GNU Linux-libre 4.4.284-gnu1

[releases.git] / kernel / sched / deadline.c

/*
 * Deadline Scheduling Class (SCHED_DEADLINE)
 *
 * Earliest Deadline First (EDF) + Constant Bandwidth Server (CBS).
 *
 * Tasks that periodically executes their instances for less than their
 * runtime won't miss any of their deadlines.
 * Tasks that are not periodic or sporadic or that tries to execute more
 * than their reserved bandwidth will be slowed down (and may potentially
 * miss some of their deadlines), and won't affect any other task.
 *
 * Copyright (C) 2012 Dario Faggioli <raistlin@linux.it>,
 *                    Juri Lelli <juri.lelli@gmail.com>,
 *                    Michael Trimarchi <michael@amarulasolutions.com>,
 *                    Fabio Checconi <fchecconi@gmail.com>
 */
#include "sched.h"

#include <linux/slab.h>

struct dl_bandwidth def_dl_bandwidth;

static inline struct task_struct *dl_task_of(struct sched_dl_entity *dl_se)
{
        return container_of(dl_se, struct task_struct, dl);
}

static inline struct rq *rq_of_dl_rq(struct dl_rq *dl_rq)
{
        return container_of(dl_rq, struct rq, dl);
}

static inline struct dl_rq *dl_rq_of_se(struct sched_dl_entity *dl_se)
{
        struct task_struct *p = dl_task_of(dl_se);
        struct rq *rq = task_rq(p);

        return &rq->dl;
}

static inline int on_dl_rq(struct sched_dl_entity *dl_se)
{
        return !RB_EMPTY_NODE(&dl_se->rb_node);
}

static inline int is_leftmost(struct task_struct *p, struct dl_rq *dl_rq)
{
        struct sched_dl_entity *dl_se = &p->dl;

        return dl_rq->rb_leftmost == &dl_se->rb_node;
}

void init_dl_bandwidth(struct dl_bandwidth *dl_b, u64 period, u64 runtime)
{
        raw_spin_lock_init(&dl_b->dl_runtime_lock);
        dl_b->dl_period = period;
        dl_b->dl_runtime = runtime;
}

void init_dl_bw(struct dl_bw *dl_b)
{
        raw_spin_lock_init(&dl_b->lock);
        raw_spin_lock(&def_dl_bandwidth.dl_runtime_lock);
        if (global_rt_runtime() == RUNTIME_INF)
                dl_b->bw = -1;
        else
                dl_b->bw = to_ratio(global_rt_period(), global_rt_runtime());
        raw_spin_unlock(&def_dl_bandwidth.dl_runtime_lock);
        dl_b->total_bw = 0;
}

void init_dl_rq(struct dl_rq *dl_rq)
{
        dl_rq->rb_root = RB_ROOT;

#ifdef CONFIG_SMP
        /* zero means no -deadline tasks */
        dl_rq->earliest_dl.curr = dl_rq->earliest_dl.next = 0;

        dl_rq->dl_nr_migratory = 0;
        dl_rq->overloaded = 0;
        dl_rq->pushable_dl_tasks_root = RB_ROOT;
#else
        init_dl_bw(&dl_rq->dl_bw);
#endif
}

#ifdef CONFIG_SMP

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

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

        cpumask_set_cpu(rq->cpu, rq->rd->dlo_mask);
        /*
         * Must be visible before the overload count is
         * set (as in sched_rt.c).
         *
         * Matched by the barrier in pull_dl_task().
         */
        smp_wmb();
        atomic_inc(&rq->rd->dlo_count);
}

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

        atomic_dec(&rq->rd->dlo_count);
        cpumask_clear_cpu(rq->cpu, rq->rd->dlo_mask);
}

static void update_dl_migration(struct dl_rq *dl_rq)
{
        if (dl_rq->dl_nr_migratory && dl_rq->dl_nr_running > 1) {
                if (!dl_rq->overloaded) {
                        dl_set_overload(rq_of_dl_rq(dl_rq));
                        dl_rq->overloaded = 1;
                }
        } else if (dl_rq->overloaded) {
                dl_clear_overload(rq_of_dl_rq(dl_rq));
                dl_rq->overloaded = 0;
        }
}

static void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        struct task_struct *p = dl_task_of(dl_se);

        if (p->nr_cpus_allowed > 1)
                dl_rq->dl_nr_migratory++;

        update_dl_migration(dl_rq);
}

static void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        struct task_struct *p = dl_task_of(dl_se);

        if (p->nr_cpus_allowed > 1)
                dl_rq->dl_nr_migratory--;

        update_dl_migration(dl_rq);
}

/*
 * The list of pushable -deadline task is not a plist, like in
 * sched_rt.c, it is an rb-tree with tasks ordered by deadline.
 */
static void enqueue_pushable_dl_task(struct rq *rq, struct task_struct *p)
{
        struct dl_rq *dl_rq = &rq->dl;
        struct rb_node **link = &dl_rq->pushable_dl_tasks_root.rb_node;
        struct rb_node *parent = NULL;
        struct task_struct *entry;
        int leftmost = 1;

        BUG_ON(!RB_EMPTY_NODE(&p->pushable_dl_tasks));

        while (*link) {
                parent = *link;
                entry = rb_entry(parent, struct task_struct,
                                 pushable_dl_tasks);
                if (dl_entity_preempt(&p->dl, &entry->dl))
                        link = &parent->rb_left;
                else {
                        link = &parent->rb_right;
                        leftmost = 0;
                }
        }

        if (leftmost)
                dl_rq->pushable_dl_tasks_leftmost = &p->pushable_dl_tasks;

        rb_link_node(&p->pushable_dl_tasks, parent, link);
        rb_insert_color(&p->pushable_dl_tasks, &dl_rq->pushable_dl_tasks_root);
}

static void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
{
        struct dl_rq *dl_rq = &rq->dl;

        if (RB_EMPTY_NODE(&p->pushable_dl_tasks))
                return;

        if (dl_rq->pushable_dl_tasks_leftmost == &p->pushable_dl_tasks) {
                struct rb_node *next_node;

                next_node = rb_next(&p->pushable_dl_tasks);
                dl_rq->pushable_dl_tasks_leftmost = next_node;
        }

        rb_erase(&p->pushable_dl_tasks, &dl_rq->pushable_dl_tasks_root);
        RB_CLEAR_NODE(&p->pushable_dl_tasks);
}

static inline int has_pushable_dl_tasks(struct rq *rq)
{
        return !RB_EMPTY_ROOT(&rq->dl.pushable_dl_tasks_root);
}

static int push_dl_task(struct rq *rq);

static inline bool need_pull_dl_task(struct rq *rq, struct task_struct *prev)
{
        return dl_task(prev);
}

static DEFINE_PER_CPU(struct callback_head, dl_push_head);
static DEFINE_PER_CPU(struct callback_head, dl_pull_head);

static void push_dl_tasks(struct rq *);
static void pull_dl_task(struct rq *);

static inline void queue_push_tasks(struct rq *rq)
{
        if (!has_pushable_dl_tasks(rq))
                return;

        queue_balance_callback(rq, &per_cpu(dl_push_head, rq->cpu), push_dl_tasks);
}

static inline void queue_pull_task(struct rq *rq)
{
        queue_balance_callback(rq, &per_cpu(dl_pull_head, rq->cpu), pull_dl_task);
}

static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq);

static struct rq *dl_task_offline_migration(struct rq *rq, struct task_struct *p)
{
        struct rq *later_rq = NULL;
        bool fallback = false;

        later_rq = find_lock_later_rq(p, rq);

        if (!later_rq) {
                int cpu;

