注册tick event handler为tick_handle_periodic，在每个系统tick到来时将回调此tick event handler：
clockevents_register_device
tick_check_new_device
tick_setup_device
tick_setup_periodic
tick_set_periodic_handler
static inline void tick_set_periodic_handler(struct clock_event_device *dev, int broadcast)
{
dev->event_handler = tick_handle_periodic;
}
每个tick到来回去处理timer部分的逻辑，检查timer是否expire，如果expire，执行timer回调
tick_handle_periodic
tick_periodic
update_process_times
run_local_timers
reference：
Linux时间子系统之（十二）：periodic tick
http://www.wowotech.net/timer_subsystem/periodic-tick.html
Linux时间子系统之定时器层（Timer）
https://blog.csdn.net/Roland_Sun/article/details/105775145