sched/fair: optimize entity_tick()

entity_tick() will be called to check preemption by calculating each
sched_entity's time_slice in a task group tree from bottom to top.

If a need_resched_flag is set by a checking of a sched_entity,
there is no necessary to check preemption of the sched_entity's
parent and ancestor entity.

So we can test if the need_resched_flag has been set before calling
check_preempt_tick() to avoid unnecessary calculations.

Signed-off-by: zhangpeng.00 <zhangpeng.00@bytedance.com>

kernel/sched/fair.c

@@ -4757,7 +4757,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 		return;
 #endif
 
-	if (cfs_rq->nr_running > 1)
+	if (cfs_rq->nr_running > 1 && !test_tsk_need_resched(rq_of(cfs_rq)->curr))
 		check_preempt_tick(cfs_rq, curr);
 }