例如，内核可以持续读取设备上的一个内存寄存器，或者当一个定时器到期时就回头检查哪个寄存器。

此时，当特定事件发生时，设备驱动程序会代表内核指示设备产生硬件中断。内核将中断其他活动，然后调用一个驱动程序
所注册的处理函数，以满足设备的需要。当事件是接收到一个帧时，处理函数就会把该帧排入队列某处，然后通知内核。

对并发的唯一限制就是何时，在一个CPU上每个软IRQ都只能有一个实例运行。
新式的软IRQ模型只有10种模型(include/linux/interrupt.h):

 1:  /* PLEASE, avoid to allocate new softirqs, if you need not _really_ high

 2:     frequency threaded job scheduling. For almost all the purposes

 3:     tasklets are more than enough. F.e. all serial device BHs et

 4:     al. should be converted to tasklets, not to softirqs.

 5:   */

 6:

 7:  enum

 8:  {

 9:    HI_SOFTIRQ=,

10:    TIMER_SOFTIRQ,

11:    NET_TX_SOFTIRQ,

12:    NET_RX_SOFTIRQ,

13:    BLOCK_SOFTIRQ,

14:    BLOCK_IOPOLL_SOFTIRQ,

15:    TASKLET_SOFTIRQ,

16:    SCHED_SOFTIRQ,

17:    HRTIMER_SOFTIRQ,

18:    RCU_SOFTIRQ,    /* Preferable RCU should always be the last softirq */

19:

20:    NR_SOFTIRQS

21:  };

 1:  /*

 2:   *    Initialize the DEV module. At boot time this walks the device list and

 3:   *    unhooks any devices that fail to initialise (normally hardware not

 4:   *    present) and leaves us with a valid list of present and active devices.

 5:   *

 6:   */

 7:

 8:  /*

 9:   *       This is called single threaded during boot, so no need

10:   *       to take the rtnl semaphore.

11:   */

12:  static int __init net_dev_init(void)

13:  {

14:    int i, rc = -ENOMEM;

15:

16:    BUG_ON(!dev_boot_phase);

17:

18:    if (dev_proc_init())

19:        goto out;

20:

21:    if (netdev_kobject_init())

22:        goto out;

23:

24:    INIT_LIST_HEAD(&ptype_all);

25:    for (i = ; i < PTYPE_HASH_SIZE; i++)

26:        INIT_LIST_HEAD(&ptype_base[i]);

27:

28:    if (register_pernet_subsys(&netdev_net_ops))

29:        goto out;

30:

31:    /*

32:     *  Initialise the packet receive queues.

33:     */

34:

35:    for_each_possible_cpu(i) {

36:        struct softnet_data *sd = &per_cpu(softnet_data, i);

37:

38:        memset(sd, , sizeof(*sd));

39:        skb_queue_head_init(&sd->input_pkt_queue);

40:        skb_queue_head_init(&sd->process_queue);

41:        sd->completion_queue = NULL;

42:        INIT_LIST_HEAD(&sd->poll_list);

43:        sd->output_queue = NULL;

44:        sd->output_queue_tailp = &sd->output_queue;

45:  #ifdef CONFIG_RPS

46:        sd->csd.func = rps_trigger_softirq;

47:        sd->csd.info = sd;

48:        sd->csd.flags = ;

49:        sd->cpu = i;

50:  #endif

51:

52:        sd->backlog.poll = process_backlog;

53:        sd->backlog.weight = weight_p;

54:        sd->backlog.gro_list = NULL;

55:        sd->backlog.gro_count = ;

56:    }

57:

58:    dev_boot_phase = ;

59:

60:    /* The loopback device is special if any other network devices

61:     * is present in a network namespace the loopback device must

62:     * be present. Since we now dynamically allocate and free the

63:     * loopback device ensure this invariant is maintained by

64:     * keeping the loopback device as the first device on the

65:     * list of network devices.  Ensuring the loopback devices

66:     * is the first device that appears and the last network device

67:     * that disappears.

68:     */

69:    if (register_pernet_device(&loopback_net_ops))

70:        goto out;

71:

72:    if (register_pernet_device(&default_device_ops))

73:        goto out;

74:

75:    open_softirq(NET_TX_SOFTIRQ, net_tx_action);

76:    open_softirq(NET_RX_SOFTIRQ, net_rx_action);

77:

78:    hotcpu_notifier(dev_cpu_callback, );

79:    dst_init();

80:    dev_mcast_init();

81:    rc = ;

82:  out:

83:    return rc;

84:  }

85:

86:  subsys_initcall(net_dev_init);