FreeBSD/Linux Kernel Cross Reference
sys/kernel/sched_rt.c

     /*
      * Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
      * policies)
      */
     
     #ifdef CONFIG_RT_GROUP_SCHED
     
     #define rt_entity_is_task(rt_se) (!(rt_se)->my_q)
     
    static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
    {
    #ifdef CONFIG_SCHED_DEBUG
            WARN_ON_ONCE(!rt_entity_is_task(rt_se));
    #endif
            return container_of(rt_se, struct task_struct, rt);
    }
    
    static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
    {
            return rt_rq->rq;
    }
    
    static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
    {
            return rt_se->rt_rq;
    }
    
    #else /* CONFIG_RT_GROUP_SCHED */
    
    #define rt_entity_is_task(rt_se) (1)
    
    static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
    {
            return container_of(rt_se, struct task_struct, rt);
    }
    
    static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
    {
            return container_of(rt_rq, struct rq, rt);
    }
    
    static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
    {
            struct task_struct *p = rt_task_of(rt_se);
            struct rq *rq = task_rq(p);
    
            return &rq->rt;
    }
    
    #endif /* CONFIG_RT_GROUP_SCHED */
    
    #ifdef CONFIG_SMP
    
    static inline int rt_overloaded(struct rq *rq)
    {
            return atomic_read(&rq->rd->rto_count);
    }
    
    static inline void rt_set_overload(struct rq *rq)
    {
            if (!rq->online)
                    return;
    
            cpumask_set_cpu(rq->cpu, rq->rd->rto_mask);
            /*
             * Make sure the mask is visible before we set
             * the overload count. That is checked to determine
             * if we should look at the mask. It would be a shame
             * if we looked at the mask, but the mask was not
             * updated yet.
             */
            wmb();
            atomic_inc(&rq->rd->rto_count);
    }
    
    static inline void rt_clear_overload(struct rq *rq)
    {
            if (!rq->online)
                    return;
    
            /* the order here really doesn't matter */
            atomic_dec(&rq->rd->rto_count);
            cpumask_clear_cpu(rq->cpu, rq->rd->rto_mask);
    }
    
    static void update_rt_migration(struct rt_rq *rt_rq)
    {
            if (rt_rq->rt_nr_migratory && rt_rq->rt_nr_total > 1) {
                    if (!rt_rq->overloaded) {
                            rt_set_overload(rq_of_rt_rq(rt_rq));
                            rt_rq->overloaded = 1;
                    }
            } else if (rt_rq->overloaded) {
                    rt_clear_overload(rq_of_rt_rq(rt_rq));
                    rt_rq->overloaded = 0;
            }
    }
    
    static void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
           if (!rt_entity_is_task(rt_se))
                   return;
   
           rt_rq = &rq_of_rt_rq(rt_rq)->rt;
   
           rt_rq->rt_nr_total++;
           if (rt_se->nr_cpus_allowed > 1)
                   rt_rq->rt_nr_migratory++;
   
           update_rt_migration(rt_rq);
   }
   
   static void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
           if (!rt_entity_is_task(rt_se))
                   return;
   
           rt_rq = &rq_of_rt_rq(rt_rq)->rt;
   
           rt_rq->rt_nr_total--;
           if (rt_se->nr_cpus_allowed > 1)
                   rt_rq->rt_nr_migratory--;
   
           update_rt_migration(rt_rq);
   }
   
   static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
   {
           plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);
           plist_node_init(&p->pushable_tasks, p->prio);
           plist_add(&p->pushable_tasks, &rq->rt.pushable_tasks);
   }
   
   static void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
   {
           plist_del(&p->pushable_tasks, &rq->rt.pushable_tasks);
   }
   
   static inline int has_pushable_tasks(struct rq *rq)
   {
           return !plist_head_empty(&rq->rt.pushable_tasks);
   }
   
   #else
   
   static inline void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
   {
   }
   
   static inline void dequeue_pushable_task(struct rq *rq, struct task_struct *p)
   {
   }
   
   static inline
   void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
   }
   
   static inline
   void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
   }
   
   #endif /* CONFIG_SMP */
   
   static inline int on_rt_rq(struct sched_rt_entity *rt_se)
   {
           return !list_empty(&rt_se->run_list);
   }
   
   #ifdef CONFIG_RT_GROUP_SCHED
   
   static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
   {
           if (!rt_rq->tg)
                   return RUNTIME_INF;
   
           return rt_rq->rt_runtime;
   }
   
   static inline u64 sched_rt_period(struct rt_rq *rt_rq)
   {
           return ktime_to_ns(rt_rq->tg->rt_bandwidth.rt_period);
   }
   
   typedef struct task_group *rt_rq_iter_t;
   
   static inline struct task_group *next_task_group(struct task_group *tg)
   {
           do {
                   tg = list_entry_rcu(tg->list.next,
                           typeof(struct task_group), list);
           } while (&tg->list != &task_groups && task_group_is_autogroup(tg));
   
           if (&tg->list == &task_groups)
                   tg = NULL;
   
           return tg;
   }
   
   #define for_each_rt_rq(rt_rq, iter, rq)                                 \
           for (iter = container_of(&task_groups, typeof(*iter), list);    \
                   (iter = next_task_group(iter)) &&                       \
                   (rt_rq = iter->rt_rq[cpu_of(rq)]);)
   
   static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
   {
           list_add_rcu(&rt_rq->leaf_rt_rq_list,
                           &rq_of_rt_rq(rt_rq)->leaf_rt_rq_list);
   }
   
   static inline void list_del_leaf_rt_rq(struct rt_rq *rt_rq)
   {
           list_del_rcu(&rt_rq->leaf_rt_rq_list);
   }
   
   #define for_each_leaf_rt_rq(rt_rq, rq) \
           list_for_each_entry_rcu(rt_rq, &rq->leaf_rt_rq_list, leaf_rt_rq_list)
   
