rt.c

Go to the documentation of this file.

/*
 * Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
 * policies)
 */

#include "sched.h"

#include <linux/slab.h>

static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);

struct rt_bandwidth def_rt_bandwidth;

static enum hrtimer_restart sched_rt_period_timer(struct hrtimer *timer)
{
    struct rt_bandwidth *rt_b =
        container_of(timer, struct rt_bandwidth, rt_period_timer);
    ktime_t now;
    int overrun;
    int idle = 0;

    for (;;) {
        now = hrtimer_cb_get_time(timer);
        overrun = hrtimer_forward(timer, now, rt_b->rt_period);

        if (!overrun)
            break;

        idle = do_sched_rt_period_timer(rt_b, overrun);
    }

    return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
}

void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime)
{
    rt_b->rt_period = ns_to_ktime(period);
    rt_b->rt_runtime = runtime;

    raw_spin_lock_init(&rt_b->rt_runtime_lock);

    hrtimer_init(&rt_b->rt_period_timer,
            CLOCK_MONOTONIC, HRTIMER_MODE_REL);
    rt_b->rt_period_timer.function = sched_rt_period_timer;
}

static void start_rt_bandwidth(struct rt_bandwidth *rt_b)
{
    if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
        return;

    if (hrtimer_active(&rt_b->rt_period_timer))
        return;

    raw_spin_lock(&rt_b->rt_runtime_lock);
    start_bandwidth_timer(&rt_b->rt_period_timer, rt_b->rt_period);
    raw_spin_unlock(&rt_b->rt_runtime_lock);
}

void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq)
{
    struct rt_prio_array *array;
    int i;

    array = &rt_rq->active;
    for (i = 0; i < MAX_RT_PRIO; i++) {
        INIT_LIST_HEAD(array->queue + i);
        __clear_bit(i, array->bitmap);
    }
    /* delimiter for bitsearch: */
    __set_bit(MAX_RT_PRIO, array->bitmap);

#if defined CONFIG_SMP
    rt_rq->highest_prio.curr = MAX_RT_PRIO;
    rt_rq->highest_prio.next = MAX_RT_PRIO;
    rt_rq->rt_nr_migratory = 0;
    rt_rq->overloaded = 0;
    plist_head_init(&rt_rq->pushable_tasks);
#endif

    rt_rq->rt_time = 0;
    rt_rq->rt_throttled = 0;
    rt_rq->rt_runtime = 0;
    raw_spin_lock_init(&rt_rq->rt_runtime_lock);
}

#ifdef CONFIG_RT_GROUP_SCHED
static void destroy_rt_bandwidth(struct rt_bandwidth *rt_b)
{
    hrtimer_cancel(&rt_b->rt_period_timer);
}

#define rt_entity_is_task(rt_se) (!(rt_se)->my_q)

static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
{
#ifdef CONFIG_SCHED_DEBUG
    WARN_ON_ONCE(!rt_entity_is_task(rt_se));
#endif
    return container_of(rt_se, struct task_struct, rt);
}

static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
{
    return rt_rq->rq;
}

static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
{
    return rt_se->rt_rq;
}

void free_rt_sched_group(struct task_group *tg)
{
    int i;

    if (tg->rt_se)
        destroy_rt_bandwidth(&tg->rt_bandwidth);

    for_each_possible_cpu(i) {
        if (tg->rt_rq)
            kfree(tg->rt_rq[i]);
        if (tg->rt_se)
            kfree(tg->rt_se[i]);
    }

    kfree(tg->rt_rq);
    kfree(tg->rt_se);
}

void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq,
        struct sched_rt_entity *rt_se, int cpu,
        struct sched_rt_entity *parent)
{
    struct rq *rq = cpu_rq(cpu);

    rt_rq->highest_prio.curr = MAX_RT_PRIO;
    rt_rq->rt_nr_boosted = 0;
    rt_rq->rq = rq;
    rt_rq->tg = tg;

    tg->rt_rq[cpu] = rt_rq;
    tg->rt_se[cpu] = rt_se;

    if (!rt_se)
        return;

    if (!parent)
        rt_se->rt_rq = &rq->rt;
    else
        rt_se->rt_rq = parent->my_q;

    rt_se->my_q = rt_rq;
    rt_se->parent = parent;
    INIT_LIST_HEAD(&rt_se->run_list);
}

int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
{
    struct rt_rq *rt_rq;
    struct sched_rt_entity *rt_se;
    int i;

    tg->rt_rq = kzalloc(sizeof(rt_rq) * nr_cpu_ids, GFP_KERNEL);
    if (!tg->rt_rq)
        goto err;
    tg->rt_se = kzalloc(sizeof(rt_se) * nr_cpu_ids, GFP_KERNEL);
    if (!tg->rt_se)
        goto err;

    init_rt_bandwidth(&tg->rt_bandwidth,
            ktime_to_ns(def_rt_bandwidth.rt_period), 0);

    for_each_possible_cpu(i) {
        rt_rq = kzalloc_node(sizeof(struct rt_rq),
                     GFP_KERNEL, cpu_to_node(i));
        if (!rt_rq)
            goto err;

        rt_se = kzalloc_node(sizeof(struct sched_rt_entity),
                     GFP_KERNEL, cpu_to_node(i));
        if (!rt_se)
            goto err_free_rq;

        init_rt_rq(rt_rq, cpu_rq(i));
        rt_rq->rt_runtime = tg->rt_bandwidth.rt_runtime;
        init_tg_rt_entry(tg, rt_rq, rt_se, i, parent->rt_se[i]);
    }

    return 1;

err_free_rq:
    kfree(rt_rq);
err:
    return 0;
}

#else /* CONFIG_RT_GROUP_SCHED */

#define rt_entity_is_task(rt_se) (1)

static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
{
    return container_of(rt_se, struct task_struct, rt);
}

static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
{
    return container_of(rt_rq, struct rq, rt);
}

static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
{
    struct task_struct *p = rt_task_of(rt_se);
    struct rq *rq = task_rq(p);

    return &rq->rt;
}

void free_rt_sched_group(struct task_group *tg) { }

int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
{
    return 1;
}
#endif /* CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_SMP

static inline int rt_overloaded(struct rq *rq)
{
    return atomic_read(&rq->rd->rto_count);
}

static inline void rt_set_overload(struct rq *rq)
{
    if (!rq->online)
        return;

    cpumask_set_cpu(rq->cpu, rq->rd->rto_mask);
    /*
     * Make sure the mask is visible before we set
     * the overload count. That is checked to determine
     * if we should look at the mask. It would be a shame
     * if we looked at the mask, but the mask was not
     * updated yet.
     */
    wmb();
    atomic_inc(&rq->rd->rto_count);
}

static inline void rt_clear_overload(struct rq *rq)
{
    if (!rq->online)
        return;

