sched: Add enqueue/dequeue flags

[linux-flexiantxendom0-natty.git] / kernel / sched_fair.c

/*
 * Completely Fair Scheduling (CFS) Class (SCHED_NORMAL/SCHED_BATCH)
 *
 *  Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 *  Interactivity improvements by Mike Galbraith
 *  (C) 2007 Mike Galbraith <efault@gmx.de>
 *
 *  Various enhancements by Dmitry Adamushko.
 *  (C) 2007 Dmitry Adamushko <dmitry.adamushko@gmail.com>
 *
 *  Group scheduling enhancements by Srivatsa Vaddagiri
 *  Copyright IBM Corporation, 2007
 *  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
 *
 *  Scaled math optimizations by Thomas Gleixner
 *  Copyright (C) 2007, Thomas Gleixner <tglx@linutronix.de>
 *
 *  Adaptive scheduling granularity, math enhancements by Peter Zijlstra
 *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
 */

#include <linux/latencytop.h>
#include <linux/sched.h>

/*
 * Targeted preemption latency for CPU-bound tasks:
 * (default: 5ms * (1 + ilog(ncpus)), units: nanoseconds)
 *
 * NOTE: this latency value is not the same as the concept of
 * 'timeslice length' - timeslices in CFS are of variable length
 * and have no persistent notion like in traditional, time-slice
 * based scheduling concepts.
 *
 * (to see the precise effective timeslice length of your workload,
 *  run vmstat and monitor the context-switches (cs) field)
 */
unsigned int sysctl_sched_latency = 6000000ULL;
unsigned int normalized_sysctl_sched_latency = 6000000ULL;

/*
 * The initial- and re-scaling of tunables is configurable
 * (default SCHED_TUNABLESCALING_LOG = *(1+ilog(ncpus))
 *
 * Options are:
 * SCHED_TUNABLESCALING_NONE - unscaled, always *1
 * SCHED_TUNABLESCALING_LOG - scaled logarithmical, *1+ilog(ncpus)
 * SCHED_TUNABLESCALING_LINEAR - scaled linear, *ncpus
 */
enum sched_tunable_scaling sysctl_sched_tunable_scaling
        = SCHED_TUNABLESCALING_LOG;

/*
 * Minimal preemption granularity for CPU-bound tasks:
 * (default: 2 msec * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_min_granularity = 2000000ULL;
unsigned int normalized_sysctl_sched_min_granularity = 2000000ULL;

/*
 * is kept at sysctl_sched_latency / sysctl_sched_min_granularity
 */
static unsigned int sched_nr_latency = 3;

/*
 * After fork, child runs first. If set to 0 (default) then
 * parent will (try to) run first.
 */
unsigned int sysctl_sched_child_runs_first __read_mostly;

/*
 * sys_sched_yield() compat mode
 *
 * This option switches the agressive yield implementation of the
 * old scheduler back on.
 */
unsigned int __read_mostly sysctl_sched_compat_yield;

/*
 * SCHED_OTHER wake-up granularity.
 * (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
 *
 * This option delays the preemption effects of decoupled workloads
 * and reduces their over-scheduling. Synchronous workloads will still
 * have immediate wakeup/sleep latencies.
 */
unsigned int sysctl_sched_wakeup_granularity = 1000000UL;
unsigned int normalized_sysctl_sched_wakeup_granularity = 1000000UL;

const_debug unsigned int sysctl_sched_migration_cost = 500000UL;

static const struct sched_class fair_sched_class;

/**************************************************************
 * CFS operations on generic schedulable entities:
 */

#ifdef CONFIG_FAIR_GROUP_SCHED

/* cpu runqueue to which this cfs_rq is attached */
static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
{
        return cfs_rq->rq;
}

/* An entity is a task if it doesn't "own" a runqueue */
#define entity_is_task(se)      (!se->my_q)

static inline struct task_struct *task_of(struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
        WARN_ON_ONCE(!entity_is_task(se));
#endif
        return container_of(se, struct task_struct, se);
}

/* Walk up scheduling entities hierarchy */
#define for_each_sched_entity(se) \
                for (; se; se = se->parent)

static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
{
        return p->se.cfs_rq;
}

/* runqueue on which this entity is (to be) queued */
static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
{
        return se->cfs_rq;
}

/* runqueue "owned" by this group */
static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
{
        return grp->my_q;
}

/* Given a group's cfs_rq on one cpu, return its corresponding cfs_rq on
 * another cpu ('this_cpu')
 */
static inline struct cfs_rq *cpu_cfs_rq(struct cfs_rq *cfs_rq, int this_cpu)
{
        return cfs_rq->tg->cfs_rq[this_cpu];
}

/* Iterate thr' all leaf cfs_rq's on a runqueue */
#define for_each_leaf_cfs_rq(rq, cfs_rq) \
        list_for_each_entry_rcu(cfs_rq, &rq->leaf_cfs_rq_list, leaf_cfs_rq_list)

/* Do the two (enqueued) entities belong to the same group ? */
static inline int
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
        if (se->cfs_rq == pse->cfs_rq)
                return 1;

        return 0;
}

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
        return se->parent;
}

/* return depth at which a sched entity is present in the hierarchy */
static inline int depth_se(struct sched_entity *se)
{
        int depth = 0;

        for_each_sched_entity(se)
                depth++;

        return depth;
}

static void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
        int se_depth, pse_depth;

        /*
         * preemption test can be made between sibling entities who are in the
         * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
         * both tasks until we find their ancestors who are siblings of common
         * parent.
         */

        /* First walk up until both entities are at same depth */
        se_depth = depth_se(*se);
        pse_depth = depth_se(*pse);

        while (se_depth > pse_depth) {
                se_depth--;
                *se = parent_entity(*se);
        }

        while (pse_depth > se_depth) {
                pse_depth--;
                *pse = parent_entity(*pse);
        }

        while (!is_same_group(*se, *pse)) {
                *se = parent_entity(*se);
                *pse = parent_entity(*pse);
        }
}

#else   /* !CONFIG_FAIR_GROUP_SCHED */

static inline struct task_struct *task_of(struct sched_entity *se)
{
        return container_of(se, struct task_struct, se);
}

static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
{
        return container_of(cfs_rq, struct rq, cfs);
}

#define entity_is_task(se)      1

#define for_each_sched_entity(se) \
                for (; se; se = NULL)

static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
{
        return &task_rq(p)->cfs;
}

static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
{
        struct task_struct *p = task_of(se);
        struct rq *rq = task_rq(p);

        return &rq->cfs;
}

/* runqueue "owned" by this group */
static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
{
        return NULL;
}

static inline struct cfs_rq *cpu_cfs_rq(struct cfs_rq *cfs_rq, int this_cpu)
{
        return &cpu_rq(this_cpu)->cfs;
}

#define for_each_leaf_cfs_rq(rq, cfs_rq) \
                for (cfs_rq = &rq->cfs; cfs_rq; cfs_rq = NULL)

static inline int
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
        return 1;
}

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
        return NULL;
}

static inline void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
}

#endif  /* CONFIG_FAIR_GROUP_SCHED */


/**************************************************************
 * Scheduling class tree data structure manipulation methods:
 */

static inline u64 max_vruntime(u64 min_vruntime, u64 vruntime)
{
        s64 delta = (s64)(vruntime - min_vruntime);
        if (delta > 0)
                min_vruntime = vruntime;

        return min_vruntime;
}

static inline u64 min_vruntime(u64 min_vruntime, u64 vruntime)
{
        s64 delta = (s64)(vruntime - min_vruntime);
        if (delta < 0)
                min_vruntime = vruntime;

        return min_vruntime;
}

static inline int entity_before(struct sched_entity *a,
                                struct sched_entity *b)
{
        return (s64)(a->vruntime - b->vruntime) < 0;
}

static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        return se->vruntime - cfs_rq->min_vruntime;
}

static void update_min_vruntime(struct cfs_rq *cfs_rq)
{
        u64 vruntime = cfs_rq->min_vruntime;

        if (cfs_rq->curr)
                vruntime = cfs_rq->curr->vruntime;

        if (cfs_rq->rb_leftmost) {
                struct sched_entity *se = rb_entry(cfs_rq->rb_leftmost,
                                                   struct sched_entity,
                                                   run_node);

                if (!cfs_rq->curr)
                        vruntime = se->vruntime;
                else
                        vruntime = min_vruntime(vruntime, se->vruntime);
        }

        cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
}

/*
 * Enqueue an entity into the rb-tree:
 */
static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        struct rb_node **link = &cfs_rq->tasks_timeline.rb_node;
        struct rb_node *parent = NULL;
        struct sched_entity *entry;
        s64 key = entity_key(cfs_rq, se);
        int leftmost = 1;

        /*
         * Find the right place in the rbtree:
         */
        while (*link) {
                parent = *link;
                entry = rb_entry(parent, struct sched_entity, run_node);
                /*
                 * We dont care about collisions. Nodes with
                 * the same key stay together.
                 */
                if (key < entity_key(cfs_rq, entry)) {
                        link = &parent->rb_left;
                } else {
                        link = &parent->rb_right;
                        leftmost = 0;
                }
        }

        /*
         * Maintain a cache of leftmost tree entries (it is frequently
         * used):
         */
        if (leftmost)
                cfs_rq->rb_leftmost = &se->run_node;

        rb_link_node(&se->run_node, parent, link);
        rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline);
}

static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        if (cfs_rq->rb_leftmost == &se->run_node) {
                struct rb_node *next_node;

                next_node = rb_next(&se->run_node);
                cfs_rq->rb_leftmost = next_node;
        }

        rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
}

static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq)
{
        struct rb_node *left = cfs_rq->rb_leftmost;

        if (!left)
                return NULL;

        return rb_entry(left, struct sched_entity, run_node);
}

static struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
{
        struct rb_node *last = rb_last(&cfs_rq->tasks_timeline);

        if (!last)
                return NULL;

        return rb_entry(last, struct sched_entity, run_node);
}

/**************************************************************
 * Scheduling class statistics methods:
 */

#ifdef CONFIG_SCHED_DEBUG
int sched_proc_update_handler(struct ctl_table *table, int write,
                void __user *buffer, size_t *lenp,
                loff_t *ppos)
{
        int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
        int factor = get_update_sysctl_factor();

        if (ret || !write)
                return ret;

        sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
                                        sysctl_sched_min_granularity);

#define WRT_SYSCTL(name) \
        (normalized_sysctl_##name = sysctl_##name / (factor))
        WRT_SYSCTL(sched_min_granularity);
        WRT_SYSCTL(sched_latency);
        WRT_SYSCTL(sched_wakeup_granularity);
        WRT_SYSCTL(sched_shares_ratelimit);
#undef WRT_SYSCTL

        return 0;
}
#endif

/*
 * delta /= w
 */
static inline unsigned long
calc_delta_fair(unsigned long delta, struct sched_entity *se)
{
        if (unlikely(se->load.weight != NICE_0_LOAD))
                delta = calc_delta_mine(delta, NICE_0_LOAD, &se->load);

        return delta;
}

/*
 * The idea is to set a period in which each task runs once.
 *
 * When there are too many tasks (sysctl_sched_nr_latency) we have to stretch
 * this period because otherwise the slices get too small.
 *
 * p = (nr <= nl) ? l : l*nr/nl
 */
static u64 __sched_period(unsigned long nr_running)
{
        u64 period = sysctl_sched_latency;
        unsigned long nr_latency = sched_nr_latency;

        if (unlikely(nr_running > nr_latency)) {
                period = sysctl_sched_min_granularity;
                period *= nr_running;
        }

        return period;
}

/*
 * We calculate the wall-time slice from the period by taking a part
 * proportional to the weight.
 *
 * s = p*P[w/rw]
 */
static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);

        for_each_sched_entity(se) {
                struct load_weight *load;
                struct load_weight lw;

                cfs_rq = cfs_rq_of(se);
                load = &cfs_rq->load;

                if (unlikely(!se->on_rq)) {
                        lw = cfs_rq->load;

                        update_load_add(&lw, se->load.weight);
                        load = &lw;
                }
                slice = calc_delta_mine(slice, se->load.weight, load);
        }
        return slice;
}

/*
 * We calculate the vruntime slice of a to be inserted task
 *
 * vs = s/w
 */
static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        return calc_delta_fair(sched_slice(cfs_rq, se), se);
}

/*
 * Update the current task's runtime statistics. Skip current tasks that
 * are not in our scheduling class.
 */
static inline void
__update_curr(struct cfs_rq *cfs_rq, struct sched_entity *curr,
              unsigned long delta_exec)
{
        unsigned long delta_exec_weighted;

        schedstat_set(curr->statistics.exec_max,
                      max((u64)delta_exec, curr->statistics.exec_max));

        curr->sum_exec_runtime += delta_exec;
        schedstat_add(cfs_rq, exec_clock, delta_exec);
        delta_exec_weighted = calc_delta_fair(delta_exec, curr);

        curr->vruntime += delta_exec_weighted;
        update_min_vruntime(cfs_rq);
}

static void update_curr(struct cfs_rq *cfs_rq)
{
        struct sched_entity *curr = cfs_rq->curr;
        u64 now = rq_of(cfs_rq)->clock;
        unsigned long delta_exec;

        if (unlikely(!curr))
                return;