   #define for_each_sched_rt_entity(rt_se) \
           for (; rt_se; rt_se = rt_se->parent)
   
   static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
   {
           return rt_se->my_q;
   }
   
   static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head);
   static void dequeue_rt_entity(struct sched_rt_entity *rt_se);
   
   static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
   {
           struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
           struct sched_rt_entity *rt_se;
   
           int cpu = cpu_of(rq_of_rt_rq(rt_rq));
   
           rt_se = rt_rq->tg->rt_se[cpu];
   
           if (rt_rq->rt_nr_running) {
                   if (rt_se && !on_rt_rq(rt_se))
                           enqueue_rt_entity(rt_se, false);
                   if (rt_rq->highest_prio.curr < curr->prio)
                           resched_task(curr);
           }
   }
   
   static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
   {
           struct sched_rt_entity *rt_se;
           int cpu = cpu_of(rq_of_rt_rq(rt_rq));
   
           rt_se = rt_rq->tg->rt_se[cpu];
   
           if (rt_se && on_rt_rq(rt_se))
                   dequeue_rt_entity(rt_se);
   }
   
   static inline int rt_rq_throttled(struct rt_rq *rt_rq)
   {
           return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;
   }
   
   static int rt_se_boosted(struct sched_rt_entity *rt_se)
   {
           struct rt_rq *rt_rq = group_rt_rq(rt_se);
           struct task_struct *p;
   
           if (rt_rq)
                   return !!rt_rq->rt_nr_boosted;
   
           p = rt_task_of(rt_se);
           return p->prio != p->normal_prio;
   }
   
   #ifdef CONFIG_SMP
   static inline const struct cpumask *sched_rt_period_mask(void)
   {
           return cpu_rq(smp_processor_id())->rd->span;
   }
   #else
   static inline const struct cpumask *sched_rt_period_mask(void)
   {
           return cpu_online_mask;
   }
   #endif
   
   static inline
   struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
   {
           return container_of(rt_b, struct task_group, rt_bandwidth)->rt_rq[cpu];
   }
   
   static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
   {
           return &rt_rq->tg->rt_bandwidth;
   }
   
   #else /* !CONFIG_RT_GROUP_SCHED */
   
   static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
   {
           return rt_rq->rt_runtime;
   }
   
   static inline u64 sched_rt_period(struct rt_rq *rt_rq)
   {
           return ktime_to_ns(def_rt_bandwidth.rt_period);
   }
   
   typedef struct rt_rq *rt_rq_iter_t;
   
   #define for_each_rt_rq(rt_rq, iter, rq) \
           for ((void) iter, rt_rq = &rq->rt; rt_rq; rt_rq = NULL)
   
   static inline void list_add_leaf_rt_rq(struct rt_rq *rt_rq)
   {
   }
   
   static inline void list_del_leaf_rt_rq(struct rt_rq *rt_rq)
   {
   }
   
   #define for_each_leaf_rt_rq(rt_rq, rq) \
           for (rt_rq = &rq->rt; rt_rq; rt_rq = NULL)
   
   #define for_each_sched_rt_entity(rt_se) \
           for (; rt_se; rt_se = NULL)
   
   static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
   {
           return NULL;
   }
   
   static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
   {
           if (rt_rq->rt_nr_running)
                   resched_task(rq_of_rt_rq(rt_rq)->curr);
   }
   
   static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
   {
   }
   
   static inline int rt_rq_throttled(struct rt_rq *rt_rq)
   {
           return rt_rq->rt_throttled;
   }
   
   static inline const struct cpumask *sched_rt_period_mask(void)
   {
           return cpu_online_mask;
   }
   
   static inline
   struct rt_rq *sched_rt_period_rt_rq(struct rt_bandwidth *rt_b, int cpu)
   {
           return &cpu_rq(cpu)->rt;
   }
   
   static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
   {
           return &def_rt_bandwidth;
   }
   
   #endif /* CONFIG_RT_GROUP_SCHED */
   
   #ifdef CONFIG_SMP
   /*
    * We ran out of runtime, see if we can borrow some from our neighbours.
    */
   static int do_balance_runtime(struct rt_rq *rt_rq)
   {
           struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
           struct root_domain *rd = cpu_rq(smp_processor_id())->rd;
           int i, weight, more = 0;
           u64 rt_period;
   
           weight = cpumask_weight(rd->span);
   
           raw_spin_lock(&rt_b->rt_runtime_lock);
           rt_period = ktime_to_ns(rt_b->rt_period);
           for_each_cpu(i, rd->span) {
                   struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
                   s64 diff;
   
                   if (iter == rt_rq)
                           continue;
   
                   raw_spin_lock(&iter->rt_runtime_lock);
                   /*
                    * Either all rqs have inf runtime and there's nothing to steal
                    * or __disable_runtime() below sets a specific rq to inf to
                    * indicate its been disabled and disalow stealing.
                    */
                   if (iter->rt_runtime == RUNTIME_INF)
                           goto next;
   
                   /*
                    * From runqueues with spare time, take 1/n part of their
                    * spare time, but no more than our period.
                    */
                   diff = iter->rt_runtime - iter->rt_time;
                   if (diff > 0) {
                           diff = div_u64((u64)diff, weight);
                           if (rt_rq->rt_runtime + diff > rt_period)
                                   diff = rt_period - rt_rq->rt_runtime;
                           iter->rt_runtime -= diff;
                           rt_rq->rt_runtime += diff;
                           more = 1;
                           if (rt_rq->rt_runtime == rt_period) {
                                   raw_spin_unlock(&iter->rt_runtime_lock);
                                   break;
                           }
                   }
   next:
                   raw_spin_unlock(&iter->rt_runtime_lock);
           }
           raw_spin_unlock(&rt_b->rt_runtime_lock);
   
           return more;
   }
   
   /*
    * Ensure this RQ takes back all the runtime it lend to its neighbours.
    */
   static void __disable_runtime(struct rq *rq)
   {
           struct root_domain *rd = rq->rd;
           rt_rq_iter_t iter;
           struct rt_rq *rt_rq;
   
           if (unlikely(!scheduler_running))
                   return;
   
           for_each_rt_rq(rt_rq, iter, rq) {
                   struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
                   s64 want;
                   int i;
   
                   raw_spin_lock(&rt_b->rt_runtime_lock);
                   raw_spin_lock(&rt_rq->rt_runtime_lock);
                   /*
                    * Either we're all inf and nobody needs to borrow, or we're
                    * already disabled and thus have nothing to do, or we have
                    * exactly the right amount of runtime to take out.
                    */
                   if (rt_rq->rt_runtime == RUNTIME_INF ||
                                   rt_rq->rt_runtime == rt_b->rt_runtime)
                           goto balanced;
                   raw_spin_unlock(&rt_rq->rt_runtime_lock);
   
                   /*
                    * Calculate the difference between what we started out with
                    * and what we current have, that's the amount of runtime
                    * we lend and now have to reclaim.
                    */
                   want = rt_b->rt_runtime - rt_rq->rt_runtime;
   
                   /*
                    * Greedy reclaim, take back as much as we can.
                    */
                   for_each_cpu(i, rd->span) {
                           struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i);
                           s64 diff;
   
                           /*
                            * Can't reclaim from ourselves or disabled runqueues.
                            */
                           if (iter == rt_rq || iter->rt_runtime == RUNTIME_INF)
                                   continue;
   
                           raw_spin_lock(&iter->rt_runtime_lock);
                           if (want > 0) {
                                   diff = min_t(s64, iter->rt_runtime, want);
                                   iter->rt_runtime -= diff;
                                   want -= diff;
                           } else {
                                   iter->rt_runtime -= want;
                                   want -= want;
                           }
                           raw_spin_unlock(&iter->rt_runtime_lock);
   
