557 lines
13 KiB
C
557 lines
13 KiB
C
/*
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* Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
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* policies)
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*/
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#ifdef CONFIG_SMP
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static cpumask_t rt_overload_mask;
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static atomic_t rto_count;
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static inline int rt_overloaded(void)
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{
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return atomic_read(&rto_count);
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}
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static inline cpumask_t *rt_overload(void)
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{
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return &rt_overload_mask;
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}
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static inline void rt_set_overload(struct rq *rq)
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{
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cpu_set(rq->cpu, rt_overload_mask);
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/*
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* Make sure the mask is visible before we set
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* the overload count. That is checked to determine
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* if we should look at the mask. It would be a shame
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* if we looked at the mask, but the mask was not
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* updated yet.
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*/
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wmb();
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atomic_inc(&rto_count);
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}
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static inline void rt_clear_overload(struct rq *rq)
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{
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/* the order here really doesn't matter */
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atomic_dec(&rto_count);
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cpu_clear(rq->cpu, rt_overload_mask);
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}
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#endif /* CONFIG_SMP */
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/*
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* Update the current task's runtime statistics. Skip current tasks that
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* are not in our scheduling class.
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*/
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static void update_curr_rt(struct rq *rq)
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{
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struct task_struct *curr = rq->curr;
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u64 delta_exec;
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if (!task_has_rt_policy(curr))
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return;
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delta_exec = rq->clock - curr->se.exec_start;
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if (unlikely((s64)delta_exec < 0))
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delta_exec = 0;
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schedstat_set(curr->se.exec_max, max(curr->se.exec_max, delta_exec));
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curr->se.sum_exec_runtime += delta_exec;
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curr->se.exec_start = rq->clock;
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cpuacct_charge(curr, delta_exec);
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}
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static inline void inc_rt_tasks(struct task_struct *p, struct rq *rq)
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{
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WARN_ON(!rt_task(p));
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rq->rt.rt_nr_running++;
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#ifdef CONFIG_SMP
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if (p->prio < rq->rt.highest_prio)
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rq->rt.highest_prio = p->prio;
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if (rq->rt.rt_nr_running > 1)
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rt_set_overload(rq);
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#endif /* CONFIG_SMP */
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}
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static inline void dec_rt_tasks(struct task_struct *p, struct rq *rq)
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{
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WARN_ON(!rt_task(p));
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WARN_ON(!rq->rt.rt_nr_running);
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rq->rt.rt_nr_running--;
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#ifdef CONFIG_SMP
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if (rq->rt.rt_nr_running) {
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struct rt_prio_array *array;
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WARN_ON(p->prio < rq->rt.highest_prio);
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if (p->prio == rq->rt.highest_prio) {
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/* recalculate */
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array = &rq->rt.active;
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rq->rt.highest_prio =
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sched_find_first_bit(array->bitmap);
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} /* otherwise leave rq->highest prio alone */
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} else
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rq->rt.highest_prio = MAX_RT_PRIO;
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if (rq->rt.rt_nr_running < 2)
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rt_clear_overload(rq);
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#endif /* CONFIG_SMP */
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}
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static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
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{
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struct rt_prio_array *array = &rq->rt.active;
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list_add_tail(&p->run_list, array->queue + p->prio);
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__set_bit(p->prio, array->bitmap);
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inc_cpu_load(rq, p->se.load.weight);
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inc_rt_tasks(p, rq);
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}
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/*
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* Adding/removing a task to/from a priority array:
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*/
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static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
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{
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struct rt_prio_array *array = &rq->rt.active;
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update_curr_rt(rq);
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list_del(&p->run_list);
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if (list_empty(array->queue + p->prio))
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__clear_bit(p->prio, array->bitmap);
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dec_cpu_load(rq, p->se.load.weight);
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dec_rt_tasks(p, rq);
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}
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/*
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* Put task to the end of the run list without the overhead of dequeue
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* followed by enqueue.
