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 19:13:18 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     Ingo Molnar <mingo@...nel.org>
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


On 2023/10/9 18:16, Ingo Molnar wrote:
> * 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:


Okay. I will send v2.

>> 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