/*
 * 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>
#include <linux/cpumask.h>
#include <linux/cpuidle.h>
#include <linux/slab.h>
#include <linux/profile.h>
#include <linux/interrupt.h>
#include <linux/mempolicy.h>
#include <linux/migrate.h>
#include <linux/task_work.h>

#include <trace/events/sched.h>

#include "sched.h"

/*
 * Targeted preemption latency for CPU-bound tasks:
 * (default: 6ms * (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: 0.75 msec * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_min_granularity = 750000ULL;
unsigned int normalized_sysctl_sched_min_granularity = 750000ULL;

/*
 * is kept at sysctl_sched_latency / sysctl_sched_min_granularity
 */
static unsigned int sched_nr_latency = 8;

/*
 * 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;

/*
 * 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;

/*
 * The exponential sliding  window over which load is averaged for shares
 * distribution.
 * (default: 10msec)
 */
unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;

#ifdef CONFIG_CFS_BANDWIDTH
/*
 * Amount of runtime to allocate from global (tg) to local (per-cfs_rq) pool
 * each time a cfs_rq requests quota.
 *
 * Note: in the case that the slice exceeds the runtime remaining (either due
 * to consumption or the quota being specified to be smaller than the slice)
 * we will always only issue the remaining available time.
 *
 * default: 5 msec, units: microseconds
  */
unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;
#endif

static inline void update_load_add(struct load_weight *lw, unsigned long inc)
{
        lw->weight += inc;
        lw->inv_weight = 0;
}

static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
{
        lw->weight -= dec;
        lw->inv_weight = 0;
}

static inline void update_load_set(struct load_weight *lw, unsigned long w)
{
        lw->weight = w;
        lw->inv_weight = 0;
}

/*
 * Increase the granularity value when there are more CPUs,
 * because with more CPUs the 'effective latency' as visible
 * to users decreases. But the relationship is not linear,
 * so pick a second-best guess by going with the log2 of the
 * number of CPUs.
 *
 * This idea comes from the SD scheduler of Con Kolivas:
 */
static unsigned int get_update_sysctl_factor(void)
{
        unsigned int cpus = min_t(unsigned int, num_online_cpus(), 8);
        unsigned int factor;

        switch (sysctl_sched_tunable_scaling) {
        case SCHED_TUNABLESCALING_NONE:
                factor = 1;
                break;
        case SCHED_TUNABLESCALING_LINEAR:
                factor = cpus;
                break;
        case SCHED_TUNABLESCALING_LOG:
        default:
                factor = 1 + ilog2(cpus);
                break;
        }

        return factor;
}

static void update_sysctl(void)
{
        unsigned int factor = get_update_sysctl_factor();

#define SET_SYSCTL(name) \
        (sysctl_##name = (factor) * normalized_sysctl_##name)
        SET_SYSCTL(sched_min_granularity);
        SET_SYSCTL(sched_latency);
        SET_SYSCTL(sched_wakeup_granularity);
#undef SET_SYSCTL
}

void sched_init_granularity(void)
{
        update_sysctl();
}

#define WMULT_CONST     (~0U)
#define WMULT_SHIFT     32

static void __update_inv_weight(struct load_weight *lw)
{
        unsigned long w;

        if (likely(lw->inv_weight))
                return;

        w = scale_load_down(lw->weight);

        if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
                lw->inv_weight = 1;
        else if (unlikely(!w))
                lw->inv_weight = WMULT_CONST;
        else
                lw->inv_weight = WMULT_CONST / w;
}

/*
 * delta_exec * weight / lw.weight
 *   OR
 * (delta_exec * (weight * lw->inv_weight)) >> WMULT_SHIFT
 *
 * Either weight := NICE_0_LOAD and lw \e prio_to_wmult[], in which case
 * we're guaranteed shift stays positive because inv_weight is guaranteed to
 * fit 32 bits, and NICE_0_LOAD gives another 10 bits; therefore shift >= 22.
 *
 * Or, weight =< lw.weight (because lw.weight is the runqueue weight), thus
 * weight/lw.weight <= 1, and therefore our shift will also be positive.
 */
static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight *lw)
{
        u64 fact = scale_load_down(weight);
        int shift = WMULT_SHIFT;

        __update_inv_weight(lw);

        if (unlikely(fact >> 32)) {
                while (fact >> 32) {
                        fact >>= 1;
                        shift--;
                }
        }

        /* hint to use a 32x32->64 mul */
        fact = (u64)(u32)fact * lw->inv_weight;

        while (fact >> 32) {
                fact >>= 1;
                shift--;
        }

        return mul_u64_u32_shr(delta_exec, fact, shift);
}


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;
}

static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq,
                                       int force_update);

static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
        if (!cfs_rq->on_list) {
                /*
                 * Ensure we either appear before our parent (if already
                 * enqueued) or force our parent to appear after us when it is
                 * enqueued.  The fact that we always enqueue bottom-up
                 * reduces this to two cases.
                 */
                if (cfs_rq->tg->parent &&
                    cfs_rq->tg->parent->cfs_rq[cpu_of(rq_of(cfs_rq))]->on_list) {
                        list_add_rcu(&cfs_rq->leaf_cfs_rq_list,
                                &rq_of(cfs_rq)->leaf_cfs_rq_list);
                } else {
                        list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
                                &rq_of(cfs_rq)->leaf_cfs_rq_list);
                }

                cfs_rq->on_list = 1;
                /* We should have no load, but we need to update last_decay. */
                update_cfs_rq_blocked_load(cfs_rq, 0);
        }
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
        if (cfs_rq->on_list) {
                list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
                cfs_rq->on_list = 0;
        }
}

/* 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 struct cfs_rq *
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
        if (se->cfs_rq == pse->cfs_rq)
                return se->cfs_rq;

        return NULL;
}

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

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 = (*se)->depth;
        pse_depth = (*pse)->depth;

        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 void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

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

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 */

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec);

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

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

        return max_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 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);
        }

        /* ensure we never gain time by being placed backwards. */
        cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
#ifndef CONFIG_64BIT
        smp_wmb();
        cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
}

/*
 * 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;
        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 (entity_before(se, 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);
}

struct sched_entity *__pick_first_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_next_entity(struct sched_entity *se)
{
        struct rb_node *next = rb_next(&se->run_node);

        if (!next)
                return NULL;

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

#ifdef CONFIG_SCHED_DEBUG
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:
 */

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);
        unsigned 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);
#undef WRT_SYSCTL

        return 0;
}
#endif

/*
 * delta /= w
 */
static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
{
        if (unlikely(se->load.weight != NICE_0_LOAD))
                delta = __calc_delta(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 (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(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);
}

#ifdef CONFIG_SMP
static int select_idle_sibling(struct task_struct *p, int cpu);
static unsigned long task_h_load(struct task_struct *p);

static inline void __update_task_entity_contrib(struct sched_entity *se);
static inline void __update_task_entity_utilization(struct sched_entity *se);

/* Give new task start runnable values to heavy its load in infant time */
void init_task_runnable_average(struct task_struct *p)
{
        u32 slice;

        slice = sched_slice(task_cfs_rq(p), &p->se) >> 10;
        p->se.avg.runnable_avg_sum = p->se.avg.running_avg_sum = slice;
        p->se.avg.avg_period = slice;
        __update_task_entity_contrib(&p->se);
        __update_task_entity_utilization(&p->se);
}
#else
void init_task_runnable_average(struct task_struct *p)
{
}
#endif

/*
 * Update the current task's runtime statistics.
 */
static void update_curr(struct cfs_rq *cfs_rq)
{
        struct sched_entity *curr = cfs_rq->curr;
        u64 now = rq_clock_task(rq_of(cfs_rq));
        u64 delta_exec;

        if (unlikely(!curr))
                return;

        delta_exec = now - curr->exec_start;
        if (unlikely((s64)delta_exec <= 0))
                return;

        curr->exec_start = now;

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

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

        curr->vruntime += calc_delta_fair(delta_exec, curr);
        update_min_vruntime(cfs_rq);

        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);
        }

        account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static void update_curr_fair(struct rq *rq)
{
        update_curr(cfs_rq_of(&rq->curr->se));
}

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

/*
 * 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_clock(rq_of(cfs_rq)) - 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_clock(rq_of(cfs_rq)) - se->statistics.wait_start);
#ifdef CONFIG_SCHEDSTATS
        if (entity_is_task(se)) {
                trace_sched_stat_wait(task_of(se),
                        rq_clock(rq_of(cfs_rq)) - 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_clock_task(rq_of(cfs_rq));
}

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

#ifdef CONFIG_NUMA_BALANCING
/*
 * Approximate time to scan a full NUMA task in ms. The task scan period is
 * calculated based on the tasks virtual memory size and
 * numa_balancing_scan_size.
 */
unsigned int sysctl_numa_balancing_scan_period_min = 1000;
unsigned int sysctl_numa_balancing_scan_period_max = 60000;

/* Portion of address space to scan in MB */
unsigned int sysctl_numa_balancing_scan_size = 256;

/* Scan @scan_size MB every @scan_period after an initial @scan_delay in ms */
unsigned int sysctl_numa_balancing_scan_delay = 1000;

static unsigned int task_nr_scan_windows(struct task_struct *p)
{
        unsigned long rss = 0;
        unsigned long nr_scan_pages;

        /*
         * Calculations based on RSS as non-present and empty pages are skipped
         * by the PTE scanner and NUMA hinting faults should be trapped based
         * on resident pages
         */
        nr_scan_pages = sysctl_numa_balancing_scan_size << (20 - PAGE_SHIFT);
        rss = get_mm_rss(p->mm);
        if (!rss)
                rss = nr_scan_pages;

        rss = round_up(rss, nr_scan_pages);
        return rss / nr_scan_pages;
}

/* For sanitys sake, never scan more PTEs than MAX_SCAN_WINDOW MB/sec. */
#define MAX_SCAN_WINDOW 2560

static unsigned int task_scan_min(struct task_struct *p)
{
        unsigned int scan_size = READ_ONCE(sysctl_numa_balancing_scan_size);
        unsigned int scan, floor;
        unsigned int windows = 1;

        if (scan_size < MAX_SCAN_WINDOW)
                windows = MAX_SCAN_WINDOW / scan_size;
        floor = 1000 / windows;

        scan = sysctl_numa_balancing_scan_period_min / task_nr_scan_windows(p);
        return max_t(unsigned int, floor, scan);
}

static unsigned int task_scan_max(struct task_struct *p)
{
        unsigned int smin = task_scan_min(p);
        unsigned int smax;

        /* Watch for min being lower than max due to floor calculations */
        smax = sysctl_numa_balancing_scan_period_max / task_nr_scan_windows(p);
        return max(smin, smax);
}

static void account_numa_enqueue(struct rq *rq, struct task_struct *p)
{
        rq->nr_numa_running += (p->numa_preferred_nid != -1);
        rq->nr_preferred_running += (p->numa_preferred_nid == task_node(p));
}

static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
        rq->nr_numa_running -= (p->numa_preferred_nid != -1);
        rq->nr_preferred_running -= (p->numa_preferred_nid == task_node(p));
}

struct numa_group {
        atomic_t refcount;

        spinlock_t lock; /* nr_tasks, tasks */
        int nr_tasks;
        pid_t gid;

        struct rcu_head rcu;
        nodemask_t active_nodes;
        unsigned long total_faults;
        /*
         * Faults_cpu is used to decide whether memory should move
         * towards the CPU. As a consequence, these stats are weighted
         * more by CPU use than by memory faults.
         */
        unsigned long *faults_cpu;
        unsigned long faults[0];
};

/* Shared or private faults. */
#define NR_NUMA_HINT_FAULT_TYPES 2

/* Memory and CPU locality */
#define NR_NUMA_HINT_FAULT_STATS (NR_NUMA_HINT_FAULT_TYPES * 2)

/* Averaged statistics, and temporary buffers. */
#define NR_NUMA_HINT_FAULT_BUCKETS (NR_NUMA_HINT_FAULT_STATS * 2)

pid_t task_numa_group_id(struct task_struct *p)
{
        return p->numa_group ? p->numa_group->gid : 0;
}

