sched/fair: Move task sched_avg attach to enqueue_task_fair()

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

Since enqueue_task_fair() -> enqueue_entity() -> update_load_avg()
loop will do attach, we can move this work to update_load_avg().

wake_up_new_task(p)
  post_init_entity_util_avg(p)
    attach_entity_cfs_rq()  --> (1)
  activate_task(rq, p)
    enqueue_task() := enqueue_task_fair()
      enqueue_entity() loop
        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 move attach from (1) to (2), update related comments too.
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20220818124805.601-9-zhouchengming@bytedance.com

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 */
@@ -3838,8 +3834,7 @@ static void migrate_se_pelt_lag(struct sched_entity *se) {}
  * @cfs_rq: cfs_rq to update
  *
  * The cfs_rq avg is the direct sum of all its entities (blocked and runnable)
- * avg. The immediate corollary is that all (fair) tasks must be attached, see
- * post_init_entity_util_avg().
+ * avg. The immediate corollary is that all (fair) tasks must be attached.
  *
  * cfs_rq->avg is used for task_h_load() and update_cfs_share() for example.
  *
@@ -4072,8 +4067,8 @@ static void remove_entity_load_avg(struct sched_entity *se)
 
 	/*
 	 * tasks cannot exit without having gone through wake_up_new_task() ->
-	 * post_init_entity_util_avg() which will have added things to the
-	 * cfs_rq, so we can remove unconditionally.
+	 * enqueue_task_fair() which will have added things to the cfs_rq,
+	 * so we can remove unconditionally.
 	 */
 
 	sync_entity_load_avg(se);