                /*
                 * If we cannot preempt any rq, fall back to pick any
                 * online cpu.
                 */
                fallback = true;
                cpu = cpumask_any_and(cpu_active_mask, tsk_cpus_allowed(p));
                if (cpu >= nr_cpu_ids) {
                        /*
                         * Fail to find any suitable cpu.
                         * The task will never come back!
                         */
                        BUG_ON(dl_bandwidth_enabled());

                        /*
                         * If admission control is disabled we
                         * try a little harder to let the task
                         * run.
                         */
                        cpu = cpumask_any(cpu_active_mask);
                }
                later_rq = cpu_rq(cpu);
                double_lock_balance(rq, later_rq);
        }

        /*
         * By now the task is replenished and enqueued; migrate it.
         */
        deactivate_task(rq, p, 0);
        set_task_cpu(p, later_rq->cpu);
        activate_task(later_rq, p, 0);

        if (!fallback)
                resched_curr(later_rq);

        double_unlock_balance(later_rq, rq);

        return later_rq;
}

#else

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

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

static inline
void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
}

static inline
void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
}

static inline bool need_pull_dl_task(struct rq *rq, struct task_struct *prev)
{
        return false;
}

static inline void pull_dl_task(struct rq *rq)
{
}

static inline void queue_push_tasks(struct rq *rq)
{
}

static inline void queue_pull_task(struct rq *rq)
{
}
#endif /* CONFIG_SMP */

static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags);
static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags);
static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
                                  int flags);

/*
 * We are being explicitly informed that a new instance is starting,
 * and this means that:
 *  - the absolute deadline of the entity has to be placed at
 *    current time + relative deadline;
 *  - the runtime of the entity has to be set to the maximum value.
 *
 * The capability of specifying such event is useful whenever a -deadline
 * entity wants to (try to!) synchronize its behaviour with the scheduler's
 * one, and to (try to!) reconcile itself with its own scheduling
 * parameters.
 */
static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se,
                                       struct sched_dl_entity *pi_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq);

        WARN_ON(!dl_se->dl_new || dl_se->dl_throttled);

        /*
         * We use the regular wall clock time to set deadlines in the
         * future; in fact, we must consider execution overheads (time
         * spent on hardirq context, etc.).
         */
        dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
        dl_se->runtime = pi_se->dl_runtime;
        dl_se->dl_new = 0;
}

/*
 * Pure Earliest Deadline First (EDF) scheduling does not deal with the
 * possibility of a entity lasting more than what it declared, and thus
 * exhausting its runtime.
 *
 * Here we are interested in making runtime overrun possible, but we do
 * not want a entity which is misbehaving to affect the scheduling of all
 * other entities.
 * Therefore, a budgeting strategy called Constant Bandwidth Server (CBS)
 * is used, in order to confine each entity within its own bandwidth.
 *
 * This function deals exactly with that, and ensures that when the runtime
 * of a entity is replenished, its deadline is also postponed. That ensures
 * the overrunning entity can't interfere with other entity in the system and
 * can't make them miss their deadlines. Reasons why this kind of overruns
 * could happen are, typically, a entity voluntarily trying to overcome its
 * runtime, or it just underestimated it during sched_setattr().
 */
static void replenish_dl_entity(struct sched_dl_entity *dl_se,
                                struct sched_dl_entity *pi_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq);

        BUG_ON(pi_se->dl_runtime <= 0);

        /*
         * This could be the case for a !-dl task that is boosted.
         * Just go with full inherited parameters.
         */
        if (dl_se->dl_deadline == 0) {
                dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
                dl_se->runtime = pi_se->dl_runtime;
        }

        /*
         * We keep moving the deadline away until we get some
         * available runtime for the entity. This ensures correct
         * handling of situations where the runtime overrun is
         * arbitrary large.
         */
        while (dl_se->runtime <= 0) {
                dl_se->deadline += pi_se->dl_period;
                dl_se->runtime += pi_se->dl_runtime;
        }

        /*
         * At this point, the deadline really should be "in
         * the future" with respect to rq->clock. If it's
         * not, we are, for some reason, lagging too much!
         * Anyway, after having warn userspace abut that,
         * we still try to keep the things running by
         * resetting the deadline and the budget of the
         * entity.
         */
        if (dl_time_before(dl_se->deadline, rq_clock(rq))) {
                printk_deferred_once("sched: DL replenish lagged to much\n");
                dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
                dl_se->runtime = pi_se->dl_runtime;
        }

        if (dl_se->dl_yielded)
                dl_se->dl_yielded = 0;
        if (dl_se->dl_throttled)
                dl_se->dl_throttled = 0;
}

/*
 * Here we check if --at time t-- an entity (which is probably being
 * [re]activated or, in general, enqueued) can use its remaining runtime
 * and its current deadline _without_ exceeding the bandwidth it is
 * assigned (function returns true if it can't). We are in fact applying
 * one of the CBS rules: when a task wakes up, if the residual runtime
 * over residual deadline fits within the allocated bandwidth, then we
 * can keep the current (absolute) deadline and residual budget without
 * disrupting the schedulability of the system. Otherwise, we should
 * refill the runtime and set the deadline a period in the future,
 * because keeping the current (absolute) deadline of the task would
 * result in breaking guarantees promised to other tasks (refer to
 * Documentation/scheduler/sched-deadline.txt for more informations).
 *
 * This function returns true if:
 *
 *   runtime / (deadline - t) > dl_runtime / dl_deadline ,
 *
 * IOW we can't recycle current parameters.
 *
 * Notice that the bandwidth check is done against the deadline. For
 * task with deadline equal to period this is the same of using
 * dl_period instead of dl_deadline in the equation above.
 */
static bool dl_entity_overflow(struct sched_dl_entity *dl_se,
                               struct sched_dl_entity *pi_se, u64 t)
{
        u64 left, right;

        /*
         * left and right are the two sides of the equation above,
         * after a bit of shuffling to use multiplications instead
         * of divisions.
         *
         * Note that none of the time values involved in the two
         * multiplications are absolute: dl_deadline and dl_runtime
         * are the relative deadline and the maximum runtime of each
         * instance, runtime is the runtime left for the last instance
         * and (deadline - t), since t is rq->clock, is the time left
         * to the (absolute) deadline. Even if overflowing the u64 type
         * is very unlikely to occur in both cases, here we scale down
         * as we want to avoid that risk at all. Scaling down by 10
         * means that we reduce granularity to 1us. We are fine with it,
         * since this is only a true/false check and, anyway, thinking
         * of anything below microseconds resolution is actually fiction
         * (but still we want to give the user that illusion >;).
         */
        left = (pi_se->dl_deadline >> DL_SCALE) * (dl_se->runtime >> DL_SCALE);
        right = ((dl_se->deadline - t) >> DL_SCALE) *
                (pi_se->dl_runtime >> DL_SCALE);

        return dl_time_before(right, left);
}

/*
 * Revised wakeup rule [1]: For self-suspending tasks, rather then
 * re-initializing task's runtime and deadline, the revised wakeup
 * rule adjusts the task's runtime to avoid the task to overrun its
 * density.
 *
 * Reasoning: a task may overrun the density if:
 *    runtime / (deadline - t) > dl_runtime / dl_deadline
 *
 * Therefore, runtime can be adjusted to:
 *     runtime = (dl_runtime / dl_deadline) * (deadline - t)
 *
 * In such way that runtime will be equal to the maximum density
 * the task can use without breaking any rule.
 *
 * [1] Luca Abeni, Giuseppe Lipari, and Juri Lelli. 2015. Constant
 * bandwidth server revisited. SIGBED Rev. 11, 4 (January 2015), 19-24.
 */
static void
update_dl_revised_wakeup(struct sched_dl_entity *dl_se, struct rq *rq)
{
        u64 laxity = dl_se->deadline - rq_clock(rq);

