[sfrench/cifs-2.6.git] / kernel / sched / fair.c

// SPDX-License-Identifier: GPL-2.0
/*
 * 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
 */
#include "sched.h"

#include <trace/events/sched.h>

/*
 * Targeted preemption latency for CPU-bound tasks:
 *
 * 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)
 *
 * (default: 6ms * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_latency                       = 6000000ULL;
static unsigned int normalized_sysctl_sched_latency     = 6000000ULL;

/*
 * The initial- and re-scaling of tunables is configurable
 *
 * Options are:
 *
 *   SCHED_TUNABLESCALING_NONE - unscaled, always *1
 *   SCHED_TUNABLESCALING_LOG - scaled logarithmical, *1+ilog(ncpus)
 *   SCHED_TUNABLESCALING_LINEAR - scaled linear, *ncpus
 *
 * (default SCHED_TUNABLESCALING_LOG = *(1+ilog(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;
static unsigned int normalized_sysctl_sched_min_granularity     = 750000ULL;

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

const_debug unsigned int sysctl_sched_migration_cost    = 500000UL;

#ifdef CONFIG_SMP
/*
 * For asym packing, by default the lower numbered CPU has higher priority.
 */
int __weak arch_asym_cpu_priority(int cpu)
{
        return -cpu;
}

/*
 * The margin used when comparing utilization with CPU capacity:
 * util * margin < capacity * 1024
 *
 * (default: ~20%)
 */
static unsigned int capacity_margin                     = 1280;
#endif

#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 sched_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;
}

static inline struct task_struct *task_of(struct sched_entity *se)
{
        SCHED_WARN_ON(!entity_is_task(se));
        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 inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
        if (!cfs_rq->on_list) {
                struct rq *rq = rq_of(cfs_rq);
                int cpu = cpu_of(rq);
                /*
                 * 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 and a special case for the root
                 * cfs_rq. Furthermore, it also means that we will always reset
                 * tmp_alone_branch either when the branch is connected
                 * to a tree or when we reach the beg of the tree
                 */
                if (cfs_rq->tg->parent &&
                    cfs_rq->tg->parent->cfs_rq[cpu]->on_list) {
                        /*
                         * If parent is already on the list, we add the child
                         * just before. Thanks to circular linked property of
                         * the list, this means to put the child at the tail
                         * of the list that starts by parent.
                         */
                        list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
                                &(cfs_rq->tg->parent->cfs_rq[cpu]->leaf_cfs_rq_list));
                        /*
                         * The branch is now connected to its tree so we can
                         * reset tmp_alone_branch to the beginning of the
                         * list.
                         */
                        rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
                } else if (!cfs_rq->tg->parent) {
                        /*
                         * cfs rq without parent should be put
                         * at the tail of the list.
                         */
                        list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
                                &rq->leaf_cfs_rq_list);
                        /*
                         * We have reach the beg of a tree so we can reset
                         * tmp_alone_branch to the beginning of the list.
                         */
                        rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
                } else {
                        /*
                         * The parent has not already been added so we want to
                         * make sure that it will be put after us.
                         * tmp_alone_branch points to the beg of the branch
                         * where we will add parent.
                         */
                        list_add_rcu(&cfs_rq->leaf_cfs_rq_list,
                                rq->tmp_alone_branch);
                        /*
                         * update tmp_alone_branch to points to the new beg
                         * of the branch
                         */
                        rq->tmp_alone_branch = &cfs_rq->leaf_cfs_rq_list;
                }

                cfs_rq->on_list = 1;
        }
}

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 through 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 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)
{
        struct sched_entity *curr = cfs_rq->curr;
        struct rb_node *leftmost = rb_first_cached(&cfs_rq->tasks_timeline);

        u64 vruntime = cfs_rq->min_vruntime;

        if (curr) {
                if (curr->on_rq)
                        vruntime = curr->vruntime;
                else
                        curr = NULL;
        }

        if (leftmost) { /* non-empty tree */
                struct sched_entity *se;
                se = rb_entry(leftmost, struct sched_entity, run_node);

                if (!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_root.rb_node;
        struct rb_node *parent = NULL;
        struct sched_entity *entry;
        bool leftmost = true;

        /*
         * 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 = false;
                }
        }

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

static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        rb_erase_cached(&se->run_node, &cfs_rq->tasks_timeline);
}

struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
{
        struct rb_node *left = rb_first_cached(&cfs_rq->tasks_timeline);

        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.rb_root);

        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)
{
        if (unlikely(nr_running > sched_nr_latency))
                return nr_running * sysctl_sched_min_granularity;
        else
                return sysctl_sched_latency;
}

/*
 * 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
#include "pelt.h"
#include "sched-pelt.h"

static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
static unsigned long task_h_load(struct task_struct *p);
static unsigned long capacity_of(int cpu);

/* Give new sched_entity start runnable values to heavy its load in infant time */
void init_entity_runnable_average(struct sched_entity *se)
{
        struct sched_avg *sa = &se->avg;

        memset(sa, 0, sizeof(*sa));

        /*
         * Tasks are initialized with full load to be seen as heavy tasks until
         * they get a chance to stabilize to their real load level.
         * Group entities are initialized with zero load to reflect the fact that
         * nothing has been attached to the task group yet.
         */
        if (entity_is_task(se))
                sa->runnable_load_avg = sa->load_avg = scale_load_down(se->load.weight);

        se->runnable_weight = se->load.weight;

        /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
}

static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);
static void attach_entity_cfs_rq(struct sched_entity *se);

