【linux kernel】 softirq 软中断讨论

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早看到这篇文章，就不写了，懒：

 Linux中断（interrupt）子系统之五：软件中断（softIRQ）： http://blog.csdn.net/droidphone/article/details/7518428

1.1.  数据结构

struct softirq_action

{

    void    (*action)(struct softirq_action *);

};

2  static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;

softirq_vec是一个struct softirq_action数组，使用open_softirq注册

Softirq.c (src\kernel):52 中：

2  irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;

其操作：raise_softirq_irqoff→or_softirq_pending置位bitmap：irq_stat[cpu].__softirq_pending

1.2.  软中断注册

void open_softirq(int nr, void (*action)(struct softirq_action *))

{

    softirq_vec[nr].action = action;

}

不是链表结构。

可被注册的有

enum

{

    HI_SOFTIRQ=0,

    TIMER_SOFTIRQ,

    NET_TX_SOFTIRQ,

    NET_RX_SOFTIRQ,

    BLOCK_SOFTIRQ,

    BLOCK_IOPOLL_SOFTIRQ,

    TASKLET_SOFTIRQ,

    SCHED_SOFTIRQ,

    HRTIMER_SOFTIRQ,

    RCU_SOFTIRQ,    /* Preferable RCU should always be the last softirq */

    NR_SOFTIRQS

};

如在softirq_init中有open_softirq(TASKLET_SOFTIRQ, tasklet_action);

这说明 tasklet是被放入软中断中执行的。

1.3.  软中断执行流程

1.3.1.   路径1：

open_softirq注册→raise_softirq→raise_softirq_irqoff→raise_softirq_irqoff→wakeup_softirqd

在wakeup_softirqd中唤醒ksoftirqd进程，

static struct smp_hotplug_thread softirq_threads = {

    .store          = &ksoftirqd,

    .thread_should_run  = ksoftirqd_should_run,

    .thread_fn      = run_ksoftirqd,

    .thread_comm        = "ksoftirqd/%u",

};

执行.thread_fn = run_ksoftirqd  →__do_softirq

在 _do_softirq中有

h = softirq_vec;

……………………………

h->action(h); 即为具体注册函数

……………………………

Ksoftirqd:是个线程, 其流程为

start_kernel→rest_init→kernel_init→kernel_init_freeable

→do_basic_setup→do_initcalls→spawn_ksoftirqd

→smpboot_register_percpu_thread(&softirq_threads)

1.3.2.   路径2：

open_softirq注册→raise_softirq→raise_softirq_irqoff→raise_softirq_irqoff→irq_exit(在中断退出时执行)→invoke_softirq→do_softirq(或wakeup_softirqd) →__do_softirq→ h->action(h); 即为具体注册函数