        /*
         * If the task has deadline < period, and the deadline is in the past,
         * it should already be throttled before this check.
         *
         * See update_dl_entity() comments for further details.
         */
        WARN_ON(dl_time_before(dl_se->deadline, rq_clock(rq)));

        dl_se->runtime = (dl_se->dl_density * laxity) >> 20;
}

/*
 * Regarding the deadline, a task with implicit deadline has a relative
 * deadline == relative period. A task with constrained deadline has a
 * relative deadline <= relative period.
 *
 * We support constrained deadline tasks. However, there are some restrictions
 * applied only for tasks which do not have an implicit deadline. See
 * update_dl_entity() to know more about such restrictions.
 *
 * The dl_is_implicit() returns true if the task has an implicit deadline.
 */
static inline bool dl_is_implicit(struct sched_dl_entity *dl_se)
{
        return dl_se->dl_deadline == dl_se->dl_period;
}

/*
 * When a deadline entity is placed in the runqueue, its runtime and deadline
 * might need to be updated. This is done by a CBS wake up rule. There are two
 * different rules: 1) the original CBS; and 2) the Revisited CBS.
 *
 * When the task is starting a new period, the Original CBS is used. In this
 * case, the runtime is replenished and a new absolute deadline is set.
 *
 * When a task is queued before the begin of the next period, using the
 * remaining runtime and deadline could make the entity to overflow, see
 * dl_entity_overflow() to find more about runtime overflow. When such case
 * is detected, the runtime and deadline need to be updated.
 *
 * If the task has an implicit deadline, i.e., deadline == period, the Original
 * CBS is applied. the runtime is replenished and a new absolute deadline is
 * set, as in the previous cases.
 *
 * However, the Original CBS does not work properly for tasks with
 * deadline < period, which are said to have a constrained deadline. By
 * applying the Original CBS, a constrained deadline task would be able to run
 * runtime/deadline in a period. With deadline < period, the task would
 * overrun the runtime/period allowed bandwidth, breaking the admission test.
 *
 * In order to prevent this misbehave, the Revisited CBS is used for
 * constrained deadline tasks when a runtime overflow is detected. In the
 * Revisited CBS, rather than replenishing & setting a new absolute deadline,
 * the remaining runtime of the task is reduced to avoid runtime overflow.
 * Please refer to the comments update_dl_revised_wakeup() function to find
 * more about the Revised CBS rule.
 */
static void update_dl_entity(struct sched_dl_entity *dl_se,
                             struct sched_dl_entity *pi_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq);

        /*
         * The arrival of a new instance needs special treatment, i.e.,
         * the actual scheduling parameters have to be "renewed".
         */
        if (dl_se->dl_new) {
                setup_new_dl_entity(dl_se, pi_se);
                return;
        }

        if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
            dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {

                if (unlikely(!dl_is_implicit(dl_se) &&
                             !dl_time_before(dl_se->deadline, rq_clock(rq)) &&
                             !dl_se->dl_boosted)){
                        update_dl_revised_wakeup(dl_se, rq);
                        return;
                }

                dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
                dl_se->runtime = pi_se->dl_runtime;
        }
}

static inline u64 dl_next_period(struct sched_dl_entity *dl_se)
{
        return dl_se->deadline - dl_se->dl_deadline + dl_se->dl_period;
}

/*
 * If the entity depleted all its runtime, and if we want it to sleep
 * while waiting for some new execution time to become available, we
 * set the bandwidth replenishment timer to the replenishment instant
 * and try to activate it.
 *
 * Notice that it is important for the caller to know if the timer
 * actually started or not (i.e., the replenishment instant is in
 * the future or in the past).
 */
static int start_dl_timer(struct task_struct *p)
{
        struct sched_dl_entity *dl_se = &p->dl;
        struct hrtimer *timer = &dl_se->dl_timer;
        struct rq *rq = task_rq(p);
        ktime_t now, act;
        s64 delta;

        lockdep_assert_held(&rq->lock);

        /*
         * We want the timer to fire at the deadline, but considering
         * that it is actually coming from rq->clock and not from
         * hrtimer's time base reading.
         */
        act = ns_to_ktime(dl_next_period(dl_se));
        now = hrtimer_cb_get_time(timer);
        delta = ktime_to_ns(now) - rq_clock(rq);
        act = ktime_add_ns(act, delta);

        /*
         * If the expiry time already passed, e.g., because the value
         * chosen as the deadline is too small, don't even try to
         * start the timer in the past!
         */
        if (ktime_us_delta(act, now) < 0)
                return 0;

        /*
         * !enqueued will guarantee another callback; even if one is already in
         * progress. This ensures a balanced {get,put}_task_struct().
         *
         * The race against __run_timer() clearing the enqueued state is
         * harmless because we're holding task_rq()->lock, therefore the timer
         * expiring after we've done the check will wait on its task_rq_lock()
         * and observe our state.
         */
        if (!hrtimer_is_queued(timer)) {
                get_task_struct(p);
                hrtimer_start(timer, act, HRTIMER_MODE_ABS);
        }

        return 1;
}

/*
 * This is the bandwidth enforcement timer callback. If here, we know
 * a task is not on its dl_rq, since the fact that the timer was running
 * means the task is throttled and needs a runtime replenishment.
 *
 * However, what we actually do depends on the fact the task is active,
 * (it is on its rq) or has been removed from there by a call to
 * dequeue_task_dl(). In the former case we must issue the runtime
 * replenishment and add the task back to the dl_rq; in the latter, we just
 * do nothing but clearing dl_throttled, so that runtime and deadline
 * updating (and the queueing back to dl_rq) will be done by the
 * next call to enqueue_task_dl().
 */
static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
{
        struct sched_dl_entity *dl_se = container_of(timer,
                                                     struct sched_dl_entity,
                                                     dl_timer);
        struct task_struct *p = dl_task_of(dl_se);
        unsigned long flags;
        struct rq *rq;

        rq = task_rq_lock(p, &flags);

        /*
         * The task might have changed its scheduling policy to something
         * different than SCHED_DEADLINE (through switched_fromd_dl()).
         */
        if (!dl_task(p)) {
                __dl_clear_params(p);
                goto unlock;
        }

        /*
         * This is possible if switched_from_dl() raced against a running
         * callback that took the above !dl_task() path and we've since then
         * switched back into SCHED_DEADLINE.
         *
         * There's nothing to do except drop our task reference.
         */
        if (dl_se->dl_new)
                goto unlock;