        /*
         * Get the amount of time the current task was running
         * since the last time we changed load (this cannot
         * overflow on 32 bits):
         */
        delta_exec = (unsigned long)(now - curr->exec_start);
        if (!delta_exec)
                return;

        __update_curr(cfs_rq, curr, delta_exec);
        curr->exec_start = now;

        if (entity_is_task(curr)) {
                struct task_struct *curtask = task_of(curr);

                trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
                cpuacct_charge(curtask, delta_exec);
                account_group_exec_runtime(curtask, delta_exec);
        }
}

static inline void
update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        schedstat_set(se->statistics.wait_start, rq_of(cfs_rq)->clock);
}

/*
 * Task is being enqueued - update stats:
 */
static void update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /*
         * Are we enqueueing a waiting task? (for current tasks
         * a dequeue/enqueue event is a NOP)
         */
        if (se != cfs_rq->curr)
                update_stats_wait_start(cfs_rq, se);
}

static void
update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        schedstat_set(se->statistics.wait_max, max(se->statistics.wait_max,
                        rq_of(cfs_rq)->clock - se->statistics.wait_start));
        schedstat_set(se->statistics.wait_count, se->statistics.wait_count + 1);
        schedstat_set(se->statistics.wait_sum, se->statistics.wait_sum +
                        rq_of(cfs_rq)->clock - se->statistics.wait_start);
#ifdef CONFIG_SCHEDSTATS
        if (entity_is_task(se)) {
                trace_sched_stat_wait(task_of(se),
                        rq_of(cfs_rq)->clock - se->statistics.wait_start);
        }
#endif
        schedstat_set(se->statistics.wait_start, 0);
}

static inline void
update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /*
         * Mark the end of the wait period if dequeueing a
         * waiting task:
         */
        if (se != cfs_rq->curr)
                update_stats_wait_end(cfs_rq, se);
}

/*
 * We are picking a new current task - update its stats:
 */
static inline void
update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /*
         * We are starting a new run period:
         */
        se->exec_start = rq_of(cfs_rq)->clock;
}

/**************************************************
 * Scheduling class queueing methods:
 */

#if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED
static void
add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
{
        cfs_rq->task_weight += weight;
}
#else
static inline void
add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
{
}
#endif

static void
account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        update_load_add(&cfs_rq->load, se->load.weight);
        if (!parent_entity(se))
                inc_cpu_load(rq_of(cfs_rq), se->load.weight);
        if (entity_is_task(se)) {
                add_cfs_task_weight(cfs_rq, se->load.weight);
                list_add(&se->group_node, &cfs_rq->tasks);
        }
        cfs_rq->nr_running++;
        se->on_rq = 1;
}

static void
account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        update_load_sub(&cfs_rq->load, se->load.weight);
        if (!parent_entity(se))
                dec_cpu_load(rq_of(cfs_rq), se->load.weight);
        if (entity_is_task(se)) {
                add_cfs_task_weight(cfs_rq, -se->load.weight);
                list_del_init(&se->group_node);
        }
        cfs_rq->nr_running--;
        se->on_rq = 0;
}

static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHEDSTATS
        struct task_struct *tsk = NULL;

        if (entity_is_task(se))
                tsk = task_of(se);

        if (se->statistics.sleep_start) {
                u64 delta = rq_of(cfs_rq)->clock - se->statistics.sleep_start;

                if ((s64)delta < 0)
                        delta = 0;

                if (unlikely(delta > se->statistics.sleep_max))
                        se->statistics.sleep_max = delta;

                se->statistics.sleep_start = 0;
                se->statistics.sum_sleep_runtime += delta;

                if (tsk) {
                        account_scheduler_latency(tsk, delta >> 10, 1);
                        trace_sched_stat_sleep(tsk, delta);
                }
        }
        if (se->statistics.block_start) {
                u64 delta = rq_of(cfs_rq)->clock - se->statistics.block_start;

                if ((s64)delta < 0)
                        delta = 0;

                if (unlikely(delta > se->statistics.block_max))
                        se->statistics.block_max = delta;

                se->statistics.block_start = 0;
                se->statistics.sum_sleep_runtime += delta;

                if (tsk) {
                        if (tsk->in_iowait) {
                                se->statistics.iowait_sum += delta;
                                se->statistics.iowait_count++;
                                trace_sched_stat_iowait(tsk, delta);
                        }

                        /*
                         * Blocking time is in units of nanosecs, so shift by
                         * 20 to get a milliseconds-range estimation of the
                         * amount of time that the task spent sleeping:
                         */
                        if (unlikely(prof_on == SLEEP_PROFILING)) {
                                profile_hits(SLEEP_PROFILING,
                                                (void *)get_wchan(tsk),
                                                delta >> 20);
                        }
                        account_scheduler_latency(tsk, delta >> 10, 0);
                }
        }
#endif
}

static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
        s64 d = se->vruntime - cfs_rq->min_vruntime;

        if (d < 0)
                d = -d;

        if (d > 3*sysctl_sched_latency)
                schedstat_inc(cfs_rq, nr_spread_over);
#endif
}

static void
place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
{
        u64 vruntime = cfs_rq->min_vruntime;

        /*
         * The 'current' period is already promised to the current tasks,
         * however the extra weight of the new task will slow them down a
         * little, place the new task so that it fits in the slot that
         * stays open at the end.
         */
        if (initial && sched_feat(START_DEBIT))
                vruntime += sched_vslice(cfs_rq, se);

        /* sleeps up to a single latency don't count. */
        if (!initial) {
                unsigned long thresh = sysctl_sched_latency;

                /*
                 * Halve their sleep time's effect, to allow
                 * for a gentler effect of sleepers:
                 */
                if (sched_feat(GENTLE_FAIR_SLEEPERS))
                        thresh >>= 1;

                vruntime -= thresh;
        }

        /* ensure we never gain time by being placed backwards. */
        vruntime = max_vruntime(se->vruntime, vruntime);

        se->vruntime = vruntime;
}

static void
enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        /*
         * Update the normalized vruntime before updating min_vruntime
         * through callig update_curr().
         */
        if (!(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_WAKING))
                se->vruntime += cfs_rq->min_vruntime;

        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);
        account_entity_enqueue(cfs_rq, se);

        if (flags & ENQUEUE_WAKEUP) {
                place_entity(cfs_rq, se, 0);
                enqueue_sleeper(cfs_rq, se);
        }

        update_stats_enqueue(cfs_rq, se);
        check_spread(cfs_rq, se);
        if (se != cfs_rq->curr)
                __enqueue_entity(cfs_rq, se);
}

static void __clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        if (!se || cfs_rq->last == se)
                cfs_rq->last = NULL;

        if (!se || cfs_rq->next == se)
                cfs_rq->next = NULL;
}

static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        for_each_sched_entity(se)
                __clear_buddies(cfs_rq_of(se), se);
}

static void
dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);

        update_stats_dequeue(cfs_rq, se);
        if (flags & DEQUEUE_SLEEP) {
#ifdef CONFIG_SCHEDSTATS
                if (entity_is_task(se)) {
                        struct task_struct *tsk = task_of(se);

                        if (tsk->state & TASK_INTERRUPTIBLE)
                                se->statistics.sleep_start = rq_of(cfs_rq)->clock;
                        if (tsk->state & TASK_UNINTERRUPTIBLE)
                                se->statistics.block_start = rq_of(cfs_rq)->clock;
                }
#endif
        }

        clear_buddies(cfs_rq, se);

        if (se != cfs_rq->curr)
                __dequeue_entity(cfs_rq, se);
        account_entity_dequeue(cfs_rq, se);
        update_min_vruntime(cfs_rq);

        /*
         * Normalize the entity after updating the min_vruntime because the
         * update can refer to the ->curr item and we need to reflect this
         * movement in our normalized position.
         */
        if (!(flags & DEQUEUE_SLEEP))
                se->vruntime -= cfs_rq->min_vruntime;
}

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void
check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
        unsigned long ideal_runtime, delta_exec;

        ideal_runtime = sched_slice(cfs_rq, curr);
        delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
        if (delta_exec > ideal_runtime) {
                resched_task(rq_of(cfs_rq)->curr);
                /*
                 * The current task ran long enough, ensure it doesn't get
                 * re-elected due to buddy favours.
                 */
                clear_buddies(cfs_rq, curr);
                return;
        }

        /*
         * Ensure that a task that missed wakeup preemption by a
         * narrow margin doesn't have to wait for a full slice.
         * This also mitigates buddy induced latencies under load.
         */
        if (!sched_feat(WAKEUP_PREEMPT))
                return;

        if (delta_exec < sysctl_sched_min_granularity)
                return;

        if (cfs_rq->nr_running > 1) {
                struct sched_entity *se = __pick_next_entity(cfs_rq);
                s64 delta = curr->vruntime - se->vruntime;

                if (delta > ideal_runtime)
                        resched_task(rq_of(cfs_rq)->curr);
        }
}

static void
set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        /* 'current' is not kept within the tree. */
        if (se->on_rq) {
                /*
                 * Any task has to be enqueued before it get to execute on
                 * a CPU. So account for the time it spent waiting on the
                 * runqueue.
                 */
                update_stats_wait_end(cfs_rq, se);
                __dequeue_entity(cfs_rq, se);
        }

        update_stats_curr_start(cfs_rq, se);
        cfs_rq->curr = se;
#ifdef CONFIG_SCHEDSTATS
        /*
         * Track our maximum slice length, if the CPU's load is at
         * least twice that of our own weight (i.e. dont track it
         * when there are only lesser-weight tasks around):
         */
        if (rq_of(cfs_rq)->load.weight >= 2*se->load.weight) {
                se->statistics.slice_max = max(se->statistics.slice_max,
                        se->sum_exec_runtime - se->prev_sum_exec_runtime);
        }
#endif
        se->prev_sum_exec_runtime = se->sum_exec_runtime;
}

static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);

static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
{
        struct sched_entity *se = __pick_next_entity(cfs_rq);
        struct sched_entity *left = se;

        if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
                se = cfs_rq->next;

        /*
         * Prefer last buddy, try to return the CPU to a preempted task.
         */
        if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
                se = cfs_rq->last;

        clear_buddies(cfs_rq, se);

        return se;
}

static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
{
        /*
         * If still on the runqueue then deactivate_task()
         * was not called and update_curr() has to be done:
         */
        if (prev->on_rq)
                update_curr(cfs_rq);

        check_spread(cfs_rq, prev);
        if (prev->on_rq) {
                update_stats_wait_start(cfs_rq, prev);
                /* Put 'current' back into the tree. */
                __enqueue_entity(cfs_rq, prev);
        }
        cfs_rq->curr = NULL;
}

static void
entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
{
        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);

#ifdef CONFIG_SCHED_HRTICK
        /*
         * queued ticks are scheduled to match the slice, so don't bother
         * validating it and just reschedule.
         */
        if (queued) {
                resched_task(rq_of(cfs_rq)->curr);
                return;
        }
        /*
         * don't let the period tick interfere with the hrtick preemption
         */
        if (!sched_feat(DOUBLE_TICK) &&
                        hrtimer_active(&rq_of(cfs_rq)->hrtick_timer))
                return;
#endif

        if (cfs_rq->nr_running > 1 || !sched_feat(WAKEUP_PREEMPT))
                check_preempt_tick(cfs_rq, curr);
}

/**************************************************
 * CFS operations on tasks:
 */

#ifdef CONFIG_SCHED_HRTICK
static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        WARN_ON(task_rq(p) != rq);

        if (hrtick_enabled(rq) && cfs_rq->nr_running > 1) {
                u64 slice = sched_slice(cfs_rq, se);
                u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
                s64 delta = slice - ran;

                if (delta < 0) {
                        if (rq->curr == p)
                                resched_task(p);
                        return;
                }

                /*
                 * Don't schedule slices shorter than 10000ns, that just
                 * doesn't make sense. Rely on vruntime for fairness.
                 */
                if (rq->curr != p)
                        delta = max_t(s64, 10000LL, delta);

                hrtick_start(rq, delta);
        }
}

/*
 * called from enqueue/dequeue and updates the hrtick when the
 * current task is from our class and nr_running is low enough
 * to matter.
 */
static void hrtick_update(struct rq *rq)
{
        struct task_struct *curr = rq->curr;