/*
 * With new tasks being created, their initial util_avgs are extrapolated
 * based on the cfs_rq's current util_avg:
 *
 *   util_avg = cfs_rq->util_avg / (cfs_rq->load_avg + 1) * se.load.weight
 *
 * However, in many cases, the above util_avg does not give a desired
 * value. Moreover, the sum of the util_avgs may be divergent, such
 * as when the series is a harmonic series.
 *
 * To solve this problem, we also cap the util_avg of successive tasks to
 * only 1/2 of the left utilization budget:
 *
 *   util_avg_cap = (cpu_scale - cfs_rq->avg.util_avg) / 2^n
 *
 * where n denotes the nth task and cpu_scale the CPU capacity.
 *
 * For example, for a CPU with 1024 of capacity, a simplest series from
 * the beginning would be like:
 *
 *  task  util_avg: 512, 256, 128,  64,  32,   16,    8, ...
 * cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ...
 *
 * Finally, that extrapolated util_avg is clamped to the cap (util_avg_cap)
 * if util_avg > util_avg_cap.
 */
void post_init_entity_util_avg(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        struct sched_avg *sa = &se->avg;
        long cpu_scale = arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq)));
        long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2;

        if (cap > 0) {
                if (cfs_rq->avg.util_avg != 0) {
                        sa->util_avg  = cfs_rq->avg.util_avg * se->load.weight;
                        sa->util_avg /= (cfs_rq->avg.load_avg + 1);

                        if (sa->util_avg > cap)
                                sa->util_avg = cap;
                } else {
                        sa->util_avg = cap;
                }
        }

        if (entity_is_task(se)) {
                struct task_struct *p = task_of(se);
                if (p->sched_class != &fair_sched_class) {
                        /*
                         * For !fair tasks do:
                         *
                        update_cfs_rq_load_avg(now, cfs_rq);
                        attach_entity_load_avg(cfs_rq, se, 0);
                        switched_from_fair(rq, p);
                         *
                         * such that the next switched_to_fair() has the
                         * expected state.
                         */
                        se->avg.last_update_time = cfs_rq_clock_task(cfs_rq);
                        return;
                }
        }

        attach_entity_cfs_rq(se);
}

#else /* !CONFIG_SMP */
void init_entity_runnable_average(struct sched_entity *se)
{
}
void post_init_entity_util_avg(struct sched_entity *se)
{
}
static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
{
}
#endif /* CONFIG_SMP */

/*
 * 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);
                cgroup_account_cputime(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)
{
        u64 wait_start, prev_wait_start;

        if (!schedstat_enabled())
                return;

        wait_start = rq_clock(rq_of(cfs_rq));
        prev_wait_start = schedstat_val(se->statistics.wait_start);

        if (entity_is_task(se) && task_on_rq_migrating(task_of(se)) &&
            likely(wait_start > prev_wait_start))
                wait_start -= prev_wait_start;

        __schedstat_set(se->statistics.wait_start, wait_start);
}

static inline void
update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        struct task_struct *p;
        u64 delta;

        if (!schedstat_enabled())
                return;

        delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);

        if (entity_is_task(se)) {
                p = task_of(se);
                if (task_on_rq_migrating(p)) {
                        /*
                         * Preserve migrating task's wait time so wait_start
                         * time stamp can be adjusted to accumulate wait time
                         * prior to migration.
                         */
                        __schedstat_set(se->statistics.wait_start, delta);
                        return;
                }
                trace_sched_stat_wait(p, delta);
        }

        __schedstat_set(se->statistics.wait_max,
                      max(schedstat_val(se->statistics.wait_max), delta));
        __schedstat_inc(se->statistics.wait_count);
        __schedstat_add(se->statistics.wait_sum, delta);
        __schedstat_set(se->statistics.wait_start, 0);
}

static inline void
update_stats_enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        struct task_struct *tsk = NULL;
        u64 sleep_start, block_start;

        if (!schedstat_enabled())
                return;

        sleep_start = schedstat_val(se->statistics.sleep_start);
        block_start = schedstat_val(se->statistics.block_start);

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

        if (sleep_start) {
                u64 delta = rq_clock(rq_of(cfs_rq)) - sleep_start;

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

                if (unlikely(delta > schedstat_val(se->statistics.sleep_max)))
                        __schedstat_set(se->statistics.sleep_max, delta);

                __schedstat_set(se->statistics.sleep_start, 0);
                __schedstat_add(se->statistics.sum_sleep_runtime, delta);

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

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

                if (unlikely(delta > schedstat_val(se->statistics.block_max)))
                        __schedstat_set(se->statistics.block_max, delta);

                __schedstat_set(se->statistics.block_start, 0);
                __schedstat_add(se->statistics.sum_sleep_runtime, delta);

                if (tsk) {
                        if (tsk->in_iowait) {
                                __schedstat_add(se->statistics.iowait_sum, delta);
                                __schedstat_inc(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);
                }
        }
}

/*
 * Task is being enqueued - update stats:
 */
static inline void
update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
        if (!schedstat_enabled())
                return;

        /*
         * 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);

        if (flags & ENQUEUE_WAKEUP)
                update_stats_enqueue_sleeper(cfs_rq, se);
}

static inline void
update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{

        if (!schedstat_enabled())
                return;

        /*
         * Mark the end of the wait period if dequeueing a
         * waiting task:
         */
        if (se != cfs_rq->curr)
                update_stats_wait_end(cfs_rq, se);

        if ((flags & DEQUEUE_SLEEP) && entity_is_task(se)) {
                struct task_struct *tsk = task_of(se);

                if (tsk->state & TASK_INTERRUPTIBLE)
                        __schedstat_set(se->statistics.sleep_start,
                                      rq_clock(rq_of(cfs_rq)));
                if (tsk->state & TASK_UNINTERRUPTIBLE)
                        __schedstat_set(se->statistics.block_start,
                                      rq_clock(rq_of(cfs_rq)));
        }
}

/*
 * 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;

struct numa_group {
        atomic_t refcount;

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

        struct rcu_head rcu;
        unsigned long total_faults;
        unsigned long max_faults_cpu;
        /*
         * 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];
};

static inline unsigned long group_faults_priv(struct numa_group *ng);
static inline unsigned long group_faults_shared(struct numa_group *ng);

