[PATCH RFC v2] sched/fair: simplify the work when reweighting entity

[Jiang Biao]

From: Jiang Biao <benbjiang@xxxxxxxxxxx>

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@xxxxxxxxxxx>
---
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