TOMOYO Linux Cross Reference
Linux/kernel/sched/fair.c

   /*
    * Completely Fair Scheduling (CFS) Class (SCHED_NORMAL/SCHED_BATCH)
    *
    *  Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
    *
    *  Interactivity improvements by Mike Galbraith
    *  (C) 2007 Mike Galbraith <efault@gmx.de>
    *
    *  Various enhancements by Dmitry Adamushko.
   *  (C) 2007 Dmitry Adamushko <dmitry.adamushko@gmail.com>
   *
   *  Group scheduling enhancements by Srivatsa Vaddagiri
   *  Copyright IBM Corporation, 2007
   *  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
   *
   *  Scaled math optimizations by Thomas Gleixner
   *  Copyright (C) 2007, Thomas Gleixner <tglx@linutronix.de>
   *
   *  Adaptive scheduling granularity, math enhancements by Peter Zijlstra
   *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
   */
  
  #include <linux/sched.h>
  #include <linux/latencytop.h>
  #include <linux/cpumask.h>
  #include <linux/cpuidle.h>
  #include <linux/slab.h>
  #include <linux/profile.h>
  #include <linux/interrupt.h>
  #include <linux/mempolicy.h>
  #include <linux/migrate.h>
  #include <linux/task_work.h>
  
  #include <trace/events/sched.h>
  
  #include "sched.h"
  
  /*
   * Targeted preemption latency for CPU-bound tasks:
   * (default: 6ms * (1 + ilog(ncpus)), units: nanoseconds)
   *
   * NOTE: this latency value is not the same as the concept of
   * 'timeslice length' - timeslices in CFS are of variable length
   * and have no persistent notion like in traditional, time-slice
   * based scheduling concepts.
   *
   * (to see the precise effective timeslice length of your workload,
   *  run vmstat and monitor the context-switches (cs) field)
   */
  unsigned int sysctl_sched_latency = 6000000ULL;
  unsigned int normalized_sysctl_sched_latency = 6000000ULL;
  
  /*
   * The initial- and re-scaling of tunables is configurable
   * (default SCHED_TUNABLESCALING_LOG = *(1+ilog(ncpus))
   *
   * Options are:
   * SCHED_TUNABLESCALING_NONE - unscaled, always *1
   * SCHED_TUNABLESCALING_LOG - scaled logarithmical, *1+ilog(ncpus)
   * SCHED_TUNABLESCALING_LINEAR - scaled linear, *ncpus
   */
  enum sched_tunable_scaling sysctl_sched_tunable_scaling
          = SCHED_TUNABLESCALING_LOG;
  
  /*
   * Minimal preemption granularity for CPU-bound tasks:
   * (default: 0.75 msec * (1 + ilog(ncpus)), units: nanoseconds)
   */
  unsigned int sysctl_sched_min_granularity = 750000ULL;
  unsigned int normalized_sysctl_sched_min_granularity = 750000ULL;
  
  /*
   * is kept at sysctl_sched_latency / sysctl_sched_min_granularity
   */
  static unsigned int sched_nr_latency = 8;
  
  /*
   * After fork, child runs first. If set to 0 (default) then
   * parent will (try to) run first.
   */
  unsigned int sysctl_sched_child_runs_first __read_mostly;
  
  /*
   * SCHED_OTHER wake-up granularity.
   * (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
   *
   * This option delays the preemption effects of decoupled workloads
   * and reduces their over-scheduling. Synchronous workloads will still
   * have immediate wakeup/sleep latencies.
   */
  unsigned int sysctl_sched_wakeup_granularity = 1000000UL;
  unsigned int normalized_sysctl_sched_wakeup_granularity = 1000000UL;
  
  const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
  
  /*
   * The exponential sliding  window over which load is averaged for shares
   * distribution.
   * (default: 10msec)
  */
 unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;
 
 #ifdef CONFIG_CFS_BANDWIDTH
 /*
  * Amount of runtime to allocate from global (tg) to local (per-cfs_rq) pool
  * each time a cfs_rq requests quota.
  *
  * Note: in the case that the slice exceeds the runtime remaining (either due
  * to consumption or the quota being specified to be smaller than the slice)
  * we will always only issue the remaining available time.
  *
  * default: 5 msec, units: microseconds
   */
 unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;
 #endif
 
 static inline void update_load_add(struct load_weight *lw, unsigned long inc)
 {
         lw->weight += inc;
         lw->inv_weight = 0;
 }
 
 static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
 {
         lw->weight -= dec;
         lw->inv_weight = 0;
 }
 
 static inline void update_load_set(struct load_weight *lw, unsigned long w)
 {
         lw->weight = w;
         lw->inv_weight = 0;
 }
 
 /*
  * Increase the granularity value when there are more CPUs,
  * because with more CPUs the 'effective latency' as visible
  * to users decreases. But the relationship is not linear,
  * so pick a second-best guess by going with the log2 of the
  * number of CPUs.
  *
  * This idea comes from the SD scheduler of Con Kolivas:
  */
 static unsigned int get_update_sysctl_factor(void)
 {
         unsigned int cpus = min_t(unsigned int, num_online_cpus(), 8);
         unsigned int factor;
 
         switch (sysctl_sched_tunable_scaling) {
         case SCHED_TUNABLESCALING_NONE:
                 factor = 1;
                 break;
         case SCHED_TUNABLESCALING_LINEAR:
                 factor = cpus;
                 break;
         case SCHED_TUNABLESCALING_LOG:
         default:
                 factor = 1 + ilog2(cpus);
                 break;
         }
 
         return factor;
 }
 
 static void update_sysctl(void)
 {
         unsigned int factor = get_update_sysctl_factor();
 
 #define SET_SYSCTL(name) \
         (sysctl_##name = (factor) * normalized_sysctl_##name)
         SET_SYSCTL(sched_min_granularity);
         SET_SYSCTL(sched_latency);
         SET_SYSCTL(sched_wakeup_granularity);
 #undef SET_SYSCTL
 }
 
 void sched_init_granularity(void)
 {
         update_sysctl();
 }
 
 #define WMULT_CONST     (~0U)
 #define WMULT_SHIFT     32
 
 static void __update_inv_weight(struct load_weight *lw)
 {
         unsigned long w;
 
         if (likely(lw->inv_weight))
                 return;
 
         w = scale_load_down(lw->weight);
 
         if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
                 lw->inv_weight = 1;
         else if (unlikely(!w))
                 lw->inv_weight = WMULT_CONST;
         else
                 lw->inv_weight = WMULT_CONST / w;
 }
 
 /*
  * delta_exec * weight / lw.weight
  *   OR
  * (delta_exec * (weight * lw->inv_weight)) >> WMULT_SHIFT
  *
  * Either weight := NICE_0_LOAD and lw \e 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;
 }
 
 /* An entity is a task if it doesn't "own" a runqueue */
 #define entity_is_task(se)      (!se->my_q)
 
 static inline struct task_struct *task_of(struct sched_entity *se)
 {
 #ifdef CONFIG_SCHED_DEBUG
         WARN_ON_ONCE(!entity_is_task(se));
 #endif
         return container_of(se, struct task_struct, se);
 }
 
 /* Walk up scheduling entities hierarchy */
 #define for_each_sched_entity(se) \
                 for (; se; se = se->parent)
 
 static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
 {
         return p->se.cfs_rq;
 }
 
 /* runqueue on which this entity is (to be) queued */
 static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
 {
         return se->cfs_rq;
 }
 
 /* runqueue "owned" by this group */
 static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
 {
         return grp->my_q;
 }
 
 static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 {
         if (!cfs_rq->on_list) {
                 /*
                  * Ensure we either appear before our parent (if already
                  * enqueued) or force our parent to appear after us when it is
                  * enqueued.  The fact that we always enqueue bottom-up
                  * reduces this to two cases.
                  */
                 if (cfs_rq->tg->parent &&
                     cfs_rq->tg->parent->cfs_rq[cpu_of(rq_of(cfs_rq))]->on_list) {
                         list_add_rcu(&cfs_rq->leaf_cfs_rq_list,
                                 &rq_of(cfs_rq)->leaf_cfs_rq_list);
                 } else {
                         list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
                                 &rq_of(cfs_rq)->leaf_cfs_rq_list);
                 }
 
                 cfs_rq->on_list = 1;
         }
 }
 
 static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 {
         if (cfs_rq->on_list) {
                 list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
                 cfs_rq->on_list = 0;
         }
 }
 
 /* Iterate thr' all leaf cfs_rq's on a runqueue */
 #define for_each_leaf_cfs_rq(rq, cfs_rq) \
         list_for_each_entry_rcu(cfs_rq, &rq->leaf_cfs_rq_list, leaf_cfs_rq_list)
 
 /* Do the two (enqueued) entities belong to the same group ? */
 static inline struct cfs_rq *
 is_same_group(struct sched_entity *se, struct sched_entity *pse)
 {
         if (se->cfs_rq == pse->cfs_rq)
                 return se->cfs_rq;
 
         return NULL;
 }
 
 static inline struct sched_entity *parent_entity(struct sched_entity *se)
 {
         return se->parent;
 }
 
 static void
 find_matching_se(struct sched_entity **se, struct sched_entity **pse)
 {
         int se_depth, pse_depth;
 
         /*
          * preemption test can be made between sibling entities who are in the
          * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
          * both tasks until we find their ancestors who are siblings of common
          * parent.
          */
 
         /* First walk up until both entities are at same depth */
         se_depth = (*se)->depth;
         pse_depth = (*pse)->depth;
 
         while (se_depth > pse_depth) {
                 se_depth--;
                 *se = parent_entity(*se);
         }
 
         while (pse_depth > se_depth) {
                 pse_depth--;
                 *pse = parent_entity(*pse);
         }
 
         while (!is_same_group(*se, *pse)) {
                 *se = parent_entity(*se);
                 *pse = parent_entity(*pse);
         }
 }
 
 #else   /* !CONFIG_FAIR_GROUP_SCHED */
 
 static inline struct task_struct *task_of(struct sched_entity *se)
 {
         return container_of(se, struct task_struct, se);
 }
 
 static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
 {
         return container_of(cfs_rq, struct rq, cfs);
 }
 
 #define entity_is_task(se)      1
 
 #define for_each_sched_entity(se) \
                 for (; se; se = NULL)
 
 static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
 {
         return &task_rq(p)->cfs;
 }
 
 static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
 {
         struct task_struct *p = task_of(se);
         struct rq *rq = task_rq(p);
 
         return &rq->cfs;
 }
 
 /* runqueue "owned" by this group */
 static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
 {
         return NULL;
 }
 
 static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 {
 }
 
 static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 {
 }
 
 #define for_each_leaf_cfs_rq(rq, cfs_rq) \
                 for (cfs_rq = &rq->cfs; cfs_rq; cfs_rq = NULL)
 
 static inline struct sched_entity *parent_entity(struct sched_entity *se)
 {
         return NULL;
 }
 
 static inline void
 find_matching_se(struct sched_entity **se, struct sched_entity **pse)
 {
 }
 
 #endif  /* CONFIG_FAIR_GROUP_SCHED */
 
 static __always_inline
 void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec);
 
 /**************************************************************
  * Scheduling class tree data structure manipulation methods:
  */
 
 static inline u64 max_vruntime(u64 max_vruntime, u64 vruntime)
 {
         s64 delta = (s64)(vruntime - max_vruntime);
         if (delta > 0)
                 max_vruntime = vruntime;
 
         return max_vruntime;
 }
 
 static inline u64 min_vruntime(u64 min_vruntime, u64 vruntime)
 {
         s64 delta = (s64)(vruntime - min_vruntime);
         if (delta < 0)
                 min_vruntime = vruntime;
 
         return min_vruntime;
 }
 
 static inline int entity_before(struct sched_entity *a,
                                 struct sched_entity *b)
 {
         return (s64)(a->vruntime - b->vruntime) < 0;
 }
 
 static void update_min_vruntime(struct cfs_rq *cfs_rq)
 {
         struct sched_entity *curr = cfs_rq->curr;
 
         u64 vruntime = cfs_rq->min_vruntime;
 
         if (curr) {
                 if (curr->on_rq)
                         vruntime = curr->vruntime;
                 else
                         curr = NULL;
         }
 
         if (cfs_rq->rb_leftmost) {
                 struct sched_entity *se = rb_entry(cfs_rq->rb_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_node;
         struct rb_node *parent = NULL;
         struct sched_entity *entry;
         int leftmost = 1;
 
         /*
          * Find the right place in the rbtree:
          */
         while (*link) {
                 parent = *link;
                 entry = rb_entry(parent, struct sched_entity, run_node);
                 /*
                  * We dont care about collisions. Nodes with
                  * the same key stay together.
                  */
                 if (entity_before(se, entry)) {
                         link = &parent->rb_left;
                 } else {
                         link = &parent->rb_right;
                         leftmost = 0;
                 }
         }
 
         /*
          * Maintain a cache of leftmost tree entries (it is frequently
          * used):
          */
         if (leftmost)
                 cfs_rq->rb_leftmost = &se->run_node;
 
         rb_link_node(&se->run_node, parent, link);
         rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline);
 }
 
 static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         if (cfs_rq->rb_leftmost == &se->run_node) {
                 struct rb_node *next_node;
 
                 next_node = rb_next(&se->run_node);
                 cfs_rq->rb_leftmost = next_node;
         }
 
         rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
 }
 
 struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
 {
         struct rb_node *left = cfs_rq->rb_leftmost;
 
         if (!left)
                 return NULL;
 
         return rb_entry(left, struct sched_entity, run_node);
 }
 
 static struct sched_entity *__pick_next_entity(struct sched_entity *se)
 {
         struct rb_node *next = rb_next(&se->run_node);
 
         if (!next)
                 return NULL;
 
         return rb_entry(next, struct sched_entity, run_node);
 }
 
 #ifdef CONFIG_SCHED_DEBUG
 struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
 {
         struct rb_node *last = rb_last(&cfs_rq->tasks_timeline);
 
         if (!last)
                 return NULL;
 
         return rb_entry(last, struct sched_entity, run_node);
 }
 
 /**************************************************************
  * Scheduling class statistics methods:
  */
 
 int sched_proc_update_handler(struct ctl_table *table, int write,
                 void __user *buffer, size_t *lenp,
                 loff_t *ppos)
 {
         int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
         unsigned int factor = get_update_sysctl_factor();
 
         if (ret || !write)
                 return ret;
 
         sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
                                         sysctl_sched_min_granularity);
 
 #define WRT_SYSCTL(name) \
         (normalized_sysctl_##name = sysctl_##name / (factor))
         WRT_SYSCTL(sched_min_granularity);
         WRT_SYSCTL(sched_latency);
         WRT_SYSCTL(sched_wakeup_granularity);
 #undef WRT_SYSCTL
 
         return 0;
 }
 #endif
 
 /*
  * delta /= w
  */
 static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
 {
         if (unlikely(se->load.weight != NICE_0_LOAD))
                 delta = __calc_delta(delta, NICE_0_LOAD, &se->load);
 
         return delta;
 }
 
 /*
  * The idea is to set a period in which each task runs once.
  *
  * When there are too many tasks (sched_nr_latency) we have to stretch
  * this period because otherwise the slices get too small.
  *
  * p = (nr <= nl) ? l : l*nr/nl
  */
 static u64 __sched_period(unsigned long nr_running)
 {
         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
 static int select_idle_sibling(struct task_struct *p, int cpu);
 static unsigned long task_h_load(struct task_struct *p);
 
 /*
  * We choose a half-life close to 1 scheduling period.
  * Note: The tables runnable_avg_yN_inv and runnable_avg_yN_sum are
  * dependent on this value.
  */
 #define LOAD_AVG_PERIOD 32
 #define LOAD_AVG_MAX 47742 /* maximum possible load avg */
 #define LOAD_AVG_MAX_N 345 /* number of full periods to produce LOAD_AVG_MAX */
 
 /* 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;
 
         sa->last_update_time = 0;
         /*
          * sched_avg's period_contrib should be strictly less then 1024, so
          * we give it 1023 to make sure it is almost a period (1024us), and
          * will definitely be update (after enqueue).
          */
         sa->period_contrib = 1023;
         /*
          * Tasks are intialized with full load to be seen as heavy tasks until
          * they get a chance to stabilize to their real load level.
          * Group entities are intialized with zero load to reflect the fact that
          * nothing has been attached to the task group yet.
          */
         if (entity_is_task(se))
                 sa->load_avg = scale_load_down(se->load.weight);
         sa->load_sum = sa->load_avg * LOAD_AVG_MAX;
         /*
          * At this point, util_avg won't be used in select_task_rq_fair anyway
          */
         sa->util_avg = 0;
         sa->util_sum = 0;
         /* 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 int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq, bool update_freq);
 static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force);
 static void attach_entity_load_avg(struct cfs_rq *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 = (1024 - cfs_rq->avg.util_avg) / 2^n
  *
  * where n denotes the nth task.
  *
  * For example, 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 cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;
         u64 now = cfs_rq_clock_task(cfs_rq);
         int tg_update;
 
         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;
                 }
                 sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
         }
 
         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, false);
                         attach_entity_load_avg(cfs_rq, se);
                         switched_from_fair(rq, p);
                          *
                          * such that the next switched_to_fair() has the
                          * expected state.
                          */
                         se->avg.last_update_time = now;
                         return;
                 }
         }
 
         tg_update = update_cfs_rq_load_avg(now, cfs_rq, false);
         attach_entity_load_avg(cfs_rq, se);
         if (tg_update)
                 update_tg_load_avg(cfs_rq, false);
 }
 
 #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);
                 cpuacct_charge(curtask, delta_exec);
                 account_group_exec_runtime(curtask, delta_exec);
         }
 
         account_cfs_rq_runtime(cfs_rq, delta_exec);
 }
 
 static void update_curr_fair(struct rq *rq)
 {
         update_curr(cfs_rq_of(&rq->curr->se));
 }
 
 #ifdef CONFIG_SCHEDSTATS
 static inline void
 update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         u64 wait_start = rq_clock(rq_of(cfs_rq));
 
         if (entity_is_task(se) && task_on_rq_migrating(task_of(se)) &&
             likely(wait_start > se->statistics.wait_start))
                 wait_start -= se->statistics.wait_start;
 
         se->statistics.wait_start = wait_start;
 }
 
 static void
 update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         struct task_struct *p;
         u64 delta;
 
         delta = rq_clock(rq_of(cfs_rq)) - 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.
                          */
                         se->statistics.wait_start = delta;
                         return;
                 }
                 trace_sched_stat_wait(p, delta);
         }
 
         se->statistics.wait_max = max(se->statistics.wait_max, delta);
         se->statistics.wait_count++;
         se->statistics.wait_sum += delta;
         se->statistics.wait_start = 0;
 }
 
 /*
  * Task is being enqueued - update stats:
  */
 static inline void
 update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         /*
          * Are we enqueueing a waiting task? (for current tasks
          * a dequeue/enqueue event is a NOP)
          */
         if (se != cfs_rq->curr)
                 update_stats_wait_start(cfs_rq, se);
 }
 
 static inline void
 update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
         /*
          * 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) {
                 if (entity_is_task(se)) {
                         struct task_struct *tsk = task_of(se);
 
                         if (tsk->state & TASK_INTERRUPTIBLE)
                                 se->statistics.sleep_start = rq_clock(rq_of(cfs_rq));
                         if (tsk->state & TASK_UNINTERRUPTIBLE)
                                 se->statistics.block_start = rq_clock(rq_of(cfs_rq));
                 }
         }
 
 }
 #else
 static inline void
 update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 }
 
 static inline void
 update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 }
 
 static inline void
 update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 }
 
 static inline void
 update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
 }
 #endif
 
 /*
  * We are picking a new current task - update its stats:
  */
 static inline void
 update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         /*
          * We are starting a new run period:
          */
         se->exec_start = rq_clock_task(rq_of(cfs_rq));
 }
 
 /**************************************************
  * Scheduling class queueing methods:
  */
 
 #ifdef CONFIG_NUMA_BALANCING
 /*
  * Approximate time to scan a full NUMA task in ms. The task scan period is
  * calculated based on the tasks virtual memory size and
  * numa_balancing_scan_size.
  */
 unsigned int sysctl_numa_balancing_scan_period_min = 1000;
 unsigned int sysctl_numa_balancing_scan_period_max = 60000;
 
 /* Portion of address space to scan in MB */
 unsigned int sysctl_numa_balancing_scan_size = 256;
 
 /* Scan @scan_size MB every @scan_period after an initial @scan_delay in ms */
 unsigned int sysctl_numa_balancing_scan_delay = 1000;
 
 static unsigned int task_nr_scan_windows(struct task_struct *p)
 {
         unsigned long rss = 0;
         unsigned long nr_scan_pages;
 
         /*
          * Calculations based on RSS as non-present and empty pages are skipped
          * by the PTE scanner and NUMA hinting faults should be trapped based
          * on resident pages
          */
         nr_scan_pages = sysctl_numa_balancing_scan_size << (20 - PAGE_SHIFT);
         rss = get_mm_rss(p->mm);
         if (!rss)
                 rss = nr_scan_pages;
 
         rss = round_up(rss, nr_scan_pages);
         return rss / nr_scan_pages;
 }
 
 /* For sanitys sake, never scan more PTEs than MAX_SCAN_WINDOW MB/sec. */
 #define MAX_SCAN_WINDOW 2560
 
 static unsigned int task_scan_min(struct task_struct *p)
 {
         unsigned int scan_size = READ_ONCE(sysctl_numa_balancing_scan_size);
         unsigned int scan, floor;
         unsigned int windows = 1;
 
         if (scan_size < MAX_SCAN_WINDOW)
                 windows = MAX_SCAN_WINDOW / scan_size;
         floor = 1000 / windows;
 
         scan = sysctl_numa_balancing_scan_period_min / task_nr_scan_windows(p);
         return max_t(unsigned int, floor, scan);
 }
 
 static unsigned int task_scan_max(struct task_struct *p)
 {
         unsigned int smin = task_scan_min(p);
         unsigned int smax;
 
         /* Watch for min being lower than max due to floor calculations */
         smax = sysctl_numa_balancing_scan_period_max / task_nr_scan_windows(p);
         return max(smin, smax);
 }
 
 static void account_numa_enqueue(struct rq *rq, struct task_struct *p)
 {
         rq->nr_numa_running += (p->numa_preferred_nid != -1);
         rq->nr_preferred_running += (p->numa_preferred_nid == task_node(p));
 }
 
 static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
 {
         rq->nr_numa_running -= (p->numa_preferred_nid != -1);
         rq->nr_preferred_running -= (p->numa_preferred_nid == task_node(p));
 }
 
 struct numa_group {
         atomic_t refcount;
 
         spinlock_t lock; /* nr_tasks, tasks */
         int nr_tasks;
         pid_t gid;
         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];
 };
 
 /* 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)];
 }
 
 /*
  * 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);
 
         /*
          * Multi-stage node selection is used in conjunction with a periodic
          * migration fault to build a temporal task<->page relation. By using
          * a two-stage filter we remove short/unlikely relations.
          *
          * Using P(p) ~ n_p / n_t as per frequentist probability, we can equate
          * a task's usage of a particular page (n_p) per total usage of this
          * page (n_t) (in a given time-span) to a probability.
          *
          * Our periodic faults will sample this probability and getting the
          * same result twice in a row, given these samples are fully
          * independent, is then given by P(n)^2, provided our sample period
          * is sufficiently short compared to the usage pattern.
          *
          * This quadric squishes small probabilities, making it less likely we
          * act on an unlikely task<->page relation.
          */
         last_cpupid = page_cpupid_xchg_last(page, this_cpupid);
         if (!cpupid_pid_unset(last_cpupid) &&
                                 cpupid_to_nid(last_cpupid) != dst_nid)
                 return false;
 