    /* the order here really doesn't matter */
    atomic_dec(&rq->rd->rto_count);
    cpumask_clear_cpu(rq->cpu, rq->rd->rto_mask);
}

static void update_rt_migration(struct rt_rq *rt_rq)
{
    if (rt_rq->rt_nr_migratory && rt_rq->rt_nr_total > 1) {
        if (!rt_rq->overloaded) {
            rt_set_overload(rq_of_rt_rq(rt_rq));
            rt_rq->overloaded = 1;
        }
    } else if (rt_rq->overloaded) {
        rt_clear_overload(rq_of_rt_rq(rt_rq));
        rt_rq->overloaded = 0;
    }
}

static void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
    struct task_struct *p;

    if (!rt_entity_is_task(rt_se))
        return;

    p = rt_task_of(rt_se);
    rt_rq = &rq_of_rt_rq(rt_rq)->rt;

    rt_rq->rt_nr_total++;
    if (p->nr_cpus_allowed > 1)
        rt_rq->rt_nr_migratory++;

    update_rt_migration(rt_rq);
}

static void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
    struct task_struct *p;

    if (!rt_entity_is_task(rt_se))
        return;

    p = rt_task_of(rt_se);
    rt_rq = &rq_of_rt_rq(rt_rq)->rt;

    rt_rq->rt_nr_total--;
    if (p->nr_cpus_allowed > 1)
        rt_rq->rt_nr_migratory--;

    update_rt_migration(rt_rq);
}

static inline int has_pushable_tasks(struct rq *rq)
{
    return !plist_head_empty(&rq->rt.pushable_tasks);
}

static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
{
    plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);
    plist_node_init(&p->pushable_tasks, p->prio);
    plist_add(&p->pushable_tasks, &rq->rt.pushable_tasks);

    /* Update the highest prio pushable task */
    if (p->prio < rq->rt.highest_prio.next)
        rq->rt.highest_prio.next = p->prio;
}

static void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
{
    plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);

    /* Update the new highest prio pushable task */
    if (has_pushable_tasks(rq)) {
        p = plist_first_entry(&rq->rt.pushable_tasks,
                      struct task_struct, pushable_tasks);
        rq->rt.highest_prio.next = p->prio;
    } else
        rq->rt.highest_prio.next = MAX_RT_PRIO;
}

#else

static inline void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
{
}

static inline void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
{
}

static inline
void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
}

static inline
void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
}

#endif /* CONFIG_SMP */

static inline int on_rt_rq(struct sched_rt_entity *rt_se)
{
    return !list_empty(&rt_se->run_list);
}

#ifdef CONFIG_RT_GROUP_SCHED

static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
    if (!rt_rq->tg)
        return RUNTIME_INF;

    return rt_rq->rt_runtime;
}

static inline u64 sched_rt_period(struct rt_rq *rt_rq)
{
    return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
}

typedef struct task_group *rt_rq_iter_t;

static inline struct task_group *next_task_group(struct task_group *tg)
{
    do {
        tg = list_entry_rcu(tg->list.next,
            typeof(struct task_group), list);
    } while (&tg->list != &task_groups && task_group_is_autogroup(tg));

    if (&tg->list == &task_groups)
        tg = NULL;

    return tg;
}

#define for_each_rt_rq(rt_rq, iter, rq)                 \
    for (iter = container_of(&task_groups, typeof(*iter), list);    \
        (iter = next_task_group(iter)) &&           \
        (rt_rq = iter->rt_rq[cpu_of(rq)]);)

static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
{
    list_add_rcu(&rt_rq->leaf_rt_rq_list,
            &rq_of_rt_rq(rt_rq)->leaf_rt_rq_list);
}

static inline void list_del_leaf_rt_rq(struct rt_rq *rt_rq)
{
    list_del_rcu(&rt_rq->leaf_rt_rq_list);
}

#define for_each_leaf_rt_rq(rt_rq, rq) \
    list_for_each_entry_rcu(rt_rq, &rq->leaf_rt_rq_list, leaf_rt_rq_list)

#define for_each_sched_rt_entity(rt_se) \
    for (; rt_se; rt_se = rt_se->parent)

static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
{
    return rt_se->my_q;
}

static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head);
static void dequeue_rt_entity(struct sched_rt_entity *rt_se);

static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
    struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
    struct sched_rt_entity *rt_se;

    int cpu = cpu_of(rq_of_rt_rq(rt_rq));

    rt_se = rt_rq->tg->rt_se[cpu];

    if (rt_rq->rt_nr_running) {
        if (rt_se && !on_rt_rq(rt_se))
            enqueue_rt_entity(rt_se, false);
        if (rt_rq->highest_prio.curr < curr->prio)
            resched_task(curr);
    }
}

static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
    struct sched_rt_entity *rt_se;
    int cpu = cpu_of(rq_of_rt_rq(rt_rq));

    rt_se = rt_rq->tg->rt_se[cpu];

    if (rt_se && on_rt_rq(rt_se))
        dequeue_rt_entity(rt_se);
}

static inline int rt_rq_throttled(struct rt_rq *rt_rq)
{
    return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;
}

static int rt_se_boosted(struct sched_rt_entity *rt_se)
{
    struct rt_rq *rt_rq = group_rt_rq(rt_se);
    struct task_struct *p;

    if (rt_rq)
        return !!rt_rq->rt_nr_boosted;

    p = rt_task_of(rt_se);
    return p->prio != p->normal_prio;
}

#ifdef CONFIG_SMP
static inline const struct cpumask *sched_rt_period_mask(void)
{
    return cpu_rq(smp_processor_id())->rd->span;
}
#else
static inline const struct cpumask *sched_rt_period_mask(void)
{
    return cpu_online_mask;
}
#endif

static inline
struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
{
    return container_of(rt_b, struct task_group, rt_bandwidth)->rt_rq[cpu];
}

static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
{
    return &rt_rq->tg->rt_bandwidth;
}

#else /* !CONFIG_RT_GROUP_SCHED */

static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
    return rt_rq->rt_runtime;
}

static inline u64 sched_rt_period(struct rt_rq *rt_rq)
{
    return ktime_to_ns(def_rt_bandwidth.rt_period);
}

typedef struct rt_rq *rt_rq_iter_t;

#define for_each_rt_rq(rt_rq, iter, rq) \
    for ((void) iter, rt_rq = &rq->rt; rt_rq; rt_rq = NULL)

static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
{
}

static inline void list_del_leaf_rt_rq(struct rt_rq *rt_rq)
{
}

#define for_each_leaf_rt_rq(rt_rq, rq) \
    for (rt_rq = &rq->rt; rt_rq; rt_rq = NULL)

#define for_each_sched_rt_entity(rt_se) \
    for (; rt_se; rt_se = NULL)

static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
{
    return NULL;
}

static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
    if (rt_rq->rt_nr_running)
        resched_task(rq_of_rt_rq(rt_rq)->curr);
}

static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
}

static inline int rt_rq_throttled(struct rt_rq *rt_rq)
{
    return rt_rq->rt_throttled;
}

static inline const struct cpumask *sched_rt_period_mask(void)
{
    return cpu_online_mask;
}

static inline
struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
{
    return &cpu_rq(cpu)->rt;
}

static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
{
    return &def_rt_bandwidth;
}