        /*
         * The task might have been boosted by someone else and might be in the
         * boosting/deboosting path, its not throttled.
         */
        if (dl_se->dl_boosted)
                goto unlock;

        /*
         * Spurious timer due to start_dl_timer() race; or we already received
         * a replenishment from rt_mutex_setprio().
         */
        if (!dl_se->dl_throttled)
                goto unlock;

        sched_clock_tick();
        update_rq_clock(rq);

        /*
         * If the throttle happened during sched-out; like:
         *
         *   schedule()
         *     deactivate_task()
         *       dequeue_task_dl()
         *         update_curr_dl()
         *           start_dl_timer()
         *         __dequeue_task_dl()
         *     prev->on_rq = 0;
         *
         * We can be both throttled and !queued. Replenish the counter
         * but do not enqueue -- wait for our wakeup to do that.
         */
        if (!task_on_rq_queued(p)) {
                replenish_dl_entity(dl_se, dl_se);
                goto unlock;
        }

        enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
        if (dl_task(rq->curr))
                check_preempt_curr_dl(rq, p, 0);
        else
                resched_curr(rq);

#ifdef CONFIG_SMP
        /*
         * Perform balancing operations here; after the replenishments.  We
         * cannot drop rq->lock before this, otherwise the assertion in
         * start_dl_timer() about not missing updates is not true.
         *
         * If we find that the rq the task was on is no longer available, we
         * need to select a new rq.
         *
         * XXX figure out if select_task_rq_dl() deals with offline cpus.
         */
        if (unlikely(!rq->online))
                rq = dl_task_offline_migration(rq, p);

        /*
         * Queueing this task back might have overloaded rq, check if we need
         * to kick someone away.
         */
        if (has_pushable_dl_tasks(rq)) {
                /*
                 * Nothing relies on rq->lock after this, so its safe to drop
                 * rq->lock.
                 */
                lockdep_unpin_lock(&rq->lock);
                push_dl_task(rq);
                lockdep_pin_lock(&rq->lock);
        }
#endif

unlock:
        task_rq_unlock(rq, p, &flags);

        /*
         * This can free the task_struct, including this hrtimer, do not touch
         * anything related to that after this.
         */
        put_task_struct(p);

        return HRTIMER_NORESTART;
}

void init_dl_task_timer(struct sched_dl_entity *dl_se)
{
        struct hrtimer *timer = &dl_se->dl_timer;

        hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        timer->function = dl_task_timer;
}

/*
 * During the activation, CBS checks if it can reuse the current task's
 * runtime and period. If the deadline of the task is in the past, CBS
 * cannot use the runtime, and so it replenishes the task. This rule
 * works fine for implicit deadline tasks (deadline == period), and the
 * CBS was designed for implicit deadline tasks. However, a task with
 * constrained deadline (deadine < period) might be awakened after the
 * deadline, but before the next period. In this case, replenishing the
 * task would allow it to run for runtime / deadline. As in this case
 * deadline < period, CBS enables a task to run for more than the
 * runtime / period. In a very loaded system, this can cause a domino
 * effect, making other tasks miss their deadlines.
 *
 * To avoid this problem, in the activation of a constrained deadline
 * task after the deadline but before the next period, throttle the
 * task and set the replenishing timer to the begin of the next period,
 * unless it is boosted.
 */
static inline void dl_check_constrained_dl(struct sched_dl_entity *dl_se)
{
        struct task_struct *p = dl_task_of(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq_of_se(dl_se));

        if (dl_time_before(dl_se->deadline, rq_clock(rq)) &&
            dl_time_before(rq_clock(rq), dl_next_period(dl_se))) {
                if (unlikely(dl_se->dl_boosted || !start_dl_timer(p)))
                        return;
                dl_se->dl_throttled = 1;
                if (dl_se->runtime > 0)
                        dl_se->runtime = 0;
        }
}

static
int dl_runtime_exceeded(struct sched_dl_entity *dl_se)
{
        return (dl_se->runtime <= 0);
}

extern bool sched_rt_bandwidth_account(struct rt_rq *rt_rq);

/*
 * Update the current task's runtime statistics (provided it is still
 * a -deadline task and has not been removed from the dl_rq).
 */
static void update_curr_dl(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        struct sched_dl_entity *dl_se = &curr->dl;
        u64 delta_exec;

        if (!dl_task(curr) || !on_dl_rq(dl_se))
                return;

        /*
         * Consumed budget is computed considering the time as
         * observed by schedulable tasks (excluding time spent
         * in hardirq context, etc.). Deadlines are instead
         * computed using hard walltime. This seems to be the more
         * natural solution, but the full ramifications of this
         * approach need further study.
         */
        delta_exec = rq_clock_task(rq) - curr->se.exec_start;
        if (unlikely((s64)delta_exec <= 0))
                return;

        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(rq);
        cpuacct_charge(curr, delta_exec);

        sched_rt_avg_update(rq, delta_exec);

        dl_se->runtime -= dl_se->dl_yielded ? 0 : delta_exec;
        if (dl_runtime_exceeded(dl_se)) {
                dl_se->dl_throttled = 1;
                __dequeue_task_dl(rq, curr, 0);
                if (unlikely(dl_se->dl_boosted || !start_dl_timer(curr)))
                        enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);

                if (!is_leftmost(curr, &rq->dl))
                        resched_curr(rq);
        }

        /*
         * Because -- for now -- we share the rt bandwidth, we need to
         * account our runtime there too, otherwise actual rt tasks
         * would be able to exceed the shared quota.
         *
         * Account to the root rt group for now.
         *
         * The solution we're working towards is having the RT groups scheduled
         * using deadline servers -- however there's a few nasties to figure
         * out before that can happen.
         */
        if (rt_bandwidth_enabled()) {
                struct rt_rq *rt_rq = &rq->rt;

                raw_spin_lock(&rt_rq->rt_runtime_lock);
                /*
                 * We'll let actual RT tasks worry about the overflow here, we
                 * have our own CBS to keep us inline; only account when RT
                 * bandwidth is relevant.
                 */
                if (sched_rt_bandwidth_account(rt_rq))
                        rt_rq->rt_time += delta_exec;
                raw_spin_unlock(&rt_rq->rt_runtime_lock);
        }
}

#ifdef CONFIG_SMP

static struct task_struct *pick_next_earliest_dl_task(struct rq *rq, int cpu);

static inline u64 next_deadline(struct rq *rq)
{
        struct task_struct *next = pick_next_earliest_dl_task(rq, rq->cpu);

        if (next && dl_prio(next->prio))
                return next->dl.deadline;
        else
                return 0;
}

static void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline)
{
        struct rq *rq = rq_of_dl_rq(dl_rq);

        if (dl_rq->earliest_dl.curr == 0 ||
            dl_time_before(deadline, dl_rq->earliest_dl.curr)) {
                /*
                 * If the dl_rq had no -deadline tasks, or if the new task
                 * has shorter deadline than the current one on dl_rq, we
                 * know that the previous earliest becomes our next earliest,
                 * as the new task becomes the earliest itself.
                 */
                dl_rq->earliest_dl.next = dl_rq->earliest_dl.curr;
                dl_rq->earliest_dl.curr = deadline;
                cpudl_set(&rq->rd->cpudl, rq->cpu, deadline, 1);
        } else if (dl_rq->earliest_dl.next == 0 ||
                   dl_time_before(deadline, dl_rq->earliest_dl.next)) {
                /*
                 * On the other hand, if the new -deadline task has a
                 * a later deadline than the earliest one on dl_rq, but
                 * it is earlier than the next (if any), we must
                 * recompute the next-earliest.
                 */
                dl_rq->earliest_dl.next = next_deadline(rq);
        }
}

static void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline)
{
        struct rq *rq = rq_of_dl_rq(dl_rq);

