[PATCH v2 0/1] powerpc, arm64: move preempt dynamic key into kernel/sched

[PATCH v2 0/1] powerpc, arm64: move preempt dynamic key into kernel/sched

[Shrikanth Hegde]

Current usage of preempt dynamic key is not specific to architecture and
can be moved into sched/core instead. Most of the code around it looks
similar. (same code for powerpc, arm64). 

Since preemption is more associated with scheduler rather than
entry/exit, it is probably better it should be moved. 

This is tested on powerVM PREEMPT_DYNAMIC=y/n and on arm64 by Mark

v1->v2:
- Rebase to 6.16-rc6
- Collected the tags

Ingo, Peter, 
Can this go via tip sched tree? 

Both arm64, powerpc have acked the changes and been tested. 

Shrikanth Hegde (1):
  sched: preempt: Move dynamic keys into kernel/sched

 arch/arm64/include/asm/preempt.h   |  1 -
 arch/arm64/kernel/entry-common.c   |  8 --------
 arch/powerpc/include/asm/preempt.h | 16 ----------------
 arch/powerpc/kernel/interrupt.c    |  4 ----
 include/linux/irq-entry-common.h   |  1 -
 include/linux/sched.h              |  8 ++++++++
 kernel/entry/common.c              |  1 -
 kernel/sched/core.c                |  4 ++++
 8 files changed, 12 insertions(+), 31 deletions(-)
 delete mode 100644 arch/powerpc/include/asm/preempt.h

-- 
2.43.0

[PATCH v2 1/1] sched: preempt: Move dynamic keys into kernel/sched

[Shrikanth Hegde]

Dynamic preemption can be static key or static call based.
Static key is used to check kernel preemption depending on
the current preemption model. i.e enable for lazy, full. 

Code is currently spread across entry/common.c, arm64 and latest being
powerpc. There is little arch specific to it. arm64, powerpc have the
same code. It is better to move it into kernel/sched since preemption 
is more closely associated with scheduler.  

Plus, Any new arch that wants dynamic preemption enabled need to have 
only HAVE_PREEMPT_DYNAMIC_KEY. 

Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Madhavan Srinivasan <maddy@linux.ibm.com>
---
 arch/arm64/include/asm/preempt.h   |  1 -
 arch/arm64/kernel/entry-common.c   |  8 --------
 arch/powerpc/include/asm/preempt.h | 16 ----------------
 arch/powerpc/kernel/interrupt.c    |  4 ----
 include/linux/irq-entry-common.h   |  1 -
 include/linux/sched.h              |  8 ++++++++
 kernel/entry/common.c              |  1 -
 kernel/sched/core.c                |  4 ++++
 8 files changed, 12 insertions(+), 31 deletions(-)
 delete mode 100644 arch/powerpc/include/asm/preempt.h

diff --git a/arch/arm64/include/asm/preempt.h b/arch/arm64/include/asm/preempt.h
index 0159b625cc7f..a9348e65d75e 100644
--- a/arch/arm64/include/asm/preempt.h
+++ b/arch/arm64/include/asm/preempt.h
@@ -87,7 +87,6 @@ void preempt_schedule_notrace(void);
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 
-DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
 void dynamic_preempt_schedule(void);
 #define __preempt_schedule()		dynamic_preempt_schedule()
 void dynamic_preempt_schedule_notrace(void);
diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 7c1970b341b8..f4985ae4d8a9 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -259,14 +259,6 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs)
 		lockdep_hardirqs_on(CALLER_ADDR0);
 }
 
-#ifdef CONFIG_PREEMPT_DYNAMIC
-DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
-#define need_irq_preemption() \
-	(static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
-#else
-#define need_irq_preemption()	(IS_ENABLED(CONFIG_PREEMPTION))
-#endif
-
 static void __sched arm64_preempt_schedule_irq(void)
 {
 	if (!need_irq_preemption())
diff --git a/arch/powerpc/include/asm/preempt.h b/arch/powerpc/include/asm/preempt.h
deleted file mode 100644
index 000e2b9681f3..000000000000
--- a/arch/powerpc/include/asm/preempt.h
+++ /dev/null
@@ -1,16 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef __ASM_POWERPC_PREEMPT_H
-#define __ASM_POWERPC_PREEMPT_H
-
-#include <asm-generic/preempt.h>
-
-#if defined(CONFIG_PREEMPT_DYNAMIC)
-#include <linux/jump_label.h>
-DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
-#define need_irq_preemption() \
-	(static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
-#else
-#define need_irq_preemption()   (IS_ENABLED(CONFIG_PREEMPTION))
-#endif
-
-#endif /* __ASM_POWERPC_PREEMPT_H */
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index e0c681d0b076..4d62d785ad26 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -25,10 +25,6 @@
 unsigned long global_dbcr0[NR_CPUS];
 #endif
 