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_start(struct task_struct *p)
{
        unsigned long smin = task_scan_min(p);
        unsigned long period = smin;

        /* Scale the maximum scan period with the amount of shared memory. */
        if (p->numa_group) {
                struct numa_group *ng = p->numa_group;
                unsigned long shared = group_faults_shared(ng);
                unsigned long private = group_faults_priv(ng);

                period *= atomic_read(&ng->refcount);
                period *= shared + 1;
                period /= private + shared + 1;
        }

        return max(smin, period);
}

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

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

        /* Scale the maximum scan period with the amount of shared memory. */
        if (p->numa_group) {
                struct numa_group *ng = p->numa_group;
                unsigned long shared = group_faults_shared(ng);
                unsigned long private = group_faults_priv(ng);
                unsigned long period = smax;

                period *= atomic_read(&ng->refcount);
                period *= shared + 1;
                period /= private + shared + 1;

                smax = max(smax, period);
        }

        return max(smin, smax);
}

void init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
{
        int mm_users = 0;
        struct mm_struct *mm = p->mm;

        if (mm) {
                mm_users = atomic_read(&mm->mm_users);
                if (mm_users == 1) {
                        mm->numa_next_scan = jiffies + msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
                        mm->numa_scan_seq = 0;
                }
        }
        p->node_stamp                   = 0;
        p->numa_scan_seq                = mm ? mm->numa_scan_seq : 0;
        p->numa_scan_period             = sysctl_numa_balancing_scan_delay;
        p->numa_work.next               = &p->numa_work;
        p->numa_faults                  = NULL;
        p->numa_group                   = NULL;
        p->last_task_numa_placement     = 0;
        p->last_sum_exec_runtime        = 0;

        /* New address space, reset the preferred nid */
        if (!(clone_flags & CLONE_VM)) {
                p->numa_preferred_nid = NUMA_NO_NODE;
                return;
        }

        /*
         * New thread, keep existing numa_preferred_nid which should be copied
         * already by arch_dup_task_struct but stagger when scans start.
         */
        if (mm) {
                unsigned int delay;

                delay = min_t(unsigned int, task_scan_max(current),
                        current->numa_scan_period * mm_users * NSEC_PER_MSEC);
                delay += 2 * TICK_NSEC;
                p->node_stamp = delay;
        }
}

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

/* 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)];
}

static inline unsigned long group_faults_priv(struct numa_group *ng)
{
        unsigned long faults = 0;
        int node;

        for_each_online_node(node) {
                faults += ng->faults[task_faults_idx(NUMA_MEM, node, 1)];
        }

        return faults;
}

static inline unsigned long group_faults_shared(struct numa_group *ng)
{
        unsigned long faults = 0;
        int node;

        for_each_online_node(node) {
                faults += ng->faults[task_faults_idx(NUMA_MEM, node, 0)];
        }

        return faults;
}

/*
 * A node triggering more than 1/3 as many NUMA faults as the maximum is
 * considered part of a numa group's pseudo-interleaving set. Migrations
 * between these nodes are slowed down, to allow things to settle down.
 */
#define ACTIVE_NODE_FRACTION 3

static bool numa_is_active_node(int nid, struct numa_group *ng)
{
        return group_faults_cpu(ng, nid) * ACTIVE_NODE_FRACTION > ng->max_faults_cpu;
}

/* 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);
        last_cpupid = page_cpupid_xchg_last(page, this_cpupid);

        /*
         * Allow first faults or private faults to migrate immediately early in
         * the lifetime of a task. The magic number 4 is based on waiting for
         * two full passes of the "multi-stage node selection" test that is
         * executed below.
         */
        if ((p->numa_preferred_nid == NUMA_NO_NODE || p->numa_scan_seq <= 4) &&
            (cpupid_pid_unset(last_cpupid) || cpupid_match_pid(p, last_cpupid)))
                return true;

        /*
         * 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.
         */
        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;

        /*
         * Destination node is much more heavily used than the source
         * node? Allow migration.
         */
        if (group_faults_cpu(ng, dst_nid) > group_faults_cpu(ng, src_nid) *
                                        ACTIVE_NODE_FRACTION)
                return true;

        /*
         * Distribute memory according to CPU & memory use on each node,
         * with 3/4 hysteresis to avoid unnecessary memory migrations:
         *
         * faults_cpu(dst)   3   faults_cpu(src)
         * --------------- * - > ---------------
         * faults_mem(dst)   4   faults_mem(src)
         */
        return group_faults_cpu(ng, dst_nid) * group_faults(p, src_nid) * 3 >
               group_faults_cpu(ng, src_nid) * group_faults(p, dst_nid) * 4;
}

static unsigned long weighted_cpuload(struct rq *rq);
static unsigned long source_load(int cpu, int type);
static unsigned long target_load(int cpu, int type);

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

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

/*
 * XXX borrowed from update_sg_lb_stats
 */
static void update_numa_stats(struct numa_stats *ns, int nid)
{
        int cpu;

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

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

}

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)
{
        struct rq *rq = cpu_rq(env->dst_cpu);

        /* Bail out if run-queue part of active NUMA balance. */
        if (xchg(&rq->numa_migrate_on, 1))
                return;

        /*
         * Clear previous best_cpu/rq numa-migrate flag, since task now
         * found a better CPU to move/swap.
         */
        if (env->best_cpu != -1) {
                rq = cpu_rq(env->best_cpu);
                WRITE_ONCE(rq->numa_migrate_on, 0);
        }

        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;

        imb = abs(dst_load * src_capacity - src_load * dst_capacity);

        orig_src_load = env->src_stats.load;
        orig_dst_load = env->dst_stats.load;

        old_imb = abs(orig_dst_load * src_capacity - orig_src_load * dst_capacity);

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

/*
 * Maximum NUMA importance can be 1998 (2*999);
 * SMALLIMP @ 30 would be close to 1998/64.
 * Used to deter task migration.
 */
#define SMALLIMP        30