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*/
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static void requeue_task_rt(struct rq *rq, struct task_struct *p)
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{
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struct rt_prio_array *array = &rq->rt.active;
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list_move_tail(&p->run_list, array->queue + p->prio);
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}
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static void
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yield_task_rt(struct rq *rq)
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{
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requeue_task_rt(rq, rq->curr);
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}
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/*
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* Preempt the current task with a newly woken task if needed:
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*/
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static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
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{
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if (p->prio < rq->curr->prio)
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resched_task(rq->curr);
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}
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static struct task_struct *pick_next_task_rt(struct rq *rq)
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{
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struct rt_prio_array *array = &rq->rt.active;
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struct task_struct *next;
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struct list_head *queue;
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int idx;
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idx = sched_find_first_bit(array->bitmap);
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if (idx >= MAX_RT_PRIO)
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return NULL;
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queue = array->queue + idx;
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next = list_entry(queue->next, struct task_struct, run_list);
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next->se.exec_start = rq->clock;
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return next;
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}
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static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
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{
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update_curr_rt(rq);
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p->se.exec_start = 0;
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}
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#ifdef CONFIG_SMP
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/* Only try algorithms three times */
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#define RT_MAX_TRIES 3
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static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
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static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
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/* Return the second highest RT task, NULL otherwise */
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static struct task_struct *pick_next_highest_task_rt(struct rq *rq)
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{
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struct rt_prio_array *array = &rq->rt.active;
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struct task_struct *next;
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struct list_head *queue;
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int idx;
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assert_spin_locked(&rq->lock);
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if (likely(rq->rt.rt_nr_running < 2))
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return NULL;
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idx = sched_find_first_bit(array->bitmap);
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if (unlikely(idx >= MAX_RT_PRIO)) {
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WARN_ON(1); /* rt_nr_running is bad */
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return NULL;
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}
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queue = array->queue + idx;
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next = list_entry(queue->next, struct task_struct, run_list);
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if (unlikely(next != rq->curr))
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return next;
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if (queue->next->next != queue) {
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/* same prio task */
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next = list_entry(queue->next->next, struct task_struct, run_list);
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return next;
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}
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/* slower, but more flexible */
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idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
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if (unlikely(idx >= MAX_RT_PRIO)) {
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WARN_ON(1); /* rt_nr_running was 2 and above! */
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return NULL;
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}
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queue = array->queue + idx;
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next = list_entry(queue->next, struct task_struct, run_list);
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return next;
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}
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static DEFINE_PER_CPU(cpumask_t, local_cpu_mask);
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/* Will lock the rq it finds */
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static struct rq *find_lock_lowest_rq(struct task_struct *task,
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struct rq *this_rq)
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{
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struct rq *lowest_rq = NULL;
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int cpu;
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int tries;
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cpumask_t *cpu_mask = &__get_cpu_var(local_cpu_mask);
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cpus_and(*cpu_mask, cpu_online_map, task->cpus_allowed);
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for (tries = 0; tries < RT_MAX_TRIES; tries++) {
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/*
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* Scan each rq for the lowest prio.
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*/
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for_each_cpu_mask(cpu, *cpu_mask) {
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struct rq *rq = &per_cpu(runqueues, cpu);
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if (cpu == this_rq->cpu)
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continue;
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/* We look for lowest RT prio or non-rt CPU */
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if (rq->rt.highest_prio >= MAX_RT_PRIO) {
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lowest_rq = rq;
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break;
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}
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/* no locking for now */
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if (rq->rt.highest_prio > task->prio &&
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(!lowest_rq || rq->rt.highest_prio > lowest_rq->rt.highest_prio)) {
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lowest_rq = rq;
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}
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}
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if (!lowest_rq)
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break;
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/* if the prio of this runqueue changed, try again */
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if (double_lock_balance(this_rq, lowest_rq)) {
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/*
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* We had to unlock the run queue. In
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* the mean time, task could have
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* migrated already or had its affinity changed.
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* Also make sure that it wasn't scheduled on its rq.