-#if defined(CONFIG_PREEMPT_DYNAMIC)
-DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
-#endif
-
 #ifdef CONFIG_PPC_BOOK3S_64
 DEFINE_STATIC_KEY_FALSE(interrupt_exit_not_reentrant);
 static inline bool exit_must_hard_disable(void)
diff --git a/include/linux/irq-entry-common.h b/include/linux/irq-entry-common.h
index 8af374331900..5bb752f0a69c 100644
--- a/include/linux/irq-entry-common.h
+++ b/include/linux/irq-entry-common.h
@@ -343,7 +343,6 @@ void raw_irqentry_exit_cond_resched(void);
 DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
 #define irqentry_exit_cond_resched()	static_call(irqentry_exit_cond_resched)()
 #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
-DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
 void dynamic_irqentry_exit_cond_resched(void);
 #define irqentry_exit_cond_resched()	dynamic_irqentry_exit_cond_resched()
 #endif
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 54a91261e99b..df9a87de0f83 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2076,6 +2076,14 @@ static inline int _cond_resched(void)
 
 #endif /* !CONFIG_PREEMPTION || CONFIG_PREEMPT_DYNAMIC */
 
+#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
+#define need_irq_preemption() \
+	(static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
+#else
+#define need_irq_preemption()   (IS_ENABLED(CONFIG_PREEMPTION))
+#endif
+
 #define cond_resched() ({			\
 	__might_resched(__FILE__, __LINE__, 0);	\
 	_cond_resched();			\
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index b82032777310..0ffe3d5a6c44 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -157,7 +157,6 @@ void raw_irqentry_exit_cond_resched(void)
 #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
 #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
-DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
 void dynamic_irqentry_exit_cond_resched(void)
 {
 	if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c73c9ca6ca01..8425008c99f1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6999,6 +6999,10 @@ EXPORT_SYMBOL(dynamic_preempt_schedule_notrace);
 
 #endif /* CONFIG_PREEMPTION */
 
+#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
+#endif
+
 /*
  * This is the entry point to schedule() from kernel preemption
  * off of IRQ context.
-- 
2.43.0

Re: [PATCH v2 1/1] sched: preempt: Move dynamic keys into kernel/sched

[Venkat]

> On 16 Jul 2025, at 3:17 PM, Shrikanth Hegde <sshegde@linux.ibm.com> wrote:
> 
> Dynamic preemption can be static key or static call based.
> Static key is used to check kernel preemption depending on
> the current preemption model. i.e enable for lazy, full. 
> 
> Code is currently spread across entry/common.c, arm64 and latest being
> powerpc. There is little arch specific to it. arm64, powerpc have the
> same code. It is better to move it into kernel/sched since preemption 
> is more closely associated with scheduler.  
> 
> Plus, Any new arch that wants dynamic preemption enabled need to have 
> only HAVE_PREEMPT_DYNAMIC_KEY. 
> 
> Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Will Deacon <will@kernel.org>
> Acked-by: Madhavan Srinivasan <maddy@linux.ibm.com>
> ---
> arch/arm64/include/asm/preempt.h   |  1 -
> arch/arm64/kernel/entry-common.c   |  8 --------
> arch/powerpc/include/asm/preempt.h | 16 ----------------
> arch/powerpc/kernel/interrupt.c    |  4 ----
> include/linux/irq-entry-common.h   |  1 -
> include/linux/sched.h              |  8 ++++++++
> kernel/entry/common.c              |  1 -
> kernel/sched/core.c                |  4 ++++
> 8 files changed, 12 insertions(+), 31 deletions(-)
> delete mode 100644 arch/powerpc/include/asm/preempt.h
> 
> diff --git a/arch/arm64/include/asm/preempt.h b/arch/arm64/include/asm/preempt.h
> index 0159b625cc7f..a9348e65d75e 100644
> --- a/arch/arm64/include/asm/preempt.h
> +++ b/arch/arm64/include/asm/preempt.h
> @@ -87,7 +87,6 @@ void preempt_schedule_notrace(void);
> 
> #ifdef CONFIG_PREEMPT_DYNAMIC
> 
> -DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> void dynamic_preempt_schedule(void);
> #define __preempt_schedule() dynamic_preempt_schedule()
> void dynamic_preempt_schedule_notrace(void);
> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
> index 7c1970b341b8..f4985ae4d8a9 100644
> --- a/arch/arm64/kernel/entry-common.c
> +++ b/arch/arm64/kernel/entry-common.c
> @@ -259,14 +259,6 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs)
> lockdep_hardirqs_on(CALLER_ADDR0);
> }
> 
> -#ifdef CONFIG_PREEMPT_DYNAMIC
> -DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> -#define need_irq_preemption() \
> - (static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> -#else
> -#define need_irq_preemption() (IS_ENABLED(CONFIG_PREEMPTION))
> -#endif
> -
> static void __sched arm64_preempt_schedule_irq(void)
> {
> if (!need_irq_preemption())
> diff --git a/arch/powerpc/include/asm/preempt.h b/arch/powerpc/include/asm/preempt.h
> deleted file mode 100644
> index 000e2b9681f3..000000000000
> --- a/arch/powerpc/include/asm/preempt.h
> +++ /dev/null
> @@ -1,16 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0 */
> -#ifndef __ASM_POWERPC_PREEMPT_H
> -#define __ASM_POWERPC_PREEMPT_H
> -
> -#include <asm-generic/preempt.h>
> -
> -#if defined(CONFIG_PREEMPT_DYNAMIC)
> -#include <linux/jump_label.h>
> -DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> -#define need_irq_preemption() \
> - (static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> -#else
> -#define need_irq_preemption()   (IS_ENABLED(CONFIG_PREEMPTION))
> -#endif
> -
> -#endif /* __ASM_POWERPC_PREEMPT_H */
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index e0c681d0b076..4d62d785ad26 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -25,10 +25,6 @@
> unsigned long global_dbcr0[NR_CPUS];
> #endif
> 
> -#if defined(CONFIG_PREEMPT_DYNAMIC)
> -DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> -#endif
> -
> #ifdef CONFIG_PPC_BOOK3S_64
> DEFINE_STATIC_KEY_FALSE(interrupt_exit_not_reentrant);
> static inline bool exit_must_hard_disable(void)
> diff --git a/include/linux/irq-entry-common.h b/include/linux/irq-entry-common.h
> index 8af374331900..5bb752f0a69c 100644
> --- a/include/linux/irq-entry-common.h
> +++ b/include/linux/irq-entry-common.h
> @@ -343,7 +343,6 @@ void raw_irqentry_exit_cond_resched(void);
> DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> #define irqentry_exit_cond_resched() static_call(irqentry_exit_cond_resched)()
> #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> -DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> void dynamic_irqentry_exit_cond_resched(void);
> #define irqentry_exit_cond_resched() dynamic_irqentry_exit_cond_resched()
> #endif
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 54a91261e99b..df9a87de0f83 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2076,6 +2076,14 @@ static inline int _cond_resched(void)
> 
> #endif /* !CONFIG_PREEMPTION || CONFIG_PREEMPT_DYNAMIC */
> 
> +#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> +#define need_irq_preemption() \
> + (static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> +#else
> +#define need_irq_preemption()   (IS_ENABLED(CONFIG_PREEMPTION))
> +#endif
> +
> #define cond_resched() ({ \
> __might_resched(__FILE__, __LINE__, 0); \
> _cond_resched(); \
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index b82032777310..0ffe3d5a6c44 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -157,7 +157,6 @@ void raw_irqentry_exit_cond_resched(void)
> #if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> #elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> -DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> void dynamic_irqentry_exit_cond_resched(void)
> {
> if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c73c9ca6ca01..8425008c99f1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6999,6 +6999,10 @@ EXPORT_SYMBOL(dynamic_preempt_schedule_notrace);
> 
> #endif /* CONFIG_PREEMPTION */
> 
> +#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> +#endif
> +
> /*
>  * This is the entry point to schedule() from kernel preemption
>  * off of IRQ context.
> -- 
> 2.43.0
> 