/*
 * 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, bool maymove)
{
        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;

        if (READ_ONCE(dst_rq->numa_migrate_on))
                return;

        rcu_read_lock();
        cur = task_rcu_dereference(&dst_rq->curr);
        if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
                cur = NULL;

        /*
         * 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;

        if (!cur) {
                if (maymove && moveimp >= env->best_imp)
                        goto assign;
                else
                        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 remote accesses that would be expected to
         * be incurred if the tasks were swapped.
         */
        /* Skip this swap candidate if cannot move to the source cpu */
        if (!cpumask_test_cpu(env->src_cpu, &cur->cpus_allowed))
                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 && env->p->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 (maymove && moveimp > imp && moveimp > env->best_imp) {
                imp = moveimp;
                cur = NULL;
                goto assign;
        }

        /*
         * If the NUMA importance is less than SMALLIMP,
         * task migration might only result in ping pong
         * of tasks and also hurt performance due to cache
         * misses.
         */
        if (imp < SMALLIMP || imp <= env->best_imp + SMALLIMP / 2)
                goto unlock;

        /*
         * In the overloaded case, try and keep the load balanced.
         */
        load = task_h_load(env->p) - task_h_load(cur);
        if (!load)
                goto assign;

        dst_load = env->dst_stats.load + load;
        src_load = env->src_stats.load - load;

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

assign:
        /*
         * One idle CPU per node is evaluated for a task numa move.
         * Call select_idle_sibling to maybe find a better one.
         */
        if (!cur) {
                /*
                 * select_idle_siblings() uses an per-CPU cpumask that
                 * can be used from IRQ context.
                 */
                local_irq_disable();
                env->dst_cpu = select_idle_sibling(env->p, env->src_cpu,
                                                   env->dst_cpu);
                local_irq_enable();
        }

        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)
{
        long src_load, dst_load, load;
        bool maymove = false;
        int cpu;

        load = task_h_load(env->p);
        dst_load = env->dst_stats.load + load;
        src_load = env->src_stats.load - load;

        /*
         * If the improvement from just moving env->p direction is better
         * than swapping tasks around, check if a move is possible.
         */
        maymove = !load_too_imbalanced(src_load, dst_load, env);

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

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

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;
        struct rq *best_rq;
        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)) {
                sched_setnuma(p, 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. */
        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 && 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);
                        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 = cpu_to_node(env.best_cpu);

                if (nid != p->numa_preferred_nid)
                        sched_setnuma(p, nid);
        }

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

        best_rq = cpu_rq(env.best_cpu);
        if (env.best_task == NULL) {
                ret = migrate_task_to(p, env.best_cpu);
                WRITE_ONCE(best_rq->numa_migrate_on, 0);
                if (ret != 0)
                        trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
                return ret;
        }

        ret = migrate_swap(p, env.best_task, env.best_cpu, env.src_cpu);
        WRITE_ONCE(best_rq->numa_migrate_on, 0);

        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 == NUMA_NO_NODE || !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 out how many nodes on the workload is actively running on. 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.
 */
static void numa_group_count_active_nodes(struct numa_group *numa_group)
{
        unsigned long faults, max_faults = 0;
        int nid, active_nodes = 0;

        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 (faults * ACTIVE_NODE_FRACTION > max_faults)
                        active_nodes++;
        }

        numa_group->max_faults_cpu = max_faults;
        numa_group->active_nodes = 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 lr_ratio, ps_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);
        lr_ratio = (local * NUMA_PERIOD_SLOTS) / (local + remote);
        ps_ratio = (private * NUMA_PERIOD_SLOTS) / (private + shared);

        if (ps_ratio >= NUMA_PERIOD_THRESHOLD) {
                /*
                 * Most memory accesses are local. There is no need to
                 * do fast NUMA scanning, since memory is already local.
                 */
                int slot = ps_ratio - NUMA_PERIOD_THRESHOLD;
                if (!slot)
                        slot = 1;
                diff = slot * period_slot;
        } else if (lr_ratio >= NUMA_PERIOD_THRESHOLD) {
                /*
                 * Most memory accesses are shared with other tasks.
                 * There is no point in continuing fast NUMA scanning,
                 * since other tasks may just move the memory elsewhere.
                 */
                int slot = lr_ratio - NUMA_PERIOD_THRESHOLD;
                if (!slot)
                        slot = 1;
                diff = slot * period_slot;
        } else {
                /*
                 * Private memory faults exceed (SLOTS-THRESHOLD)/SLOTS,
                 * yet they are not on the local NUMA node. Speed up
                 * NUMA scanning to get the memory moved over.
                 */
                int ratio = max(lr_ratio, ps_ratio);
                diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;
        }

        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.load_sum;
                *period = LOAD_AVG_MAX;
        }

        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 = NUMA_NO_NODE;
        unsigned long max_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 (!p->numa_group) {
                        if (faults > max_faults) {
                                max_faults = faults;
                                max_nid = nid;
                        }
                } else if (group_faults > max_faults) {
                        max_faults = group_faults;
                        max_nid = nid;
                }
        }

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

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

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

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);
                grp->active_nodes = 1;
                grp->max_faults_cpu = 0;
                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;

                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);
        struct numa_group *ng;
        int priv;

        if (!static_branch_likely(&sched_numa_balancing))
                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.
         */
        ng = p->numa_group;
        if (!priv && !local && ng && ng->active_nodes > 1 &&
                                numa_is_active_node(cpu_node, ng) &&
                                numa_is_active_node(mem_node, ng))
                local = 1;

        /*
         * Retry to migrate task to preferred node periodically, in case it
         * previously failed, or the scheduler moved us.
         */
        if (time_after(jiffies, p->numa_migrate_retry)) {
                task_numa_placement(p);
                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;
        u64 runtime = p->se.sum_exec_runtime;
        struct vm_area_struct *vma;
        unsigned long start, end;
        unsigned long nr_pte_updates = 0;
        long pages, virtpages;

