linux 内核延时

#忙等待：等的时间很短，等的时间不能睡眠
void ndelay(unsigned long nsecs)
void udelay(unsigned long usecs)

在使用ndelay或者udelay的时候CPU是忙等待，会一直占用着CPU的资源

睡延时：不消耗CPU资源，在睡眠等待的时候可以让当前task调度出去，让出CPU去执行其他的TASK
void msleep(unsigned int msecs)
unsigned long msleep_interruptible(unsigned int msecs)
void ssleep(unsigned int seconds)

定时器：
struct timer_list {
/*
* All fields that change during normal runtime grouped to the
* same cacheline
*/
struct hlist_node entry;
unsigned long expires;
void (*function)(struct timer_list *);
u32 flags;

#ifdef CONFIG_LOCKDEP
struct lockdep_map lockdep_map;
#endif
};
描述一个事情周期性的按照一定的时间去执行，当定时器满后，对应的注册的function会被调用，而expires是到期的时间(jiffies)

void init_timers(void)
void add_timer(struct timer_list *timer)
int del_timer(struct timer_list * timer)
int mod_timer(struct timer_list *timer, unsigned long expires)

void nr_destroy_socket(struct sock *sk)
{
	struct sk_buff *skb;

	nr_remove_socket(sk);

	nr_stop_heartbeat(sk);
	nr_stop_t1timer(sk);
	nr_stop_t2timer(sk);
	nr_stop_t4timer(sk);
	nr_stop_idletimer(sk);

	nr_clear_queues(sk);		/* Flush the queues */

	while ((skb = skb_dequeue(&sk->sk_receive_queue)) != NULL) {
		if (skb->sk != sk) { /* A pending connection */
			/* Queue the unaccepted socket for death */
			sock_set_flag(skb->sk, SOCK_DEAD);
			nr_start_heartbeat(skb->sk);
			nr_sk(skb->sk)->state = NR_STATE_0;
		}

		kfree_skb(skb);
	}

	if (sk_has_allocations(sk)) {
		/* Defer: outstanding buffers */
		sk->sk_timer.function = nr_destroy_timer;
		sk->sk_timer.expires  = jiffies + 2 * HZ;
		add_timer(&sk->sk_timer);
	} else
		sock_put(sk);
}

/*
 *	Handler for deferred kills.
 */
static void nr_destroy_timer(struct timer_list *t)
{
	struct sock *sk = from_timer(sk, t, sk_timer);
	bh_lock_sock(sk);
	sock_hold(sk);
	nr_destroy_socket(sk);
	bh_unlock_sock(sk);
	sock_put(sk);
}