long flags;

        switch (action) {
        case CPU_UP_PREPARE:
                p = kthread_create(migration_thread, hcpu, "migration/%d",cpu);
                if (IS_ERR(p))
                        return NOTIFY_BAD;
                kthread_bind(p, cpu);
                /* Must be high prio: stop_machine expects to yield to it. */
                rq = task_rq_lock(p, &flags);
                __setscheduler(p, SCHED_FIFO, MAX_RT_PRIO-1);
                task_rq_unlock(rq, &flags);
                cpu_rq(cpu)->migration_thread = p;
                break;
        case CPU_ONLINE:
                /* Strictly unneccessary, as first user will wake it. */
                wake_up_process(cpu_rq(cpu)->migration_thread);
                break;
#ifdef CONFIG_HOTPLUG_CPU
        case CPU_UP_CANCELED:
                /* Unbind it from offline cpu so it can run.  Fall thru. */
                kthread_bind(cpu_rq(cpu)->migration_thread,smp_processor_id());
        case CPU_DEAD:
                kthread_stop(cpu_rq(cpu)->migration_thread);
                cpu_rq(cpu)->migration_thread = NULL;
                BUG_ON(cpu_rq(cpu)->nr_running != 0);
                break;
#endif
        }
        return NOTIFY_OK;
}

static struct notifier_block __devinitdata migration_notifier = {
        .notifier_call = migration_call,
};

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

/*
 * 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.
 *
 * Note: spinlock debugging needs this even on !CONFIG_SMP.
 */
spinlock_t kernel_flag __cacheline_aligned_in_smp = SPIN_LOCK_UNLOCKED;
EXPORT_SYMBOL(kernel_flag);

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;
                rq->best_expired_prio = MAX_PRIO;

                spin_lock_init(&rq->lock);
                INIT_LIST_HEAD(&rq->migration_queue);
                INIT_LIST_HEAD(&rq->hold_queue);
                atomic_set(&rq->nr_iowait, 0);
                nr_running_init(rq);

                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_forked_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);
}

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

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


#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
/*
 * This could be a long-held lock.  If another CPU holds it for a long time,
 * and that CPU is not asked to reschedule then *this* CPU will spin on the
 * lock for a long time, even if *this* CPU is asked to reschedule.
 *
 * So what we do here, in the slow (contended) path is to spin on the lock by
 * hand while permitting preemption.
 *
 * Called inside preempt_disable().
 */
void __sched __preempt_spin_lock(spinlock_t *lock)
{
        if (preempt_count() > 1) {
                _raw_spin_lock(lock);
                return;
        }
        do {
                preempt_enable();
                while (spin_is_locked(lock))
                        cpu_relax();
                preempt_disable();
        } while (!_raw_spin_trylock(lock));
}

EXPORT_SYMBOL(__preempt_spin_lock);

void __sched __preempt_write_lock(rwlock_t *lock)
{
        if (preempt_count() > 1) {
                _raw_write_lock(lock);
                return;
        }

        do {
                preempt_enable();
                while (rwlock_is_locked(lock))
                        cpu_relax();
                preempt_disable();
        } while (!_raw_write_trylock(lock));
}

EXPORT_SYMBOL(__preempt_write_lock);
#endif /* defined(CONFIG_SMP) && defined(CONFIG_PREEMPT) */