[PATCH v2] sched: Convert last bits of deprecated static key usage

[PATCH v2] sched: Convert last bits of deprecated static key usage

[Hongyan Xia]

From: Hongyan Xia <hongyan.xia@transsion.com>

Raw static keys have no type information and do not prevent mis-matches
(like static_key_false() on a default TRUE key). The helper names
static_key_{true/false}() are also confusing, hence the deprecation.

We have already converted other sites in previous patches. Convert the
last sites of deprecated static key APIs. After this fix, scheduler code
has zero deprecated static key APIs now.

sk_dynamic_* uses static_key_{enable/disable}(), which aren't really
deprecated, but take the opportunity to move to the new static_branch_*
APIs to be consistent.

No functional change.

Signed-off-by: Hongyan Xia <hongyan.xia@transsion.com>
---
Changed in v2:
- Explain why old ones are deprecated.
- Rebase and fix a big conflict in core.c.

 kernel/sched/core.c | 8 ++++----
 kernel/sched/fair.c | 8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5a61650f12b7..792931f5ef13 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7881,8 +7881,8 @@ int sched_dynamic_mode(const char *str)
 	return -EINVAL;
 }
 
-# define preempt_dynamic_key_enable(f)	static_key_enable(&sk_dynamic_##f.key)
-# define preempt_dynamic_key_disable(f)	static_key_disable(&sk_dynamic_##f.key)
+# define preempt_dynamic_branch_enable(f)	static_branch_enable(&sk_dynamic_##f)
+# define preempt_dynamic_branch_disable(f)	static_branch_disable(&sk_dynamic_##f)
 
 static DEFINE_MUTEX(sched_dynamic_mutex);
 
@@ -7890,13 +7890,13 @@ static void __sched_dynamic_update(int mode)
 {
 	switch (mode) {
 	case preempt_dynamic_full:
-		preempt_dynamic_key_disable(preempt_lazy);
+		preempt_dynamic_branch_disable(preempt_lazy);
 		if (mode != preempt_dynamic_mode)
 			pr_info("Dynamic Preempt: full\n");
 		break;
 
 	case preempt_dynamic_lazy:
-		preempt_dynamic_key_enable(preempt_lazy);
+		preempt_dynamic_branch_enable(preempt_lazy);
 		if (mode != preempt_dynamic_mode)
 			pr_info("Dynamic Preempt: lazy\n");
 		break;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b8bd308c2d5b..d8abc940ab0f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6575,21 +6575,21 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 #ifdef CONFIG_CFS_BANDWIDTH
 
 #ifdef CONFIG_JUMP_LABEL
-static struct static_key __cfs_bandwidth_used;
+static DEFINE_STATIC_KEY_FALSE(__cfs_bandwidth_used);
 
 static inline bool cfs_bandwidth_used(void)
 {
-	return static_key_false(&__cfs_bandwidth_used);
+	return static_branch_unlikely(&__cfs_bandwidth_used);
 }
 
 void cfs_bandwidth_usage_inc(void)
 {
-	static_key_slow_inc_cpuslocked(&__cfs_bandwidth_used);
+	static_branch_inc_cpuslocked(&__cfs_bandwidth_used);
 }
 
 void cfs_bandwidth_usage_dec(void)
 {
-	static_key_slow_dec_cpuslocked(&__cfs_bandwidth_used);
+	static_branch_dec_cpuslocked(&__cfs_bandwidth_used);
 }
 #else /* !CONFIG_JUMP_LABEL: */
 static bool cfs_bandwidth_used(void)
-- 
2.47.3

Re: [PATCH v2] sched: Convert last bits of deprecated static key usage

[Valentin Schneider]

On 03/09/26 11:57, Hongyan Xia wrote:
> From: Hongyan Xia <hongyan.xia@transsion.com>
>
> Raw static keys have no type information and do not prevent mis-matches
> (like static_key_false() on a default TRUE key). The helper names
> static_key_{true/false}() are also confusing, hence the deprecation.
>
> We have already converted other sites in previous patches. Convert the
> last sites of deprecated static key APIs. After this fix, scheduler code
> has zero deprecated static key APIs now.
>
> sk_dynamic_* uses static_key_{enable/disable}(), which aren't really
> deprecated, but take the opportunity to move to the new static_branch_*
> APIs to be consistent.
>
> No functional change.
>
> Signed-off-by: Hongyan Xia <hongyan.xia@transsion.com>

Some comprehension/changelog explanation nit below, otherwise:

