linux schedule函数学习

本文就schedule函数与各调度器使用逻辑方向来研究学习
函数嵌套调用大体为


#define TASK_RUNNING 0x00000000
#define TASK_INTERRUPTIBLE 0x00000001
#define TASK_UNINTERRUPTIBLE 0x00000002
TASK_RUNNING状态宏定义为0
pick_next_task：

static struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
	struct task_struct *next, *p, *max = NULL;
	const struct cpumask *smt_mask;
	bool fi_before = false;
	bool core_clock_updated = (rq == rq->core);
	unsigned long cookie;
	int i, cpu, occ = 0;
	struct rq *rq_i;
	bool need_sync;

	if (!sched_core_enabled(rq))
		return __pick_next_task(rq, prev, rf);
	走上面的分支，下面代码省略掉
	……

__pick_next_task:

这里需要注意的是对于fair调度器，挑选task是有两个流程的，需要结合fair调度器的相关函数来一起看。
put_prev_task_balance：

static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
				  struct rq_flags *rf)
{
#ifdef CONFIG_SMP
	const struct sched_class *class;
	/*
	 * We must do the balancing pass before put_prev_task(), such
	 * that when we release the rq->lock the task is in the same
	 * state as before we took rq->lock.
	 *
	 * We can terminate the balance pass as soon as we know there is
	 * a runnable task of @class priority or higher.
	 */
	for_class_range(class, prev->sched_class, &idle_sched_class) {
		if (class->balance(rq, prev, rf))
			break;
	}
#endif

	put_prev_task(rq, prev);
}
static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
{
	WARN_ON_ONCE(rq->curr != prev);
	prev->sched_class->put_prev_task(rq, prev);
}

这里最终会调用调度器的回调函数put_prev_task，对于deadline来说这会将当前task进行插入到二叉树当中，因为pick_next_task的时候已经将task从二叉树中删除了，如果没有重新插入二叉树，那么这个task将永远不会运行第二次，对于其它调度器有对应的回调函数。可以对应的去研究学习