        /*
         * Since we may have removed our earliest (and/or next earliest)
         * task we must recompute them.
         */
        if (!dl_rq->dl_nr_running) {
                dl_rq->earliest_dl.curr = 0;
                dl_rq->earliest_dl.next = 0;
                cpudl_set(&rq->rd->cpudl, rq->cpu, 0, 0);
        } else {
                struct rb_node *leftmost = dl_rq->rb_leftmost;
                struct sched_dl_entity *entry;

                entry = rb_entry(leftmost, struct sched_dl_entity, rb_node);
                dl_rq->earliest_dl.curr = entry->deadline;
                dl_rq->earliest_dl.next = next_deadline(rq);
                cpudl_set(&rq->rd->cpudl, rq->cpu, entry->deadline, 1);
        }
}

#else

static inline void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline) {}
static inline void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline) {}

#endif /* CONFIG_SMP */

static inline
void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        int prio = dl_task_of(dl_se)->prio;
        u64 deadline = dl_se->deadline;

        WARN_ON(!dl_prio(prio));
        dl_rq->dl_nr_running++;
        add_nr_running(rq_of_dl_rq(dl_rq), 1);

        inc_dl_deadline(dl_rq, deadline);
        inc_dl_migration(dl_se, dl_rq);
}

static inline
void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        int prio = dl_task_of(dl_se)->prio;

        WARN_ON(!dl_prio(prio));
        WARN_ON(!dl_rq->dl_nr_running);
        dl_rq->dl_nr_running--;
        sub_nr_running(rq_of_dl_rq(dl_rq), 1);

        dec_dl_deadline(dl_rq, dl_se->deadline);
        dec_dl_migration(dl_se, dl_rq);
}

static void __enqueue_dl_entity(struct sched_dl_entity *dl_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
        struct rb_node **link = &dl_rq->rb_root.rb_node;
        struct rb_node *parent = NULL;
        struct sched_dl_entity *entry;
        int leftmost = 1;

        BUG_ON(!RB_EMPTY_NODE(&dl_se->rb_node));

        while (*link) {
                parent = *link;
                entry = rb_entry(parent, struct sched_dl_entity, rb_node);
                if (dl_time_before(dl_se->deadline, entry->deadline))
                        link = &parent->rb_left;
                else {
                        link = &parent->rb_right;
                        leftmost = 0;
                }
        }

        if (leftmost)
                dl_rq->rb_leftmost = &dl_se->rb_node;

        rb_link_node(&dl_se->rb_node, parent, link);
        rb_insert_color(&dl_se->rb_node, &dl_rq->rb_root);

        inc_dl_tasks(dl_se, dl_rq);
}

static void __dequeue_dl_entity(struct sched_dl_entity *dl_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);

        if (RB_EMPTY_NODE(&dl_se->rb_node))
                return;

        if (dl_rq->rb_leftmost == &dl_se->rb_node) {
                struct rb_node *next_node;

                next_node = rb_next(&dl_se->rb_node);
                dl_rq->rb_leftmost = next_node;
        }

        rb_erase(&dl_se->rb_node, &dl_rq->rb_root);
        RB_CLEAR_NODE(&dl_se->rb_node);

        dec_dl_tasks(dl_se, dl_rq);
}

static void
enqueue_dl_entity(struct sched_dl_entity *dl_se,
                  struct sched_dl_entity *pi_se, int flags)
{
        BUG_ON(on_dl_rq(dl_se));

        /*
         * If this is a wakeup or a new instance, the scheduling
         * parameters of the task might need updating. Otherwise,
         * we want a replenishment of its runtime.
         */
        if (dl_se->dl_new || flags & ENQUEUE_WAKEUP)
                update_dl_entity(dl_se, pi_se);
        else if (flags & ENQUEUE_REPLENISH)
                replenish_dl_entity(dl_se, pi_se);

        __enqueue_dl_entity(dl_se);
}

static void dequeue_dl_entity(struct sched_dl_entity *dl_se)
{
        __dequeue_dl_entity(dl_se);
}

static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
{
        struct task_struct *pi_task = rt_mutex_get_top_task(p);
        struct sched_dl_entity *pi_se = &p->dl;

        /*
         * Use the scheduling parameters of the top pi-waiter
         * task if we have one and its (absolute) deadline is
         * smaller than our one... OTW we keep our runtime and
         * deadline.
         */
        if (pi_task && p->dl.dl_boosted && dl_prio(pi_task->normal_prio)) {
                pi_se = &pi_task->dl;
        } else if (!dl_prio(p->normal_prio)) {
                /*
                 * Special case in which we have a !SCHED_DEADLINE task
                 * that is going to be deboosted, but exceedes its
                 * runtime while doing so. No point in replenishing
                 * it, as it's going to return back to its original
                 * scheduling class after this.
                 */
                BUG_ON(!p->dl.dl_boosted || flags != ENQUEUE_REPLENISH);
                return;
        }

        /*
         * Check if a constrained deadline task was activated
         * after the deadline but before the next period.
         * If that is the case, the task will be throttled and
         * the replenishment timer will be set to the next period.
         */
        if (!p->dl.dl_throttled && !dl_is_implicit(&p->dl))
                dl_check_constrained_dl(&p->dl);

        /*
         * If p is throttled, we do nothing. In fact, if it exhausted
         * its budget it needs a replenishment and, since it now is on
         * its rq, the bandwidth timer callback (which clearly has not
         * run yet) will take care of this.
         */
        if (p->dl.dl_throttled && !(flags & ENQUEUE_REPLENISH))
                return;

        enqueue_dl_entity(&p->dl, pi_se, flags);

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

static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
{
        dequeue_dl_entity(&p->dl);
        dequeue_pushable_dl_task(rq, p);
}

static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
{
        update_curr_dl(rq);
        __dequeue_task_dl(rq, p, flags);
}

/*
 * Yield task semantic for -deadline tasks is:
 *
 *   get off from the CPU until our next instance, with
 *   a new runtime. This is of little use now, since we
 *   don't have a bandwidth reclaiming mechanism. Anyway,
 *   bandwidth reclaiming is planned for the future, and
 *   yield_task_dl will indicate that some spare budget
 *   is available for other task instances to use it.
 */
static void yield_task_dl(struct rq *rq)
{
        struct task_struct *p = rq->curr;

        /*
         * We make the task go to sleep until its current deadline by
         * forcing its runtime to zero. This way, update_curr_dl() stops
         * it and the bandwidth timer will wake it up and will give it
         * new scheduling parameters (thanks to dl_yielded=1).
         */
        if (p->dl.runtime > 0) {
                rq->curr->dl.dl_yielded = 1;
                p->dl.runtime = 0;
        }
        update_rq_clock(rq);
        update_curr_dl(rq);
        /*
         * Tell update_rq_clock() that we've just updated,
         * so we don't do microscopic update in schedule()
         * and double the fastpath cost.
         */
        rq_clock_skip_update(rq, true);
}