                           if (!want)
                                   break;
                   }
   
                   raw_spin_lock(&rt_rq->rt_runtime_lock);
                   /*
                    * We cannot be left wanting - that would mean some runtime
                    * leaked out of the system.
                    */
                   BUG_ON(want);
   balanced:
                   /*
                    * Disable all the borrow logic by pretending we have inf
                    * runtime - in which case borrowing doesn't make sense.
                    */
                   rt_rq->rt_runtime = RUNTIME_INF;
                   raw_spin_unlock(&rt_rq->rt_runtime_lock);
                   raw_spin_unlock(&rt_b->rt_runtime_lock);
           }
   }
   
   static void disable_runtime(struct rq *rq)
   {
           unsigned long flags;
   
           raw_spin_lock_irqsave(&rq->lock, flags);
           __disable_runtime(rq);
           raw_spin_unlock_irqrestore(&rq->lock, flags);
   }
   
   static void __enable_runtime(struct rq *rq)
   {
           rt_rq_iter_t iter;
           struct rt_rq *rt_rq;
   
           if (unlikely(!scheduler_running))
                   return;
   
           /*
            * Reset each runqueue's bandwidth settings
            */
           for_each_rt_rq(rt_rq, iter, rq) {
                   struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
   
                   raw_spin_lock(&rt_b->rt_runtime_lock);
                   raw_spin_lock(&rt_rq->rt_runtime_lock);
                   rt_rq->rt_runtime = rt_b->rt_runtime;
                   rt_rq->rt_time = 0;
                   rt_rq->rt_throttled = 0;
                   raw_spin_unlock(&rt_rq->rt_runtime_lock);
                   raw_spin_unlock(&rt_b->rt_runtime_lock);
           }
   }
   
   static void enable_runtime(struct rq *rq)
   {
           unsigned long flags;
   
           raw_spin_lock_irqsave(&rq->lock, flags);
           __enable_runtime(rq);
           raw_spin_unlock_irqrestore(&rq->lock, flags);
   }
   
   static int balance_runtime(struct rt_rq *rt_rq)
   {
           int more = 0;
   
           if (rt_rq->rt_time > rt_rq->rt_runtime) {
                   raw_spin_unlock(&rt_rq->rt_runtime_lock);
                   more = do_balance_runtime(rt_rq);
                   raw_spin_lock(&rt_rq->rt_runtime_lock);
           }
   
           return more;
   }
   #else /* !CONFIG_SMP */
   static inline int balance_runtime(struct rt_rq *rt_rq)
   {
           return 0;
   }
   #endif /* CONFIG_SMP */
   
   static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
   {
           int i, idle = 1;
           const struct cpumask *span;
   
           if (!rt_bandwidth_enabled() || rt_b->rt_runtime == RUNTIME_INF)
                   return 1;
   
           span = sched_rt_period_mask();
           for_each_cpu(i, span) {
                   int enqueue = 0;
                   struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i);
                   struct rq *rq = rq_of_rt_rq(rt_rq);
   
                   raw_spin_lock(&rq->lock);
                   if (rt_rq->rt_time) {
                           u64 runtime;
   
                           raw_spin_lock(&rt_rq->rt_runtime_lock);
                           if (rt_rq->rt_throttled)
                                   balance_runtime(rt_rq);
                           runtime = rt_rq->rt_runtime;
                           rt_rq->rt_time -= min(rt_rq->rt_time, overrun*runtime);
                           if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) {
                                   rt_rq->rt_throttled = 0;
                                   enqueue = 1;
   
                                   /*
                                    * Force a clock update if the CPU was idle,
                                    * lest wakeup -> unthrottle time accumulate.
                                    */
                                   if (rt_rq->rt_nr_running && rq->curr == rq->idle)
                                           rq->skip_clock_update = -1;
                           }
                           if (rt_rq->rt_time || rt_rq->rt_nr_running)
                                   idle = 0;
                           raw_spin_unlock(&rt_rq->rt_runtime_lock);
                   } else if (rt_rq->rt_nr_running) {
                           idle = 0;
                           if (!rt_rq_throttled(rt_rq))
                                   enqueue = 1;
                   }
   
                   if (enqueue)
                           sched_rt_rq_enqueue(rt_rq);
                   raw_spin_unlock(&rq->lock);
           }
   
           return idle;
   }
   
   static inline int rt_se_prio(struct sched_rt_entity *rt_se)
   {
   #ifdef CONFIG_RT_GROUP_SCHED
           struct rt_rq *rt_rq = group_rt_rq(rt_se);
   
           if (rt_rq)
                   return rt_rq->highest_prio.curr;
   #endif
   
           return rt_task_of(rt_se)->prio;
   }
   
   static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
   {
           u64 runtime = sched_rt_runtime(rt_rq);
   
           if (rt_rq->rt_throttled)
                   return rt_rq_throttled(rt_rq);
   
           if (sched_rt_runtime(rt_rq) >= sched_rt_period(rt_rq))
                   return 0;
   
           balance_runtime(rt_rq);
           runtime = sched_rt_runtime(rt_rq);
           if (runtime == RUNTIME_INF)
                   return 0;
   
           if (rt_rq->rt_time > runtime) {
                   rt_rq->rt_throttled = 1;
                   if (rt_rq_throttled(rt_rq)) {
                           sched_rt_rq_dequeue(rt_rq);
                           return 1;
                   }
           }
   
           return 0;
   }
   
   /*
    * Update the current task's runtime statistics. Skip current tasks that
    * are not in our scheduling class.
    */
   static void update_curr_rt(struct rq *rq)
   {
           struct task_struct *curr = rq->curr;
           struct sched_rt_entity *rt_se = &curr->rt;
           struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
           u64 delta_exec;
   
           if (curr->sched_class != &rt_sched_class)
                   return;
   
           delta_exec = rq->clock_task - curr->se.exec_start;
           if (unlikely((s64)delta_exec < 0))
                   delta_exec = 0;
   
           schedstat_set(curr->se.statistics.exec_max, max(curr->se.statistics.exec_max, delta_exec));
   
           curr->se.sum_exec_runtime += delta_exec;
           account_group_exec_runtime(curr, delta_exec);
   
           curr->se.exec_start = rq->clock_task;
           cpuacct_charge(curr, delta_exec);
   
           sched_rt_avg_update(rq, delta_exec);
   
           if (!rt_bandwidth_enabled())
                   return;
   
           for_each_sched_rt_entity(rt_se) {
                   rt_rq = rt_rq_of_se(rt_se);
   
                   if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
                           raw_spin_lock(&rt_rq->rt_runtime_lock);
                           rt_rq->rt_time += delta_exec;
                           if (sched_rt_runtime_exceeded(rt_rq))
                                   resched_task(curr);
                           raw_spin_unlock(&rt_rq->rt_runtime_lock);
                   }
           }
   }
   
