tick_init 函数

static struct notifier_block tick_notifier = {
.notifier_call = tick_notify,
};

//函数所在文件

//  kernel\time\tick-common.c

/**

 * tick_init - initialize the tick control
 *
 * Register the notifier with the clockevents framework
 */
void __init tick_init(void)
{
clockevents_register_notifier(&tick_notifier);

}

/**
 * clockevents_register_notifier - register a clock events change listener
 */
int clockevents_register_notifier(struct notifier_block *nb)
{
unsigned long flags;
int ret;


raw_spin_lock_irqsave(&clockevents_lock, flags);
ret = raw_notifier_chain_register(&clockevents_chain, nb);
raw_spin_unlock_irqrestore(&clockevents_lock, flags);


return ret;
}

/*
 * Raw notifier chain routines.  There is no protection;
 * the caller must provide it.  Use at your own risk!
 */


/**
 * raw_notifier_chain_register - Add notifier to a raw notifier chain
 * @nh: Pointer to head of the raw notifier chain
 * @n: New entry in notifier chain
 *
 * Adds a notifier to a raw notifier chain.
 * All locking must be provided by the caller.
 *
 * Currently always returns zero.
 */
int raw_notifier_chain_register(struct raw_notifier_head *nh,
struct notifier_block *n)
{
return notifier_chain_register(&nh->head, n);
}

/*
 * Notifier chain core routines.  The exported routines below
 * are layered on top of these, with appropriate locking added.
 */


static int notifier_chain_register(struct notifier_block **nl,
struct notifier_block *n)
{
while ((*nl) != NULL) {
if (n->priority > (*nl)->priority)
break;
nl = &((*nl)->next);
}
n->next = *nl;
rcu_assign_pointer(*nl, n);
return 0;
}

可以看到，tick_init的作用就是调用 clockevents_register_notifier 函数向 clockevents_chain 通知链注册元素： tick_notifier。这个元素的回调函数指明了，时钟事件设备信息发生变化时（例如新加入一个时钟事件设备等等），应该执行的操作，该回调函数为 tick_notify。