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

        if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)
                hrtick_start_fair(rq, curr);
}
#else /* !CONFIG_SCHED_HRTICK */
static inline void
hrtick_start_fair(struct rq *rq, struct task_struct *p)
{
}

static inline void hrtick_update(struct rq *rq)
{
}
#endif

/*
 * The enqueue_task method is called before nr_running is
 * increased. Here we update the fair scheduling stats and
 * then put the task into the rbtree:
 */
static void
enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se;

        for_each_sched_entity(se) {
                if (se->on_rq)
                        break;
                cfs_rq = cfs_rq_of(se);
                enqueue_entity(cfs_rq, se, flags);
                flags = ENQUEUE_WAKEUP;
        }

        hrtick_update(rq);
}

/*
 * The dequeue_task method is called before nr_running is
 * decreased. We remove the task from the rbtree and
 * update the fair scheduling stats:
 */
static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &p->se;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                dequeue_entity(cfs_rq, se, flags);
                /* Don't dequeue parent if it has other entities besides us */
                if (cfs_rq->load.weight)
                        break;
                flags |= DEQUEUE_SLEEP;
        }

        hrtick_update(rq);
}

/*
 * sched_yield() support is very simple - we dequeue and enqueue.
 *
 * If compat_yield is turned on then we requeue to the end of the tree.
 */
static void yield_task_fair(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
        struct sched_entity *rightmost, *se = &curr->se;

        /*
         * Are we the only task in the tree?
         */
        if (unlikely(cfs_rq->nr_running == 1))
                return;

        clear_buddies(cfs_rq, se);

        if (likely(!sysctl_sched_compat_yield) && curr->policy != SCHED_BATCH) {
                update_rq_clock(rq);
                /*
                 * Update run-time statistics of the 'current'.
                 */
                update_curr(cfs_rq);

                return;
        }
        /*
         * Find the rightmost entry in the rbtree:
         */
        rightmost = __pick_last_entity(cfs_rq);
        /*
         * Already in the rightmost position?
         */
        if (unlikely(!rightmost || entity_before(rightmost, se)))
                return;

        /*
         * Minimally necessary key value to be last in the tree:
         * Upon rescheduling, sched_class::put_prev_task() will place
         * 'current' within the tree based on its new key value.
         */
        se->vruntime = rightmost->vruntime + 1;
}

#ifdef CONFIG_SMP

static void task_waking_fair(struct rq *rq, struct task_struct *p)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        se->vruntime -= cfs_rq->min_vruntime;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
/*
 * effective_load() calculates the load change as seen from the root_task_group
 *
 * Adding load to a group doesn't make a group heavier, but can cause movement
 * of group shares between cpus. Assuming the shares were perfectly aligned one
 * can calculate the shift in shares.
 *
 * The problem is that perfectly aligning the shares is rather expensive, hence
 * we try to avoid doing that too often - see update_shares(), which ratelimits
 * this change.
 *
 * We compensate this by not only taking the current delta into account, but
 * also considering the delta between when the shares were last adjusted and
 * now.
 *
 * We still saw a performance dip, some tracing learned us that between
 * cgroup:/ and cgroup:/foo balancing the number of affine wakeups increased
 * significantly. Therefore try to bias the error in direction of failing
 * the affine wakeup.
 *
 */
static long effective_load(struct task_group *tg, int cpu,
                long wl, long wg)
{
        struct sched_entity *se = tg->se[cpu];

        if (!tg->parent)
                return wl;

        /*
         * By not taking the decrease of shares on the other cpu into
         * account our error leans towards reducing the affine wakeups.
         */
        if (!wl && sched_feat(ASYM_EFF_LOAD))
                return wl;

        for_each_sched_entity(se) {
                long S, rw, s, a, b;
                long more_w;

                /*
                 * Instead of using this increment, also add the difference
                 * between when the shares were last updated and now.
                 */
                more_w = se->my_q->load.weight - se->my_q->rq_weight;
                wl += more_w;
                wg += more_w;

                S = se->my_q->tg->shares;
                s = se->my_q->shares;
                rw = se->my_q->rq_weight;

                a = S*(rw + wl);
                b = S*rw + s*wg;

                wl = s*(a-b);

                if (likely(b))
                        wl /= b;

                /*
                 * Assume the group is already running and will
                 * thus already be accounted for in the weight.
                 *
                 * That is, moving shares between CPUs, does not
                 * alter the group weight.
                 */
                wg = 0;
        }

        return wl;
}

#else

static inline unsigned long effective_load(struct task_group *tg, int cpu,
                unsigned long wl, unsigned long wg)
{
        return wl;
}

#endif

static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
{
        unsigned long this_load, load;
        int idx, this_cpu, prev_cpu;
        unsigned long tl_per_task;
        unsigned int imbalance;
        struct task_group *tg;
        unsigned long weight;
        int balanced;

        idx       = sd->wake_idx;
        this_cpu  = smp_processor_id();
        prev_cpu  = task_cpu(p);
        load      = source_load(prev_cpu, idx);
        this_load = target_load(this_cpu, idx);

        /*
         * If sync wakeup then subtract the (maximum possible)
         * effect of the currently running task from the load
         * of the current CPU:
         */
        if (sync) {
                tg = task_group(current);
                weight = current->se.load.weight;

                this_load += effective_load(tg, this_cpu, -weight, -weight);
                load += effective_load(tg, prev_cpu, 0, -weight);
        }

        tg = task_group(p);
        weight = p->se.load.weight;

        imbalance = 100 + (sd->imbalance_pct - 100) / 2;

        /*
         * In low-load situations, where prev_cpu is idle and this_cpu is idle
         * due to the sync cause above having dropped this_load to 0, we'll
         * always have an imbalance, but there's really nothing you can do
         * about that, so that's good too.
         *
         * Otherwise check if either cpus are near enough in load to allow this
         * task to be woken on this_cpu.
         */
        balanced = !this_load ||
                100*(this_load + effective_load(tg, this_cpu, weight, weight)) <=
                imbalance*(load + effective_load(tg, prev_cpu, 0, weight));

        /*
         * If the currently running task will sleep within
         * a reasonable amount of time then attract this newly
         * woken task:
         */
        if (sync && balanced)
                return 1;

        schedstat_inc(p, se.statistics.nr_wakeups_affine_attempts);
        tl_per_task = cpu_avg_load_per_task(this_cpu);

        if (balanced ||
            (this_load <= load &&
             this_load + target_load(prev_cpu, idx) <= tl_per_task)) {
                /*
                 * This domain has SD_WAKE_AFFINE and
                 * p is cache cold in this domain, and
                 * there is no bad imbalance.
                 */
                schedstat_inc(sd, ttwu_move_affine);
                schedstat_inc(p, se.statistics.nr_wakeups_affine);

                return 1;
        }
        return 0;
}

/*
 * find_idlest_group finds and returns the least busy CPU group within the
 * domain.
 */
static struct sched_group *
find_idlest_group(struct sched_domain *sd, struct task_struct *p,
                  int this_cpu, int load_idx)
{
        struct sched_group *idlest = NULL, *this = NULL, *group = sd->groups;
        unsigned long min_load = ULONG_MAX, this_load = 0;
        int imbalance = 100 + (sd->imbalance_pct-100)/2;

        do {
                unsigned long load, avg_load;
                int local_group;
                int i;

                /* Skip over this group if it has no CPUs allowed */
                if (!cpumask_intersects(sched_group_cpus(group),
                                        &p->cpus_allowed))
                        continue;

                local_group = cpumask_test_cpu(this_cpu,
                                               sched_group_cpus(group));

                /* Tally up the load of all CPUs in the group */
                avg_load = 0;

                for_each_cpu(i, sched_group_cpus(group)) {
                        /* Bias balancing toward cpus of our domain */
                        if (local_group)
                                load = source_load(i, load_idx);
                        else
                                load = target_load(i, load_idx);

                        avg_load += load;
                }

                /* Adjust by relative CPU power of the group */
                avg_load = (avg_load * SCHED_LOAD_SCALE) / group->cpu_power;

                if (local_group) {
                        this_load = avg_load;
                        this = group;
                } else if (avg_load < min_load) {
                        min_load = avg_load;
                        idlest = group;
                }
        } while (group = group->next, group != sd->groups);

        if (!idlest || 100*this_load < imbalance*min_load)
                return NULL;
        return idlest;
}

/*
 * find_idlest_cpu - find the idlest cpu among the cpus in group.
 */
static int
find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
{
        unsigned long load, min_load = ULONG_MAX;
        int idlest = -1;
        int i;

        /* Traverse only the allowed CPUs */
        for_each_cpu_and(i, sched_group_cpus(group), &p->cpus_allowed) {
                load = weighted_cpuload(i);

                if (load < min_load || (load == min_load && i == this_cpu)) {
                        min_load = load;
                        idlest = i;
                }
        }

        return idlest;
}

/*
 * Try and locate an idle CPU in the sched_domain.
 */
static int
select_idle_sibling(struct task_struct *p, struct sched_domain *sd, int target)
{
        int cpu = smp_processor_id();
        int prev_cpu = task_cpu(p);
        int i;

        /*
         * If this domain spans both cpu and prev_cpu (see the SD_WAKE_AFFINE
         * test in select_task_rq_fair) and the prev_cpu is idle then that's
         * always a better target than the current cpu.
         */
        if (target == cpu && !cpu_rq(prev_cpu)->cfs.nr_running)
                return prev_cpu;

        /*
         * Otherwise, iterate the domain and find an elegible idle cpu.
         */
        for_each_cpu_and(i, sched_domain_span(sd), &p->cpus_allowed) {
                if (!cpu_rq(i)->cfs.nr_running) {
                        target = i;
                        break;
                }
        }

        return target;
}

/*
 * sched_balance_self: balance the current task (running on cpu) in domains
 * that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
 * SD_BALANCE_EXEC.
 *
 * Balance, ie. select the least loaded group.
 *
 * Returns the target CPU number, or the same CPU if no balancing is needed.
 *
 * preempt must be disabled.
 */
static int
select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_flags)
{
        struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
        int cpu = smp_processor_id();
        int prev_cpu = task_cpu(p);
        int new_cpu = cpu;
        int want_affine = 0, cpu_idle = !current->pid;
        int want_sd = 1;
        int sync = wake_flags & WF_SYNC;

        if (sd_flag & SD_BALANCE_WAKE) {
                if (cpumask_test_cpu(cpu, &p->cpus_allowed))
                        want_affine = 1;
                new_cpu = prev_cpu;
        }

        for_each_domain(cpu, tmp) {
                if (!(tmp->flags & SD_LOAD_BALANCE))
                        continue;

                /*
                 * If power savings logic is enabled for a domain, see if we
                 * are not overloaded, if so, don't balance wider.
                 */
                if (tmp->flags & (SD_POWERSAVINGS_BALANCE|SD_PREFER_LOCAL)) {
                        unsigned long power = 0;
                        unsigned long nr_running = 0;
                        unsigned long capacity;
                        int i;

                        for_each_cpu(i, sched_domain_span(tmp)) {
                                power += power_of(i);
                                nr_running += cpu_rq(i)->cfs.nr_running;
                        }

                        capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);

                        if (tmp->flags & SD_POWERSAVINGS_BALANCE)
                                nr_running /= 2;

                        if (nr_running < capacity)
                                want_sd = 0;
                }

                /*
                 * While iterating the domains looking for a spanning
                 * WAKE_AFFINE domain, adjust the affine target to any idle cpu
                 * in cache sharing domains along the way.
                 */
                if (want_affine) {
                        int target = -1;

                        /*
                         * If both cpu and prev_cpu are part of this domain,
                         * cpu is a valid SD_WAKE_AFFINE target.
                         */
                        if (cpumask_test_cpu(prev_cpu, sched_domain_span(tmp)))
                                target = cpu;

                        /*
                         * If there's an idle sibling in this domain, make that
                         * the wake_affine target instead of the current cpu.
                         */
                        if (!cpu_idle && tmp->flags & SD_SHARE_PKG_RESOURCES)
                                target = select_idle_sibling(p, tmp, target);

                        if (target >= 0) {
                                if (tmp->flags & SD_WAKE_AFFINE) {
                                        affine_sd = tmp;
                                        want_affine = 0;
                                        if (target != cpu)
                                                cpu_idle = 1;
                                }
                                cpu = target;
                        }
                }

                if (!want_sd && !want_affine)
                        break;

                if (!(tmp->flags & sd_flag))
                        continue;

                if (want_sd)
                        sd = tmp;
        }

#ifdef CONFIG_FAIR_GROUP_SCHED
        if (sched_feat(LB_SHARES_UPDATE)) {
                /*
                 * Pick the largest domain to update shares over
                 */
                tmp = sd;
                if (affine_sd && (!tmp ||
                                  cpumask_weight(sched_domain_span(affine_sd)) >
                                  cpumask_weight(sched_domain_span(sd))))
                        tmp = affine_sd;

                if (tmp) {
                        raw_spin_unlock(&rq->lock);
                        update_shares(tmp);
                        raw_spin_lock(&rq->lock);
                }
        }
#endif

        if (affine_sd) {
                if (cpu_idle || cpu == prev_cpu || wake_affine(affine_sd, p, sync))
                        return cpu;
        }

        while (sd) {
                int load_idx = sd->forkexec_idx;
                struct sched_group *group;
                int weight;

                if (!(sd->flags & sd_flag)) {
                        sd = sd->child;
                        continue;
                }

                if (sd_flag & SD_BALANCE_WAKE)
                        load_idx = sd->wake_idx;

                group = find_idlest_group(sd, p, cpu, load_idx);
                if (!group) {
                        sd = sd->child;
                        continue;
                }

                new_cpu = find_idlest_cpu(group, p, cpu);
                if (new_cpu == -1 || new_cpu == cpu) {
                        /* Now try balancing at a lower domain level of cpu */
                        sd = sd->child;
                        continue;
                }

