linux动态时钟探索

 1 struct tick_sched {
 2     struct hrtimer            sched_timer;//用于实现时钟的定时器
 3     unsigned long            check_clocks;
 4     enum tick_nohz_mode        nohz_mode;
 5     ktime_t                idle_tick;//禁用周期时钟之前，上一个时钟信号到期时间。
 6     int                inidle;
 7     int                tick_stopped;//周期时钟是否已经停用，若停用，则置为1
 8     unsigned long            idle_jiffies;//存储周期时钟禁用时的jiffy值
 9     unsigned long            idle_calls;//内核试图停用周期时钟次数。
10     unsigned long            idle_sleeps;//成功停用周期时钟次数。
11     int                idle_active;
12     ktime_t                idle_entrytime;
13     ktime_t                idle_waketime;
14     ktime_t                idle_exittime;
15     ktime_t                idle_sleeptime;//周期时钟上一次禁用的准确时间
16     ktime_t                idle_lastupdate;
17     ktime_t                sleep_length;//周期时钟禁用的时间长度
18     unsigned long            last_jiffies;
19     unsigned long            next_jiffies;//下一个定时器到期的jiffy值
20     ktime_t                idle_expires;//下一个将到期的经典定时器到期时间的jiffy值
21     int                do_timer_last;
22 }

 1 static void tick_nohz_switch_to_nohz(void)
 2 {
 3     struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 4     ktime_t next;
 5     if (!tick_nohz_enabled)//若没有启动动态时钟直接返回
 6         return;
 7     local_irq_disable();
 8     if (tick_switch_to_oneshot(tick_nohz_handler)) {//切换时钟设备的处理函数为tick_nohz_switch_to_nohz
 9         local_irq_enable();
10         return;
11     }
12     ts->nohz_mode = NOHZ_MODE_LOWRES;//设置为低分辨率
13     /*
14      * Recycle the hrtimer in ts, so we can share the
15      * hrtimer_forward with the highres code.
16      */
17 //更新jiffy值
18     hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
19     /* Get the next period */
20     next = tick_init_jiffy_update();
21 //设置下一个时钟事件
22     for (;;) {
23         hrtimer_set_expires(&ts->sched_timer, next);
24         if (!tick_program_event(next, 0))
25             break;
26         next = ktime_add(next, tick_period);
27     }
28     local_irq_enable();
29     printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
30      smp_processor_id());
31 }