/*
 * The averaged statistics, shared & private, memory & cpu,
 * occupy the first half of the array. The second half of the
 * array is for current counters, which are averaged into the
 * first set by task_numa_placement.
 */
static inline int task_faults_idx(enum numa_faults_stats s, int nid, int priv)
{
        return NR_NUMA_HINT_FAULT_TYPES * (s * nr_node_ids + nid) + priv;
}

static inline unsigned long task_faults(struct task_struct *p, int nid)
{
        if (!p->numa_faults)
                return 0;

        return p->numa_faults[task_faults_idx(NUMA_MEM, nid, 0)] +
                p->numa_faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults(struct task_struct *p, int nid)
{
        if (!p->numa_group)
                return 0;

        return p->numa_group->faults[task_faults_idx(NUMA_MEM, nid, 0)] +
                p->numa_group->faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
{
        return group->faults_cpu[task_faults_idx(NUMA_MEM, nid, 0)] +
                group->faults_cpu[task_faults_idx(NUMA_MEM, nid, 1)];
}

/* Handle placement on systems where not all nodes are directly connected. */
static unsigned long score_nearby_nodes(struct task_struct *p, int nid,
                                        int maxdist, bool task)
{
        unsigned long score = 0;
        int node;

        /*
         * All nodes are directly connected, and the same distance
         * from each other. No need for fancy placement algorithms.
         */
        if (sched_numa_topology_type == NUMA_DIRECT)
                return 0;

        /*
         * This code is called for each node, introducing N^2 complexity,
         * which should be ok given the number of nodes rarely exceeds 8.
         */
        for_each_online_node(node) {
                unsigned long faults;
                int dist = node_distance(nid, node);

                /*
                 * The furthest away nodes in the system are not interesting
                 * for placement; nid was already counted.
                 */
                if (dist == sched_max_numa_distance || node == nid)
                        continue;

                /*
                 * On systems with a backplane NUMA topology, compare groups
                 * of nodes, and move tasks towards the group with the most
                 * memory accesses. When comparing two nodes at distance
                 * "hoplimit", only nodes closer by than "hoplimit" are part
                 * of each group. Skip other nodes.
                 */
                if (sched_numa_topology_type == NUMA_BACKPLANE &&
                                        dist > maxdist)
                        continue;

                /* Add up the faults from nearby nodes. */
                if (task)
                        faults = task_faults(p, node);
                else
                        faults = group_faults(p, node);

                /*
                 * On systems with a glueless mesh NUMA topology, there are
                 * no fixed "groups of nodes". Instead, nodes that are not
                 * directly connected bounce traffic through intermediate
                 * nodes; a numa_group can occupy any set of nodes.
                 * The further away a node is, the less the faults count.
                 * This seems to result in good task placement.
                 */
                if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
                        faults *= (sched_max_numa_distance - dist);
                        faults /= (sched_max_numa_distance - LOCAL_DISTANCE);
                }

                score += faults;
        }

        return score;
}

/*
 * These return the fraction of accesses done by a particular task, or
 * task group, on a particular numa node.  The group weight is given a
 * larger multiplier, in order to group tasks together that are almost
 * evenly spread out between numa nodes.
 */
static inline unsigned long task_weight(struct task_struct *p, int nid,
                                        int dist)
{
        unsigned long faults, total_faults;

        if (!p->numa_faults)
                return 0;

        total_faults = p->total_numa_faults;

        if (!total_faults)
                return 0;

        faults = task_faults(p, nid);
        faults += score_nearby_nodes(p, nid, dist, true);

        return 1000 * faults / total_faults;
}

static inline unsigned long group_weight(struct task_struct *p, int nid,
                                         int dist)
{
        unsigned long faults, total_faults;

        if (!p->numa_group)
                return 0;

        total_faults = p->numa_group->total_faults;

        if (!total_faults)
                return 0;

        faults = group_faults(p, nid);
        faults += score_nearby_nodes(p, nid, dist, false);

        return 1000 * faults / total_faults;
}

bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
                                int src_nid, int dst_cpu)
{
        struct numa_group *ng = p->numa_group;
        int dst_nid = cpu_to_node(dst_cpu);
        int last_cpupid, this_cpupid;

        this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);

        /*
         * Multi-stage node selection is used in conjunction with a periodic
         * migration fault to build a temporal task<->page relation. By using
         * a two-stage filter we remove short/unlikely relations.
         *
         * Using P(p) ~ n_p / n_t as per frequentist probability, we can equate
         * a task's usage of a particular page (n_p) per total usage of this
         * page (n_t) (in a given time-span) to a probability.
         *
         * Our periodic faults will sample this probability and getting the
         * same result twice in a row, given these samples are fully
         * independent, is then given by P(n)^2, provided our sample period
         * is sufficiently short compared to the usage pattern.
         *
         * This quadric squishes small probabilities, making it less likely we
         * act on an unlikely task<->page relation.
         */
        last_cpupid = page_cpupid_xchg_last(page, this_cpupid);
        if (!cpupid_pid_unset(last_cpupid) &&
                                cpupid_to_nid(last_cpupid) != dst_nid)
                return false;

        /* Always allow migrate on private faults */
        if (cpupid_match_pid(p, last_cpupid))
                return true;

        /* A shared fault, but p->numa_group has not been set up yet. */
        if (!ng)
                return true;

        /*
         * Do not migrate if the destination is not a node that
         * is actively used by this numa group.
         */
        if (!node_isset(dst_nid, ng->active_nodes))
                return false;

        /*
         * Source is a node that is not actively used by this
         * numa group, while the destination is. Migrate.
         */
        if (!node_isset(src_nid, ng->active_nodes))
                return true;

        /*
         * Both source and destination are nodes in active
         * use by this numa group. Maximize memory bandwidth
         * by migrating from more heavily used groups, to less
         * heavily used ones, spreading the load around.
         * Use a 1/4 hysteresis to avoid spurious page movement.
         */
        return group_faults(p, dst_nid) < (group_faults(p, src_nid) * 3 / 4);
}

static unsigned long weighted_cpuload(const int cpu);
static unsigned long source_load(int cpu, int type);
static unsigned long target_load(int cpu, int type);
static unsigned long capacity_of(int cpu);
static long effective_load(struct task_group *tg, int cpu, long wl, long wg);

/* Cached statistics for all CPUs within a node */
struct numa_stats {
        unsigned long nr_running;
        unsigned long load;

        /* Total compute capacity of CPUs on a node */
        unsigned long compute_capacity;

        /* Approximate capacity in terms of runnable tasks on a node */
        unsigned long task_capacity;
        int has_free_capacity;
};

/*
 * XXX borrowed from update_sg_lb_stats
 */
static void update_numa_stats(struct numa_stats *ns, int nid)
{
        int smt, cpu, cpus = 0;
        unsigned long capacity;

        memset(ns, 0, sizeof(*ns));
        for_each_cpu(cpu, cpumask_of_node(nid)) {
                struct rq *rq = cpu_rq(cpu);

                ns->nr_running += rq->nr_running;
                ns->load += weighted_cpuload(cpu);
                ns->compute_capacity += capacity_of(cpu);

                cpus++;
        }

        /*
         * If we raced with hotplug and there are no CPUs left in our mask
         * the @ns structure is NULL'ed and task_numa_compare() will
         * not find this node attractive.
         *
         * We'll either bail at !has_free_capacity, or we'll detect a huge
         * imbalance and bail there.
         */
        if (!cpus)
                return;

        /* smt := ceil(cpus / capacity), assumes: 1 < smt_power < 2 */
        smt = DIV_ROUND_UP(SCHED_CAPACITY_SCALE * cpus, ns->compute_capacity);
        capacity = cpus / smt; /* cores */

        ns->task_capacity = min_t(unsigned, capacity,
                DIV_ROUND_CLOSEST(ns->compute_capacity, SCHED_CAPACITY_SCALE));
        ns->has_free_capacity = (ns->nr_running < ns->task_capacity);
}

struct task_numa_env {
        struct task_struct *p;

        int src_cpu, src_nid;
        int dst_cpu, dst_nid;

        struct numa_stats src_stats, dst_stats;

        int imbalance_pct;
        int dist;

        struct task_struct *best_task;
        long best_imp;
        int best_cpu;
};

static void task_numa_assign(struct task_numa_env *env,
                             struct task_struct *p, long imp)
{
        if (env->best_task)
                put_task_struct(env->best_task);
        if (p)
                get_task_struct(p);

        env->best_task = p;
        env->best_imp = imp;
        env->best_cpu = env->dst_cpu;
}

static bool load_too_imbalanced(long src_load, long dst_load,
                                struct task_numa_env *env)
{
        long imb, old_imb;
        long orig_src_load, orig_dst_load;
        long src_capacity, dst_capacity;

        /*
         * The load is corrected for the CPU capacity available on each node.
         *
         * src_load        dst_load
         * ------------ vs ---------
         * src_capacity    dst_capacity
         */
        src_capacity = env->src_stats.compute_capacity;
        dst_capacity = env->dst_stats.compute_capacity;

        /* We care about the slope of the imbalance, not the direction. */
        if (dst_load < src_load)
                swap(dst_load, src_load);

        /* Is the difference below the threshold? */
        imb = dst_load * src_capacity * 100 -
              src_load * dst_capacity * env->imbalance_pct;
        if (imb <= 0)
                return false;

        /*
         * The imbalance is above the allowed threshold.
         * Compare it with the old imbalance.
         */
        orig_src_load = env->src_stats.load;
        orig_dst_load = env->dst_stats.load;

        if (orig_dst_load < orig_src_load)
                swap(orig_dst_load, orig_src_load);

        old_imb = orig_dst_load * src_capacity * 100 -
                  orig_src_load * dst_capacity * env->imbalance_pct;

        /* Would this change make things worse? */
        return (imb > old_imb);
}

/*
 * This checks if the overall compute and NUMA accesses of the system would
 * be improved if the source tasks was migrated to the target dst_cpu taking
 * into account that it might be best if task running on the dst_cpu should
 * be exchanged with the source task
 */
static void task_numa_compare(struct task_numa_env *env,
                              long taskimp, long groupimp)
{
        struct rq *src_rq = cpu_rq(env->src_cpu);
        struct rq *dst_rq = cpu_rq(env->dst_cpu);
        struct task_struct *cur;
        long src_load, dst_load;
        long load;
        long imp = env->p->numa_group ? groupimp : taskimp;
        long moveimp = imp;
        int dist = env->dist;

        rcu_read_lock();

        raw_spin_lock_irq(&dst_rq->lock);
        cur = dst_rq->curr;
        /*
         * No need to move the exiting task, and this ensures that ->curr
         * wasn't reaped and thus get_task_struct() in task_numa_assign()
         * is safe under RCU read lock.
         * Note that rcu_read_lock() itself can't protect from the final
         * put_task_struct() after the last schedule().
         */
        if ((cur->flags & PF_EXITING) || is_idle_task(cur))
                cur = NULL;
        raw_spin_unlock_irq(&dst_rq->lock);

        /*
         * Because we have preemption enabled we can get migrated around and
         * end try selecting ourselves (current == env->p) as a swap candidate.
         */
        if (cur == env->p)
                goto unlock;

        /*
         * "imp" is the fault differential for the source task between the
         * source and destination node. Calculate the total differential for
         * the source task and potential destination task. The more negative
         * the value is, the more rmeote accesses that would be expected to
         * be incurred if the tasks were swapped.
         */
        if (cur) {
                /* Skip this swap candidate if cannot move to the source cpu */
                if (!cpumask_test_cpu(env->src_cpu, tsk_cpus_allowed(cur)))
                        goto unlock;

                /*
                 * If dst and source tasks are in the same NUMA group, or not
                 * in any group then look only at task weights.
                 */
                if (cur->numa_group == env->p->numa_group) {
                        imp = taskimp + task_weight(cur, env->src_nid, dist) -
                              task_weight(cur, env->dst_nid, dist);
                        /*
                         * Add some hysteresis to prevent swapping the
                         * tasks within a group over tiny differences.
                         */
                        if (cur->numa_group)
                                imp -= imp/16;
                } else {
                        /*
                         * Compare the group weights. If a task is all by
                         * itself (not part of a group), use the task weight
                         * instead.
                         */
                        if (cur->numa_group)
                                imp += group_weight(cur, env->src_nid, dist) -
                                       group_weight(cur, env->dst_nid, dist);
                        else
                                imp += task_weight(cur, env->src_nid, dist) -
                                       task_weight(cur, env->dst_nid, dist);
                }
        }

        if (imp <= env->best_imp && moveimp <= env->best_imp)
                goto unlock;

        if (!cur) {
                /* Is there capacity at our destination? */
                if (env->src_stats.nr_running <= env->src_stats.task_capacity &&
                    !env->dst_stats.has_free_capacity)
                        goto unlock;

                goto balance;
        }

        /* Balance doesn't matter much if we're running a task per cpu */
        if (imp > env->best_imp && src_rq->nr_running == 1 &&
                        dst_rq->nr_running == 1)
                goto assign;

