仅作为内核代码中时间管理模块的笔记,3.10内核,很乱,不喜勿喷。
先有time,后有timer。
常用的time结构有哪些?除了大名鼎鼎的jiffies和jiffies64之外,还有常用的一些结构如下:
ktime_t 经常用在timer中,
union ktime { s64 tv64; #if BITS_PER_LONG != 64 && !defined(CONFIG_KTIME_SCALAR) struct { # ifdef __BIG_ENDIAN s32 sec, nsec; # else s32 nsec, sec; # endif } tv; #endif }; typedef union ktime ktime_t; /* Kill this */
经常用在fs中的timespec,低一点精度的timeval,以及时区结构timezone。主要用来做时间戳等。
struct timespec { __kernel_time_t tv_sec; /* seconds */ long tv_nsec; /* nanoseconds */ };
这些结构之间的常用转换函数:
/* convert a timespec to ktime_t format: */ static inline ktime_t timespec_to_ktime(struct timespec ts) { return ktime_set(ts.tv_sec, ts.tv_nsec); } /* convert a timespec64 to ktime_t format: */ static inline ktime_t timespec64_to_ktime(struct timespec64 ts) { return ktime_set(ts.tv_sec, ts.tv_nsec); } /* convert a timeval to ktime_t format: */ static inline ktime_t timeval_to_ktime(struct timeval tv) { return ktime_set(tv.tv_sec, tv.tv_usec * NSEC_PER_USEC); } /* Map the ktime_t to timespec conversion to ns_to_timespec function */ #define ktime_to_timespec(kt) ns_to_timespec((kt).tv64) /* Map the ktime_t to timespec conversion to ns_to_timespec function */ #define ktime_to_timespec64(kt) ns_to_timespec64((kt).tv64) /* Map the ktime_t to timeval conversion to ns_to_timeval function */ #define ktime_to_timeval(kt) ns_to_timeval((kt).tv64) /* Convert ktime_t to nanoseconds - NOP in the scalar storage format: */ #define ktime_to_ns(kt) ((kt).tv64)
比如有时候自己不想那么高精度的时间戳怎么办呢?内核还提供了这个函数,取到秒级,最方便的是这个函数还被导出了,很好用。
unsigned long get_seconds(void) { struct timekeeper *tk = &timekeeper; return tk->xtime_sec; } EXPORT_SYMBOL(get_seconds);
还有个有趣的问题是,这个时间的维护,精度要更高的话,就需要用顺序锁去读取 timekeeper 变量。
struct timespec current_kernel_time(void) { struct timekeeper *tk = &timekeeper; struct timespec64 now; unsigned long seq; do { seq = read_seqcount_begin(&timekeeper_seq); now = tk_xtime(tk); } while (read_seqcount_retry(&timekeeper_seq, seq)); return timespec64_to_timespec(now); } EXPORT_SYMBOL(current_kernel_time);
好了,time除了用来做时间戳之前,另外一个大的应用就是timer的超时时间了。在描述timer之前,有必要描述linux 关于时间管理的几个大的概念,
低精度的timer定义:
crash> tvec_base struct tvec_base { spinlock_t lock; struct timer_list *running_timer; unsigned long timer_jiffies; unsigned long next_timer; unsigned long active_timers; struct tvec_root tv1; struct tvec tv2; struct tvec tv3; struct tvec tv4; struct tvec tv5; unsigned long all_timers; }
低精度定时器结构:
struct timer_list {---------------------低精度定时器结构, struct list_head entry;-------------用这个挂入到时间轮的链表中,与高精度的rb_node类比 unsigned long expires;--------------超期时间 struct tvec_base *base;-------------指向某个cpu的 tvec_base void (*function)(unsigned long);----回调 unsigned long data; int slack; int start_pid; void *start_site; char start_comm[16]; }
常用的配套函数有:add_timer,mod_timer,add_timer_on(指定cpu添加timer),del_timer,DEFINE_TIMER,setup_timer等,这些在协议栈代码里面非常常见,一般用来等待超时。既然是超时,那么对时间精度要求就不那么高了,所以实现的时候,用了著名的定时器轮。
add_timer的流程和mod_timer的流程差不多,先判断该timer是不是pending,pending的意思就是从定时器轮已经摘取了,可能正在执行中,它的特征就是 该timer的 entry的next是否为NULL
static inline int timer_pending(const struct timer_list * timer) { return timer->entry.next != NULL; }
一句话总结:正等待被调度执行的定时器对象就是pending的。如果一个定时器不是pending的,那么肯定在定时器轮上。
接下来,自然要先从原来的位置摘除,
static inline void detach_timer(struct timer_list *timer, bool clear_pending) { struct list_head *entry = &timer->entry; debug_deactivate(timer); __list_del(entry->prev, entry->next);-----如果timer以前没加入在定时器轮中,则这个啥都不做。 if (clear_pending) entry->next = NULL; entry->prev = LIST_POISON2; }
然后根据这个定时器的超时时间,加入到定时器轮中对应的vec中,主要改动两个,一个是timer的base,还有一个是timer的entry的所处的位置。
crash> p tvec_bases:0 per_cpu(tvec_bases, 0) = $30 = (struct tvec_base *) 0xffffffff81ea71c0 <boot_tvec_bases> crash> tvec_bases PER-CPU DATA TYPE: struct tvec_base *tvec_bases; PER-CPU ADDRESSES: [0]: ffff8827dca13948 [1]: ffff8827dca53948 [2]: ffff8827dca93948 [3]: ffff8827dcad3948 [4]: ffff8827dcb13948 [5]: ffff8827dcb53948 [6]: ffff8827dcb93948 。。。。