        SCHED_WARN_ON(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_start(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 */
        virtpages = pages * 8;     /* Scan up to this much virtual space */
        if (!pages)
                return;


        if (!down_read_trylock(&mm->mmap_sem))
                return;
        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);

                        /*
                         * Try to scan sysctl_numa_balancing_size worth of
                         * hpages that have at least one present PTE that
                         * is not already pte-numa. If the VMA contains
                         * areas that are unused or already full of prot_numa
                         * PTEs, scan up to virtpages, to skip through those
                         * areas faster.
                         */
                        if (nr_pte_updates)
                                pages -= (end - start) >> PAGE_SHIFT;
                        virtpages -= (end - start) >> PAGE_SHIFT;

                        start = end;
                        if (pages <= 0 || virtpages <= 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);

        /*
         * Make sure tasks use at least 32x as much time to run other code
         * than they used here, to limit NUMA PTE scanning overhead to 3% max.
         * Usually update_task_scan_period slows down scanning enough; on an
         * overloaded system we need to limit overhead on a per task basis.
         */
        if (unlikely(p->se.sum_exec_runtime != runtime)) {
                u64 diff = p->se.sum_exec_runtime - runtime;
                p->node_stamp += 32 * diff;
        }
}

/*
 * 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_start(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);
                }
        }
}

static void update_scan_period(struct task_struct *p, int new_cpu)
{
        int src_nid = cpu_to_node(task_cpu(p));
        int dst_nid = cpu_to_node(new_cpu);

        if (!static_branch_likely(&sched_numa_balancing))
                return;

        if (!p->mm || !p->numa_faults || (p->flags & PF_EXITING))
                return;

        if (src_nid == dst_nid)
                return;

        /*
         * Allow resets if faults have been trapped before one scan
         * has completed. This is most likely due to a new task that
         * is pulled cross-node due to wakeups or load balancing.
         */
        if (p->numa_scan_seq) {
                /*
                 * Avoid scan adjustments if moving to the preferred
                 * node or if the task was not previously running on
                 * the preferred node.
                 */
                if (dst_nid == p->numa_preferred_nid ||
                    (p->numa_preferred_nid != NUMA_NO_NODE &&
                        src_nid != p->numa_preferred_nid))
                        return;
        }

        p->numa_scan_period = task_scan_start(p);
}

#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)
{
}

static inline void update_scan_period(struct task_struct *p, int new_cpu)
{
}

#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);
#ifdef CONFIG_SMP
        if (entity_is_task(se)) {
                account_numa_dequeue(rq_of(cfs_rq), task_of(se));
                list_del_init(&se->group_node);
        }
#endif
        cfs_rq->nr_running--;
}

/*
 * Signed add and clamp on underflow.
 *
 * Explicitly do a load-store to ensure the intermediate value never hits
 * memory. This allows lockless observations without ever seeing the negative
 * values.
 */
#define add_positive(_ptr, _val) do {                           \
        typeof(_ptr) ptr = (_ptr);                              \
        typeof(_val) val = (_val);                              \
        typeof(*ptr) res, var = READ_ONCE(*ptr);                \
                                                                \
        res = var + val;                                        \
                                                                \
        if (val < 0 && res > var)                               \
                res = 0;                                        \
                                                                \
        WRITE_ONCE(*ptr, res);                                  \
} while (0)

/*
 * Unsigned subtract and clamp on underflow.
 *
 * Explicitly do a load-store to ensure the intermediate value never hits
 * memory. This allows lockless observations without ever seeing the negative
 * values.
 */
#define sub_positive(_ptr, _val) do {                           \
        typeof(_ptr) ptr = (_ptr);                              \
        typeof(*ptr) val = (_val);                              \
        typeof(*ptr) res, var = READ_ONCE(*ptr);                \
        res = var - val;                                        \
        if (res > var)                                          \
                res = 0;                                        \
        WRITE_ONCE(*ptr, res);                                  \
} while (0)

/*
 * Remove and clamp on negative, from a local variable.
 *
 * A variant of sub_positive(), which does not use explicit load-store
 * and is thus optimized for local variable updates.
 */
#define lsub_positive(_ptr, _val) do {                          \
        typeof(_ptr) ptr = (_ptr);                              \
        *ptr -= min_t(typeof(*ptr), *ptr, _val);                \
} while (0)

#ifdef CONFIG_SMP
static inline void
enqueue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        cfs_rq->runnable_weight += se->runnable_weight;

        cfs_rq->avg.runnable_load_avg += se->avg.runnable_load_avg;
        cfs_rq->avg.runnable_load_sum += se_runnable(se) * se->avg.runnable_load_sum;
}

static inline void
dequeue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        cfs_rq->runnable_weight -= se->runnable_weight;

        sub_positive(&cfs_rq->avg.runnable_load_avg, se->avg.runnable_load_avg);
        sub_positive(&cfs_rq->avg.runnable_load_sum,
                     se_runnable(se) * se->avg.runnable_load_sum);
}

static inline void
enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        cfs_rq->avg.load_avg += se->avg.load_avg;
        cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
}

static inline void
dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
        sub_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
        sub_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
}
#else
static inline void
enqueue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
static inline void
dequeue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
static inline void
enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
static inline void
dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
#endif

static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
                            unsigned long weight, unsigned long runnable)
{
        if (se->on_rq) {
                /* commit outstanding execution time */
                if (cfs_rq->curr == se)
                        update_curr(cfs_rq);
                account_entity_dequeue(cfs_rq, se);
                dequeue_runnable_load_avg(cfs_rq, se);
        }
        dequeue_load_avg(cfs_rq, se);

        se->runnable_weight = runnable;
        update_load_set(&se->load, weight);

#ifdef CONFIG_SMP
        do {
                u32 divider = LOAD_AVG_MAX - 1024 + se->avg.period_contrib;

                se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum, divider);
                se->avg.runnable_load_avg =
                        div_u64(se_runnable(se) * se->avg.runnable_load_sum, divider);
        } while (0);
#endif