         /* Always allow migrate on private faults */
         if (cpupid_match_pid(p, last_cpupid))
                 return true;
 
         /* A shared fault, but p->numa_group has not been set up yet. */
         if (!ng)
                 return true;
 
         /*
          * 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(const int cpu);
 static unsigned long source_load(int cpu, int type);
 static unsigned long target_load(int cpu, int type);
 static unsigned long capacity_of(int cpu);
 static long effective_load(struct task_group *tg, int cpu, long wl, long wg);
 
 /* Cached statistics for all CPUs within a node */
 struct numa_stats {
         unsigned long nr_running;
         unsigned long load;
 
         /* Total compute capacity of CPUs on a node */
         unsigned long compute_capacity;
 
         /* Approximate capacity in terms of runnable tasks on a node */
         unsigned long task_capacity;
         int has_free_capacity;
 };
 
 /*
  * XXX borrowed from update_sg_lb_stats
  */
 static void update_numa_stats(struct numa_stats *ns, int nid)
 {
         int smt, cpu, cpus = 0;
         unsigned long capacity;
 
         memset(ns, 0, sizeof(*ns));
         for_each_cpu(cpu, cpumask_of_node(nid)) {
                 struct rq *rq = cpu_rq(cpu);
 
                 ns->nr_running += rq->nr_running;
                 ns->load += weighted_cpuload(cpu);
                 ns->compute_capacity += capacity_of(cpu);
 
                 cpus++;
         }
 
         /*
          * If we raced with hotplug and there are no CPUs left in our mask
          * the @ns structure is NULL'ed and task_numa_compare() will
          * not find this node attractive.
          *
          * We'll either bail at !has_free_capacity, or we'll detect a huge
          * imbalance and bail there.
          */
         if (!cpus)
                 return;
 
         /* smt := ceil(cpus / capacity), assumes: 1 < smt_power < 2 */
         smt = DIV_ROUND_UP(SCHED_CAPACITY_SCALE * cpus, ns->compute_capacity);
         capacity = cpus / smt; /* cores */
 
         ns->task_capacity = min_t(unsigned, capacity,
                 DIV_ROUND_CLOSEST(ns->compute_capacity, SCHED_CAPACITY_SCALE));
         ns->has_free_capacity = (ns->nr_running < ns->task_capacity);
 }
 
 struct task_numa_env {
         struct task_struct *p;
 
         int src_cpu, src_nid;
         int dst_cpu, dst_nid;
 
         struct numa_stats src_stats, dst_stats;
 
         int imbalance_pct;
         int dist;
 
         struct task_struct *best_task;
         long best_imp;
         int best_cpu;
 };
 
 static void task_numa_assign(struct task_numa_env *env,
                              struct task_struct *p, long imp)
 {
         if (env->best_task)
                 put_task_struct(env->best_task);
         if (p)
                 get_task_struct(p);
 
         env->best_task = p;
         env->best_imp = imp;
         env->best_cpu = env->dst_cpu;
 }
 
 static bool load_too_imbalanced(long src_load, long dst_load,
                                 struct task_numa_env *env)
 {
         long imb, old_imb;
         long orig_src_load, orig_dst_load;
         long src_capacity, dst_capacity;
 
         /*
          * The load is corrected for the CPU capacity available on each node.
          *
          * src_load        dst_load
          * ------------ vs ---------
          * src_capacity    dst_capacity
          */
         src_capacity = env->src_stats.compute_capacity;
         dst_capacity = env->dst_stats.compute_capacity;
 
         /* We care about the slope of the imbalance, not the direction. */
         if (dst_load < src_load)
                 swap(dst_load, src_load);
 
         /* Is the difference below the threshold? */
         imb = dst_load * src_capacity * 100 -
               src_load * dst_capacity * env->imbalance_pct;
         if (imb <= 0)
                 return false;
 
         /*
          * The imbalance is above the allowed threshold.
          * Compare it with the old imbalance.
          */
         orig_src_load = env->src_stats.load;
         orig_dst_load = env->dst_stats.load;
 
         if (orig_dst_load < orig_src_load)
                 swap(orig_dst_load, orig_src_load);
 
         old_imb = orig_dst_load * src_capacity * 100 -
                   orig_src_load * dst_capacity * env->imbalance_pct;
 
         /* Would this change make things worse? */
         return (imb > old_imb);
 }
 
 /*
  * This checks if the overall compute and NUMA accesses of the system would
  * be improved if the source tasks was migrated to the target dst_cpu taking
  * into account that it might be best if task running on the dst_cpu should
  * be exchanged with the source task
  */
 static void task_numa_compare(struct task_numa_env *env,
                               long taskimp, long groupimp)
 {
         struct rq *src_rq = cpu_rq(env->src_cpu);
         struct rq *dst_rq = cpu_rq(env->dst_cpu);
         struct task_struct *cur;
         long src_load, dst_load;
         long load;
         long imp = env->p->numa_group ? groupimp : taskimp;
         long moveimp = imp;
         int dist = env->dist;
 
         rcu_read_lock();
         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;
 
         /*
          * "imp" is the fault differential for the source task between the
          * source and destination node. Calculate the total differential for
          * the source task and potential destination task. The more negative
          * the value is, the more rmeote accesses that would be expected to
          * be incurred if the tasks were swapped.
          */
         if (cur) {
                 /* Skip this swap candidate if cannot move to the source cpu */
                 if (!cpumask_test_cpu(env->src_cpu, tsk_cpus_allowed(cur)))
                         goto unlock;
 
                 /*
                  * If dst and source tasks are in the same NUMA group, or not
                  * in any group then look only at task weights.
                  */
                 if (cur->numa_group == env->p->numa_group) {
                         imp = taskimp + task_weight(cur, env->src_nid, dist) -
                               task_weight(cur, env->dst_nid, dist);
                         /*
                          * Add some hysteresis to prevent swapping the
                          * tasks within a group over tiny differences.
                          */
                         if (cur->numa_group)
                                 imp -= imp/16;
                 } else {
                         /*
                          * Compare the group weights. If a task is all by
                          * itself (not part of a group), use the task weight
                          * instead.
                          */
                         if (cur->numa_group)
                                 imp += group_weight(cur, env->src_nid, dist) -
                                        group_weight(cur, env->dst_nid, dist);
                         else
                                 imp += task_weight(cur, env->src_nid, dist) -
                                        task_weight(cur, env->dst_nid, dist);
                 }
         }
 
         if (imp <= env->best_imp && moveimp <= env->best_imp)
                 goto unlock;
 
         if (!cur) {
                 /* Is there capacity at our destination? */
                 if (env->src_stats.nr_running <= env->src_stats.task_capacity &&
                     !env->dst_stats.has_free_capacity)
                         goto unlock;
 
                 goto balance;
         }
 
         /* Balance doesn't matter much if we're running a task per cpu */
         if (imp > env->best_imp && src_rq->nr_running == 1 &&
                         dst_rq->nr_running == 1)
                 goto assign;
 
         /*
          * In the overloaded case, try and keep the load balanced.
          */
 balance:
         load = task_h_load(env->p);
         dst_load = env->dst_stats.load + load;
         src_load = env->src_stats.load - load;
 
         if (moveimp > imp && moveimp > env->best_imp) {
                 /*
                  * If the improvement from just moving env->p direction is
                  * better than swapping tasks around, check if a move is
                  * possible. Store a slightly smaller score than moveimp,
                  * so an actually idle CPU will win.
                  */
                 if (!load_too_imbalanced(src_load, dst_load, env)) {
                         imp = moveimp - 1;
                         cur = NULL;
                         goto assign;
                 }
         }
 
         if (imp <= env->best_imp)
                 goto unlock;
 
         if (cur) {
                 load = task_h_load(cur);
                 dst_load -= load;
                 src_load += load;
         }
 
         if (load_too_imbalanced(src_load, dst_load, env))
                 goto unlock;
 
         /*
          * One idle CPU per node is evaluated for a task numa move.
          * Call select_idle_sibling to maybe find a better one.
          */
         if (!cur)
                 env->dst_cpu = select_idle_sibling(env->p, env->dst_cpu);
 
 assign:
         task_numa_assign(env, cur, imp);
 unlock:
         rcu_read_unlock();
 }
 
 static void task_numa_find_cpu(struct task_numa_env *env,
                                 long taskimp, long groupimp)
 {
         int cpu;
 
         for_each_cpu(cpu, cpumask_of_node(env->dst_nid)) {
                 /* Skip this CPU if the source task cannot migrate */
                 if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p)))
                         continue;
 
                 env->dst_cpu = cpu;
                 task_numa_compare(env, taskimp, groupimp);
         }
 }
 
 /* Only move tasks to a NUMA node less busy than the current node. */
 static bool numa_has_capacity(struct task_numa_env *env)
 {
         struct numa_stats *src = &env->src_stats;
         struct numa_stats *dst = &env->dst_stats;
 
         if (src->has_free_capacity && !dst->has_free_capacity)
                 return false;
 
         /*
          * Only consider a task move if the source has a higher load
          * than the destination, corrected for CPU capacity on each node.
          *
          *      src->load                dst->load
          * --------------------- vs ---------------------
          * src->compute_capacity    dst->compute_capacity
          */
         if (src->load * dst->compute_capacity * env->imbalance_pct >
 
             dst->load * src->compute_capacity * 100)
                 return true;
 
         return false;
 }
 
 static int task_numa_migrate(struct task_struct *p)
 {
         struct task_numa_env env = {
                 .p = p,
 
                 .src_cpu = task_cpu(p),
                 .src_nid = task_node(p),
 
                 .imbalance_pct = 112,
 
                 .best_task = NULL,
                 .best_imp = 0,
                 .best_cpu = -1,
         };
         struct sched_domain *sd;
         unsigned long taskweight, groupweight;
         int nid, ret, dist;
         long taskimp, groupimp;
 
         /*
          * Pick the lowest SD_NUMA domain, as that would have the smallest
          * imbalance and would be the first to start moving tasks about.
          *
          * And we want to avoid any moving of tasks about, as that would create
          * random movement of tasks -- counter the numa conditions we're trying
          * to satisfy here.
          */
         rcu_read_lock();
         sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
         if (sd)
                 env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
         rcu_read_unlock();
 
         /*
          * Cpusets can break the scheduler domain tree into smaller
          * balance domains, some of which do not cross NUMA boundaries.
          * Tasks that are "trapped" in such domains cannot be migrated
          * elsewhere, so there is no point in (re)trying.
          */
         if (unlikely(!sd)) {
                 p->numa_preferred_nid = task_node(p);
                 return -EINVAL;
         }
 
         env.dst_nid = p->numa_preferred_nid;
         dist = env.dist = node_distance(env.src_nid, env.dst_nid);
         taskweight = task_weight(p, env.src_nid, dist);
         groupweight = group_weight(p, env.src_nid, dist);
         update_numa_stats(&env.src_stats, env.src_nid);
         taskimp = task_weight(p, env.dst_nid, dist) - taskweight;
         groupimp = group_weight(p, env.dst_nid, dist) - groupweight;
         update_numa_stats(&env.dst_stats, env.dst_nid);
 
         /* Try to find a spot on the preferred nid. */
         if (numa_has_capacity(&env))
                 task_numa_find_cpu(&env, taskimp, groupimp);
 
         /*
          * Look at other nodes in these cases:
          * - there is no space available on the preferred_nid
          * - the task is part of a numa_group that is interleaved across
          *   multiple NUMA nodes; in order to better consolidate the group,
          *   we need to check other locations.
          */
         if (env.best_cpu == -1 || (p->numa_group && p->numa_group->active_nodes > 1)) {
                 for_each_online_node(nid) {
                         if (nid == env.src_nid || nid == p->numa_preferred_nid)
                                 continue;
 
                         dist = node_distance(env.src_nid, env.dst_nid);
                         if (sched_numa_topology_type == NUMA_BACKPLANE &&
                                                 dist != env.dist) {
                                 taskweight = task_weight(p, env.src_nid, dist);
                                 groupweight = group_weight(p, env.src_nid, dist);
                         }
 
                         /* Only consider nodes where both task and groups benefit */
                         taskimp = task_weight(p, nid, dist) - taskweight;
                         groupimp = group_weight(p, nid, dist) - groupweight;
                         if (taskimp < 0 && groupimp < 0)
                                 continue;
 
                         env.dist = dist;
                         env.dst_nid = nid;
                         update_numa_stats(&env.dst_stats, env.dst_nid);
                         if (numa_has_capacity(&env))
                                 task_numa_find_cpu(&env, taskimp, groupimp);
                 }
         }
 
         /*
          * If the task is part of a workload that spans multiple NUMA nodes,
          * and is migrating into one of the workload's active nodes, remember
          * this node as the task's preferred numa node, so the workload can
          * settle down.
          * A task that migrated to a second choice node will be better off
          * trying for a better one later. Do not set the preferred node here.
          */
         if (p->numa_group) {
                 struct numa_group *ng = p->numa_group;
 
                 if (env.best_cpu == -1)
                         nid = env.src_nid;
                 else
                         nid = env.dst_nid;
 
                 if (ng->active_nodes > 1 && numa_is_active_node(env.dst_nid, ng))
                         sched_setnuma(p, env.dst_nid);
         }
 
         /* No better CPU than the current one was found. */
         if (env.best_cpu == -1)
                 return -EAGAIN;
 
         /*
          * Reset the scan period if the task is being rescheduled on an
          * alternative node to recheck if the tasks is now properly placed.
          */
         p->numa_scan_period = task_scan_min(p);
 
         if (env.best_task == NULL) {
                 ret = migrate_task_to(p, env.best_cpu);
                 if (ret != 0)
                         trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
                 return ret;
         }
 
         ret = migrate_swap(p, env.best_task);
         if (ret != 0)
                 trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
         put_task_struct(env.best_task);
         return ret;
 }
 
 /* Attempt to migrate a task to a CPU on the preferred node. */
 static void numa_migrate_preferred(struct task_struct *p)
 {
         unsigned long interval = HZ;
 
         /* This task has no NUMA fault statistics yet */
         if (unlikely(p->numa_preferred_nid == -1 || !p->numa_faults))
                 return;
 
         /* Periodically retry migrating the task to the preferred node */
         interval = min(interval, msecs_to_jiffies(p->numa_scan_period) / 16);
         p->numa_migrate_retry = jiffies + interval;
 
         /* Success if task is already running on preferred CPU */
         if (task_node(p) == p->numa_preferred_nid)
                 return;
 
         /* Otherwise, try migrate to a CPU on the preferred node */
         task_numa_migrate(p);
 }
 
 /*
  * Find 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 ratio;
         int diff;
 
         unsigned long remote = p->numa_faults_locality[0];
         unsigned long local = p->numa_faults_locality[1];
 
         /*
          * If there were no record hinting faults then either the task is
          * completely idle or all activity is areas that are not of interest
          * to automatic numa balancing. Related to that, if there were failed
          * migration then it implies we are migrating too quickly or the local
          * node is overloaded. In either case, scan slower
          */
         if (local + shared == 0 || p->numa_faults_locality[2]) {
                 p->numa_scan_period = min(p->numa_scan_period_max,
                         p->numa_scan_period << 1);
 
                 p->mm->numa_next_scan = jiffies +
                         msecs_to_jiffies(p->numa_scan_period);
 
                 return;
         }
 
         /*
          * Prepare to scale scan period relative to the current period.
          *       == NUMA_PERIOD_THRESHOLD scan period stays the same
          *       <  NUMA_PERIOD_THRESHOLD scan period decreases (scan faster)
          *       >= NUMA_PERIOD_THRESHOLD scan period increases (scan slower)
          */
         period_slot = DIV_ROUND_UP(p->numa_scan_period, NUMA_PERIOD_SLOTS);
         ratio = (local * NUMA_PERIOD_SLOTS) / (local + remote);
         if (ratio >= NUMA_PERIOD_THRESHOLD) {
                 int slot = ratio - NUMA_PERIOD_THRESHOLD;
                 if (!slot)
                         slot = 1;
                 diff = slot * period_slot;
         } else {
                 diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;
 
                 /*
                  * Scale scan rate increases based on sharing. There is an
                  * inverse relationship between the degree of sharing and
                  * the adjustment made to the scanning period. Broadly
                  * speaking the intent is that there is little point
                  * scanning faster if shared accesses dominate as it may
                  * simply bounce migrations uselessly
                  */
                 ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared + 1));
                 diff = (diff * ratio) / NUMA_PERIOD_SLOTS;
         }
 
         p->numa_scan_period = clamp(p->numa_scan_period + diff,
                         task_scan_min(p), task_scan_max(p));
         memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
 }
 
 /*
  * Get the fraction of time the task has been running since the last
  * NUMA placement cycle. The scheduler keeps similar statistics, but
  * decays those on a 32ms period, which is orders of magnitude off
  * from the dozens-of-seconds NUMA balancing period. Use the scheduler
  * stats only if the task is so new there are no NUMA statistics yet.
  */
 static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period)
 {
         u64 runtime, delta, now;
         /* Use the start of this time slice to avoid calculations. */
         now = p->se.exec_start;
         runtime = p->se.sum_exec_runtime;
 
         if (p->last_task_numa_placement) {
                 delta = runtime - p->last_sum_exec_runtime;
                 *period = now - p->last_task_numa_placement;
         } else {
                 delta = p->se.avg.load_sum / p->se.load.weight;
                 *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 = -1, max_group_nid = -1;
         unsigned long max_faults = 0, max_group_faults = 0;
         unsigned long fault_types[2] = { 0, 0 };
         unsigned long total_faults;
         u64 runtime, period;
         spinlock_t *group_lock = NULL;
 
         /*
          * The p->mm->numa_scan_seq field gets updated without
          * exclusive access. Use READ_ONCE() here to ensure
          * that the field is read in a single access:
          */
         seq = READ_ONCE(p->mm->numa_scan_seq);
         if (p->numa_scan_seq == seq)
                 return;
         p->numa_scan_seq = seq;
         p->numa_scan_period_max = task_scan_max(p);
 
         total_faults = p->numa_faults_locality[0] +
                        p->numa_faults_locality[1];
         runtime = numa_get_avg_runtime(p, &period);
 
         /* If the task is part of a group prevent parallel updates to group stats */
         if (p->numa_group) {
                 group_lock = &p->numa_group->lock;
                 spin_lock_irq(group_lock);
         }
 
         /* Find the node with the highest number of faults */
         for_each_online_node(nid) {
                 /* Keep track of the offsets in numa_faults array */
                 int mem_idx, membuf_idx, cpu_idx, cpubuf_idx;
                 unsigned long faults = 0, group_faults = 0;
                 int priv;
 
                 for (priv = 0; priv < NR_NUMA_HINT_FAULT_TYPES; priv++) {
                         long diff, f_diff, f_weight;
 
                         mem_idx = task_faults_idx(NUMA_MEM, nid, priv);
                         membuf_idx = task_faults_idx(NUMA_MEMBUF, nid, priv);
                         cpu_idx = task_faults_idx(NUMA_CPU, nid, priv);
                         cpubuf_idx = task_faults_idx(NUMA_CPUBUF, nid, priv);
 
                         /* Decay existing window, copy faults since last scan */
                         diff = p->numa_faults[membuf_idx] - p->numa_faults[mem_idx] / 2;
                         fault_types[priv] += p->numa_faults[membuf_idx];
                         p->numa_faults[membuf_idx] = 0;
 
                         /*
                          * Normalize the faults_from, so all tasks in a group
                          * count according to CPU use, instead of by the raw
                          * number of faults. Tasks with little runtime have
                          * little over-all impact on throughput, and thus their
                          * faults are less important.
                          */
                         f_weight = div64_u64(runtime << 16, period + 1);
                         f_weight = (f_weight * p->numa_faults[cpubuf_idx]) /
                                    (total_faults + 1);
                         f_diff = f_weight - p->numa_faults[cpu_idx] / 2;
                         p->numa_faults[cpubuf_idx] = 0;
 
                         p->numa_faults[mem_idx] += diff;
                         p->numa_faults[cpu_idx] += f_diff;
                         faults += p->numa_faults[mem_idx];
                         p->total_numa_faults += diff;
                         if (p->numa_group) {
                                 /*
                                  * safe because we can only change our own group
                                  *
                                  * mem_idx represents the offset for a given
                                  * nid and priv in a specific region because it
                                  * is at the beginning of the numa_faults array.
                                  */
                                 p->numa_group->faults[mem_idx] += diff;
                                 p->numa_group->faults_cpu[mem_idx] += f_diff;
                                 p->numa_group->total_faults += diff;
                                 group_faults += p->numa_group->faults[mem_idx];
                         }
                 }
 
                 if (faults > max_faults) {
                         max_faults = faults;
                         max_nid = nid;
                 }
 
                 if (group_faults > max_group_faults) {
                         max_group_faults = group_faults;
                         max_group_nid = nid;
                 }
         }
 
         update_task_scan_period(p, fault_types[0], fault_types[1]);
 
         if (p->numa_group) {
                 numa_group_count_active_nodes(p->numa_group);
                 spin_unlock_irq(group_lock);
                 max_nid = preferred_group_nid(p, max_group_nid);
         }
 
         if (max_faults) {
                 /* Set the new preferred node */
                 if (max_nid != p->numa_preferred_nid)
                         sched_setnuma(p, max_nid);
 
                 if (task_node(p) != p->numa_preferred_nid)
                         numa_migrate_preferred(p);
         }
 }
 
 static inline int get_numa_group(struct numa_group *grp)
 {
         return atomic_inc_not_zero(&grp->refcount);
 }
 
 static inline void put_numa_group(struct numa_group *grp)
 {
         if (atomic_dec_and_test(&grp->refcount))
                 kfree_rcu(grp, rcu);
 }
 
 static void task_numa_group(struct task_struct *p, int cpupid, int flags,
                         int *priv)
 {
         struct numa_group *grp, *my_grp;
         struct task_struct *tsk;
         bool join = false;
         int cpu = cpupid_to_cpu(cpupid);
         int i;
 
         if (unlikely(!p->numa_group)) {
                 unsigned int size = sizeof(struct numa_group) +
                                     4*nr_node_ids*sizeof(unsigned long);
 
                 grp = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
                 if (!grp)
                         return;
 
                 atomic_set(&grp->refcount, 1);
                 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;
 
         task_numa_placement(p);
 
         /*
          * Retry task to preferred node migration periodically, in case it
          * case it previously failed, or the scheduler moved us.
          */
         if (time_after(jiffies, p->numa_migrate_retry))
                 numa_migrate_preferred(p);
 
         if (migrated)
                 p->numa_pages_migrated += pages;
         if (flags & TNF_MIGRATE_FAIL)
                 p->numa_faults_locality[2] += pages;
 
         p->numa_faults[task_faults_idx(NUMA_MEMBUF, mem_node, priv)] += pages;
         p->numa_faults[task_faults_idx(NUMA_CPUBUF, cpu_node, priv)] += pages;
         p->numa_faults_locality[local] += pages;
 }
 
 static void reset_ptenuma_scan(struct task_struct *p)
 {
         /*
          * We only did a read acquisition of the mmap sem, so
          * p->mm->numa_scan_seq is written to without exclusive access
          * and the update is not guaranteed to be atomic. That's not
          * much of an issue though, since this is just used for
          * statistical sampling. Use READ_ONCE/WRITE_ONCE, which are not
          * expensive, to avoid any form of compiler optimizations:
          */
         WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
         p->mm->numa_scan_offset = 0;
 }
 