#ifdef CONFIG_SMP

static int find_later_rq(struct task_struct *task);

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

        if (sd_flag != SD_BALANCE_WAKE)
                goto out;

        rq = cpu_rq(cpu);

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

        /*
         * If we are dealing with a -deadline task, we must
         * decide where to wake it up.
         * If it has a later deadline and the current task
         * on this rq can't move (provided the waking task
         * can!) we prefer to send it somewhere else. On the
         * other hand, if it has a shorter deadline, we
         * try to make it stay here, it might be important.
         */
        if (unlikely(dl_task(curr)) &&
            (curr->nr_cpus_allowed < 2 ||
             !dl_entity_preempt(&p->dl, &curr->dl)) &&
            (p->nr_cpus_allowed > 1)) {
                int target = find_later_rq(p);

                if (target != -1 &&
                                (dl_time_before(p->dl.deadline,
                                        cpu_rq(target)->dl.earliest_dl.curr) ||
                                (cpu_rq(target)->dl.dl_nr_running == 0)))
                        cpu = target;
        }
        rcu_read_unlock();

out:
        return cpu;
}

static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
{
        /*
         * Current can't be migrated, useless to reschedule,
         * let's hope p can move out.
         */
        if (rq->curr->nr_cpus_allowed == 1 ||
            cpudl_find(&rq->rd->cpudl, rq->curr, NULL) == -1)
                return;

        /*
         * p is migratable, so let's not schedule it and
         * see if it is pushed or pulled somewhere else.
         */
        if (p->nr_cpus_allowed != 1 &&
            cpudl_find(&rq->rd->cpudl, p, NULL) != -1)
                return;

        resched_curr(rq);
}

#endif /* CONFIG_SMP */

/*
 * Only called when both the current and waking task are -deadline
 * tasks.
 */
static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
                                  int flags)
{
        if (dl_entity_preempt(&p->dl, &rq->curr->dl)) {
                resched_curr(rq);
                return;
        }

#ifdef CONFIG_SMP
        /*
         * In the unlikely case current and p have the same deadline
         * let us try to decide what's the best thing to do...
         */
        if ((p->dl.deadline == rq->curr->dl.deadline) &&
            !test_tsk_need_resched(rq->curr))
                check_preempt_equal_dl(rq, p);
#endif /* CONFIG_SMP */
}

#ifdef CONFIG_SCHED_HRTICK
static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
{
        hrtick_start(rq, p->dl.runtime);
}
#else /* !CONFIG_SCHED_HRTICK */
static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
{
}
#endif

static struct sched_dl_entity *pick_next_dl_entity(struct rq *rq,
                                                   struct dl_rq *dl_rq)
{
        struct rb_node *left = dl_rq->rb_leftmost;

        if (!left)
                return NULL;

        return rb_entry(left, struct sched_dl_entity, rb_node);
}

struct task_struct *pick_next_task_dl(struct rq *rq, struct task_struct *prev)
{
        struct sched_dl_entity *dl_se;
        struct task_struct *p;
        struct dl_rq *dl_rq;

        dl_rq = &rq->dl;

        if (need_pull_dl_task(rq, prev)) {
                /*
                 * This is OK, because current is on_cpu, which avoids it being
                 * picked for load-balance and preemption/IRQs are still
                 * disabled avoiding further scheduler activity on it and we're
                 * being very careful to re-start the picking loop.
                 */
                lockdep_unpin_lock(&rq->lock);
                pull_dl_task(rq);
                lockdep_pin_lock(&rq->lock);
                /*
                 * pull_rt_task() can drop (and re-acquire) rq->lock; this
                 * means a stop task can slip in, in which case we need to
                 * re-start task selection.
                 */
                if (rq->stop && task_on_rq_queued(rq->stop))
                        return RETRY_TASK;
        }

        /*
         * When prev is DL, we may throttle it in put_prev_task().
         * So, we update time before we check for dl_nr_running.
         */
        if (prev->sched_class == &dl_sched_class)
                update_curr_dl(rq);

        if (unlikely(!dl_rq->dl_nr_running))
                return NULL;

        put_prev_task(rq, prev);

        dl_se = pick_next_dl_entity(rq, dl_rq);
        BUG_ON(!dl_se);

        p = dl_task_of(dl_se);
        p->se.exec_start = rq_clock_task(rq);

        /* Running task will never be pushed. */
       dequeue_pushable_dl_task(rq, p);

        if (hrtick_enabled(rq))
                start_hrtick_dl(rq, p);

        queue_push_tasks(rq);

        return p;
}

static void put_prev_task_dl(struct rq *rq, struct task_struct *p)
{
        update_curr_dl(rq);

        if (on_dl_rq(&p->dl) && p->nr_cpus_allowed > 1)
                enqueue_pushable_dl_task(rq, p);
}

static void task_tick_dl(struct rq *rq, struct task_struct *p, int queued)
{
        update_curr_dl(rq);

        /*
         * Even when we have runtime, update_curr_dl() might have resulted in us
         * not being the leftmost task anymore. In that case NEED_RESCHED will
         * be set and schedule() will start a new hrtick for the next task.
         */
        if (hrtick_enabled(rq) && queued && p->dl.runtime > 0 &&
            is_leftmost(p, &rq->dl))
                start_hrtick_dl(rq, p);
}

static void task_fork_dl(struct task_struct *p)
{
        /*
         * SCHED_DEADLINE tasks cannot fork and this is achieved through
         * sched_fork()
         */
}

static void task_dead_dl(struct task_struct *p)
{
        struct dl_bw *dl_b = dl_bw_of(task_cpu(p));

        /*
         * Since we are TASK_DEAD we won't slip out of the domain!
         */
        raw_spin_lock_irq(&dl_b->lock);
        /* XXX we should retain the bw until 0-lag */
        dl_b->total_bw -= p->dl.dl_bw;
        raw_spin_unlock_irq(&dl_b->lock);
}

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

        p->se.exec_start = rq_clock_task(rq);

        /* You can't push away the running task */
        dequeue_pushable_dl_task(rq, p);
}

#ifdef CONFIG_SMP

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

static int pick_dl_task(struct rq *rq, struct task_struct *p, int cpu)
{
        if (!task_running(rq, p) &&
            cpumask_test_cpu(cpu, tsk_cpus_allowed(p)))
                return 1;
        return 0;
}

/* Returns the second earliest -deadline task, NULL otherwise */
static struct task_struct *pick_next_earliest_dl_task(struct rq *rq, int cpu)
{
        struct rb_node *next_node = rq->dl.rb_leftmost;
        struct sched_dl_entity *dl_se;
        struct task_struct *p = NULL;

next_node:
        next_node = rb_next(next_node);
        if (next_node) {
                dl_se = rb_entry(next_node, struct sched_dl_entity, rb_node);
                p = dl_task_of(dl_se);

                if (pick_dl_task(rq, p, cpu))
                        return p;

                goto next_node;
        }

        return NULL;
}

/*
 * Return the earliest pushable rq's task, which is suitable to be executed
 * on the CPU, NULL otherwise:
 */
static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu)
{
        struct rb_node *next_node = rq->dl.pushable_dl_tasks_leftmost;
        struct task_struct *p = NULL;

        if (!has_pushable_dl_tasks(rq))
                return NULL;

next_node:
        if (next_node) {
                p = rb_entry(next_node, struct task_struct, pushable_dl_tasks);

                if (pick_dl_task(rq, p, cpu))
                        return p;

                next_node = rb_next(next_node);
                goto next_node;
        }

        return NULL;
}

static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);

static int find_later_rq(struct task_struct *task)
{
        struct sched_domain *sd;
        struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
        int this_cpu = smp_processor_id();
        int best_cpu, cpu = task_cpu(task);