#endif /* CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_SMP
/*
 * We ran out of runtime, see if we can borrow some from our neighbours.
 */
static int do_balance_runtime(struct rt_rq *rt_rq)
{
    struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
    struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
    int i, weight, more = 0;
    u64 rt_period;

    weight = cpumask_weight(rd->span);

    raw_spin_lock(&rt_b->rt_runtime_lock);
    rt_period = ktime_to_ns(rt_b->rt_period);
    for_each_cpu(i, rd->span) {
        struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
        s64 diff;

        if (iter == rt_rq)
            continue;

        raw_spin_lock(&iter->rt_runtime_lock);
        /*
         * Either all rqs have inf runtime and there's nothing to steal
         * or __disable_runtime() below sets a specific rq to inf to
         * indicate its been disabled and disalow stealing.
         */
        if (iter->rt_runtime == RUNTIME_INF)
            goto next;

        /*
         * From runqueues with spare time, take 1/n part of their
         * spare time, but no more than our period.
         */
        diff = iter->rt_runtime - iter->rt_time;
        if (diff > 0) {
            diff = div_u64((u64)diff, weight);
            if (rt_rq->rt_runtime + diff > rt_period)
                diff = rt_period - rt_rq->rt_runtime;
            iter->rt_runtime -= diff;
            rt_rq->rt_runtime += diff;
            more = 1;
            if (rt_rq->rt_runtime == rt_period) {
                raw_spin_unlock(&iter->rt_runtime_lock);
                break;
            }
        }
next:
        raw_spin_unlock(&iter->rt_runtime_lock);
    }
    raw_spin_unlock(&rt_b->rt_runtime_lock);

    return more;
}

/*
 * Ensure this RQ takes back all the runtime it lend to its neighbours.
 */
static void __disable_runtime(struct rq *rq)
{
    struct root_domain *rd = rq->rd;
    rt_rq_iter_t iter;
    struct rt_rq *rt_rq;

    if (unlikely(!scheduler_running))
        return;

    for_each_rt_rq(rt_rq, iter, rq) {
        struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
        s64 want;
        int i;

        raw_spin_lock(&rt_b->rt_runtime_lock);
        raw_spin_lock(&rt_rq->rt_runtime_lock);
        /*
         * Either we're all inf and nobody needs to borrow, or we're
         * already disabled and thus have nothing to do, or we have
         * exactly the right amount of runtime to take out.
         */
        if (rt_rq->rt_runtime == RUNTIME_INF ||
                rt_rq->rt_runtime == rt_b->rt_runtime)
            goto balanced;
        raw_spin_unlock(&rt_rq->rt_runtime_lock);

        /*
         * Calculate the difference between what we started out with
         * and what we current have, that's the amount of runtime
         * we lend and now have to reclaim.
         */
        want = rt_b->rt_runtime - rt_rq->rt_runtime;

        /*
         * Greedy reclaim, take back as much as we can.
         */
        for_each_cpu(i, rd->span) {
            struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
            s64 diff;

            /*
             * Can't reclaim from ourselves or disabled runqueues.
             */
            if (iter == rt_rq || iter->rt_runtime == RUNTIME_INF)
                continue;

            raw_spin_lock(&iter->rt_runtime_lock);
            if (want > 0) {
                diff = min_t(s64, iter->rt_runtime, want);
                iter->rt_runtime -= diff;
                want -= diff;
            } else {
                iter->rt_runtime -= want;
                want -= want;
            }
            raw_spin_unlock(&iter->rt_runtime_lock);

            if (!want)
                break;
        }

        raw_spin_lock(&rt_rq->rt_runtime_lock);
        /*
         * We cannot be left wanting - that would mean some runtime
         * leaked out of the system.
         */
        BUG_ON(want);
balanced:
        /*
         * Disable all the borrow logic by pretending we have inf
         * runtime - in which case borrowing doesn't make sense.
         */
        rt_rq->rt_runtime = RUNTIME_INF;
        rt_rq->rt_throttled = 0;
        raw_spin_unlock(&rt_rq->rt_runtime_lock);
        raw_spin_unlock(&rt_b->rt_runtime_lock);
    }
}

static void disable_runtime(struct rq *rq)
{
    unsigned long flags;

    raw_spin_lock_irqsave(&rq->lock, flags);
    __disable_runtime(rq);
    raw_spin_unlock_irqrestore(&rq->lock, flags);
}

static void __enable_runtime(struct rq *rq)
{
    rt_rq_iter_t iter;
    struct rt_rq *rt_rq;

    if (unlikely(!scheduler_running))
        return;

    /*
     * Reset each runqueue's bandwidth settings
     */
    for_each_rt_rq(rt_rq, iter, rq) {
        struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);

        raw_spin_lock(&rt_b->rt_runtime_lock);
        raw_spin_lock(&rt_rq->rt_runtime_lock);
        rt_rq->rt_runtime = rt_b->rt_runtime;
        rt_rq->rt_time = 0;
        rt_rq->rt_throttled = 0;
        raw_spin_unlock(&rt_rq->rt_runtime_lock);
        raw_spin_unlock(&rt_b->rt_runtime_lock);
    }
}

static void enable_runtime(struct rq *rq)
{
    unsigned long flags;

    raw_spin_lock_irqsave(&rq->lock, flags);
    __enable_runtime(rq);
    raw_spin_unlock_irqrestore(&rq->lock, flags);
}

int update_runtime(struct notifier_block *nfb, unsigned long action, void *hcpu)
{
    int cpu = (int)(long)hcpu;

    switch (action) {
    case CPU_DOWN_PREPARE:
    case CPU_DOWN_PREPARE_FROZEN:
        disable_runtime(cpu_rq(cpu));
        return NOTIFY_OK;

    case CPU_DOWN_FAILED:
    case CPU_DOWN_FAILED_FROZEN:
    case CPU_ONLINE:
    case CPU_ONLINE_FROZEN:
        enable_runtime(cpu_rq(cpu));
        return NOTIFY_OK;

    default:
        return NOTIFY_DONE;
    }
}

static int balance_runtime(struct rt_rq *rt_rq)
{
    int more = 0;

    if (!sched_feat(RT_RUNTIME_SHARE))
        return more;

    if (rt_rq->rt_time > rt_rq->rt_runtime) {
        raw_spin_unlock(&rt_rq->rt_runtime_lock);
        more = do_balance_runtime(rt_rq);
        raw_spin_lock(&rt_rq->rt_runtime_lock);
    }

    return more;
}
#else /* !CONFIG_SMP */
static inline int balance_runtime(struct rt_rq *rt_rq)
{
    return 0;
}
#endif /* CONFIG_SMP */