 /*
  * The expensive part of numa migration is done from task_work context.
  * Triggered from task_tick_numa().
  */
 void task_numa_work(struct callback_head *work)
 {
         unsigned long migrate, next_scan, now = jiffies;
         struct task_struct *p = current;
         struct mm_struct *mm = p->mm;
         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;
 
         WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));
 
         work->next = work; /* protect against double add */
         /*
          * Who cares about NUMA placement when they're dying.
          *
          * NOTE: make sure not to dereference p->mm before this check,
          * exit_task_work() happens _after_ exit_mm() so we could be called
          * without p->mm even though we still had it when we enqueued this
          * work.
          */
         if (p->flags & PF_EXITING)
                 return;
 
         if (!mm->numa_next_scan) {
                 mm->numa_next_scan = now +
                         msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
         }
 
         /*
          * Enforce maximal scan/migration frequency..
          */
         migrate = mm->numa_next_scan;
         if (time_before(now, migrate))
                 return;
 
         if (p->numa_scan_period == 0) {
                 p->numa_scan_period_max = task_scan_max(p);
                 p->numa_scan_period = task_scan_min(p);
         }
 
         next_scan = now + msecs_to_jiffies(p->numa_scan_period);
         if (cmpxchg(&mm->numa_next_scan, migrate, next_scan) != migrate)
                 return;
 
         /*
          * Delay this task enough that another task of this mm will likely win
          * the next time around.
          */
         p->node_stamp += 2 * TICK_NSEC;
 
         start = mm->numa_scan_offset;
         pages = sysctl_numa_balancing_scan_size;
         pages <<= 20 - PAGE_SHIFT; /* MB in pages */
         virtpages = pages * 8;     /* Scan up to this much virtual space */
         if (!pages)
                 return;
 
 
         down_read(&mm->mmap_sem);
         vma = find_vma(mm, start);
         if (!vma) {
                 reset_ptenuma_scan(p);
                 start = 0;
                 vma = mm->mmap;
         }
         for (; vma; vma = vma->vm_next) {
                 if (!vma_migratable(vma) || !vma_policy_mof(vma) ||
                         is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_MIXEDMAP)) {
                         continue;
                 }
 
                 /*
                  * Shared library pages mapped by multiple processes are not
                  * migrated as it is expected they are cache replicated. Avoid
                  * hinting faults in read-only file-backed mappings or the vdso
                  * as migrating the pages will be of marginal benefit.
                  */
                 if (!vma->vm_mm ||
                     (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ)))
                         continue;
 
                 /*
                  * Skip inaccessible VMAs to avoid any confusion between
                  * PROT_NONE and NUMA hinting ptes
                  */
                 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                         continue;
 
                 do {
                         start = max(start, vma->vm_start);
                         end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
                         end = min(end, vma->vm_end);
                         nr_pte_updates = change_prot_numa(vma, start, end);
 
                         /*
                          * 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_min(curr);
                 curr->node_stamp += period;
 
                 if (!time_before(jiffies, curr->mm->numa_next_scan)) {
                         init_task_work(work, task_numa_work); /* TODO: move this into sched_fork() */
                         task_work_add(curr, work, true);
                 }
         }
 }
 #else
 static void task_tick_numa(struct rq *rq, struct task_struct *curr)
 {
 }
 
 static inline void account_numa_enqueue(struct rq *rq, struct task_struct *p)
 {
 }
 
 static inline void account_numa_dequeue(struct rq *rq, struct task_struct *p)
 {
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
 static void
 account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         update_load_add(&cfs_rq->load, se->load.weight);
         if (!parent_entity(se))
                 update_load_add(&rq_of(cfs_rq)->load, se->load.weight);
 #ifdef CONFIG_SMP
         if (entity_is_task(se)) {
                 struct rq *rq = rq_of(cfs_rq);
 
                 account_numa_enqueue(rq, task_of(se));
                 list_add(&se->group_node, &rq->cfs_tasks);
         }
 #endif
         cfs_rq->nr_running++;
 }
 
 static void
 account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         update_load_sub(&cfs_rq->load, se->load.weight);
         if (!parent_entity(se))
                 update_load_sub(&rq_of(cfs_rq)->load, se->load.weight);
 #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--;
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 # ifdef CONFIG_SMP
 static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
 {
         long tg_weight, load, shares;
 
         /*
          * This really should be: cfs_rq->avg.load_avg, but instead we use
          * cfs_rq->load.weight, which is its upper bound. This helps ramp up
          * the shares for small weight interactive tasks.
          */
         load = scale_load_down(cfs_rq->load.weight);
 
         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;
 
         if (shares < MIN_SHARES)
                 shares = MIN_SHARES;
         if (shares > tg->shares)
                 shares = tg->shares;
 
         return shares;
 }
 # else /* CONFIG_SMP */
 static inline long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
 {
         return tg->shares;
 }
 # endif /* CONFIG_SMP */
 
 static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
                             unsigned long weight)
 {
         if (se->on_rq) {
                 /* commit outstanding execution time */
                 if (cfs_rq->curr == se)
                         update_curr(cfs_rq);
                 account_entity_dequeue(cfs_rq, se);
         }
 
         update_load_set(&se->load, weight);
 
         if (se->on_rq)
                 account_entity_enqueue(cfs_rq, se);
 }
 
 static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
 
 static void update_cfs_shares(struct cfs_rq *cfs_rq)
 {
         struct task_group *tg;
         struct sched_entity *se;
         long shares;
 
         tg = cfs_rq->tg;
         se = tg->se[cpu_of(rq_of(cfs_rq))];
         if (!se || throttled_hierarchy(cfs_rq))
                 return;
 #ifndef CONFIG_SMP
         if (likely(se->load.weight == tg->shares))
                 return;
 #endif
         shares = calc_cfs_shares(cfs_rq, tg);
 
         reweight_entity(cfs_rq_of(se), se, shares);
 }
 #else /* CONFIG_FAIR_GROUP_SCHED */
 static inline void update_cfs_shares(struct cfs_rq *cfs_rq)
 {
 }
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
 #ifdef CONFIG_SMP
 /* Precomputed fixed inverse multiplies for multiplication by y^n */
 static const u32 runnable_avg_yN_inv[] = {
         0xffffffff, 0xfa83b2da, 0xf5257d14, 0xefe4b99a, 0xeac0c6e6, 0xe5b906e6,
         0xe0ccdeeb, 0xdbfbb796, 0xd744fcc9, 0xd2a81d91, 0xce248c14, 0xc9b9bd85,
         0xc5672a10, 0xc12c4cc9, 0xbd08a39e, 0xb8fbaf46, 0xb504f333, 0xb123f581,
         0xad583ee9, 0xa9a15ab4, 0xa5fed6a9, 0xa2704302, 0x9ef5325f, 0x9b8d39b9,
         0x9837f050, 0x94f4efa8, 0x91c3d373, 0x8ea4398a, 0x8b95c1e3, 0x88980e80,
         0x85aac367, 0x82cd8698,
 };
 
 /*
  * Precomputed \Sum y^k { 1<=k<=n }.  These are floor(true_value) to prevent
  * over-estimates when re-combining.
  */
 static const u32 runnable_avg_yN_sum[] = {
             0, 1002, 1982, 2941, 3880, 4798, 5697, 6576, 7437, 8279, 9103,
          9909,10698,11470,12226,12966,13690,14398,15091,15769,16433,17082,
         17718,18340,18949,19545,20128,20698,21256,21802,22336,22859,23371,
 };
 
 /*
  * Precomputed \Sum y^k { 1<=k<=n, where n%32=0). Values are rolled down to
  * lower integers. See Documentation/scheduler/sched-avg.txt how these
  * were generated:
  */
 static const u32 __accumulated_sum_N32[] = {
             0, 23371, 35056, 40899, 43820, 45281,
         46011, 46376, 46559, 46650, 46696, 46719,
 };
 
 /*
  * Approximate:
  *   val * y^n,    where y^32 ~= 0.5 (~1 scheduling period)
  */
 static __always_inline u64 decay_load(u64 val, u64 n)
 {
         unsigned int local_n;
 
         if (!n)
                 return val;
         else if (unlikely(n > LOAD_AVG_PERIOD * 63))
                 return 0;
 
         /* after bounds checking we can collapse to 32-bit */
         local_n = n;
 
         /*
          * As y^PERIOD = 1/2, we can combine
          *    y^n = 1/2^(n/PERIOD) * y^(n%PERIOD)
          * With a look-up table which covers y^n (n<PERIOD)
          *
          * To achieve constant time decay_load.
          */
         if (unlikely(local_n >= LOAD_AVG_PERIOD)) {
                 val >>= local_n / LOAD_AVG_PERIOD;
                 local_n %= LOAD_AVG_PERIOD;
         }
 
         val = mul_u64_u32_shr(val, runnable_avg_yN_inv[local_n], 32);
         return val;
 }
 
 /*
  * For updates fully spanning n periods, the contribution to runnable
  * average will be: \Sum 1024*y^n
  *
  * We can compute this reasonably efficiently by combining:
  *   y^PERIOD = 1/2 with precomputed \Sum 1024*y^n {for  n <PERIOD}
  */
 static u32 __compute_runnable_contrib(u64 n)
 {
         u32 contrib = 0;
 
         if (likely(n <= LOAD_AVG_PERIOD))
                 return runnable_avg_yN_sum[n];
         else if (unlikely(n >= LOAD_AVG_MAX_N))
                 return LOAD_AVG_MAX;
 
         /* Since n < LOAD_AVG_MAX_N, n/LOAD_AVG_PERIOD < 11 */
         contrib = __accumulated_sum_N32[n/LOAD_AVG_PERIOD];
         n %= LOAD_AVG_PERIOD;
         contrib = decay_load(contrib, n);
         return contrib + runnable_avg_yN_sum[n];
 }
 
 #define cap_scale(v, s) ((v)*(s) >> SCHED_CAPACITY_SHIFT)
 
 /*
  * We can represent the historical contribution to runnable average as the
  * coefficients of a geometric series.  To do this we sub-divide our runnable
  * history into segments of approximately 1ms (1024us); label the segment that
  * occurred N-ms ago p_N, with p_0 corresponding to the current period, e.g.
  *
  * [<- 1024us ->|<- 1024us ->|<- 1024us ->| ...
  *      p0            p1           p2
  *     (now)       (~1ms ago)  (~2ms ago)
  *
  * Let u_i denote the fraction of p_i that the entity was runnable.
  *
  * We then designate the fractions u_i as our co-efficients, yielding the
  * following representation of historical load:
  *   u_0 + u_1*y + u_2*y^2 + u_3*y^3 + ...
  *
  * We choose y based on the with of a reasonably scheduling period, fixing:
  *   y^32 = 0.5
  *
  * This means that the contribution to load ~32ms ago (u_32) will be weighted
  * approximately half as much as the contribution to load within the last ms
  * (u_0).
  *
  * When a period "rolls over" and we have new u_0`, multiplying the previous
  * sum again by y is sufficient to update:
  *   load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... )
  *            = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1}]
  */
 static __always_inline int
 __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
                   unsigned long weight, int running, struct cfs_rq *cfs_rq)
 {
         u64 delta, scaled_delta, periods;
         u32 contrib;
         unsigned int delta_w, scaled_delta_w, decayed = 0;
         unsigned long scale_freq, scale_cpu;
 
         delta = now - sa->last_update_time;
         /*
          * This should only happen when time goes backwards, which it
          * unfortunately does during sched clock init when we swap over to TSC.
          */
         if ((s64)delta < 0) {
                 sa->last_update_time = now;
                 return 0;
         }
 
         /*
          * Use 1024ns as the unit of measurement since it's a reasonable
          * approximation of 1us and fast to compute.
          */
         delta >>= 10;
         if (!delta)
                 return 0;
         sa->last_update_time = now;
 
         scale_freq = arch_scale_freq_capacity(NULL, cpu);
         scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
 
         /* delta_w is the amount already accumulated against our next period */
         delta_w = sa->period_contrib;
         if (delta + delta_w >= 1024) {
                 decayed = 1;
 
                 /* how much left for next period will start over, we don't know yet */
                 sa->period_contrib = 0;
 
                 /*
                  * Now that we know we're crossing a period boundary, figure
                  * out how much from delta we need to complete the current
                  * period and accrue it.
                  */
                 delta_w = 1024 - delta_w;
                 scaled_delta_w = cap_scale(delta_w, scale_freq);
                 if (weight) {
                         sa->load_sum += weight * scaled_delta_w;
                         if (cfs_rq) {
                                 cfs_rq->runnable_load_sum +=
                                                 weight * scaled_delta_w;
                         }
                 }
                 if (running)
                         sa->util_sum += scaled_delta_w * scale_cpu;
 
                 delta -= delta_w;
 
                 /* Figure out how many additional periods this update spans */
                 periods = delta / 1024;
                 delta %= 1024;
 
                 sa->load_sum = decay_load(sa->load_sum, periods + 1);
                 if (cfs_rq) {
                         cfs_rq->runnable_load_sum =
                                 decay_load(cfs_rq->runnable_load_sum, periods + 1);
                 }
                 sa->util_sum = decay_load((u64)(sa->util_sum), periods + 1);
 
                 /* Efficiently calculate \sum (1..n_period) 1024*y^i */
                 contrib = __compute_runnable_contrib(periods);
                 contrib = cap_scale(contrib, scale_freq);
                 if (weight) {
                         sa->load_sum += weight * contrib;
                         if (cfs_rq)
                                 cfs_rq->runnable_load_sum += weight * contrib;
                 }
                 if (running)
                         sa->util_sum += contrib * scale_cpu;
         }
 
         /* Remainder of delta accrued against u_0` */
         scaled_delta = cap_scale(delta, scale_freq);
         if (weight) {
                 sa->load_sum += weight * scaled_delta;
                 if (cfs_rq)
                         cfs_rq->runnable_load_sum += weight * scaled_delta;
         }
         if (running)
                 sa->util_sum += scaled_delta * scale_cpu;
 
         sa->period_contrib += delta;
 
         if (decayed) {
                 sa->load_avg = div_u64(sa->load_sum, LOAD_AVG_MAX);
                 if (cfs_rq) {
                         cfs_rq->runnable_load_avg =
                                 div_u64(cfs_rq->runnable_load_sum, LOAD_AVG_MAX);
                 }
                 sa->util_avg = sa->util_sum / LOAD_AVG_MAX;
         }
 
         return decayed;
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 /*
  * Updating tg's load_avg is necessary before update_cfs_share (which is done)
  * and effective_load (which is not done because it is too costly).
  */
 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)
 {
         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) {
                 u64 p_last_update_time;
                 u64 n_last_update_time;
 
 #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(p_last_update_time, cpu_of(rq_of(prev)),
                                   &se->avg, 0, 0, NULL);
                 se->avg.last_update_time = n_last_update_time;
         }
 }
 #else /* CONFIG_FAIR_GROUP_SCHED */
 static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force) {}
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
 static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq)
 {
         struct rq *rq = rq_of(cfs_rq);
         int cpu = cpu_of(rq);
 
         if (cpu == smp_processor_id() && &rq->cfs == cfs_rq) {
                 unsigned long max = rq->cpu_capacity_orig;
 
                 /*
                  * 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 -- added to that it only calls on the local
                  * CPU, so if we enqueue remotely we'll miss an update, but
                  * the next tick/schedule should update.
                  *
                  * 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_clock(rq),
                                     min(cfs_rq->avg.util_avg, max), max);
         }
 }
 
 /*
  * 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)
 
 /**
  * update_cfs_rq_load_avg - update the cfs_rq's load/util averages
  * @now: current time, as per cfs_rq_clock_task()
  * @cfs_rq: cfs_rq to update
  * @update_freq: should we call cfs_rq_util_change() or will the call do so
  *
  * The cfs_rq avg is the direct sum of all its entities (blocked and runnable)
  * avg. The immediate corollary is that all (fair) tasks must be attached, see
  * post_init_entity_util_avg().
  *
  * cfs_rq->avg is used for task_h_load() and update_cfs_share() for example.
  *
  * Returns true if the load decayed or we removed utilization. It is expected
  * that one calls update_tg_load_avg() on this condition, but after you've
  * modified the cfs_rq avg (attach/detach), such that we propagate the new
  * avg up.
  */
 static inline int
 update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq, bool update_freq)
 {
         struct sched_avg *sa = &cfs_rq->avg;
         int decayed, removed_load = 0, removed_util = 0;
 
         if (atomic_long_read(&cfs_rq->removed_load_avg)) {
                 s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
                 sub_positive(&sa->load_avg, r);
                 sub_positive(&sa->load_sum, r * LOAD_AVG_MAX);
                 removed_load = 1;
         }
 
         if (atomic_long_read(&cfs_rq->removed_util_avg)) {
                 long r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);
                 sub_positive(&sa->util_avg, r);
                 sub_positive(&sa->util_sum, r * LOAD_AVG_MAX);
                 removed_util = 1;
         }
 
         decayed = __update_load_avg(now, cpu_of(rq_of(cfs_rq)), sa,
                 scale_load_down(cfs_rq->load.weight), cfs_rq->curr != NULL, cfs_rq);
 
 #ifndef CONFIG_64BIT
         smp_wmb();
         cfs_rq->load_last_update_time_copy = sa->last_update_time;
 #endif
 
         if (update_freq && (decayed || removed_util))
                 cfs_rq_util_change(cfs_rq);
 
         return decayed || removed_load;
 }
 
 /* Update task and its cfs_rq load average */
 static inline void update_load_avg(struct sched_entity *se, int update_tg)
 {
         struct cfs_rq *cfs_rq = cfs_rq_of(se);
         u64 now = cfs_rq_clock_task(cfs_rq);
         struct rq *rq = rq_of(cfs_rq);
         int cpu = cpu_of(rq);
 
         /*
          * Track task load average for carrying it to new CPU after migrated, and
          * track group sched_entity load average for task_h_load calc in migration
          */
         __update_load_avg(now, cpu, &se->avg,
                           se->on_rq * scale_load_down(se->load.weight),
                           cfs_rq->curr == se, NULL);
 
         if (update_cfs_rq_load_avg(now, cfs_rq, true) && update_tg)
                 update_tg_load_avg(cfs_rq, 0);
 }
 
 /**
  * attach_entity_load_avg - attach this entity to its cfs_rq load avg
  * @cfs_rq: cfs_rq to attach to
  * @se: sched_entity to attach
  *
  * Must call update_cfs_rq_load_avg() before this, since we rely on
  * cfs_rq->avg.last_update_time being current.
  */
 static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         if (!sched_feat(ATTACH_AGE_LOAD))
                 goto skip_aging;
 
         /*
          * If we got migrated (either between CPUs or between cgroups) we'll
          * have aged the average right before clearing @last_update_time.
          *
          * Or we're fresh through post_init_entity_util_avg().
          */
         if (se->avg.last_update_time) {
                 __update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
                                   &se->avg, 0, 0, NULL);
 
                 /*
                  * XXX: we could have just aged the entire load away if we've been
                  * absent from the fair class for too long.
                  */
         }
 
 skip_aging:
         se->avg.last_update_time = cfs_rq->avg.last_update_time;
         cfs_rq->avg.load_avg += se->avg.load_avg;
         cfs_rq->avg.load_sum += se->avg.load_sum;
         cfs_rq->avg.util_avg += se->avg.util_avg;
         cfs_rq->avg.util_sum += se->avg.util_sum;
 
         cfs_rq_util_change(cfs_rq);
 }
 
 /**
  * detach_entity_load_avg - detach this entity from its cfs_rq load avg
  * @cfs_rq: cfs_rq to detach from
  * @se: sched_entity to detach
  *
  * Must call update_cfs_rq_load_avg() before this, since we rely on
  * cfs_rq->avg.last_update_time being current.
  */
 static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         __update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
                           &se->avg, se->on_rq * scale_load_down(se->load.weight),
                           cfs_rq->curr == se, NULL);
 
         sub_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
         sub_positive(&cfs_rq->avg.load_sum, se->avg.load_sum);
         sub_positive(&cfs_rq->avg.util_avg, se->avg.util_avg);
         sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum);
 
         cfs_rq_util_change(cfs_rq);
 }
 
 /* Add the load generated by se into cfs_rq's load average */
 static inline void
 enqueue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         struct sched_avg *sa = &se->avg;
         u64 now = cfs_rq_clock_task(cfs_rq);
         int migrated, decayed;
 
         migrated = !sa->last_update_time;
         if (!migrated) {
                 __update_load_avg(now, cpu_of(rq_of(cfs_rq)), sa,
                         se->on_rq * scale_load_down(se->load.weight),
                         cfs_rq->curr == se, NULL);
         }
 
         decayed = update_cfs_rq_load_avg(now, cfs_rq, !migrated);
 
         cfs_rq->runnable_load_avg += sa->load_avg;
         cfs_rq->runnable_load_sum += sa->load_sum;
 
         if (migrated)
                 attach_entity_load_avg(cfs_rq, se);
 
         if (decayed || migrated)
                 update_tg_load_avg(cfs_rq, 0);
 }
 
 /* Remove the runnable load generated by se from cfs_rq's runnable load average */
 static inline void
 dequeue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         update_load_avg(se, 1);
 
         cfs_rq->runnable_load_avg =
                 max_t(long, cfs_rq->runnable_load_avg - se->avg.load_avg, 0);
         cfs_rq->runnable_load_sum =
                 max_t(s64,  cfs_rq->runnable_load_sum - se->avg.load_sum, 0);
 }
 
 #ifndef CONFIG_64BIT
 static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
 {
         u64 last_update_time_copy;
         u64 last_update_time;
 
         do {
                 last_update_time_copy = cfs_rq->load_last_update_time_copy;
                 smp_rmb();
                 last_update_time = cfs_rq->avg.last_update_time;
         } while (last_update_time != last_update_time_copy);
 
         return last_update_time;
 }
 #else
 static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
 {
         return cfs_rq->avg.last_update_time;
 }
 #endif
 
 /*
  * Task first catches up with cfs_rq, and then subtract
  * itself from the cfs_rq (task must be off the queue now).
  */
 void remove_entity_load_avg(struct sched_entity *se)
 {
         struct cfs_rq *cfs_rq = cfs_rq_of(se);
         u64 last_update_time;
 
         /*
          * tasks cannot exit without having gone through wake_up_new_task() ->
          * post_init_entity_util_avg() which will have added things to the
          * cfs_rq, so we can remove unconditionally.
          *
          * Similarly for groups, they will have passed through
          * post_init_entity_util_avg() before unregister_sched_fair_group()
          * calls this.
          */
 
         last_update_time = cfs_rq_last_update_time(cfs_rq);
 
         __update_load_avg(last_update_time, cpu_of(rq_of(cfs_rq)), &se->avg, 0, 0, NULL);
         atomic_long_add(se->avg.load_avg, &cfs_rq->removed_load_avg);
         atomic_long_add(se->avg.util_avg, &cfs_rq->removed_util_avg);
 }
 
 static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq)
 {
         return cfs_rq->runnable_load_avg;
 }
 
 static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq)
 {
         return cfs_rq->avg.load_avg;
 }
 
 static int idle_balance(struct rq *this_rq);
 