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

void reweight_task(struct task_struct *p, int prio)
{
        struct sched_entity *se = &p->se;
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        struct load_weight *load = &se->load;
        unsigned long weight = scale_load(sched_prio_to_weight[prio]);

        reweight_entity(cfs_rq, se, weight, weight);
        load->inv_weight = sched_prio_to_wmult[prio];
}

#ifdef CONFIG_FAIR_GROUP_SCHED
#ifdef CONFIG_SMP
/*
 * All this does is approximate the hierarchical proportion which includes that
 * global sum we all love to hate.
 *
 * That is, the weight of a group entity, is the proportional share of the
 * group weight based on the group runqueue weights. That is:
 *
 *                     tg->weight * grq->load.weight
 *   ge->load.weight = -----------------------------               (1)
 *                        \Sum grq->load.weight
 *
 * Now, because computing that sum is prohibitively expensive to compute (been
 * there, done that) we approximate it with this average stuff. The average
 * moves slower and therefore the approximation is cheaper and more stable.
 *
 * So instead of the above, we substitute:
 *
 *   grq->load.weight -> grq->avg.load_avg                         (2)
 *
 * which yields the following:
 *
 *                     tg->weight * grq->avg.load_avg
 *   ge->load.weight = ------------------------------              (3)
 *                              tg->load_avg
 *
 * Where: tg->load_avg ~= \Sum grq->avg.load_avg
 *
 * That is shares_avg, and it is right (given the approximation (2)).
 *
 * The problem with it is that because the average is slow -- it was designed
 * to be exactly that of course -- this leads to transients in boundary
 * conditions. In specific, the case where the group was idle and we start the
 * one task. It takes time for our CPU's grq->avg.load_avg to build up,
 * yielding bad latency etc..
 *
 * Now, in that special case (1) reduces to:
 *
 *                     tg->weight * grq->load.weight
 *   ge->load.weight = ----------------------------- = tg->weight   (4)
 *                          grp->load.weight
 *
 * That is, the sum collapses because all other CPUs are idle; the UP scenario.
 *
 * So what we do is modify our approximation (3) to approach (4) in the (near)
 * UP case, like:
 *
 *   ge->load.weight =
 *
 *              tg->weight * grq->load.weight
 *     ---------------------------------------------------         (5)
 *     tg->load_avg - grq->avg.load_avg + grq->load.weight
 *
 * But because grq->load.weight can drop to 0, resulting in a divide by zero,
 * we need to use grq->avg.load_avg as its lower bound, which then gives:
 *
 *
 *                     tg->weight * grq->load.weight
 *   ge->load.weight = -----------------------------               (6)
 *                              tg_load_avg'
 *
 * Where:
 *
 *   tg_load_avg' = tg->load_avg - grq->avg.load_avg +
 *                  max(grq->load.weight, grq->avg.load_avg)
 *
 * And that is shares_weight and is icky. In the (near) UP case it approaches
 * (4) while in the normal case it approaches (3). It consistently
 * overestimates the ge->load.weight and therefore:
 *
 *   \Sum ge->load.weight >= tg->weight
 *
 * hence icky!
 */
static long calc_group_shares(struct cfs_rq *cfs_rq)
{
        long tg_weight, tg_shares, load, shares;
        struct task_group *tg = cfs_rq->tg;

        tg_shares = READ_ONCE(tg->shares);

        load = max(scale_load_down(cfs_rq->load.weight), cfs_rq->avg.load_avg);

        tg_weight = atomic_long_read(&tg->load_avg);

        /* Ensure tg_weight >= load */
        tg_weight -= cfs_rq->tg_load_avg_contrib;
        tg_weight += load;

        shares = (tg_shares * load);
        if (tg_weight)
                shares /= tg_weight;

        /*
         * MIN_SHARES has to be unscaled here to support per-CPU partitioning
         * of a group with small tg->shares value. It is a floor value which is
         * assigned as a minimum load.weight to the sched_entity representing
         * the group on a CPU.
         *
         * E.g. on 64-bit for a group with tg->shares of scale_load(15)=15*1024
         * on an 8-core system with 8 tasks each runnable on one CPU shares has
         * to be 15*1024*1/8=1920 instead of scale_load(MIN_SHARES)=2*1024. In
         * case no task is runnable on a CPU MIN_SHARES=2 should be returned
         * instead of 0.
         */
        return clamp_t(long, shares, MIN_SHARES, tg_shares);
}

/*
 * This calculates the effective runnable weight for a group entity based on
 * the group entity weight calculated above.
 *
 * Because of the above approximation (2), our group entity weight is
 * an load_avg based ratio (3). This means that it includes blocked load and
 * does not represent the runnable weight.
 *
 * Approximate the group entity's runnable weight per ratio from the group
 * runqueue:
 *
 *                                           grq->avg.runnable_load_avg
 *   ge->runnable_weight = ge->load.weight * -------------------------- (7)
 *                                               grq->avg.load_avg
 *
 * However, analogous to above, since the avg numbers are slow, this leads to
 * transients in the from-idle case. Instead we use:
 *
 *   ge->runnable_weight = ge->load.weight *
 *
 *              max(grq->avg.runnable_load_avg, grq->runnable_weight)
 *              -----------------------------------------------------   (8)
 *                    max(grq->avg.load_avg, grq->load.weight)
 *
 * Where these max() serve both to use the 'instant' values to fix the slow
 * from-idle and avoid the /0 on to-idle, similar to (6).
 */
static long calc_group_runnable(struct cfs_rq *cfs_rq, long shares)
{
        long runnable, load_avg;

        load_avg = max(cfs_rq->avg.load_avg,
                       scale_load_down(cfs_rq->load.weight));

        runnable = max(cfs_rq->avg.runnable_load_avg,
                       scale_load_down(cfs_rq->runnable_weight));

        runnable *= shares;
        if (load_avg)
                runnable /= load_avg;

        return clamp_t(long, runnable, MIN_SHARES, shares);
}
#endif /* CONFIG_SMP */

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);