static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
{
    int i, idle = 1, throttled = 0;
    const struct cpumask *span;

    span = sched_rt_period_mask();
#ifdef CONFIG_RT_GROUP_SCHED
    /*
     * FIXME: isolated CPUs should really leave the root task group,
     * whether they are isolcpus or were isolated via cpusets, lest
     * the timer run on a CPU which does not service all runqueues,
     * potentially leaving other CPUs indefinitely throttled.  If
     * isolation is really required, the user will turn the throttle
     * off to kill the perturbations it causes anyway.  Meanwhile,
     * this maintains functionality for boot and/or troubleshooting.
     */
    if (rt_b == &root_task_group.rt_bandwidth)
        span = cpu_online_mask;
#endif
    for_each_cpu(i, span) {
        int enqueue = 0;
        struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
        struct rq *rq = rq_of_rt_rq(rt_rq);

        raw_spin_lock(&rq->lock);
        if (rt_rq->rt_time) {
            u64 runtime;

            raw_spin_lock(&rt_rq->rt_runtime_lock);
            if (rt_rq->rt_throttled)
                balance_runtime(rt_rq);
            runtime = rt_rq->rt_runtime;
            rt_rq->rt_time -= min(rt_rq->rt_time, overrun*runtime);
            if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) {
                rt_rq->rt_throttled = 0;
                enqueue = 1;

                /*
                 * Force a clock update if the CPU was idle,
                 * lest wakeup -> unthrottle time accumulate.
                 */
                if (rt_rq->rt_nr_running && rq->curr == rq->idle)
                    rq->skip_clock_update = -1;
            }
            if (rt_rq->rt_time || rt_rq->rt_nr_running)
                idle = 0;
            raw_spin_unlock(&rt_rq->rt_runtime_lock);
        } else if (rt_rq->rt_nr_running) {
            idle = 0;
            if (!rt_rq_throttled(rt_rq))
                enqueue = 1;
        }
        if (rt_rq->rt_throttled)
            throttled = 1;

        if (enqueue)
            sched_rt_rq_enqueue(rt_rq);
        raw_spin_unlock(&rq->lock);
    }

    if (!throttled && (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF))
        return 1;

    return idle;
}

static inline int rt_se_prio(struct sched_rt_entity *rt_se)
{
#ifdef CONFIG_RT_GROUP_SCHED
    struct rt_rq *rt_rq = group_rt_rq(rt_se);

    if (rt_rq)
        return rt_rq->highest_prio.curr;
#endif

    return rt_task_of(rt_se)->prio;
}

static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
{
    u64 runtime = sched_rt_runtime(rt_rq);

    if (rt_rq->rt_throttled)
        return rt_rq_throttled(rt_rq);

    if (runtime >= sched_rt_period(rt_rq))
        return 0;

    balance_runtime(rt_rq);
    runtime = sched_rt_runtime(rt_rq);
    if (runtime == RUNTIME_INF)
        return 0;

    if (rt_rq->rt_time > runtime) {
        struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);

        /*
         * Don't actually throttle groups that have no runtime assigned
         * but accrue some time due to boosting.
         */
        if (likely(rt_b->rt_runtime)) {
            static bool once = false;

            rt_rq->rt_throttled = 1;

            if (!once) {
                once = true;
                printk_sched("sched: RT throttling activated\n");
            }
        } else {
            /*
             * In case we did anyway, make it go away,
             * replenishment is a joke, since it will replenish us
             * with exactly 0 ns.
             */
            rt_rq->rt_time = 0;
        }

        if (rt_rq_throttled(rt_rq)) {
            sched_rt_rq_dequeue(rt_rq);
            return 1;
        }
    }

    return 0;
}

/*
 * Update the current task's runtime statistics. Skip current tasks that
 * are not in our scheduling class.
 */
static void update_curr_rt(struct rq *rq)
{
    struct task_struct *curr = rq->curr;
    struct sched_rt_entity *rt_se = &curr->rt;
    struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
    u64 delta_exec;

    if (curr->sched_class != &rt_sched_class)
        return;

    delta_exec = rq->clock_task - curr->se.exec_start;
    if (unlikely((s64)delta_exec < 0))
        delta_exec = 0;

    schedstat_set(curr->se.statistics.exec_max,
              max(curr->se.statistics.exec_max, delta_exec));

    curr->se.sum_exec_runtime += delta_exec;
    account_group_exec_runtime(curr, delta_exec);

    curr->se.exec_start = rq->clock_task;
    cpuacct_charge(curr, delta_exec);

    sched_rt_avg_update(rq, delta_exec);

    if (!rt_bandwidth_enabled())
        return;

    for_each_sched_rt_entity(rt_se) {
        rt_rq = rt_rq_of_se(rt_se);

        if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
            raw_spin_lock(&rt_rq->rt_runtime_lock);
            rt_rq->rt_time += delta_exec;
            if (sched_rt_runtime_exceeded(rt_rq))
                resched_task(curr);
            raw_spin_unlock(&rt_rq->rt_runtime_lock);
        }
    }
}

#if defined CONFIG_SMP

static void
inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
{
    struct rq *rq = rq_of_rt_rq(rt_rq);

    if (rq->online && prio < prev_prio)
        cpupri_set(&rq->rd->cpupri, rq->cpu, prio);
}

static void
dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
{
    struct rq *rq = rq_of_rt_rq(rt_rq);

    if (rq->online && rt_rq->highest_prio.curr != prev_prio)
        cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio.curr);
}

#else /* CONFIG_SMP */

static inline
void inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) {}
static inline
void dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) {}

#endif /* CONFIG_SMP */

#if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
static void
inc_rt_prio(struct rt_rq *rt_rq, int prio)
{
    int prev_prio = rt_rq->highest_prio.curr;

    if (prio < prev_prio)
        rt_rq->highest_prio.curr = prio;

    inc_rt_prio_smp(rt_rq, prio, prev_prio);
}

static void
dec_rt_prio(struct rt_rq *rt_rq, int prio)
{
    int prev_prio = rt_rq->highest_prio.curr;

    if (rt_rq->rt_nr_running) {

        WARN_ON(prio < prev_prio);

        /*
         * This may have been our highest task, and therefore
         * we may have some recomputation to do
         */
        if (prio == prev_prio) {
            struct rt_prio_array *array = &rt_rq->active;

            rt_rq->highest_prio.curr =
                sched_find_first_bit(array->bitmap);
        }

    } else
        rt_rq->highest_prio.curr = MAX_RT_PRIO;

    dec_rt_prio_smp(rt_rq, prio, prev_prio);
}

#else

static inline void inc_rt_prio(struct rt_rq *rt_rq, int prio) {}
static inline void dec_rt_prio(struct rt_rq *rt_rq, int prio) {}