 #else /* CONFIG_SMP */
 
 static inline int
 update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq, bool update_freq)
 {
         return 0;
 }
 
 static inline void update_load_avg(struct sched_entity *se, int not_used)
 {
         struct cfs_rq *cfs_rq = cfs_rq_of(se);
         struct rq *rq = rq_of(cfs_rq);
 
         cpufreq_trigger_update(rq_clock(rq));
 }
 
 static inline void
 enqueue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
 static inline void
 dequeue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
 static inline void remove_entity_load_avg(struct sched_entity *se) {}
 
 static inline void
 attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
 static inline void
 detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
 
 static inline int idle_balance(struct rq *rq)
 {
         return 0;
 }
 
 #endif /* CONFIG_SMP */
 
 static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 #ifdef CONFIG_SCHEDSTATS
         struct task_struct *tsk = NULL;
 
         if (entity_is_task(se))
                 tsk = task_of(se);
 
         if (se->statistics.sleep_start) {
                 u64 delta = rq_clock(rq_of(cfs_rq)) - se->statistics.sleep_start;
 
                 if ((s64)delta < 0)
                         delta = 0;
 
                 if (unlikely(delta > se->statistics.sleep_max))
                         se->statistics.sleep_max = delta;
 
                 se->statistics.sleep_start = 0;
                 se->statistics.sum_sleep_runtime += delta;
 
                 if (tsk) {
                         account_scheduler_latency(tsk, delta >> 10, 1);
                         trace_sched_stat_sleep(tsk, delta);
                 }
         }
         if (se->statistics.block_start) {
                 u64 delta = rq_clock(rq_of(cfs_rq)) - se->statistics.block_start;
 
                 if ((s64)delta < 0)
                         delta = 0;
 
                 if (unlikely(delta > se->statistics.block_max))
                         se->statistics.block_max = delta;
 
                 se->statistics.block_start = 0;
                 se->statistics.sum_sleep_runtime += delta;
 
                 if (tsk) {
                         if (tsk->in_iowait) {
                                 se->statistics.iowait_sum += delta;
                                 se->statistics.iowait_count++;
                                 trace_sched_stat_iowait(tsk, delta);
                         }
 
                         trace_sched_stat_blocked(tsk, delta);
 
                         /*
                          * Blocking time is in units of nanosecs, so shift by
                          * 20 to get a milliseconds-range estimation of the
                          * amount of time that the task spent sleeping:
                          */
                         if (unlikely(prof_on == SLEEP_PROFILING)) {
                                 profile_hits(SLEEP_PROFILING,
                                                 (void *)get_wchan(tsk),
                                                 delta >> 20);
                         }
                         account_scheduler_latency(tsk, delta >> 10, 0);
                 }
         }
 #endif
 }
 
 static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 #ifdef CONFIG_SCHED_DEBUG
         s64 d = se->vruntime - cfs_rq->min_vruntime;
 
         if (d < 0)
                 d = -d;
 
         if (d > 3*sysctl_sched_latency)
                 schedstat_inc(cfs_rq, nr_spread_over);
 #endif
 }
 
 static void
 place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 {
         u64 vruntime = cfs_rq->min_vruntime;
 
         /*
          * The 'current' period is already promised to the current tasks,
          * however the extra weight of the new task will slow them down a
          * little, place the new task so that it fits in the slot that
          * stays open at the end.
          */
         if (initial && sched_feat(START_DEBIT))
                 vruntime += sched_vslice(cfs_rq, se);
 
         /* sleeps up to a single latency don't count. */
         if (!initial) {
                 unsigned long thresh = sysctl_sched_latency;
 
                 /*
                  * Halve their sleep time's effect, to allow
                  * for a gentler effect of sleepers:
                  */
                 if (sched_feat(GENTLE_FAIR_SLEEPERS))
                         thresh >>= 1;
 
                 vruntime -= thresh;
         }
 
         /* ensure we never gain time by being placed backwards. */
         se->vruntime = max_vruntime(se->vruntime, vruntime);
 }
 
 static void check_enqueue_throttle(struct cfs_rq *cfs_rq);
 
 static inline void check_schedstat_required(void)
 {
 #ifdef CONFIG_SCHEDSTATS
         if (schedstat_enabled())
                 return;
 
         /* Force schedstat enabled if a dependent tracepoint is active */
         if (trace_sched_stat_wait_enabled()    ||
                         trace_sched_stat_sleep_enabled()   ||
                         trace_sched_stat_iowait_enabled()  ||
                         trace_sched_stat_blocked_enabled() ||
                         trace_sched_stat_runtime_enabled())  {
                 printk_deferred_once("Scheduler tracepoints stat_sleep, stat_iowait, "
                              "stat_blocked and stat_runtime require the "
                              "kernel parameter schedstats=enabled or "
                              "kernel.sched_schedstats=1\n");
         }
 #endif
 }
 
 
 /*
  * MIGRATION
  *
  *      dequeue
  *        update_curr()
  *          update_min_vruntime()
  *        vruntime -= min_vruntime
  *
  *      enqueue
  *        update_curr()
  *          update_min_vruntime()
  *        vruntime += min_vruntime
  *
  * this way the vruntime transition between RQs is done when both
  * min_vruntime are up-to-date.
  *
  * WAKEUP (remote)
  *
  *      ->migrate_task_rq_fair() (p->state == TASK_WAKING)
  *        vruntime -= min_vruntime
  *
  *      enqueue
  *        update_curr()
  *          update_min_vruntime()
  *        vruntime += min_vruntime
  *
  * this way we don't have the most up-to-date min_vruntime on the originating
  * CPU and an up-to-date min_vruntime on the destination CPU.
  */
 
 static void
 enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
         bool renorm = !(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_MIGRATED);
         bool curr = cfs_rq->curr == se;
 
         /*
          * If we're the current task, we must renormalise before calling
          * update_curr().
          */
         if (renorm && curr)
                 se->vruntime += cfs_rq->min_vruntime;
 
         update_curr(cfs_rq);
 
         /*
          * Otherwise, renormalise after, such that we're placed at the current
          * moment in time, instead of some random moment in the past. Being
          * placed in the past could significantly boost this task to the
          * fairness detriment of existing tasks.
          */
         if (renorm && !curr)
                 se->vruntime += cfs_rq->min_vruntime;
 
         enqueue_entity_load_avg(cfs_rq, se);
         account_entity_enqueue(cfs_rq, se);
         update_cfs_shares(cfs_rq);
 
         if (flags & ENQUEUE_WAKEUP) {
                 place_entity(cfs_rq, se, 0);
                 if (schedstat_enabled())
                         enqueue_sleeper(cfs_rq, se);
         }
 
         check_schedstat_required();
         if (schedstat_enabled()) {
                 update_stats_enqueue(cfs_rq, se);
                 check_spread(cfs_rq, se);
         }
         if (!curr)
                 __enqueue_entity(cfs_rq, se);
         se->on_rq = 1;
 
         if (cfs_rq->nr_running == 1) {
                 list_add_leaf_cfs_rq(cfs_rq);
                 check_enqueue_throttle(cfs_rq);
         }
 }
 
 static void __clear_buddies_last(struct sched_entity *se)
 {
         for_each_sched_entity(se) {
                 struct cfs_rq *cfs_rq = cfs_rq_of(se);
                 if (cfs_rq->last != se)
                         break;
 
                 cfs_rq->last = NULL;
         }
 }
 
 static void __clear_buddies_next(struct sched_entity *se)
 {
         for_each_sched_entity(se) {
                 struct cfs_rq *cfs_rq = cfs_rq_of(se);
                 if (cfs_rq->next != se)
                         break;
 
                 cfs_rq->next = NULL;
         }
 }
 
 static void __clear_buddies_skip(struct sched_entity *se)
 {
         for_each_sched_entity(se) {
                 struct cfs_rq *cfs_rq = cfs_rq_of(se);
                 if (cfs_rq->skip != se)
                         break;
 
                 cfs_rq->skip = NULL;
         }
 }
 
 static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         if (cfs_rq->last == se)
                 __clear_buddies_last(se);
 
         if (cfs_rq->next == se)
                 __clear_buddies_next(se);
 
         if (cfs_rq->skip == se)
                 __clear_buddies_skip(se);
 }
 
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
 
 static void
 dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
         /*
          * Update run-time statistics of the 'current'.
          */
         update_curr(cfs_rq);
         dequeue_entity_load_avg(cfs_rq, se);
 
         if (schedstat_enabled())
                 update_stats_dequeue(cfs_rq, se, flags);
 
         clear_buddies(cfs_rq, se);
 
         if (se != cfs_rq->curr)
                 __dequeue_entity(cfs_rq, se);
         se->on_rq = 0;
         account_entity_dequeue(cfs_rq, se);
 
         /*
          * Normalize after update_curr(); which will also have moved
          * min_vruntime if @se is the one holding it back. But before doing
          * update_min_vruntime() again, which will discount @se's position and
          * can move min_vruntime forward still more.
          */
         if (!(flags & DEQUEUE_SLEEP))
                 se->vruntime -= cfs_rq->min_vruntime;
 
         /* return excess runtime on last dequeue */
         return_cfs_rq_runtime(cfs_rq);
 
         update_cfs_shares(cfs_rq);
 
         /*
          * Now advance min_vruntime if @se was the entity holding it back,
          * except when: DEQUEUE_SAVE && !DEQUEUE_MOVE, in this case we'll be
          * put back on, and if we advance min_vruntime, we'll be placed back
          * further than we started -- ie. we'll be penalized.
          */
         if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE)
                 update_min_vruntime(cfs_rq);
 }
 
 /*
  * Preempt the current task with a newly woken task if needed:
  */
 static void
 check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 {
         unsigned long ideal_runtime, delta_exec;
         struct sched_entity *se;
         s64 delta;
 
         ideal_runtime = sched_slice(cfs_rq, curr);
         delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
         if (delta_exec > ideal_runtime) {
                 resched_curr(rq_of(cfs_rq));
                 /*
                  * The current task ran long enough, ensure it doesn't get
                  * re-elected due to buddy favours.
                  */
                 clear_buddies(cfs_rq, curr);
                 return;
         }
 
         /*
          * Ensure that a task that missed wakeup preemption by a
          * narrow margin doesn't have to wait for a full slice.
          * This also mitigates buddy induced latencies under load.
          */
         if (delta_exec < sysctl_sched_min_granularity)
                 return;
 
         se = __pick_first_entity(cfs_rq);
         delta = curr->vruntime - se->vruntime;
 
         if (delta < 0)
                 return;
 
         if (delta > ideal_runtime)
                 resched_curr(rq_of(cfs_rq));
 }
 
 static void
 set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         /* 'current' is not kept within the tree. */
         if (se->on_rq) {
                 /*
                  * Any task has to be enqueued before it get to execute on
                  * a CPU. So account for the time it spent waiting on the
                  * runqueue.
                  */
                 if (schedstat_enabled())
                         update_stats_wait_end(cfs_rq, se);
                 __dequeue_entity(cfs_rq, se);
                 update_load_avg(se, 1);
         }
 
         update_stats_curr_start(cfs_rq, se);
         cfs_rq->curr = se;
 #ifdef CONFIG_SCHEDSTATS
         /*
          * Track our maximum slice length, if the CPU's load is at
          * least twice that of our own weight (i.e. dont track it
          * when there are only lesser-weight tasks around):
          */
         if (schedstat_enabled() && rq_of(cfs_rq)->load.weight >= 2*se->load.weight) {
                 se->statistics.slice_max = max(se->statistics.slice_max,
                         se->sum_exec_runtime - se->prev_sum_exec_runtime);
         }
 #endif
         se->prev_sum_exec_runtime = se->sum_exec_runtime;
 }
 
 static int
 wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);
 
 /*
  * Pick the next process, keeping these things in mind, in this order:
  * 1) keep things fair between processes/task groups
  * 2) pick the "next" process, since someone really wants that to run
  * 3) pick the "last" process, for cache locality
  * 4) do not run the "skip" process, if something else is available
  */
 static struct sched_entity *
 pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 {
         struct sched_entity *left = __pick_first_entity(cfs_rq);
         struct sched_entity *se;
 
         /*
          * If curr is set we have to see if its left of the leftmost entity
          * still in the tree, provided there was anything in the tree at all.
          */
         if (!left || (curr && entity_before(curr, left)))
                 left = curr;
 
         se = left; /* ideally we run the leftmost entity */
 
         /*
          * Avoid running the skip buddy, if running something else can
          * be done without getting too unfair.
          */
         if (cfs_rq->skip == se) {
                 struct sched_entity *second;
 
                 if (se == curr) {
                         second = __pick_first_entity(cfs_rq);
                 } else {
                         second = __pick_next_entity(se);
                         if (!second || (curr && entity_before(curr, second)))
                                 second = curr;
                 }
 
                 if (second && wakeup_preempt_entity(second, left) < 1)
                         se = second;
         }
 
         /*
          * Prefer last buddy, try to return the CPU to a preempted task.
          */
         if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
                 se = cfs_rq->last;
 
         /*
          * Someone really wants this to run. If it's not unfair, run it.
          */
         if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
                 se = cfs_rq->next;
 
         clear_buddies(cfs_rq, se);
 
         return se;
 }
 
 static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq);
 
 static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
 {
         /*
          * If still on the runqueue then deactivate_task()
          * was not called and update_curr() has to be done:
          */
         if (prev->on_rq)
                 update_curr(cfs_rq);
 
         /* throttle cfs_rqs exceeding runtime */
         check_cfs_rq_runtime(cfs_rq);
 
         if (schedstat_enabled()) {
                 check_spread(cfs_rq, prev);
                 if (prev->on_rq)
                         update_stats_wait_start(cfs_rq, prev);
         }
 
         if (prev->on_rq) {
                 /* Put 'current' back into the tree. */
                 __enqueue_entity(cfs_rq, prev);
                 /* in !on_rq case, update occurred at dequeue */
                 update_load_avg(prev, 0);
         }
         cfs_rq->curr = NULL;
 }
 
 static void
 entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 {
         /*
          * Update run-time statistics of the 'current'.
          */
         update_curr(cfs_rq);
 
         /*
          * Ensure that runnable average is periodically updated.
          */
         update_load_avg(curr, 1);
         update_cfs_shares(cfs_rq);
 
 #ifdef CONFIG_SCHED_HRTICK
         /*
          * queued ticks are scheduled to match the slice, so don't bother
          * validating it and just reschedule.
          */
         if (queued) {
                 resched_curr(rq_of(cfs_rq));
                 return;
         }
         /*
          * don't let the period tick interfere with the hrtick preemption
          */
         if (!sched_feat(DOUBLE_TICK) &&
                         hrtimer_active(&rq_of(cfs_rq)->hrtick_timer))
                 return;
 #endif
 
         if (cfs_rq->nr_running > 1)
                 check_preempt_tick(cfs_rq, curr);
 }
 
 
 /**************************************************
  * CFS bandwidth control machinery
  */
 
 #ifdef CONFIG_CFS_BANDWIDTH
 
 #ifdef HAVE_JUMP_LABEL
 static struct static_key __cfs_bandwidth_used;
 
 static inline bool cfs_bandwidth_used(void)
 {
         return static_key_false(&__cfs_bandwidth_used);
 }
 
 void cfs_bandwidth_usage_inc(void)
 {
         static_key_slow_inc(&__cfs_bandwidth_used);
 }
 
 void cfs_bandwidth_usage_dec(void)
 {
         static_key_slow_dec(&__cfs_bandwidth_used);
 }
 #else /* HAVE_JUMP_LABEL */
 static bool cfs_bandwidth_used(void)
 {
         return true;
 }
 
 void cfs_bandwidth_usage_inc(void) {}
 void cfs_bandwidth_usage_dec(void) {}
 #endif /* HAVE_JUMP_LABEL */
 
 /*
  * default period for cfs group bandwidth.
  * default: 0.1s, units: nanoseconds
  */
 static inline u64 default_cfs_period(void)
 {
         return 100000000ULL;
 }
 
 static inline u64 sched_cfs_bandwidth_slice(void)
 {
         return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
 }
 
 /*
  * Replenish runtime according to assigned quota and update expiration time.
  * We use sched_clock_cpu directly instead of rq->clock to avoid adding
  * additional synchronization around rq->lock.
  *
  * requires cfs_b->lock
  */
 void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
 {
         u64 now;
 
         if (cfs_b->quota == RUNTIME_INF)
                 return;
 
         now = sched_clock_cpu(smp_processor_id());
         cfs_b->runtime = cfs_b->quota;
         cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period);
 }
 
 static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
 {
         return &tg->cfs_bandwidth;
 }
 
 /* rq->task_clock normalized against any time this cfs_rq has spent throttled */
 static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
 {
         if (unlikely(cfs_rq->throttle_count))
                 return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
 
         return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
 }
 
 /* returns 0 on failure to allocate runtime */
 static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 {
         struct task_group *tg = cfs_rq->tg;
         struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
         u64 amount = 0, min_amount, expires;
 
         /* note: this is a positive sum as runtime_remaining <= 0 */
         min_amount = sched_cfs_bandwidth_slice() - cfs_rq->runtime_remaining;
 
         raw_spin_lock(&cfs_b->lock);
         if (cfs_b->quota == RUNTIME_INF)
                 amount = min_amount;
         else {
                 start_cfs_bandwidth(cfs_b);
 
                 if (cfs_b->runtime > 0) {
                         amount = min(cfs_b->runtime, min_amount);
                         cfs_b->runtime -= amount;
                         cfs_b->idle = 0;
                 }
         }
         expires = cfs_b->runtime_expires;
         raw_spin_unlock(&cfs_b->lock);
 
         cfs_rq->runtime_remaining += amount;
         /*
          * we may have advanced our local expiration to account for allowed
          * spread between our sched_clock and the one on which runtime was
          * issued.
          */
         if ((s64)(expires - cfs_rq->runtime_expires) > 0)
                 cfs_rq->runtime_expires = expires;
 
         return cfs_rq->runtime_remaining > 0;
 }
 
 /*
  * Note: This depends on the synchronization provided by sched_clock and the
  * fact that rq->clock snapshots this value.
  */
 static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 {
         struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
 
         /* if the deadline is ahead of our clock, nothing to do */
         if (likely((s64)(rq_clock(rq_of(cfs_rq)) - cfs_rq->runtime_expires) < 0))
                 return;
 
         if (cfs_rq->runtime_remaining < 0)
                 return;
 
         /*
          * If the local deadline has passed we have to consider the
          * possibility that our sched_clock is 'fast' and the global deadline
          * has not truly expired.
          *
          * Fortunately we can check determine whether this the case by checking
          * whether the global deadline has advanced. It is valid to compare
          * cfs_b->runtime_expires without any locks since we only care about
          * exact equality, so a partial write will still work.
          */
 
         if (cfs_rq->runtime_expires != cfs_b->runtime_expires) {
                 /* extend local deadline, drift is bounded above by 2 ticks */
                 cfs_rq->runtime_expires += TICK_NSEC;
         } else {
                 /* global deadline is ahead, expiration has passed */
                 cfs_rq->runtime_remaining = 0;
         }
 }
 
 static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
 {
         /* dock delta_exec before expiring quota (as it could span periods) */
         cfs_rq->runtime_remaining -= delta_exec;
         expire_cfs_rq_runtime(cfs_rq);
 
         if (likely(cfs_rq->runtime_remaining > 0))
                 return;
 
         /*
          * if we're unable to extend our runtime we resched so that the active
          * hierarchy can be throttled
          */
         if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->curr))
                 resched_curr(rq_of(cfs_rq));
 }
 
 static __always_inline
 void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
 {
         if (!cfs_bandwidth_used() || !cfs_rq->runtime_enabled)
                 return;
 
         __account_cfs_rq_runtime(cfs_rq, delta_exec);
 }
 
 static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
 {
         return cfs_bandwidth_used() && cfs_rq->throttled;
 }
 
 /* check whether cfs_rq, or any parent, is throttled */
 static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
 {
         return cfs_bandwidth_used() && cfs_rq->throttle_count;
 }
 
 /*
  * Ensure that neither of the group entities corresponding to src_cpu or
  * dest_cpu are members of a throttled hierarchy when performing group
  * load-balance operations.
  */
 static inline int throttled_lb_pair(struct task_group *tg,
                                     int src_cpu, int dest_cpu)
 {
         struct cfs_rq *src_cfs_rq, *dest_cfs_rq;
 
         src_cfs_rq = tg->cfs_rq[src_cpu];
         dest_cfs_rq = tg->cfs_rq[dest_cpu];
 
         return throttled_hierarchy(src_cfs_rq) ||
                throttled_hierarchy(dest_cfs_rq);
 }
 
 /* updated child weight may affect parent so we have to do this bottom up */
 static int tg_unthrottle_up(struct task_group *tg, void *data)
 {
         struct rq *rq = data;
         struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
 
         cfs_rq->throttle_count--;
         if (!cfs_rq->throttle_count) {
                 /* adjust cfs_rq_clock_task() */
                 cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
                                              cfs_rq->throttled_clock_task;
         }
 
         return 0;
 }
 
 static int tg_throttle_down(struct task_group *tg, void *data)
 {
         struct rq *rq = data;
         struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
 
         /* group is entering throttled state, stop time */
         if (!cfs_rq->throttle_count)
                 cfs_rq->throttled_clock_task = rq_clock_task(rq);
         cfs_rq->throttle_count++;
 
         return 0;
 }
 
 static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
 {
         struct rq *rq = rq_of(cfs_rq);
         struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
         struct sched_entity *se;
         long task_delta, dequeue = 1;
         bool empty;
 
         se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
 
         /* freeze hierarchy runnable averages while throttled */
         rcu_read_lock();
         walk_tg_tree_from(cfs_rq->tg, tg_throttle_down, tg_nop, (void *)rq);
         rcu_read_unlock();
 
         task_delta = cfs_rq->h_nr_running;
         for_each_sched_entity(se) {
                 struct cfs_rq *qcfs_rq = cfs_rq_of(se);
                 /* throttled entity or throttle-on-deactivate */
                 if (!se->on_rq)
                         break;
 
                 if (dequeue)
                         dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
                 qcfs_rq->h_nr_running -= task_delta;
 
                 if (qcfs_rq->load.weight)
                         dequeue = 0;
         }
 
         if (!se)
                 sub_nr_running(rq, task_delta);
 
         cfs_rq->throttled = 1;
         cfs_rq->throttled_clock = rq_clock(rq);
         raw_spin_lock(&cfs_b->lock);
         empty = list_empty(&cfs_b->throttled_cfs_rq);
 
         /*
          * Add to the _head_ of the list, so that an already-started
          * distribute_cfs_runtime will not see us
          */
         list_add_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);
 
         /*
          * If we're the first throttled task, make sure the bandwidth
          * timer is running.
          */
         if (empty)
                 start_cfs_bandwidth(cfs_b);
 
         raw_spin_unlock(&cfs_b->lock);
 }
 
 void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 {
         struct rq *rq = rq_of(cfs_rq);
         struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
         struct sched_entity *se;
         int enqueue = 1;
         long task_delta;
 
         se = cfs_rq->tg->se[cpu_of(rq)];
 
         cfs_rq->throttled = 0;
 
         update_rq_clock(rq);
 
         raw_spin_lock(&cfs_b->lock);
         cfs_b->throttled_time += rq_clock(rq) - cfs_rq->throttled_clock;
         list_del_rcu(&cfs_rq->throttled_list);
         raw_spin_unlock(&cfs_b->lock);
 
         /* update hierarchical throttle state */
         walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq);
 
         if (!cfs_rq->load.weight)
                 return;
 
         task_delta = cfs_rq->h_nr_running;
         for_each_sched_entity(se) {
                 if (se->on_rq)
                         enqueue = 0;
 
                 cfs_rq = cfs_rq_of(se);
                 if (enqueue)
                         enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
                 cfs_rq->h_nr_running += task_delta;
 
                 if (cfs_rq_throttled(cfs_rq))
                         break;
         }
 
         if (!se)
                 add_nr_running(rq, task_delta);
 
