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From:   Peng Zhang <zhangpeng.00@bytedance.com>
To:     mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, bsegall@google.com,
        linux-kernel@vger.kernel.org
Cc:     "zhangpeng.00" <zhangpeng.00@bytedance.com>
Subject: [PATCH] sched/fair: optimize entity_tick()
Date:   Mon, 18 Jul 2022 17:49:37 +0800
Message-Id: <20220718094937.37360-1-zhangpeng.00@bytedance.com>
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From: "zhangpeng.00" <zhangpeng.00@bytedance.com>

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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a78d2e3b9d49..ee23afe22ac7 100644
--- a/kernel/sched/fair.c
+++ b/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);
 }
 
-- 
2.20.1