从有资格的任务中挑选最早截止时间

945		if (left && vruntime_eligible(cfs_rq,946					__node_2_se(left)->min_vruntime)) {947			node = left;948			continue;949		}950951		se = __node_2_se(node);952953		/*954		 * The left subtree either is empty or has no eligible955		 * entity, so check the current node since it is the one956		 * with earliest deadline that might be eligible.957		 */958		if (entity_eligible(cfs_rq, se)) {959			best = se;960			break;961		}962963		node = node->rb_right;964	}