         /* determine whether we need to wake up potentially idle cpu */
         if (rq->curr == rq->idle && rq->cfs.nr_running)
                 resched_curr(rq);
 }
 
 static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
                 u64 remaining, u64 expires)
 {
         struct cfs_rq *cfs_rq;
         u64 runtime;
         u64 starting_runtime = remaining;
 
         rcu_read_lock();
         list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq,
                                 throttled_list) {
                 struct rq *rq = rq_of(cfs_rq);
 
                 raw_spin_lock(&rq->lock);
                 if (!cfs_rq_throttled(cfs_rq))
                         goto next;
 
                 runtime = -cfs_rq->runtime_remaining + 1;
                 if (runtime > remaining)
                         runtime = remaining;
                 remaining -= runtime;
 
                 cfs_rq->runtime_remaining += runtime;
                 cfs_rq->runtime_expires = expires;
 
                 /* we check whether we're throttled above */
                 if (cfs_rq->runtime_remaining > 0)
                         unthrottle_cfs_rq(cfs_rq);
 
 next:
                 raw_spin_unlock(&rq->lock);
 
                 if (!remaining)
                         break;
         }
         rcu_read_unlock();
 
         return starting_runtime - remaining;
 }
 
 /*
  * Responsible for refilling a task_group's bandwidth and unthrottling its
  * cfs_rqs as appropriate. If there has been no activity within the last
  * period the timer is deactivated until scheduling resumes; cfs_b->idle is
  * used to track this state.
  */
 static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
 {
         u64 runtime, runtime_expires;
         int throttled;
 
         /* no need to continue the timer with no bandwidth constraint */
         if (cfs_b->quota == RUNTIME_INF)
                 goto out_deactivate;
 
         throttled = !list_empty(&cfs_b->throttled_cfs_rq);
         cfs_b->nr_periods += overrun;
 
         /*
          * idle depends on !throttled (for the case of a large deficit), and if
          * we're going inactive then everything else can be deferred
          */
         if (cfs_b->idle && !throttled)
                 goto out_deactivate;
 
         __refill_cfs_bandwidth_runtime(cfs_b);
 
         if (!throttled) {
                 /* mark as potentially idle for the upcoming period */
                 cfs_b->idle = 1;
                 return 0;
         }
 
         /* account preceding periods in which throttling occurred */
         cfs_b->nr_throttled += overrun;
 
         runtime_expires = cfs_b->runtime_expires;
 
         /*
          * This check is repeated as we are holding onto the new bandwidth while
          * we unthrottle. This can potentially race with an unthrottled group
          * trying to acquire new bandwidth from the global pool. This can result
          * in us over-using our runtime if it is all used during this loop, but
          * only by limited amounts in that extreme case.
          */
         while (throttled && cfs_b->runtime > 0) {
                 runtime = cfs_b->runtime;
                 raw_spin_unlock(&cfs_b->lock);
                 /* we can't nest cfs_b->lock while distributing bandwidth */
                 runtime = distribute_cfs_runtime(cfs_b, runtime,
                                                  runtime_expires);
                 raw_spin_lock(&cfs_b->lock);
 
                 throttled = !list_empty(&cfs_b->throttled_cfs_rq);
 
                 cfs_b->runtime -= min(runtime, cfs_b->runtime);
         }
 
         /*
          * While we are ensured activity in the period following an
          * unthrottle, this also covers the case in which the new bandwidth is
          * insufficient to cover the existing bandwidth deficit.  (Forcing the
          * timer to remain active while there are any throttled entities.)
          */
         cfs_b->idle = 0;
 
         return 0;
 
 out_deactivate:
         return 1;
 }
 
 /* a cfs_rq won't donate quota below this amount */
 static const u64 min_cfs_rq_runtime = 1 * NSEC_PER_MSEC;
 /* minimum remaining period time to redistribute slack quota */
 static const u64 min_bandwidth_expiration = 2 * NSEC_PER_MSEC;
 /* how long we wait to gather additional slack before distributing */
 static const u64 cfs_bandwidth_slack_period = 5 * NSEC_PER_MSEC;
 
 /*
  * Are we near the end of the current quota period?
  *
  * Requires cfs_b->lock for hrtimer_expires_remaining to be safe against the
  * hrtimer base being cleared by hrtimer_start. In the case of
  * migrate_hrtimers, base is never cleared, so we are fine.
  */
 static int runtime_refresh_within(struct cfs_bandwidth *cfs_b, u64 min_expire)
 {
         struct hrtimer *refresh_timer = &cfs_b->period_timer;
         u64 remaining;
 
         /* if the call-back is running a quota refresh is already occurring */
         if (hrtimer_callback_running(refresh_timer))
                 return 1;
 
         /* is a quota refresh about to occur? */
         remaining = ktime_to_ns(hrtimer_expires_remaining(refresh_timer));
         if (remaining < min_expire)
                 return 1;
 
         return 0;
 }
 
 static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
 {
         u64 min_left = cfs_bandwidth_slack_period + min_bandwidth_expiration;
 
         /* if there's a quota refresh soon don't bother with slack */
         if (runtime_refresh_within(cfs_b, min_left))
                 return;
 
         hrtimer_start(&cfs_b->slack_timer,
                         ns_to_ktime(cfs_bandwidth_slack_period),
                         HRTIMER_MODE_REL);
 }
 
 /* we know any runtime found here is valid as update_curr() precedes return */
 static void __return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 {
         struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
         s64 slack_runtime = cfs_rq->runtime_remaining - min_cfs_rq_runtime;
 
         if (slack_runtime <= 0)
                 return;
 
         raw_spin_lock(&cfs_b->lock);
         if (cfs_b->quota != RUNTIME_INF &&
             cfs_rq->runtime_expires == cfs_b->runtime_expires) {
                 cfs_b->runtime += slack_runtime;
 
                 /* we are under rq->lock, defer unthrottling using a timer */
                 if (cfs_b->runtime > sched_cfs_bandwidth_slice() &&
                     !list_empty(&cfs_b->throttled_cfs_rq))
                         start_cfs_slack_bandwidth(cfs_b);
         }
         raw_spin_unlock(&cfs_b->lock);
 
         /* even if it's not valid for return we don't want to try again */
         cfs_rq->runtime_remaining -= slack_runtime;
 }
 
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 {
         if (!cfs_bandwidth_used())
                 return;
 
         if (!cfs_rq->runtime_enabled || cfs_rq->nr_running)
                 return;
 
         __return_cfs_rq_runtime(cfs_rq);
 }
 
 /*
  * This is done with a timer (instead of inline with bandwidth return) since
  * it's necessary to juggle rq->locks to unthrottle their respective cfs_rqs.
  */
 static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
 {
         u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
         u64 expires;
 
         /* confirm we're still not at a refresh boundary */
         raw_spin_lock(&cfs_b->lock);
         if (runtime_refresh_within(cfs_b, min_bandwidth_expiration)) {
                 raw_spin_unlock(&cfs_b->lock);
                 return;
         }
 
         if (cfs_b->quota != RUNTIME_INF && cfs_b->runtime > slice)
                 runtime = cfs_b->runtime;
 
         expires = cfs_b->runtime_expires;
         raw_spin_unlock(&cfs_b->lock);
 
         if (!runtime)
                 return;
 
         runtime = distribute_cfs_runtime(cfs_b, runtime, expires);
 
         raw_spin_lock(&cfs_b->lock);
         if (expires == cfs_b->runtime_expires)
                 cfs_b->runtime -= min(runtime, cfs_b->runtime);
         raw_spin_unlock(&cfs_b->lock);
 }
 
 /*
  * When a group wakes up we want to make sure that its quota is not already
  * expired/exceeded, otherwise it may be allowed to steal additional ticks of
  * runtime as update_curr() throttling can not not trigger until it's on-rq.
  */
 static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
 {
         if (!cfs_bandwidth_used())
                 return;
 
         /* an active group must be handled by the update_curr()->put() path */
         if (!cfs_rq->runtime_enabled || cfs_rq->curr)
                 return;
 
         /* ensure the group is not already throttled */
         if (cfs_rq_throttled(cfs_rq))
                 return;
 
         /* update runtime allocation */
         account_cfs_rq_runtime(cfs_rq, 0);
         if (cfs_rq->runtime_remaining <= 0)
                 throttle_cfs_rq(cfs_rq);
 }
 
 static void sync_throttle(struct task_group *tg, int cpu)
 {
         struct cfs_rq *pcfs_rq, *cfs_rq;
 
         if (!cfs_bandwidth_used())
                 return;
 
         if (!tg->parent)
                 return;
 
         cfs_rq = tg->cfs_rq[cpu];
         pcfs_rq = tg->parent->cfs_rq[cpu];
 
         cfs_rq->throttle_count = pcfs_rq->throttle_count;
         cfs_rq->throttled_clock_task = rq_clock_task(cpu_rq(cpu));
 }
 
 /* conditionally throttle active cfs_rq's from put_prev_entity() */
 static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 {
         if (!cfs_bandwidth_used())
                 return false;
 
         if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0))
                 return false;
 
         /*
          * it's possible for a throttled entity to be forced into a running
          * state (e.g. set_curr_task), in this case we're finished.
          */
         if (cfs_rq_throttled(cfs_rq))
                 return true;
 
         throttle_cfs_rq(cfs_rq);
         return true;
 }
 
 static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer)
 {
         struct cfs_bandwidth *cfs_b =
                 container_of(timer, struct cfs_bandwidth, slack_timer);
 
         do_sched_cfs_slack_timer(cfs_b);
 
         return HRTIMER_NORESTART;
 }
 
 static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
 {
         struct cfs_bandwidth *cfs_b =
                 container_of(timer, struct cfs_bandwidth, period_timer);
         int overrun;
         int idle = 0;
 
         raw_spin_lock(&cfs_b->lock);
         for (;;) {
                 overrun = hrtimer_forward_now(timer, cfs_b->period);
                 if (!overrun)
                         break;
 
                 idle = do_sched_cfs_period_timer(cfs_b, overrun);
         }
         if (idle)
                 cfs_b->period_active = 0;
         raw_spin_unlock(&cfs_b->lock);
 
         return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
 }
 
 void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
 {
         raw_spin_lock_init(&cfs_b->lock);
         cfs_b->runtime = 0;
         cfs_b->quota = RUNTIME_INF;
         cfs_b->period = ns_to_ktime(default_cfs_period());
 
         INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
         hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
         cfs_b->period_timer.function = sched_cfs_period_timer;
         hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
         cfs_b->slack_timer.function = sched_cfs_slack_timer;
 }
 
 static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 {
         cfs_rq->runtime_enabled = 0;
         INIT_LIST_HEAD(&cfs_rq->throttled_list);
 }
 
 void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
 {
         lockdep_assert_held(&cfs_b->lock);
 
         if (!cfs_b->period_active) {
                 cfs_b->period_active = 1;
                 hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
                 hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
         }
 }
 
 static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
 {
         /* init_cfs_bandwidth() was not called */
         if (!cfs_b->throttled_cfs_rq.next)
                 return;
 
         hrtimer_cancel(&cfs_b->period_timer);
         hrtimer_cancel(&cfs_b->slack_timer);
 }
 
 static void __maybe_unused update_runtime_enabled(struct rq *rq)
 {
         struct cfs_rq *cfs_rq;
 
         for_each_leaf_cfs_rq(rq, cfs_rq) {
                 struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;
 
                 raw_spin_lock(&cfs_b->lock);
                 cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
                 raw_spin_unlock(&cfs_b->lock);
         }
 }
 
 static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
 {
         struct cfs_rq *cfs_rq;
 
         for_each_leaf_cfs_rq(rq, cfs_rq) {
                 if (!cfs_rq->runtime_enabled)
                         continue;
 
                 /*
                  * clock_task is not advancing so we just need to make sure
                  * there's some valid quota amount
                  */
                 cfs_rq->runtime_remaining = 1;
                 /*
                  * Offline rq is schedulable till cpu is completely disabled
                  * in take_cpu_down(), so we prevent new cfs throttling here.
                  */
                 cfs_rq->runtime_enabled = 0;
 
                 if (cfs_rq_throttled(cfs_rq))
                         unthrottle_cfs_rq(cfs_rq);
         }
 }
 
 #else /* CONFIG_CFS_BANDWIDTH */
 static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
 {
         return rq_clock_task(rq_of(cfs_rq));
 }
 
 static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) {}
 static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { return false; }
 static void check_enqueue_throttle(struct cfs_rq *cfs_rq) {}
 static inline void sync_throttle(struct task_group *tg, int cpu) {}
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
 
 static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
 {
         return 0;
 }
 
 static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
 {
         return 0;
 }
 
 static inline int throttled_lb_pair(struct task_group *tg,
                                     int src_cpu, int dest_cpu)
 {
         return 0;
 }
 
 void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
 #endif
 
 static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
 {
         return NULL;
 }
 static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
 static inline void update_runtime_enabled(struct rq *rq) {}
 static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}
 
 #endif /* CONFIG_CFS_BANDWIDTH */
 
 /**************************************************
  * CFS operations on tasks:
  */
 
 #ifdef CONFIG_SCHED_HRTICK
 static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 {
         struct sched_entity *se = &p->se;
         struct cfs_rq *cfs_rq = cfs_rq_of(se);
 
         WARN_ON(task_rq(p) != rq);
 
         if (cfs_rq->nr_running > 1) {
                 u64 slice = sched_slice(cfs_rq, se);
                 u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
                 s64 delta = slice - ran;
 
                 if (delta < 0) {
                         if (rq->curr == p)
                                 resched_curr(rq);
                         return;
                 }
                 hrtick_start(rq, delta);
         }
 }
 
 /*
  * called from enqueue/dequeue and updates the hrtick when the
  * current task is from our class and nr_running is low enough
  * to matter.
  */
 static void hrtick_update(struct rq *rq)
 {
         struct task_struct *curr = rq->curr;
 
         if (!hrtick_enabled(rq) || curr->sched_class != &fair_sched_class)
                 return;
 
         if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)
                 hrtick_start_fair(rq, curr);
 }
 #else /* !CONFIG_SCHED_HRTICK */
 static inline void
 hrtick_start_fair(struct rq *rq, struct task_struct *p)
 {
 }
 
 static inline void hrtick_update(struct rq *rq)
 {
 }
 #endif
 
 /*
  * The enqueue_task method is called before nr_running is
  * increased. Here we update the fair scheduling stats and
  * then put the task into the rbtree:
  */
 static void
 enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 {
         struct cfs_rq *cfs_rq;
         struct sched_entity *se = &p->se;
 
         for_each_sched_entity(se) {
                 if (se->on_rq)
                         break;
                 cfs_rq = cfs_rq_of(se);
                 enqueue_entity(cfs_rq, se, flags);
 
                 /*
                  * end evaluation on encountering a throttled cfs_rq
                  *
                  * note: in the case of encountering a throttled cfs_rq we will
                  * post the final h_nr_running increment below.
                  */
                 if (cfs_rq_throttled(cfs_rq))
                         break;
                 cfs_rq->h_nr_running++;
 
                 flags = ENQUEUE_WAKEUP;
         }
 
         for_each_sched_entity(se) {
                 cfs_rq = cfs_rq_of(se);
                 cfs_rq->h_nr_running++;
 
                 if (cfs_rq_throttled(cfs_rq))
                         break;
 
                 update_load_avg(se, 1);
                 update_cfs_shares(cfs_rq);
         }
 
         if (!se)
                 add_nr_running(rq, 1);
 
         hrtick_update(rq);
 }
 
 static void set_next_buddy(struct sched_entity *se);
 
 /*
  * The dequeue_task method is called before nr_running is
  * decreased. We remove the task from the rbtree and
  * update the fair scheduling stats:
  */
 static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 {
         struct cfs_rq *cfs_rq;
         struct sched_entity *se = &p->se;
         int task_sleep = flags & DEQUEUE_SLEEP;
 
         for_each_sched_entity(se) {
                 cfs_rq = cfs_rq_of(se);
                 dequeue_entity(cfs_rq, se, flags);
 
                 /*
                  * end evaluation on encountering a throttled cfs_rq
                  *
                  * note: in the case of encountering a throttled cfs_rq we will
                  * post the final h_nr_running decrement below.
                 */
                 if (cfs_rq_throttled(cfs_rq))
                         break;
                 cfs_rq->h_nr_running--;
 
                 /* Don't dequeue parent if it has other entities besides us */
                 if (cfs_rq->load.weight) {
                         /* Avoid re-evaluating load for this entity: */
                         se = parent_entity(se);
                         /*
                          * Bias pick_next to pick a task from this cfs_rq, as
                          * p is sleeping when it is within its sched_slice.
                          */
                         if (task_sleep && se && !throttled_hierarchy(cfs_rq))
                                 set_next_buddy(se);
                         break;
                 }
                 flags |= DEQUEUE_SLEEP;
         }
 
         for_each_sched_entity(se) {
                 cfs_rq = cfs_rq_of(se);
                 cfs_rq->h_nr_running--;
 
                 if (cfs_rq_throttled(cfs_rq))
                         break;
 
                 update_load_avg(se, 1);
                 update_cfs_shares(cfs_rq);
         }
 
         if (!se)
                 sub_nr_running(rq, 1);
 
         hrtick_update(rq);
 }
 
 #ifdef CONFIG_SMP
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * per rq 'load' arrray crap; XXX kill this.
  */
 
 /*
  * The exact cpuload calculated at every tick would be:
  *
  *   load' = (1 - 1/2^i) * load + (1/2^i) * cur_load
  *
  * If a cpu misses updates for n ticks (as it was idle) and update gets
  * called on the n+1-th tick when cpu may be busy, then we have:
  *
  *   load_n   = (1 - 1/2^i)^n * load_0
  *   load_n+1 = (1 - 1/2^i)   * load_n + (1/2^i) * cur_load
  *
  * decay_load_missed() below does efficient calculation of
  *
  *   load' = (1 - 1/2^i)^n * load
  *
  * Because x^(n+m) := x^n * x^m we can decompose any x^n in power-of-2 factors.
  * This allows us to precompute the above in said factors, thereby allowing the
  * reduction of an arbitrary n in O(log_2 n) steps. (See also
  * fixed_power_int())
  *
  * The calculation is approximated on a 128 point scale.
  */
 #define DEGRADE_SHIFT           7
 
 static const u8 degrade_zero_ticks[CPU_LOAD_IDX_MAX] = {0, 8, 32, 64, 128};
 static const u8 degrade_factor[CPU_LOAD_IDX_MAX][DEGRADE_SHIFT + 1] = {
         {   0,   0,  0,  0,  0,  0, 0, 0 },
         {  64,  32,  8,  0,  0,  0, 0, 0 },
         {  96,  72, 40, 12,  1,  0, 0, 0 },
         { 112,  98, 75, 43, 15,  1, 0, 0 },
         { 120, 112, 98, 76, 45, 16, 2, 0 }
 };
 
 /*
  * Update cpu_load for any missed ticks, due to tickless idle. The backlog
  * would be when CPU is idle and so we just decay the old load without
  * adding any new load.
  */
 static unsigned long
 decay_load_missed(unsigned long load, unsigned long missed_updates, int idx)
 {
         int j = 0;
 
         if (!missed_updates)
                 return load;
 
         if (missed_updates >= degrade_zero_ticks[idx])
                 return 0;
 
         if (idx == 1)
                 return load >> missed_updates;
 
         while (missed_updates) {
                 if (missed_updates % 2)
                         load = (load * degrade_factor[idx][j]) >> DEGRADE_SHIFT;
 
                 missed_updates >>= 1;
                 j++;
         }
         return load;
 }
 #endif /* CONFIG_NO_HZ_COMMON */
 
 /**
  * __cpu_load_update - update the rq->cpu_load[] statistics
  * @this_rq: The rq to update statistics for
  * @this_load: The current load
  * @pending_updates: The number of missed updates
  *
  * Update rq->cpu_load[] statistics. This function is usually called every
  * scheduler tick (TICK_NSEC).
  *
  * This function computes a decaying average:
  *
  *   load[i]' = (1 - 1/2^i) * load[i] + (1/2^i) * load
  *
  * Because of NOHZ it might not get called on every tick which gives need for
  * the @pending_updates argument.
  *
  *   load[i]_n = (1 - 1/2^i) * load[i]_n-1 + (1/2^i) * load_n-1
  *             = A * load[i]_n-1 + B ; A := (1 - 1/2^i), B := (1/2^i) * load
  *             = A * (A * load[i]_n-2 + B) + B
  *             = A * (A * (A * load[i]_n-3 + B) + B) + B
  *             = A^3 * load[i]_n-3 + (A^2 + A + 1) * B
  *             = A^n * load[i]_0 + (A^(n-1) + A^(n-2) + ... + 1) * B
  *             = A^n * load[i]_0 + ((1 - A^n) / (1 - A)) * B
  *             = (1 - 1/2^i)^n * (load[i]_0 - load) + load
  *
  * In the above we've assumed load_n := load, which is true for NOHZ_FULL as
  * any change in load would have resulted in the tick being turned back on.
  *
  * For regular NOHZ, this reduces to:
  *
  *   load[i]_n = (1 - 1/2^i)^n * load[i]_0
  *
  * see decay_load_misses(). For NOHZ_FULL we get to subtract and add the extra
  * term.
  */
 static void cpu_load_update(struct rq *this_rq, unsigned long this_load,
                             unsigned long pending_updates)
 {
         unsigned long __maybe_unused tickless_load = this_rq->cpu_load[0];
         int i, scale;
 
         this_rq->nr_load_updates++;
 
         /* Update our load: */
         this_rq->cpu_load[0] = this_load; /* Fasttrack for idx 0 */
         for (i = 1, scale = 2; i < CPU_LOAD_IDX_MAX; i++, scale += scale) {
                 unsigned long old_load, new_load;
 
                 /* scale is effectively 1 << i now, and >> i divides by scale */
 
                 old_load = this_rq->cpu_load[i];
 #ifdef CONFIG_NO_HZ_COMMON
                 old_load = decay_load_missed(old_load, pending_updates - 1, i);
                 if (tickless_load) {
                         old_load -= decay_load_missed(tickless_load, pending_updates - 1, i);
                         /*
                          * old_load can never be a negative value because a
                          * decayed tickless_load cannot be greater than the
                          * original tickless_load.
                          */
                         old_load += tickless_load;
                 }
 #endif
                 new_load = this_load;
                 /*
                  * Round up the averaging division if load is increasing. This
                  * prevents us from getting stuck on 9 if the load is 10, for
                  * example.
                  */
                 if (new_load > old_load)
                         new_load += scale - 1;
 
                 this_rq->cpu_load[i] = (old_load * (scale - 1) + new_load) >> i;
         }
 
         sched_avg_update(this_rq);
 }
 
 /* Used instead of source_load when we know the type == 0 */
 static unsigned long weighted_cpuload(const int cpu)
 {
         return cfs_rq_runnable_load_avg(&cpu_rq(cpu)->cfs);
 }
 
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * There is no sane way to deal with nohz on smp when using jiffies because the
  * cpu doing the jiffies update might drift wrt the cpu doing the jiffy reading
  * causing off-by-one errors in observed deltas; {0,2} instead of {1,1}.
  *
  * Therefore we need to avoid the delta approach from the regular tick when
  * possible since that would seriously skew the load calculation. This is why we
  * use cpu_load_update_periodic() for CPUs out of nohz. However we'll rely on
  * jiffies deltas for updates happening while in nohz mode (idle ticks, idle
  * loop exit, nohz_idle_balance, nohz full exit...)
  *
  * This means we might still be one tick off for nohz periods.
  */
 
 static void cpu_load_update_nohz(struct rq *this_rq,
                                  unsigned long curr_jiffies,
                                  unsigned long load)
 {
         unsigned long pending_updates;
 
         pending_updates = curr_jiffies - this_rq->last_load_update_tick;
         if (pending_updates) {
                 this_rq->last_load_update_tick = curr_jiffies;
                 /*
                  * In the regular NOHZ case, we were idle, this means load 0.
                  * In the NOHZ_FULL case, we were non-idle, we should consider
                  * its weighted load.
                  */
                 cpu_load_update(this_rq, load, pending_updates);
         }
 }
 
