[PATCH 1/2] sched/fair: Clean up attach_entity_load_avg()

[Yuyang Du <yuyang.du@intel.com>]

attach_entity_load_avg() is called (indirectly) from:

 - switched_to_fair(): switch between classes to fair
 - task_move_group_fair(): move between task groups
 - enqueue_entity_load_avg(): enqueue entity

Only in switched_to_fair() is it possible that the task's last_update_time
is not 0 and therefore the task needs sched avgs update, so move the task
sched avgs update to switched_to_fair() only. In addition, code comments are
clarified.

No functionality change.

Signed-off-by: Yuyang Du <yuyang.du@intel.com>
---
 kernel/sched/fair.c |   39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 218f8e8..e89c39b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2961,24 +2961,6 @@ static inline void update_load_avg(struct sched_entity *se, int update_tg)
 
 static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	if (!sched_feat(ATTACH_AGE_LOAD))
-		goto skip_aging;
-
-	/*
-	 * If we got migrated (either between CPUs or between cgroups) we'll
-	 * have aged the average right before clearing @last_update_time.
-	 */
-	if (se->avg.last_update_time) {
-		__update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
-				  &se->avg, 0, 0, NULL);
-
-		/*
-		 * XXX: we could have just aged the entire load away if we've been
-		 * absent from the fair class for too long.
-		 */
-	}
-
-skip_aging:
 	se->avg.last_update_time = cfs_rq->avg.last_update_time;
 	cfs_rq->avg.load_avg += se->avg.load_avg;
 	cfs_rq->avg.load_sum += se->avg.load_sum;
@@ -8418,6 +8400,27 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
 
 static void switched_to_fair(struct rq *rq, struct task_struct *p)
 {
+#ifdef CONFIG_SMP
+	struct sched_entity *se = &p->se;
+
+	if (!sched_feat(ATTACH_AGE_LOAD))
+		goto skip_aging;
+
+	/*
+	 * If we change between classes, age the averages before attaching them.
+	 */
+	if (se->avg.last_update_time) {
+		__update_load_avg(cfs_rq_of(se)->avg.last_update_time, cpu_of(rq),
+				  &se->avg, 0, 0, NULL);
+
+		/*
+		 * XXX: we could have just aged the entire load away if we've been
+		 * absent from the fair class for too long.
+		 */
+	}
+
+skip_aging:
+#endif
 	attach_task_cfs_rq(p);
 
 	if (task_on_rq_queued(p)) {
-- 
1.7.9.5