linux-kernel - Re: [PATCH 2/2] sched/rt: Move sched_rt_entity::back to under the CONFIG_RT_GROUP

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Date:   Mon, 9 Oct 2023 12:16:26 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Yajun Deng <yajun.deng@...ux.dev>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] sched/rt: Move sched_rt_entity::back to under the
 CONFIG_RT_GROUP_SCHED block


* Yajun Deng <yajun.deng@...ux.dev> wrote:

> The member back in struct sched_rt_entity only related to RT_GROUP_SCHED,
> So move sched_rt_entity::back to under the CONFIG_RT_GROUP_SCHED block. It
> will save a few bytes.
> 
> Also, init child when parent isn't NULL in init_tg_rt_entry().
> 
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
>  include/linux/sched.h |  2 +-
>  kernel/sched/rt.c     | 18 +++++++++---------
>  2 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 292c31697248..d0fe56603e60 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -597,8 +597,8 @@ struct sched_rt_entity {
>  	unsigned short			on_rq;
>  	unsigned short			on_list;
>  
> -	struct sched_rt_entity		*back;
>  #ifdef CONFIG_RT_GROUP_SCHED
> +	struct sched_rt_entity		*back;
>  	struct sched_rt_entity		*parent;
>  	/* rq on which this entity is (to be) queued: */
>  	struct rt_rq			*rt_rq;

Title claims this change - the rest of the changes should be in a separate 
patch:

> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 642edbd24ffb..7b3105b875f1 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -233,8 +233,10 @@ void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq,
>  
>  	if (!parent)
>  		rt_se->rt_rq = &rq->rt;
> -	else
> +	else {
>  		rt_se->rt_rq = parent->my_q;
> +		parent->back = rt_se;
> +	}
>  
>  	rt_se->my_q = rt_rq;
>  	rt_se->parent = parent;
> @@ -1441,23 +1443,21 @@ static void __dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flag
>   */
>  static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
>  {
> -	struct sched_rt_entity *back = NULL;
> +	struct sched_rt_entity *root = NULL;
>  	unsigned int rt_nr_running;
>  
> -	for_each_sched_rt_entity(rt_se) {
> -		rt_se->back = back;
> -		back = rt_se;
> -	}
> +	for_each_sched_rt_entity(rt_se)
> +		root = rt_se;
>  
> -	rt_nr_running = rt_rq_of_se(back)->rt_nr_running;
> +	rt_nr_running = rt_rq_of_se(root)->rt_nr_running;
>  
> -	rt_se = back;
> +	rt_se = root;
>  	for_each_sched_rt_entity_back(rt_se) {
>  		if (on_rt_rq(rt_se))
>  			__dequeue_rt_entity(rt_se, flags);
>  	}
>  
> -	dequeue_top_rt_rq(rt_rq_of_se(back), rt_nr_running);
> +	dequeue_top_rt_rq(rt_rq_of_se(root), rt_nr_running);
>  }
>  
>  static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
> -- 
> 2.25.1

Thanks,

	Ingo