        /*
         * In the overloaded case, try and keep the load balanced.
         */
balance:
        load = task_h_load(env->p);
        dst_load = env->dst_stats.load + load;
        src_load = env->src_stats.load - load;

        if (moveimp > imp && moveimp > env->best_imp) {
                /*
                 * If the improvement from just moving env->p direction is
                 * better than swapping tasks around, check if a move is
                 * possible. Store a slightly smaller score than moveimp,
                 * so an actually idle CPU will win.
                 */
                if (!load_too_imbalanced(src_load, dst_load, env)) {
                        imp = moveimp - 1;
                        cur = NULL;
                        goto assign;
                }
        }

        if (imp <= env->best_imp)
                goto unlock;

        if (cur) {
                load = task_h_load(cur);
                dst_load -= load;
                src_load += load;
        }

        if (load_too_imbalanced(src_load, dst_load, env))
                goto unlock;

        /*
         * One idle CPU per node is evaluated for a task numa move.
         * Call select_idle_sibling to maybe find a better one.
         */
        if (!cur)
                env->dst_cpu = select_idle_sibling(env->p, env->dst_cpu);

assign:
        task_numa_assign(env, cur, imp);
unlock:
        rcu_read_unlock();
}

static void task_numa_find_cpu(struct task_numa_env *env,
                                long taskimp, long groupimp)
{
        int cpu;

        for_each_cpu(cpu, cpumask_of_node(env->dst_nid)) {
                /* Skip this CPU if the source task cannot migrate */
                if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p)))
                        continue;

                env->dst_cpu = cpu;
                task_numa_compare(env, taskimp, groupimp);
        }
}

/* Only move tasks to a NUMA node less busy than the current node. */
static bool numa_has_capacity(struct task_numa_env *env)
{
        struct numa_stats *src = &env->src_stats;
        struct numa_stats *dst = &env->dst_stats;

        if (src->has_free_capacity && !dst->has_free_capacity)
                return false;

        /*
         * Only consider a task move if the source has a higher load
         * than the destination, corrected for CPU capacity on each node.
         *
         *      src->load                dst->load
         * --------------------- vs ---------------------
         * src->compute_capacity    dst->compute_capacity
         */
        if (src->load * dst->compute_capacity >
            dst->load * src->compute_capacity)
                return true;

        return false;
}

static int task_numa_migrate(struct task_struct *p)
{
        struct task_numa_env env = {
                .p = p,

                .src_cpu = task_cpu(p),
                .src_nid = task_node(p),

                .imbalance_pct = 112,

                .best_task = NULL,
                .best_imp = 0,
                .best_cpu = -1
        };
        struct sched_domain *sd;
        unsigned long taskweight, groupweight;
        int nid, ret, dist;
        long taskimp, groupimp;

        /*
         * Pick the lowest SD_NUMA domain, as that would have the smallest
         * imbalance and would be the first to start moving tasks about.
         *
         * And we want to avoid any moving of tasks about, as that would create
         * random movement of tasks -- counter the numa conditions we're trying
         * to satisfy here.
         */
        rcu_read_lock();
        sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
        if (sd)
                env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
        rcu_read_unlock();

        /*
         * Cpusets can break the scheduler domain tree into smaller
         * balance domains, some of which do not cross NUMA boundaries.
         * Tasks that are "trapped" in such domains cannot be migrated
         * elsewhere, so there is no point in (re)trying.
         */
        if (unlikely(!sd)) {
                p->numa_preferred_nid = task_node(p);
                return -EINVAL;
        }

        env.dst_nid = p->numa_preferred_nid;
        dist = env.dist = node_distance(env.src_nid, env.dst_nid);
        taskweight = task_weight(p, env.src_nid, dist);
        groupweight = group_weight(p, env.src_nid, dist);
        update_numa_stats(&env.src_stats, env.src_nid);
        taskimp = task_weight(p, env.dst_nid, dist) - taskweight;
        groupimp = group_weight(p, env.dst_nid, dist) - groupweight;
        update_numa_stats(&env.dst_stats, env.dst_nid);

        /* Try to find a spot on the preferred nid. */
        if (numa_has_capacity(&env))
                task_numa_find_cpu(&env, taskimp, groupimp);

        /*
         * Look at other nodes in these cases:
         * - there is no space available on the preferred_nid
         * - the task is part of a numa_group that is interleaved across
         *   multiple NUMA nodes; in order to better consolidate the group,
         *   we need to check other locations.
         */
        if (env.best_cpu == -1 || (p->numa_group &&
                        nodes_weight(p->numa_group->active_nodes) > 1)) {
                for_each_online_node(nid) {
                        if (nid == env.src_nid || nid == p->numa_preferred_nid)
                                continue;

                        dist = node_distance(env.src_nid, env.dst_nid);
                        if (sched_numa_topology_type == NUMA_BACKPLANE &&
                                                dist != env.dist) {
                                taskweight = task_weight(p, env.src_nid, dist);
                                groupweight = group_weight(p, env.src_nid, dist);
                        }

                        /* Only consider nodes where both task and groups benefit */
                        taskimp = task_weight(p, nid, dist) - taskweight;
                        groupimp = group_weight(p, nid, dist) - groupweight;
                        if (taskimp < 0 && groupimp < 0)
                                continue;

                        env.dist = dist;
                        env.dst_nid = nid;
                        update_numa_stats(&env.dst_stats, env.dst_nid);
                        if (numa_has_capacity(&env))
                                task_numa_find_cpu(&env, taskimp, groupimp);
                }
        }

        /*
         * If the task is part of a workload that spans multiple NUMA nodes,
         * and is migrating into one of the workload's active nodes, remember
         * this node as the task's preferred numa node, so the workload can
         * settle down.
         * A task that migrated to a second choice node will be better off
         * trying for a better one later. Do not set the preferred node here.
         */
        if (p->numa_group) {
                if (env.best_cpu == -1)
                        nid = env.src_nid;
                else
                        nid = env.dst_nid;

                if (node_isset(nid, p->numa_group->active_nodes))
                        sched_setnuma(p, env.dst_nid);
        }

        /* No better CPU than the current one was found. */
        if (env.best_cpu == -1)
                return -EAGAIN;

        /*
         * Reset the scan period if the task is being rescheduled on an
         * alternative node to recheck if the tasks is now properly placed.
         */
        p->numa_scan_period = task_scan_min(p);

        if (env.best_task == NULL) {
                ret = migrate_task_to(p, env.best_cpu);
                if (ret != 0)
                        trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
                return ret;
        }

        ret = migrate_swap(p, env.best_task);
        if (ret != 0)
                trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
        put_task_struct(env.best_task);
        return ret;
}

/* Attempt to migrate a task to a CPU on the preferred node. */
static void numa_migrate_preferred(struct task_struct *p)
{
        unsigned long interval = HZ;

        /* This task has no NUMA fault statistics yet */
        if (unlikely(p->numa_preferred_nid == -1 || !p->numa_faults))
                return;

        /* Periodically retry migrating the task to the preferred node */
        interval = min(interval, msecs_to_jiffies(p->numa_scan_period) / 16);
        p->numa_migrate_retry = jiffies + interval;

        /* Success if task is already running on preferred CPU */
        if (task_node(p) == p->numa_preferred_nid)
                return;

        /* Otherwise, try migrate to a CPU on the preferred node */
        task_numa_migrate(p);
}

/*
 * Find the nodes on which the workload is actively running. We do this by
 * tracking the nodes from which NUMA hinting faults are triggered. This can
 * be different from the set of nodes where the workload's memory is currently
 * located.
 *
 * The bitmask is used to make smarter decisions on when to do NUMA page
 * migrations, To prevent flip-flopping, and excessive page migrations, nodes
 * are added when they cause over 6/16 of the maximum number of faults, but
 * only removed when they drop below 3/16.
 */
static void update_numa_active_node_mask(struct numa_group *numa_group)
{
        unsigned long faults, max_faults = 0;
        int nid;

        for_each_online_node(nid) {
                faults = group_faults_cpu(numa_group, nid);
                if (faults > max_faults)
                        max_faults = faults;
        }

        for_each_online_node(nid) {
                faults = group_faults_cpu(numa_group, nid);
                if (!node_isset(nid, numa_group->active_nodes)) {
                        if (faults > max_faults * 6 / 16)
                                node_set(nid, numa_group->active_nodes);
                } else if (faults < max_faults * 3 / 16)
                        node_clear(nid, numa_group->active_nodes);
        }
}

/*
 * When adapting the scan rate, the period is divided into NUMA_PERIOD_SLOTS
 * increments. The more local the fault statistics are, the higher the scan
 * period will be for the next scan window. If local/(local+remote) ratio is
 * below NUMA_PERIOD_THRESHOLD (where range of ratio is 1..NUMA_PERIOD_SLOTS)
 * the scan period will decrease. Aim for 70% local accesses.
 */
#define NUMA_PERIOD_SLOTS 10
#define NUMA_PERIOD_THRESHOLD 7

/*
 * Increase the scan period (slow down scanning) if the majority of
 * our memory is already on our local node, or if the majority of
 * the page accesses are shared with other processes.
 * Otherwise, decrease the scan period.
 */
static void update_task_scan_period(struct task_struct *p,
                        unsigned long shared, unsigned long private)
{
        unsigned int period_slot;
        int ratio;
        int diff;

        unsigned long remote = p->numa_faults_locality[0];
        unsigned long local = p->numa_faults_locality[1];

        /*
         * If there were no record hinting faults then either the task is
         * completely idle or all activity is areas that are not of interest
         * to automatic numa balancing. Related to that, if there were failed
         * migration then it implies we are migrating too quickly or the local
         * node is overloaded. In either case, scan slower
         */
        if (local + shared == 0 || p->numa_faults_locality[2]) {
                p->numa_scan_period = min(p->numa_scan_period_max,
                        p->numa_scan_period << 1);

                p->mm->numa_next_scan = jiffies +
                        msecs_to_jiffies(p->numa_scan_period);

                return;
        }

        /*
         * Prepare to scale scan period relative to the current period.
         *       == NUMA_PERIOD_THRESHOLD scan period stays the same
         *       <  NUMA_PERIOD_THRESHOLD scan period decreases (scan faster)
         *       >= NUMA_PERIOD_THRESHOLD scan period increases (scan slower)
         */
        period_slot = DIV_ROUND_UP(p->numa_scan_period, NUMA_PERIOD_SLOTS);
        ratio = (local * NUMA_PERIOD_SLOTS) / (local + remote);
        if (ratio >= NUMA_PERIOD_THRESHOLD) {
                int slot = ratio - NUMA_PERIOD_THRESHOLD;
                if (!slot)
                        slot = 1;
                diff = slot * period_slot;
        } else {
                diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;

                /*
                 * Scale scan rate increases based on sharing. There is an
                 * inverse relationship between the degree of sharing and
                 * the adjustment made to the scanning period. Broadly
                 * speaking the intent is that there is little point
                 * scanning faster if shared accesses dominate as it may
                 * simply bounce migrations uselessly
                 */
                ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared + 1));
                diff = (diff * ratio) / NUMA_PERIOD_SLOTS;
        }

        p->numa_scan_period = clamp(p->numa_scan_period + diff,
                        task_scan_min(p), task_scan_max(p));
        memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
}

