dpdk中的timer子系统的使用

dpdk中要使用timer 必须分为下面三步
第一步：在dpdk中要使用timer，必须初始化RTE timer library
其源码分析如下：
void
rte_timer_subsystem_init(void)
{
	unsigned lcore_id;

	/* since priv_timer is static, it's zeroed by default, so only init some
	 * fields.
	 */
	for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id ++) {
		rte_spinlock_init(&priv_timer[lcore_id].list_lock);
		priv_timer[lcore_id].prev_lcore = lcore_id;
	}
}
可见time子系统初始化是给每一个cpu初始化一个spin lock，并记录当前的cpu id
第二步：必须为每个timer的回调函数初始化一个rte_timer结构体
void
rte_timer_init(struct rte_timer *tim)
{
	union rte_timer_status status;

	status.state = RTE_TIMER_STOP;
	status.owner = RTE_TIMER_NO_OWNER;
	tim->status.u32 = status.u32;
}
可以看到只是初始化rte_timer的status 变量
第三步：设置timer工作的模式
int
rte_timer_reset(struct rte_timer *tim, uint64_t ticks,
		enum rte_timer_type type, unsigned tim_lcore,
		rte_timer_cb_t fct, void *arg)
{
	#得到当前时间
	uint64_t cur_time = rte_get_timer_cycles();
	uint64_t period;

	if (unlikely((tim_lcore != (unsigned)LCORE_ID_ANY) &&
			!(rte_lcore_is_enabled(tim_lcore) ||
			  rte_lcore_has_role(tim_lcore, ROLE_SERVICE) == 0)))
		return -1;
	#如果type是PERIODICAL，说明是周期timer，这里就要设置timer的周期，否则周期就是零
	if (type == PERIODICAL)
		period = ticks;
	else
		period = 0;
	#获得当前时间和周期后继续设置timer
	return __rte_timer_reset(tim,  cur_time + ticks, period, tim_lcore,
			  fct, arg, 0);
}

static int
__rte_timer_reset(struct rte_timer *tim, uint64_t expire,
		  uint64_t period, unsigned tim_lcore,
		  rte_timer_cb_t fct, void *arg,
		  int local_is_locked)
{
	union rte_timer_status prev_status, status;
	int ret;
	#获得当前cpu id
	unsigned lcore_id = rte_lcore_id();

	/* round robin for tim_lcore */
	#这里检查timer是否可以建立在其他core上
	if (tim_lcore == (unsigned)LCORE_ID_ANY) {
		if (lcore_id < RTE_MAX_LCORE) {
			/* EAL thread with valid lcore_id */
			tim_lcore = rte_get_next_lcore(
				priv_timer[lcore_id].prev_lcore,
				0, 1);
			priv_timer[lcore_id].prev_lcore = tim_lcore;
		} else
			/* non-EAL thread do not run rte_timer_manage(),
			 * so schedule the timer on the first enabled lcore. */
			tim_lcore = rte_get_next_lcore(LCORE_ID_ANY, 0, 1);
	}

	/* wait that the timer is in correct status before update,
	 * and mark it as being configured */
	#只是timer状态
	ret = timer_set_config_state(tim, &prev_status);
	if (ret < 0)
		return -1;
	#用于debug函数，release版本为空函数
	__TIMER_STAT_ADD(reset, 1);
	#如果timer已经在运行状态说明这次是要update状态
	if (prev_status.state == RTE_TIMER_RUNNING &&
	    lcore_id < RTE_MAX_LCORE) {
		priv_timer[lcore_id].updated = 1;
	}

	/* remove it from list */
	#如果timer是pending的，则调用timer_del删除timer
	if (prev_status.state == RTE_TIMER_PENDING) {
		timer_del(tim, prev_status, local_is_locked);
		__TIMER_STAT_ADD(pending, -1);
	}
	#设置time的周期，下次到期时间，回调函数，以及参数
	tim->period = period;
	tim->expire = expire;
	tim->f = fct;
	tim->arg = arg;
	#debug函数，打印状态
	__TIMER_STAT_ADD(pending, 1);
	#添加这个timer后，这个timer就开始正常工作了
	timer_add(tim, tim_lcore, local_is_locked);

	/* update state: as we are in CONFIG state, only us can modify
	 * the state so we don't need to use cmpset() here */
	rte_wmb();
	
	status.state = RTE_TIMER_PENDING;
	status.owner = (int16_t)tim_lcore;
	tim->status.u32 = status.u32;

	return 0;
}