[PATCH v4 5/8] sched: Enable sched_feat callbacks on enable/disable

[David Vernet <void@manifault.com>]

When a scheduler feature is enabled or disabled, the sched_feat_enable()
and sched_feat_disable() functions are invoked respectively for that
feature. For features that don't require resetting any state, this works
fine. However, there will be an upcoming feature called SHARED_RUNQ
which needs to drain all tasks from a set of global shared runqueues in
order to avoid stale tasks from staying in the queues after the feature
has been disabled.

This patch therefore defines a new SCHED_FEAT_CALLBACK macro which
allows scheduler features to specify a callback that should be invoked
when a feature is enabled or disabled respectively. The SCHED_FEAT macro
assumes a NULL callback.

Signed-off-by: David Vernet <void@manifault.com>
---
 kernel/sched/core.c  |  4 ++--
 kernel/sched/debug.c | 18 ++++++++++++++----
 kernel/sched/sched.h | 16 ++++++++++------
 3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9ad7f0255e14..045ac2539f37 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -124,12 +124,12 @@ DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
  * sysctl_sched_features, defined in sched.h, to allow constants propagation
  * at compile time and compiler optimization based on features default.
  */
-#define SCHED_FEAT(name, enabled)	\
+#define SCHED_FEAT_CALLBACK(name, enabled, cb)	\
 	(1UL << __SCHED_FEAT_##name) * enabled |
 const_debug unsigned int sysctl_sched_features =
 #include "features.h"
 	0;
-#undef SCHED_FEAT
+#undef SCHED_FEAT_CALLBACK
 
 /*
  * Print a warning if need_resched is set for the given duration (if
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 168eecc209b4..0b72799c7e84 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -44,14 +44,14 @@ static unsigned long nsec_low(unsigned long long nsec)
 
 #define SPLIT_NS(x) nsec_high(x), nsec_low(x)
 
-#define SCHED_FEAT(name, enabled)	\
+#define SCHED_FEAT_CALLBACK(name, enabled, cb)	\
 	#name ,
 
 static const char * const sched_feat_names[] = {
 #include "features.h"
 };
 
-#undef SCHED_FEAT
+#undef SCHED_FEAT_CALLBACK
 
 static int sched_feat_show(struct seq_file *m, void *v)
 {
@@ -72,22 +72,32 @@ static int sched_feat_show(struct seq_file *m, void *v)
 #define jump_label_key__true  STATIC_KEY_INIT_TRUE
 #define jump_label_key__false STATIC_KEY_INIT_FALSE
 
-#define SCHED_FEAT(name, enabled)	\
+#define SCHED_FEAT_CALLBACK(name, enabled, cb)	\
 	jump_label_key__##enabled ,
 
 struct static_key sched_feat_keys[__SCHED_FEAT_NR] = {
 #include "features.h"
 };
 
-#undef SCHED_FEAT
+#undef SCHED_FEAT_CALLBACK
+
+#define SCHED_FEAT_CALLBACK(name, enabled, cb) cb,
+static const sched_feat_change_f sched_feat_cbs[__SCHED_FEAT_NR] = {
+#include "features.h"
+};
+#undef SCHED_FEAT_CALLBACK
 
 static void sched_feat_disable(int i)
 {
+	if (sched_feat_cbs[i])
+		sched_feat_cbs[i](false);
 	static_key_disable_cpuslocked(&sched_feat_keys[i]);
 }
 
 static void sched_feat_enable(int i)
 {
+	if (sched_feat_cbs[i])
+		sched_feat_cbs[i](true);
 	static_key_enable_cpuslocked(&sched_feat_keys[i]);
 }
 #else
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 53fe2294eec7..517e67a0cc9a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2091,6 +2091,8 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
 #endif
 }
 
+#define SCHED_FEAT(name, enabled) SCHED_FEAT_CALLBACK(name, enabled, NULL)
+
 /*
  * Tunables that become constants when CONFIG_SCHED_DEBUG is off:
  */
@@ -2100,7 +2102,7 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
 # define const_debug const
 #endif
 
-#define SCHED_FEAT(name, enabled)	\
+#define SCHED_FEAT_CALLBACK(name, enabled, cb)	\
 	__SCHED_FEAT_##name ,
 
 enum {
@@ -2108,7 +2110,7 @@ enum {
 	__SCHED_FEAT_NR,
 };
 
-#undef SCHED_FEAT
+#undef SCHED_FEAT_CALLBACK
 
 #ifdef CONFIG_SCHED_DEBUG
 
@@ -2119,14 +2121,14 @@ enum {
 extern const_debug unsigned int sysctl_sched_features;
 
 #ifdef CONFIG_JUMP_LABEL
-#define SCHED_FEAT(name, enabled)					\
+#define SCHED_FEAT_CALLBACK(name, enabled, cb)				\
 static __always_inline bool static_branch_##name(struct static_key *key) \
 {									\
 	return static_key_##enabled(key);				\
 }
 
 #include "features.h"
-#undef SCHED_FEAT
+#undef SCHED_FEAT_CALLBACK
 
 extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
 #define sched_feat(x) (static_branch_##x(&sched_feat_keys[__SCHED_FEAT_##x]))
@@ -2144,17 +2146,19 @@ extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
  * constants propagation at compile time and compiler optimization based on
  * features default.
  */
-#define SCHED_FEAT(name, enabled)	\
+#define SCHED_FEAT_CALLBACK(name, enabled, cb)	\
 	(1UL << __SCHED_FEAT_##name) * enabled |
 static const_debug __maybe_unused unsigned int sysctl_sched_features =
 #include "features.h"
 	0;
-#undef SCHED_FEAT
+#undef SCHED_FEAT_CALLBACK
 
 #define sched_feat(x) !!(sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
 
 #endif /* SCHED_DEBUG */
 
+typedef void (*sched_feat_change_f)(bool enabling);
+
 extern struct static_key_false sched_numa_balancing;
 extern struct static_key_false sched_schedstats;
 
-- 
2.42.1