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From:   Jiang Biao <benbjiang@gmail.com>
To:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org
Cc:     dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, linux-kernel@vger.kernel.org,
        Jiang Biao <benbjiang@tencent.com>
Subject: [PATCH RFC v2] sched/fair: simplify the work when reweighting entity
Date:   Fri,  7 Aug 2020 00:14:06 +0800
Message-Id: <20200806161406.22629-1-benbjiang@tencent.com>
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From: Jiang Biao <benbjiang@tencent.com>

If a se is on_rq when reweighting entity, all we need should be
updating the load of cfs_rq, other dequeue/enqueue work could be
redundant, such as,
* nr_running--/nr_running++

Even though the following dequeue/enqueue path would never be reached
* account_numa_dequeue/account_numa_enqueue
* list_del/list_add from/into cfs_tasks
but it could be a little confusing.

Simplifying the logic could be helpful to reduce a litte overhead for
hot path, and make it cleaner and more readable.

Signed-off-by: Jiang Biao <benbjiang@tencent.com>
---
v2<-v1: 
- Amend the commit log.

 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 04fa8dbcfa4d..18a8fc7bd0de 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3086,7 +3086,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 		/* commit outstanding execution time */
 		if (cfs_rq->curr == se)
 			update_curr(cfs_rq);
-		account_entity_dequeue(cfs_rq, se);
+		update_load_sub(&cfs_rq->load, se->load.weight);
 	}
 	dequeue_load_avg(cfs_rq, se);
 
@@ -3102,7 +3102,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 
 	enqueue_load_avg(cfs_rq, se);
 	if (se->on_rq)
-		account_entity_enqueue(cfs_rq, se);
+		update_load_add(&cfs_rq->load, se->load.weight);
 
 }
 
-- 
2.21.0