/*
 * Recomputes the group entity based on the current state of its group
 * runqueue.
 */
static void update_cfs_group(struct sched_entity *se)
{
        struct cfs_rq *gcfs_rq = group_cfs_rq(se);
        long shares, runnable;

        if (!gcfs_rq)
                return;

        if (throttled_hierarchy(gcfs_rq))
                return;

#ifndef CONFIG_SMP
        runnable = shares = READ_ONCE(gcfs_rq->tg->shares);

        if (likely(se->load.weight == shares))
                return;
#else
        shares   = calc_group_shares(gcfs_rq);
        runnable = calc_group_runnable(gcfs_rq, shares);
#endif

        reweight_entity(cfs_rq_of(se), se, shares, runnable);
}

#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void update_cfs_group(struct sched_entity *se)
{
}
#endif /* CONFIG_FAIR_GROUP_SCHED */

static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
{
        struct rq *rq = rq_of(cfs_rq);

        if (&rq->cfs == cfs_rq || (flags & SCHED_CPUFREQ_MIGRATION)) {
                /*
                 * There are a few boundary cases this might miss but it should
                 * get called often enough that that should (hopefully) not be
                 * a real problem.
                 *
                 * It will not get called when we go idle, because the idle
                 * thread is a different class (!fair), nor will the utilization
                 * number include things like RT tasks.
                 *
                 * As is, the util number is not freq-invariant (we'd have to
                 * implement arch_scale_freq_capacity() for that).
                 *
                 * See cpu_util().
                 */
                cpufreq_update_util(rq, flags);
        }
}

#ifdef CONFIG_SMP
#ifdef CONFIG_FAIR_GROUP_SCHED
/**
 * update_tg_load_avg - update the tg's load avg
 * @cfs_rq: the cfs_rq whose avg changed
 * @force: update regardless of how small the difference
 *
 * This function 'ensures': tg->load_avg := \Sum tg->cfs_rq[]->avg.load.
 * However, because tg->load_avg is a global value there are performance
 * considerations.
 *
 * In order to avoid having to look at the other cfs_rq's, we use a
 * differential update where we store the last value we propagated. This in
 * turn allows skipping updates if the differential is 'small'.
 *
 * Updating tg's load_avg is necessary before update_cfs_share().
 */
static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
{
        long delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib;

        /*
         * No need to update load_avg for root_task_group as it is not used.
         */
        if (cfs_rq->tg == &root_task_group)
                return;

        if (force || abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
                atomic_long_add(delta, &cfs_rq->tg->load_avg);
                cfs_rq->tg_load_avg_contrib = cfs_rq->avg.load_avg;
        }
}

/*
 * Called within set_task_rq() right before setting a task's CPU. The
 * caller only guarantees p->pi_lock is held; no other assumptions,
 * including the state of rq->lock, should be made.
 */
void set_task_rq_fair(struct sched_entity *se,
                      struct cfs_rq *prev, struct cfs_rq *next)
{
        u64 p_last_update_time;
        u64 n_last_update_time;

        if (!sched_feat(ATTACH_AGE_LOAD))
                return;

        /*
         * We are supposed to update the task to "current" time, then its up to
         * date and ready to go to new CPU/cfs_rq. But we have difficulty in
         * getting what current time is, so simply throw away the out-of-date
         * time. This will result in the wakee task is less decayed, but giving
         * the wakee more load sounds not bad.
         */
        if (!(se->avg.last_update_time && prev))
                return;

#ifndef CONFIG_64BIT
        {
                u64 p_last_update_time_copy;
                u64 n_last_update_time_copy;

                do {
                        p_last_update_time_copy = prev->load_last_update_time_copy;
                        n_last_update_time_copy = next->load_last_update_time_copy;

                        smp_rmb();

                        p_last_update_time = prev->avg.last_update_time;
                        n_last_update_time = next->avg.last_update_time;

                } while (p_last_update_time != p_last_update_time_copy ||
                         n_last_update_time != n_last_update_time_copy);
        }
#else
        p_last_update_time = prev->avg.last_update_time;
        n_last_update_time = next->avg.last_update_time;
#endif
        __update_load_avg_blocked_se(p_last_update_time, cpu_of(rq_of(prev)), se);
        se->avg.last_update_time = n_last_update_time;
}


/*
 * When on migration a sched_entity joins/leaves the PELT hierarchy, we need to
 * propagate its contribution. The key to this propagation is the invariant
 * that for each group:
 *
 *   ge->avg == grq->avg                                                (1)
 *
 * _IFF_ we look at the pure running and runnable sums. Because they
 * represent the very same entity, just at different points in the hierarchy.
 *
 * Per the above update_tg_cfs_util() is trivial and simply copies the running
 * sum over (but still wrong, because the group entity and group rq do not have
 * their PELT windows aligned).
 *
 * However, update_tg_cfs_runnable() is more complex. So we have:
 *
 *   ge->avg.load_avg = ge->load.weight * ge->avg.runnable_avg          (2)
 *
 * And since, like util, the runnable part should be directly transferable,
 * the following would _appear_ to be the straight forward approach:
 *
 *   grq->avg.load_avg = grq->load.weight * grq->avg.runnable_avg       (3)
 *
 * And per (1) we have:
 *
 *   ge->avg.runnable_avg == grq->avg.runnable_avg
 *
 * Which gives:
 *
 *                      ge->load.weight * grq->avg.load_avg
 *   ge->avg.load_avg = -----------------------------------             (4)
 *                               grq->load.weight
 *
 * Except that is wrong!
 *
 * Because while for entities historical weight is not important and we
 * really only care about our future and therefore can consider a pure
 * runnable sum, runqueues can NOT do this.
 *
 * We specifically want runqueues to have a load_avg that includes
 * historical weights. Those represent the blocked load, the load we expect
 * to (shortly) return to us. This only works by keeping the weights as
 * integral part of the sum. We therefore cannot decompose as per (3).
 *
 * Another reason this doesn't work is that runnable isn't a 0-sum entity.
 * Imagine a rq with 2 tasks that each are runnable 2/3 of the time. Then the
 * rq itself is runnable anywhere between 2/3 and 1 depending on how the
 * runnable section of these tasks overlap (or not). If they were to perfectly
 * align the rq as a whole would be runnable 2/3 of the time. If however we
 * always have at least 1 runnable task, the rq as a whole is always runnable.
 *
 * So we'll have to approximate.. :/
 *
 * Given the constraint:
 *
 *   ge->avg.running_sum <= ge->avg.runnable_sum <= LOAD_AVG_MAX
 *
 * We can construct a rule that adds runnable to a rq by assuming minimal
 * overlap.
 *
 * On removal, we'll assume each task is equally runnable; which yields:
 *
 *   grq->avg.runnable_sum = grq->avg.load_sum / grq->load.weight
 *
 * XXX: only do this for the part of runnable > running ?
 *
 */

