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在rt_sched_class定义的next是fair_sched_class,const struct sched_class rt_sched_class = {	.next			= &fair_sched_class,在fair_sched_class定义的next是idle_sched_classconst struct sched_class fair_sched_class = {	.next			= &idle_sched_class,从这里也可以看出调度的优先级是是rt>fair>idle而idle_sched_class的定义如下：const struct sched_class idle_sched_class = {	/* .next is NULL */	/* no enqueue/yield_task for idle tasks */	/* dequeue is not valid, we print a debug message there: */	.dequeue_task		= dequeue_task_idle,	.check_preempt_curr	= check_preempt_curr_idle,	.pick_next_task		= pick_next_task_idle,	.put_prev_task		= put_prev_task_idle,这里可以看到idle_sched_class的next是null，从这里可以知道idle_sched_class 就是最低优先级的.这里我们重点看看idle_sched_class的pick_next_task的实现static struct task_struct *pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf){	put_prev_task(rq, prev);	update_idle_core(rq);	schedstat_inc(rq->sched_goidle);	return rq->idle;}void init_idle(struct task_struct *idle, int cpu){        rq->curr = rq->idle = idle;}可以看到这里的rq->idle 就是idle进程

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