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This document was automatically translated by Qwen/Qwen3-8B model, for reference only.

• Source document: kernel/core_api/softirq.md

• Translation time: 2025-05-19 01:41:38

• Translation model: Qwen/Qwen3-8B

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Soft Interrupt

  Software interrupt, also known as the bottom half of an interrupt, is used to delay the processing of work that was not completed by the hard interrupt (the top half of the interrupt). Dividing the interrupt into two stages can effectively solve the problems of long interrupt handling time and interrupt loss.

1. Design Philosophy

  Each CPU has its own pending status. Soft interrupts are “initiated by which CPU, executed by which CPU”, and the pending status of each CPU is not shared. The same soft interrupt vector can run concurrently on multiple cores.

  When we need to register a new soft interrupt, we need to implement the SoftirqVec feature for the soft interrupt handler, and then call the register_softirq function to register the soft interrupt handler within the soft interrupt mechanism.

  Please note that due to the reentrancy and concurrency of soft interrupts, the soft interrupt handler must ensure thread safety itself.

2. Soft Interrupt Vector Number

pub enum SoftirqNumber {
    /// 时钟软中断信号
    TIMER = 0,
    /// 帧缓冲区刷新软中断
    VideoRefresh = 1, 
}

3. Soft Interrupt API

3.1. SoftirqVec Feature

pub trait SoftirqVec: Send + Sync + Debug {
    fn run(&self);
}

  The feature that the soft interrupt handler needs to implement. It needs to implement the run function to handle the soft interrupt. When the soft interrupt is executed, the run function will be called.

3.2. Softirq API

3.2.1. Register Soft Interrupt Vector

pub fn register_softirq(&self,
        softirq_num: SoftirqNumber,
        handler: Arc<dyn SoftirqVec>,
    ) -> Result<i32, SystemError>

• Parameters:

  • softirq_num: Interrupt vector number

  • handler: The structure corresponding to the interrupt function, which needs to point to a structure variable that implements the SoftirqVec feature

• Return:

  • Ok(i32): 0

  • Err(SystemError): Error code

3.2.2. Unregister Soft Interrupt Vector

pub fn unregister_softirq(&self, softirq_num: SoftirqNumber)

• Parameters:

  • softirq_num: Interrupt vector number

3.2.3. Execute Soft Interrupt

pub fn do_softirq(&self)

• Purpose: Execute the soft interrupt function (only called after hard interrupt execution)

3.2.4. Clear the Pending Flag of Soft Interrupt

pub unsafe fn clear_softirq_pending(&self, softirq_num: SoftirqNumber)

• Purpose: Clear the pending flag of the specified soft interrupt on the current CPU. Please note that this function is unsafe because it directly modifies the pending flag without locking.

• Parameters:

  • softirq_num: Interrupt vector number

3.2.5. Mark Soft Interrupt as to be Executed

pub fn raise_softirq(&self, softirq_num: SoftirqNumber)

• Purpose: Mark the specified soft interrupt as to be executed on the current CPU

• Parameters:

  • softirq_num: Interrupt vector number

3.3. Usage Example

#[derive(Debug)]
/// SoftirqExample中断结构体
pub struct SoftirqExample {
    running: AtomicBool,
}
/// SoftirqExample中断需要处理的逻辑
fn softirq_example_func() {
    println!("addressed SoftirqExample");
}
impl SoftirqVec for SoftirqExample {
    fn run(&self) {
        if self.set_run() == false {
            return;
        }

        softirq_example_func();

        self.clear_run();
    }
}
impl SoftirqExample {
    pub fn new() -> SoftirqExample {
        SoftirqExample {
            running: AtomicBool::new(false),
        }
    }

    fn set_run(&self) -> bool {
        let x = self
            .running
            .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed);
        if x.is_ok() {
            return true;
        } else {
            return false;
        }
    }

    fn clear_run(&self) {
        self.running.store(false, Ordering::Release);
    }
}
fn main() {
    let softirq_example = Arc::new(SoftirqExample::new());
    let softirq_num = 2;
    // 注册SoftirqExample中断
    softirq_vectors()
        .register_softirq(SoftirqNumber::from(softirq_num as u64), softirq_example)
        .expect("failed to register SoftirqExample");

    // 标志SoftirqExample中断需要执行
    softirq_vectors().raise_softirq(SoftirqNumber::from(softirq_num as u64));

    // 标志SoftirqExample中断不需要执行
    softirq_vectors().clear_softirq_pending(SoftirqNumber::from(softirq_num as u64));

    // 解注册SoftirqExample中断
    softirq_vectors().unregister_softirq(SoftirqNumber::from(softirq_num as u64));
}