[PATCH v4 8/9] sched/fair: defer task sched_avg attach to enqueue_entity()

[Chengming Zhou]

When wake_up_new_task(), we would use post_init_entity_util_avg()
to init util_avg/runnable_avg based on cpu's util_avg at that time,
then attach task sched_avg to cfs_rq.

Since enqueue_entity() would always attach any unattached task entity,
so we can defer this work to enqueue_entity().

post_init_entity_util_avg(p)
  attach_entity_cfs_rq()  --> (1)
activate_task(rq, p)
  enqueue_task() := enqueue_task_fair()
  enqueue_entity()
    update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH)
      if (!se->avg.last_update_time && (flags & DO_ATTACH))
        attach_entity_load_avg()  --> (2)

This patch defer attach from (1) to (2)

Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
---
 kernel/sched/fair.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 90aba33a3780..2063e30b2a8f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -799,8 +799,6 @@ void init_entity_runnable_average(struct sched_entity *se)
 	/* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
 }
 
-static void attach_entity_cfs_rq(struct sched_entity *se);
-
 /*
  * With new tasks being created, their initial util_avgs are extrapolated
  * based on the cfs_rq's current util_avg:
@@ -863,8 +861,6 @@ void post_init_entity_util_avg(struct task_struct *p)
 		se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
 		return;
 	}
-
-	attach_entity_cfs_rq(se);
 }
 
 #else /* !CONFIG_SMP */
-- 
2.36.1