/*
 * Get the fraction of time the task has been running since the last
 * NUMA placement cycle. The scheduler keeps similar statistics, but
 * decays those on a 32ms period, which is orders of magnitude off
 * from the dozens-of-seconds NUMA balancing period. Use the scheduler
 * stats only if the task is so new there are no NUMA statistics yet.
 */
static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period)
{
        u64 runtime, delta, now;
        /* Use the start of this time slice to avoid calculations. */
        now = p->se.exec_start;
        runtime = p->se.sum_exec_runtime;

        if (p->last_task_numa_placement) {
                delta = runtime - p->last_sum_exec_runtime;
                *period = now - p->last_task_numa_placement;
        } else {
                delta = p->se.avg.runnable_avg_sum;
                *period = p->se.avg.avg_period;
        }

        p->last_sum_exec_runtime = runtime;
        p->last_task_numa_placement = now;

        return delta;
}

/*
 * Determine the preferred nid for a task in a numa_group. This needs to
 * be done in a way that produces consistent results with group_weight,
 * otherwise workloads might not converge.
 */
static int preferred_group_nid(struct task_struct *p, int nid)
{
        nodemask_t nodes;
        int dist;

        /* Direct connections between all NUMA nodes. */
        if (sched_numa_topology_type == NUMA_DIRECT)
                return nid;

        /*
         * On a system with glueless mesh NUMA topology, group_weight
         * scores nodes according to the number of NUMA hinting faults on
         * both the node itself, and on nearby nodes.
         */
        if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
                unsigned long score, max_score = 0;
                int node, max_node = nid;

                dist = sched_max_numa_distance;

                for_each_online_node(node) {
                        score = group_weight(p, node, dist);
                        if (score > max_score) {
                                max_score = score;
                                max_node = node;
                        }
                }
                return max_node;
        }

        /*
         * Finding the preferred nid in a system with NUMA backplane
         * interconnect topology is more involved. The goal is to locate
         * tasks from numa_groups near each other in the system, and
         * untangle workloads from different sides of the system. This requires
         * searching down the hierarchy of node groups, recursively searching
         * inside the highest scoring group of nodes. The nodemask tricks
         * keep the complexity of the search down.
         */
        nodes = node_online_map;
        for (dist = sched_max_numa_distance; dist > LOCAL_DISTANCE; dist--) {
                unsigned long max_faults = 0;
                nodemask_t max_group = NODE_MASK_NONE;
                int a, b;

                /* Are there nodes at this distance from each other? */
                if (!find_numa_distance(dist))
                        continue;

                for_each_node_mask(a, nodes) {
                        unsigned long faults = 0;
                        nodemask_t this_group;
                        nodes_clear(this_group);

                        /* Sum group's NUMA faults; includes a==b case. */
                        for_each_node_mask(b, nodes) {
                                if (node_distance(a, b) < dist) {
                                        faults += group_faults(p, b);
                                        node_set(b, this_group);
                                        node_clear(b, nodes);
                                }
                        }

                        /* Remember the top group. */
                        if (faults > max_faults) {
                                max_faults = faults;
                                max_group = this_group;
                                /*
                                 * subtle: at the smallest distance there is
                                 * just one node left in each "group", the
                                 * winner is the preferred nid.
                                 */
                                nid = a;
                        }
                }
                /* Next round, evaluate the nodes within max_group. */
                if (!max_faults)
                        break;
                nodes = max_group;
        }
        return nid;
}

static void task_numa_placement(struct task_struct *p)
{
        int seq, nid, max_nid = -1, max_group_nid = -1;
        unsigned long max_faults = 0, max_group_faults = 0;
        unsigned long fault_types[2] = { 0, 0 };
        unsigned long total_faults;
        u64 runtime, period;
        spinlock_t *group_lock = NULL;

        /*
         * The p->mm->numa_scan_seq field gets updated without
         * exclusive access. Use READ_ONCE() here to ensure
         * that the field is read in a single access:
         */
        seq = READ_ONCE(p->mm->numa_scan_seq);
        if (p->numa_scan_seq == seq)
                return;
        p->numa_scan_seq = seq;
        p->numa_scan_period_max = task_scan_max(p);

        total_faults = p->numa_faults_locality[0] +
                       p->numa_faults_locality[1];
        runtime = numa_get_avg_runtime(p, &period);

        /* If the task is part of a group prevent parallel updates to group stats */
        if (p->numa_group) {
                group_lock = &p->numa_group->lock;
                spin_lock_irq(group_lock);
        }

        /* Find the node with the highest number of faults */
        for_each_online_node(nid) {
                /* Keep track of the offsets in numa_faults array */
                int mem_idx, membuf_idx, cpu_idx, cpubuf_idx;
                unsigned long faults = 0, group_faults = 0;
                int priv;

                for (priv = 0; priv < NR_NUMA_HINT_FAULT_TYPES; priv++) {
                        long diff, f_diff, f_weight;

                        mem_idx = task_faults_idx(NUMA_MEM, nid, priv);
                        membuf_idx = task_faults_idx(NUMA_MEMBUF, nid, priv);
                        cpu_idx = task_faults_idx(NUMA_CPU, nid, priv);
                        cpubuf_idx = task_faults_idx(NUMA_CPUBUF, nid, priv);

                        /* Decay existing window, copy faults since last scan */
                        diff = p->numa_faults[membuf_idx] - p->numa_faults[mem_idx] / 2;
                        fault_types[priv] += p->numa_faults[membuf_idx];
                        p->numa_faults[membuf_idx] = 0;

                        /*
                         * Normalize the faults_from, so all tasks in a group
                         * count according to CPU use, instead of by the raw
                         * number of faults. Tasks with little runtime have
                         * little over-all impact on throughput, and thus their
                         * faults are less important.
                         */
                        f_weight = div64_u64(runtime << 16, period + 1);
                        f_weight = (f_weight * p->numa_faults[cpubuf_idx]) /
                                   (total_faults + 1);
                        f_diff = f_weight - p->numa_faults[cpu_idx] / 2;
                        p->numa_faults[cpubuf_idx] = 0;

                        p->numa_faults[mem_idx] += diff;
                        p->numa_faults[cpu_idx] += f_diff;
                        faults += p->numa_faults[mem_idx];
                        p->total_numa_faults += diff;
                        if (p->numa_group) {
                                /*
                                 * safe because we can only change our own group
                                 *
                                 * mem_idx represents the offset for a given
                                 * nid and priv in a specific region because it
                                 * is at the beginning of the numa_faults array.
                                 */
                                p->numa_group->faults[mem_idx] += diff;
                                p->numa_group->faults_cpu[mem_idx] += f_diff;
                                p->numa_group->total_faults += diff;
                                group_faults += p->numa_group->faults[mem_idx];
                        }
                }

                if (faults > max_faults) {
                        max_faults = faults;
                        max_nid = nid;
                }

                if (group_faults > max_group_faults) {
                        max_group_faults = group_faults;
                        max_group_nid = nid;
                }
        }

        update_task_scan_period(p, fault_types[0], fault_types[1]);

        if (p->numa_group) {
                update_numa_active_node_mask(p->numa_group);
                spin_unlock_irq(group_lock);
                max_nid = preferred_group_nid(p, max_group_nid);
        }

        if (max_faults) {
                /* Set the new preferred node */
                if (max_nid != p->numa_preferred_nid)
                        sched_setnuma(p, max_nid);

                if (task_node(p) != p->numa_preferred_nid)
                        numa_migrate_preferred(p);
        }
}

static inline int get_numa_group(struct numa_group *grp)
{
        return atomic_inc_not_zero(&grp->refcount);
}

static inline void put_numa_group(struct numa_group *grp)
{
        if (atomic_dec_and_test(&grp->refcount))
                kfree_rcu(grp, rcu);
}

static void task_numa_group(struct task_struct *p, int cpupid, int flags,
                        int *priv)
{
        struct numa_group *grp, *my_grp;
        struct task_struct *tsk;
        bool join = false;
        int cpu = cpupid_to_cpu(cpupid);
        int i;

        if (unlikely(!p->numa_group)) {
                unsigned int size = sizeof(struct numa_group) +
                                    4*nr_node_ids*sizeof(unsigned long);

                grp = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
                if (!grp)
                        return;

                atomic_set(&grp->refcount, 1);
                spin_lock_init(&grp->lock);
                grp->gid = p->pid;
                /* Second half of the array tracks nids where faults happen */
                grp->faults_cpu = grp->faults + NR_NUMA_HINT_FAULT_TYPES *
                                                nr_node_ids;

                node_set(task_node(current), grp->active_nodes);

                for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
                        grp->faults[i] = p->numa_faults[i];

                grp->total_faults = p->total_numa_faults;

                grp->nr_tasks++;
                rcu_assign_pointer(p->numa_group, grp);
        }

        rcu_read_lock();
        tsk = READ_ONCE(cpu_rq(cpu)->curr);

        if (!cpupid_match_pid(tsk, cpupid))
                goto no_join;

        grp = rcu_dereference(tsk->numa_group);
        if (!grp)
                goto no_join;

        my_grp = p->numa_group;
        if (grp == my_grp)
                goto no_join;

        /*
         * Only join the other group if its bigger; if we're the bigger group,
         * the other task will join us.
         */
        if (my_grp->nr_tasks > grp->nr_tasks)
                goto no_join;

        /*
         * Tie-break on the grp address.
         */
        if (my_grp->nr_tasks == grp->nr_tasks && my_grp > grp)
                goto no_join;

        /* Always join threads in the same process. */
        if (tsk->mm == current->mm)
                join = true;

        /* Simple filter to avoid false positives due to PID collisions */
        if (flags & TNF_SHARED)
                join = true;

        /* Update priv based on whether false sharing was detected */
        *priv = !join;

        if (join && !get_numa_group(grp))
                goto no_join;

        rcu_read_unlock();

        if (!join)
                return;

        BUG_ON(irqs_disabled());
        double_lock_irq(&my_grp->lock, &grp->lock);

        for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
                my_grp->faults[i] -= p->numa_faults[i];
                grp->faults[i] += p->numa_faults[i];
        }
        my_grp->total_faults -= p->total_numa_faults;
        grp->total_faults += p->total_numa_faults;

        my_grp->nr_tasks--;
        grp->nr_tasks++;

        spin_unlock(&my_grp->lock);
        spin_unlock_irq(&grp->lock);

        rcu_assign_pointer(p->numa_group, grp);

        put_numa_group(my_grp);
        return;

no_join:
        rcu_read_unlock();
        return;
}

void task_numa_free(struct task_struct *p)
{
        struct numa_group *grp = p->numa_group;
        void *numa_faults = p->numa_faults;
        unsigned long flags;
        int i;

        if (grp) {
                spin_lock_irqsave(&grp->lock, flags);
                for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
                        grp->faults[i] -= p->numa_faults[i];
                grp->total_faults -= p->total_numa_faults;

                grp->nr_tasks--;
                spin_unlock_irqrestore(&grp->lock, flags);
                RCU_INIT_POINTER(p->numa_group, NULL);
                put_numa_group(grp);
        }

        p->numa_faults = NULL;
        kfree(numa_faults);
}

/*
 * Got a PROT_NONE fault for a page on @node.
 */
void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
{
        struct task_struct *p = current;
        bool migrated = flags & TNF_MIGRATED;
        int cpu_node = task_node(current);
        int local = !!(flags & TNF_FAULT_LOCAL);
        int priv;

        if (!numabalancing_enabled)
                return;

        /* for example, ksmd faulting in a user's mm */
        if (!p->mm)
                return;

        /* Allocate buffer to track faults on a per-node basis */
        if (unlikely(!p->numa_faults)) {
                int size = sizeof(*p->numa_faults) *
                           NR_NUMA_HINT_FAULT_BUCKETS * nr_node_ids;

                p->numa_faults = kzalloc(size, GFP_KERNEL|__GFP_NOWARN);
                if (!p->numa_faults)
                        return;

                p->total_numa_faults = 0;
                memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
        }

        /*
         * First accesses are treated as private, otherwise consider accesses
         * to be private if the accessing pid has not changed
         */
        if (unlikely(last_cpupid == (-1 & LAST_CPUPID_MASK))) {
                priv = 1;
        } else {
                priv = cpupid_match_pid(p, last_cpupid);
                if (!priv && !(flags & TNF_NO_GROUP))
                        task_numa_group(p, last_cpupid, flags, &priv);
        }