<Resending to the right thread>


Tested this patch, by applying on top of mainline kernel. 

Dynamically changed the preemption modes, and its working as expected. Hence,

Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>

Regards,
Venkat.

Re: [PATCH v2 1/1] sched: preempt: Move dynamic keys into kernel/sched

[Shrikanth Hegde]

On 7/16/25 15:17, Shrikanth Hegde wrote:
> Dynamic preemption can be static key or static call based.
> Static key is used to check kernel preemption depending on
> the current preemption model. i.e enable for lazy, full.
> 
> Code is currently spread across entry/common.c, arm64 and latest being
> powerpc. There is little arch specific to it. arm64, powerpc have the
> same code. It is better to move it into kernel/sched since preemption
> is more closely associated with scheduler.
> 
> Plus, Any new arch that wants dynamic preemption enabled need to have
> only HAVE_PREEMPT_DYNAMIC_KEY.
> 
> Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Will Deacon <will@kernel.org>
> Acked-by: Madhavan Srinivasan <maddy@linux.ibm.com>
> ---
>   arch/arm64/include/asm/preempt.h   |  1 -
>   arch/arm64/kernel/entry-common.c   |  8 --------
>   arch/powerpc/include/asm/preempt.h | 16 ----------------
>   arch/powerpc/kernel/interrupt.c    |  4 ----
>   include/linux/irq-entry-common.h   |  1 -
>   include/linux/sched.h              |  8 ++++++++
>   kernel/entry/common.c              |  1 -
>   kernel/sched/core.c                |  4 ++++
>   8 files changed, 12 insertions(+), 31 deletions(-)
>   delete mode 100644 arch/powerpc/include/asm/preempt.h
> 

Hi Ingo, Peter.

Does this change makes sense? Are there any further concerns that you see?
Also can it go via tip tree?

Patch applies on 6.17-rc1 (at commit ca76508b9352e8c770b58213cc6c4700e459b7c2)

Re: [PATCH v2 1/1] sched: preempt: Move dynamic keys into kernel/sched

[Venkat]

Tested this patch, by applying on top of mainline kernel. 

Dynamically changed the preemption modes, and its working as expected. Hence,

Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>

Regards,
Venkat.