                /* Now try balancing at a lower domain level of new_cpu */
                cpu = new_cpu;
                weight = cpumask_weight(sched_domain_span(sd));
                sd = NULL;
                for_each_domain(cpu, tmp) {
                        if (weight <= cpumask_weight(sched_domain_span(tmp)))
                                break;
                        if (tmp->flags & sd_flag)
                                sd = tmp;
                }
                /* while loop will break here if sd == NULL */
        }

        return new_cpu;
}
#endif /* CONFIG_SMP */

static unsigned long
wakeup_gran(struct sched_entity *curr, struct sched_entity *se)
{
        unsigned long gran = sysctl_sched_wakeup_granularity;

        /*
         * Since its curr running now, convert the gran from real-time
         * to virtual-time in his units.
         *
         * By using 'se' instead of 'curr' we penalize light tasks, so
         * they get preempted easier. That is, if 'se' < 'curr' then
         * the resulting gran will be larger, therefore penalizing the
         * lighter, if otoh 'se' > 'curr' then the resulting gran will
         * be smaller, again penalizing the lighter task.
         *
         * This is especially important for buddies when the leftmost
         * task is higher priority than the buddy.
         */
        if (unlikely(se->load.weight != NICE_0_LOAD))
                gran = calc_delta_fair(gran, se);

        return gran;
}

/*
 * Should 'se' preempt 'curr'.
 *
 *             |s1
 *        |s2
 *   |s3
 *         g
 *      |<--->|c
 *
 *  w(c, s1) = -1
 *  w(c, s2) =  0
 *  w(c, s3) =  1
 *
 */
static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
{
        s64 gran, vdiff = curr->vruntime - se->vruntime;

        if (vdiff <= 0)
                return -1;

        gran = wakeup_gran(curr, se);
        if (vdiff > gran)
                return 1;

        return 0;
}

static void set_last_buddy(struct sched_entity *se)
{
        if (likely(task_of(se)->policy != SCHED_IDLE)) {
                for_each_sched_entity(se)
                        cfs_rq_of(se)->last = se;
        }
}

static void set_next_buddy(struct sched_entity *se)
{
        if (likely(task_of(se)->policy != SCHED_IDLE)) {
                for_each_sched_entity(se)
                        cfs_rq_of(se)->next = se;
        }
}

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
{
        struct task_struct *curr = rq->curr;
        struct sched_entity *se = &curr->se, *pse = &p->se;
        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
        int scale = cfs_rq->nr_running >= sched_nr_latency;

        if (unlikely(rt_prio(p->prio)))
                goto preempt;

        if (unlikely(p->sched_class != &fair_sched_class))
                return;

        if (unlikely(se == pse))
                return;

        if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK))
                set_next_buddy(pse);

        /*
         * We can come here with TIF_NEED_RESCHED already set from new task
         * wake up path.
         */
        if (test_tsk_need_resched(curr))
                return;

        /*
         * Batch and idle tasks do not preempt (their preemption is driven by
         * the tick):
         */
        if (unlikely(p->policy != SCHED_NORMAL))
                return;

        /* Idle tasks are by definition preempted by everybody. */
        if (unlikely(curr->policy == SCHED_IDLE))
                goto preempt;

        if (!sched_feat(WAKEUP_PREEMPT))
                return;

        update_curr(cfs_rq);
        find_matching_se(&se, &pse);
        BUG_ON(!pse);
        if (wakeup_preempt_entity(se, pse) == 1)
                goto preempt;

        return;

preempt:
        resched_task(curr);
        /*
         * Only set the backward buddy when the current task is still
         * on the rq. This can happen when a wakeup gets interleaved
         * with schedule on the ->pre_schedule() or idle_balance()
         * point, either of which can * drop the rq lock.
         *
         * Also, during early boot the idle thread is in the fair class,
         * for obvious reasons its a bad idea to schedule back to it.
         */
        if (unlikely(!se->on_rq || curr == rq->idle))
                return;

        if (sched_feat(LAST_BUDDY) && scale && entity_is_task(se))
                set_last_buddy(se);
}

static struct task_struct *pick_next_task_fair(struct rq *rq)
{
        struct task_struct *p;
        struct cfs_rq *cfs_rq = &rq->cfs;
        struct sched_entity *se;

        if (!cfs_rq->nr_running)
                return NULL;

        do {
                se = pick_next_entity(cfs_rq);
                set_next_entity(cfs_rq, se);
                cfs_rq = group_cfs_rq(se);
        } while (cfs_rq);

        p = task_of(se);
        hrtick_start_fair(rq, p);

        return p;
}

/*
 * Account for a descheduled task:
 */
static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
{
        struct sched_entity *se = &prev->se;
        struct cfs_rq *cfs_rq;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                put_prev_entity(cfs_rq, se);
        }
}

#ifdef CONFIG_SMP
/**************************************************
 * Fair scheduling class load-balancing methods:
 */

/*
 * pull_task - move a task from a remote runqueue to the local runqueue.
 * Both runqueues must be locked.
 */
static void pull_task(struct rq *src_rq, struct task_struct *p,
                      struct rq *this_rq, int this_cpu)
{
        deactivate_task(src_rq, p, 0);
        set_task_cpu(p, this_cpu);
        activate_task(this_rq, p, 0);
        check_preempt_curr(this_rq, p, 0);
}

/*
 * can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
 */
static
int can_migrate_task(struct task_struct *p, struct rq *rq, int this_cpu,
                     struct sched_domain *sd, enum cpu_idle_type idle,
                     int *all_pinned)
{
        int tsk_cache_hot = 0;
        /*
         * We do not migrate tasks that are:
         * 1) running (obviously), or
         * 2) cannot be migrated to this CPU due to cpus_allowed, or
         * 3) are cache-hot on their current CPU.
         */
        if (!cpumask_test_cpu(this_cpu, &p->cpus_allowed)) {
                schedstat_inc(p, se.statistics.nr_failed_migrations_affine);
                return 0;
        }
        *all_pinned = 0;

        if (task_running(rq, p)) {
                schedstat_inc(p, se.statistics.nr_failed_migrations_running);
                return 0;
        }

        /*
         * Aggressive migration if:
         * 1) task is cache cold, or
         * 2) too many balance attempts have failed.
         */

        tsk_cache_hot = task_hot(p, rq->clock, sd);
        if (!tsk_cache_hot ||
                sd->nr_balance_failed > sd->cache_nice_tries) {
#ifdef CONFIG_SCHEDSTATS
                if (tsk_cache_hot) {
                        schedstat_inc(sd, lb_hot_gained[idle]);
                        schedstat_inc(p, se.statistics.nr_forced_migrations);
                }
#endif
                return 1;
        }

        if (tsk_cache_hot) {
                schedstat_inc(p, se.statistics.nr_failed_migrations_hot);
                return 0;
        }
        return 1;
}

/*
 * move_one_task tries to move exactly one task from busiest to this_rq, as
 * part of active balancing operations within "domain".
 * Returns 1 if successful and 0 otherwise.
 *
 * Called with both runqueues locked.
 */
static int
move_one_task(struct rq *this_rq, int this_cpu, struct rq *busiest,
              struct sched_domain *sd, enum cpu_idle_type idle)
{
        struct task_struct *p, *n;
        struct cfs_rq *cfs_rq;
        int pinned = 0;

        for_each_leaf_cfs_rq(busiest, cfs_rq) {
                list_for_each_entry_safe(p, n, &cfs_rq->tasks, se.group_node) {

                        if (!can_migrate_task(p, busiest, this_cpu,
                                                sd, idle, &pinned))
                                continue;

                        pull_task(busiest, p, this_rq, this_cpu);
                        /*
                         * Right now, this is only the second place pull_task()
                         * is called, so we can safely collect pull_task()
                         * stats here rather than inside pull_task().
                         */
                        schedstat_inc(sd, lb_gained[idle]);
                        return 1;
                }
        }

        return 0;
}

static unsigned long
balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
              unsigned long max_load_move, struct sched_domain *sd,
              enum cpu_idle_type idle, int *all_pinned,
              int *this_best_prio, struct cfs_rq *busiest_cfs_rq)
{
        int loops = 0, pulled = 0, pinned = 0;
        long rem_load_move = max_load_move;
        struct task_struct *p, *n;

        if (max_load_move == 0)
                goto out;

        pinned = 1;

        list_for_each_entry_safe(p, n, &busiest_cfs_rq->tasks, se.group_node) {
                if (loops++ > sysctl_sched_nr_migrate)
                        break;

                if ((p->se.load.weight >> 1) > rem_load_move ||
                    !can_migrate_task(p, busiest, this_cpu, sd, idle, &pinned))
                        continue;

                pull_task(busiest, p, this_rq, this_cpu);
                pulled++;
                rem_load_move -= p->se.load.weight;

#ifdef CONFIG_PREEMPT
                /*
                 * NEWIDLE balancing is a source of latency, so preemptible
                 * kernels will stop after the first task is pulled to minimize
                 * the critical section.
                 */
                if (idle == CPU_NEWLY_IDLE)
                        break;
#endif

                /*
                 * We only want to steal up to the prescribed amount of
                 * weighted load.
                 */
                if (rem_load_move <= 0)
                        break;

                if (p->prio < *this_best_prio)
                        *this_best_prio = p->prio;
        }
out:
        /*
         * Right now, this is one of only two places pull_task() is called,
         * so we can safely collect pull_task() stats here rather than
         * inside pull_task().
         */
        schedstat_add(sd, lb_gained[idle], pulled);

        if (all_pinned)
                *all_pinned = pinned;

        return max_load_move - rem_load_move;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static unsigned long
load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
                  unsigned long max_load_move,
                  struct sched_domain *sd, enum cpu_idle_type idle,
                  int *all_pinned, int *this_best_prio)
{
        long rem_load_move = max_load_move;
        int busiest_cpu = cpu_of(busiest);
        struct task_group *tg;

        rcu_read_lock();
        update_h_load(busiest_cpu);

        list_for_each_entry_rcu(tg, &task_groups, list) {
                struct cfs_rq *busiest_cfs_rq = tg->cfs_rq[busiest_cpu];
                unsigned long busiest_h_load = busiest_cfs_rq->h_load;
                unsigned long busiest_weight = busiest_cfs_rq->load.weight;
                u64 rem_load, moved_load;

                /*
                 * empty group
                 */
                if (!busiest_cfs_rq->task_weight)
                        continue;

                rem_load = (u64)rem_load_move * busiest_weight;
                rem_load = div_u64(rem_load, busiest_h_load + 1);

                moved_load = balance_tasks(this_rq, this_cpu, busiest,
                                rem_load, sd, idle, all_pinned, this_best_prio,
                                busiest_cfs_rq);

                if (!moved_load)
                        continue;

                moved_load *= busiest_h_load;
                moved_load = div_u64(moved_load, busiest_weight + 1);

                rem_load_move -= moved_load;
                if (rem_load_move < 0)
                        break;
        }
        rcu_read_unlock();

        return max_load_move - rem_load_move;
}
#else
static unsigned long
load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
                  unsigned long max_load_move,
                  struct sched_domain *sd, enum cpu_idle_type idle,
                  int *all_pinned, int *this_best_prio)
{
        return balance_tasks(this_rq, this_cpu, busiest,
                        max_load_move, sd, idle, all_pinned,
                        this_best_prio, &busiest->cfs);
}
#endif

/*
 * move_tasks tries to move up to max_load_move weighted load from busiest to
 * this_rq, as part of a balancing operation within domain "sd".
 * Returns 1 if successful and 0 otherwise.
 *
 * Called with both runqueues locked.
 */
static int move_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
                      unsigned long max_load_move,
                      struct sched_domain *sd, enum cpu_idle_type idle,
                      int *all_pinned)
{
        unsigned long total_load_moved = 0, load_moved;
        int this_best_prio = this_rq->curr->prio;

        do {
                load_moved = load_balance_fair(this_rq, this_cpu, busiest,
                                max_load_move - total_load_moved,
                                sd, idle, all_pinned, &this_best_prio);

                total_load_moved += load_moved;