        /*
         * If a workload spans multiple NUMA nodes, a shared fault that
         * occurs wholly within the set of nodes that the workload is
         * actively using should be counted as local. This allows the
         * scan rate to slow down when a workload has settled down.
         */
        if (!priv && !local && p->numa_group &&
                        node_isset(cpu_node, p->numa_group->active_nodes) &&
                        node_isset(mem_node, p->numa_group->active_nodes))
                local = 1;

        task_numa_placement(p);

        /*
         * Retry task to preferred node migration periodically, in case it
         * case it previously failed, or the scheduler moved us.
         */
        if (time_after(jiffies, p->numa_migrate_retry))
                numa_migrate_preferred(p);

        if (migrated)
                p->numa_pages_migrated += pages;
        if (flags & TNF_MIGRATE_FAIL)
                p->numa_faults_locality[2] += pages;

        p->numa_faults[task_faults_idx(NUMA_MEMBUF, mem_node, priv)] += pages;
        p->numa_faults[task_faults_idx(NUMA_CPUBUF, cpu_node, priv)] += pages;
        p->numa_faults_locality[local] += pages;
}

static void reset_ptenuma_scan(struct task_struct *p)
{
        /*
         * We only did a read acquisition of the mmap sem, so
         * p->mm->numa_scan_seq is written to without exclusive access
         * and the update is not guaranteed to be atomic. That's not
         * much of an issue though, since this is just used for
         * statistical sampling. Use READ_ONCE/WRITE_ONCE, which are not
         * expensive, to avoid any form of compiler optimizations:
         */
        WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
        p->mm->numa_scan_offset = 0;
}

/*
 * The expensive part of numa migration is done from task_work context.
 * Triggered from task_tick_numa().
 */
void task_numa_work(struct callback_head *work)
{
        unsigned long migrate, next_scan, now = jiffies;
        struct task_struct *p = current;
        struct mm_struct *mm = p->mm;
        struct vm_area_struct *vma;
        unsigned long start, end;
        unsigned long nr_pte_updates = 0;
        long pages;

        WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));

        work->next = work; /* protect against double add */
        /*
         * Who cares about NUMA placement when they're dying.
         *
         * NOTE: make sure not to dereference p->mm before this check,
         * exit_task_work() happens _after_ exit_mm() so we could be called
         * without p->mm even though we still had it when we enqueued this
         * work.
         */
        if (p->flags & PF_EXITING)
                return;

        if (!mm->numa_next_scan) {
                mm->numa_next_scan = now +
                        msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
        }

        /*
         * Enforce maximal scan/migration frequency..
         */
        migrate = mm->numa_next_scan;
        if (time_before(now, migrate))
                return;

        if (p->numa_scan_period == 0) {
                p->numa_scan_period_max = task_scan_max(p);
                p->numa_scan_period = task_scan_min(p);
        }

        next_scan = now + msecs_to_jiffies(p->numa_scan_period);
        if (cmpxchg(&mm->numa_next_scan, migrate, next_scan) != migrate)
                return;

        /*
         * Delay this task enough that another task of this mm will likely win
         * the next time around.
         */
        p->node_stamp += 2 * TICK_NSEC;

        start = mm->numa_scan_offset;
        pages = sysctl_numa_balancing_scan_size;
        pages <<= 20 - PAGE_SHIFT; /* MB in pages */
        if (!pages)
                return;

        down_read(&mm->mmap_sem);
        vma = find_vma(mm, start);
        if (!vma) {
                reset_ptenuma_scan(p);
                start = 0;
                vma = mm->mmap;
        }
        for (; vma; vma = vma->vm_next) {
                if (!vma_migratable(vma) || !vma_policy_mof(vma) ||
                        is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_MIXEDMAP)) {
                        continue;
                }

                /*
                 * Shared library pages mapped by multiple processes are not
                 * migrated as it is expected they are cache replicated. Avoid
                 * hinting faults in read-only file-backed mappings or the vdso
                 * as migrating the pages will be of marginal benefit.
                 */
                if (!vma->vm_mm ||
                    (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ)))
                        continue;

                /*
                 * Skip inaccessible VMAs to avoid any confusion between
                 * PROT_NONE and NUMA hinting ptes
                 */
                if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                        continue;

                do {
                        start = max(start, vma->vm_start);
                        end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
                        end = min(end, vma->vm_end);
                        nr_pte_updates += change_prot_numa(vma, start, end);

                        /*
                         * Scan sysctl_numa_balancing_scan_size but ensure that
                         * at least one PTE is updated so that unused virtual
                         * address space is quickly skipped.
                         */
                        if (nr_pte_updates)
                                pages -= (end - start) >> PAGE_SHIFT;

                        start = end;
                        if (pages <= 0)
                                goto out;

                        cond_resched();
                } while (end != vma->vm_end);
        }

out:
        /*
         * It is possible to reach the end of the VMA list but the last few
         * VMAs are not guaranteed to the vma_migratable. If they are not, we
         * would find the !migratable VMA on the next scan but not reset the
         * scanner to the start so check it now.
         */
        if (vma)
                mm->numa_scan_offset = start;
        else
                reset_ptenuma_scan(p);
        up_read(&mm->mmap_sem);
}

/*
 * Drive the periodic memory faults..
 */
void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
        struct callback_head *work = &curr->numa_work;
        u64 period, now;

        /*
         * We don't care about NUMA placement if we don't have memory.
         */
        if (!curr->mm || (curr->flags & PF_EXITING) || work->next != work)
                return;

        /*
         * Using runtime rather than walltime has the dual advantage that
         * we (mostly) drive the selection from busy threads and that the
         * task needs to have done some actual work before we bother with
         * NUMA placement.
         */
        now = curr->se.sum_exec_runtime;
        period = (u64)curr->numa_scan_period * NSEC_PER_MSEC;

        if (now - curr->node_stamp > period) {
                if (!curr->node_stamp)
                        curr->numa_scan_period = task_scan_min(curr);
                curr->node_stamp += period;

                if (!time_before(jiffies, curr->mm->numa_next_scan)) {
                        init_task_work(work, task_numa_work); /* TODO: move this into sched_fork() */
                        task_work_add(curr, work, true);
                }
        }
}
#else
static void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
}

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

static inline void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
}
#endif /* CONFIG_NUMA_BALANCING */

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))
                update_load_add(&rq_of(cfs_rq)->load, se->load.weight);
#ifdef CONFIG_SMP
        if (entity_is_task(se)) {
                struct rq *rq = rq_of(cfs_rq);

                account_numa_enqueue(rq, task_of(se));
                list_add(&se->group_node, &rq->cfs_tasks);
        }
#endif
        cfs_rq->nr_running++;
}

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))
                update_load_sub(&rq_of(cfs_rq)->load, se->load.weight);
        if (entity_is_task(se)) {
                account_numa_dequeue(rq_of(cfs_rq), task_of(se));
                list_del_init(&se->group_node);
        }
        cfs_rq->nr_running--;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
# ifdef CONFIG_SMP
static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
{
        long tg_weight;

        /*
         * Use this CPU's actual weight instead of the last load_contribution
         * to gain a more accurate current total weight. See
         * update_cfs_rq_load_contribution().
         */
        tg_weight = atomic_long_read(&tg->load_avg);
        tg_weight -= cfs_rq->tg_load_contrib;
        tg_weight += cfs_rq->load.weight;

        return tg_weight;
}

static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
{
        long tg_weight, load, shares;

        tg_weight = calc_tg_weight(tg, cfs_rq);
        load = cfs_rq->load.weight;

        shares = (tg->shares * load);
        if (tg_weight)
                shares /= tg_weight;

        if (shares < MIN_SHARES)
                shares = MIN_SHARES;
        if (shares > tg->shares)
                shares = tg->shares;

        return shares;
}
# else /* CONFIG_SMP */
static inline long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
{
        return tg->shares;
}
# endif /* CONFIG_SMP */
static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
                            unsigned long weight)
{
        if (se->on_rq) {
                /* commit outstanding execution time */
                if (cfs_rq->curr == se)
                        update_curr(cfs_rq);
                account_entity_dequeue(cfs_rq, se);
        }

        update_load_set(&se->load, weight);

        if (se->on_rq)
                account_entity_enqueue(cfs_rq, se);
}

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);

static void update_cfs_shares(struct cfs_rq *cfs_rq)
{
        struct task_group *tg;
        struct sched_entity *se;
        long shares;

        tg = cfs_rq->tg;
        se = tg->se[cpu_of(rq_of(cfs_rq))];
        if (!se || throttled_hierarchy(cfs_rq))
                return;
#ifndef CONFIG_SMP
        if (likely(se->load.weight == tg->shares))
                return;
#endif
        shares = calc_cfs_shares(cfs_rq, tg);

        reweight_entity(cfs_rq_of(se), se, shares);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void update_cfs_shares(struct cfs_rq *cfs_rq)
{
}
#endif /* CONFIG_FAIR_GROUP_SCHED */

#ifdef CONFIG_SMP
/*
 * We choose a half-life close to 1 scheduling period.
 * Note: The tables below are dependent on this value.
 */
#define LOAD_AVG_PERIOD 32
#define LOAD_AVG_MAX 47742 /* maximum possible load avg */
#define LOAD_AVG_MAX_N 345 /* number of full periods to produce LOAD_MAX_AVG */

/* Precomputed fixed inverse multiplies for multiplication by y^n */
static const u32 runnable_avg_yN_inv[] = {
        0xffffffff, 0xfa83b2da, 0xf5257d14, 0xefe4b99a, 0xeac0c6e6, 0xe5b906e6,
        0xe0ccdeeb, 0xdbfbb796, 0xd744fcc9, 0xd2a81d91, 0xce248c14, 0xc9b9bd85,
        0xc5672a10, 0xc12c4cc9, 0xbd08a39e, 0xb8fbaf46, 0xb504f333, 0xb123f581,
        0xad583ee9, 0xa9a15ab4, 0xa5fed6a9, 0xa2704302, 0x9ef5325f, 0x9b8d39b9,
        0x9837f050, 0x94f4efa8, 0x91c3d373, 0x8ea4398a, 0x8b95c1e3, 0x88980e80,
        0x85aac367, 0x82cd8698,
};

/*
 * Precomputed \Sum y^k { 1<=k<=n }.  These are floor(true_value) to prevent
 * over-estimates when re-combining.
 */
static const u32 runnable_avg_yN_sum[] = {
            0, 1002, 1982, 2941, 3880, 4798, 5697, 6576, 7437, 8279, 9103,
         9909,10698,11470,12226,12966,13690,14398,15091,15769,16433,17082,
        17718,18340,18949,19545,20128,20698,21256,21802,22336,22859,23371,
};

/*
 * Approximate:
 *   val * y^n,    where y^32 ~= 0.5 (~1 scheduling period)
 */
static __always_inline u64 decay_load(u64 val, u64 n)
{
        unsigned int local_n;

        if (!n)
                return val;
        else if (unlikely(n > LOAD_AVG_PERIOD * 63))
                return 0;

        /* after bounds checking we can collapse to 32-bit */
        local_n = n;

        /*
         * As y^PERIOD = 1/2, we can combine
         *    y^n = 1/2^(n/PERIOD) * y^(n%PERIOD)
         * With a look-up table which covers y^n (n<PERIOD)
         *
         * To achieve constant time decay_load.
         */
        if (unlikely(local_n >= LOAD_AVG_PERIOD)) {
                val >>= local_n / LOAD_AVG_PERIOD;
                local_n %= LOAD_AVG_PERIOD;
        }

        val *= runnable_avg_yN_inv[local_n];
        /* We don't use SRR here since we always want to round down. */
        return val >> 32;
}

/*
 * For updates fully spanning n periods, the contribution to runnable
 * average will be: \Sum 1024*y^n
 *
 * We can compute this reasonably efficiently by combining:
 *   y^PERIOD = 1/2 with precomputed \Sum 1024*y^n {for  n <PERIOD}
 */
static u32 __compute_runnable_contrib(u64 n)
{
        u32 contrib = 0;

        if (likely(n <= LOAD_AVG_PERIOD))
                return runnable_avg_yN_sum[n];
        else if (unlikely(n >= LOAD_AVG_MAX_N))
                return LOAD_AVG_MAX;

