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

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Message-Id: <20231005162317.3343678-3-yajun.deng@linux.dev>
Date:   Fri,  6 Oct 2023 00:23:17 +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, Yajun Deng <yajun.deng@...ux.dev>
Subject: [PATCH 2/2] sched/rt: Move sched_rt_entity::back to under the CONFIG_RT_GROUP_SCHED block

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;
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