#endif /* CONFIG_SMP || CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_RT_GROUP_SCHED

static void
inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
    if (rt_se_boosted(rt_se))
        rt_rq->rt_nr_boosted++;

    if (rt_rq->tg)
        start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
}

static void
dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
    if (rt_se_boosted(rt_se))
        rt_rq->rt_nr_boosted--;

    WARN_ON(!rt_rq->rt_nr_running && rt_rq->rt_nr_boosted);
}

#else /* CONFIG_RT_GROUP_SCHED */

static void
inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
    start_rt_bandwidth(&def_rt_bandwidth);
}

static inline
void dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) {}

#endif /* CONFIG_RT_GROUP_SCHED */

static inline
void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
    int prio = rt_se_prio(rt_se);

    WARN_ON(!rt_prio(prio));
    rt_rq->rt_nr_running++;

    inc_rt_prio(rt_rq, prio);
    inc_rt_migration(rt_se, rt_rq);
    inc_rt_group(rt_se, rt_rq);
}

static inline
void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
    WARN_ON(!rt_prio(rt_se_prio(rt_se)));
    WARN_ON(!rt_rq->rt_nr_running);
    rt_rq->rt_nr_running--;

    dec_rt_prio(rt_rq, rt_se_prio(rt_se));
    dec_rt_migration(rt_se, rt_rq);
    dec_rt_group(rt_se, rt_rq);
}

static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
{
    struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
    struct rt_prio_array *array = &rt_rq->active;
    struct rt_rq *group_rq = group_rt_rq(rt_se);
    struct list_head *queue = array->queue + rt_se_prio(rt_se);

    /*
     * Don't enqueue the group if its throttled, or when empty.
     * The latter is a consequence of the former when a child group
     * get throttled and the current group doesn't have any other
     * active members.
     */
    if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
        return;

    if (!rt_rq->rt_nr_running)
        list_add_leaf_rt_rq(rt_rq);

    if (head)
        list_add(&rt_se->run_list, queue);
    else
        list_add_tail(&rt_se->run_list, queue);
    __set_bit(rt_se_prio(rt_se), array->bitmap);

    inc_rt_tasks(rt_se, rt_rq);
}

static void __dequeue_rt_entity(struct sched_rt_entity *rt_se)
{
    struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
    struct rt_prio_array *array = &rt_rq->active;

    list_del_init(&rt_se->run_list);
    if (list_empty(array->queue + rt_se_prio(rt_se)))
        __clear_bit(rt_se_prio(rt_se), array->bitmap);

    dec_rt_tasks(rt_se, rt_rq);
    if (!rt_rq->rt_nr_running)
        list_del_leaf_rt_rq(rt_rq);
}

/*
 * Because the prio of an upper entry depends on the lower
 * entries, we must remove entries top - down.
 */
static void dequeue_rt_stack(struct sched_rt_entity *rt_se)
{
    struct sched_rt_entity *back = NULL;

    for_each_sched_rt_entity(rt_se) {
        rt_se->back = back;
        back = rt_se;
    }

    for (rt_se = back; rt_se; rt_se = rt_se->back) {
        if (on_rt_rq(rt_se))
            __dequeue_rt_entity(rt_se);
    }
}

static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
{
    dequeue_rt_stack(rt_se);
    for_each_sched_rt_entity(rt_se)
        __enqueue_rt_entity(rt_se, head);
}

static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
{
    dequeue_rt_stack(rt_se);

    for_each_sched_rt_entity(rt_se) {
        struct rt_rq *rt_rq = group_rt_rq(rt_se);

        if (rt_rq && rt_rq->rt_nr_running)
            __enqueue_rt_entity(rt_se, false);
    }
}

/*
 * Adding/removing a task to/from a priority array:
 */
static void
enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
{
    struct sched_rt_entity *rt_se = &p->rt;

    if (flags & ENQUEUE_WAKEUP)
        rt_se->timeout = 0;

    enqueue_rt_entity(rt_se, flags & ENQUEUE_HEAD);

    if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
        enqueue_pushable_task(rq, p);

    inc_nr_running(rq);
}

static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
{
    struct sched_rt_entity *rt_se = &p->rt;

    update_curr_rt(rq);
    dequeue_rt_entity(rt_se);

    dequeue_pushable_task(rq, p);

    dec_nr_running(rq);
}

/*
 * Put task to the head or the end of the run list without the overhead of
 * dequeue followed by enqueue.
 */
static void
requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se, int head)
{
    if (on_rt_rq(rt_se)) {
        struct rt_prio_array *array = &rt_rq->active;
        struct list_head *queue = array->queue + rt_se_prio(rt_se);

        if (head)
            list_move(&rt_se->run_list, queue);
        else
            list_move_tail(&rt_se->run_list, queue);
    }
}

static void requeue_task_rt(struct rq *rq, struct task_struct *p, int head)
{
    struct sched_rt_entity *rt_se = &p->rt;
    struct rt_rq *rt_rq;

    for_each_sched_rt_entity(rt_se) {
        rt_rq = rt_rq_of_se(rt_se);
        requeue_rt_entity(rt_rq, rt_se, head);
    }
}

static void yield_task_rt(struct rq *rq)
{
    requeue_task_rt(rq, rq->curr, 0);
}

#ifdef CONFIG_SMP
static int find_lowest_rq(struct task_struct *task);

static int
select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)
{
    struct task_struct *curr;
    struct rq *rq;
    int cpu;

    cpu = task_cpu(p);

    if (p->nr_cpus_allowed == 1)
        goto out;

    /* For anything but wake ups, just return the task_cpu */
    if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK)
        goto out;

    rq = cpu_rq(cpu);

    rcu_read_lock();
    curr = ACCESS_ONCE(rq->curr); /* unlocked access */

    /*
     * If the current task on @p's runqueue is an RT task, then
     * try to see if we can wake this RT task up on another
     * runqueue. Otherwise simply start this RT task
     * on its current runqueue.
     *
     * We want to avoid overloading runqueues. If the woken
     * task is a higher priority, then it will stay on this CPU
     * and the lower prio task should be moved to another CPU.
     * Even though this will probably make the lower prio task
     * lose its cache, we do not want to bounce a higher task
     * around just because it gave up its CPU, perhaps for a
     * lock?
     *
     * For equal prio tasks, we just let the scheduler sort it out.
     *
     * Otherwise, just let it ride on the affined RQ and the
     * post-schedule router will push the preempted task away
     *
     * This test is optimistic, if we get it wrong the load-balancer
     * will have to sort it out.
     */
    if (curr && unlikely(rt_task(curr)) &&
        (curr->nr_cpus_allowed < 2 ||
         curr->prio <= p->prio) &&
        (p->nr_cpus_allowed > 1)) {
        int target = find_lowest_rq(p);

        if (target != -1)
            cpu = target;
    }
    rcu_read_unlock();

out:
    return cpu;
}

static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
{
    if (rq->curr->nr_cpus_allowed == 1)
        return;

    if (p->nr_cpus_allowed != 1
        && cpupri_find(&rq->rd->cpupri, p, NULL))
        return;

    if (!cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
        return;

