linux-kernel - [RFC PATCH 3/9] sched: Always initialize rt_rq's task

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Message-ID: <20241216201305.19761-4-mkoutny@suse.com>
Date: Mon, 16 Dec 2024 21:12:59 +0100
From: Michal Koutný <mkoutny@...e.com>
To: cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Frederic Weisbecker <fweisbecker@...e.com>
Subject: [RFC PATCH 3/9] sched: Always initialize rt_rq's task_group

rt_rq->tg may be NULL which denotes the root task_group.
Store the pointer to root_task_group directly so that callers may use
rt_rq->tg homogenously.

root_task_group exists always with CONFIG_CGROUPS_SCHED,
CONFIG_RT_GROUP_SCHED depends on that.

This changes root level rt_rq's default limit from infinity to the
value of (originally) global RT throttling.

Signed-off-by: Michal Koutný <mkoutny@...e.com>
---
 kernel/sched/rt.c    | 7 ++-----
 kernel/sched/sched.h | 2 ++
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 1940301c40f7d..41fed8865cb09 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -89,6 +89,7 @@ void init_rt_rq(struct rt_rq *rt_rq)
 	rt_rq->rt_throttled = 0;
 	rt_rq->rt_runtime = 0;
 	raw_spin_lock_init(&rt_rq->rt_runtime_lock);
+	rt_rq->tg = &root_task_group;
 #endif
 }
 
@@ -484,9 +485,6 @@ static inline bool rt_task_fits_capacity(struct task_struct *p, int cpu)
 
 static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
 {
-	if (!rt_rq->tg)
-		return RUNTIME_INF;
-
 	return rt_rq->rt_runtime;
 }
 
@@ -1156,8 +1154,7 @@ inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 	if (rt_se_boosted(rt_se))
 		rt_rq->rt_nr_boosted++;
 
-	if (rt_rq->tg)
-		start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
+	start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
 }
 
 static void
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 76f5f53a645fc..38325bd32a0e0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -820,6 +820,8 @@ struct rt_rq {
 	unsigned int		rt_nr_boosted;
 
 	struct rq		*rq;
+#endif
+#ifdef CONFIG_CGROUP_SCHED
 	struct task_group	*tg;
 #endif
 };
-- 
2.47.1