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

        if (task->nr_cpus_allowed == 1)
                return -1;

        /*
         * We have to consider system topology and task affinity
         * first, then we can look for a suitable cpu.
         */
        best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
                        task, later_mask);
        if (best_cpu == -1)
                return -1;

        /*
         * If we are here, some target has been found,
         * the most suitable of which is cached in best_cpu.
         * This is, among the runqueues where the current tasks
         * have later deadlines than the task's one, the rq
         * with the latest possible one.
         *
         * Now we check how well this matches with task's
         * affinity and system topology.
         *
         * The last cpu where the task run is our first
         * guess, since it is most likely cache-hot there.
         */
        if (cpumask_test_cpu(cpu, later_mask))
                return cpu;
        /*
         * Check if this_cpu is to be skipped (i.e., it is
         * not in the mask) or not.
         */
        if (!cpumask_test_cpu(this_cpu, later_mask))
                this_cpu = -1;

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

                        /*
                         * If possible, preempting this_cpu is
                         * cheaper than migrating.
                         */
                        if (this_cpu != -1 &&
                            cpumask_test_cpu(this_cpu, sched_domain_span(sd))) {
                                rcu_read_unlock();
                                return this_cpu;
                        }

                        /*
                         * Last chance: if best_cpu is valid and is
                         * in the mask, that becomes our choice.
                         */
                        if (best_cpu < nr_cpu_ids &&
                            cpumask_test_cpu(best_cpu, sched_domain_span(sd))) {
                                rcu_read_unlock();
                                return best_cpu;
                        }
                }
        }
        rcu_read_unlock();

        /*
         * At this point, all our guesses failed, we just return
         * 'something', and let the caller sort the things out.
         */
        if (this_cpu != -1)
                return this_cpu;

        cpu = cpumask_any(later_mask);
        if (cpu < nr_cpu_ids)
                return cpu;

        return -1;
}

/* Locks the rq it finds */
static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
{
        struct rq *later_rq = NULL;
        int tries;
        int cpu;

        for (tries = 0; tries < DL_MAX_TRIES; tries++) {
                cpu = find_later_rq(task);

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

                later_rq = cpu_rq(cpu);

                if (later_rq->dl.dl_nr_running &&
                    !dl_time_before(task->dl.deadline,
                                        later_rq->dl.earliest_dl.curr)) {
                        /*
                         * Target rq has tasks of equal or earlier deadline,
                         * retrying does not release any lock and is unlikely
                         * to yield a different result.
                         */
                        later_rq = NULL;
                        break;
                }

                /* Retry if something changed. */
                if (double_lock_balance(rq, later_rq)) {
                        if (unlikely(task_rq(task) != rq ||
                                     !cpumask_test_cpu(later_rq->cpu,
                                                       &task->cpus_allowed) ||
                                     task_running(rq, task) ||
                                     !task_on_rq_queued(task))) {
                                double_unlock_balance(rq, later_rq);
                                later_rq = NULL;
                                break;
                        }
                }

                /*
                 * If the rq we found has no -deadline task, or
                 * its earliest one has a later deadline than our
                 * task, the rq is a good one.
                 */
                if (!later_rq->dl.dl_nr_running ||
                    dl_time_before(task->dl.deadline,
                                   later_rq->dl.earliest_dl.curr))
                        break;

                /* Otherwise we try again. */
                double_unlock_balance(rq, later_rq);
                later_rq = NULL;
        }

        return later_rq;
}

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

        if (!has_pushable_dl_tasks(rq))
                return NULL;

        p = rb_entry(rq->dl.pushable_dl_tasks_leftmost,
                     struct task_struct, pushable_dl_tasks);

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

        BUG_ON(!task_on_rq_queued(p));
        BUG_ON(!dl_task(p));

        return p;
}

/*
 * See if the non running -deadline tasks on this rq
 * can be sent to some other CPU where they can preempt
 * and start executing.
 */
static int push_dl_task(struct rq *rq)
{
        struct task_struct *next_task;
        struct rq *later_rq;
        int ret = 0;

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

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

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

        /*
         * If next_task preempts rq->curr, and rq->curr
         * can move away, it makes sense to just reschedule
         * without going further in pushing next_task.
         */
        if (dl_task(rq->curr) &&
            dl_time_before(next_task->dl.deadline, rq->curr->dl.deadline) &&
            rq->curr->nr_cpus_allowed > 1) {
                resched_curr(rq);
                return 0;
        }

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

        /* Will lock the rq it'll find */
        later_rq = find_lock_later_rq(next_task, rq);
        if (!later_rq) {
                struct task_struct *task;

                /*
                 * We must check all this again, since
                 * find_lock_later_rq releases rq->lock and it is
                 * then possible that next_task has migrated.
                 */
                task = pick_next_pushable_dl_task(rq);
                if (task_cpu(next_task) == rq->cpu && task == next_task) {
                        /*
                         * The task is still there. We don't try
                         * again, some other cpu will pull it when ready.
                         */
                        goto out;
                }

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

                put_task_struct(next_task);
                next_task = task;
                goto retry;
        }

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

        resched_curr(later_rq);

        double_unlock_balance(rq, later_rq);

out:
        put_task_struct(next_task);

        return ret;
}

static void push_dl_tasks(struct rq *rq)
{
        /* push_dl_task() will return true if it moved a -deadline task */
        while (push_dl_task(rq))
                ;
}

static void pull_dl_task(struct rq *this_rq)
{
        int this_cpu = this_rq->cpu, cpu;
        struct task_struct *p;
        bool resched = false;
        struct rq *src_rq;
        u64 dmin = LONG_MAX;

        if (likely(!dl_overloaded(this_rq)))
                return;

        /*
         * Match the barrier from dl_set_overloaded; this guarantees that if we
         * see overloaded we must also see the dlo_mask bit.
         */
        smp_rmb();

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

                src_rq = cpu_rq(cpu);

                /*
                 * It looks racy, abd it is! However, as in sched_rt.c,
                 * we are fine with this.
                 */
                if (this_rq->dl.dl_nr_running &&
                    dl_time_before(this_rq->dl.earliest_dl.curr,
                                   src_rq->dl.earliest_dl.next))
                        continue;

                /* Might drop this_rq->lock */
                double_lock_balance(this_rq, src_rq);

                /*
                 * If there are no more pullable tasks on the
                 * rq, we're done with it.
                 */
                if (src_rq->dl.dl_nr_running <= 1)
                        goto skip;

                p = pick_earliest_pushable_dl_task(src_rq, this_cpu);

