linux软中断

                   

 在由内核执行的几个任务之间有些不是紧急的，在必要情况下他们可以延迟一段时间。一个中断处理程序的几个中断服务例程之间是串行执行的，并且通常在一个中断的处理程序结束前，不应该再次出现这个中断。相反，可延迟中断可以在开中断的情况下执行。

linux中所谓的可延迟函数，包括软中断和tasklet以及通过中作队列执行的函数（这个以后说），软中断的分配是静态的（即值编译时定义），而tasklet的分配和初始化可以在运行时进行。

软中断

软中断所使用的数据结构定义为

static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;

其中softirq_action类型为一个函数指针，从这里也可以看出，软中断的个数是有限的有NR_SOFTIRQS个，具体的定义如下:

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,            NR_SOFTIRQS};

可以看出，一共10个软中断。

struct softirq_action{        void       (*action)(struct softirq_action *);};

软中断的初始化

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

上面函数中，参数nr为softirq_vec[]数组的下标，初始化就是初始化softirq_vec[]数组内容。

初始化了软中断后，要执行，接下来要做的是激活软中断，运用下面函数

void raise_softirq(unsigned int nr){        unsigned long flags;                local_irq_save(flags);                raise_softirq_irqoff(nr);        local_irq_restore(flags); //恢复中断}

具体的激活工作由raise_softirq_irqoff函数实现

inline void raise_softirq_irqoff(unsigned int nr){                       __raise_softirq_irqoff(nr);                if (!in_interrupt())                wakeup_softirqd();/*唤醒本地的内核线程*/}

守护线程softirqd就是对软中断的处理

static int 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;}

下面是软中断的执行

asmlinkage void do_softirq(void){        __u32 pending;        unsigned long flags;        if (in_interrupt())                return;        local_irq_save(flags);        pending = local_softirq_pending();        if (pending)                __do_softirq();        local_irq_restore(flags);}

 

具体由__do_softirq函数实现

asmlinkage void __do_softirq(void){        struct softirq_action *h;        __u32 pending;

                int max_restart = MAX_SOFTIRQ_RESTART;        int cpu;

                pending = local_softirq_pending();        account_system_vtime(current);

                __local_bh_disable((unsigned long)__builtin_return_address(0));        lockdep_softirq_enter();        cpu = smp_processor_id();restart:                set_softirq_pending(0);                local_irq_enable();        h = softirq_vec;        do {                if (pending & 1) {                        int prev_count = preempt_count();                        kstat_incr_softirqs_this_cpu(h - softirq_vec);                        trace_softirq_entry(h, softirq_vec);                        h->action(h);                        trace_softirq_exit(h, softirq_vec);                        if (unlikely(prev_count != preempt_count())) {                                printk(KERN_ERR "huh, entered softirq %td %s %p"                                       "with preempt_count x,"                                       " exited with x?\n", h - softirq_vec,                                       softirq_to_name[h - softirq_vec],                                       h->action, prev_count, preempt_count());                                preempt_count() = prev_count;                        }                        rcu_bh_qs(cpu);                }                h++;                pending >>= 1;        } while (pending);        local_irq_disable();        pending = local_softirq_pending();        if (pending && --max_restart)                goto restart;        if (pending)                wakeup_softirqd();        lockdep_softirq_exit();        account_system_vtime(current);        _local_bh_enable();}

到此，linux内核软中断的大致执行和实现基本上分析完了，中间有很多地方没有注释的，主要是考虑到需要别的实现机制以及有的比较易懂。能够自己看懂。

http://www.linuxso.com/linuxrumen/14467.html