[PATCH v2 4/4] sched/numa: Convert sched_numa_balancing to a static_branch

[Srikar Dronamraju]

Variable sched_numa_balancing toggles numa_balancing feature. Hence
moving from a simple read mostly variable to a more apt static_branch.

Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
---
 kernel/sched/core.c  | 10 +++++++---
 kernel/sched/fair.c  |  6 +++---
 kernel/sched/sched.h |  6 +-----
 3 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d02570b..5f330d5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2057,12 +2057,16 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 #endif /* CONFIG_NUMA_BALANCING */
 }
 
+DEFINE_STATIC_KEY_FALSE(sched_numa_balancing);
+
 #ifdef CONFIG_NUMA_BALANCING
-__read_mostly bool sched_numa_balancing;
 
 void set_numabalancing_state(bool enabled)
 {
-	sched_numa_balancing = enabled;
+	if (enabled)
+		static_branch_enable(&sched_numa_balancing);
+	else
+		static_branch_disable(&sched_numa_balancing);
 }
 
 #ifdef CONFIG_PROC_SYSCTL
@@ -2071,7 +2075,7 @@ int sysctl_numa_balancing(struct ctl_table *table, int write,
 {
 	struct ctl_table t;
 	int err;
-	int state = sched_numa_balancing;
+	int state = static_branch_likely(&sched_numa_balancing);
 
 	if (write && !capable(CAP_SYS_ADMIN))
 		return -EPERM;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f67f2bc..aab730e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2069,7 +2069,7 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
 	int local = !!(flags & TNF_FAULT_LOCAL);
 	int priv;
 
-	if (!sched_numa_balancing)
+	if (!static_branch_likely(&sched_numa_balancing))
 		return;
 
 	/* for example, ksmd faulting in a user's mm */
@@ -5524,7 +5524,7 @@ static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
 	unsigned long src_faults, dst_faults;
 	int src_nid, dst_nid;
 
-	if (!sched_numa_balancing)
+	if (!static_branch_likely(&sched_numa_balancing))
 		return -1;
 
 	if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
@@ -7810,7 +7810,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
 		entity_tick(cfs_rq, se, queued);
 	}
 
-	if (sched_numa_balancing)
+	if (!static_branch_unlikely(&sched_numa_balancing))
 		task_tick_numa(rq, curr);
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 953be0f..72cae5d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1003,11 +1003,7 @@ extern struct static_key sched_feat_keys[__SCHED_FEAT_NR];
 #define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
 #endif /* SCHED_DEBUG && HAVE_JUMP_LABEL */
 
-#ifdef CONFIG_NUMA_BALANCING
-extern bool sched_numa_balancing;
-#else
-#define sched_numa_balancing (0)
-#endif /* CONFIG_NUMA_BALANCING */
+extern struct static_key_false sched_numa_balancing;
 
 static inline u64 global_rt_period(void)
 {
-- 
1.8.3.1

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