软中断代码相关

有32路软中断，

static struct softirq_action softirq_vec[32] __cacheline_aligned_in_smp;

结构体类型

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

 

看处理软中断的函数

 define invoke_softirq() do_softirq()

 

smlinkage 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();//关键处理函数

 local_irq_restore(flags);
}

 

 

/*
 * We restart softirq processing MAX_SOFTIRQ_RESTART times,
 * and we fall back to softirqd after that.
 *
 * This number has been established via experimentation.
 * The two things to balance is latency against fairness -
 * we want to handle softirqs as soon as possible, but they
 * should not be able to lock up the box.
 */
#define MAX_SOFTIRQ_RESTART 10

asmlinkage void __do_softirq(void)
{
 struct softirq_action *h;
 __u32 pending;
 int max_restart = MAX_SOFTIRQ_RESTART;
 int cpu;

 pending = local_softirq_pending();//取得软中断pending位
 account_system_vtime(current);

 __local_bh_disable((unsigned long)__builtin_return_address(0));//关软中断处理
 trace_softirq_enter();

 cpu = smp_processor_id();
restart:
 /* Reset the pending bitmask before enabling irqs */
 set_softirq_pending(0);//清软中断的pengding位

 local_irq_enable();//开中断

 h = softirq_vec;//取32路软中断的头

 do {
  if (pending & 1) {
   h->action(h);
   rcu_bh_qsctr_inc(cpu);
  }
  h++;
  pending >>= 1;
 } while (pending);//循环处理pending置位的softirq_vec结构体

 local_irq_disable();//处理完毕后，关中断

 pending = local_softirq_pending();//再取一次软中断的pending位，可能在处理软中断的时候，有被置位（因为开中断了）
 if (pending && --max_restart)
  goto restart;//如果置位了，则再遍历处理一次软中断

//max_restart设定成10，就是说，最多处理10次，如果还有pending，那么

 if (pending)
  wakeup_softirqd();//唤醒内核线程去处理其他的软中断。

 trace_softirq_exit();

 account_system_vtime(current);
 _local_bh_enable();//开软中断
}

之所以在软中断处理函数的开头和结尾一个关中断一个开软中断，是为了保证软中断处理的串行化，就是不然软中断嵌套执行。