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Subject[tip: sched/core] sched/fair: Move task sched_avg attach to enqueue_task_fair()
The following commit has been merged into the sched/core branch of tip:

Commit-ID: d6531ab6e50149ab2a144b0f4787cb9277d0893f
Gitweb: https://git.kernel.org/tip/d6531ab6e50149ab2a144b0f4787cb9277d0893f
Author: Chengming Zhou <zhouchengming@bytedance.com>
AuthorDate: Thu, 18 Aug 2022 20:48:04 +08:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 23 Aug 2022 11:01:19 +02:00

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 | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fd1aa4c..ef325b5 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 */
@@ -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);
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