Re: [PATCH -next v7 5/7] arm64: entry: Refactor preempt_schedule_irq() check code

[Jinjie Ruan <ruanjinjie@xxxxxxxxxx>]

On 2025/8/12 19:13, Mark Rutland wrote:
> On Tue, Jul 29, 2025 at 09:54:54AM +0800, Jinjie Ruan wrote:
>> ARM64 requires an additional check whether to reschedule on return
>> from interrupt. So add arch_irqentry_exit_need_resched() as the default
>> NOP implementation and hook it up into the need_resched() condition in
>> raw_irqentry_exit_cond_resched(). This allows ARM64 to implement
>> the architecture specific version for switching over to
>> the generic entry code.
>>
>> To align the structure of the code with irqentry_exit_cond_resched()
>> from the generic entry code, hoist the need_irq_preemption()
>> and IS_ENABLED() check earlier. And different preemption check functions
>> are defined based on whether dynamic preemption is enabled.
>>
>> Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
>> Suggested-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
>> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
>> ---
>>  arch/arm64/include/asm/preempt.h |  4 ++++
>>  arch/arm64/kernel/entry-common.c | 35 ++++++++++++++++++--------------
>>  kernel/entry/common.c            | 16 ++++++++++++++-
>>  3 files changed, 39 insertions(+), 16 deletions(-)
> 
> Can you please split the change to kernel/entry/common.c into a separate
> patch? That doesn't depend on the arm64-specific changes, and it'll make
> it easier to handle any conflcits when merging this.

Sure, I'll split the change into separate patch.

> 
> Mark.
> 
>>
>> diff --git a/arch/arm64/include/asm/preempt.h 
>> b/arch/arm64/include/asm/preempt.h
>> index 0159b625cc7f..0f0ba250efe8 100644
>> --- a/arch/arm64/include/asm/preempt.h
>> +++ b/arch/arm64/include/asm/preempt.h
>> @@ -85,6 +85,7 @@ static inline bool should_resched(int preempt_offset)
>>  void preempt_schedule(void);
>>  void preempt_schedule_notrace(void);
>>  
>> +void raw_irqentry_exit_cond_resched(void);
>>  #ifdef CONFIG_PREEMPT_DYNAMIC
>>  
>>  DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
>> @@ -92,11 +93,14 @@ void dynamic_preempt_schedule(void);
>>  #define __preempt_schedule()                dynamic_preempt_schedule()
>>  void dynamic_preempt_schedule_notrace(void);
>>  #define __preempt_schedule_notrace()        
>> dynamic_preempt_schedule_notrace()
>> +void dynamic_irqentry_exit_cond_resched(void);
>> +#define irqentry_exit_cond_resched()        
>> dynamic_irqentry_exit_cond_resched()
>>  
>>  #else /* CONFIG_PREEMPT_DYNAMIC */
>>  
>>  #define __preempt_schedule()                preempt_schedule()
>>  #define __preempt_schedule_notrace()        preempt_schedule_notrace()
>> +#define irqentry_exit_cond_resched()        raw_irqentry_exit_cond_resched()
>>  
>>  #endif /* CONFIG_PREEMPT_DYNAMIC */
>>  #endif /* CONFIG_PREEMPTION */
>> diff --git a/arch/arm64/kernel/entry-common.c 
>> b/arch/arm64/kernel/entry-common.c
>> index 7c2299c1ba79..4f92664fd46c 100644
>> --- a/arch/arm64/kernel/entry-common.c
>> +++ b/arch/arm64/kernel/entry-common.c
>> @@ -285,19 +285,8 @@ 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 inline bool arm64_preempt_schedule_irq(void)
>>  {
>> -    if (!need_irq_preemption())
>> -            return false;
>> -
>>      /*
>>       * DAIF.DA are cleared at the start of IRQ/FIQ handling, and when GIC
>>       * priority masking is used the GIC irqchip driver will clear DAIF.IF
>> @@ -672,6 +661,24 @@ static __always_inline void __el1_pnmi(struct pt_regs 
>> *regs,
>>      arm64_exit_nmi(regs, state);
>>  }
>>  
>> +void raw_irqentry_exit_cond_resched(void)
>> +{
>> +    if (!preempt_count()) {
>> +            if (need_resched() && arm64_preempt_schedule_irq())
>> +                    preempt_schedule_irq();
>> +    }
>> +}
>> +
>> +#ifdef CONFIG_PREEMPT_DYNAMIC
>> +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
>> +
>>  static __always_inline void __el1_irq(struct pt_regs *regs,
>>                                    void (*handler)(struct pt_regs *))
>>  {
>> @@ -681,10 +688,8 @@ static __always_inline void __el1_irq(struct pt_regs 
>> *regs,
>>      do_interrupt_handler(regs, handler);
>>      irq_exit_rcu();
>>  
>> -    if (!preempt_count() && need_resched()) {
>> -            if (arm64_preempt_schedule_irq())
>> -                    preempt_schedule_irq();
>> -    }
>> +    if (IS_ENABLED(CONFIG_PREEMPTION))
>> +            irqentry_exit_cond_resched();
>>  
>>      exit_to_kernel_mode(regs, state);
>>  }
>> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
>> index b82032777310..4aa9656fa1b4 100644
>> --- a/kernel/entry/common.c
>> +++ b/kernel/entry/common.c
>> @@ -142,6 +142,20 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs 
>> *regs)
>>      return ret;
>>  }
>>  
>> +/**
>> + * arch_irqentry_exit_need_resched - Architecture specific need resched 
>> function
>> + *
>> + * Invoked from raw_irqentry_exit_cond_resched() to check if need resched.
>> + * Defaults return true.
>> + *
>> + * The main purpose is to permit arch to skip preempt a task from an IRQ.
>> + */
>> +static inline bool arch_irqentry_exit_need_resched(void);
>> +
>> +#ifndef arch_irqentry_exit_need_resched
>> +static inline bool arch_irqentry_exit_need_resched(void) { return true; }
>> +#endif
>> +
>>  void raw_irqentry_exit_cond_resched(void)
>>  {
>>      if (!preempt_count()) {
>> @@ -149,7 +163,7 @@ void raw_irqentry_exit_cond_resched(void)
>>              rcu_irq_exit_check_preempt();
>>              if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
>>                      WARN_ON_ONCE(!on_thread_stack());
>> -            if (need_resched())
>> +            if (need_resched() && arch_irqentry_exit_need_resched())
>>                      preempt_schedule_irq();
>>      }
>>  }
>> -- 
>> 2.34.1
>>
> 
>