   #if defined CONFIG_SMP
   
   static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu);
   
   static inline int next_prio(struct rq *rq)
   {
           struct task_struct *next = pick_next_highest_task_rt(rq, rq->cpu);
   
           if (next && rt_prio(next->prio))
                   return next->prio;
           else
                   return MAX_RT_PRIO;
   }
   
   static void
   inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
   {
           struct rq *rq = rq_of_rt_rq(rt_rq);
   
           if (prio < prev_prio) {
   
                   /*
                    * If the new task is higher in priority than anything on the
                    * run-queue, we know that the previous high becomes our
                    * next-highest.
                    */
                   rt_rq->highest_prio.next = prev_prio;
   
                   if (rq->online)
                           cpupri_set(&rq->rd->cpupri, rq->cpu, prio);
   
           } else if (prio == rt_rq->highest_prio.curr)
                   /*
                    * If the next task is equal in priority to the highest on
                    * the run-queue, then we implicitly know that the next highest
                    * task cannot be any lower than current
                    */
                   rt_rq->highest_prio.next = prio;
           else if (prio < rt_rq->highest_prio.next)
                   /*
                    * Otherwise, we need to recompute next-highest
                    */
                   rt_rq->highest_prio.next = next_prio(rq);
   }
   
   static void
   dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
   {
           struct rq *rq = rq_of_rt_rq(rt_rq);
   
           if (rt_rq->rt_nr_running && (prio <= rt_rq->highest_prio.next))
                   rt_rq->highest_prio.next = next_prio(rq);
   
           if (rq->online && rt_rq->highest_prio.curr != prev_prio)
                   cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio.curr);
   }
   
   #else /* CONFIG_SMP */
   
   static inline
   void inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) {}
   static inline
   void dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) {}
   
   #endif /* CONFIG_SMP */
   
   #if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
   static void
   inc_rt_prio(struct rt_rq *rt_rq, int prio)
   {
           int prev_prio = rt_rq->highest_prio.curr;
   
           if (prio < prev_prio)
                   rt_rq->highest_prio.curr = prio;
   
           inc_rt_prio_smp(rt_rq, prio, prev_prio);
   }
   
   static void
   dec_rt_prio(struct rt_rq *rt_rq, int prio)
   {
           int prev_prio = rt_rq->highest_prio.curr;
   
           if (rt_rq->rt_nr_running) {
   
                   WARN_ON(prio < prev_prio);
   
                   /*
                    * This may have been our highest task, and therefore
                    * we may have some recomputation to do
                    */
                   if (prio == prev_prio) {
                           struct rt_prio_array *array = &rt_rq->active;
   
                           rt_rq->highest_prio.curr =
                                   sched_find_first_bit(array->bitmap);
                   }
   
           } else
                   rt_rq->highest_prio.curr = MAX_RT_PRIO;
   
           dec_rt_prio_smp(rt_rq, prio, prev_prio);
   }
   
   #else
   
   static inline void inc_rt_prio(struct rt_rq *rt_rq, int prio) {}
   static inline void dec_rt_prio(struct rt_rq *rt_rq, int prio) {}
   
   #endif /* CONFIG_SMP || CONFIG_RT_GROUP_SCHED */
   
   #ifdef CONFIG_RT_GROUP_SCHED
   
   static void
   inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
           if (rt_se_boosted(rt_se))
                   rt_rq->rt_nr_boosted++;
   
           if (rt_rq->tg)
                   start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
   }
   
   static void
   dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
           if (rt_se_boosted(rt_se))
                   rt_rq->rt_nr_boosted--;
   
           WARN_ON(!rt_rq->rt_nr_running && rt_rq->rt_nr_boosted);
   }
   
   #else /* CONFIG_RT_GROUP_SCHED */
   
   static void
   inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
           start_rt_bandwidth(&def_rt_bandwidth);
   }
   
   static inline
   void dec_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq) {}
   
   #endif /* CONFIG_RT_GROUP_SCHED */
   
   static inline
   void inc_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
           int prio = rt_se_prio(rt_se);
   
           WARN_ON(!rt_prio(prio));
           rt_rq->rt_nr_running++;
   
           inc_rt_prio(rt_rq, prio);
           inc_rt_migration(rt_se, rt_rq);
           inc_rt_group(rt_se, rt_rq);
   }
   
   static inline
   void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
   {
           WARN_ON(!rt_prio(rt_se_prio(rt_se)));
           WARN_ON(!rt_rq->rt_nr_running);
           rt_rq->rt_nr_running--;
   
           dec_rt_prio(rt_rq, rt_se_prio(rt_se));
           dec_rt_migration(rt_se, rt_rq);
           dec_rt_group(rt_se, rt_rq);
   }
   
   static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
   {
           struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
           struct rt_prio_array *array = &rt_rq->active;
           struct rt_rq *group_rq = group_rt_rq(rt_se);
           struct list_head *queue = array->queue + rt_se_prio(rt_se);
   
           /*
            * Don't enqueue the group if its throttled, or when empty.
            * The latter is a consequence of the former when a child group
            * get throttled and the current group doesn't have any other
            * active members.
            */
           if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
                   return;
   
           if (!rt_rq->rt_nr_running)
                   list_add_leaf_rt_rq(rt_rq);
   
           if (head)
                   list_add(&rt_se->run_list, queue);
           else
                   list_add_tail(&rt_se->run_list, queue);
           __set_bit(rt_se_prio(rt_se), array->bitmap);
   
           inc_rt_tasks(rt_se, rt_rq);
   }
   
   static void __dequeue_rt_entity(struct sched_rt_entity *rt_se)
   {
           struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
           struct rt_prio_array *array = &rt_rq->active;
   
           list_del_init(&rt_se->run_list);
           if (list_empty(array->queue + rt_se_prio(rt_se)))
                   __clear_bit(rt_se_prio(rt_se), array->bitmap);
   
           dec_rt_tasks(rt_se, rt_rq);
           if (!rt_rq->rt_nr_running)
                   list_del_leaf_rt_rq(rt_rq);
   }
   
   /*
    * Because the prio of an upper entry depends on the lower
    * entries, we must remove entries top - down.
    */
   static void dequeue_rt_stack(struct sched_rt_entity *rt_se)
   {
           struct sched_rt_entity *back = NULL;
   
           for_each_sched_rt_entity(rt_se) {
                   rt_se->back = back;
                   back = rt_se;
           }
   
           for (rt_se = back; rt_se; rt_se = rt_se->back) {
                   if (on_rt_rq(rt_se))
                           __dequeue_rt_entity(rt_se);
           }
   }
   
   static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
   {
           dequeue_rt_stack(rt_se);
           for_each_sched_rt_entity(rt_se)
                   __enqueue_rt_entity(rt_se, head);
   }
   
   static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
   {
           dequeue_rt_stack(rt_se);
   
           for_each_sched_rt_entity(rt_se) {
                   struct rt_rq *rt_rq = group_rt_rq(rt_se);
   
                   if (rt_rq && rt_rq->rt_nr_running)
                           __enqueue_rt_entity(rt_se, false);
           }
   }
   
