Re: [PATCH 4/5] sched: dynamic: Simplify irqentry_exit_cond_resched()

[Shrikanth Hegde <sshegde@linux.ibm.com>]

+cc Christophe.

On 7/3/26 7:03 PM, Mark Rutland wrote:
> PREEMPT_DYNAMIC is now limited to the FULL and LAZY preemption models.
> In either model, irqentry_exit_cond_resched() is always called and never
> disabled.
> 
> Remove the unnecessary code for this when PREEMPT_DYNAMIC is selected.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: John Stultz <jstultz@google.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>   arch/powerpc/include/asm/preempt.h |  7 -------
>   include/linux/irq-entry-common.h   | 17 +----------------
>   kernel/entry/common.c              | 17 ++---------------
>   kernel/sched/core.c                |  7 -------
>   4 files changed, 3 insertions(+), 45 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/preempt.h b/arch/powerpc/include/asm/preempt.h
> index 000e2b9681f30..79fc1f9df88d9 100644
> --- a/arch/powerpc/include/asm/preempt.h
> +++ b/arch/powerpc/include/asm/preempt.h
> @@ -4,13 +4,6 @@
>   
>   #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
>   

JFYI,
Christophe had sent this patch, I am sure you guys will sort out the
conflicts. (I don't see it merged yet, but likely might)

https://lore.kernel.org/all/2bf10a0afffefb6aca44bf2f864cc17471a80e31.1781870889.git.chleroy@kernel.org/

>   #endif /* __ASM_POWERPC_PREEMPT_H */
> diff --git a/include/linux/irq-entry-common.h b/include/linux/irq-entry-common.h
> index 1fabf0f5ea8e7..de7e10de91d04 100644
> --- a/include/linux/irq-entry-common.h
> +++ b/include/linux/irq-entry-common.h
> @@ -346,22 +346,7 @@ typedef struct irqentry_state {
>    *
>    * Conditional reschedule with additional sanity checks.
>    */
> -void raw_irqentry_exit_cond_resched(void);
> -
> -#ifdef CONFIG_PREEMPT_DYNAMIC
> -#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> -#define irqentry_exit_cond_resched_dynamic_enabled	raw_irqentry_exit_cond_resched
> -#define irqentry_exit_cond_resched_dynamic_disabled	NULL
> -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
> -#else /* CONFIG_PREEMPT_DYNAMIC */
> -#define irqentry_exit_cond_resched()	raw_irqentry_exit_cond_resched()
> -#endif /* CONFIG_PREEMPT_DYNAMIC */
> +void irqentry_exit_cond_resched(void);
>   
>   /**
>    * irqentry_enter_from_kernel_mode - Establish state before invoking the irq handler
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index e3d381fd3d251..e234b04373fea 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -123,7 +123,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
>   /**
>    * arch_irqentry_exit_need_resched - Architecture specific need resched function
>    *
> - * Invoked from raw_irqentry_exit_cond_resched() to check if resched is needed.
> + * Invoked from irqentry_exit_cond_resched() to check if resched is needed.
>    * Defaults return true.
>    *
>    * The main purpose is to permit arch to avoid preemption of a task from an IRQ.
> @@ -134,7 +134,7 @@ static inline bool arch_irqentry_exit_need_resched(void);
>   static inline bool arch_irqentry_exit_need_resched(void) { return true; }
>   #endif
>   
> -void raw_irqentry_exit_cond_resched(void)
> +void irqentry_exit_cond_resched(void)
>   {
>   	if (!preempt_count()) {
>   		/* Sanity check RCU and thread stack */
> @@ -145,19 +145,6 @@ void raw_irqentry_exit_cond_resched(void)
>   			preempt_schedule_irq();
>   	}
>   }
> -#ifdef CONFIG_PREEMPT_DYNAMIC
> -#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))
> -		return;
> -	raw_irqentry_exit_cond_resched();
> -}
> -#endif
> -#endif
>   
>   noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
>   {
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index f88b9ef70a0dd..4f754f4a472f8 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7788,9 +7788,6 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write);
>   # endif
>   
>   /*
> - * SC:irqentry_exit_cond_resched
> - *
> - *
>    * NONE:
>    *   (unselectable)
>    *
> @@ -7798,11 +7795,9 @@ EXPORT_SYMBOL(__cond_resched_rwlock_write);
>    *   (unselectable)
>    *
>    * FULL:
> - *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
>    *   dynamic_preempt_lazy       <- false
>    *
>    * LAZY:
> - *   irqentry_exit_cond_resched <- irqentry_exit_cond_resched
>    *   dynamic_preempt_lazy       <- true
>    */
>   
> @@ -7846,14 +7841,12 @@ static void __sched_dynamic_update(int mode)
>   {
>   	switch (mode) {
>   	case preempt_dynamic_full:
> -		preempt_dynamic_enable(irqentry_exit_cond_resched);
>   		preempt_dynamic_key_disable(preempt_lazy);
>   		if (mode != preempt_dynamic_mode)
>   			pr_info("Dynamic Preempt: full\n");
>   		break;
>   
>   	case preempt_dynamic_lazy:
> -		preempt_dynamic_enable(irqentry_exit_cond_resched);
>   		preempt_dynamic_key_enable(preempt_lazy);
>   		if (mode != preempt_dynamic_mode)
>   			pr_info("Dynamic Preempt: lazy\n");

Change per se, looks good to me.

Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>