dev_cpu_dead

Kernel: 4.12.6

每个cpu都有自己的softnet_data结构，用来处理数据包接收，但是当softnet_data所在cpu无法工作时，即CPUHP_NET_DEV_DEAD状态，就需要将工作转交给其他cpu处理；

 static int dev_cpu_dead(unsigned int oldcpu)
 {
     struct sk_buff **list_skb;
     struct sk_buff *skb;
     unsigned int cpu;
     struct softnet_data *sd, *oldsd, *remsd = NULL;

     //禁用本地中断
     local_irq_disable();
     //获取当前cpu
     cpu = smp_processor_id();
     //找到sd
     sd = &per_cpu(softnet_data, cpu);
     //原sd
     oldsd = &per_cpu(softnet_data, oldcpu);

     /* Find end of our completion_queue. */
     //找到当前cpu完成队列尾部
     list_skb = &sd->completion_queue;
     while (*list_skb)
         list_skb = &(*list_skb)->next;
     /* Append completion queue from offline CPU. */
     //将旧cpu队列连接到当前cpu队列尾部
     *list_skb = oldsd->completion_queue;
     oldsd->completion_queue = NULL;

     /* Append output queue from offline CPU. */
     //将旧cpu的outputqueue挂到当前cpu尾部
     if (oldsd->output_queue) {
         *sd->output_queue_tailp = oldsd->output_queue;
         sd->output_queue_tailp = oldsd->output_queue_tailp;
         oldsd->output_queue = NULL;
         oldsd->output_queue_tailp = &oldsd->output_queue;
     }
     /* Append NAPI poll list from offline CPU, with one exception :
      * process_backlog() must be called by cpu owning percpu backlog.
      * We properly handle process_queue & input_pkt_queue later.
      */
     //将napi poll list挂到当前cpu poll list尾部
     while (!list_empty(&oldsd->poll_list)) {
         struct napi_struct *napi = list_first_entry(&oldsd->poll_list,
                                 struct napi_struct,
                                 poll_list);

         list_del_init(&napi->poll_list);
         if (napi->poll == process_backlog)
             napi->state = ;
         else
             ____napi_schedule(sd, napi);
     }

     //触发发送软中断
     raise_softirq_irqoff(NET_TX_SOFTIRQ);

     //启用中断
     local_irq_enable();

 #ifdef CONFIG_RPS
     remsd = oldsd->rps_ipi_list;
     oldsd->rps_ipi_list = NULL;
 #endif
     /* send out pending IPI's on offline CPU */
     net_rps_send_ipi(remsd);

     /* Process offline CPU's input_pkt_queue */
     //把process_queue和input_queue中的skb添加到当前cpu的backlog中
     while ((skb = __skb_dequeue(&oldsd->process_queue))) {
         netif_rx_ni(skb);
         input_queue_head_incr(oldsd);
     }
     while ((skb = skb_dequeue(&oldsd->input_pkt_queue))) {
         netif_rx_ni(skb);
         input_queue_head_incr(oldsd);
     }

     return ;
 }