内核在时钟中断发生后执行检测各个定时器是否到期，到期后的定时器处理函数将作为软中断在底半部执行。实质上，时钟中断处理程序会唤起TIMER_SOFTIRQ软中断，运行当前处理器上到期的所有定时器。linux提供的内核定时器数据结构为timer_list。

一. 定义

timer_list定义在linux/timer.h中，实现在kernel/timer.c中。

struct timer_list {    struct list head_entry;    unsigned long expires;    //到期时间    struct tves_base *base;    void (*func)(unsigned long);    unsigned long data;    int slack;#ifdef CONFIG_TIMER_STATS    int start_pid;    void *start_site;    char start_comm[16];#endif#ifdef CONFIG_LOCKDEP    struct lockdep_map lockdep_map;#endif};

内核相关定义：HZ和jiffies

HZ  时钟频率

jiffies 32位无符号数，当前时钟计数

# define HZ     CONFIG_HZ   /* Internal kernel timer frequency */# define USER_HZ    100     /* some user interfaces are */

linux/jiffies.h/* * The 64-bit value is not atomic - you MUST NOT read it * without sampling the sequence number in jiffies_lock. * get_jiffies_64() will do this for you as appropriate. */extern u64 __jiffy_data jiffies_64;extern unsigned long volatile __jiffy_data jiffies;#if (BITS_PER_LONG < 64) u64 get_jiffies_64(void);#elsestatic inline u64 get_jiffies_64(void){    return (u64)jiffies;}#endif

二. 函数

初始化定时器

init_timer(&mytimer);

DEFINE_TIMER(_name, _function, _expires, _data);

TIMER_INITIALIZER(_function, _expires, _data);

setup_timer(timer, fn, data);

首次使能定时器

add_timer(&mytimer);

再次使能定时器

mod_timer(&mytimer, unsigned long expires);

删除定时器

del_timer_sync(&mytimer); //删除前要等待定时器处理完，不能发生在中断上下文。

del_timer(&mytimer); //删除定时器

三. 示例

#include 
     
      #include 
      
       #include 
       
        #include 
        
         #inlcude 
         
          MODULE_LISENCE("GPL");extern struct task_struct *current;struct timer_list mytimer;void timer_handler(unsigned long arg){    printk("timer arg = %d\n", arg);    mod_timer(&mytimer, jiffies + HZ * 5);    return;}static int __init akae_init(void){    int local = 0;    printk("module name is %s\n", KBUILD_MODNAME);    printk("akae_init at %p\n", akae_init);    printk("jiffies at %p\n", &jiffies);    printk("jiffies is %ld\n", jiffies);    printk("The process is \"%s\" (pid %i)\n", current->name, curent->pid);        init_timer(&mytimer);    printk("HZ is %d\n", HZ);    mytimer.expires = jiffies + HZ * 5;    mytimer.function = timer_handler;    mytimer.data = 100;    add_timer(&mytimer);    return 0;}static void __exit akae_exit(void){    printk("module eixt.\n");    printk("akae_exit at %p\n", akae_exit);    del_timer_sync(&mytimer);    return;}module_init(akae_init);module_exit(akae_exit);