linux-kernel - Re: [PATCH v2] sched/rt: move back to RT_GROUP

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Date:   Thu, 28 Sep 2023 16:52:22 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     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
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/rt: move back to RT_GROUP_SCHED and rename it
 child

Hi, Steve,

Kindly ping...

Thank.

On 2023/9/20 22:01, Yajun Deng wrote:
> The member back in struct sched_rt_entity only related to RT_GROUP_SCHED,
> it should not place out of RT_GROUP_SCHED, move back to RT_GROUP_SCHED
> and rename it child. This would save a few bytes.
>
> Init child when parent isn't NULL in init_tg_rt_entry() and introduce
> for_each_sched_rt_entity_reverse() to iterate rt_se from top to down.
>
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
> v2: fix the "uninitialized symbol 'root'" warning
> v1: https://lore.kernel.org/all/20230919035114.2364567-1-yajun.deng@linux.dev/
> ---
>   include/linux/sched.h |  2 +-
>   kernel/sched/rt.c     | 25 ++++++++++++++++---------
>   2 files changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 7fcf1b82cfa6..cd05f4bb6a26 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -594,8 +594,8 @@ 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		*child;
>   	struct sched_rt_entity		*parent;
>   	/* rq on which this entity is (to be) queued: */
>   	struct rt_rq			*rt_rq;
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 0597ba0f85ff..473a21b76c62 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -230,8 +230,10 @@ 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->child = rt_se;
> +	}
>   
>   	rt_se->my_q = rt_rq;
>   	rt_se->parent = parent;
> @@ -564,6 +566,9 @@ static inline struct task_group *next_task_group(struct task_group *tg)
>   #define for_each_sched_rt_entity(rt_se) \
>   	for (; rt_se; rt_se = rt_se->parent)
>   
> +#define for_each_sched_rt_entity_reverse(rt_se) \
> +	for (; rt_se; rt_se = rt_se->child)
> +
>   static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
>   {
>   	return rt_se->my_q;
> @@ -669,6 +674,9 @@ typedef struct rt_rq *rt_rq_iter_t;
>   #define for_each_sched_rt_entity(rt_se) \
>   	for (; rt_se; rt_se = NULL)
>   
> +#define for_each_sched_rt_entity_reverse(rt_se) \
> +	for_each_sched_rt_entity(rt_se)
> +
>   static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
>   {
>   	return NULL;
> @@ -1481,22 +1489,21 @@ 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;
>   
> -	for (rt_se = back; rt_se; rt_se = rt_se->back) {
> +	rt_se = root;
> +	for_each_sched_rt_entity_reverse(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)