#ifdef CONFIG_PREEMPT
                /*
                 * NEWIDLE balancing is a source of latency, so preemptible
                 * kernels will stop after the first task is pulled to minimize
                 * the critical section.
                 */
                if (idle == CPU_NEWLY_IDLE && this_rq->nr_running)
                        break;

                if (raw_spin_is_contended(&this_rq->lock) ||
                                raw_spin_is_contended(&busiest->lock))
                        break;
#endif
        } while (load_moved && max_load_move > total_load_moved);

        return total_load_moved > 0;
}

/********** Helpers for find_busiest_group ************************/
/*
 * sd_lb_stats - Structure to store the statistics of a sched_domain
 *              during load balancing.
 */
struct sd_lb_stats {
        struct sched_group *busiest; /* Busiest group in this sd */
        struct sched_group *this;  /* Local group in this sd */
        unsigned long total_load;  /* Total load of all groups in sd */
        unsigned long total_pwr;   /*   Total power of all groups in sd */
        unsigned long avg_load;    /* Average load across all groups in sd */

        /** Statistics of this group */
        unsigned long this_load;
        unsigned long this_load_per_task;
        unsigned long this_nr_running;

        /* Statistics of the busiest group */
        unsigned long max_load;
        unsigned long busiest_load_per_task;
        unsigned long busiest_nr_running;
        unsigned long busiest_group_capacity;

        int group_imb; /* Is there imbalance in this sd */
#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
        int power_savings_balance; /* Is powersave balance needed for this sd */
        struct sched_group *group_min; /* Least loaded group in sd */
        struct sched_group *group_leader; /* Group which relieves group_min */
        unsigned long min_load_per_task; /* load_per_task in group_min */
        unsigned long leader_nr_running; /* Nr running of group_leader */
        unsigned long min_nr_running; /* Nr running of group_min */
#endif
};

/*
 * sg_lb_stats - stats of a sched_group required for load_balancing
 */
struct sg_lb_stats {
        unsigned long avg_load; /*Avg load across the CPUs of the group */
        unsigned long group_load; /* Total load over the CPUs of the group */
        unsigned long sum_nr_running; /* Nr tasks running in the group */
        unsigned long sum_weighted_load; /* Weighted load of group's tasks */
        unsigned long group_capacity;
        int group_imb; /* Is there an imbalance in the group ? */
};

/**
 * group_first_cpu - Returns the first cpu in the cpumask of a sched_group.
 * @group: The group whose first cpu is to be returned.
 */
static inline unsigned int group_first_cpu(struct sched_group *group)
{
        return cpumask_first(sched_group_cpus(group));
}

/**
 * get_sd_load_idx - Obtain the load index for a given sched domain.
 * @sd: The sched_domain whose load_idx is to be obtained.
 * @idle: The Idle status of the CPU for whose sd load_icx is obtained.
 */
static inline int get_sd_load_idx(struct sched_domain *sd,
                                        enum cpu_idle_type idle)
{
        int load_idx;

        switch (idle) {
        case CPU_NOT_IDLE:
                load_idx = sd->busy_idx;
                break;

        case CPU_NEWLY_IDLE:
                load_idx = sd->newidle_idx;
                break;
        default:
                load_idx = sd->idle_idx;
                break;
        }

        return load_idx;
}


#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
/**
 * init_sd_power_savings_stats - Initialize power savings statistics for
 * the given sched_domain, during load balancing.
 *
 * @sd: Sched domain whose power-savings statistics are to be initialized.
 * @sds: Variable containing the statistics for sd.
 * @idle: Idle status of the CPU at which we're performing load-balancing.
 */
static inline void init_sd_power_savings_stats(struct sched_domain *sd,
        struct sd_lb_stats *sds, enum cpu_idle_type idle)
{
        /*
         * Busy processors will not participate in power savings
         * balance.
         */
        if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
                sds->power_savings_balance = 0;
        else {
                sds->power_savings_balance = 1;
                sds->min_nr_running = ULONG_MAX;
                sds->leader_nr_running = 0;
        }
}

/**
 * update_sd_power_savings_stats - Update the power saving stats for a
 * sched_domain while performing load balancing.
 *
 * @group: sched_group belonging to the sched_domain under consideration.
 * @sds: Variable containing the statistics of the sched_domain
 * @local_group: Does group contain the CPU for which we're performing
 *              load balancing ?
 * @sgs: Variable containing the statistics of the group.
 */
static inline void update_sd_power_savings_stats(struct sched_group *group,
        struct sd_lb_stats *sds, int local_group, struct sg_lb_stats *sgs)
{

        if (!sds->power_savings_balance)
                return;

        /*
         * If the local group is idle or completely loaded
         * no need to do power savings balance at this domain
         */
        if (local_group && (sds->this_nr_running >= sgs->group_capacity ||
                                !sds->this_nr_running))
                sds->power_savings_balance = 0;

        /*
         * If a group is already running at full capacity or idle,
         * don't include that group in power savings calculations
         */
        if (!sds->power_savings_balance ||
                sgs->sum_nr_running >= sgs->group_capacity ||
                !sgs->sum_nr_running)
                return;

        /*
         * Calculate the group which has the least non-idle load.
         * This is the group from where we need to pick up the load
         * for saving power
         */
        if ((sgs->sum_nr_running < sds->min_nr_running) ||
            (sgs->sum_nr_running == sds->min_nr_running &&
             group_first_cpu(group) > group_first_cpu(sds->group_min))) {
                sds->group_min = group;
                sds->min_nr_running = sgs->sum_nr_running;
                sds->min_load_per_task = sgs->sum_weighted_load /
                                                sgs->sum_nr_running;
        }

        /*
         * Calculate the group which is almost near its
         * capacity but still has some space to pick up some load
         * from other group and save more power
         */
        if (sgs->sum_nr_running + 1 > sgs->group_capacity)
                return;

        if (sgs->sum_nr_running > sds->leader_nr_running ||
            (sgs->sum_nr_running == sds->leader_nr_running &&
             group_first_cpu(group) < group_first_cpu(sds->group_leader))) {
                sds->group_leader = group;
                sds->leader_nr_running = sgs->sum_nr_running;
        }
}

/**
 * check_power_save_busiest_group - see if there is potential for some power-savings balance
 * @sds: Variable containing the statistics of the sched_domain
 *      under consideration.
 * @this_cpu: Cpu at which we're currently performing load-balancing.
 * @imbalance: Variable to store the imbalance.
 *
 * Description:
 * Check if we have potential to perform some power-savings balance.
 * If yes, set the busiest group to be the least loaded group in the
 * sched_domain, so that it's CPUs can be put to idle.
 *
 * Returns 1 if there is potential to perform power-savings balance.
 * Else returns 0.
 */
static inline int check_power_save_busiest_group(struct sd_lb_stats *sds,
                                        int this_cpu, unsigned long *imbalance)
{
        if (!sds->power_savings_balance)
                return 0;

        if (sds->this != sds->group_leader ||
                        sds->group_leader == sds->group_min)
                return 0;

        *imbalance = sds->min_load_per_task;
        sds->busiest = sds->group_min;

        return 1;

}
#else /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
static inline void init_sd_power_savings_stats(struct sched_domain *sd,
        struct sd_lb_stats *sds, enum cpu_idle_type idle)
{
        return;
}

static inline void update_sd_power_savings_stats(struct sched_group *group,
        struct sd_lb_stats *sds, int local_group, struct sg_lb_stats *sgs)
{
        return;
}

static inline int check_power_save_busiest_group(struct sd_lb_stats *sds,
                                        int this_cpu, unsigned long *imbalance)
{
        return 0;
}
#endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */


unsigned long default_scale_freq_power(struct sched_domain *sd, int cpu)
{
        return SCHED_LOAD_SCALE;
}

unsigned long __weak arch_scale_freq_power(struct sched_domain *sd, int cpu)
{
        return default_scale_freq_power(sd, cpu);
}

unsigned long default_scale_smt_power(struct sched_domain *sd, int cpu)
{
        unsigned long weight = cpumask_weight(sched_domain_span(sd));
        unsigned long smt_gain = sd->smt_gain;

        smt_gain /= weight;

        return smt_gain;
}

unsigned long __weak arch_scale_smt_power(struct sched_domain *sd, int cpu)
{
        return default_scale_smt_power(sd, cpu);
}

unsigned long scale_rt_power(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        u64 total, available;

        sched_avg_update(rq);

        total = sched_avg_period() + (rq->clock - rq->age_stamp);
        available = total - rq->rt_avg;

        if (unlikely((s64)total < SCHED_LOAD_SCALE))
                total = SCHED_LOAD_SCALE;

        total >>= SCHED_LOAD_SHIFT;

        return div_u64(available, total);
}

static void update_cpu_power(struct sched_domain *sd, int cpu)
{
        unsigned long weight = cpumask_weight(sched_domain_span(sd));
        unsigned long power = SCHED_LOAD_SCALE;
        struct sched_group *sdg = sd->groups;

        if (sched_feat(ARCH_POWER))
                power *= arch_scale_freq_power(sd, cpu);
        else
                power *= default_scale_freq_power(sd, cpu);

        power >>= SCHED_LOAD_SHIFT;

        if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
                if (sched_feat(ARCH_POWER))
                        power *= arch_scale_smt_power(sd, cpu);
                else
                        power *= default_scale_smt_power(sd, cpu);

                power >>= SCHED_LOAD_SHIFT;
        }

        power *= scale_rt_power(cpu);
        power >>= SCHED_LOAD_SHIFT;

        if (!power)
                power = 1;

        sdg->cpu_power = power;
}

static void update_group_power(struct sched_domain *sd, int cpu)
{
        struct sched_domain *child = sd->child;
        struct sched_group *group, *sdg = sd->groups;
        unsigned long power;

        if (!child) {
                update_cpu_power(sd, cpu);
                return;
        }

        power = 0;

        group = child->groups;
        do {
                power += group->cpu_power;
                group = group->next;
        } while (group != child->groups);

        sdg->cpu_power = power;
}

/**
 * update_sg_lb_stats - Update sched_group's statistics for load balancing.
 * @sd: The sched_domain whose statistics are to be updated.
 * @group: sched_group whose statistics are to be updated.
 * @this_cpu: Cpu for which load balance is currently performed.
 * @idle: Idle status of this_cpu
 * @load_idx: Load index of sched_domain of this_cpu for load calc.
 * @sd_idle: Idle status of the sched_domain containing group.
 * @local_group: Does group contain this_cpu.
 * @cpus: Set of cpus considered for load balancing.
 * @balance: Should we balance.
 * @sgs: variable to hold the statistics for this group.
 */
static inline void update_sg_lb_stats(struct sched_domain *sd,
                        struct sched_group *group, int this_cpu,
                        enum cpu_idle_type idle, int load_idx, int *sd_idle,
                        int local_group, const struct cpumask *cpus,
                        int *balance, struct sg_lb_stats *sgs)
{
        unsigned long load, max_cpu_load, min_cpu_load;
        int i;
        unsigned int balance_cpu = -1, first_idle_cpu = 0;
        unsigned long avg_load_per_task = 0;

        if (local_group)
                balance_cpu = group_first_cpu(group);

        /* Tally up the load of all CPUs in the group */
        max_cpu_load = 0;
        min_cpu_load = ~0UL;

        for_each_cpu_and(i, sched_group_cpus(group), cpus) {
                struct rq *rq = cpu_rq(i);

                if (*sd_idle && rq->nr_running)
                        *sd_idle = 0;

                /* Bias balancing toward cpus of our domain */
                if (local_group) {
                        if (idle_cpu(i) && !first_idle_cpu) {
                                first_idle_cpu = 1;
                                balance_cpu = i;
                        }

                        load = target_load(i, load_idx);
                } else {
                        load = source_load(i, load_idx);
                        if (load > max_cpu_load)
                                max_cpu_load = load;
                        if (min_cpu_load > load)
                                min_cpu_load = load;
                }

                sgs->group_load += load;
                sgs->sum_nr_running += rq->nr_running;
                sgs->sum_weighted_load += weighted_cpuload(i);

        }

        /*
         * First idle cpu or the first cpu(busiest) in this sched group
         * is eligible for doing load balancing at this and above
         * domains. In the newly idle case, we will allow all the cpu's
         * to do the newly idle load balance.
         */
        if (idle != CPU_NEWLY_IDLE && local_group &&
            balance_cpu != this_cpu) {
                *balance = 0;
                return;
        }

        update_group_power(sd, this_cpu);

        /* Adjust by relative CPU power of the group */
        sgs->avg_load = (sgs->group_load * SCHED_LOAD_SCALE) / group->cpu_power;

        /*
         * Consider the group unbalanced when the imbalance is larger
         * than the average weight of two tasks.
         *
         * APZ: with cgroup the avg task weight can vary wildly and
         *      might not be a suitable number - should we keep a
         *      normalized nr_running number somewhere that negates
         *      the hierarchy?
         */
        if (sgs->sum_nr_running)
                avg_load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;

        if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
                sgs->group_imb = 1;

        sgs->group_capacity =
                DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
}

/**
 * update_sd_lb_stats - Update sched_group's statistics for load balancing.
 * @sd: sched_domain whose statistics are to be updated.
 * @this_cpu: Cpu for which load balance is currently performed.
 * @idle: Idle status of this_cpu
 * @sd_idle: Idle status of the sched_domain containing group.
 * @cpus: Set of cpus considered for load balancing.
 * @balance: Should we balance.
 * @sds: variable to hold the statistics for this sched_domain.
 */
static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
                        enum cpu_idle_type idle, int *sd_idle,
                        const struct cpumask *cpus, int *balance,
                        struct sd_lb_stats *sds)
{
        struct sched_domain *child = sd->child;
        struct sched_group *group = sd->groups;
        struct sg_lb_stats sgs;
        int load_idx, prefer_sibling = 0;

        if (child && child->flags & SD_PREFER_SIBLING)
                prefer_sibling = 1;

        init_sd_power_savings_stats(sd, sds, idle);
        load_idx = get_sd_load_idx(sd, idle);

        do {
                int local_group;

                local_group = cpumask_test_cpu(this_cpu,
                                               sched_group_cpus(group));
                memset(&sgs, 0, sizeof(sgs));
                update_sg_lb_stats(sd, group, this_cpu, idle, load_idx, sd_idle,
                                local_group, cpus, balance, &sgs);

                if (local_group && !(*balance))
                        return;

                sds->total_load += sgs.group_load;
                sds->total_pwr += group->cpu_power;

                /*
                 * In case the child domain prefers tasks go to siblings
                 * first, lower the group capacity to one so that we'll try
                 * and move all the excess tasks away.
                 */
                if (prefer_sibling)
                        sgs.group_capacity = min(sgs.group_capacity, 1UL);

                if (local_group) {
                        sds->this_load = sgs.avg_load;
                        sds->this = group;
                        sds->this_nr_running = sgs.sum_nr_running;
                        sds->this_load_per_task = sgs.sum_weighted_load;
                } else if (sgs.avg_load > sds->max_load &&
                           (sgs.sum_nr_running > sgs.group_capacity ||
                                sgs.group_imb)) {
                        sds->max_load = sgs.avg_load;
                        sds->busiest = group;
                        sds->busiest_nr_running = sgs.sum_nr_running;
                        sds->busiest_group_capacity = sgs.group_capacity;
                        sds->busiest_load_per_task = sgs.sum_weighted_load;
                        sds->group_imb = sgs.group_imb;
                }

                update_sd_power_savings_stats(group, sds, local_group, &sgs);
                group = group->next;
        } while (group != sd->groups);
}

/**
 * fix_small_imbalance - Calculate the minor imbalance that exists
 *                      amongst the groups of a sched_domain, during
 *                      load balancing.
 * @sds: Statistics of the sched_domain whose imbalance is to be calculated.
 * @this_cpu: The cpu at whose sched_domain we're performing load-balance.
 * @imbalance: Variable to store the imbalance.
 */
static inline void fix_small_imbalance(struct sd_lb_stats *sds,
                                int this_cpu, unsigned long *imbalance)
{
        unsigned long tmp, pwr_now = 0, pwr_move = 0;
        unsigned int imbn = 2;
        unsigned long scaled_busy_load_per_task;

        if (sds->this_nr_running) {
                sds->this_load_per_task /= sds->this_nr_running;
                if (sds->busiest_load_per_task >
                                sds->this_load_per_task)
                        imbn = 1;
        } else
                sds->this_load_per_task =
                        cpu_avg_load_per_task(this_cpu);

        scaled_busy_load_per_task = sds->busiest_load_per_task
                                                 * SCHED_LOAD_SCALE;
        scaled_busy_load_per_task /= sds->busiest->cpu_power;

        if (sds->max_load - sds->this_load + scaled_busy_load_per_task >=
                        (scaled_busy_load_per_task * imbn)) {
                *imbalance = sds->busiest_load_per_task;
                return;
        }

        /*
         * OK, we don't have enough imbalance to justify moving tasks,
         * however we may be able to increase total CPU power used by
         * moving them.
         */

        pwr_now += sds->busiest->cpu_power *
                        min(sds->busiest_load_per_task, sds->max_load);
        pwr_now += sds->this->cpu_power *
                        min(sds->this_load_per_task, sds->this_load);
        pwr_now /= SCHED_LOAD_SCALE;

        /* Amount of load we'd subtract */
        tmp = (sds->busiest_load_per_task * SCHED_LOAD_SCALE) /
                sds->busiest->cpu_power;
        if (sds->max_load > tmp)
                pwr_move += sds->busiest->cpu_power *
                        min(sds->busiest_load_per_task, sds->max_load - tmp);

        /* Amount of load we'd add */
        if (sds->max_load * sds->busiest->cpu_power <
                sds->busiest_load_per_task * SCHED_LOAD_SCALE)
                tmp = (sds->max_load * sds->busiest->cpu_power) /
                        sds->this->cpu_power;
        else
                tmp = (sds->busiest_load_per_task * SCHED_LOAD_SCALE) /
                        sds->this->cpu_power;
        pwr_move += sds->this->cpu_power *
                        min(sds->this_load_per_task, sds->this_load + tmp);
        pwr_move /= SCHED_LOAD_SCALE;

        /* Move if we gain throughput */
        if (pwr_move > pwr_now)
                *imbalance = sds->busiest_load_per_task;
}

/**
 * calculate_imbalance - Calculate the amount of imbalance present within the
 *                       groups of a given sched_domain during load balance.
 * @sds: statistics of the sched_domain whose imbalance is to be calculated.
 * @this_cpu: Cpu for which currently load balance is being performed.
 * @imbalance: The variable to store the imbalance.
 */
static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
                unsigned long *imbalance)
{
        unsigned long max_pull, load_above_capacity = ~0UL;

        sds->busiest_load_per_task /= sds->busiest_nr_running;
        if (sds->group_imb) {
                sds->busiest_load_per_task =
                        min(sds->busiest_load_per_task, sds->avg_load);
        }

        /*
         * In the presence of smp nice balancing, certain scenarios can have
         * max load less than avg load(as we skip the groups at or below
         * its cpu_power, while calculating max_load..)
         */
        if (sds->max_load < sds->avg_load) {
                *imbalance = 0;
                return fix_small_imbalance(sds, this_cpu, imbalance);
        }

        if (!sds->group_imb) {
                /*
                 * Don't want to pull so many tasks that a group would go idle.
                 */
                load_above_capacity = (sds->busiest_nr_running -
                                                sds->busiest_group_capacity);

                load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_LOAD_SCALE);

                load_above_capacity /= sds->busiest->cpu_power;
        }

        /*
         * We're trying to get all the cpus to the average_load, so we don't
         * want to push ourselves above the average load, nor do we wish to
         * reduce the max loaded cpu below the average load. At the same time,
         * we also don't want to reduce the group load below the group capacity
         * (so that we can implement power-savings policies etc). Thus we look
         * for the minimum possible imbalance.
         * Be careful of negative numbers as they'll appear as very large values
         * with unsigned longs.
         */
        max_pull = min(sds->max_load - sds->avg_load, load_above_capacity);

        /* How much load to actually move to equalise the imbalance */
        *imbalance = min(max_pull * sds->busiest->cpu_power,
                (sds->avg_load - sds->this_load) * sds->this->cpu_power)
                        / SCHED_LOAD_SCALE;

        /*
         * if *imbalance is less than the average load per runnable task
         * there is no gaurantee that any tasks will be moved so we'll have
         * a think about bumping its value to force at least one task to be
         * moved
         */
        if (*imbalance < sds->busiest_load_per_task)
                return fix_small_imbalance(sds, this_cpu, imbalance);

}
/******* find_busiest_group() helpers end here *********************/

/**
 * find_busiest_group - Returns the busiest group within the sched_domain
 * if there is an imbalance. If there isn't an imbalance, and
 * the user has opted for power-savings, it returns a group whose
 * CPUs can be put to idle by rebalancing those tasks elsewhere, if
 * such a group exists.
 *
 * Also calculates the amount of weighted load which should be moved
 * to restore balance.
 *
 * @sd: The sched_domain whose busiest group is to be returned.
 * @this_cpu: The cpu for which load balancing is currently being performed.
 * @imbalance: Variable which stores amount of weighted load which should
 *              be moved to restore balance/put a group to idle.
 * @idle: The idle status of this_cpu.
 * @sd_idle: The idleness of sd
 * @cpus: The set of CPUs under consideration for load-balancing.
 * @balance: Pointer to a variable indicating if this_cpu
 *      is the appropriate cpu to perform load balancing at this_level.
 *
 * Returns:     - the busiest group if imbalance exists.
 *              - If no imbalance and user has opted for power-savings balance,
 *                 return the least loaded group whose CPUs can be
 *                 put to idle by rebalancing its tasks onto our group.
 */
static struct sched_group *
find_busiest_group(struct sched_domain *sd, int this_cpu,
                   unsigned long *imbalance, enum cpu_idle_type idle,
                   int *sd_idle, const struct cpumask *cpus, int *balance)
{
        struct sd_lb_stats sds;

        memset(&sds, 0, sizeof(sds));

        /*
         * Compute the various statistics relavent for load balancing at
         * this level.
         */
        update_sd_lb_stats(sd, this_cpu, idle, sd_idle, cpus,
                                        balance, &sds);

        /* Cases where imbalance does not exist from POV of this_cpu */
        /* 1) this_cpu is not the appropriate cpu to perform load balancing
         *    at this level.
         * 2) There is no busy sibling group to pull from.
         * 3) This group is the busiest group.
         * 4) This group is more busy than the avg busieness at this
         *    sched_domain.
         * 5) The imbalance is within the specified limit.
         */
        if (!(*balance))
                goto ret;

        if (!sds.busiest || sds.busiest_nr_running == 0)
                goto out_balanced;

        if (sds.this_load >= sds.max_load)
                goto out_balanced;

        sds.avg_load = (SCHED_LOAD_SCALE * sds.total_load) / sds.total_pwr;

        if (sds.this_load >= sds.avg_load)
                goto out_balanced;

        if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load)
                goto out_balanced;

        /* Looks like there is an imbalance. Compute it */
        calculate_imbalance(&sds, this_cpu, imbalance);
        return sds.busiest;

out_balanced:
        /*
         * There is no obvious imbalance. But check if we can do some balancing
         * to save power.
         */
        if (check_power_save_busiest_group(&sds, this_cpu, imbalance))
                return sds.busiest;
ret:
        *imbalance = 0;
        return NULL;
}

/*
 * find_busiest_queue - find the busiest runqueue among the cpus in group.
 */
static struct rq *
find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
                   unsigned long imbalance, const struct cpumask *cpus)
{
        struct rq *busiest = NULL, *rq;
        unsigned long max_load = 0;
        int i;

        for_each_cpu(i, sched_group_cpus(group)) {
                unsigned long power = power_of(i);
                unsigned long capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
                unsigned long wl;

                if (!cpumask_test_cpu(i, cpus))
                        continue;

                rq = cpu_rq(i);
                wl = weighted_cpuload(i);

                /*
                 * When comparing with imbalance, use weighted_cpuload()
                 * which is not scaled with the cpu power.
                 */
                if (capacity && rq->nr_running == 1 && wl > imbalance)
                        continue;

                /*
                 * For the load comparisons with the other cpu's, consider
                 * the weighted_cpuload() scaled with the cpu power, so that
                 * the load can be moved away from the cpu that is potentially
                 * running at a lower capacity.
                 */
                wl = (wl * SCHED_LOAD_SCALE) / power;

                if (wl > max_load) {
                        max_load = wl;
                        busiest = rq;
                }
        }

        return busiest;
}

/*
 * Max backoff if we encounter pinned tasks. Pretty arbitrary value, but
 * so long as it is large enough.
 */
#define MAX_PINNED_INTERVAL     512

/* Working cpumask for load_balance and load_balance_newidle. */
static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);

static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle)
{
        if (idle == CPU_NEWLY_IDLE) {
                /*
                 * The only task running in a non-idle cpu can be moved to this
                 * cpu in an attempt to completely freeup the other CPU
                 * package.
                 *
                 * The package power saving logic comes from
                 * find_busiest_group(). If there are no imbalance, then
                 * f_b_g() will return NULL. However when sched_mc={1,2} then
                 * f_b_g() will select a group from which a running task may be
                 * pulled to this cpu in order to make the other package idle.
                 * If there is no opportunity to make a package idle and if
                 * there are no imbalance, then f_b_g() will return NULL and no
                 * action will be taken in load_balance_newidle().
                 *
                 * Under normal task pull operation due to imbalance, there
                 * will be more than one task in the source run queue and
                 * move_tasks() will succeed.  ld_moved will be true and this
                 * active balance code will not be triggered.
                 */
                if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
                    !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
                        return 0;

                if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
                        return 0;
        }

        return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
}

/*
 * Check this_cpu to ensure it is balanced within domain. Attempt to move
 * tasks if there is an imbalance.
 */
static int load_balance(int this_cpu, struct rq *this_rq,
                        struct sched_domain *sd, enum cpu_idle_type idle,
                        int *balance)
{
        int ld_moved, all_pinned = 0, active_balance = 0, sd_idle = 0;
        struct sched_group *group;
        unsigned long imbalance;
        struct rq *busiest;
        unsigned long flags;
        struct cpumask *cpus = __get_cpu_var(load_balance_tmpmask);

        cpumask_copy(cpus, cpu_active_mask);

        /*
         * When power savings policy is enabled for the parent domain, idle
         * sibling can pick up load irrespective of busy siblings. In this case,
         * let the state of idle sibling percolate up as CPU_IDLE, instead of
         * portraying it as CPU_NOT_IDLE.
         */
        if (idle != CPU_NOT_IDLE && sd->flags & SD_SHARE_CPUPOWER &&
            !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
                sd_idle = 1;

        schedstat_inc(sd, lb_count[idle]);

redo:
        update_shares(sd);
        group = find_busiest_group(sd, this_cpu, &imbalance, idle, &sd_idle,
                                   cpus, balance);

        if (*balance == 0)
                goto out_balanced;

        if (!group) {
                schedstat_inc(sd, lb_nobusyg[idle]);
                goto out_balanced;
        }

        busiest = find_busiest_queue(group, idle, imbalance, cpus);
        if (!busiest) {
                schedstat_inc(sd, lb_nobusyq[idle]);
                goto out_balanced;
        }

        BUG_ON(busiest == this_rq);

        schedstat_add(sd, lb_imbalance[idle], imbalance);

        ld_moved = 0;
        if (busiest->nr_running > 1) {
                /*
                 * Attempt to move tasks. If find_busiest_group has found
                 * an imbalance but busiest->nr_running <= 1, the group is
                 * still unbalanced. ld_moved simply stays zero, so it is
                 * correctly treated as an imbalance.
                 */
                local_irq_save(flags);
                double_rq_lock(this_rq, busiest);
                ld_moved = move_tasks(this_rq, this_cpu, busiest,
                                      imbalance, sd, idle, &all_pinned);
                double_rq_unlock(this_rq, busiest);
                local_irq_restore(flags);

                /*
                 * some other cpu did the load balance for us.
                 */
                if (ld_moved && this_cpu != smp_processor_id())
                        resched_cpu(this_cpu);

                /* All tasks on this runqueue were pinned by CPU affinity */
                if (unlikely(all_pinned)) {
                        cpumask_clear_cpu(cpu_of(busiest), cpus);
                        if (!cpumask_empty(cpus))
                                goto redo;
                        goto out_balanced;
                }
        }

        if (!ld_moved) {
                schedstat_inc(sd, lb_failed[idle]);
                sd->nr_balance_failed++;

                if (need_active_balance(sd, sd_idle, idle)) {
                        raw_spin_lock_irqsave(&busiest->lock, flags);

                        /* don't kick the migration_thread, if the curr
                         * task on busiest cpu can't be moved to this_cpu
                         */
                        if (!cpumask_test_cpu(this_cpu,
                                              &busiest->curr->cpus_allowed)) {
                                raw_spin_unlock_irqrestore(&busiest->lock,
                                                            flags);
                                all_pinned = 1;
                                goto out_one_pinned;
                        }

                        if (!busiest->active_balance) {
                                busiest->active_balance = 1;
                                busiest->push_cpu = this_cpu;
                                active_balance = 1;
                        }
                        raw_spin_unlock_irqrestore(&busiest->lock, flags);
                        if (active_balance)
                                wake_up_process(busiest->migration_thread);

                        /*
                         * We've kicked active balancing, reset the failure
                         * counter.
                         */
                        sd->nr_balance_failed = sd->cache_nice_tries+1;
                }
        } else
                sd->nr_balance_failed = 0;

        if (likely(!active_balance)) {
                /* We were unbalanced, so reset the balancing interval */
                sd->balance_interval = sd->min_interval;
        } else {
                /*
                 * If we've begun active balancing, start to back off. This
                 * case may not be covered by the all_pinned logic if there
                 * is only 1 task on the busy runqueue (because we don't call
                 * move_tasks).
                 */
                if (sd->balance_interval < sd->max_interval)
                        sd->balance_interval *= 2;
        }

        if (!ld_moved && !sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
            !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
                ld_moved = -1;

        goto out;

out_balanced:
        schedstat_inc(sd, lb_balanced[idle]);

        sd->nr_balance_failed = 0;

out_one_pinned:
        /* tune up the balancing interval */
        if ((all_pinned && sd->balance_interval < MAX_PINNED_INTERVAL) ||
                        (sd->balance_interval < sd->max_interval))
                sd->balance_interval *= 2;

        if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
            !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
                ld_moved = -1;
        else
                ld_moved = 0;
out:
        if (ld_moved)
                update_shares(sd);
        return ld_moved;
}

/*
 * idle_balance is called by schedule() if this_cpu is about to become
 * idle. Attempts to pull tasks from other CPUs.
 */
static void idle_balance(int this_cpu, struct rq *this_rq)
{
        struct sched_domain *sd;
        int pulled_task = 0;
        unsigned long next_balance = jiffies + HZ;

        this_rq->idle_stamp = this_rq->clock;

        if (this_rq->avg_idle < sysctl_sched_migration_cost)
                return;

        /*
         * Drop the rq->lock, but keep IRQ/preempt disabled.
         */
        raw_spin_unlock(&this_rq->lock);

        for_each_domain(this_cpu, sd) {
                unsigned long interval;
                int balance = 1;

                if (!(sd->flags & SD_LOAD_BALANCE))
                        continue;

                if (sd->flags & SD_BALANCE_NEWIDLE) {
                        /* If we've pulled tasks over stop searching: */
                        pulled_task = load_balance(this_cpu, this_rq,
                                                   sd, CPU_NEWLY_IDLE, &balance);
                }

                interval = msecs_to_jiffies(sd->balance_interval);
                if (time_after(next_balance, sd->last_balance + interval))
                        next_balance = sd->last_balance + interval;
                if (pulled_task) {
                        this_rq->idle_stamp = 0;
                        break;
                }
        }

        raw_spin_lock(&this_rq->lock);

        if (pulled_task || time_after(jiffies, this_rq->next_balance)) {
                /*
                 * We are going idle. next_balance may be set based on
                 * a busy processor. So reset next_balance.
                 */
                this_rq->next_balance = next_balance;
        }
}

/*
 * active_load_balance is run by migration threads. It pushes running tasks
 * off the busiest CPU onto idle CPUs. It requires at least 1 task to be
 * running on each physical CPU where possible, and avoids physical /
 * logical imbalances.
 *
 * Called with busiest_rq locked.
 */
static void active_load_balance(struct rq *busiest_rq, int busiest_cpu)
{
        int target_cpu = busiest_rq->push_cpu;
        struct sched_domain *sd;
        struct rq *target_rq;

        /* Is there any task to move? */
        if (busiest_rq->nr_running <= 1)
                return;

        target_rq = cpu_rq(target_cpu);

        /*
         * This condition is "impossible", if it occurs
         * we need to fix it. Originally reported by
         * Bjorn Helgaas on a 128-cpu setup.
         */
        BUG_ON(busiest_rq == target_rq);

        /* move a task from busiest_rq to target_rq */
        double_lock_balance(busiest_rq, target_rq);

        /* Search for an sd spanning us and the target CPU. */
        for_each_domain(target_cpu, sd) {
                if ((sd->flags & SD_LOAD_BALANCE) &&
                    cpumask_test_cpu(busiest_cpu, sched_domain_span(sd)))
                                break;
        }

        if (likely(sd)) {
                schedstat_inc(sd, alb_count);

                if (move_one_task(target_rq, target_cpu, busiest_rq,
                                  sd, CPU_IDLE))
                        schedstat_inc(sd, alb_pushed);
                else
                        schedstat_inc(sd, alb_failed);
        }
        double_unlock_balance(busiest_rq, target_rq);
}

#ifdef CONFIG_NO_HZ
static struct {
        atomic_t load_balancer;
        cpumask_var_t cpu_mask;
        cpumask_var_t ilb_grp_nohz_mask;
} nohz ____cacheline_aligned = {
        .load_balancer = ATOMIC_INIT(-1),
};

int get_nohz_load_balancer(void)
{
        return atomic_read(&nohz.load_balancer);
}

#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
/**
 * lowest_flag_domain - Return lowest sched_domain containing flag.
 * @cpu:        The cpu whose lowest level of sched domain is to
 *              be returned.
 * @flag:       The flag to check for the lowest sched_domain
 *              for the given cpu.
 *
 * Returns the lowest sched_domain of a cpu which contains the given flag.
 */
static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
{
        struct sched_domain *sd;

        for_each_domain(cpu, sd)
                if (sd && (sd->flags & flag))
                        break;

        return sd;
}

/**
 * for_each_flag_domain - Iterates over sched_domains containing the flag.
 * @cpu:        The cpu whose domains we're iterating over.
 * @sd:         variable holding the value of the power_savings_sd
 *              for cpu.
 * @flag:       The flag to filter the sched_domains to be iterated.
 *
 * Iterates over all the scheduler domains for a given cpu that has the 'flag'
 * set, starting from the lowest sched_domain to the highest.
 */
#define for_each_flag_domain(cpu, sd, flag) \
        for (sd = lowest_flag_domain(cpu, flag); \
                (sd && (sd->flags & flag)); sd = sd->parent)

/**
 * is_semi_idle_group - Checks if the given sched_group is semi-idle.
 * @ilb_group:  group to be checked for semi-idleness
 *
 * Returns:     1 if the group is semi-idle. 0 otherwise.
 *
 * We define a sched_group to be semi idle if it has atleast one idle-CPU
 * and atleast one non-idle CPU. This helper function checks if the given
 * sched_group is semi-idle or not.
 */
static inline int is_semi_idle_group(struct sched_group *ilb_group)
{
        cpumask_and(nohz.ilb_grp_nohz_mask, nohz.cpu_mask,
                                        sched_group_cpus(ilb_group));

        /*
         * A sched_group is semi-idle when it has atleast one busy cpu
         * and atleast one idle cpu.
         */
        if (cpumask_empty(nohz.ilb_grp_nohz_mask))
                return 0;

        if (cpumask_equal(nohz.ilb_grp_nohz_mask, sched_group_cpus(ilb_group)))
                return 0;

        return 1;
}
/**
 * find_new_ilb - Finds the optimum idle load balancer for nomination.
 * @cpu:        The cpu which is nominating a new idle_load_balancer.
 *
 * Returns:     Returns the id of the idle load balancer if it exists,
 *              Else, returns >= nr_cpu_ids.
 *
 * This algorithm picks the idle load balancer such that it belongs to a
 * semi-idle powersavings sched_domain. The idea is to try and avoid
 * completely idle packages/cores just for the purpose of idle load balancing
 * when there are other idle cpu's which are better suited for that job.
 */
static int find_new_ilb(int cpu)
{
        struct sched_domain *sd;
        struct sched_group *ilb_group;

        /*
         * Have idle load balancer selection from semi-idle packages only
         * when power-aware load balancing is enabled
         */
        if (!(sched_smt_power_savings || sched_mc_power_savings))
                goto out_done;

        /*
         * Optimize for the case when we have no idle CPUs or only one
         * idle CPU. Don't walk the sched_domain hierarchy in such cases
         */
        if (cpumask_weight(nohz.cpu_mask) < 2)
                goto out_done;

        for_each_flag_domain(cpu, sd, SD_POWERSAVINGS_BALANCE) {
                ilb_group = sd->groups;

                do {
                        if (is_semi_idle_group(ilb_group))
                                return cpumask_first(nohz.ilb_grp_nohz_mask);

                        ilb_group = ilb_group->next;

                } while (ilb_group != sd->groups);
        }

out_done:
        return cpumask_first(nohz.cpu_mask);
}
#else /*  (CONFIG_SCHED_MC || CONFIG_SCHED_SMT) */
static inline int find_new_ilb(int call_cpu)
{
        return cpumask_first(nohz.cpu_mask);
}
#endif

