update_min_vruntime()流程图

linux kernel scheduler cfs的update_min_vruntime() 看起来还挺绕的。含义其实也简单，总一句话，将 cfs_rq->min_vruntime 设置为：

max( cfs_rq->vruntime, min(leftmost_se->vruntime, cfs_rq->curr->vruntime) )。

画个流程图，给它整个明明白白。

// 将 cfs_rq->min_vruntime 更新为 min(leftmost_se->vruntime, cfs_rq->curr->vruntime)
static void update_min_vruntime(struct cfs_rq *cfs_rq)
{
	struct sched_entity *curr = cfs_rq->curr;
	struct rb_node *leftmost = rb_first_cached(&cfs_rq->tasks_timeline);

	u64 vruntime = cfs_rq->min_vruntime;

	if (curr) {
		if (curr->on_rq)
			vruntime = curr->vruntime;
		else
			curr = NULL;
	}

	if (leftmost) { /* non-empty tree */
		struct sched_entity *se = __node_2_se(leftmost);

		if (!curr)
			vruntime = se->vruntime;
		else
			vruntime = min_vruntime(vruntime, se->vruntime);
	}

	/* ensure we never gain time by being placed backwards. */
	cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
#ifndef CONFIG_64BIT
	smp_wmb();
	cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
}