    /*
     * There appears to be other cpus that can accept
     * current and none to run 'p', so lets reschedule
     * to try and push current away:
     */
    requeue_task_rt(rq, p, 1);
    resched_task(rq->curr);
}

#endif /* CONFIG_SMP */

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flags)
{
    if (p->prio < rq->curr->prio) {
        resched_task(rq->curr);
        return;
    }

#ifdef CONFIG_SMP
    /*
     * If:
     *
     * - the newly woken task is of equal priority to the current task
     * - the newly woken task is non-migratable while current is migratable
     * - current will be preempted on the next reschedule
     *
     * we should check to see if current can readily move to a different
     * cpu.  If so, we will reschedule to allow the push logic to try
     * to move current somewhere else, making room for our non-migratable
     * task.
     */
    if (p->prio == rq->curr->prio && !test_tsk_need_resched(rq->curr))
        check_preempt_equal_prio(rq, p);
#endif
}

static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
                           struct rt_rq *rt_rq)
{
    struct rt_prio_array *array = &rt_rq->active;
    struct sched_rt_entity *next = NULL;
    struct list_head *queue;
    int idx;

    idx = sched_find_first_bit(array->bitmap);
    BUG_ON(idx >= MAX_RT_PRIO);

    queue = array->queue + idx;
    next = list_entry(queue->next, struct sched_rt_entity, run_list);

    return next;
}

static struct task_struct *_pick_next_task_rt(struct rq *rq)
{
    struct sched_rt_entity *rt_se;
    struct task_struct *p;
    struct rt_rq *rt_rq;

    rt_rq = &rq->rt;

    if (!rt_rq->rt_nr_running)
        return NULL;

    if (rt_rq_throttled(rt_rq))
        return NULL;

    do {
        rt_se = pick_next_rt_entity(rq, rt_rq);
        BUG_ON(!rt_se);
        rt_rq = group_rt_rq(rt_se);
    } while (rt_rq);

    p = rt_task_of(rt_se);
    p->se.exec_start = rq->clock_task;

    return p;
}

static struct task_struct *pick_next_task_rt(struct rq *rq)
{
    struct task_struct *p = _pick_next_task_rt(rq);

    /* The running task is never eligible for pushing */
    if (p)
        dequeue_pushable_task(rq, p);

#ifdef CONFIG_SMP
    /*
     * We detect this state here so that we can avoid taking the RQ
     * lock again later if there is no need to push
     */
    rq->post_schedule = has_pushable_tasks(rq);
#endif

    return p;
}

static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
{
    update_curr_rt(rq);

    /*
     * The previous task needs to be made eligible for pushing
     * if it is still active
     */
    if (on_rt_rq(&p->rt) && p->nr_cpus_allowed > 1)
        enqueue_pushable_task(rq, p);
}

#ifdef CONFIG_SMP

/* Only try algorithms three times */
#define RT_MAX_TRIES 3

static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
{
    if (!task_running(rq, p) &&
        (cpu < 0 || cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) &&
        (p->nr_cpus_allowed > 1))
        return 1;
    return 0;
}

/* Return the second highest RT task, NULL otherwise */
static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu)
{
    struct task_struct *next = NULL;
    struct sched_rt_entity *rt_se;
    struct rt_prio_array *array;
    struct rt_rq *rt_rq;
    int idx;

    for_each_leaf_rt_rq(rt_rq, rq) {
        array = &rt_rq->active;
        idx = sched_find_first_bit(array->bitmap);
next_idx:
        if (idx >= MAX_RT_PRIO)
            continue;
        if (next && next->prio <= idx)
            continue;
        list_for_each_entry(rt_se, array->queue + idx, run_list) {
            struct task_struct *p;

            if (!rt_entity_is_task(rt_se))
                continue;

            p = rt_task_of(rt_se);
            if (pick_rt_task(rq, p, cpu)) {
                next = p;
                break;
            }
        }
        if (!next) {
            idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
            goto next_idx;
        }
    }

    return next;
}

static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);

static int find_lowest_rq(struct task_struct *task)
{
    struct sched_domain *sd;
    struct cpumask *lowest_mask = __get_cpu_var(local_cpu_mask);
    int this_cpu = smp_processor_id();
    int cpu      = task_cpu(task);

    /* Make sure the mask is initialized first */
    if (unlikely(!lowest_mask))
        return -1;

    if (task->nr_cpus_allowed == 1)
        return -1; /* No other targets possible */

    if (!cpupri_find(&task_rq(task)->rd->cpupri, task, lowest_mask))
        return -1; /* No targets found */

    /*
     * At this point we have built a mask of cpus representing the
     * lowest priority tasks in the system.  Now we want to elect
     * the best one based on our affinity and topology.
     *
     * We prioritize the last cpu that the task executed on since
     * it is most likely cache-hot in that location.
     */
    if (cpumask_test_cpu(cpu, lowest_mask))
        return cpu;

    /*
     * Otherwise, we consult the sched_domains span maps to figure
     * out which cpu is logically closest to our hot cache data.
     */
    if (!cpumask_test_cpu(this_cpu, lowest_mask))
        this_cpu = -1; /* Skip this_cpu opt if not among lowest */

    rcu_read_lock();
    for_each_domain(cpu, sd) {
        if (sd->flags & SD_WAKE_AFFINE) {
            int best_cpu;

            /*
             * "this_cpu" is cheaper to preempt than a
             * remote processor.
             */
            if (this_cpu != -1 &&
                cpumask_test_cpu(this_cpu, sched_domain_span(sd))) {
                rcu_read_unlock();
                return this_cpu;
            }

            best_cpu = cpumask_first_and(lowest_mask,
                             sched_domain_span(sd));
            if (best_cpu < nr_cpu_ids) {
                rcu_read_unlock();
                return best_cpu;
            }
        }
    }
    rcu_read_unlock();

    /*
     * And finally, if there were no matches within the domains
     * just give the caller *something* to work with from the compatible
     * locations.
     */
    if (this_cpu != -1)
        return this_cpu;

    cpu = cpumask_any(lowest_mask);
    if (cpu < nr_cpu_ids)
        return cpu;
    return -1;
}

/* Will lock the rq it finds */
static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
{
    struct rq *lowest_rq = NULL;
    int tries;
    int cpu;

    for (tries = 0; tries < RT_MAX_TRIES; tries++) {
        cpu = find_lowest_rq(task);

        if ((cpu == -1) || (cpu == rq->cpu))
            break;

        lowest_rq = cpu_rq(cpu);

        /* if the prio of this runqueue changed, try again */
        if (double_lock_balance(rq, lowest_rq)) {
            /*
             * We had to unlock the run queue. In
             * the mean time, task could have
             * migrated already or had its affinity changed.
             * Also make sure that it wasn't scheduled on its rq.
             */
            if (unlikely(task_rq(task) != rq ||
                     !cpumask_test_cpu(lowest_rq->cpu,
                               tsk_cpus_allowed(task)) ||
                     task_running(rq, task) ||
                     !task->on_rq)) {

                double_unlock_balance(rq, lowest_rq);
                lowest_rq = NULL;
                break;
            }
        }