 /*
  * Called from nohz_idle_balance() to update the load ratings before doing the
  * idle balance.
  */
 static void cpu_load_update_idle(struct rq *this_rq)
 {
         /*
          * bail if there's load or we're actually up-to-date.
          */
         if (weighted_cpuload(cpu_of(this_rq)))
                 return;
 
         cpu_load_update_nohz(this_rq, READ_ONCE(jiffies), 0);
 }
 
 /*
  * Record CPU load on nohz entry so we know the tickless load to account
  * on nohz exit. cpu_load[0] happens then to be updated more frequently
  * than other cpu_load[idx] but it should be fine as cpu_load readers
  * shouldn't rely into synchronized cpu_load[*] updates.
  */
 void cpu_load_update_nohz_start(void)
 {
         struct rq *this_rq = this_rq();
 
         /*
          * This is all lockless but should be fine. If weighted_cpuload changes
          * concurrently we'll exit nohz. And cpu_load write can race with
          * cpu_load_update_idle() but both updater would be writing the same.
          */
         this_rq->cpu_load[0] = weighted_cpuload(cpu_of(this_rq));
 }
 
 /*
  * Account the tickless load in the end of a nohz frame.
  */
 void cpu_load_update_nohz_stop(void)
 {
         unsigned long curr_jiffies = READ_ONCE(jiffies);
         struct rq *this_rq = this_rq();
         unsigned long load;
 
         if (curr_jiffies == this_rq->last_load_update_tick)
                 return;
 
         load = weighted_cpuload(cpu_of(this_rq));
         raw_spin_lock(&this_rq->lock);
         update_rq_clock(this_rq);
         cpu_load_update_nohz(this_rq, curr_jiffies, load);
         raw_spin_unlock(&this_rq->lock);
 }
 #else /* !CONFIG_NO_HZ_COMMON */
 static inline void cpu_load_update_nohz(struct rq *this_rq,
                                         unsigned long curr_jiffies,
                                         unsigned long load) { }
 #endif /* CONFIG_NO_HZ_COMMON */
 
 static void cpu_load_update_periodic(struct rq *this_rq, unsigned long load)
 {
 #ifdef CONFIG_NO_HZ_COMMON
         /* See the mess around cpu_load_update_nohz(). */
         this_rq->last_load_update_tick = READ_ONCE(jiffies);
 #endif
         cpu_load_update(this_rq, load, 1);
 }
 
 /*
  * Called from scheduler_tick()
  */
 void cpu_load_update_active(struct rq *this_rq)
 {
         unsigned long load = weighted_cpuload(cpu_of(this_rq));
 
         if (tick_nohz_tick_stopped())
                 cpu_load_update_nohz(this_rq, READ_ONCE(jiffies), load);
         else
                 cpu_load_update_periodic(this_rq, load);
 }
 
 /*
  * Return a low guess at the load of a migration-source cpu weighted
  * according to the scheduling class and "nice" value.
  *
  * We want to under-estimate the load of migration sources, to
  * balance conservatively.
  */
 static unsigned long source_load(int cpu, int type)
 {
         struct rq *rq = cpu_rq(cpu);
         unsigned long total = weighted_cpuload(cpu);
 
         if (type == 0 || !sched_feat(LB_BIAS))
                 return total;
 
         return min(rq->cpu_load[type-1], total);
 }
 
 /*
  * Return a high guess at the load of a migration-target cpu weighted
  * according to the scheduling class and "nice" value.
  */
 static unsigned long target_load(int cpu, int type)
 {
         struct rq *rq = cpu_rq(cpu);
         unsigned long total = weighted_cpuload(cpu);
 
         if (type == 0 || !sched_feat(LB_BIAS))
                 return total;
 
         return max(rq->cpu_load[type-1], total);
 }
 
 static unsigned long capacity_of(int cpu)
 {
         return cpu_rq(cpu)->cpu_capacity;
 }
 
 static unsigned long capacity_orig_of(int cpu)
 {
         return cpu_rq(cpu)->cpu_capacity_orig;
 }
 
 static unsigned long cpu_avg_load_per_task(int cpu)
 {
         struct rq *rq = cpu_rq(cpu);
         unsigned long nr_running = READ_ONCE(rq->cfs.h_nr_running);
         unsigned long load_avg = weighted_cpuload(cpu);
 
         if (nr_running)
                 return load_avg / nr_running;
 
         return 0;
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 /*
  * effective_load() calculates the load change as seen from the root_task_group
  *
  * Adding load to a group doesn't make a group heavier, but can cause movement
  * of group shares between cpus. Assuming the shares were perfectly aligned one
  * can calculate the shift in shares.
  *
  * Calculate the effective load difference if @wl is added (subtracted) to @tg
  * on this @cpu and results in a total addition (subtraction) of @wg to the
  * total group weight.
  *
  * Given a runqueue weight distribution (rw_i) we can compute a shares
  * distribution (s_i) using:
  *
  *   s_i = rw_i / \Sum rw_j                                             (1)
  *
  * Suppose we have 4 CPUs and our @tg is a direct child of the root group and
  * has 7 equal weight tasks, distributed as below (rw_i), with the resulting
  * shares distribution (s_i):
  *
  *   rw_i = {   2,   4,   1,   0 }
  *   s_i  = { 2/7, 4/7, 1/7,   0 }
  *
  * As per wake_affine() we're interested in the load of two CPUs (the CPU the
  * task used to run on and the CPU the waker is running on), we need to
  * compute the effect of waking a task on either CPU and, in case of a sync
  * wakeup, compute the effect of the current task going to sleep.
  *
  * So for a change of @wl to the local @cpu with an overall group weight change
  * of @wl we can compute the new shares distribution (s'_i) using:
  *
  *   s'_i = (rw_i + @wl) / (@wg + \Sum rw_j)                            (2)
  *
  * Suppose we're interested in CPUs 0 and 1, and want to compute the load
  * differences in waking a task to CPU 0. The additional task changes the
  * weight and shares distributions like:
  *
  *   rw'_i = {   3,   4,   1,   0 }
  *   s'_i  = { 3/8, 4/8, 1/8,   0 }
  *
  * We can then compute the difference in effective weight by using:
  *
  *   dw_i = S * (s'_i - s_i)                                            (3)
  *
  * Where 'S' is the group weight as seen by its parent.
  *
  * Therefore the effective change in loads on CPU 0 would be 5/56 (3/8 - 2/7)
  * times the weight of the group. The effect on CPU 1 would be -4/56 (4/8 -
  * 4/7) times the weight of the group.
  */
 static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
 {
         struct sched_entity *se = tg->se[cpu];
 
         if (!tg->parent)        /* the trivial, non-cgroup case */
                 return wl;
 
         for_each_sched_entity(se) {
                 struct cfs_rq *cfs_rq = se->my_q;
                 long W, w = cfs_rq_load_avg(cfs_rq);
 
                 tg = cfs_rq->tg;
 
                 /*
                  * W = @wg + \Sum rw_j
                  */
                 W = wg + atomic_long_read(&tg->load_avg);
 
                 /* Ensure \Sum rw_j >= rw_i */
                 W -= cfs_rq->tg_load_avg_contrib;
                 W += w;
 
                 /*
                  * w = rw_i + @wl
                  */
                 w += wl;
 
                 /*
                  * wl = S * s'_i; see (2)
                  */
                 if (W > 0 && w < W)
                         wl = (w * (long)tg->shares) / W;
                 else
                         wl = tg->shares;
 
                 /*
                  * Per the above, wl is the new se->load.weight value; since
                  * those are clipped to [MIN_SHARES, ...) do so now. See
                  * calc_cfs_shares().
                  */
                 if (wl < MIN_SHARES)
                         wl = MIN_SHARES;
 
                 /*
                  * wl = dw_i = S * (s'_i - s_i); see (3)
                  */
                 wl -= se->avg.load_avg;
 
                 /*
                  * Recursively apply this logic to all parent groups to compute
                  * the final effective load change on the root group. Since
                  * only the @tg group gets extra weight, all parent groups can
                  * only redistribute existing shares. @wl is the shift in shares
                  * resulting from this level per the above.
                  */
                 wg = 0;
         }
 
         return wl;
 }
 #else
 
 static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
 {
         return wl;
 }
 
 #endif
 
 static void record_wakee(struct task_struct *p)
 {
         /*
          * Only decay a single time; tasks that have less then 1 wakeup per
          * jiffy will not have built up many flips.
          */
         if (time_after(jiffies, current->wakee_flip_decay_ts + HZ)) {
                 current->wakee_flips >>= 1;
                 current->wakee_flip_decay_ts = jiffies;
         }
 
         if (current->last_wakee != p) {
                 current->last_wakee = p;
                 current->wakee_flips++;
         }
 }
 
 /*
  * Detect M:N waker/wakee relationships via a switching-frequency heuristic.
  *
  * A waker of many should wake a different task than the one last awakened
  * at a frequency roughly N times higher than one of its wakees.
  *
  * In order to determine whether we should let the load spread vs consolidating
  * to shared cache, we look for a minimum 'flip' frequency of llc_size in one
  * partner, and a factor of lls_size higher frequency in the other.
  *
  * With both conditions met, we can be relatively sure that the relationship is
  * non-monogamous, with partner count exceeding socket size.
  *
  * Waker/wakee being client/server, worker/dispatcher, interrupt source or
  * whatever is irrelevant, spread criteria is apparent partner count exceeds
  * socket size.
  */
 static int wake_wide(struct task_struct *p)
 {
         unsigned int master = current->wakee_flips;
         unsigned int slave = p->wakee_flips;
         int factor = this_cpu_read(sd_llc_size);
 
         if (master < slave)
                 swap(master, slave);
         if (slave < factor || master < slave * factor)
                 return 0;
         return 1;
 }
 
 static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 {
         s64 this_load, load;
         s64 this_eff_load, prev_eff_load;
         int idx, this_cpu, prev_cpu;
         struct task_group *tg;
         unsigned long weight;
         int balanced;
 
         idx       = sd->wake_idx;
         this_cpu  = smp_processor_id();
         prev_cpu  = task_cpu(p);
         load      = source_load(prev_cpu, idx);
         this_load = target_load(this_cpu, idx);
 
         /*
          * If sync wakeup then subtract the (maximum possible)
          * effect of the currently running task from the load
          * of the current CPU:
          */
         if (sync) {
                 tg = task_group(current);
                 weight = current->se.avg.load_avg;
 
                 this_load += effective_load(tg, this_cpu, -weight, -weight);
                 load += effective_load(tg, prev_cpu, 0, -weight);
         }
 
         tg = task_group(p);
         weight = p->se.avg.load_avg;
 
         /*
          * In low-load situations, where prev_cpu is idle and this_cpu is idle
          * due to the sync cause above having dropped this_load to 0, we'll
          * always have an imbalance, but there's really nothing you can do
          * about that, so that's good too.
          *
          * Otherwise check if either cpus are near enough in load to allow this
          * task to be woken on this_cpu.
          */
         this_eff_load = 100;
         this_eff_load *= capacity_of(prev_cpu);
 
         prev_eff_load = 100 + (sd->imbalance_pct - 100) / 2;
         prev_eff_load *= capacity_of(this_cpu);
 
         if (this_load > 0) {
                 this_eff_load *= this_load +
                         effective_load(tg, this_cpu, weight, weight);
 
                 prev_eff_load *= load + effective_load(tg, prev_cpu, 0, weight);
         }
 
         balanced = this_eff_load <= prev_eff_load;
 
         schedstat_inc(p, se.statistics.nr_wakeups_affine_attempts);
 
         if (!balanced)
                 return 0;
 
         schedstat_inc(sd, ttwu_move_affine);
         schedstat_inc(p, se.statistics.nr_wakeups_affine);
 
         return 1;
 }
 
 /*
  * find_idlest_group finds and returns the least busy CPU group within the
  * domain.
  */
 static struct sched_group *
 find_idlest_group(struct sched_domain *sd, struct task_struct *p,
                   int this_cpu, int sd_flag)
 {
         struct sched_group *idlest = NULL, *group = sd->groups;
         unsigned long min_load = ULONG_MAX, this_load = 0;
         int load_idx = sd->forkexec_idx;
         int imbalance = 100 + (sd->imbalance_pct-100)/2;
 
         if (sd_flag & SD_BALANCE_WAKE)
                 load_idx = sd->wake_idx;
 
         do {
                 unsigned long load, avg_load;
                 int local_group;
                 int i;
 
                 /* Skip over this group if it has no CPUs allowed */
                 if (!cpumask_intersects(sched_group_cpus(group),
                                         tsk_cpus_allowed(p)))
                         continue;
 
                 local_group = cpumask_test_cpu(this_cpu,
                                                sched_group_cpus(group));
 
                 /* Tally up the load of all CPUs in the group */
                 avg_load = 0;
 
                 for_each_cpu(i, sched_group_cpus(group)) {
                         /* Bias balancing toward cpus of our domain */
                         if (local_group)
                                 load = source_load(i, load_idx);
                         else
                                 load = target_load(i, load_idx);
 
                         avg_load += load;
                 }
 
                 /* Adjust by relative CPU capacity of the group */
                 avg_load = (avg_load * SCHED_CAPACITY_SCALE) / group->sgc->capacity;
 
                 if (local_group) {
                         this_load = avg_load;
                 } else if (avg_load < min_load) {
                         min_load = avg_load;
                         idlest = group;
                 }
         } while (group = group->next, group != sd->groups);
 
         if (!idlest || 100*this_load < imbalance*min_load)
                 return NULL;
         return idlest;
 }
 
 /*
  * find_idlest_cpu - find the idlest cpu among the cpus in group.
  */
 static int
 find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
 {
         unsigned long load, min_load = ULONG_MAX;
         unsigned int min_exit_latency = UINT_MAX;
         u64 latest_idle_timestamp = 0;
         int least_loaded_cpu = this_cpu;
         int shallowest_idle_cpu = -1;
         int i;
 
         /* Traverse only the allowed CPUs */
         for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) {
                 if (idle_cpu(i)) {
                         struct rq *rq = cpu_rq(i);
                         struct cpuidle_state *idle = idle_get_state(rq);
                         if (idle && idle->exit_latency < min_exit_latency) {
                                 /*
                                  * We give priority to a CPU whose idle state
                                  * has the smallest exit latency irrespective
                                  * of any idle timestamp.
                                  */
                                 min_exit_latency = idle->exit_latency;
                                 latest_idle_timestamp = rq->idle_stamp;
                                 shallowest_idle_cpu = i;
                         } else if ((!idle || idle->exit_latency == min_exit_latency) &&
                                    rq->idle_stamp > latest_idle_timestamp) {
                                 /*
                                  * If equal or no active idle state, then
                                  * the most recently idled CPU might have
                                  * a warmer cache.
                                  */
                                 latest_idle_timestamp = rq->idle_stamp;
                                 shallowest_idle_cpu = i;
                         }
                 } else if (shallowest_idle_cpu == -1) {
                         load = weighted_cpuload(i);
                         if (load < min_load || (load == min_load && i == this_cpu)) {
                                 min_load = load;
                                 least_loaded_cpu = i;
                         }
                 }
         }
 
         return shallowest_idle_cpu != -1 ? shallowest_idle_cpu : least_loaded_cpu;
 }
 
 /*
  * Try and locate an idle CPU in the sched_domain.
  */
 static int select_idle_sibling(struct task_struct *p, int target)
 {
         struct sched_domain *sd;
         struct sched_group *sg;
         int i = task_cpu(p);
 
         if (idle_cpu(target))
                 return target;
 
         /*
          * If the prevous cpu is cache affine and idle, don't be stupid.
          */
         if (i != target && cpus_share_cache(i, target) && idle_cpu(i))
                 return i;
 
         /*
          * Otherwise, iterate the domains and find an eligible idle cpu.
          *
          * A completely idle sched group at higher domains is more
          * desirable than an idle group at a lower level, because lower
          * domains have smaller groups and usually share hardware
          * resources which causes tasks to contend on them, e.g. x86
          * hyperthread siblings in the lowest domain (SMT) can contend
          * on the shared cpu pipeline.
          *
          * However, while we prefer idle groups at higher domains
          * finding an idle cpu at the lowest domain is still better than
          * returning 'target', which we've already established, isn't
          * idle.
          */
         sd = rcu_dereference(per_cpu(sd_llc, target));
         for_each_lower_domain(sd) {
                 sg = sd->groups;
                 do {
                         if (!cpumask_intersects(sched_group_cpus(sg),
                                                 tsk_cpus_allowed(p)))
                                 goto next;
 
                         /* Ensure the entire group is idle */
                         for_each_cpu(i, sched_group_cpus(sg)) {
                                 if (i == target || !idle_cpu(i))
                                         goto next;
                         }
 
                         /*
                          * It doesn't matter which cpu we pick, the
                          * whole group is idle.
                          */
                         target = cpumask_first_and(sched_group_cpus(sg),
                                         tsk_cpus_allowed(p));
                         goto done;
 next:
                         sg = sg->next;
                 } while (sg != sd->groups);
         }
 done:
         return target;
 }
 
 /*
  * cpu_util returns the amount of capacity of a CPU that is used by CFS
  * tasks. The unit of the return value must be the one of capacity so we can
  * compare the utilization with the capacity of the CPU that is available for
  * CFS task (ie cpu_capacity).
  *
  * cfs_rq.avg.util_avg is the sum of running time of runnable tasks plus the
  * recent utilization of currently non-runnable tasks on a CPU. It represents
  * the amount of utilization of a CPU in the range [0..capacity_orig] where
  * capacity_orig is the cpu_capacity available at the highest frequency
  * (arch_scale_freq_capacity()).
  * The utilization of a CPU converges towards a sum equal to or less than the
  * current capacity (capacity_curr <= capacity_orig) of the CPU because it is
  * the running time on this CPU scaled by capacity_curr.
  *
  * Nevertheless, cfs_rq.avg.util_avg can be higher than capacity_curr or even
  * higher than capacity_orig because of unfortunate rounding in
  * cfs.avg.util_avg or just after migrating tasks and new task wakeups until
  * the average stabilizes with the new running time. We need to check that the
  * utilization stays within the range of [0..capacity_orig] and cap it if
  * necessary. Without utilization capping, a group could be seen as overloaded
  * (CPU0 utilization at 121% + CPU1 utilization at 80%) whereas CPU1 has 20% of
  * available capacity. We allow utilization to overshoot capacity_curr (but not
  * capacity_orig) as it useful for predicting the capacity required after task
  * migrations (scheduler-driven DVFS).
  */
 static int cpu_util(int cpu)
 {
         unsigned long util = cpu_rq(cpu)->cfs.avg.util_avg;
         unsigned long capacity = capacity_orig_of(cpu);
 
         return (util >= capacity) ? capacity : util;
 }
 
 /*
  * select_task_rq_fair: Select target runqueue for the waking task in domains
  * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
  * SD_BALANCE_FORK, or SD_BALANCE_EXEC.
  *
  * Balances load by selecting the idlest cpu in the idlest group, or under
  * certain conditions an idle sibling cpu if the domain has SD_WAKE_AFFINE set.
  *
  * Returns the target cpu number.
  *
  * preempt must be disabled.
  */
 static int
 select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
 {
         struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
         int cpu = smp_processor_id();
         int new_cpu = prev_cpu;
         int want_affine = 0;
         int sync = wake_flags & WF_SYNC;
 
         if (sd_flag & SD_BALANCE_WAKE) {
                 record_wakee(p);
                 want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
         }
 
         rcu_read_lock();
         for_each_domain(cpu, tmp) {
                 if (!(tmp->flags & SD_LOAD_BALANCE))
                         break;
 
                 /*
                  * If both cpu and prev_cpu are part of this domain,
                  * cpu is a valid SD_WAKE_AFFINE target.
                  */
                 if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
                     cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
                         affine_sd = tmp;
                         break;
                 }
 
                 if (tmp->flags & sd_flag)
                         sd = tmp;
                 else if (!want_affine)
                         break;
         }
 
         if (affine_sd) {
                 sd = NULL; /* Prefer wake_affine over balance flags */
                 if (cpu != prev_cpu && wake_affine(affine_sd, p, sync))
                         new_cpu = cpu;
         }
 
         if (!sd) {
                 if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */
                         new_cpu = select_idle_sibling(p, new_cpu);
 
         } else while (sd) {
                 struct sched_group *group;
                 int weight;
 
                 if (!(sd->flags & sd_flag)) {
                         sd = sd->child;
                         continue;
                 }
 
                 group = find_idlest_group(sd, p, cpu, sd_flag);
                 if (!group) {
                         sd = sd->child;
                         continue;
                 }
 
                 new_cpu = find_idlest_cpu(group, p, cpu);
                 if (new_cpu == -1 || new_cpu == cpu) {
                         /* Now try balancing at a lower domain level of cpu */
                         sd = sd->child;
                         continue;
                 }
 
                 /* Now try balancing at a lower domain level of new_cpu */
                 cpu = new_cpu;
                 weight = sd->span_weight;
                 sd = NULL;
                 for_each_domain(cpu, tmp) {
                         if (weight <= tmp->span_weight)
                                 break;
                         if (tmp->flags & sd_flag)
                                 sd = tmp;
                 }
                 /* while loop will break here if sd == NULL */
         }
         rcu_read_unlock();
 
         return new_cpu;
 }
 
 /*
  * Called immediately before a task is migrated to a new cpu; task_cpu(p) and
  * cfs_rq_of(p) references at time of call are still valid and identify the
  * previous cpu. The caller guarantees p->pi_lock or task_rq(p)->lock is held.
  */
 static void migrate_task_rq_fair(struct task_struct *p)
 {
         /*
          * As blocked tasks retain absolute vruntime the migration needs to
          * deal with this by subtracting the old and adding the new
          * min_vruntime -- the latter is done by enqueue_entity() when placing
          * the task on the new runqueue.
          */
         if (p->state == TASK_WAKING) {
                 struct sched_entity *se = &p->se;
                 struct cfs_rq *cfs_rq = cfs_rq_of(se);
                 u64 min_vruntime;
 
 #ifndef CONFIG_64BIT
                 u64 min_vruntime_copy;
 
                 do {
                         min_vruntime_copy = cfs_rq->min_vruntime_copy;
                         smp_rmb();
                         min_vruntime = cfs_rq->min_vruntime;
                 } while (min_vruntime != min_vruntime_copy);
 #else
                 min_vruntime = cfs_rq->min_vruntime;
 #endif
 
                 se->vruntime -= min_vruntime;
         }
 
         /*
          * 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.
          */
         remove_entity_load_avg(&p->se);
 
         /* Tell new CPU we are migrated */
         p->se.avg.last_update_time = 0;
 
         /* We have migrated, no longer consider this task hot */
         p->se.exec_start = 0;
 }
 
 static void task_dead_fair(struct task_struct *p)
 {
         remove_entity_load_avg(&p->se);
 }
 #endif /* CONFIG_SMP */
 
 static unsigned long
 wakeup_gran(struct sched_entity *curr, struct sched_entity *se)
 {
         unsigned long gran = sysctl_sched_wakeup_granularity;
 