   /*
    * Adding/removing a task to/from a priority array:
    */
   static void
   enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
   {
           struct sched_rt_entity *rt_se = &p->rt;
   
           if (flags & ENQUEUE_WAKEUP)
                   rt_se->timeout = 0;
   
           enqueue_rt_entity(rt_se, flags & ENQUEUE_HEAD);
   
           if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1)
                   enqueue_pushable_task(rq, p);
   }
   
   static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
   {
           struct sched_rt_entity *rt_se = &p->rt;
   
           update_curr_rt(rq);
           dequeue_rt_entity(rt_se);
   
           dequeue_pushable_task(rq, p);
   }
   
   /*
    * Put task to the end of the run list without the overhead of dequeue
    * followed by enqueue.
    */
   static void
   requeue_rt_entity(struct rt_rq *rt_rq, struct sched_rt_entity *rt_se, int head)
   {
           if (on_rt_rq(rt_se)) {
                   struct rt_prio_array *array = &rt_rq->active;
                   struct list_head *queue = array->queue + rt_se_prio(rt_se);
   
                   if (head)
                           list_move(&rt_se->run_list, queue);
                   else
                           list_move_tail(&rt_se->run_list, queue);
           }
   }
   
   static void requeue_task_rt(struct rq *rq, struct task_struct *p, int head)
   {
           struct sched_rt_entity *rt_se = &p->rt;
           struct rt_rq *rt_rq;
   
           for_each_sched_rt_entity(rt_se) {
                  rt_rq = rt_rq_of_se(rt_se);
                  requeue_rt_entity(rt_rq, rt_se, head);
          }
  }
  
  static void yield_task_rt(struct rq *rq)
  {
          requeue_task_rt(rq, rq->curr, 0);
  }
  
  #ifdef CONFIG_SMP
  static int find_lowest_rq(struct task_struct *task);
  
  static int
  select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)
  {
          struct task_struct *curr;
          struct rq *rq;
          int cpu;
  
          if (sd_flag != SD_BALANCE_WAKE)
                  return smp_processor_id();
  
          cpu = task_cpu(p);
          rq = cpu_rq(cpu);
  
          rcu_read_lock();
          curr = ACCESS_ONCE(rq->curr); /* unlocked access */
  
          /*
           * If the current task on @p's runqueue is an RT task, then
           * try to see if we can wake this RT task up on another
           * runqueue. Otherwise simply start this RT task
           * on its current runqueue.
           *
           * We want to avoid overloading runqueues. If the woken
           * task is a higher priority, then it will stay on this CPU
           * and the lower prio task should be moved to another CPU.
           * Even though this will probably make the lower prio task
           * lose its cache, we do not want to bounce a higher task
           * around just because it gave up its CPU, perhaps for a
           * lock?
           *
           * For equal prio tasks, we just let the scheduler sort it out.
           *
           * Otherwise, just let it ride on the affined RQ and the
           * post-schedule router will push the preempted task away
           *
           * This test is optimistic, if we get it wrong the load-balancer
           * will have to sort it out.
           */
          if (curr && unlikely(rt_task(curr)) &&
              (curr->rt.nr_cpus_allowed < 2 ||
               curr->prio < p->prio) &&
              (p->rt.nr_cpus_allowed > 1)) {
                  int target = find_lowest_rq(p);
  
                  if (target != -1)
                          cpu = target;
          }
          rcu_read_unlock();
  
          return cpu;
  }
  
  static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
  {
          if (rq->curr->rt.nr_cpus_allowed == 1)
                  return;
  
          if (p->rt.nr_cpus_allowed != 1
              && cpupri_find(&rq->rd->cpupri, p, NULL))
                  return;
  
          if (!cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
                  return;
  
          /*
           * There appears to be other cpus that can accept
           * current and none to run 'p', so lets reschedule
           * to try and push current away:
           */
          requeue_task_rt(rq, p, 1);
          resched_task(rq->curr);
  }
  
  #endif /* CONFIG_SMP */
  
  /*
   * Preempt the current task with a newly woken task if needed:
   */
  static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flags)
  {
          if (p->prio < rq->curr->prio) {
                  resched_task(rq->curr);
                  return;
          }
  
  #ifdef CONFIG_SMP
          /*
           * If:
           *
           * - the newly woken task is of equal priority to the current task
           * - the newly woken task is non-migratable while current is migratable
           * - current will be preempted on the next reschedule
           *
           * we should check to see if current can readily move to a different
           * cpu.  If so, we will reschedule to allow the push logic to try
           * to move current somewhere else, making room for our non-migratable
           * task.
           */
          if (p->prio == rq->curr->prio && !test_tsk_need_resched(rq->curr))
                  check_preempt_equal_prio(rq, p);
  #endif
  }
  
  static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
                                                     struct rt_rq *rt_rq)
  {
          struct rt_prio_array *array = &rt_rq->active;
          struct sched_rt_entity *next = NULL;
          struct list_head *queue;
          int idx;
  
          idx = sched_find_first_bit(array->bitmap);
          BUG_ON(idx >= MAX_RT_PRIO);
  
          queue = array->queue + idx;
          next = list_entry(queue->next, struct sched_rt_entity, run_list);
  
          return next;
  }
  
  static struct task_struct *_pick_next_task_rt(struct rq *rq)
  {
          struct sched_rt_entity *rt_se;
          struct task_struct *p;
          struct rt_rq *rt_rq;
  
          rt_rq = &rq->rt;
  
          if (!rt_rq->rt_nr_running)
                  return NULL;
  
          if (rt_rq_throttled(rt_rq))
                  return NULL;
  
          do {
                  rt_se = pick_next_rt_entity(rq, rt_rq);
                  BUG_ON(!rt_se);
                  rt_rq = group_rt_rq(rt_se);
          } while (rt_rq);
  
          p = rt_task_of(rt_se);
          p->se.exec_start = rq->clock_task;
  
          return p;
  }
  
  static struct task_struct *pick_next_task_rt(struct rq *rq)
  {
          struct task_struct *p = _pick_next_task_rt(rq);
  
          /* The running task is never eligible for pushing */
          if (p)
                  dequeue_pushable_task(rq, p);
  