        /* Compute \Sum k^n combining precomputed values for k^i, \Sum k^j */
        do {
                contrib /= 2; /* y^LOAD_AVG_PERIOD = 1/2 */
                contrib += runnable_avg_yN_sum[LOAD_AVG_PERIOD];

                n -= LOAD_AVG_PERIOD;
        } while (n > LOAD_AVG_PERIOD);

        contrib = decay_load(contrib, n);
        return contrib + runnable_avg_yN_sum[n];
}

/*
 * We can represent the historical contribution to runnable average as the
 * coefficients of a geometric series.  To do this we sub-divide our runnable
 * history into segments of approximately 1ms (1024us); label the segment that
 * occurred N-ms ago p_N, with p_0 corresponding to the current period, e.g.
 *
 * [<- 1024us ->|<- 1024us ->|<- 1024us ->| ...
 *      p0            p1           p2
 *     (now)       (~1ms ago)  (~2ms ago)
 *
 * Let u_i denote the fraction of p_i that the entity was runnable.
 *
 * We then designate the fractions u_i as our co-efficients, yielding the
 * following representation of historical load:
 *   u_0 + u_1*y + u_2*y^2 + u_3*y^3 + ...
 *
 * We choose y based on the with of a reasonably scheduling period, fixing:
 *   y^32 = 0.5
 *
 * This means that the contribution to load ~32ms ago (u_32) will be weighted
 * approximately half as much as the contribution to load within the last ms
 * (u_0).
 *
 * When a period "rolls over" and we have new u_0`, multiplying the previous
 * sum again by y is sufficient to update:
 *   load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... )
 *            = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1}]
 */
static __always_inline int __update_entity_runnable_avg(u64 now, int cpu,
                                                        struct sched_avg *sa,
                                                        int runnable,
                                                        int running)
{
        u64 delta, periods;
        u32 runnable_contrib;
        int delta_w, decayed = 0;
        unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);

        delta = now - sa->last_runnable_update;
        /*
         * This should only happen when time goes backwards, which it
         * unfortunately does during sched clock init when we swap over to TSC.
         */
        if ((s64)delta < 0) {
                sa->last_runnable_update = now;
                return 0;
        }

        /*
         * Use 1024ns as the unit of measurement since it's a reasonable
         * approximation of 1us and fast to compute.
         */
        delta >>= 10;
        if (!delta)
                return 0;
        sa->last_runnable_update = now;

        /* delta_w is the amount already accumulated against our next period */
        delta_w = sa->avg_period % 1024;
        if (delta + delta_w >= 1024) {
                /* period roll-over */
                decayed = 1;

                /*
                 * Now that we know we're crossing a period boundary, figure
                 * out how much from delta we need to complete the current
                 * period and accrue it.
                 */
                delta_w = 1024 - delta_w;
                if (runnable)
                        sa->runnable_avg_sum += delta_w;
                if (running)
                        sa->running_avg_sum += delta_w * scale_freq
                                >> SCHED_CAPACITY_SHIFT;
                sa->avg_period += delta_w;

                delta -= delta_w;

                /* Figure out how many additional periods this update spans */
                periods = delta / 1024;
                delta %= 1024;

                sa->runnable_avg_sum = decay_load(sa->runnable_avg_sum,
                                                  periods + 1);
                sa->running_avg_sum = decay_load(sa->running_avg_sum,
                                                  periods + 1);
                sa->avg_period = decay_load(sa->avg_period,
                                                     periods + 1);

                /* Efficiently calculate \sum (1..n_period) 1024*y^i */
                runnable_contrib = __compute_runnable_contrib(periods);
                if (runnable)
                        sa->runnable_avg_sum += runnable_contrib;
                if (running)
                        sa->running_avg_sum += runnable_contrib * scale_freq
                                >> SCHED_CAPACITY_SHIFT;
                sa->avg_period += runnable_contrib;
        }

        /* Remainder of delta accrued against u_0` */
        if (runnable)
                sa->runnable_avg_sum += delta;
        if (running)
                sa->running_avg_sum += delta * scale_freq
                        >> SCHED_CAPACITY_SHIFT;
        sa->avg_period += delta;

        return decayed;
}

/* Synchronize an entity's decay with its parenting cfs_rq.*/
static inline u64 __synchronize_entity_decay(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        u64 decays = atomic64_read(&cfs_rq->decay_counter);

        decays -= se->avg.decay_count;
        se->avg.decay_count = 0;
        if (!decays)
                return 0;

        se->avg.load_avg_contrib = decay_load(se->avg.load_avg_contrib, decays);
        se->avg.utilization_avg_contrib =
                decay_load(se->avg.utilization_avg_contrib, decays);

        return decays;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
                                                 int force_update)
{
        struct task_group *tg = cfs_rq->tg;
        long tg_contrib;

        tg_contrib = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg;
        tg_contrib -= cfs_rq->tg_load_contrib;

        if (!tg_contrib)
                return;

        if (force_update || abs(tg_contrib) > cfs_rq->tg_load_contrib / 8) {
                atomic_long_add(tg_contrib, &tg->load_avg);
                cfs_rq->tg_load_contrib += tg_contrib;
        }
}

/*
 * Aggregate cfs_rq runnable averages into an equivalent task_group
 * representation for computing load contributions.
 */
static inline void __update_tg_runnable_avg(struct sched_avg *sa,
                                                  struct cfs_rq *cfs_rq)
{
        struct task_group *tg = cfs_rq->tg;
        long contrib;

        /* The fraction of a cpu used by this cfs_rq */
        contrib = div_u64((u64)sa->runnable_avg_sum << NICE_0_SHIFT,
                          sa->avg_period + 1);
        contrib -= cfs_rq->tg_runnable_contrib;

        if (abs(contrib) > cfs_rq->tg_runnable_contrib / 64) {
                atomic_add(contrib, &tg->runnable_avg);
                cfs_rq->tg_runnable_contrib += contrib;
        }
}

static inline void __update_group_entity_contrib(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = group_cfs_rq(se);
        struct task_group *tg = cfs_rq->tg;
        int runnable_avg;

        u64 contrib;

        contrib = cfs_rq->tg_load_contrib * tg->shares;
        se->avg.load_avg_contrib = div_u64(contrib,
                                     atomic_long_read(&tg->load_avg) + 1);

        /*
         * For group entities we need to compute a correction term in the case
         * that they are consuming <1 cpu so that we would contribute the same
         * load as a task of equal weight.
         *
         * Explicitly co-ordinating this measurement would be expensive, but
         * fortunately the sum of each cpus contribution forms a usable
         * lower-bound on the true value.
         *
         * Consider the aggregate of 2 contributions.  Either they are disjoint
         * (and the sum represents true value) or they are disjoint and we are
         * understating by the aggregate of their overlap.
         *
         * Extending this to N cpus, for a given overlap, the maximum amount we
         * understand is then n_i(n_i+1)/2 * w_i where n_i is the number of
         * cpus that overlap for this interval and w_i is the interval width.
         *
         * On a small machine; the first term is well-bounded which bounds the
         * total error since w_i is a subset of the period.  Whereas on a
         * larger machine, while this first term can be larger, if w_i is the
         * of consequential size guaranteed to see n_i*w_i quickly converge to
         * our upper bound of 1-cpu.
         */
        runnable_avg = atomic_read(&tg->runnable_avg);
        if (runnable_avg < NICE_0_LOAD) {
                se->avg.load_avg_contrib *= runnable_avg;
                se->avg.load_avg_contrib >>= NICE_0_SHIFT;
        }
}

static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
{
        __update_entity_runnable_avg(rq_clock_task(rq), cpu_of(rq), &rq->avg,
                        runnable, runnable);
        __update_tg_runnable_avg(&rq->avg, &rq->cfs);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
                                                 int force_update) {}
static inline void __update_tg_runnable_avg(struct sched_avg *sa,
                                                  struct cfs_rq *cfs_rq) {}
static inline void __update_group_entity_contrib(struct sched_entity *se) {}
static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {}
#endif /* CONFIG_FAIR_GROUP_SCHED */

static inline void __update_task_entity_contrib(struct sched_entity *se)
{
        u32 contrib;

        /* avoid overflowing a 32-bit type w/ SCHED_LOAD_SCALE */
        contrib = se->avg.runnable_avg_sum * scale_load_down(se->load.weight);
        contrib /= (se->avg.avg_period + 1);
        se->avg.load_avg_contrib = scale_load(contrib);
}

/* Compute the current contribution to load_avg by se, return any delta */
static long __update_entity_load_avg_contrib(struct sched_entity *se)
{
        long old_contrib = se->avg.load_avg_contrib;

        if (entity_is_task(se)) {
                __update_task_entity_contrib(se);
        } else {
                __update_tg_runnable_avg(&se->avg, group_cfs_rq(se));
                __update_group_entity_contrib(se);
        }

        return se->avg.load_avg_contrib - old_contrib;
}


static inline void __update_task_entity_utilization(struct sched_entity *se)
{
        u32 contrib;

        /* avoid overflowing a 32-bit type w/ SCHED_LOAD_SCALE */
        contrib = se->avg.running_avg_sum * scale_load_down(SCHED_LOAD_SCALE);
        contrib /= (se->avg.avg_period + 1);
        se->avg.utilization_avg_contrib = scale_load(contrib);
}

static long __update_entity_utilization_avg_contrib(struct sched_entity *se)
{
        long old_contrib = se->avg.utilization_avg_contrib;

        if (entity_is_task(se))
                __update_task_entity_utilization(se);
        else
                se->avg.utilization_avg_contrib =
                                        group_cfs_rq(se)->utilization_load_avg;

        return se->avg.utilization_avg_contrib - old_contrib;
}

static inline void subtract_blocked_load_contrib(struct cfs_rq *cfs_rq,
                                                 long load_contrib)
{
        if (likely(load_contrib < cfs_rq->blocked_load_avg))
                cfs_rq->blocked_load_avg -= load_contrib;
        else
                cfs_rq->blocked_load_avg = 0;
}

static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);

/* Update a sched_entity's runnable average */
static inline void update_entity_load_avg(struct sched_entity *se,
                                          int update_cfs_rq)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        long contrib_delta, utilization_delta;
        int cpu = cpu_of(rq_of(cfs_rq));
        u64 now;

        /*
         * For a group entity we need to use their owned cfs_rq_clock_task() in
         * case they are the parent of a throttled hierarchy.
         */
        if (entity_is_task(se))
                now = cfs_rq_clock_task(cfs_rq);
        else
                now = cfs_rq_clock_task(group_cfs_rq(se));

        if (!__update_entity_runnable_avg(now, cpu, &se->avg, se->on_rq,
                                        cfs_rq->curr == se))
                return;

        contrib_delta = __update_entity_load_avg_contrib(se);
        utilization_delta = __update_entity_utilization_avg_contrib(se);

        if (!update_cfs_rq)
                return;

        if (se->on_rq) {
                cfs_rq->runnable_load_avg += contrib_delta;
                cfs_rq->utilization_load_avg += utilization_delta;
        } else {
                subtract_blocked_load_contrib(cfs_rq, -contrib_delta);
        }
}

/*
 * Decay the load contributed by all blocked children and account this so that
 * their contribution may appropriately discounted when they wake up.
 */
static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq, int force_update)
{
        u64 now = cfs_rq_clock_task(cfs_rq) >> 20;
        u64 decays;

        decays = now - cfs_rq->last_decay;
        if (!decays && !force_update)
                return;

        if (atomic_long_read(&cfs_rq->removed_load)) {
                unsigned long removed_load;
                removed_load = atomic_long_xchg(&cfs_rq->removed_load, 0);
                subtract_blocked_load_contrib(cfs_rq, removed_load);
        }

        if (decays) {
                cfs_rq->blocked_load_avg = decay_load(cfs_rq->blocked_load_avg,
                                                      decays);
                atomic64_add(decays, &cfs_rq->decay_counter);
                cfs_rq->last_decay = now;
        }

