RT scheduler

kernel/sched/rt.c — RT queue, 선택, migration, bandwidth
kernel/sched/core.c — scheduler class의 선택 결과 소비

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;

	check_schedstat_required();
	update_stats_wait_start_rt(rt_rq_of_se(rt_se), rt_se);

	enqueue_rt_entity(rt_se, flags);

	if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
		enqueue_pushable_task(rq, p);
}

static struct sched_rt_entity *pick_next_rt_entity(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;
	if (SCHED_WARN_ON(list_empty(queue)))
		return NULL;
	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 rt_rq *rt_rq  = &rq->rt;

	do {
		rt_se = pick_next_rt_entity(rt_rq);
		if (unlikely(!rt_se))
			return NULL;
		rt_rq = group_rt_rq(rt_se);
	} while (rt_rq);

	return rt_task_of(rt_se);
}

static struct task_struct *pick_task_rt(struct rq *rq)
{
	struct task_struct *p;

	if (!sched_rt_runnable(rq))
		return NULL;

	p = _pick_next_task_rt(rq);

	return p;
}

static struct task_struct *pick_next_task_rt(struct rq *rq)
{
	struct task_struct *p = pick_task_rt(rq);

	if (p)
		set_next_task_rt(rq, p, true);

	return p;
}