        /* If this rq is still suitable use it. */
        if (lowest_rq->rt.highest_prio.curr > task->prio)
            break;

        /* try again */
        double_unlock_balance(rq, lowest_rq);
        lowest_rq = NULL;
    }

    return lowest_rq;
}

static struct task_struct *pick_next_pushable_task(struct rq *rq)
{
    struct task_struct *p;

    if (!has_pushable_tasks(rq))
        return NULL;

    p = plist_first_entry(&rq->rt.pushable_tasks,
                  struct task_struct, pushable_tasks);

    BUG_ON(rq->cpu != task_cpu(p));
    BUG_ON(task_current(rq, p));
    BUG_ON(p->nr_cpus_allowed <= 1);

    BUG_ON(!p->on_rq);
    BUG_ON(!rt_task(p));

    return p;
}

/*
 * If the current CPU has more than one RT task, see if the non
 * running task can migrate over to a CPU that is running a task
 * of lesser priority.
 */
static int push_rt_task(struct rq *rq)
{
    struct task_struct *next_task;
    struct rq *lowest_rq;
    int ret = 0;

    if (!rq->rt.overloaded)
        return 0;

    next_task = pick_next_pushable_task(rq);
    if (!next_task)
        return 0;

retry:
    if (unlikely(next_task == rq->curr)) {
        WARN_ON(1);
        return 0;
    }

    /*
     * It's possible that the next_task slipped in of
     * higher priority than current. If that's the case
     * just reschedule current.
     */
    if (unlikely(next_task->prio < rq->curr->prio)) {
        resched_task(rq->curr);
        return 0;
    }

    /* We might release rq lock */
    get_task_struct(next_task);

    /* find_lock_lowest_rq locks the rq if found */
    lowest_rq = find_lock_lowest_rq(next_task, rq);
    if (!lowest_rq) {
        struct task_struct *task;
        /*
         * find_lock_lowest_rq releases rq->lock
         * so it is possible that next_task has migrated.
         *
         * We need to make sure that the task is still on the same
         * run-queue and is also still the next task eligible for
         * pushing.
         */
        task = pick_next_pushable_task(rq);
        if (task_cpu(next_task) == rq->cpu && task == next_task) {
            /*
             * The task hasn't migrated, and is still the next
             * eligible task, but we failed to find a run-queue
             * to push it to.  Do not retry in this case, since
             * other cpus will pull from us when ready.
             */
            goto out;
        }

        if (!task)
            /* No more tasks, just exit */
            goto out;

        /*
         * Something has shifted, try again.
         */
        put_task_struct(next_task);
        next_task = task;
        goto retry;
    }

    deactivate_task(rq, next_task, 0);
    set_task_cpu(next_task, lowest_rq->cpu);
    activate_task(lowest_rq, next_task, 0);
    ret = 1;

    resched_task(lowest_rq->curr);

    double_unlock_balance(rq, lowest_rq);

out:
    put_task_struct(next_task);

    return ret;
}

static void push_rt_tasks(struct rq *rq)
{
    /* push_rt_task will return true if it moved an RT */
    while (push_rt_task(rq))
        ;
}

static int pull_rt_task(struct rq *this_rq)
{
    int this_cpu = this_rq->cpu, ret = 0, cpu;
    struct task_struct *p;
    struct rq *src_rq;

    if (likely(!rt_overloaded(this_rq)))
        return 0;

    for_each_cpu(cpu, this_rq->rd->rto_mask) {
        if (this_cpu == cpu)
            continue;

        src_rq = cpu_rq(cpu);

        /*
         * Don't bother taking the src_rq->lock if the next highest
         * task is known to be lower-priority than our current task.
         * This may look racy, but if this value is about to go
         * logically higher, the src_rq will push this task away.
         * And if its going logically lower, we do not care
         */
        if (src_rq->rt.highest_prio.next >=
            this_rq->rt.highest_prio.curr)
            continue;

        /*
         * We can potentially drop this_rq's lock in
         * double_lock_balance, and another CPU could
         * alter this_rq
         */
        double_lock_balance(this_rq, src_rq);

        /*
         * Are there still pullable RT tasks?
         */
        if (src_rq->rt.rt_nr_running <= 1)
            goto skip;

        p = pick_next_highest_task_rt(src_rq, this_cpu);

        /*
         * Do we have an RT task that preempts
         * the to-be-scheduled task?
         */
        if (p && (p->prio < this_rq->rt.highest_prio.curr)) {
            WARN_ON(p == src_rq->curr);
            WARN_ON(!p->on_rq);

            /*
             * There's a chance that p is higher in priority
             * than what's currently running on its cpu.
             * This is just that p is wakeing up and hasn't
             * had a chance to schedule. We only pull
             * p if it is lower in priority than the
             * current task on the run queue
             */
            if (p->prio < src_rq->curr->prio)
                goto skip;

            ret = 1;

            deactivate_task(src_rq, p, 0);
            set_task_cpu(p, this_cpu);
            activate_task(this_rq, p, 0);
            /*
             * We continue with the search, just in
             * case there's an even higher prio task
             * in another runqueue. (low likelihood
             * but possible)
             */
        }
skip:
        double_unlock_balance(this_rq, src_rq);
    }

    return ret;
}

static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
{
    /* Try to pull RT tasks here if we lower this rq's prio */
    if (rq->rt.highest_prio.curr > prev->prio)
        pull_rt_task(rq);
}

static void post_schedule_rt(struct rq *rq)
{
    push_rt_tasks(rq);
}

/*
 * If we are not running and we are not going to reschedule soon, we should
 * try to push tasks away now
 */
static void task_woken_rt(struct rq *rq, struct task_struct *p)
{
    if (!task_running(rq, p) &&
        !test_tsk_need_resched(rq->curr) &&
        has_pushable_tasks(rq) &&
        p->nr_cpus_allowed > 1 &&
        rt_task(rq->curr) &&
        (rq->curr->nr_cpus_allowed < 2 ||
         rq->curr->prio <= p->prio))
        push_rt_tasks(rq);
}

static void set_cpus_allowed_rt(struct task_struct *p,
                const struct cpumask *new_mask)
{
    struct rq *rq;
    int weight;

    BUG_ON(!rt_task(p));

    if (!p->on_rq)
        return;

    weight = cpumask_weight(new_mask);

    /*
     * Only update if the process changes its state from whether it
     * can migrate or not.
     */
    if ((p->nr_cpus_allowed > 1) == (weight > 1))
        return;

    rq = task_rq(p);

