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ARM Linux 如何--注册和触发--软中断
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1. 注冊軟中斷當(dāng)然是通過open_softirq
例子如下：
[cpp]?view plain
?copy 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;??}?? 軟中斷TIMER_SOFTIRQ的中斷處理函數(shù)為：run_timer_softirq
之所以成為softirq，是因為這些中斷是由硬件中斷來間接觸發(fā)的,如何間接觸發(fā)的呢：
硬件中斷處理函數(shù)-->對軟中斷的相應(yīng)位置位-->喚醒ksoftirqd線程-->執(zhí)行軟中斷的中斷處理函數(shù)
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2. 硬件中斷如何通過置位喚醒ksoftirqd線程
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))
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3. 如何執(zhí)行軟中斷的action<中斷處理函數(shù)>
對于TIMER_SOFTIRQ來說，每次system clock產(chǎn)生中斷時，即一個tick 到來時，在system clock的中斷處理函數(shù)中會調(diào)用run_local_timers來設(shè)置TIMER_SOFTIRQ觸發(fā)條件；也就是當(dāng)前CPU對應(yīng)的irq_cpustat_t結(jié)構(gòu)體中的__softirq_pending成員的第TIMER_SOFTIRQ個BIT被置為1。 而當(dāng)這個條件滿足時，ksoftirqd線程(入口函數(shù)run_ksoftirqd,cpu_callback:kthread_create(run_ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);)會被喚醒，然后按照下面的流程調(diào)用TIMER_SOFTIRQ在數(shù)組softirq_vec中注冊的action，即run_timer_softirq。
run_ksoftirqd--->do_softirq--->__do_softirq--->softirq_vec[TIMER_SOFTIRQ].action
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[cpp]?view plain
?copy 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())?{??????????????????????????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();??????????set_current_state(TASK_INTERRUPTIBLE);??????while?(!kthread_should_stop())?{??????????schedule();??????????set_current_state(TASK_INTERRUPTIBLE);??????}??????__set_current_state(TASK_RUNNING);??????return?0;??}??
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