static inline void
update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq)
{
        long delta = gcfs_rq->avg.util_avg - se->avg.util_avg;

        /* Nothing to update */
        if (!delta)
                return;

        /*
         * The relation between sum and avg is:
         *
         *   LOAD_AVG_MAX - 1024 + sa->period_contrib
         *
         * however, the PELT windows are not aligned between grq and gse.
         */

        /* Set new sched_entity's utilization */
        se->avg.util_avg = gcfs_rq->avg.util_avg;
        se->avg.util_sum = se->avg.util_avg * LOAD_AVG_MAX;

        /* Update parent cfs_rq utilization */
        add_positive(&cfs_rq->avg.util_avg, delta);
        cfs_rq->avg.util_sum = cfs_rq->avg.util_avg * LOAD_AVG_MAX;
}

static inline void
update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq)
{
        long delta_avg, running_sum, runnable_sum = gcfs_rq->prop_runnable_sum;
        unsigned long runnable_load_avg, load_avg;
        u64 runnable_load_sum, load_sum = 0;
        s64 delta_sum;

        if (!runnable_sum)
                return;

        gcfs_rq->prop_runnable_sum = 0;

        if (runnable_sum >= 0) {
                /*
                 * Add runnable; clip at LOAD_AVG_MAX. Reflects that until
                 * the CPU is saturated running == runnable.
                 */
                runnable_sum += se->avg.load_sum;
                runnable_sum = min(runnable_sum, (long)LOAD_AVG_MAX);
        } else {
                /*
                 * Estimate the new unweighted runnable_sum of the gcfs_rq by
                 * assuming all tasks are equally runnable.
                 */
                if (scale_load_down(gcfs_rq->load.weight)) {
                        load_sum = div_s64(gcfs_rq->avg.load_sum,
                                scale_load_down(gcfs_rq->load.weight));
                }

                /* But make sure to not inflate se's runnable */
                runnable_sum = min(se->avg.load_sum, load_sum);
        }

        /*
         * runnable_sum can't be lower than running_sum
         * As running sum is scale with CPU capacity wehreas the runnable sum
         * is not we rescale running_sum 1st
         */
        running_sum = se->avg.util_sum /
                arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq)));
        runnable_sum = max(runnable_sum, running_sum);

        load_sum = (s64)se_weight(se) * runnable_sum;
        load_avg = div_s64(load_sum, LOAD_AVG_MAX);

        delta_sum = load_sum - (s64)se_weight(se) * se->avg.load_sum;
        delta_avg = load_avg - se->avg.load_avg;

        se->avg.load_sum = runnable_sum;
        se->avg.load_avg = load_avg;
        add_positive(&cfs_rq->avg.load_avg, delta_avg);
        add_positive(&cfs_rq->avg.load_sum, delta_sum);

        runnable_load_sum = (s64)se_runnable(se) * runnable_sum;
        runnable_load_avg = div_s64(runnable_load_sum, LOAD_AVG_MAX);
        delta_sum = runnable_load_sum - se_weight(se) * se->avg.runnable_load_sum;
        delta_avg = runnable_load_avg - se->avg.runnable_load_avg;

        se->avg.runnable_load_sum = runnable_sum;
        se->avg.runnable_load_avg = runnable_load_avg;

        if (se->on_rq) {
                add_positive(&cfs_rq->avg.runnable_load_avg, delta_avg);
                add_positive(&cfs_rq->avg.runnable_load_sum, delta_sum);
        }
}

static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum)
{
        cfs_rq->propagate = 1;
        cfs_rq->prop_runnable_sum += runnable_sum;
}

/* Update task and its cfs_rq load average */
static inline int propagate_entity_load_avg(struct sched_entity *se)
{
        struct cfs_rq *cfs_rq, *gcfs_rq;

        if (entity_is_task(se))
                return 0;

        gcfs_rq = group_cfs_rq(se);
        if (!gcfs_rq->propagate)
                return 0;

        gcfs_rq->propagate = 0;

        cfs_rq = cfs_rq_of(se);

        add_tg_cfs_propagate(cfs_rq, gcfs_rq->prop_runnable_sum);

        update_tg_cfs_util(cfs_rq, se, gcfs_rq);
        update_tg_cfs_runnable(cfs_rq, se, gcfs_rq);

        return 1;
}

/*
 * Check if we need to update the load and the utilization of a blocked
 * group_entity:
 */
static inline bool skip_blocked_update(struct sched_entity *se)
{
        struct cfs_rq *gcfs_rq = group_cfs_rq(se);

        /*
         * If sched_entity still have not zero load or utilization, we have to
         * decay it:
         */
        if (se->avg.load_avg || se->avg.util_avg)