        __update_cfs_rq_tg_load_contrib(cfs_rq, force_update);
}

/* Add the load generated by se into cfs_rq's child load-average */
static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
                                                  struct sched_entity *se,
                                                  int wakeup)
{
        /*
         * We track migrations using entity decay_count <= 0, on a wake-up
         * migration we use a negative decay count to track the remote decays
         * accumulated while sleeping.
         *
         * Newly forked tasks are enqueued with se->avg.decay_count == 0, they
         * are seen by enqueue_entity_load_avg() as a migration with an already
         * constructed load_avg_contrib.
         */
        if (unlikely(se->avg.decay_count <= 0)) {
                se->avg.last_runnable_update = rq_clock_task(rq_of(cfs_rq));
                if (se->avg.decay_count) {
                        /*
                         * In a wake-up migration we have to approximate the
                         * time sleeping.  This is because we can't synchronize
                         * clock_task between the two cpus, and it is not
                         * guaranteed to be read-safe.  Instead, we can
                         * approximate this using our carried decays, which are
                         * explicitly atomically readable.
                         */
                        se->avg.last_runnable_update -= (-se->avg.decay_count)
                                                        << 20;
                        update_entity_load_avg(se, 0);
                        /* Indicate that we're now synchronized and on-rq */
                        se->avg.decay_count = 0;
                }
                wakeup = 0;
        } else {
                __synchronize_entity_decay(se);
        }

        /* migrated tasks did not contribute to our blocked load */
        if (wakeup) {
                subtract_blocked_load_contrib(cfs_rq, se->avg.load_avg_contrib);
                update_entity_load_avg(se, 0);
        }

        cfs_rq->runnable_load_avg += se->avg.load_avg_contrib;
        cfs_rq->utilization_load_avg += se->avg.utilization_avg_contrib;
        /* we force update consideration on load-balancer moves */
        update_cfs_rq_blocked_load(cfs_rq, !wakeup);
}

/*
 * Remove se's load from this cfs_rq child load-average, if the entity is
 * transitioning to a blocked state we track its projected decay using
 * blocked_load_avg.
 */
static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,
                                                  struct sched_entity *se,
                                                  int sleep)
{
        update_entity_load_avg(se, 1);
        /* we force update consideration on load-balancer moves */
        update_cfs_rq_blocked_load(cfs_rq, !sleep);

        cfs_rq->runnable_load_avg -= se->avg.load_avg_contrib;
        cfs_rq->utilization_load_avg -= se->avg.utilization_avg_contrib;
        if (sleep) {
                cfs_rq->blocked_load_avg += se->avg.load_avg_contrib;
                se->avg.decay_count = atomic64_read(&cfs_rq->decay_counter);
        } /* migrations, e.g. sleep=0 leave decay_count == 0 */
}

/*
 * Update the rq's load with the elapsed running time before entering
 * idle. if the last scheduled task is not a CFS task, idle_enter will
 * be the only way to update the runnable statistic.
 */
void idle_enter_fair(struct rq *this_rq)
{
        update_rq_runnable_avg(this_rq, 1);
}

/*
 * Update the rq's load with the elapsed idle time before a task is
 * scheduled. if the newly scheduled task is not a CFS task, idle_exit will
 * be the only way to update the runnable statistic.
 */
void idle_exit_fair(struct rq *this_rq)
{
        update_rq_runnable_avg(this_rq, 0);
}

static int idle_balance(struct rq *this_rq);

#else /* CONFIG_SMP */

static inline void update_entity_load_avg(struct sched_entity *se,
                                          int update_cfs_rq) {}
static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {}
static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
                                           struct sched_entity *se,
                                           int wakeup) {}
static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,
                                           struct sched_entity *se,
                                           int sleep) {}
static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq,
                                              int force_update) {}

static inline int idle_balance(struct rq *rq)
{
        return 0;
}

#endif /* CONFIG_SMP */

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_clock(rq_of(cfs_rq)) - 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_clock(rq_of(cfs_rq)) - 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);
                        }

                        trace_sched_stat_blocked(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. */
        se->vruntime = max_vruntime(se->vruntime, vruntime);
}

static void check_enqueue_throttle(struct cfs_rq *cfs_rq);

static void
enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        /*
         * Update the normalized vruntime before updating min_vruntime
         * through calling 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);
        enqueue_entity_load_avg(cfs_rq, se, flags & ENQUEUE_WAKEUP);
        account_entity_enqueue(cfs_rq, se);
        update_cfs_shares(cfs_rq);

        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);
        se->on_rq = 1;

        if (cfs_rq->nr_running == 1) {
                list_add_leaf_cfs_rq(cfs_rq);
                check_enqueue_throttle(cfs_rq);
        }
}

static void __clear_buddies_last(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->last != se)
                        break;

                cfs_rq->last = NULL;
        }
}

static void __clear_buddies_next(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->next != se)
                        break;

                cfs_rq->next = NULL;
        }
}

static void __clear_buddies_skip(struct sched_entity *se)
{
        for_each_sched_entity(se) {
                struct cfs_rq *cfs_rq = cfs_rq_of(se);
                if (cfs_rq->skip != se)
                        break;

                cfs_rq->skip = NULL;
        }
}

static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        if (cfs_rq->last == se)
                __clear_buddies_last(se);

        if (cfs_rq->next == se)
                __clear_buddies_next(se);

        if (cfs_rq->skip == se)
                __clear_buddies_skip(se);
}

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);

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);
        dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP);

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

        clear_buddies(cfs_rq, se);

        if (se != cfs_rq->curr)
                __dequeue_entity(cfs_rq, se);
        se->on_rq = 0;
        account_entity_dequeue(cfs_rq, se);

        /*
         * 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;

        /* return excess runtime on last dequeue */
        return_cfs_rq_runtime(cfs_rq);

        update_min_vruntime(cfs_rq);
        update_cfs_shares(cfs_rq);
}

/*
 * 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;
        struct sched_entity *se;
        s64 delta;

        ideal_runtime = sched_slice(cfs_rq, curr);
        delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
        if (delta_exec > ideal_runtime) {
                resched_curr(rq_of(cfs_rq));
                /*
                 * 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 (delta_exec < sysctl_sched_min_granularity)
                return;

        se = __pick_first_entity(cfs_rq);
        delta = curr->vruntime - se->vruntime;

        if (delta < 0)
                return;

        if (delta > ideal_runtime)
                resched_curr(rq_of(cfs_rq));
}

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_entity_load_avg(se, 1);
        }

        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);

/*
 * Pick the next process, keeping these things in mind, in this order:
 * 1) keep things fair between processes/task groups
 * 2) pick the "next" process, since someone really wants that to run
 * 3) pick the "last" process, for cache locality
 * 4) do not run the "skip" process, if something else is available
 */
static struct sched_entity *
pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
        struct sched_entity *left = __pick_first_entity(cfs_rq);
        struct sched_entity *se;

        /*
         * If curr is set we have to see if its left of the leftmost entity
         * still in the tree, provided there was anything in the tree at all.
         */
        if (!left || (curr && entity_before(curr, left)))
                left = curr;

        se = left; /* ideally we run the leftmost entity */

        /*
         * Avoid running the skip buddy, if running something else can
         * be done without getting too unfair.
         */
        if (cfs_rq->skip == se) {
                struct sched_entity *second;

                if (se == curr) {
                        second = __pick_first_entity(cfs_rq);
                } else {
                        second = __pick_next_entity(se);
                        if (!second || (curr && entity_before(curr, second)))
                                second = curr;
                }

                if (second && wakeup_preempt_entity(second, left) < 1)
                        se = second;
        }

        /*
         * 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;

        /*
         * Someone really wants this to run. If it's not unfair, run it.
         */
        if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
                se = cfs_rq->next;

        clear_buddies(cfs_rq, se);

        return se;
}

static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq);

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);

        /* throttle cfs_rqs exceeding runtime */
        check_cfs_rq_runtime(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);
                /* in !on_rq case, update occurred at dequeue */
                update_entity_load_avg(prev, 1);
        }
        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);

        /*
         * Ensure that runnable average is periodically updated.
         */
        update_entity_load_avg(curr, 1);
        update_cfs_rq_blocked_load(cfs_rq, 1);
        update_cfs_shares(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_curr(rq_of(cfs_rq));
                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)
                check_preempt_tick(cfs_rq, curr);
}


/**************************************************
 * CFS bandwidth control machinery
 */

#ifdef CONFIG_CFS_BANDWIDTH

#ifdef HAVE_JUMP_LABEL
static struct static_key __cfs_bandwidth_used;

static inline bool cfs_bandwidth_used(void)
{
        return static_key_false(&__cfs_bandwidth_used);
}

void cfs_bandwidth_usage_inc(void)
{
        static_key_slow_inc(&__cfs_bandwidth_used);
}

void cfs_bandwidth_usage_dec(void)
{
        static_key_slow_dec(&__cfs_bandwidth_used);
}
#else /* HAVE_JUMP_LABEL */
static bool cfs_bandwidth_used(void)
{
        return true;
}

void cfs_bandwidth_usage_inc(void) {}
void cfs_bandwidth_usage_dec(void) {}
#endif /* HAVE_JUMP_LABEL */

/*
 * default period for cfs group bandwidth.
 * default: 0.1s, units: nanoseconds
 */
static inline u64 default_cfs_period(void)
{
        return 100000000ULL;
}

static inline u64 sched_cfs_bandwidth_slice(void)
{
        return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
}

/*
 * Replenish runtime according to assigned quota and update expiration time.
 * We use sched_clock_cpu directly instead of rq->clock to avoid adding
 * additional synchronization around rq->lock.
 *
 * requires cfs_b->lock
 */
void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
{
        u64 now;

        if (cfs_b->quota == RUNTIME_INF)
                return;

        now = sched_clock_cpu(smp_processor_id());
        cfs_b->runtime = cfs_b->quota;
        cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period);
}

static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
        return &tg->cfs_bandwidth;
}

/* rq->task_clock normalized against any time this cfs_rq has spent throttled */
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
        if (unlikely(cfs_rq->throttle_count))
                return cfs_rq->throttled_clock_task;

        return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
}

/* returns 0 on failure to allocate runtime */
static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct task_group *tg = cfs_rq->tg;
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
        u64 amount = 0, min_amount, expires;

        /* note: this is a positive sum as runtime_remaining <= 0 */
        min_amount = sched_cfs_bandwidth_slice() - cfs_rq->runtime_remaining;

        raw_spin_lock(&cfs_b->lock);
        if (cfs_b->quota == RUNTIME_INF)
                amount = min_amount;
        else {
                start_cfs_bandwidth(cfs_b);

                if (cfs_b->runtime > 0) {
                        amount = min(cfs_b->runtime, min_amount);
                        cfs_b->runtime -= amount;
                        cfs_b->idle = 0;
                }
        }
        expires = cfs_b->runtime_expires;
        raw_spin_unlock(&cfs_b->lock);

        cfs_rq->runtime_remaining += amount;
        /*
         * we may have advanced our local expiration to account for allowed
         * spread between our sched_clock and the one on which runtime was
         * issued.
         */
        if ((s64)(expires - cfs_rq->runtime_expires) > 0)
                cfs_rq->runtime_expires = expires;

        return cfs_rq->runtime_remaining > 0;
}

/*
 * Note: This depends on the synchronization provided by sched_clock and the
 * fact that rq->clock snapshots this value.
 */
static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);

        /* if the deadline is ahead of our clock, nothing to do */
        if (likely((s64)(rq_clock(rq_of(cfs_rq)) - cfs_rq->runtime_expires) < 0))
                return;

        if (cfs_rq->runtime_remaining < 0)
                return;

        /*
         * If the local deadline has passed we have to consider the
         * possibility that our sched_clock is 'fast' and the global deadline
         * has not truly expired.
         *
         * Fortunately we can check determine whether this the case by checking
         * whether the global deadline has advanced. It is valid to compare
         * cfs_b->runtime_expires without any locks since we only care about
         * exact equality, so a partial write will still work.
         */

        if (cfs_rq->runtime_expires != cfs_b->runtime_expires) {
                /* extend local deadline, drift is bounded above by 2 ticks */
                cfs_rq->runtime_expires += TICK_NSEC;
        } else {
                /* global deadline is ahead, expiration has passed */
                cfs_rq->runtime_remaining = 0;
        }
}

static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
{
        /* dock delta_exec before expiring quota (as it could span periods) */
        cfs_rq->runtime_remaining -= delta_exec;
        expire_cfs_rq_runtime(cfs_rq);

        if (likely(cfs_rq->runtime_remaining > 0))
                return;