/*
 * This routine will try to nominate the ilb (idle load balancing)
 * owner among the cpus whose ticks are stopped. ilb owner will do the idle
 * load balancing on behalf of all those cpus. If all the cpus in the system
 * go into this tickless mode, then there will be no ilb owner (as there is
 * no need for one) and all the cpus will sleep till the next wakeup event
 * arrives...
 *
 * For the ilb owner, tick is not stopped. And this tick will be used
 * for idle load balancing. ilb owner will still be part of
 * nohz.cpu_mask..
 *
 * While stopping the tick, this cpu will become the ilb owner if there
 * is no other owner. And will be the owner till that cpu becomes busy
 * or if all cpus in the system stop their ticks at which point
 * there is no need for ilb owner.
 *
 * When the ilb owner becomes busy, it nominates another owner, during the
 * next busy scheduler_tick()
 */
int select_nohz_load_balancer(int stop_tick)
{
        int cpu = smp_processor_id();

        if (stop_tick) {
                cpu_rq(cpu)->in_nohz_recently = 1;

                if (!cpu_active(cpu)) {
                        if (atomic_read(&nohz.load_balancer) != cpu)
                                return 0;

                        /*
                         * If we are going offline and still the leader,
                         * give up!
                         */
                        if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
                                BUG();

                        return 0;
                }

                cpumask_set_cpu(cpu, nohz.cpu_mask);

                /* time for ilb owner also to sleep */
                if (cpumask_weight(nohz.cpu_mask) == num_active_cpus()) {
                        if (atomic_read(&nohz.load_balancer) == cpu)
                                atomic_set(&nohz.load_balancer, -1);
                        return 0;
                }

                if (atomic_read(&nohz.load_balancer) == -1) {
                        /* make me the ilb owner */
                        if (atomic_cmpxchg(&nohz.load_balancer, -1, cpu) == -1)
                                return 1;
                } else if (atomic_read(&nohz.load_balancer) == cpu) {
                        int new_ilb;

                        if (!(sched_smt_power_savings ||
                                                sched_mc_power_savings))
                                return 1;
                        /*
                         * Check to see if there is a more power-efficient
                         * ilb.
                         */
                        new_ilb = find_new_ilb(cpu);
                        if (new_ilb < nr_cpu_ids && new_ilb != cpu) {
                                atomic_set(&nohz.load_balancer, -1);
                                resched_cpu(new_ilb);
                                return 0;
                        }
                        return 1;
                }
        } else {
                if (!cpumask_test_cpu(cpu, nohz.cpu_mask))
                        return 0;

                cpumask_clear_cpu(cpu, nohz.cpu_mask);

                if (atomic_read(&nohz.load_balancer) == cpu)
                        if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
                                BUG();
        }
        return 0;
}
#endif

static DEFINE_SPINLOCK(balancing);

/*
 * It checks each scheduling domain to see if it is due to be balanced,
 * and initiates a balancing operation if so.
 *
 * Balancing parameters are set up in arch_init_sched_domains.
 */
static void rebalance_domains(int cpu, enum cpu_idle_type idle)
{
        int balance = 1;
        struct rq *rq = cpu_rq(cpu);
        unsigned long interval;
        struct sched_domain *sd;
        /* Earliest time when we have to do rebalance again */
        unsigned long next_balance = jiffies + 60*HZ;
        int update_next_balance = 0;
        int need_serialize;

        for_each_domain(cpu, sd) {
                if (!(sd->flags & SD_LOAD_BALANCE))
                        continue;

                interval = sd->balance_interval;
                if (idle != CPU_IDLE)
                        interval *= sd->busy_factor;

                /* scale ms to jiffies */
                interval = msecs_to_jiffies(interval);
                if (unlikely(!interval))
                        interval = 1;
                if (interval > HZ*NR_CPUS/10)
                        interval = HZ*NR_CPUS/10;

                need_serialize = sd->flags & SD_SERIALIZE;

                if (need_serialize) {
                        if (!spin_trylock(&balancing))
                                goto out;
                }

                if (time_after_eq(jiffies, sd->last_balance + interval)) {
                        if (load_balance(cpu, rq, sd, idle, &balance)) {
                                /*
                                 * We've pulled tasks over so either we're no
                                 * longer idle, or one of our SMT siblings is
                                 * not idle.
                                 */
                                idle = CPU_NOT_IDLE;
                        }
                        sd->last_balance = jiffies;
                }
                if (need_serialize)
                        spin_unlock(&balancing);
out:
                if (time_after(next_balance, sd->last_balance + interval)) {
                        next_balance = sd->last_balance + interval;
                        update_next_balance = 1;
                }

                /*
                 * Stop the load balance at this level. There is another
                 * CPU in our sched group which is doing load balancing more
                 * actively.
                 */
                if (!balance)
                        break;
        }

        /*
         * next_balance will be updated only when there is a need.
         * When the cpu is attached to null domain for ex, it will not be
         * updated.
         */
        if (likely(update_next_balance))
                rq->next_balance = next_balance;
}

/*
 * run_rebalance_domains is triggered when needed from the scheduler tick.
 * In CONFIG_NO_HZ case, the idle load balance owner will do the
 * rebalancing for all the cpus for whom scheduler ticks are stopped.
 */
static void run_rebalance_domains(struct softirq_action *h)
{
        int this_cpu = smp_processor_id();
        struct rq *this_rq = cpu_rq(this_cpu);
        enum cpu_idle_type idle = this_rq->idle_at_tick ?
                                                CPU_IDLE : CPU_NOT_IDLE;

        rebalance_domains(this_cpu, idle);

#ifdef CONFIG_NO_HZ
        /*
         * If this cpu is the owner for idle load balancing, then do the
         * balancing on behalf of the other idle cpus whose ticks are
         * stopped.
         */
        if (this_rq->idle_at_tick &&
            atomic_read(&nohz.load_balancer) == this_cpu) {
                struct rq *rq;
                int balance_cpu;

                for_each_cpu(balance_cpu, nohz.cpu_mask) {
                        if (balance_cpu == this_cpu)
                                continue;

                        /*
                         * If this cpu gets work to do, stop the load balancing
                         * work being done for other cpus. Next load
                         * balancing owner will pick it up.
                         */
                        if (need_resched())
                                break;

                        rebalance_domains(balance_cpu, CPU_IDLE);

                        rq = cpu_rq(balance_cpu);
                        if (time_after(this_rq->next_balance, rq->next_balance))
                                this_rq->next_balance = rq->next_balance;
                }
        }
#endif
}

static inline int on_null_domain(int cpu)
{
        return !rcu_dereference_sched(cpu_rq(cpu)->sd);
}

/*
 * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
 *
 * In case of CONFIG_NO_HZ, this is the place where we nominate a new
 * idle load balancing owner or decide to stop the periodic load balancing,
 * if the whole system is idle.
 */
static inline void trigger_load_balance(struct rq *rq, int cpu)
{
#ifdef CONFIG_NO_HZ
        /*
         * If we were in the nohz mode recently and busy at the current
         * scheduler tick, then check if we need to nominate new idle
         * load balancer.
         */
        if (rq->in_nohz_recently && !rq->idle_at_tick) {
                rq->in_nohz_recently = 0;

                if (atomic_read(&nohz.load_balancer) == cpu) {
                        cpumask_clear_cpu(cpu, nohz.cpu_mask);
                        atomic_set(&nohz.load_balancer, -1);
                }

                if (atomic_read(&nohz.load_balancer) == -1) {
                        int ilb = find_new_ilb(cpu);

                        if (ilb < nr_cpu_ids)
                                resched_cpu(ilb);
                }
        }

        /*
         * If this cpu is idle and doing idle load balancing for all the
         * cpus with ticks stopped, is it time for that to stop?
         */
        if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) == cpu &&
            cpumask_weight(nohz.cpu_mask) == num_online_cpus()) {
                resched_cpu(cpu);
                return;
        }

        /*
         * If this cpu is idle and the idle load balancing is done by
         * someone else, then no need raise the SCHED_SOFTIRQ
         */
        if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) != cpu &&
            cpumask_test_cpu(cpu, nohz.cpu_mask))
                return;
#endif
        /* Don't need to rebalance while attached to NULL domain */
        if (time_after_eq(jiffies, rq->next_balance) &&
            likely(!on_null_domain(cpu)))
                raise_softirq(SCHED_SOFTIRQ);
}

static void rq_online_fair(struct rq *rq)
{
        update_sysctl();
}

static void rq_offline_fair(struct rq *rq)
{
        update_sysctl();
}

#else   /* CONFIG_SMP */

/*
 * on UP we do not need to balance between CPUs:
 */
static inline void idle_balance(int cpu, struct rq *rq)
{
}

#endif /* CONFIG_SMP */

/*
 * scheduler tick hitting a task of our scheduling class:
 */
static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
{
        struct cfs_rq *cfs_rq;
        struct sched_entity *se = &curr->se;

        for_each_sched_entity(se) {
                cfs_rq = cfs_rq_of(se);
                entity_tick(cfs_rq, se, queued);
        }
}

/*
 * called on fork with the child task as argument from the parent's context
 *  - child not yet on the tasklist
 *  - preemption disabled
 */
static void task_fork_fair(struct task_struct *p)
{
        struct cfs_rq *cfs_rq = task_cfs_rq(current);
        struct sched_entity *se = &p->se, *curr = cfs_rq->curr;
        int this_cpu = smp_processor_id();
        struct rq *rq = this_rq();
        unsigned long flags;

        raw_spin_lock_irqsave(&rq->lock, flags);

        if (unlikely(task_cpu(p) != this_cpu))
                __set_task_cpu(p, this_cpu);

        update_curr(cfs_rq);

        if (curr)
                se->vruntime = curr->vruntime;
        place_entity(cfs_rq, se, 1);

        if (sysctl_sched_child_runs_first && curr && entity_before(curr, se)) {
                /*
                 * Upon rescheduling, sched_class::put_prev_task() will place
                 * 'current' within the tree based on its new key value.
                 */
                swap(curr->vruntime, se->vruntime);
                resched_task(rq->curr);
        }

        se->vruntime -= cfs_rq->min_vruntime;

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

/*
 * Priority of the task has changed. Check to see if we preempt
 * the current task.
 */
static void prio_changed_fair(struct rq *rq, struct task_struct *p,
                              int oldprio, int running)
{
        /*
         * Reschedule if we are currently running on this runqueue and
         * our priority decreased, or if we are not currently running on
         * this runqueue and our priority is higher than the current's
         */
        if (running) {
                if (p->prio > oldprio)
                        resched_task(rq->curr);
        } else
                check_preempt_curr(rq, p, 0);
}

/*
 * We switched to the sched_fair class.
 */
static void switched_to_fair(struct rq *rq, struct task_struct *p,
                             int running)
{
        /*
         * We were most likely switched from sched_rt, so
         * kick off the schedule if running, otherwise just see
         * if we can still preempt the current task.
         */
        if (running)
                resched_task(rq->curr);
        else
                check_preempt_curr(rq, p, 0);
}

/* Account for a task changing its policy or group.
 *
 * This routine is mostly called to set cfs_rq->curr field when a task
 * migrates between groups/classes.
 */
static void set_curr_task_fair(struct rq *rq)
{
        struct sched_entity *se = &rq->curr->se;

        for_each_sched_entity(se)
                set_next_entity(cfs_rq_of(se), se);
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void moved_group_fair(struct task_struct *p, int on_rq)
{
        struct cfs_rq *cfs_rq = task_cfs_rq(p);

        update_curr(cfs_rq);
        if (!on_rq)
                place_entity(cfs_rq, &p->se, 1);
}
#endif

static unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task)
{
        struct sched_entity *se = &task->se;
        unsigned int rr_interval = 0;

        /*
         * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
         * idle runqueue:
         */
        if (rq->cfs.load.weight)
                rr_interval = NS_TO_JIFFIES(sched_slice(&rq->cfs, se));

        return rr_interval;
}

/*
 * All the scheduling class methods:
 */
static const struct sched_class fair_sched_class = {
        .next                   = &idle_sched_class,
        .enqueue_task           = enqueue_task_fair,
        .dequeue_task           = dequeue_task_fair,
        .yield_task             = yield_task_fair,

        .check_preempt_curr     = check_preempt_wakeup,

        .pick_next_task         = pick_next_task_fair,
        .put_prev_task          = put_prev_task_fair,

#ifdef CONFIG_SMP
        .select_task_rq         = select_task_rq_fair,

        .rq_online              = rq_online_fair,
        .rq_offline             = rq_offline_fair,

        .task_waking            = task_waking_fair,
#endif

        .set_curr_task          = set_curr_task_fair,
        .task_tick              = task_tick_fair,
        .task_fork              = task_fork_fair,

        .prio_changed           = prio_changed_fair,
        .switched_to            = switched_to_fair,

        .get_rr_interval        = get_rr_interval_fair,

#ifdef CONFIG_FAIR_GROUP_SCHED
        .moved_group            = moved_group_fair,
#endif
};

#ifdef CONFIG_SCHED_DEBUG
static void print_cfs_stats(struct seq_file *m, int cpu)
{
        struct cfs_rq *cfs_rq;

        rcu_read_lock();
        for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
                print_cfs_rq(m, cpu, cfs_rq);
        rcu_read_unlock();
}
#endif