    /*
     * The process used to be able to migrate OR it can now migrate
     */
    if (weight <= 1) {
        if (!task_current(rq, p))
            dequeue_pushable_task(rq, p);
        BUG_ON(!rq->rt.rt_nr_migratory);
        rq->rt.rt_nr_migratory--;
    } else {
        if (!task_current(rq, p))
            enqueue_pushable_task(rq, p);
        rq->rt.rt_nr_migratory++;
    }

    update_rt_migration(&rq->rt);
}

/* Assumes rq->lock is held */
static void rq_online_rt(struct rq *rq)
{
    if (rq->rt.overloaded)
        rt_set_overload(rq);

    __enable_runtime(rq);

    cpupri_set(&rq->rd->cpupri, rq->cpu, rq->rt.highest_prio.curr);
}

/* Assumes rq->lock is held */
static void rq_offline_rt(struct rq *rq)
{
    if (rq->rt.overloaded)
        rt_clear_overload(rq);

    __disable_runtime(rq);

    cpupri_set(&rq->rd->cpupri, rq->cpu, CPUPRI_INVALID);
}

/*
 * When switch from the rt queue, we bring ourselves to a position
 * that we might want to pull RT tasks from other runqueues.
 */
static void switched_from_rt(struct rq *rq, struct task_struct *p)
{
    /*
     * If there are other RT tasks then we will reschedule
     * and the scheduling of the other RT tasks will handle
     * the balancing. But if we are the last RT task
     * we may need to handle the pulling of RT tasks
     * now.
     */
    if (p->on_rq && !rq->rt.rt_nr_running)
        pull_rt_task(rq);
}

void init_sched_rt_class(void)
{
    unsigned int i;

    for_each_possible_cpu(i) {
        zalloc_cpumask_var_node(&per_cpu(local_cpu_mask, i),
                    GFP_KERNEL, cpu_to_node(i));
    }
}
#endif /* CONFIG_SMP */

/*
 * When switching a task to RT, we may overload the runqueue
 * with RT tasks. In this case we try to push them off to
 * other runqueues.
 */
static void switched_to_rt(struct rq *rq, struct task_struct *p)
{
    int check_resched = 1;

    /*
     * If we are already running, then there's nothing
     * that needs to be done. But if we are not running
     * we may need to preempt the current running task.
     * If that current running task is also an RT task
     * then see if we can move to another run queue.
     */
    if (p->on_rq && rq->curr != p) {
#ifdef CONFIG_SMP
        if (rq->rt.overloaded && push_rt_task(rq) &&
            /* Don't resched if we changed runqueues */
            rq != task_rq(p))
            check_resched = 0;
#endif /* CONFIG_SMP */
        if (check_resched && p->prio < rq->curr->prio)
            resched_task(rq->curr);
    }
}

/*
 * Priority of the task has changed. This may cause
 * us to initiate a push or pull.
 */
static void
prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
{
    if (!p->on_rq)
        return;

    if (rq->curr == p) {
#ifdef CONFIG_SMP
        /*
         * If our priority decreases while running, we
         * may need to pull tasks to this runqueue.
         */
        if (oldprio < p->prio)
            pull_rt_task(rq);
        /*
         * If there's a higher priority task waiting to run
         * then reschedule. Note, the above pull_rt_task
         * can release the rq lock and p could migrate.
         * Only reschedule if p is still on the same runqueue.
         */
        if (p->prio > rq->rt.highest_prio.curr && rq->curr == p)
            resched_task(p);
#else
        /* For UP simply resched on drop of prio */
        if (oldprio < p->prio)
            resched_task(p);
#endif /* CONFIG_SMP */
    } else {
        /*
         * This task is not running, but if it is
         * greater than the current running task
         * then reschedule.
         */
        if (p->prio < rq->curr->prio)
            resched_task(rq->curr);
    }
}

static void watchdog(struct rq *rq, struct task_struct *p)
{
    unsigned long soft, hard;

    /* max may change after cur was read, this will be fixed next tick */
    soft = task_rlimit(p, RLIMIT_RTTIME);
    hard = task_rlimit_max(p, RLIMIT_RTTIME);

    if (soft != RLIM_INFINITY) {
        unsigned long next;

        p->rt.timeout++;
        next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
        if (p->rt.timeout > next)
            p->cputime_expires.sched_exp = p->se.sum_exec_runtime;
    }
}

static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
{
    struct sched_rt_entity *rt_se = &p->rt;

    update_curr_rt(rq);

    watchdog(rq, p);

    /*
     * RR tasks need a special form of timeslice management.
     * FIFO tasks have no timeslices.
     */
    if (p->policy != SCHED_RR)
        return;

    if (--p->rt.time_slice)
        return;

    p->rt.time_slice = RR_TIMESLICE;

    /*
     * Requeue to the end of queue if we (and all of our ancestors) are the
     * only element on the queue
     */
    for_each_sched_rt_entity(rt_se) {
        if (rt_se->run_list.prev != rt_se->run_list.next) {
            requeue_task_rt(rq, p, 0);
            set_tsk_need_resched(p);
            return;
        }
    }
}

static void set_curr_task_rt(struct rq *rq)
{
    struct task_struct *p = rq->curr;

    p->se.exec_start = rq->clock_task;

    /* The running task is never eligible for pushing */
    dequeue_pushable_task(rq, p);
}

static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
{
    /*
     * Time slice is 0 for SCHED_FIFO tasks
     */
    if (task->policy == SCHED_RR)
        return RR_TIMESLICE;
    else
        return 0;
}

const struct sched_class rt_sched_class = {
    .next           = &fair_sched_class,
    .enqueue_task       = enqueue_task_rt,
    .dequeue_task       = dequeue_task_rt,
    .yield_task     = yield_task_rt,

    .check_preempt_curr = check_preempt_curr_rt,

    .pick_next_task     = pick_next_task_rt,
    .put_prev_task      = put_prev_task_rt,

#ifdef CONFIG_SMP
    .select_task_rq     = select_task_rq_rt,

    .set_cpus_allowed       = set_cpus_allowed_rt,
    .rq_online              = rq_online_rt,
    .rq_offline             = rq_offline_rt,
    .pre_schedule       = pre_schedule_rt,
    .post_schedule      = post_schedule_rt,
    .task_woken     = task_woken_rt,
    .switched_from      = switched_from_rt,
#endif

    .set_curr_task          = set_curr_task_rt,
    .task_tick      = task_tick_rt,

    .get_rr_interval    = get_rr_interval_rt,

    .prio_changed       = prio_changed_rt,
    .switched_to        = switched_to_rt,
};

#ifdef CONFIG_SCHED_DEBUG
extern void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq);

void print_rt_stats(struct seq_file *m, int cpu)
{
    rt_rq_iter_t iter;
    struct rt_rq *rt_rq;

    rcu_read_lock();
    for_each_rt_rq(rt_rq, iter, cpu_rq(cpu))
        print_rt_rq(m, cpu, rt_rq);
    rcu_read_unlock();
}
#endif /* CONFIG_SCHED_DEBUG */