        /*
         * if we're unable to extend our runtime we resched so that the active
         * hierarchy can be throttled
         */
        if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->curr))
                resched_curr(rq_of(cfs_rq));
}

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
{
        if (!cfs_bandwidth_used() || !cfs_rq->runtime_enabled)
                return;

        __account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
        return cfs_bandwidth_used() && cfs_rq->throttled;
}

/* check whether cfs_rq, or any parent, is throttled */
static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
        return cfs_bandwidth_used() && cfs_rq->throttle_count;
}

/*
 * Ensure that neither of the group entities corresponding to src_cpu or
 * dest_cpu are members of a throttled hierarchy when performing group
 * load-balance operations.
 */
static inline int throttled_lb_pair(struct task_group *tg,
                                    int src_cpu, int dest_cpu)
{
        struct cfs_rq *src_cfs_rq, *dest_cfs_rq;

        src_cfs_rq = tg->cfs_rq[src_cpu];
        dest_cfs_rq = tg->cfs_rq[dest_cpu];

        return throttled_hierarchy(src_cfs_rq) ||
               throttled_hierarchy(dest_cfs_rq);
}

/* updated child weight may affect parent so we have to do this bottom up */
static int tg_unthrottle_up(struct task_group *tg, void *data)
{
        struct rq *rq = data;
        struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

        cfs_rq->throttle_count--;
#ifdef CONFIG_SMP
        if (!cfs_rq->throttle_count) {
                /* adjust cfs_rq_clock_task() */
                cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
                                             cfs_rq->throttled_clock_task;
        }
#endif

        return 0;
}

static int tg_throttle_down(struct task_group *tg, void *data)
{
        struct rq *rq = data;
        struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

        /* group is entering throttled state, stop time */
        if (!cfs_rq->throttle_count)
                cfs_rq->throttled_clock_task = rq_clock_task(rq);
        cfs_rq->throttle_count++;

        return 0;
}

static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
{
        struct rq *rq = rq_of(cfs_rq);
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        struct sched_entity *se;
        long task_delta, dequeue = 1;
        bool empty;

        se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];

        /* freeze hierarchy runnable averages while throttled */
        rcu_read_lock();
        walk_tg_tree_from(cfs_rq->tg, tg_throttle_down, tg_nop, (void *)rq);
        rcu_read_unlock();

        task_delta = cfs_rq->h_nr_running;
        for_each_sched_entity(se) {
                struct cfs_rq *qcfs_rq = cfs_rq_of(se);
                /* throttled entity or throttle-on-deactivate */
                if (!se->on_rq)
                        break;

                if (dequeue)
                        dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
                qcfs_rq->h_nr_running -= task_delta;

                if (qcfs_rq->load.weight)
                        dequeue = 0;
        }

        if (!se)
                sub_nr_running(rq, task_delta);

        cfs_rq->throttled = 1;
        cfs_rq->throttled_clock = rq_clock(rq);
        raw_spin_lock(&cfs_b->lock);
        empty = list_empty(&cfs_b->throttled_cfs_rq);

        /*
         * Add to the _head_ of the list, so that an already-started
         * distribute_cfs_runtime will not see us
         */
        list_add_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);

        /*
         * If we're the first throttled task, make sure the bandwidth
         * timer is running.
         */
        if (empty)
                start_cfs_bandwidth(cfs_b);

        raw_spin_unlock(&cfs_b->lock);
}

void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
{
        struct rq *rq = rq_of(cfs_rq);
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        struct sched_entity *se;
        int enqueue = 1;
        long task_delta;

        se = cfs_rq->tg->se[cpu_of(rq)];

        cfs_rq->throttled = 0;

        update_rq_clock(rq);

        raw_spin_lock(&cfs_b->lock);
        cfs_b->throttled_time += rq_clock(rq) - cfs_rq->throttled_clock;
        list_del_rcu(&cfs_rq->throttled_list);
        raw_spin_unlock(&cfs_b->lock);

        /* update hierarchical throttle state */
        walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq);

        if (!cfs_rq->load.weight)
                return;

        task_delta = cfs_rq->h_nr_running;
        for_each_sched_entity(se) {
                if (se->on_rq)
                        enqueue = 0;

                cfs_rq = cfs_rq_of(se);
                if (enqueue)
                        enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
                cfs_rq->h_nr_running += task_delta;

                if (cfs_rq_throttled(cfs_rq))
                        break;
        }

        if (!se)
                add_nr_running(rq, task_delta);

        /* determine whether we need to wake up potentially idle cpu */
        if (rq->curr == rq->idle && rq->cfs.nr_running)
                resched_curr(rq);
}

static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
                u64 remaining, u64 expires)
{
        struct cfs_rq *cfs_rq;
        u64 runtime;
        u64 starting_runtime = remaining;

        rcu_read_lock();
        list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq,
                                throttled_list) {
                struct rq *rq = rq_of(cfs_rq);

                raw_spin_lock(&rq->lock);
                if (!cfs_rq_throttled(cfs_rq))
                        goto next;

                runtime = -cfs_rq->runtime_remaining + 1;
                if (runtime > remaining)
                        runtime = remaining;
                remaining -= runtime;

                cfs_rq->runtime_remaining += runtime;
                cfs_rq->runtime_expires = expires;

                /* we check whether we're throttled above */
                if (cfs_rq->runtime_remaining > 0)
                        unthrottle_cfs_rq(cfs_rq);

next:
                raw_spin_unlock(&rq->lock);

                if (!remaining)
                        break;
        }
        rcu_read_unlock();

        return starting_runtime - remaining;
}

/*
 * Responsible for refilling a task_group's bandwidth and unthrottling its
 * cfs_rqs as appropriate. If there has been no activity within the last
 * period the timer is deactivated until scheduling resumes; cfs_b->idle is
 * used to track this state.
 */
static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
{
        u64 runtime, runtime_expires;
        int throttled;

        /* no need to continue the timer with no bandwidth constraint */
        if (cfs_b->quota == RUNTIME_INF)
                goto out_deactivate;

        throttled = !list_empty(&cfs_b->throttled_cfs_rq);
        cfs_b->nr_periods += overrun;

        /*
         * idle depends on !throttled (for the case of a large deficit), and if
         * we're going inactive then everything else can be deferred
         */
        if (cfs_b->idle && !throttled)
                goto out_deactivate;

        __refill_cfs_bandwidth_runtime(cfs_b);

        if (!throttled) {
                /* mark as potentially idle for the upcoming period */
                cfs_b->idle = 1;
                return 0;
        }

        /* account preceding periods in which throttling occurred */
        cfs_b->nr_throttled += overrun;

        runtime_expires = cfs_b->runtime_expires;

        /*
         * This check is repeated as we are holding onto the new bandwidth while
         * we unthrottle. This can potentially race with an unthrottled group
         * trying to acquire new bandwidth from the global pool. This can result
         * in us over-using our runtime if it is all used during this loop, but
         * only by limited amounts in that extreme case.
         */
        while (throttled && cfs_b->runtime > 0) {
                runtime = cfs_b->runtime;
                raw_spin_unlock(&cfs_b->lock);
                /* we can't nest cfs_b->lock while distributing bandwidth */
                runtime = distribute_cfs_runtime(cfs_b, runtime,
                                                 runtime_expires);
                raw_spin_lock(&cfs_b->lock);

                throttled = !list_empty(&cfs_b->throttled_cfs_rq);

                cfs_b->runtime -= min(runtime, cfs_b->runtime);
        }

        /*
         * While we are ensured activity in the period following an
         * unthrottle, this also covers the case in which the new bandwidth is
         * insufficient to cover the existing bandwidth deficit.  (Forcing the
         * timer to remain active while there are any throttled entities.)
         */
        cfs_b->idle = 0;

        return 0;

out_deactivate:
        return 1;
}

/* a cfs_rq won't donate quota below this amount */
static const u64 min_cfs_rq_runtime = 1 * NSEC_PER_MSEC;
/* minimum remaining period time to redistribute slack quota */
static const u64 min_bandwidth_expiration = 2 * NSEC_PER_MSEC;
/* how long we wait to gather additional slack before distributing */
static const u64 cfs_bandwidth_slack_period = 5 * NSEC_PER_MSEC;

/*
 * Are we near the end of the current quota period?
 *
 * Requires cfs_b->lock for hrtimer_expires_remaining to be safe against the
 * hrtimer base being cleared by hrtimer_start. In the case of
 * migrate_hrtimers, base is never cleared, so we are fine.
 */
static int runtime_refresh_within(struct cfs_bandwidth *cfs_b, u64 min_expire)
{
        struct hrtimer *refresh_timer = &cfs_b->period_timer;
        u64 remaining;

        /* if the call-back is running a quota refresh is already occurring */
        if (hrtimer_callback_running(refresh_timer))
                return 1;

        /* is a quota refresh about to occur? */
        remaining = ktime_to_ns(hrtimer_expires_remaining(refresh_timer));
        if (remaining < min_expire)
                return 1;

        return 0;
}

static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
{
        u64 min_left = cfs_bandwidth_slack_period + min_bandwidth_expiration;

        /* if there's a quota refresh soon don't bother with slack */
        if (runtime_refresh_within(cfs_b, min_left))
                return;

        hrtimer_start(&cfs_b->slack_timer,
                        ns_to_ktime(cfs_bandwidth_slack_period),
                        HRTIMER_MODE_REL);
}

/* we know any runtime found here is valid as update_curr() precedes return */
static void __return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
        s64 slack_runtime = cfs_rq->runtime_remaining - min_cfs_rq_runtime;

        if (slack_runtime <= 0)
                return;

        raw_spin_lock(&cfs_b->lock);
        if (cfs_b->quota != RUNTIME_INF &&
            cfs_rq->runtime_expires == cfs_b->runtime_expires) {
                cfs_b->runtime += slack_runtime;

                /* we are under rq->lock, defer unthrottling using a timer */
                if (cfs_b->runtime > sched_cfs_bandwidth_slice() &&
                    !list_empty(&cfs_b->throttled_cfs_rq))
                        start_cfs_slack_bandwidth(cfs_b);
        }
        raw_spin_unlock(&cfs_b->lock);

        /* even if it's not valid for return we don't want to try again */
        cfs_rq->runtime_remaining -= slack_runtime;
}

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
        if (!cfs_bandwidth_used())
                return;

        if (!cfs_rq->runtime_enabled || cfs_rq->nr_running)
                return;

        __return_cfs_rq_runtime(cfs_rq);
}

/*
 * This is done with a timer (instead of inline with bandwidth return) since
 * it's necessary to juggle rq->locks to unthrottle their respective cfs_rqs.
 */
static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
{
        u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
        u64 expires;

        /* confirm we're still not at a refresh boundary */
        raw_spin_lock(&cfs_b->lock);
        if (runtime_refresh_within(cfs_b, min_bandwidth_expiration)) {
                raw_spin_unlock(&cfs_b->lock);
                return;
        }

        if (cfs_b->quota != RUNTIME_INF && cfs_b->runtime > slice)
                runtime = cfs_b->runtime;

        expires = cfs_b->runtime_expires;
        raw_spin_unlock(&cfs_b->lock);

        if (!runtime)
                return;

        runtime = distribute_cfs_runtime(cfs_b, runtime, expires);

        raw_spin_lock(&cfs_b->lock);
        if (expires == cfs_b->runtime_expires)
                cfs_b->runtime -= min(runtime, cfs_b->runtime);
        raw_spin_unlock(&cfs_b->lock);
}

/*
 * When a group wakes up we want to make sure that its quota is not already
 * expired/exceeded, otherwise it may be allowed to steal additional ticks of
 * runtime as update_curr() throttling can not not trigger until it's on-rq.
 */
static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
{
        if (!cfs_bandwidth_used())
                return;

        /* an active group must be handled by the update_curr()->put() path */
        if (!cfs_rq->runtime_enabled || cfs_rq->curr)
                return;

        /* ensure the group is not already throttled */
        if (cfs_rq_throttled(cfs_rq))
                return;

        /* update runtime allocation */
        account_cfs_rq_runtime(cfs_rq, 0);
        if (cfs_rq->runtime_remaining <= 0)
                throttle_cfs_rq(cfs_rq);
}

/* conditionally throttle active cfs_rq's from put_prev_entity() */
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq)