[PATCH] sched: Avoid unnecessary work in reweight_entity

[Michael Wang <wangyun@linux.vnet.ibm.com>]

From: Michael Wang <wangyun@linux.vnet.ibm.com>

In original code, using account_entity_dequeue and account_entity_enqueue
as a pair will do some work unnecessary, this patch combine the work of
them to save time.

Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
---
 kernel/sched/fair.c  |   32 ++++++++++++++++++++++++--------
 kernel/sched/sched.h |    8 ++++++++
 2 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 84adb2d..e380518 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -782,11 +782,23 @@ add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
 {
 	cfs_rq->task_weight += weight;
 }
+
+static void
+sub_add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long sub, unsigned long add)
+{
+	cfs_rq->task_weight -= sub;
+	cfs_rq->task_weight += add;
+}
 #else
 static inline void
 add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
 {
 }
+
+static void
+sub_add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long sub, unsigned long add)
+{
+}
 #endif
 
 static void
@@ -938,20 +950,24 @@ static inline void update_entity_shares_tick(struct cfs_rq *cfs_rq)
 {
 }
 # endif /* CONFIG_SMP */
+
 static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 			    unsigned long weight)
 {
+	/* commit outstanding execution time */
+	if (cfs_rq->curr == se)
+		update_curr(cfs_rq);
+
 	if (se->on_rq) {
-		/* commit outstanding execution time */
-		if (cfs_rq->curr == se)
-			update_curr(cfs_rq);
-		account_entity_dequeue(cfs_rq, se);
+		update_load_sub_add(&cfs_rq->load, se->load.weight, weight);
+		if (!parent_entity(se)) {
+			update_load_sub_add(&rq_of(cfs_rq), se->load.weight, weight);
+		}
+		if (entity_is_task(se)) {
+			sub_add_cfs_task_weight(cfs_rq, se->load.weight, weight);
+		}
 	}
-
 	update_load_set(&se->load, weight);
-
-	if (se->on_rq)
-		account_entity_enqueue(cfs_rq, se);
 }
 
 static void update_cfs_shares(struct cfs_rq *cfs_rq)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 98c0c26..ec4430f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -779,6 +779,14 @@ static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
 	lw->inv_weight = 0;
 }
 
+static inline void update_load_sub_add(struct load_weight *lw, unsigned long dec,
+					unsigned long inc)
+{
+	lw->weight -= dec;
+	lw->weight += inc;
+	lw->inv_weight = 0;
+}
+
 static inline void update_load_set(struct load_weight *lw, unsigned long w)
 {
 	lw->weight = w;
-- 
1.7.4.1