关于internal_add_timer 的一个问题

[liulin063326]

Note: kernel 2.4

static inline void internal_add_timer(struct timer_list *timer)
{
	/*
	 * must be cli-ed when calling this
	 */
	unsigned long expires = timer->expires;
	unsigned long idx = expires - timer_jiffies;
	struct list_head * vec;
	if (idx < TVR_SIZE) {
		int i = expires & TVR_MASK;
		vec = tv1.vec + i;
	} else if (idx < 1 << (TVR_BITS + TVN_BITS)) {
		int i = (expires >> TVR_BITS) & TVN_MASK;
		vec = tv2.vec + i;
	} else if (idx < 1 << (TVR_BITS + 2 * TVN_BITS)) {
		int i = (expires >> (TVR_BITS + TVN_BITS)) & TVN_MASK;
		vec =  tv3.vec + i;
	} else if (idx < 1 << (TVR_BITS + 3 * TVN_BITS)) {
		int i = (expires >> (TVR_BITS + 2 * TVN_BITS)) & TVN_MASK;
		vec = tv4.vec + i;
	} else if ((signed long) idx < 0) {
		/* can happen if you add a timer with expires == jiffies,
		 * or you set a timer to go off in the past
		 */
		vec = tv1.vec + tv1.index;
	} else if (idx <= 0xffffffffUL) {
		int i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK;
		vec = tv5.vec + i;
	} else {
		/* Can only get here on architectures with 64-bit jiffies */
		INIT_LIST_HEAD(&timer->list);
		return;
	}
	/*
	 * Timers are FIFO!
	 */
	list_add(&timer->list, vec->prev);
}

每个 vec （哈希表）中有个index用来表示下一次要处理的队列， 为什么插入的时候不依据这个index插入， 成为如下，

static inline void internal_add_timer(struct timer_list *timer)
{
	/*
	 * must be cli-ed when calling this
	 */
	unsigned long expires = timer->expires;
	unsigned long idx = expires - timer_jiffies;
	struct list_head * vec;
	if (idx < TVR_SIZE) {
		int i = expires & TVR_MASK;
		vec = tv1.vec + tv1.index + i;
	} else if (idx < 1 << (TVR_BITS + TVN_BITS)) {
		int i = (expires >> TVR_BITS) & TVN_MASK;
		vec = tv2.vec + tv2.index + i;
	} else if (idx < 1 << (TVR_BITS + 2 * TVN_BITS)) {
		int i = (expires >> (TVR_BITS + TVN_BITS)) & TVN_MASK;
		vec =  tv3.vec + tv3.index + i;
	} else if (idx < 1 << (TVR_BITS + 3 * TVN_BITS)) {
		int i = (expires >> (TVR_BITS + 2 * TVN_BITS)) & TVN_MASK;
		vec = tv4.vec + tv4.index+ i;
	} else if ((signed long) idx < 0) {
		/* can happen if you add a timer with expires == jiffies,
		 * or you set a timer to go off in the past
		 */
		vec = tv1.vec + tv1.index;
	} else if (idx <= 0xffffffffUL) {
		int i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK;
		vec = tv5.vec + tv5.index+ i;
	} else {
		/* Can only get here on architectures with 64-bit jiffies */
		INIT_LIST_HEAD(&timer->list);
		return;
	}
	/*
	 * Timers are FIFO!
	 */
	list_add(&timer->list, vec->prev);
}

如此， 插入下一个Jeffies 需要处理的timer，就会被放在

 tv1.vec + tv1.index + i;

另外备注处理timer的函数

static inline void run_timer_list(void)
{
	spin_lock_irq(&timerlist_lock);
	while ((long)(jiffies - timer_jiffies) >= 0) {
		struct list_head *head, *curr;
		if (!tv1.index) {
			int n = 1;
			do {
				cascade_timers(tvecs[n]);
			} while (tvecs[n]->index == 1 && ++n < NOOF_TVECS);
		}
repeat:
		head = tv1.vec + tv1.index;
		curr = head->next;
		if (curr != head) {
			struct timer_list *timer;
			void (*fn)(unsigned long);
			unsigned long data;

			timer = list_entry(curr, struct timer_list, list);
 			fn = timer->function;
 			data= timer->data;

			detach_timer(timer);
			timer->list.next = timer->list.prev = NULL;
			timer_enter(timer);
			spin_unlock_irq(&timerlist_lock);
			fn(data);
			spin_lock_irq(&timerlist_lock);
			timer_exit();
			goto repeat;
		}
		++timer_jiffies; 
		tv1.index = (tv1.index + 1) & TVR_MASK;
	}
	spin_unlock_irq(&timerlist_lock);
}