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

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Message-Id: <6A55B96B-C9B6-46CE-A17F-1E580DFF8300@linux.ibm.com>
Date: Mon, 4 Aug 2025 12:36:17 +0530
From: Venkat <venkat88@...ux.ibm.com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: mingo@...hat.com, Peter Zijlstra <peterz@...radead.org>,
        tglx@...utronix.de, maddy@...ux.ibm.com, will@...nel.org,
        mark.rutland@....com, bigeasy@...utronix.de,
        LKML <linux-kernel@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 1/1] sched: preempt: Move dynamic keys into
 kernel/sched



> On 16 Jul 2025, at 3:17 PM, Shrikanth Hegde <sshegde@...ux.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@...utronix.de>
> Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
> Acked-by: Mark Rutland <mark.rutland@....com>
> Acked-by: Will Deacon <will@...nel.org>
> Acked-by: Madhavan Srinivasan <maddy@...ux.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@...ux.ibm.com>

Regards,
Venkat.