[PATCH v2 1/2] sched/rt: Use 'back' only if CONFIG_RT_GROUP_SCHED is enabled

[Yajun Deng <yajun.deng@linux.dev>]

The 'back' member in struct sched_rt_entity only related to
CONFIG_RT_GROUP_SCHED, so there is no need to init it in dequeue_rt_stack.

Init the 'back' member in init_tg_rt_entry and use it only if
CONFIG_RT_GROUP_SCHED is enabled.

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
---
 kernel/sched/rt.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 63e49c8ffc4d..842a2cfd6dcc 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -230,10 +230,12 @@ void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq,
 	if (!rt_se)
 		return;
 
-	if (!parent)
+	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;
@@ -604,6 +606,11 @@ static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
 	return &rt_rq->tg->rt_bandwidth;
 }
 
+static struct sched_rt_entity *rt_se_back(struct sched_rt_entity *se)
+{
+	return se->back;
+}
+
 #else /* !CONFIG_RT_GROUP_SCHED */
 
 static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
@@ -666,6 +673,11 @@ static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq)
 	return &def_rt_bandwidth;
 }
 
+static inline struct sched_rt_entity *rt_se_back(struct sched_rt_entity *se)
+{
+	return NULL;
+}
+
 #endif /* CONFIG_RT_GROUP_SCHED */
 
 bool sched_rt_bandwidth_account(struct rt_rq *rt_rq)
@@ -1428,14 +1440,12 @@ static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
 	struct sched_rt_entity *back = NULL;
 	unsigned int rt_nr_running;
 
-	for_each_sched_rt_entity(rt_se) {
-		rt_se->back = back;
+	for_each_sched_rt_entity(rt_se)
 		back = rt_se;
-	}
 
 	rt_nr_running = rt_rq_of_se(back)->rt_nr_running;
 
-	for (rt_se = back; rt_se; rt_se = rt_se->back) {
+	for (rt_se = back; rt_se; rt_se = rt_se_back(rt_se)) {
 		if (on_rt_rq(rt_se))
 			__dequeue_rt_entity(rt_se, flags);
 	}
-- 
2.25.1