  #ifdef CONFIG_SMP
          /*
           * We detect this state here so that we can avoid taking the RQ
           * lock again later if there is no need to push
           */
          rq->post_schedule = has_pushable_tasks(rq);
  #endif
  
          return p;
  }
  
  static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
  {
          update_curr_rt(rq);
          p->se.exec_start = 0;
  
          /*
           * The previous task needs to be made eligible for pushing
           * if it is still active
           */
          if (on_rt_rq(&p->rt) && p->rt.nr_cpus_allowed > 1)
                  enqueue_pushable_task(rq, p);
  }
  
  #ifdef CONFIG_SMP
  
  /* Only try algorithms three times */
  #define RT_MAX_TRIES 3
  
  static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
  
  static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
  {
          if (!task_running(rq, p) &&
              (cpu < 0 || cpumask_test_cpu(cpu, &p->cpus_allowed)) &&
              (p->rt.nr_cpus_allowed > 1))
                  return 1;
          return 0;
  }
  
  /* Return the second highest RT task, NULL otherwise */
  static struct task_struct *pick_next_highest_task_rt(struct rq *rq, int cpu)
  {
          struct task_struct *next = NULL;
          struct sched_rt_entity *rt_se;
          struct rt_prio_array *array;
          struct rt_rq *rt_rq;
          int idx;
  
          for_each_leaf_rt_rq(rt_rq, rq) {
                  array = &rt_rq->active;
                  idx = sched_find_first_bit(array->bitmap);
  next_idx:
                  if (idx >= MAX_RT_PRIO)
                          continue;
                  if (next && next->prio < idx)
                          continue;
                  list_for_each_entry(rt_se, array->queue + idx, run_list) {
                          struct task_struct *p;
  
                          if (!rt_entity_is_task(rt_se))
                                  continue;
  
                          p = rt_task_of(rt_se);
                          if (pick_rt_task(rq, p, cpu)) {
                                  next = p;
                                  break;
                          }
                  }
                  if (!next) {
                          idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
                          goto next_idx;
                  }
          }
  
          return next;
  }
  
  static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);
  
  static int find_lowest_rq(struct task_struct *task)
  {
          struct sched_domain *sd;
          struct cpumask *lowest_mask = __get_cpu_var(local_cpu_mask);
          int this_cpu = smp_processor_id();
          int cpu      = task_cpu(task);
  
          /* Make sure the mask is initialized first */
          if (unlikely(!lowest_mask))
                  return -1;
  
          if (task->rt.nr_cpus_allowed == 1)
                  return -1; /* No other targets possible */
  
          if (!cpupri_find(&task_rq(task)->rd->cpupri, task, lowest_mask))
                  return -1; /* No targets found */
  
          /*
           * At this point we have built a mask of cpus representing the
           * lowest priority tasks in the system.  Now we want to elect
           * the best one based on our affinity and topology.
           *
           * We prioritize the last cpu that the task executed on since
           * it is most likely cache-hot in that location.
           */
          if (cpumask_test_cpu(cpu, lowest_mask))
                  return cpu;
  
          /*
           * Otherwise, we consult the sched_domains span maps to figure
           * out which cpu is logically closest to our hot cache data.
           */
          if (!cpumask_test_cpu(this_cpu, lowest_mask))
                  this_cpu = -1; /* Skip this_cpu opt if not among lowest */
  
          rcu_read_lock();
          for_each_domain(cpu, sd) {
                  if (sd->flags & SD_WAKE_AFFINE) {
                          int best_cpu;
  
                          /*
                           * "this_cpu" is cheaper to preempt than a
                           * remote processor.
                           */
                          if (this_cpu != -1 &&
                              cpumask_test_cpu(this_cpu, sched_domain_span(sd))) {
                                  rcu_read_unlock();
                                  return this_cpu;
                          }
  
                          best_cpu = cpumask_first_and(lowest_mask,
                                                       sched_domain_span(sd));
                          if (best_cpu < nr_cpu_ids) {
                                  rcu_read_unlock();
                                  return best_cpu;
                          }
                  }
          }
          rcu_read_unlock();
  
          /*
           * And finally, if there were no matches within the domains
           * just give the caller *something* to work with from the compatible
           * locations.
           */
          if (this_cpu != -1)
                  return this_cpu;
  
          cpu = cpumask_any(lowest_mask);
          if (cpu < nr_cpu_ids)
                  return cpu;
          return -1;
  }
  
  /* Will lock the rq it finds */
  static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
  {
          struct rq *lowest_rq = NULL;
          int tries;
          int cpu;
  
          for (tries = 0; tries < RT_MAX_TRIES; tries++) {
                  cpu = find_lowest_rq(task);
  
                  if ((cpu == -1) || (cpu == rq->cpu))
                          break;
  
                  lowest_rq = cpu_rq(cpu);
  
                  /* if the prio of this runqueue changed, try again */
                  if (double_lock_balance(rq, lowest_rq)) {
                          /*
                           * We had to unlock the run queue. In
                           * the mean time, task could have
                           * migrated already or had its affinity changed.
                           * Also make sure that it wasn't scheduled on its rq.
                           */
                          if (unlikely(task_rq(task) != rq ||
                                       !cpumask_test_cpu(lowest_rq->cpu,
                                                         &task->cpus_allowed) ||
                                       task_running(rq, task) ||
                                       !task->on_rq)) {
  
                                  raw_spin_unlock(&lowest_rq->lock);
                                  lowest_rq = NULL;
                                  break;
                          }
                  }
  
                  /* If this rq is still suitable use it. */
                  if (lowest_rq->rt.highest_prio.curr > task->prio)
                          break;
  
                  /* try again */
                  double_unlock_balance(rq, lowest_rq);
                  lowest_rq = NULL;
          }
  
          return lowest_rq;
  }
  
  static struct task_struct *pick_next_pushable_task(struct rq *rq)
  {
          struct task_struct *p;
  
          if (!has_pushable_tasks(rq))
                  return NULL;
  
          p = plist_first_entry(&rq->rt.pushable_tasks,
                                struct task_struct, pushable_tasks);
  
          BUG_ON(rq->cpu != task_cpu(p));
          BUG_ON(task_current(rq, p));
          BUG_ON(p->rt.nr_cpus_allowed <= 1);
  
          BUG_ON(!p->on_rq);
          BUG_ON(!rt_task(p));
  
          return p;
  }
  
  /*
   * If the current CPU has more than one RT task, see if the non
   * running task can migrate over to a CPU that is running a task
   * of lesser priority.
   */
  static int push_rt_task(struct rq *rq)
  {
          struct task_struct *next_task;
          struct rq *lowest_rq;
  
          if (!rq->rt.overloaded)
                  return 0;
  
          next_task = pick_next_pushable_task(rq);
          if (!next_task)
                  return 0;
  
  retry:
          if (unlikely(next_task == rq->curr)) {
                  WARN_ON(1);
                  return 0;
          }
  
