linux-kernel - [PATCH] sched/fair: Optimize dequeue_task

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Message-Id: <20200811084310.27130-1-benbjiang@tencent.com>
Date:   Tue, 11 Aug 2020 16:43:10 +0800
From:   Jiang Biao <benbjiang@...il.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org
Cc:     dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, linux-kernel@...r.kernel.org,
        Jiang Biao <benbjiang@...cent.com>
Subject: [PATCH] sched/fair: Optimize dequeue_task_fair()

Similar optimization as what has been done in commit,
7d148be69e3a(sched/fair: Optimize enqueue_task_fair())

dequeue_task_fair jumps to dequeue_throttle label when cfs_rq_of(se) is
throttled which means that se can't be NULL. We can move the label after
the if (!se) statement and remove the if(!se) statment as se is always
NULL when reaching this point.

Besides, trying to keep the same pattern with enqueue_task_fair can make
it more readable.

Signed-off-by: Jiang Biao <benbjiang@...cent.com>
---
 kernel/sched/fair.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 04fa8dbcfa4d..cbbeafdfa8b7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5618,10 +5618,10 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 
 	}
 
-dequeue_throttle:
-	if (!se)
-		sub_nr_running(rq, 1);
+	/* At this point se is NULL and we are at root level*/
+	sub_nr_running(rq, 1);
 
+dequeue_throttle:
 	/* balance early to pull high priority tasks */
 	if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
 		rq->next_balance = jiffies;
-- 
2.21.0