         /*
          * Since its curr running now, convert the gran from real-time
          * to virtual-time in his units.
          *
          * By using 'se' instead of 'curr' we penalize light tasks, so
          * they get preempted easier. That is, if 'se' < 'curr' then
          * the resulting gran will be larger, therefore penalizing the
          * lighter, if otoh 'se' > 'curr' then the resulting gran will
          * be smaller, again penalizing the lighter task.
          *
          * This is especially important for buddies when the leftmost
          * task is higher priority than the buddy.
          */
         return calc_delta_fair(gran, se);
 }
 
 /*
  * Should 'se' preempt 'curr'.
  *
  *             |s1
  *        |s2
  *   |s3
  *         g
  *      |<--->|c
  *
  *  w(c, s1) = -1
  *  w(c, s2) =  0
  *  w(c, s3) =  1
  *
  */
 static int
 wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
 {
         s64 gran, vdiff = curr->vruntime - se->vruntime;
 
         if (vdiff <= 0)
                 return -1;
 
         gran = wakeup_gran(curr, se);
         if (vdiff > gran)
                 return 1;
 
         return 0;
 }
 
 static void set_last_buddy(struct sched_entity *se)
 {
         if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
                 return;
 
         for_each_sched_entity(se)
                 cfs_rq_of(se)->last = se;
 }
 
 static void set_next_buddy(struct sched_entity *se)
 {
         if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
                 return;
 
         for_each_sched_entity(se)
                 cfs_rq_of(se)->next = se;
 }
 
 static void set_skip_buddy(struct sched_entity *se)
 {
         for_each_sched_entity(se)
                 cfs_rq_of(se)->skip = se;
 }
 
 /*
  * Preempt the current task with a newly woken task if needed:
  */
 static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 {
         struct task_struct *curr = rq->curr;
         struct sched_entity *se = &curr->se, *pse = &p->se;
         struct cfs_rq *cfs_rq = task_cfs_rq(curr);
         int scale = cfs_rq->nr_running >= sched_nr_latency;
         int next_buddy_marked = 0;
 
         if (unlikely(se == pse))
                 return;
 
         /*
          * This is possible from callers such as attach_tasks(), in which we
          * unconditionally check_prempt_curr() after an enqueue (which may have
          * lead to a throttle).  This both saves work and prevents false
          * next-buddy nomination below.
          */
         if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
                 return;
 
         if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) {
                 set_next_buddy(pse);
                 next_buddy_marked = 1;
         }
 
         /*
          * We can come here with TIF_NEED_RESCHED already set from new task
          * wake up path.
          *
          * Note: this also catches the edge-case of curr being in a throttled
          * group (e.g. via set_curr_task), since update_curr() (in the
          * enqueue of curr) will have resulted in resched being set.  This
          * prevents us from potentially nominating it as a false LAST_BUDDY
          * below.
          */
         if (test_tsk_need_resched(curr))
                 return;
 
         /* Idle tasks are by definition preempted by non-idle tasks. */
         if (unlikely(curr->policy == SCHED_IDLE) &&
             likely(p->policy != SCHED_IDLE))
                 goto preempt;
 
         /*
          * Batch and idle tasks do not preempt non-idle tasks (their preemption
          * is driven by the tick):
          */
         if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
                 return;
 
         find_matching_se(&se, &pse);
         update_curr(cfs_rq_of(se));
         BUG_ON(!pse);
         if (wakeup_preempt_entity(se, pse) == 1) {
                 /*
                  * Bias pick_next to pick the sched entity that is
                  * triggering this preemption.
                  */
                 if (!next_buddy_marked)
                         set_next_buddy(pse);
                 goto preempt;
         }
 
         return;
 
 preempt:
         resched_curr(rq);
         /*
          * Only set the backward buddy when the current task is still
          * on the rq. This can happen when a wakeup gets interleaved
          * with schedule on the ->pre_schedule() or idle_balance()
          * point, either of which can * drop the rq lock.
          *
          * Also, during early boot the idle thread is in the fair class,
          * for obvious reasons its a bad idea to schedule back to it.
          */
         if (unlikely(!se->on_rq || curr == rq->idle))
                 return;
 
         if (sched_feat(LAST_BUDDY) && scale && entity_is_task(se))
                 set_last_buddy(se);
 }
 
 static struct task_struct *
 pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct pin_cookie cookie)
 {
         struct cfs_rq *cfs_rq = &rq->cfs;
         struct sched_entity *se;
         struct task_struct *p;
         int new_tasks;
 
 again:
 #ifdef CONFIG_FAIR_GROUP_SCHED
         if (!cfs_rq->nr_running)
                 goto idle;
 
         if (prev->sched_class != &fair_sched_class)
                 goto simple;
 
         /*
          * Because of the set_next_buddy() in dequeue_task_fair() it is rather
          * likely that a next task is from the same cgroup as the current.
          *
          * Therefore attempt to avoid putting and setting the entire cgroup
          * hierarchy, only change the part that actually changes.
          */
 
         do {
                 struct sched_entity *curr = cfs_rq->curr;
 
                 /*
                  * Since we got here without doing put_prev_entity() we also
                  * have to consider cfs_rq->curr. If it is still a runnable
                  * entity, update_curr() will update its vruntime, otherwise
                  * forget we've ever seen it.
                  */
                 if (curr) {
                         if (curr->on_rq)
                                 update_curr(cfs_rq);
                         else
                                 curr = NULL;
 
                         /*
                          * This call to check_cfs_rq_runtime() will do the
                          * throttle and dequeue its entity in the parent(s).
                          * Therefore the 'simple' nr_running test will indeed
                          * be correct.
                          */
                         if (unlikely(check_cfs_rq_runtime(cfs_rq)))
                                 goto simple;
                 }
 
                 se = pick_next_entity(cfs_rq, curr);
                 cfs_rq = group_cfs_rq(se);
         } while (cfs_rq);
 
         p = task_of(se);
 
         /*
          * Since we haven't yet done put_prev_entity and if the selected task
          * is a different task than we started out with, try and touch the
          * least amount of cfs_rqs.
          */
         if (prev != p) {
                 struct sched_entity *pse = &prev->se;
 
                 while (!(cfs_rq = is_same_group(se, pse))) {
                         int se_depth = se->depth;
                         int pse_depth = pse->depth;
 
                         if (se_depth <= pse_depth) {
                                 put_prev_entity(cfs_rq_of(pse), pse);
                                 pse = parent_entity(pse);
                         }
                         if (se_depth >= pse_depth) {
                                 set_next_entity(cfs_rq_of(se), se);
                                 se = parent_entity(se);
                         }
                 }
 
                 put_prev_entity(cfs_rq, pse);
                 set_next_entity(cfs_rq, se);
         }
 
         if (hrtick_enabled(rq))
                 hrtick_start_fair(rq, p);
 
         return p;
 simple:
         cfs_rq = &rq->cfs;
 #endif
 
         if (!cfs_rq->nr_running)
                 goto idle;
 
         put_prev_task(rq, prev);
 
         do {
                 se = pick_next_entity(cfs_rq, NULL);
                 set_next_entity(cfs_rq, se);
                 cfs_rq = group_cfs_rq(se);
         } while (cfs_rq);
 
         p = task_of(se);
 
         if (hrtick_enabled(rq))
                 hrtick_start_fair(rq, p);
 
         return p;
 
 idle:
         /*
          * This is OK, because current is on_cpu, which avoids it being picked
          * for load-balance and preemption/IRQs are still disabled avoiding
          * further scheduler activity on it and we're being very careful to
          * re-start the picking loop.
          */
         lockdep_unpin_lock(&rq->lock, cookie);
         new_tasks = idle_balance(rq);
         lockdep_repin_lock(&rq->lock, cookie);
         /*
          * Because idle_balance() releases (and re-acquires) rq->lock, it is
          * possible for any higher priority task to appear. In that case we
          * must re-start the pick_next_entity() loop.
          */
         if (new_tasks < 0)
                 return RETRY_TASK;
 
         if (new_tasks > 0)
                 goto again;
 
         return NULL;
 }
 
 /*
  * Account for a descheduled task:
  */
 static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
 {
         struct sched_entity *se = &prev->se;
         struct cfs_rq *cfs_rq;
 
         for_each_sched_entity(se) {
                 cfs_rq = cfs_rq_of(se);
                 put_prev_entity(cfs_rq, se);
         }
 }
 
 /*
  * sched_yield() is very simple
  *
  * The magic of dealing with the ->skip buddy is in pick_next_entity.
  */
 static void yield_task_fair(struct rq *rq)
 {
         struct task_struct *curr = rq->curr;
         struct cfs_rq *cfs_rq = task_cfs_rq(curr);
         struct sched_entity *se = &curr->se;
 
         /*
          * Are we the only task in the tree?
          */
         if (unlikely(rq->nr_running == 1))
                 return;
 
         clear_buddies(cfs_rq, se);
 
         if (curr->policy != SCHED_BATCH) {
                 update_rq_clock(rq);
                 /*
                  * Update run-time statistics of the 'current'.
                  */
                 update_curr(cfs_rq);
                 /*
                  * Tell update_rq_clock() that we've just updated,
                  * so we don't do microscopic update in schedule()
                  * and double the fastpath cost.
                  */
                 rq_clock_skip_update(rq, true);
         }
 
         set_skip_buddy(se);
 }
 
 static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preempt)
 {
         struct sched_entity *se = &p->se;
 
         /* throttled hierarchies are not runnable */
         if (!se->on_rq || throttled_hierarchy(cfs_rq_of(se)))
                 return false;
 
         /* Tell the scheduler that we'd really like pse to run next. */
         set_next_buddy(se);
 
         yield_task_fair(rq);
 
         return true;
 }
 
 #ifdef CONFIG_SMP
 /**************************************************
  * Fair scheduling class load-balancing methods.
  *
  * BASICS
  *
  * The purpose of load-balancing is to achieve the same basic fairness the
  * per-cpu scheduler provides, namely provide a proportional amount of compute
  * time to each task. This is expressed in the following equation:
  *
  *   W_i,n/P_i == W_j,n/P_j for all i,j                               (1)
  *
  * Where W_i,n is the n-th weight average for cpu i. The instantaneous weight
  * W_i,0 is defined as:
  *
  *   W_i,0 = \Sum_j w_i,j                                             (2)
  *
  * Where w_i,j is the weight of the j-th runnable task on cpu i. This weight
  * is derived from the nice value as per sched_prio_to_weight[].
  *
  * The weight average is an exponential decay average of the instantaneous
  * weight:
  *
  *   W'_i,n = (2^n - 1) / 2^n * W_i,n + 1 / 2^n * W_i,0               (3)
  *
  * C_i is the compute capacity of cpu i, typically it is the
  * fraction of 'recent' time available for SCHED_OTHER task execution. But it
  * can also include other factors [XXX].
  *
  * To achieve this balance we define a measure of imbalance which follows
  * directly from (1):
  *
  *   imb_i,j = max{ avg(W/C), W_i/C_i } - min{ avg(W/C), W_j/C_j }    (4)
  *
  * We them move tasks around to minimize the imbalance. In the continuous
  * function space it is obvious this converges, in the discrete case we get
  * a few fun cases generally called infeasible weight scenarios.
  *
  * [XXX expand on:
  *     - infeasible weights;
  *     - local vs global optima in the discrete case. ]
  *
  *
  * SCHED DOMAINS
  *
  * In order to solve the imbalance equation (4), and avoid the obvious O(n^2)
  * for all i,j solution, we create a tree of cpus that follows the hardware
  * topology where each level pairs two lower groups (or better). This results
  * in O(log n) layers. Furthermore we reduce the number of cpus going up the
  * tree to only the first of the previous level and we decrease the frequency
  * of load-balance at each level inv. proportional to the number of cpus in
  * the groups.
  *
  * This yields:
  *
  *     log_2 n     1     n
  *   \Sum       { --- * --- * 2^i } = O(n)                            (5)
  *     i = 0      2^i   2^i
  *                               `- size of each group
  *         |         |     `- number of cpus doing load-balance
  *         |         `- freq
  *         `- sum over all levels
  *
  * Coupled with a limit on how many tasks we can migrate every balance pass,
  * this makes (5) the runtime complexity of the balancer.
  *
  * An important property here is that each CPU is still (indirectly) connected
  * to every other cpu in at most O(log n) steps:
  *
  * The adjacency matrix of the resulting graph is given by:
  *
  *             log_2 n     
  *   A_i,j = \Union     (i % 2^k == 0) && i / 2^(k+1) == j / 2^(k+1)  (6)
  *             k = 0
  *
  * And you'll find that:
  *
  *   A^(log_2 n)_i,j != 0  for all i,j                                (7)
  *
  * Showing there's indeed a path between every cpu in at most O(log n) steps.
  * The task movement gives a factor of O(m), giving a convergence complexity
  * of:
  *
  *   O(nm log n),  n := nr_cpus, m := nr_tasks                        (8)
  *
  *
  * WORK CONSERVING
  *
  * In order to avoid CPUs going idle while there's still work to do, new idle
  * balancing is more aggressive and has the newly idle cpu iterate up the domain
  * tree itself instead of relying on other CPUs to bring it work.
  *
  * This adds some complexity to both (5) and (8) but it reduces the total idle
  * time.
  *
  * [XXX more?]
  *
  *
  * CGROUPS
  *
  * Cgroups make a horror show out of (2), instead of a simple sum we get:
  *
  *                                s_k,i
  *   W_i,0 = \Sum_j \Prod_k w_k * -----                               (9)
  *                                 S_k
  *
  * Where
  *
  *   s_k,i = \Sum_j w_i,j,k  and  S_k = \Sum_i s_k,i                 (10)
  *
  * w_i,j,k is the weight of the j-th runnable task in the k-th cgroup on cpu i.
  *
  * The big problem is S_k, its a global sum needed to compute a local (W_i)
  * property.
  *
  * [XXX write more on how we solve this.. _after_ merging pjt's patches that
  *      rewrite all of this once again.]
  */ 
 
 static unsigned long __read_mostly max_load_balance_interval = HZ/10;
 
 enum fbq_type { regular, remote, all };
 
 #define LBF_ALL_PINNED  0x01
 #define LBF_NEED_BREAK  0x02
 #define LBF_DST_PINNED  0x04
 #define LBF_SOME_PINNED 0x08
 
 struct lb_env {
         struct sched_domain     *sd;
 
         struct rq               *src_rq;
         int                     src_cpu;
 
         int                     dst_cpu;
         struct rq               *dst_rq;
 
         struct cpumask          *dst_grpmask;
         int                     new_dst_cpu;
         enum cpu_idle_type      idle;
         long                    imbalance;
         /* The set of CPUs under consideration for load-balancing */
         struct cpumask          *cpus;
 
         unsigned int            flags;
 
         unsigned int            loop;
         unsigned int            loop_break;
         unsigned int            loop_max;
 
         enum fbq_type           fbq_type;
         struct list_head        tasks;
 };
 
 /*
  * Is this task likely cache-hot:
  */
 static int task_hot(struct task_struct *p, struct lb_env *env)
 {
         s64 delta;
 
         lockdep_assert_held(&env->src_rq->lock);
 
         if (p->sched_class != &fair_sched_class)
                 return 0;
 
         if (unlikely(p->policy == SCHED_IDLE))
                 return 0;
 
         /*
          * Buddy candidates are cache hot:
          */
         if (sched_feat(CACHE_HOT_BUDDY) && env->dst_rq->nr_running &&
                         (&p->se == cfs_rq_of(&p->se)->next ||
                          &p->se == cfs_rq_of(&p->se)->last))
                 return 1;
 
         if (sysctl_sched_migration_cost == -1)
                 return 1;
         if (sysctl_sched_migration_cost == 0)
                 return 0;
 
         delta = rq_clock_task(env->src_rq) - p->se.exec_start;
 
         return delta < (s64)sysctl_sched_migration_cost;
 }
 
 #ifdef CONFIG_NUMA_BALANCING
 /*
  * Returns 1, if task migration degrades locality
  * Returns 0, if task migration improves locality i.e migration preferred.
  * Returns -1, if task migration is not affected by locality.
  */
 static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 {
         struct numa_group *numa_group = rcu_dereference(p->numa_group);
         unsigned long src_faults, dst_faults;
         int src_nid, dst_nid;
 
         if (!static_branch_likely(&sched_numa_balancing))
                 return -1;
 
         if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
                 return -1;
 
         src_nid = cpu_to_node(env->src_cpu);
         dst_nid = cpu_to_node(env->dst_cpu);
 
         if (src_nid == dst_nid)
                 return -1;
 
         /* Migrating away from the preferred node is always bad. */
         if (src_nid == p->numa_preferred_nid) {
                 if (env->src_rq->nr_running > env->src_rq->nr_preferred_running)
                         return 1;
                 else
                         return -1;
         }
 
         /* Encourage migration to the preferred node. */
         if (dst_nid == p->numa_preferred_nid)
                 return 0;
 
         if (numa_group) {
                 src_faults = group_faults(p, src_nid);
                 dst_faults = group_faults(p, dst_nid);
         } else {
                 src_faults = task_faults(p, src_nid);
                 dst_faults = task_faults(p, dst_nid);
         }
 
         return dst_faults < src_faults;
 }
 
 #else
 static inline int migrate_degrades_locality(struct task_struct *p,
                                              struct lb_env *env)
 {
         return -1;
 }
 #endif
 
 /*
  * can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
  */
 static
 int can_migrate_task(struct task_struct *p, struct lb_env *env)
 {
         int tsk_cache_hot;
 
         lockdep_assert_held(&env->src_rq->lock);
 
         /*
          * We do not migrate tasks that are:
          * 1) throttled_lb_pair, or
          * 2) cannot be migrated to this CPU due to cpus_allowed, or
          * 3) running (obviously), or
          * 4) are cache-hot on their current CPU.
          */
         if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
                 return 0;
 
         if (!cpumask_test_cpu(env->dst_cpu, tsk_cpus_allowed(p))) {
                 int cpu;
 
                 schedstat_inc(p, se.statistics.nr_failed_migrations_affine);
 
                 env->flags |= LBF_SOME_PINNED;
 
                 /*
                  * Remember if this task can be migrated to any other cpu in
                  * our sched_group. We may want to revisit it if we couldn't
                  * meet load balance goals by pulling other tasks on src_cpu.
                  *
                  * Also avoid computing new_dst_cpu if we have already computed
                  * one in current iteration.
                  */
                 if (!env->dst_grpmask || (env->flags & LBF_DST_PINNED))
                         return 0;
 
                 /* Prevent to re-select dst_cpu via env's cpus */
                 for_each_cpu_and(cpu, env->dst_grpmask, env->cpus) {
                         if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) {
                                 env->flags |= LBF_DST_PINNED;
                                 env->new_dst_cpu = cpu;
                                 break;
                         }
                 }
 
                 return 0;
         }
 
         /* Record that we found atleast one task that could run on dst_cpu */
         env->flags &= ~LBF_ALL_PINNED;
 
         if (task_running(env->src_rq, p)) {
                 schedstat_inc(p, se.statistics.nr_failed_migrations_running);
                 return 0;
         }
 
         /*
          * Aggressive migration if:
          * 1) destination numa is preferred
          * 2) task is cache cold, or
          * 3) too many balance attempts have failed.
          */
         tsk_cache_hot = migrate_degrades_locality(p, env);
         if (tsk_cache_hot == -1)
                 tsk_cache_hot = task_hot(p, env);
 
         if (tsk_cache_hot <= 0 ||
             env->sd->nr_balance_failed > env->sd->cache_nice_tries) {
                 if (tsk_cache_hot == 1) {
                         schedstat_inc(env->sd, lb_hot_gained[env->idle]);
                         schedstat_inc(p, se.statistics.nr_forced_migrations);
                 }
                 return 1;
         }
 
         schedstat_inc(p, se.statistics.nr_failed_migrations_hot);
         return 0;
 }
 
 /*
  * detach_task() -- detach the task for the migration specified in env
  */
 static void detach_task(struct task_struct *p, struct lb_env *env)
 {
         lockdep_assert_held(&env->src_rq->lock);
 
         p->on_rq = TASK_ON_RQ_MIGRATING;
         deactivate_task(env->src_rq, p, 0);
         set_task_cpu(p, env->dst_cpu);
 }
 
 /*
  * detach_one_task() -- tries to dequeue exactly one task from env->src_rq, as
  * part of active balancing operations within "domain".
  *
  * Returns a task if successful and NULL otherwise.
  */
 static struct task_struct *detach_one_task(struct lb_env *env)
 {
         struct task_struct *p, *n;
 
         lockdep_assert_held(&env->src_rq->lock);
 
         list_for_each_entry_safe(p, n, &env->src_rq->cfs_tasks, se.group_node) {
                 if (!can_migrate_task(p, env))
                         continue;
 
                 detach_task(p, env);
 
                 /*
                  * Right now, this is only the second place where
                  * lb_gained[env->idle] is updated (other is detach_tasks)
                  * so we can safely collect stats here rather than
                  * inside detach_tasks().
                  */
                 schedstat_inc(env->sd, lb_gained[env->idle]);
                 return p;
         }
         return NULL;
 }
 
 static const unsigned int sched_nr_migrate_break = 32;
 
 /*
  * detach_tasks() -- tries to detach up to imbalance weighted load from
  * busiest_rq, as part of a balancing operation within domain "sd".
  *
  * Returns number of detached tasks if successful and 0 otherwise.
  */
 static int detach_tasks(struct lb_env *env)
 {
         struct list_head *tasks = &env->src_rq->cfs_tasks;
         struct task_struct *p;
         unsigned long load;
         int detached = 0;
 
         lockdep_assert_held(&env->src_rq->lock);
 
         if (env->imbalance <= 0)
                 return 0;
 
         while (!list_empty(tasks)) {
                 /*
                  * We don't want to steal all, otherwise we may be treated likewise,
                  * which could at worst lead to a livelock crash.
                  */
                 if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1)
                         break;
 
                 p = list_first_entry(tasks, struct task_struct, se.group_node);
 
                 env->loop++;
                 /* We've more or less seen every task there is, call it quits */
                 if (env->loop > env->loop_max)
                         break;
 
                 /* take a breather every nr_migrate tasks */
                 if (env->loop > env->loop_break) {
                         env->loop_break += sched_nr_migrate_break;
                         env->flags |= LBF_NEED_BREAK;
                         break;
                 }
 
                 if (!can_migrate_task(p, env))
                         goto next;
 
                 load = task_h_load(p);
 
                 if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
                         goto next;
 
                 if ((load / 2) > env->imbalance)
                         goto next;
 
                 detach_task(p, env);
                 list_add(&p->se.group_node, &env->tasks);
 
                 detached++;
                 env->imbalance -= load;
 
 #ifdef CONFIG_PREEMPT
                 /*
                  * NEWIDLE balancing is a source of latency, so preemptible
                  * kernels will stop after the first task is detached to minimize
                  * the critical section.
                  */
                 if (env->idle == CPU_NEWLY_IDLE)
                         break;
 #endif
 
                 /*
                  * We only want to steal up to the prescribed amount of
                  * weighted load.
                  */
                 if (env->imbalance <= 0)
                         break;
 
                 continue;
 next:
                 list_move_tail(&p->se.group_node, tasks);
         }
 
         /*
          * Right now, this is one of only two places we collect this stat
          * so we can safely collect detach_one_task() stats here rather
          * than inside detach_one_task().
          */
         schedstat_add(env->sd, lb_gained[env->idle], detached);
 
         return detached;
 }
 
 /*
  * attach_task() -- attach the task detached by detach_task() to its new rq.
  */
 static void attach_task(struct rq *rq, struct task_struct *p)
 {
         lockdep_assert_held(&rq->lock);
 