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*/
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if (unlikely(task_rq(task) != this_rq ||
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!cpu_isset(lowest_rq->cpu, task->cpus_allowed) ||
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task_running(this_rq, task) ||
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!task->se.on_rq)) {
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spin_unlock(&lowest_rq->lock);
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lowest_rq = NULL;
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break;
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}
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}
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/* If this rq is still suitable use it. */
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if (lowest_rq->rt.highest_prio > task->prio)
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break;
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/* try again */
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spin_unlock(&lowest_rq->lock);
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lowest_rq = NULL;
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}
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return lowest_rq;
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}
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/*
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* If the current CPU has more than one RT task, see if the non
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* running task can migrate over to a CPU that is running a task
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* of lesser priority.
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*/
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static int push_rt_task(struct rq *this_rq)
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{
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struct task_struct *next_task;
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struct rq *lowest_rq;
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int ret = 0;
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int paranoid = RT_MAX_TRIES;
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assert_spin_locked(&this_rq->lock);
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next_task = pick_next_highest_task_rt(this_rq);
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if (!next_task)
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return 0;
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retry:
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if (unlikely(next_task == this_rq->curr))
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return 0;
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/*
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* It's possible that the next_task slipped in of
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* higher priority than current. If that's the case
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* just reschedule current.
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*/
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if (unlikely(next_task->prio < this_rq->curr->prio)) {
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resched_task(this_rq->curr);
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return 0;
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}
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/* We might release this_rq lock */
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get_task_struct(next_task);
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/* find_lock_lowest_rq locks the rq if found */
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lowest_rq = find_lock_lowest_rq(next_task, this_rq);
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if (!lowest_rq) {
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struct task_struct *task;
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/*
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* find lock_lowest_rq releases this_rq->lock
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* so it is possible that next_task has changed.
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* If it has, then try again.
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*/
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task = pick_next_highest_task_rt(this_rq);
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if (unlikely(task != next_task) && task && paranoid--) {
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put_task_struct(next_task);
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next_task = task;
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goto retry;
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}
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goto out;
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}
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assert_spin_locked(&lowest_rq->lock);
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deactivate_task(this_rq, next_task, 0);
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set_task_cpu(next_task, lowest_rq->cpu);
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activate_task(lowest_rq, next_task, 0);
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resched_task(lowest_rq->curr);
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spin_unlock(&lowest_rq->lock);
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ret = 1;
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out:
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put_task_struct(next_task);
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return ret;
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}
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/*
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* TODO: Currently we just use the second highest prio task on
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* the queue, and stop when it can't migrate (or there's
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* no more RT tasks). There may be a case where a lower
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* priority RT task has a different affinity than the
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* higher RT task. In this case the lower RT task could
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* possibly be able to migrate where as the higher priority
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* RT task could not. We currently ignore this issue.
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* Enhancements are welcome!
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*/
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static void push_rt_tasks(struct rq *rq)
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{
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/* push_rt_task will return true if it moved an RT */
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while (push_rt_task(rq))
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;
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}
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static void schedule_tail_balance_rt(struct rq *rq)
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{
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/*
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* If we have more than one rt_task queued, then
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* see if we can push the other rt_tasks off to other CPUS.
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* Note we may release the rq lock, and since
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* the lock was owned by prev, we need to release it
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* first via finish_lock_switch and then reaquire it here.
