centos制作网络时钟源 linux配置时钟源

 

Linux2.6中实现了一种新的定时器hrtimer。与传统定时器使用时间轮算法不同，hrtimer使用了红黑树算法。hrtimer本身可以配置成高精度和普通精度两种，在单CPU系统和多CPU系统中的实现也有区别。这里先分析最简单的配置成普通精度、单CPU的情况。配置成高精度的情况见后续文章。

1.     时钟源的定义

为了实现hrtimer，Linux为系统中每一个CPU定义了一个hrtimer_cpu_base，这个结构体的定义如下：

struct hrtimer_cpu_base {
	raw_spinlock_t			lock;
	struct hrtimer_clock_base	clock_base[HRTIMER_MAX_CLOCK_BASES];  //时钟源 #define HRTIMER_MAX_CLOCK_BASES 2
#ifdef CONFIG_HIGH_RES_TIMERS
	ktime_t				expires_next;
	int				hres_active;
	int				hang_detected;
	unsigned long			nr_events;
	unsigned long			nr_retries;
	unsigned long			nr_hangs;
	ktime_t				max_hang_time;
#endif
};
 
struct hrtimer_clock_base {
	struct hrtimer_cpu_base	*cpu_base;
	clockid_t		index;
	struct rb_root		active;
	struct rb_node		*first;
	ktime_t			resolution;
	ktime_t			(*get_time)(void);
	ktime_t			softirq_time;
#ifdef CONFIG_HIGH_RES_TIMERS
	ktime_t			offset;
#endif
};
DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
{

	.clock_base =
	{
		{
			.index = CLOCK_REALTIME,
			.get_time = &ktime_get_real,
			.resolution = KTIME_LOW_RES,
		},
		{
			.index = CLOCK_MONOTONIC,
			.get_time = &ktime_get,
			.resolution = KTIME_LOW_RES,
		},
	}
};
struct hrtimer {
	struct rb_node			node;
	ktime_t				_expires;
	ktime_t				_softexpires;
	enum hrtimer_restart		(*function)(struct hrtimer *);
	struct hrtimer_clock_base	*base;
	unsigned long			state;
#ifdef CONFIG_TIMER_STATS
	int				start_pid;
	void				*start_site;
	char				start_comm[16];
#endif
};