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内核定时器并不是用来简单的定时操作#xff0c;而是在定时时…
目录一内核定时器介绍二内核定时器相关接口三使用步骤四实例代码一内核定时器介绍
内核定时器并不是用来简单的定时操作而是在定时时间后触发事件的操作类似定时器中断是内核用来控制在未来某个时间点基于jiffies调度执行某个函数的一种机制内核中采用的定时器以jiffies为单位。 单位秒jiffies/HZ
几个重要跟时间有关的名词或变数
HZLinux核心每隔固定周期会发出timer interrupt (IRQ 0)HZ是用来定义每一秒有几次timer interrupts。举例来说HZ为1000代表每秒有1000次timer interrupts。
TickTick是HZ的倒数意即timer interrupt每发生一次中断的时间。如HZ为250时tick为4毫秒(millisecond)。
JiffiesJiffies为Linux核心变数(unsigned long)它被用来记录系统自开机以来已经过了多少tick。每发生一次timer interruptJiffies变数会被加一。值得注意的是Jiffies于系统开机时并非初始化成零而是被设为-300*HZ 类似Linux系统中time日历时间二内核定时器相关接口
和定时器先关的数据结构
struct timer_list {unsigned long expires; //未来时间点即超时时间void (*function)(unsigned long);//超时回调函数unsigned long data; //传递给回调函数的数据也就是定时器数据
};初始化定时器相关的数据结构
1. 静态定以定时器数据结构
#define DEFINE_TIMER(_name, _function, _expires, _data) \struct timer_list _name \TIMER_INITIALIZER(_function, _expires, _data)2. 动态初始化-----手动对变量进行初始化
#define init_timer(timer) \do { \static struct lock_class_key __key; \init_timer_key((timer), #timer, __key); \} while (0)可延时定时
#define init_timer_deferrable(timer) \do { \static struct lock_class_key __key; \init_timer_deferrable_key((timer), #timer, __key); \} while (0)设置定时时间
#define setup_timer(timer, fn, data) \
do { \static struct lock_class_key __key; \setup_timer_key((timer), #timer, __key, (fn), (data));\
} while (0)向内核添加定时器:
/*** add_timer - start a timer* timer: the timer to be added** The kernel will do a -function(-data) callback from the* timer interrupt at the -expires point in the future. The* current time is jiffies.** The timers -expires, -function (and if the handler uses it, -data)* fields must be set prior calling this function.** Timers with an -expires field in the past will be executed in the next* timer tick.*/
void add_timer(struct timer_list *timer)
{BUG_ON(timer_pending(timer));mod_timer(timer, timer-expires);
}从内核删除定时器
/*** del_timer - deactive a timer.* timer: the timer to be deactivated** del_timer() deactivates a timer - this works on both active and inactive* timers.** The function returns whether it has deactivated a pending timer or not.* (ie. del_timer() of an inactive timer returns 0, del_timer() of an* active timer returns 1.)*/
int del_timer(struct timer_list *timer)修改定时时间
/*** mod_timer - modify a timers timeout* timer: the timer to be modified* expires: new timeout in jiffies** mod_timer() is a more efficient way to update the expire field of an* active timer (if the timer is inactive it will be activated)** mod_timer(timer, expires) is equivalent to:** del_timer(timer); timer-expires expires; add_timer(timer);** Note that if there are multiple unserialized concurrent users of the* same timer, then mod_timer() is the only safe way to modify the timeout,* since add_timer() cannot modify an already running timer.** The function returns whether it has modified a pending timer or not.* (ie. mod_timer() of an inactive timer returns 0, mod_timer() of an* active timer returns 1.)*/
int mod_timer(struct timer_list *timer, unsigned long expires)jiffies和时间的转换
extern unsigned int jiffies_to_msecs(const unsigned long j);
extern unsigned int jiffies_to_usecs(const unsigned long j);
extern unsigned long msecs_to_jiffies(const unsigned int m);
extern unsigned long usecs_to_jiffies(const unsigned int u);三使用步骤
1、向内核添加定时器 setup_timer();设置定时器add_timer();.2、解绑定时器 int del_timer(struct timer_list *timer)四实例代码
#include linux/timer.h
#include linux/kernel.h
#include linux/module.hstruct timer_list timer;
void function(unsigned long data)
{static int count0;printk(this is timer test:%d\n,count);mod_timer(timer,jiffies1*HZ);
}
static int __init timer_module_init(void)
{timer.expires jiffies5*HZ;setup_timer(timer,function,0);add_timer(timer);return 0;
}
static void __exit timer_module_cleanup(void)
{del_timer(timer);
}module_init(timer_module_init);
module_exit(timer_module_cleanup);
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