ARM Linux 如何--注册和触发--软中断

1. 注册软中断当然是通过open_softirq

例子如下：

void __init init_timers(void)
{
    int err = timer_cpu_notify(&timers_nb, (unsigned long)CPU_UP_PREPARE,
                (void *)(long)smp_processor_id());

    init_timer_stats();

    BUG_ON(err == NOTIFY_BAD);
    register_cpu_notifier(&timers_nb);
    open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
}

void open_softirq(int nr, void (*action)(struct softirq_action *))
{
    softirq_vec[nr].action = action;
}

软中断TIMER_SOFTIRQ的中断处理函数为：run_timer_softirq

之所以成为softirq，是因为这些中断是由硬件中断来间接触发的,如何间接触发的呢：
硬件中断处理函数-->对软中断的相应位置位-->唤醒ksoftirqd线程-->执行软中断的中断处理函数

2. 硬件中断如何通过置位唤醒ksoftirqd线程

timer interrupt handler->
timer_tick->
update_process_times->
run_local_timers->
hrtimer_run_queues()和raise_softirq(TIMER_SOFTIRQ)->
raise_softirq_irqoff->
__raise_softirq_irqoff { or_softirq_pending(1UL << (nr)); }
即(local_softirq_pending() |= (x))

3. 如何执行软中断的action<中断处理函数>

对于TIMER_SOFTIRQ来说，每次system clock产生中断时，即一个tick 到来时，在system clock的中断处理函数中会调用run_local_timers来设置TIMER_SOFTIRQ触发条件；也就是当前CPU对应的irq_cpustat_t结构体中的__softirq_pending成员的第TIMER_SOFTIRQ个BIT被置为1。 而当这个条件满足时，ksoftirqd线程(入口函数run_ksoftirqd,cpu_callback:kthread_create(run_ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);)会被唤醒，然后按照下面的流程调用TIMER_SOFTIRQ在数组softirq_vec中注册的action，即run_timer_softirq。
run_ksoftirqd--->do_softirq--->__do_softirq--->softirq_vec[TIMER_SOFTIRQ].action

 

static int run_ksoftirqd(void * __bind_cpu)
{
    set_current_state(TASK_INTERRUPTIBLE);

    while (!kthread_should_stop()) {
        preempt_disable();
        if (!local_softirq_pending()) {
            preempt_enable_no_resched();
            schedule();
            preempt_disable();
        }

        __set_current_state(TASK_RUNNING);

        while (local_softirq_pending()) {
            /* Preempt disable stops cpu going offline.
               If already offline, we'll be on wrong CPU:
               don't process */
            if (cpu_is_offline((long)__bind_cpu))
                goto wait_to_die;
            do_softirq();
            preempt_enable_no_resched();
            cond_resched();
            preempt_disable();
            rcu_sched_qs((long)__bind_cpu);
        }
        preempt_enable();
        set_current_state(TASK_INTERRUPTIBLE);
    }
    __set_current_state(TASK_RUNNING);
    return 0;

wait_to_die:
    preempt_enable();
    /* Wait for kthread_stop */
    set_current_state(TASK_INTERRUPTIBLE);
    while (!kthread_should_stop()) {
        schedule();
        set_current_state(TASK_INTERRUPTIBLE);
    }
    __set_current_state(TASK_RUNNING);
    return 0;
}