sched: Introduce CONFIG_GROUP_SCHED_WEIGHT

sched_ext will soon add cgroup cpu.weigh support. The cgroup interface code
is currently gated behind CONFIG_FAIR_GROUP_SCHED. As the fair class and/or
SCX may implement the feature, put the interface code behind the new
CONFIG_CGROUP_SCHED_WEIGHT which is selected by CONFIG_FAIR_GROUP_SCHED.
This allows either sched class to enable the itnerface code without ading
more complex CONFIG tests.

When !CONFIG_FAIR_GROUP_SCHED, a dummy version of sched_group_set_shares()
is added to support later CONFIG_CGROUP_SCHED_WEIGHT &&
!CONFIG_FAIR_GROUP_SCHED builds.

No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>

init/Kconfig

@@ -1024,9 +1024,13 @@ menuconfig CGROUP_SCHED
 	  tasks.
 
 if CGROUP_SCHED
+config GROUP_SCHED_WEIGHT
+	def_bool n
+
 config FAIR_GROUP_SCHED
 	bool "Group scheduling for SCHED_OTHER"
 	depends on CGROUP_SCHED
+	select GROUP_SCHED_WEIGHT
 	default CGROUP_SCHED
 
 config CFS_BANDWIDTH

kernel/sched/core.c

@@ -9193,7 +9193,7 @@ static int cpu_uclamp_max_show(struct seq_file *sf, void *v)
 }
 #endif /* CONFIG_UCLAMP_TASK_GROUP */
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
+#ifdef CONFIG_GROUP_SCHED_WEIGHT
 static unsigned long tg_weight(struct task_group *tg)
 {
 	return scale_load_down(tg->shares);
@@ -9212,6 +9212,7 @@ static u64 cpu_shares_read_u64(struct cgroup_subsys_state *css,
 {
 	return tg_weight(css_tg(css));
 }
+#endif /* CONFIG_GROUP_SCHED_WEIGHT */
 
 #ifdef CONFIG_CFS_BANDWIDTH
 static DEFINE_MUTEX(cfs_constraints_mutex);
@@ -9557,7 +9558,6 @@ static int cpu_cfs_local_stat_show(struct seq_file *sf, void *v)
 	return 0;
 }
 #endif /* CONFIG_CFS_BANDWIDTH */
-#endif /* CONFIG_FAIR_GROUP_SCHED */
 
 #ifdef CONFIG_RT_GROUP_SCHED
 static int cpu_rt_runtime_write(struct cgroup_subsys_state *css,
@@ -9585,7 +9585,7 @@ static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
 }
 #endif /* CONFIG_RT_GROUP_SCHED */
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
+#ifdef CONFIG_GROUP_SCHED_WEIGHT
 static s64 cpu_idle_read_s64(struct cgroup_subsys_state *css,
 			       struct cftype *cft)
 {
@@ -9600,7 +9600,7 @@ static int cpu_idle_write_s64(struct cgroup_subsys_state *css,
 #endif
 
 static struct cftype cpu_legacy_files[] = {
-#ifdef CONFIG_FAIR_GROUP_SCHED
+#ifdef CONFIG_GROUP_SCHED_WEIGHT
 	{
 		.name = "shares",
 		.read_u64 = cpu_shares_read_u64,
@@ -9710,7 +9710,7 @@ static int cpu_local_stat_show(struct seq_file *sf,
 	return 0;
 }
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
+#ifdef CONFIG_GROUP_SCHED_WEIGHT
 
 static u64 cpu_weight_read_u64(struct cgroup_subsys_state *css,
 			       struct cftype *cft)
@@ -9764,7 +9764,7 @@ static int cpu_weight_nice_write_s64(struct cgroup_subsys_state *css,
 
 	return sched_group_set_shares(css_tg(css), scale_load(weight));
 }
-#endif
+#endif /* CONFIG_GROUP_SCHED_WEIGHT */
 
 static void __maybe_unused cpu_period_quota_print(struct seq_file *sf,
 						  long period, long quota)
@@ -9824,7 +9824,7 @@ static ssize_t cpu_max_write(struct kernfs_open_file *of,
 #endif
 
 static struct cftype cpu_files[] = {
-#ifdef CONFIG_FAIR_GROUP_SCHED
+#ifdef CONFIG_GROUP_SCHED_WEIGHT
 	{
 		.name = "weight",
 		.flags = CFTYPE_NOT_ON_ROOT,

kernel/sched/sched.h

@@ -483,7 +483,7 @@ struct task_group {
 
 };
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
+#ifdef CONFIG_GROUP_SCHED_WEIGHT
 #define ROOT_TASK_GROUP_LOAD	NICE_0_LOAD
 
 /*
@@ -575,6 +575,8 @@ extern void set_task_rq_fair(struct sched_entity *se,
 static inline void set_task_rq_fair(struct sched_entity *se,
 			     struct cfs_rq *prev, struct cfs_rq *next) { }
 #endif /* CONFIG_SMP */
+#else /* !CONFIG_FAIR_GROUP_SCHED */
+static inline int sched_group_set_shares(struct task_group *tg, unsigned long shares) { return 0; }
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
 #else /* CONFIG_CGROUP_SCHED */