Reviewed-by: Valentin Schneider <vschneid@redhat.com>

> @@ -6575,21 +6575,21 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
>  #ifdef CONFIG_CFS_BANDWIDTH
>
>  #ifdef CONFIG_JUMP_LABEL
> -static struct static_key __cfs_bandwidth_used;
> +static DEFINE_STATIC_KEY_FALSE(__cfs_bandwidth_used);
>
>  static inline bool cfs_bandwidth_used(void)
>  {
> -	return static_key_false(&__cfs_bandwidth_used);
> +	return static_branch_unlikely(&__cfs_bandwidth_used);
>  }

Usual likely/unlikely/true/false static key confusion for me here;

The previous definition was pretty much
 = STATIC_KEY_INIT_FALSE
due to static storage initialization.

And then for the static_key_*() naming, false == unlikely.

Because it's all #define magic I assume the compilation delta will be zero,
but I can't be bothered given I'm on a laptop running power saver mode.

Re: [PATCH v2] sched: Convert last bits of deprecated static key usage

[Valentin Schneider]

On 06/10/26 12:50, Valentin Schneider wrote:
> On 03/09/26 11:57, Hongyan Xia wrote:
>> From: Hongyan Xia <hongyan.xia@transsion.com>
>>
>> Raw static keys have no type information and do not prevent mis-matches
>> (like static_key_false() on a default TRUE key). The helper names
>> static_key_{true/false}() are also confusing, hence the deprecation.
>>
>> We have already converted other sites in previous patches. Convert the
>> last sites of deprecated static key APIs. After this fix, scheduler code
>> has zero deprecated static key APIs now.
>>
>> sk_dynamic_* uses static_key_{enable/disable}(), which aren't really
>> deprecated, but take the opportunity to move to the new static_branch_*
>> APIs to be consistent.
>>
>> No functional change.
>>
>> Signed-off-by: Hongyan Xia <hongyan.xia@transsion.com>
>
> Some comprehension/changelog explanation nit below, otherwise:
>
> Reviewed-by: Valentin Schneider <vschneid@redhat.com>
>

A quick search tells me there's still some static_key() usage spread
through the kernel, that really should be fixed in a single series powered
by coccinelle or somesuch.

Re: [PATCH v2] sched: Convert last bits of deprecated static key usage

[Hongyan Xia]

On 10/6/2026 6:50 PM, Valentin Schneider wrote:
> On 03/09/26 11:57, Hongyan Xia wrote:
>> From: Hongyan Xia <hongyan.xia@transsion.com>
>>
>> Raw static keys have no type information and do not prevent mis-matches
>> (like static_key_false() on a default TRUE key). The helper names
>> static_key_{true/false}() are also confusing, hence the deprecation.
>>
>> We have already converted other sites in previous patches. Convert the
>> last sites of deprecated static key APIs. After this fix, scheduler code
>> has zero deprecated static key APIs now.
>>
>> sk_dynamic_* uses static_key_{enable/disable}(), which aren't really
>> deprecated, but take the opportunity to move to the new static_branch_*
>> APIs to be consistent.
>>
>> No functional change.
>>
>> Signed-off-by: Hongyan Xia <hongyan.xia@transsion.com>
> 
> Some comprehension/changelog explanation nit below, otherwise:
> 
> Reviewed-by: Valentin Schneider <vschneid@redhat.com>
> 
>> @@ -6575,21 +6575,21 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
>>   #ifdef CONFIG_CFS_BANDWIDTH
>>
>>   #ifdef CONFIG_JUMP_LABEL
>> -static struct static_key __cfs_bandwidth_used;
>> +static DEFINE_STATIC_KEY_FALSE(__cfs_bandwidth_used);
>>
>>   static inline bool cfs_bandwidth_used(void)
>>   {
>> -	return static_key_false(&__cfs_bandwidth_used);
>> +	return static_branch_unlikely(&__cfs_bandwidth_used);
>>   }
> 
> Usual likely/unlikely/true/false static key confusion for me here;
> 
> The previous definition was pretty much
>   = STATIC_KEY_INIT_FALSE
> due to static storage initialization.
> 
> And then for the static_key_*() naming, false == unlikely.
> 
> Because it's all #define magic I assume the compilation delta will be zero,
> but I can't be bothered given I'm on a laptop running power saver mode.

This is exactly what I checked before sending this patch. The good news 
is that at least on my machine, the delta in the machine code is zero 
under aarch64 and x86.