         BUG_ON(task_rq(p) != rq);
         activate_task(rq, p, 0);
         p->on_rq = TASK_ON_RQ_QUEUED;
         check_preempt_curr(rq, p, 0);
 }
 
 /*
  * attach_one_task() -- attaches the task returned from detach_one_task() to
  * its new rq.
  */
 static void attach_one_task(struct rq *rq, struct task_struct *p)
 {
         raw_spin_lock(&rq->lock);
         attach_task(rq, p);
         raw_spin_unlock(&rq->lock);
 }
 
 /*
  * attach_tasks() -- attaches all tasks detached by detach_tasks() to their
  * new rq.
  */
 static void attach_tasks(struct lb_env *env)
 {
         struct list_head *tasks = &env->tasks;
         struct task_struct *p;
 
         raw_spin_lock(&env->dst_rq->lock);
 
         while (!list_empty(tasks)) {
                 p = list_first_entry(tasks, struct task_struct, se.group_node);
                 list_del_init(&p->se.group_node);
 
                 attach_task(env->dst_rq, p);
         }
 
         raw_spin_unlock(&env->dst_rq->lock);
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static void update_blocked_averages(int cpu)
 {
         struct rq *rq = cpu_rq(cpu);
         struct cfs_rq *cfs_rq;
         unsigned long flags;
 
         raw_spin_lock_irqsave(&rq->lock, flags);
         update_rq_clock(rq);
 
         /*
          * Iterates the task_group tree in a bottom up fashion, see
          * list_add_leaf_cfs_rq() for details.
          */
         for_each_leaf_cfs_rq(rq, cfs_rq) {
                 /* throttled entities do not contribute to load */
                 if (throttled_hierarchy(cfs_rq))
                         continue;
 
                 if (update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, true))
                         update_tg_load_avg(cfs_rq, 0);
         }
         raw_spin_unlock_irqrestore(&rq->lock, flags);
 }
 
 /*
  * Compute the hierarchical load factor for cfs_rq and all its ascendants.
  * This needs to be done in a top-down fashion because the load of a child
  * group is a fraction of its parents load.
  */
 static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
 {
         struct rq *rq = rq_of(cfs_rq);
         struct sched_entity *se = cfs_rq->tg->se[cpu_of(rq)];
         unsigned long now = jiffies;
         unsigned long load;
 
         if (cfs_rq->last_h_load_update == now)
                 return;
 
         cfs_rq->h_load_next = NULL;
         for_each_sched_entity(se) {
                 cfs_rq = cfs_rq_of(se);
                 cfs_rq->h_load_next = se;
                 if (cfs_rq->last_h_load_update == now)
                         break;
         }
 
         if (!se) {
                 cfs_rq->h_load = cfs_rq_load_avg(cfs_rq);
                 cfs_rq->last_h_load_update = now;
         }
 
         while ((se = cfs_rq->h_load_next) != NULL) {
                 load = cfs_rq->h_load;
                 load = div64_ul(load * se->avg.load_avg,
                         cfs_rq_load_avg(cfs_rq) + 1);
                 cfs_rq = group_cfs_rq(se);
                 cfs_rq->h_load = load;
                 cfs_rq->last_h_load_update = now;
         }
 }
 
 static unsigned long task_h_load(struct task_struct *p)
 {
         struct cfs_rq *cfs_rq = task_cfs_rq(p);
 
         update_cfs_rq_h_load(cfs_rq);
         return div64_ul(p->se.avg.load_avg * cfs_rq->h_load,
                         cfs_rq_load_avg(cfs_rq) + 1);
 }
 #else
 static inline void update_blocked_averages(int cpu)
 {
         struct rq *rq = cpu_rq(cpu);
         struct cfs_rq *cfs_rq = &rq->cfs;
         unsigned long flags;
 
         raw_spin_lock_irqsave(&rq->lock, flags);
         update_rq_clock(rq);
         update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, true);
         raw_spin_unlock_irqrestore(&rq->lock, flags);
 }
 
 static unsigned long task_h_load(struct task_struct *p)
 {
         return p->se.avg.load_avg;
 }
 #endif
 
 /********** Helpers for find_busiest_group ************************/
 
 enum group_type {
         group_other = 0,
         group_imbalanced,
         group_overloaded,
 };
 
 /*
  * sg_lb_stats - stats of a sched_group required for load_balancing
  */
 struct sg_lb_stats {
         unsigned long avg_load; /*Avg load across the CPUs of the group */
         unsigned long group_load; /* Total load over the CPUs of the group */
         unsigned long sum_weighted_load; /* Weighted load of group's tasks */
         unsigned long load_per_task;
         unsigned long group_capacity;
         unsigned long group_util; /* Total utilization of the group */
         unsigned int sum_nr_running; /* Nr tasks running in the group */
         unsigned int idle_cpus;
         unsigned int group_weight;
         enum group_type group_type;
         int group_no_capacity;
 #ifdef CONFIG_NUMA_BALANCING
         unsigned int nr_numa_running;
         unsigned int nr_preferred_running;
 #endif
 };
 
 /*
  * sd_lb_stats - Structure to store the statistics of a sched_domain
  *               during load balancing.
  */
 struct sd_lb_stats {
         struct sched_group *busiest;    /* Busiest group in this sd */
         struct sched_group *local;      /* Local group in this sd */
         unsigned long total_load;       /* Total load of all groups in sd */
         unsigned long total_capacity;   /* Total capacity of all groups in sd */
         unsigned long avg_load; /* Average load across all groups in sd */
 
         struct sg_lb_stats busiest_stat;/* Statistics of the busiest group */
         struct sg_lb_stats local_stat;  /* Statistics of the local group */
 };
 
 static inline void init_sd_lb_stats(struct sd_lb_stats *sds)
 {
         /*
          * Skimp on the clearing to avoid duplicate work. We can avoid clearing
          * local_stat because update_sg_lb_stats() does a full clear/assignment.
          * We must however clear busiest_stat::avg_load because
          * update_sd_pick_busiest() reads this before assignment.
          */
         *sds = (struct sd_lb_stats){
                 .busiest = NULL,
                 .local = NULL,
                 .total_load = 0UL,
                 .total_capacity = 0UL,
                 .busiest_stat = {
                         .avg_load = 0UL,
                         .sum_nr_running = 0,
                         .group_type = group_other,
                 },
         };
 }
 
 /**
  * get_sd_load_idx - Obtain the load index for a given sched domain.
  * @sd: The sched_domain whose load_idx is to be obtained.
  * @idle: The idle status of the CPU for whose sd load_idx is obtained.
  *
  * Return: The load index.
  */
 static inline int get_sd_load_idx(struct sched_domain *sd,
                                         enum cpu_idle_type idle)
 {
         int load_idx;
 
         switch (idle) {
         case CPU_NOT_IDLE:
                 load_idx = sd->busy_idx;
                 break;
 
         case CPU_NEWLY_IDLE:
                 load_idx = sd->newidle_idx;
                 break;
         default:
                 load_idx = sd->idle_idx;
                 break;
         }
 
         return load_idx;
 }
 
 static unsigned long scale_rt_capacity(int cpu)
 {
         struct rq *rq = cpu_rq(cpu);
         u64 total, used, age_stamp, avg;
         s64 delta;
 
         /*
          * Since we're reading these variables without serialization make sure
          * we read them once before doing sanity checks on them.
          */
         age_stamp = READ_ONCE(rq->age_stamp);
         avg = READ_ONCE(rq->rt_avg);
         delta = __rq_clock_broken(rq) - age_stamp;
 
         if (unlikely(delta < 0))
                 delta = 0;
 
         total = sched_avg_period() + delta;
 
         used = div_u64(avg, total);
 
         if (likely(used < SCHED_CAPACITY_SCALE))
                 return SCHED_CAPACITY_SCALE - used;
 
         return 1;
 }
 
 static void update_cpu_capacity(struct sched_domain *sd, int cpu)
 {
         unsigned long capacity = arch_scale_cpu_capacity(sd, cpu);
         struct sched_group *sdg = sd->groups;
 
         cpu_rq(cpu)->cpu_capacity_orig = capacity;
 
         capacity *= scale_rt_capacity(cpu);
         capacity >>= SCHED_CAPACITY_SHIFT;
 
         if (!capacity)
                 capacity = 1;
 
         cpu_rq(cpu)->cpu_capacity = capacity;
         sdg->sgc->capacity = capacity;
 }
 
 void update_group_capacity(struct sched_domain *sd, int cpu)
 {
         struct sched_domain *child = sd->child;
         struct sched_group *group, *sdg = sd->groups;
         unsigned long capacity;
         unsigned long interval;
 
         interval = msecs_to_jiffies(sd->balance_interval);
         interval = clamp(interval, 1UL, max_load_balance_interval);
         sdg->sgc->next_update = jiffies + interval;
 
         if (!child) {
                 update_cpu_capacity(sd, cpu);
                 return;
         }
 
         capacity = 0;
 
         if (child->flags & SD_OVERLAP) {
                 /*
                  * SD_OVERLAP domains cannot assume that child groups
                  * span the current group.
                  */
 
                 for_each_cpu(cpu, sched_group_cpus(sdg)) {
                         struct sched_group_capacity *sgc;
                         struct rq *rq = cpu_rq(cpu);
 
                         /*
                          * build_sched_domains() -> init_sched_groups_capacity()
                          * gets here before we've attached the domains to the
                          * runqueues.
                          *
                          * Use capacity_of(), which is set irrespective of domains
                          * in update_cpu_capacity().
                          *
                          * This avoids capacity from being 0 and
                          * causing divide-by-zero issues on boot.
                          */
                         if (unlikely(!rq->sd)) {
                                 capacity += capacity_of(cpu);
                                 continue;
                         }
 
                         sgc = rq->sd->groups->sgc;
                         capacity += sgc->capacity;
                 }
         } else  {
                 /*
                  * !SD_OVERLAP domains can assume that child groups
                  * span the current group.
                  */ 
 
                 group = child->groups;
                 do {
                         capacity += group->sgc->capacity;
                         group = group->next;
                 } while (group != child->groups);
         }
 
         sdg->sgc->capacity = capacity;
 }
 
 /*
  * Check whether the capacity of the rq has been noticeably reduced by side
  * activity. The imbalance_pct is used for the threshold.
  * Return true is the capacity is reduced
  */
 static inline int
 check_cpu_capacity(struct rq *rq, struct sched_domain *sd)
 {
         return ((rq->cpu_capacity * sd->imbalance_pct) <
                                 (rq->cpu_capacity_orig * 100));
 }
 
 /*
  * Group imbalance indicates (and tries to solve) the problem where balancing
  * groups is inadequate due to tsk_cpus_allowed() constraints.
  *
  * Imagine a situation of two groups of 4 cpus each and 4 tasks each with a
  * cpumask covering 1 cpu of the first group and 3 cpus of the second group.
  * Something like:
  *
  *      { 0 1 2 3 } { 4 5 6 7 }
  *              *     * * *
  *
  * If we were to balance group-wise we'd place two tasks in the first group and
  * two tasks in the second group. Clearly this is undesired as it will overload
  * cpu 3 and leave one of the cpus in the second group unused.
  *
  * The current solution to this issue is detecting the skew in the first group
  * by noticing the lower domain failed to reach balance and had difficulty
  * moving tasks due to affinity constraints.
  *
  * When this is so detected; this group becomes a candidate for busiest; see
  * update_sd_pick_busiest(). And calculate_imbalance() and
  * find_busiest_group() avoid some of the usual balance conditions to allow it
  * to create an effective group imbalance.
  *
  * This is a somewhat tricky proposition since the next run might not find the
  * group imbalance and decide the groups need to be balanced again. A most
  * subtle and fragile situation.
  */
 
 static inline int sg_imbalanced(struct sched_group *group)
 {
         return group->sgc->imbalance;
 }
 
 /*
  * group_has_capacity returns true if the group has spare capacity that could
  * be used by some tasks.
  * We consider that a group has spare capacity if the  * number of task is
  * smaller than the number of CPUs or if the utilization is lower than the
  * available capacity for CFS tasks.
  * For the latter, we use a threshold to stabilize the state, to take into
  * account the variance of the tasks' load and to return true if the available
  * capacity in meaningful for the load balancer.
  * As an example, an available capacity of 1% can appear but it doesn't make
  * any benefit for the load balance.
  */
 static inline bool
 group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
 {
         if (sgs->sum_nr_running < sgs->group_weight)
                 return true;
 
         if ((sgs->group_capacity * 100) >
                         (sgs->group_util * env->sd->imbalance_pct))
                 return true;
 
         return false;
 }
 
 /*
  *  group_is_overloaded returns true if the group has more tasks than it can
  *  handle.
  *  group_is_overloaded is not equals to !group_has_capacity because a group
  *  with the exact right number of tasks, has no more spare capacity but is not
  *  overloaded so both group_has_capacity and group_is_overloaded return
  *  false.
  */
 static inline bool
 group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
 {
         if (sgs->sum_nr_running <= sgs->group_weight)
                 return false;
 
         if ((sgs->group_capacity * 100) <
                         (sgs->group_util * env->sd->imbalance_pct))
                 return true;
 
         return false;
 }
 
 static inline enum
 group_type group_classify(struct sched_group *group,
                           struct sg_lb_stats *sgs)
 {
         if (sgs->group_no_capacity)
                 return group_overloaded;
 
         if (sg_imbalanced(group))
                 return group_imbalanced;
 
         return group_other;
 }
 
 /**
  * update_sg_lb_stats - Update sched_group's statistics for load balancing.
  * @env: The load balancing environment.
  * @group: sched_group whose statistics are to be updated.
  * @load_idx: Load index of sched_domain of this_cpu for load calc.
  * @local_group: Does group contain this_cpu.
  * @sgs: variable to hold the statistics for this group.
  * @overload: Indicate more than one runnable task for any CPU.
  */
 static inline void update_sg_lb_stats(struct lb_env *env,
                         struct sched_group *group, int load_idx,
                         int local_group, struct sg_lb_stats *sgs,
                         bool *overload)
 {
         unsigned long load;
         int i, nr_running;
 
         memset(sgs, 0, sizeof(*sgs));
 
         for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
                 struct rq *rq = cpu_rq(i);
 
                 /* Bias balancing toward cpus of our domain */
                 if (local_group)
                         load = target_load(i, load_idx);
                 else
                         load = source_load(i, load_idx);
 
                 sgs->group_load += load;
                 sgs->group_util += cpu_util(i);
                 sgs->sum_nr_running += rq->cfs.h_nr_running;
 
                 nr_running = rq->nr_running;
                 if (nr_running > 1)
                         *overload = true;
 
 #ifdef CONFIG_NUMA_BALANCING
                 sgs->nr_numa_running += rq->nr_numa_running;
                 sgs->nr_preferred_running += rq->nr_preferred_running;
 #endif
                 sgs->sum_weighted_load += weighted_cpuload(i);
                 /*
                  * No need to call idle_cpu() if nr_running is not 0
                  */
                 if (!nr_running && idle_cpu(i))
                         sgs->idle_cpus++;
         }
 
         /* Adjust by relative CPU capacity of the group */
         sgs->group_capacity = group->sgc->capacity;
         sgs->avg_load = (sgs->group_load*SCHED_CAPACITY_SCALE) / sgs->group_capacity;
 
         if (sgs->sum_nr_running)
                 sgs->load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;
 
         sgs->group_weight = group->group_weight;
 
         sgs->group_no_capacity = group_is_overloaded(env, sgs);
         sgs->group_type = group_classify(group, sgs);
 }
 
 /**
  * update_sd_pick_busiest - return 1 on busiest group
  * @env: The load balancing environment.
  * @sds: sched_domain statistics
  * @sg: sched_group candidate to be checked for being the busiest
  * @sgs: sched_group statistics
  *
  * Determine if @sg is a busier group than the previously selected
  * busiest group.
  *
  * Return: %true if @sg is a busier group than the previously selected
  * busiest group. %false otherwise.
  */
 static bool update_sd_pick_busiest(struct lb_env *env,
                                    struct sd_lb_stats *sds,
                                    struct sched_group *sg,
                                    struct sg_lb_stats *sgs)
 {
         struct sg_lb_stats *busiest = &sds->busiest_stat;
 
         if (sgs->group_type > busiest->group_type)
                 return true;
 
         if (sgs->group_type < busiest->group_type)
                 return false;
 
         if (sgs->avg_load <= busiest->avg_load)
                 return false;
 
         /* This is the busiest node in its class. */
         if (!(env->sd->flags & SD_ASYM_PACKING))
                 return true;
 
         /* No ASYM_PACKING if target cpu is already busy */
         if (env->idle == CPU_NOT_IDLE)
                 return true;
         /*
          * ASYM_PACKING needs to move all the work to the lowest
          * numbered CPUs in the group, therefore mark all groups
          * higher than ourself as busy.
          */
         if (sgs->sum_nr_running && env->dst_cpu < group_first_cpu(sg)) {
                 if (!sds->busiest)
                         return true;
 
                 /* Prefer to move from highest possible cpu's work */
                 if (group_first_cpu(sds->busiest) < group_first_cpu(sg))
                         return true;
         }
 
         return false;
 }
 
 #ifdef CONFIG_NUMA_BALANCING
 static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
 {
         if (sgs->sum_nr_running > sgs->nr_numa_running)
                 return regular;
         if (sgs->sum_nr_running > sgs->nr_preferred_running)
                 return remote;
         return all;
 }
 
 static inline enum fbq_type fbq_classify_rq(struct rq *rq)
 {
         if (rq->nr_running > rq->nr_numa_running)
                 return regular;
         if (rq->nr_running > rq->nr_preferred_running)
                 return remote;
         return all;
 }
 #else
 static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
 {
         return all;
 }
 
 static inline enum fbq_type fbq_classify_rq(struct rq *rq)
 {
         return regular;
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
 /**
  * update_sd_lb_stats - Update sched_domain's statistics for load balancing.
  * @env: The load balancing environment.
  * @sds: variable to hold the statistics for this sched_domain.
  */
 static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
 {
         struct sched_domain *child = env->sd->child;
         struct sched_group *sg = env->sd->groups;
         struct sg_lb_stats tmp_sgs;
         int load_idx, prefer_sibling = 0;
         bool overload = false;
 
         if (child && child->flags & SD_PREFER_SIBLING)
                 prefer_sibling = 1;
 
         load_idx = get_sd_load_idx(env->sd, env->idle);
 
         do {
                 struct sg_lb_stats *sgs = &tmp_sgs;
                 int local_group;
 
                 local_group = cpumask_test_cpu(env->dst_cpu, sched_group_cpus(sg));
                 if (local_group) {
                         sds->local = sg;
                         sgs = &sds->local_stat;
 
                         if (env->idle != CPU_NEWLY_IDLE ||
                             time_after_eq(jiffies, sg->sgc->next_update))
                                 update_group_capacity(env->sd, env->dst_cpu);
                 }
 
                 update_sg_lb_stats(env, sg, load_idx, local_group, sgs,
                                                 &overload);
 
                 if (local_group)
                         goto next_group;
 
                 /*
                  * In case the child domain prefers tasks go to siblings
                  * first, lower the sg capacity so that we'll try
                  * and move all the excess tasks away. We lower the capacity
                  * of a group only if the local group has the capacity to fit
                  * these excess tasks. The extra check prevents the case where
                  * you always pull from the heaviest group when it is already
                  * under-utilized (possible with a large weight task outweighs
                  * the tasks on the system).
                  */
                 if (prefer_sibling && sds->local &&
                     group_has_capacity(env, &sds->local_stat) &&
                     (sgs->sum_nr_running > 1)) {
                         sgs->group_no_capacity = 1;
                         sgs->group_type = group_classify(sg, sgs);
                 }
 
                 if (update_sd_pick_busiest(env, sds, sg, sgs)) {
                         sds->busiest = sg;
                         sds->busiest_stat = *sgs;
                 }
 
 next_group:
                 /* Now, start updating sd_lb_stats */
                 sds->total_load += sgs->group_load;
                 sds->total_capacity += sgs->group_capacity;
 
                 sg = sg->next;
         } while (sg != env->sd->groups);
 
         if (env->sd->flags & SD_NUMA)
                 env->fbq_type = fbq_classify_group(&sds->busiest_stat);
 
         if (!env->sd->parent) {
                 /* update overload indicator if we are at root domain */
                 if (env->dst_rq->rd->overload != overload)
                         env->dst_rq->rd->overload = overload;
         }
 
 }
 
 /**
  * check_asym_packing - Check to see if the group is packed into the
  *                      sched doman.
  *
  * This is primarily intended to used at the sibling level.  Some
  * cores like POWER7 prefer to use lower numbered SMT threads.  In the
  * case of POWER7, it can move to lower SMT modes only when higher
  * threads are idle.  When in lower SMT modes, the threads will
  * perform better since they share less core resources.  Hence when we
  * have idle threads, we want them to be the higher ones.
  *
  * This packing function is run on idle threads.  It checks to see if
  * the busiest CPU in this domain (core in the P7 case) has a higher
  * CPU number than the packing function is being run on.  Here we are
  * assuming lower CPU number will be equivalent to lower a SMT thread
  * number.
  *
  * Return: 1 when packing is required and a task should be moved to
  * this CPU.  The amount of the imbalance is returned in *imbalance.
  *
  * @env: The load balancing environment.
  * @sds: Statistics of the sched_domain which is to be packed
  */
 static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
 {
         int busiest_cpu;
 
         if (!(env->sd->flags & SD_ASYM_PACKING))
                 return 0;
 
         if (env->idle == CPU_NOT_IDLE)
                 return 0;
 
         if (!sds->busiest)
                 return 0;
 
         busiest_cpu = group_first_cpu(sds->busiest);
         if (env->dst_cpu > busiest_cpu)
                 return 0;
 
         env->imbalance = DIV_ROUND_CLOSEST(
                 sds->busiest_stat.avg_load * sds->busiest_stat.group_capacity,
                 SCHED_CAPACITY_SCALE);
 
         return 1;
 }
 
 /**
  * fix_small_imbalance - Calculate the minor imbalance that exists
  *                      amongst the groups of a sched_domain, during
  *                      load balancing.
  * @env: The load balancing environment.
  * @sds: Statistics of the sched_domain whose imbalance is to be calculated.
  */
 static inline
 void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
 {
         unsigned long tmp, capa_now = 0, capa_move = 0;
         unsigned int imbn = 2;
         unsigned long scaled_busy_load_per_task;
         struct sg_lb_stats *local, *busiest;
 
         local = &sds->local_stat;
         busiest = &sds->busiest_stat;
 
         if (!local->sum_nr_running)
                 local->load_per_task = cpu_avg_load_per_task(env->dst_cpu);
         else if (busiest->load_per_task > local->load_per_task)
                 imbn = 1;
 
         scaled_busy_load_per_task =
                 (busiest->load_per_task * SCHED_CAPACITY_SCALE) /
                 busiest->group_capacity;
 
         if (busiest->avg_load + scaled_busy_load_per_task >=
             local->avg_load + (scaled_busy_load_per_task * imbn)) {
                 env->imbalance = busiest->load_per_task;
                 return;
         }
 
         /*
          * OK, we don't have enough imbalance to justify moving tasks,
          * however we may be able to increase total CPU capacity used by
          * moving them.
          */
 
         capa_now += busiest->group_capacity *
                         min(busiest->load_per_task, busiest->avg_load);
         capa_now += local->group_capacity *
                         min(local->load_per_task, local->avg_load);