【linux kernel】 softirq 軟中斷討論

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早看到這篇文章，就不寫了，懶：

 Linux中斷（interrupt）子系統之五：軟件中斷（softIRQ）： http://blog.csdn.net/droidphone/article/details/7518428

1.1.  數據結構

struct softirq_action

{

    void    (*action)(struct softirq_action *);

};

 

²  static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;

 

softirq_vec是一個struct softirq_action數組，使用open_softirq註冊

 

Softirq.c (src\kernel):52 中：

²  irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;

其操做：raise_softirq_irqoff→or_softirq_pending置位bitmap：irq_stat[cpu].__softirq_pending

 

1.2.  軟中斷註冊

 

void open_softirq(int nr, void (*action)(struct softirq_action *))

{

    softirq_vec[nr].action = action;

}

不是鏈表結構。

 

可被註冊的有

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,    /* Preferable RCU should always be the last softirq */

 

    NR_SOFTIRQS

};

 

如在softirq_init中有open_softirq(TASKLET_SOFTIRQ, tasklet_action);

這說明 tasklet是被放入軟中斷中執行的。

1.3.  軟中斷執行流程

1.3.1.   路徑1：

open_softirq註冊→raise_softirq→raise_softirq_irqoff→raise_softirq_irqoff→wakeup_softirqd

在wakeup_softirqd中喚醒ksoftirqd進程，

 

static struct smp_hotplug_thread softirq_threads = {

    .store          = &ksoftirqd,

    .thread_should_run  = ksoftirqd_should_run,

    .thread_fn      = run_ksoftirqd,

    .thread_comm        = "ksoftirqd/%u",

};

 

執行.thread_fn = run_ksoftirqd  →__do_softirq

在 _do_softirq中有

h = softirq_vec;

……………………………

h->action(h); 即爲具體註冊函數

……………………………

 

Ksoftirqd:是個線程, 其流程爲

start_kernel→rest_init→kernel_init→kernel_init_freeable

→do_basic_setup→do_initcalls→spawn_ksoftirqd

→smpboot_register_percpu_thread(&softirq_threads)

 

 

1.3.2.   路徑2：

open_softirq註冊→raise_softirq→raise_softirq_irqoff→raise_softirq_irqoff→irq_exit(在中斷退出時執行)→invoke_softirq→do_softirq(或wakeup_softirqd) →__do_softirq→ h->action(h); 即爲具體註冊函數