          /*
           * It's possible that the next_task slipped in of
           * higher priority than current. If that's the case
           * just reschedule current.
           */
          if (unlikely(next_task->prio < rq->curr->prio)) {
                  resched_task(rq->curr);
                  return 0;
          }
  
          /* We might release rq lock */
          get_task_struct(next_task);
  
          /* find_lock_lowest_rq locks the rq if found */
          lowest_rq = find_lock_lowest_rq(next_task, rq);
          if (!lowest_rq) {
                  struct task_struct *task;
                  /*
                   * find lock_lowest_rq releases rq->lock
                   * so it is possible that next_task has migrated.
                   *
                   * We need to make sure that the task is still on the same
                   * run-queue and is also still the next task eligible for
                   * pushing.
                   */
                  task = pick_next_pushable_task(rq);
                  if (task_cpu(next_task) == rq->cpu && task == next_task) {
                          /*
                           * If we get here, the task hasn't moved at all, but
                           * it has failed to push.  We will not try again,
                           * since the other cpus will pull from us when they
                           * are ready.
                           */
                          dequeue_pushable_task(rq, next_task);
                          goto out;
                  }
  
                  if (!task)
                          /* No more tasks, just exit */
                          goto out;
  
                  /*
                   * Something has shifted, try again.
                   */
                  put_task_struct(next_task);
                  next_task = task;
                  goto retry;
          }
  
          deactivate_task(rq, next_task, 0);
          set_task_cpu(next_task, lowest_rq->cpu);
          activate_task(lowest_rq, next_task, 0);
  
          resched_task(lowest_rq->curr);
  
          double_unlock_balance(rq, lowest_rq);
  
  out:
          put_task_struct(next_task);
  
          return 1;
  }
  
  static void push_rt_tasks(struct rq *rq)
  {
          /* push_rt_task will return true if it moved an RT */
          while (push_rt_task(rq))
                  ;
  }
  
  static int pull_rt_task(struct rq *this_rq)
  {
          int this_cpu = this_rq->cpu, ret = 0, cpu;
          struct task_struct *p;
          struct rq *src_rq;
  
          if (likely(!rt_overloaded(this_rq)))
                  return 0;
  
          for_each_cpu(cpu, this_rq->rd->rto_mask) {
                  if (this_cpu == cpu)
                          continue;
  
                  src_rq = cpu_rq(cpu);
  
                  /*
                   * Don't bother taking the src_rq->lock if the next highest
                   * task is known to be lower-priority than our current task.
                   * This may look racy, but if this value is about to go
                   * logically higher, the src_rq will push this task away.
                   * And if its going logically lower, we do not care
                   */
                  if (src_rq->rt.highest_prio.next >=
                      this_rq->rt.highest_prio.curr)
                          continue;
  
                  /*
                   * We can potentially drop this_rq's lock in
                   * double_lock_balance, and another CPU could
                   * alter this_rq
                   */
                  double_lock_balance(this_rq, src_rq);
  
                  /*
                   * Are there still pullable RT tasks?
                   */
                  if (src_rq->rt.rt_nr_running <= 1)
                          goto skip;
  
                  p = pick_next_highest_task_rt(src_rq, this_cpu);
  
                  /*
                   * Do we have an RT task that preempts
                   * the to-be-scheduled task?
                   */
                  if (p && (p->prio < this_rq->rt.highest_prio.curr)) {
                          WARN_ON(p == src_rq->curr);
                          WARN_ON(!p->on_rq);
  
                          /*
                           * There's a chance that p is higher in priority
                           * than what's currently running on its cpu.
                           * This is just that p is wakeing up and hasn't
                           * had a chance to schedule. We only pull
                           * p if it is lower in priority than the
                           * current task on the run queue
                           */
                          if (p->prio < src_rq->curr->prio)
                                  goto skip;
  
                          ret = 1;
  
                          deactivate_task(src_rq, p, 0);
                          set_task_cpu(p, this_cpu);
                          activate_task(this_rq, p, 0);
                          /*
                           * We continue with the search, just in
                           * case there's an even higher prio task
                           * in another runqueue. (low likelihood
                           * but possible)
                           */
                  }
  skip:
                  double_unlock_balance(this_rq, src_rq);
          }
  
          return ret;
  }
  
  static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
  {
          /* Try to pull RT tasks here if we lower this rq's prio */
          if (rq->rt.highest_prio.curr > prev->prio)
                  pull_rt_task(rq);
  }
  
  static void post_schedule_rt(struct rq *rq)
  {
          push_rt_tasks(rq);
  }
  
  /*
   * If we are not running and we are not going to reschedule soon, we should
   * try to push tasks away now
   */
  static void task_woken_rt(struct rq *rq, struct task_struct *p)
  {
          if (!task_running(rq, p) &&
              !test_tsk_need_resched(rq->curr) &&
              has_pushable_tasks(rq) &&
              p->rt.nr_cpus_allowed > 1 &&
              rt_task(rq->curr) &&
              (rq->curr->rt.nr_cpus_allowed < 2 ||
               rq->curr->prio < p->prio))
                  push_rt_tasks(rq);
  }
  
  static void set_cpus_allowed_rt(struct task_struct *p,
                                  const struct cpumask *new_mask)
  {
          int weight = cpumask_weight(new_mask);
  
          BUG_ON(!rt_task(p));
  
          /*
           * Update the migration status of the RQ if we have an RT task
           * which is running AND changing its weight value.
           */
          if (p->on_rq && (weight != p->rt.nr_cpus_allowed)) {
                  struct rq *rq = task_rq(p);
  
                  if (!task_current(rq, p)) {
                          /*
                           * Make sure we dequeue this task from the pushable list
                           * before going further.  It will either remain off of
                           * the list because we are no longer pushable, or it
                           * will be requeued.
                           */
                          if (p->rt.nr_cpus_allowed > 1)
                                  dequeue_pushable_task(rq, p);
  
                          /*
                           * Requeue if our weight is changing and still > 1
                           */
                          if (weight > 1)
                                  enqueue_pushable_task(rq, p);
  
                  }
  
                  if ((p->rt.nr_cpus_allowed <= 1) && (weight > 1)) {
                          rq->rt.rt_nr_migratory++;
                  } else if ((p->rt.nr_cpus_allowed > 1) && (weight <= 1)) {
                          BUG_ON(!rq->rt.rt_nr_migratory);
                          rq->rt.rt_nr_migratory--;
                  }
  
                  update_rt_migration(&rq->rt);
          }
  
          cpumask_copy(&p->cpus_allowed, new_mask);
          p->rt.nr_cpus_allowed = weight;
  }
  
  /* Assumes rq->lock is held */
  static void rq_online_rt(struct rq *rq)
  {
          if (rq->rt.overloaded)
                  rt_set_overload(rq);
  