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*/
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if (unlikely(rq->rt.rt_nr_running > 1)) {
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spin_lock_irq(&rq->lock);
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push_rt_tasks(rq);
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spin_unlock_irq(&rq->lock);
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}
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}
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/*
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* Load-balancing iterator. Note: while the runqueue stays locked
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* during the whole iteration, the current task might be
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* dequeued so the iterator has to be dequeue-safe. Here we
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* achieve that by always pre-iterating before returning
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* the current task:
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*/
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static struct task_struct *load_balance_start_rt(void *arg)
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{
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struct rq *rq = arg;
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struct rt_prio_array *array = &rq->rt.active;
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struct list_head *head, *curr;
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struct task_struct *p;
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int idx;
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idx = sched_find_first_bit(array->bitmap);
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if (idx >= MAX_RT_PRIO)
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return NULL;
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head = array->queue + idx;
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curr = head->prev;
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p = list_entry(curr, struct task_struct, run_list);
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curr = curr->prev;
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rq->rt.rt_load_balance_idx = idx;
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rq->rt.rt_load_balance_head = head;
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rq->rt.rt_load_balance_curr = curr;
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return p;
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}
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static struct task_struct *load_balance_next_rt(void *arg)
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{
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struct rq *rq = arg;
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struct rt_prio_array *array = &rq->rt.active;
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struct list_head *head, *curr;
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struct task_struct *p;
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int idx;
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idx = rq->rt.rt_load_balance_idx;
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head = rq->rt.rt_load_balance_head;
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curr = rq->rt.rt_load_balance_curr;
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/*
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* If we arrived back to the head again then
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* iterate to the next queue (if any):
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*/
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if (unlikely(head == curr)) {
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int next_idx = find_next_bit(array->bitmap, MAX_RT_PRIO, idx+1);
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if (next_idx >= MAX_RT_PRIO)
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return NULL;
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idx = next_idx;
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head = array->queue + idx;
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curr = head->prev;
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rq->rt.rt_load_balance_idx = idx;
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rq->rt.rt_load_balance_head = head;
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}
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p = list_entry(curr, struct task_struct, run_list);
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curr = curr->prev;
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rq->rt.rt_load_balance_curr = curr;
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return p;
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}
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static unsigned long
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load_balance_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
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unsigned long max_load_move,
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struct sched_domain *sd, enum cpu_idle_type idle,
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int *all_pinned, int *this_best_prio)
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{
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struct rq_iterator rt_rq_iterator;
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rt_rq_iterator.start = load_balance_start_rt;
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rt_rq_iterator.next = load_balance_next_rt;
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/* pass 'busiest' rq argument into
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* load_balance_[start|next]_rt iterators
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*/
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rt_rq_iterator.arg = busiest;
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return balance_tasks(this_rq, this_cpu, busiest, max_load_move, sd,
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idle, all_pinned, this_best_prio, &rt_rq_iterator);
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}
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static int
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move_one_task_rt(struct rq *this_rq, int this_cpu, struct rq *busiest,
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struct sched_domain *sd, enum cpu_idle_type idle)
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{
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struct rq_iterator rt_rq_iterator;
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rt_rq_iterator.start = load_balance_start_rt;
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rt_rq_iterator.next = load_balance_next_rt;
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rt_rq_iterator.arg = busiest;
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return iter_move_one_task(this_rq, this_cpu, busiest, sd, idle,
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&rt_rq_iterator);
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}
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#else /* CONFIG_SMP */
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# define schedule_tail_balance_rt(rq) do { } while (0)
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#endif /* CONFIG_SMP */
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static void task_tick_rt(struct rq *rq, struct task_struct *p)
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{
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update_curr_rt(rq);
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/*
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* RR tasks need a special form of timeslice management.
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* FIFO tasks have no timeslices.
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*/
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if (p->policy != SCHED_RR)
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return;
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if (--p->time_slice)
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return;
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p->time_slice = DEF_TIMESLICE;
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/*
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* Requeue to the end of queue if we are not the only element
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* on the queue:
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*/
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if (p->run_list.prev != p->run_list.next) {
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requeue_task_rt(rq, p);
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set_tsk_need_resched(p);
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}
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}
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static void set_curr_task_rt(struct rq *rq)
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{
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struct task_struct *p = rq->curr;
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p->se.exec_start = rq->clock;
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}
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const struct sched_class rt_sched_class = {
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.next = &fair_sched_class,
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.enqueue_task = enqueue_task_rt,
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.dequeue_task = dequeue_task_rt,
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.yield_task = yield_task_rt,
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.check_preempt_curr = check_preempt_curr_rt,
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.pick_next_task = pick_next_task_rt,
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.put_prev_task = put_prev_task_rt,
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#ifdef CONFIG_SMP
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.load_balance = load_balance_rt,
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.move_one_task = move_one_task_rt,
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#endif
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.set_curr_task = set_curr_task_rt,
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.task_tick = task_tick_rt,
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};
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