                /*
                 * We found a task to be pulled if:
                 *  - it preempts our current (if there's one),
                 *  - it will preempt the last one we pulled (if any).
                 */
                if (p && dl_time_before(p->dl.deadline, dmin) &&
                    (!this_rq->dl.dl_nr_running ||
                     dl_time_before(p->dl.deadline,
                                    this_rq->dl.earliest_dl.curr))) {
                        WARN_ON(p == src_rq->curr);
                        WARN_ON(!task_on_rq_queued(p));

                        /*
                         * Then we pull iff p has actually an earlier
                         * deadline than the current task of its runqueue.
                         */
                        if (dl_time_before(p->dl.deadline,
                                           src_rq->curr->dl.deadline))
                                goto skip;

                        resched = true;

                        deactivate_task(src_rq, p, 0);
                        set_task_cpu(p, this_cpu);
                        activate_task(this_rq, p, 0);
                        dmin = p->dl.deadline;

                        /* Is there any other task even earlier? */
                }
skip:
                double_unlock_balance(this_rq, src_rq);
        }

        if (resched)
                resched_curr(this_rq);
}

/*
 * Since the task is not running and a reschedule is not going to happen
 * anytime soon on its runqueue, we try pushing it away now.
 */
static void task_woken_dl(struct rq *rq, struct task_struct *p)
{
        if (!task_running(rq, p) &&
            !test_tsk_need_resched(rq->curr) &&
            p->nr_cpus_allowed > 1 &&
            dl_task(rq->curr) &&
            (rq->curr->nr_cpus_allowed < 2 ||
             !dl_entity_preempt(&p->dl, &rq->curr->dl))) {
                push_dl_tasks(rq);
        }
}

static void set_cpus_allowed_dl(struct task_struct *p,
                                const struct cpumask *new_mask)
{
        struct root_domain *src_rd;
        struct rq *rq;

        BUG_ON(!dl_task(p));

        rq = task_rq(p);
        src_rd = rq->rd;
        /*
         * Migrating a SCHED_DEADLINE task between exclusive
         * cpusets (different root_domains) entails a bandwidth
         * update. We already made space for us in the destination
         * domain (see cpuset_can_attach()).
         */
        if (!cpumask_intersects(src_rd->span, new_mask)) {
                struct dl_bw *src_dl_b;

                src_dl_b = dl_bw_of(cpu_of(rq));
                /*
                 * We now free resources of the root_domain we are migrating
                 * off. In the worst case, sched_setattr() may temporary fail
                 * until we complete the update.
                 */
                raw_spin_lock(&src_dl_b->lock);
                __dl_clear(src_dl_b, p->dl.dl_bw);
                raw_spin_unlock(&src_dl_b->lock);
        }

        set_cpus_allowed_common(p, new_mask);
}

/* Assumes rq->lock is held */
static void rq_online_dl(struct rq *rq)
{
        if (rq->dl.overloaded)
                dl_set_overload(rq);

        cpudl_set_freecpu(&rq->rd->cpudl, rq->cpu);
        if (rq->dl.dl_nr_running > 0)
                cpudl_set(&rq->rd->cpudl, rq->cpu, rq->dl.earliest_dl.curr, 1);
}

/* Assumes rq->lock is held */
static void rq_offline_dl(struct rq *rq)
{
        if (rq->dl.overloaded)
                dl_clear_overload(rq);

        cpudl_set(&rq->rd->cpudl, rq->cpu, 0, 0);
        cpudl_clear_freecpu(&rq->rd->cpudl, rq->cpu);
}

void __init init_sched_dl_class(void)
{
        unsigned int i;

        for_each_possible_cpu(i)
                zalloc_cpumask_var_node(&per_cpu(local_cpu_mask_dl, i),
                                        GFP_KERNEL, cpu_to_node(i));
}

#endif /* CONFIG_SMP */

static void switched_from_dl(struct rq *rq, struct task_struct *p)
{
        /*
         * Start the deadline timer; if we switch back to dl before this we'll
         * continue consuming our current CBS slice. If we stay outside of
         * SCHED_DEADLINE until the deadline passes, the timer will reset the
         * task.
         */
        if (!start_dl_timer(p))
                __dl_clear_params(p);

        /*
         * Since this might be the only -deadline task on the rq,
         * this is the right place to try to pull some other one
         * from an overloaded cpu, if any.
         */
        if (!task_on_rq_queued(p) || rq->dl.dl_nr_running)
                return;

        queue_pull_task(rq);
}

/*
 * When switching to -deadline, we may overload the rq, then
 * we try to push someone off, if possible.
 */
static void switched_to_dl(struct rq *rq, struct task_struct *p)
{
        if (task_on_rq_queued(p) && rq->curr != p) {
#ifdef CONFIG_SMP
                if (p->nr_cpus_allowed > 1 && rq->dl.overloaded)
                        queue_push_tasks(rq);
#endif
                if (dl_task(rq->curr))
                        check_preempt_curr_dl(rq, p, 0);
                else
                        resched_curr(rq);
        }
}

/*
 * If the scheduling parameters of a -deadline task changed,
 * a push or pull operation might be needed.
 */
static void prio_changed_dl(struct rq *rq, struct task_struct *p,
                            int oldprio)
{
        if (task_on_rq_queued(p) || rq->curr == p) {
#ifdef CONFIG_SMP
                /*
                 * This might be too much, but unfortunately
                 * we don't have the old deadline value, and
                 * we can't argue if the task is increasing
                 * or lowering its prio, so...
                 */
                if (!rq->dl.overloaded)
                        queue_pull_task(rq);

                /*
                 * If we now have a earlier deadline task than p,
                 * then reschedule, provided p is still on this
                 * runqueue.
                 */
                if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline))
                        resched_curr(rq);
#else
                /*
                 * Again, we don't know if p has a earlier
                 * or later deadline, so let's blindly set a
                 * (maybe not needed) rescheduling point.
                 */
                resched_curr(rq);
#endif /* CONFIG_SMP */
        } else
                switched_to_dl(rq, p);
}

const struct sched_class dl_sched_class = {
        .next                   = &rt_sched_class,
        .enqueue_task           = enqueue_task_dl,
        .dequeue_task           = dequeue_task_dl,
        .yield_task             = yield_task_dl,

        .check_preempt_curr     = check_preempt_curr_dl,

        .pick_next_task         = pick_next_task_dl,
        .put_prev_task          = put_prev_task_dl,

#ifdef CONFIG_SMP
        .select_task_rq         = select_task_rq_dl,
        .set_cpus_allowed       = set_cpus_allowed_dl,
        .rq_online              = rq_online_dl,
        .rq_offline             = rq_offline_dl,
        .task_woken             = task_woken_dl,
#endif

        .set_curr_task          = set_curr_task_dl,
        .task_tick              = task_tick_dl,
        .task_fork              = task_fork_dl,
        .task_dead              = task_dead_dl,

        .prio_changed           = prio_changed_dl,
        .switched_from          = switched_from_dl,
        .switched_to            = switched_to_dl,

        .update_curr            = update_curr_dl,
};

#ifdef CONFIG_SCHED_DEBUG
extern void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq);

void print_dl_stats(struct seq_file *m, int cpu)
{
        print_dl_rq(m, cpu, &cpu_rq(cpu)->dl);
}
#endif /* CONFIG_SCHED_DEBUG */