          __enable_runtime(rq);
  
          cpupri_set(&rq->rd->cpupri, rq->cpu, rq->rt.highest_prio.curr);
  }
  
  /* Assumes rq->lock is held */
  static void rq_offline_rt(struct rq *rq)
  {
          if (rq->rt.overloaded)
                  rt_clear_overload(rq);
  
          __disable_runtime(rq);
  
          cpupri_set(&rq->rd->cpupri, rq->cpu, CPUPRI_INVALID);
  }
  
  /*
   * When switch from the rt queue, we bring ourselves to a position
   * that we might want to pull RT tasks from other runqueues.
   */
  static void switched_from_rt(struct rq *rq, struct task_struct *p)
  {
          /*
           * If there are other RT tasks then we will reschedule
           * and the scheduling of the other RT tasks will handle
           * the balancing. But if we are the last RT task
           * we may need to handle the pulling of RT tasks
           * now.
           */
          if (p->on_rq && !rq->rt.rt_nr_running)
                  pull_rt_task(rq);
  }
  
  static inline void init_sched_rt_class(void)
  {
          unsigned int i;
  
          for_each_possible_cpu(i)
                  zalloc_cpumask_var_node(&per_cpu(local_cpu_mask, i),
                                          GFP_KERNEL, cpu_to_node(i));
  }
  #endif /* CONFIG_SMP */
  
  /*
   * When switching a task to RT, we may overload the runqueue
   * with RT tasks. In this case we try to push them off to
   * other runqueues.
   */
  static void switched_to_rt(struct rq *rq, struct task_struct *p)
  {
          int check_resched = 1;
  
          /*
           * If we are already running, then there's nothing
           * that needs to be done. But if we are not running
           * we may need to preempt the current running task.
           * If that current running task is also an RT task
           * then see if we can move to another run queue.
           */
          if (p->on_rq && rq->curr != p) {
  #ifdef CONFIG_SMP
                  if (rq->rt.overloaded && push_rt_task(rq) &&
                      /* Don't resched if we changed runqueues */
                      rq != task_rq(p))
                          check_resched = 0;
  #endif /* CONFIG_SMP */
                  if (check_resched && p->prio < rq->curr->prio)
                          resched_task(rq->curr);
          }
  }
  
  /*
   * Priority of the task has changed. This may cause
   * us to initiate a push or pull.
   */
  static void
  prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
  {
          if (!p->on_rq)
                  return;
  
          if (rq->curr == p) {
  #ifdef CONFIG_SMP
                  /*
                   * If our priority decreases while running, we
                   * may need to pull tasks to this runqueue.
                   */
                  if (oldprio < p->prio)
                          pull_rt_task(rq);
                  /*
                   * If there's a higher priority task waiting to run
                   * then reschedule. Note, the above pull_rt_task
                   * can release the rq lock and p could migrate.
                   * Only reschedule if p is still on the same runqueue.
                   */
                  if (p->prio > rq->rt.highest_prio.curr && rq->curr == p)
                          resched_task(p);
  #else
                  /* For UP simply resched on drop of prio */
                  if (oldprio < p->prio)
                          resched_task(p);
  #endif /* CONFIG_SMP */
          } else {
                  /*
                   * This task is not running, but if it is
                   * greater than the current running task
                   * then reschedule.
                   */
                  if (p->prio < rq->curr->prio)
                          resched_task(rq->curr);
          }
  }
  
  static void watchdog(struct rq *rq, struct task_struct *p)
  {
          unsigned long soft, hard;
  
          /* max may change after cur was read, this will be fixed next tick */
          soft = task_rlimit(p, RLIMIT_RTTIME);
          hard = task_rlimit_max(p, RLIMIT_RTTIME);
  
          if (soft != RLIM_INFINITY) {
                  unsigned long next;
  
                  p->rt.timeout++;
                  next = DIV_ROUND_UP(min(soft, hard), USEC_PER_SEC/HZ);
                  if (p->rt.timeout > next)
                          p->cputime_expires.sched_exp = p->se.sum_exec_runtime;
          }
  }
  
  static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
  {
          update_curr_rt(rq);
  
          watchdog(rq, p);
  
          /*
           * RR tasks need a special form of timeslice management.
           * FIFO tasks have no timeslices.
           */
          if (p->policy != SCHED_RR)
                  return;
  
          if (--p->rt.time_slice)
                  return;
  
          p->rt.time_slice = DEF_TIMESLICE;
  
          /*
           * Requeue to the end of queue if we are not the only element
           * on the queue:
           */
          if (p->rt.run_list.prev != p->rt.run_list.next) {
                  requeue_task_rt(rq, p, 0);
                  set_tsk_need_resched(p);
          }
  }
  
  static void set_curr_task_rt(struct rq *rq)
  {
          struct task_struct *p = rq->curr;
  
          p->se.exec_start = rq->clock_task;
  
          /* The running task is never eligible for pushing */
          dequeue_pushable_task(rq, p);
  }
  
  static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
  {
          /*
           * Time slice is 0 for SCHED_FIFO tasks
           */
          if (task->policy == SCHED_RR)
                  return DEF_TIMESLICE;
          else
                  return 0;
  }
  
  static const struct sched_class rt_sched_class = {
          .next                   = &fair_sched_class,
          .enqueue_task           = enqueue_task_rt,
          .dequeue_task           = dequeue_task_rt,
          .yield_task             = yield_task_rt,
  
          .check_preempt_curr     = check_preempt_curr_rt,
  
          .pick_next_task         = pick_next_task_rt,
          .put_prev_task          = put_prev_task_rt,
  
  #ifdef CONFIG_SMP
          .select_task_rq         = select_task_rq_rt,
  
          .set_cpus_allowed       = set_cpus_allowed_rt,
          .rq_online              = rq_online_rt,
          .rq_offline             = rq_offline_rt,
          .pre_schedule           = pre_schedule_rt,
          .post_schedule          = post_schedule_rt,
          .task_woken             = task_woken_rt,
          .switched_from          = switched_from_rt,
  #endif
  
          .set_curr_task          = set_curr_task_rt,
          .task_tick              = task_tick_rt,
  
          .get_rr_interval        = get_rr_interval_rt,
  
          .prio_changed           = prio_changed_rt,
          .switched_to            = switched_to_rt,
  };
  
  #ifdef CONFIG_SCHED_DEBUG
  extern void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq);
  
  static void print_rt_stats(struct seq_file *m, int cpu)
  {
          rt_rq_iter_t iter;
          struct rt_rq *rt_rq;
  
          rcu_read_lock();
          for_each_rt_rq(rt_rq, iter, cpu_rq(cpu))
                  print_rt_rq(m, cpu, rt_rq);
          rcu_read_unlock();
  }
  #endif /* CONFIG_SCHED_DEBUG */
  

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