[RFC PATCH 4/9] sched: Add commadline option for RT_GROUP_SCHED toggling

["Michal Koutný" <mkoutny@suse.com>]

Only simple implementation with a static key wrapper, it will be wired
in later.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
---
 .../admin-guide/kernel-parameters.txt         |  5 ++++
 init/Kconfig                                  | 11 ++++++++
 kernel/sched/core.c                           | 25 +++++++++++++++++++
 kernel/sched/sched.h                          | 17 +++++++++++++
 4 files changed, 58 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3872bc6ec49d6..1c890c9ad8716 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5937,6 +5937,11 @@
 			Memory area to be used by remote processor image,
 			managed by CMA.
 
+	rt_group_sched=	[KNL] Enable or disable SCHED_RR/FIFO group scheduling
+			when CONFIG_RT_GROUP_SCHED=y. Defaults to
+			!CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED.
+			Format: <bool>
+
 	rw		[KNL] Mount root device read-write on boot
 
 	S		[KNL] Run init in single mode
diff --git a/init/Kconfig b/init/Kconfig
index a20e6efd3f0fb..7823e5ac0311d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1076,6 +1076,17 @@ config RT_GROUP_SCHED
 	  realtime bandwidth for them.
 	  See Documentation/scheduler/sched-rt-group.rst for more information.
 
+config RT_GROUP_SCHED_DEFAULT_DISABLED
+	bool "Require boot parameter to enable group scheduling for SCHED_RR/FIFO"
+	depends on RT_GROUP_SCHED
+	default n
+	help
+	  When set, the RT group scheduling is disabled by default. The option
+	  is in inverted form so that mere RT_GROUP_SCHED enables the group
+	  scheduling.
+
+	  Say N if unsure.
+
 config EXT_GROUP_SCHED
 	bool
 	depends on SCHED_CLASS_EXT && CGROUP_SCHED
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c6d8232ad9eea..47898f895a5a3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9844,6 +9844,31 @@ static struct cftype cpu_legacy_files[] = {
 	{ }	/* Terminate */
 };
 
+#ifdef CONFIG_RT_GROUP_SCHED
+# ifdef RT_GROUP_SCHED_DEFAULT_DISABLED
+DEFINE_STATIC_KEY_FALSE(rt_group_sched);
+# else
+DEFINE_STATIC_KEY_TRUE(rt_group_sched);
+# endif
+
+static int __init setup_rt_group_sched(char *str)
+{
+	long val;
+
+	if (kstrtol(str, 0, &val) || val < 0 || val > 1) {
+		pr_warn("Unable to set rt_group_sched\n");
+		return 1;
+	}
+	if (val)
+		static_branch_enable(&rt_group_sched);
+	else
+		static_branch_disable(&rt_group_sched);
+
+	return 1;
+}
+__setup("rt_group_sched=", setup_rt_group_sched);
+#endif /* CONFIG_RT_GROUP_SCHED */
+
 static int cpu_extra_stat_show(struct seq_file *sf,
 			       struct cgroup_subsys_state *css)
 {
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 38325bd32a0e0..1c457dc1472a3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1501,6 +1501,23 @@ static inline bool sched_group_cookie_match(struct rq *rq,
 }
 
 #endif /* !CONFIG_SCHED_CORE */
+#ifdef CONFIG_RT_GROUP_SCHED
+# ifdef RT_GROUP_SCHED_DEFAULT_DISABLED
+DECLARE_STATIC_KEY_FALSE(rt_group_sched);
+static inline bool rt_group_sched_enabled(void)
+{
+	return static_branch_unlikely(&rt_group_sched);
+}
+# else
+DECLARE_STATIC_KEY_TRUE(rt_group_sched);
+static inline bool rt_group_sched_enabled(void)
+{
+	return static_branch_likely(&rt_group_sched);
+}
+# endif /* RT_GROUP_SCHED_DEFAULT_DISABLED */
+#else
+# define rt_group_sched_enabled()	false
+#endif /* CONFIG_RT_GROUP_SCHED */
 
 static inline void lockdep_assert_rq_held(struct rq *rq)
 {
-- 
2.47.1