2023.7.15 linux timer

Dynamic tick/tickless kernel

If, however, a CPU leaves the idle state upon an interrupt (the architecture code calls handle_IRQ(), which indirectly calls tick_irq_enter()), this CPU tick device is enabled (first in one-shot mode), and before it performs any task, the tick_nohz_irq_ enter() function is called to ensure that jiffies are up to date so that the interrupt handler does not have to deal with a stale jiffy value, and then it resumes the periodic tick, which is kept active until the next call to tick_nohz_idle_stop_tick() (which is essentially called from do_idle()).

Using standard kernel low-precision (low-res) timers　　　　CONFIG_HZ

Jiffies and HZ　　　　zcat /proc/config.gz |grep CONFIG_HZ　　;　　　　#Jiffies每秒增加HZ次，一次tick 就是 1/HZ 秒

Kernel timer APIs

定时器：struct timer_list { struct hlist_node entry; unsigned long expires; void (*function)(struct timer_list *); u32 flags; );

void timer_setup( struct timer_list *timer,  void (*function)( struct timer_list *),  unsigned int flags);　　#动态设置一个定时器

#define DEFINE_TIMER(_name, _function) [...]　　　　#静态设置定时器的宏

int mod_timer(struct timer_list *timer, unsigned long expires);　　#修改一个定时器，重设它的到期时间，return 0 如果timer先前是不活动的，timer pending 或在执行func则return 1；

void add_timer(struct timer_list *timer)；　　　　#启动定时器，需要先把定时器设置好；比如 my_timer.expires = jiffies + ((12 * HZ) / 10); /* 1.2s */ add_timer(&my_timer);

删除或取消定时器：

int del_timer(struct timer_list *timer);　　　　#return 0 if timer is inactive，else 1

int del_timer_sync(struct timer_list *timer);　　　　#会等待每个核心的定时器的func完成后才return，非原子操作专用

int timer_pending(const struct timer_list *timer); #检查timer 状态