这里还有一个细节,就是timer的base,由于这个是一个指针,所以至少是4字节对齐的,也就是后面两位肯定为0,被用来做标记了,当从timer中取这个base指针的时候,就需要将这两
位处理掉,不能直接用来解引用,否则会出现访问错误。
由于低精度的定时器是以jiffies来作为最低精度的,所以精度有限制,但随着硬件以及多媒体发展的实时性较高的要求,后来,又引入了高精度定时器。它是以纳秒为精度的。高精度定时器结构如下:
crash> hrtimer struct hrtimer { struct timerqueue_node node;---------------------------用来插入到红黑树中 ktime_t _softexpires;----------------------------------超期的时间 enum hrtimer_restart (*function)(struct hrtimer *);----回调函数,肯定都有,不过它的返回值只有两个 struct hrtimer_clock_base *base;-----------------------和低精度定时器类似,也有指向一个percpu的base的一个指针,不过base结构与低精度定时器time_list不同 unsigned long state; int start_pid; void *start_site; char start_comm[16]; } SIZE: 96 它指向的base是percpu的 hrtimer_bases,注意和低精度定时器的base相区别,因为低精度的base是percpu的 tvec_base
而高精度定时器的索引,也不是低精度那个vec管理,而是红黑树来管理的。
crash> timerqueue_head struct timerqueue_head { struct rb_root head; struct timerqueue_node *next; } SIZE: 16 crash> hrtimer_clock_base struct hrtimer_clock_base { struct hrtimer_cpu_base *cpu_base; int index; clockid_t clockid; struct timerqueue_head active;------------管理同类型的hrtimer的红黑树封装 ktime_t resolution; ktime_t (*get_time)(void); ktime_t rh_reserved_softirq_time; ktime_t offset; } crash> hrtimer_cpu_base struct hrtimer_cpu_base { raw_spinlock_t lock; unsigned int active_bases; unsigned int clock_was_set; 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; struct hrtimer_clock_base clock_base[4];-------------它的地位,和时间轮的vec相当,是用来管理timer的,通过clockid来分类 int cpu;
int in_hrtirq; }
相应的percpu管理结构,与低精度的tvec_base相对比:
crash> hrtimer_bases------------整个hrtimer_interrupt都是以这个变量为基础 PER-CPU DATA TYPE: struct hrtimer_cpu_base hrtimer_bases; PER-CPU ADDRESSES: [0]: ffff8827dca13960 [1]: ffff8827dca53960 [2]: ffff8827dca93960 [3]: ffff8827dcad3960 [4]: ffff8827dcb13960 [5]: ffff8827dcb53960 [6]: ffff8827dcb93960 [7]: ffff8827dcbd3960 [8]: ffff8827dcc13960 [9]: ffff8827dcc53960 [10]: ffff8827dcc93960 。。。。 crash> p hrtimer_bases:0 per_cpu(hrtimer_bases, 0) = $16 = { lock = { raw_lock = { val = { counter = 0 } } }, active_bases = 3, clock_was_set = 6, expires_next = { tv64 = 558945095814132 }, hres_active = 1, hang_detected = 0, nr_events = 2303159495, nr_retries = 5938805, nr_hangs = 5, max_hang_time = { tv64 = 21681 }, clock_base = {{ cpu_base = 0xffff8827dca13960, index = 0, clockid = 1, active = { head = { rb_node = 0xffff881677e57e88 }, next = 0xffffe8d01d20f220 }, resolution = { tv64 = 1 }, get_time = 0xffffffff810f0670 <ktime_get>, rh_reserved_softirq_time = { tv64 = 0 }, offset = { tv64 = 0 } }, { cpu_base = 0xffff8827dca13960, index = 1, clockid = 0, active = { head = { rb_node = 0xffff881c433fbd38 }, next = 0xffff884a744a7d38 }, resolution = { tv64 = 1 }, get_time = 0xffffffff810f0ad0 <ktime_get_real>, rh_reserved_softirq_time = { tv64 = 0 }, offset = { tv64 = 1540819482621868102 } }, { cpu_base = 0xffff8827dca13960, index = 2, clockid = 7, active = { head = { rb_node = 0x0 }, next = 0x0 }, resolution = { tv64 = 1 }, get_time = 0xffffffff810f0c40 <ktime_get_boottime>, rh_reserved_softirq_time = { tv64 = 0 }, offset = { tv64 = 0 } }, { cpu_base = 0xffff8827dca13960, index = 3, clockid = 11, active = { head = { rb_node = 0x0 }, next = 0x0 }, resolution = { tv64 = 1 }, get_time = 0xffffffff810f08f0 <ktime_get_clocktai>, rh_reserved_softirq_time = { tv64 = 0 }, offset = { tv64 = 1540819482621868102 } }}, cpu = 0, in_hrtirq = 0 }
两类定时器模块的初始化,在start_kernel中,
asmlinkage void __init start_kernel(void) { 。。。。 init_timers();//定时器模块初始化 hrtimers_init();//高精度定时器模块初始化 。。。。 }
对比了两类定时器的定义,从定时器的执行再来对比一下,会加深印象。
对于低精度来说,
void __init init_timers(void) { int err; /* ensure there are enough low bits for flags in timer->base pointer */ BUILD_BUG_ON(__alignof__(struct tvec_base) & TIMER_FLAG_MASK); err = timer_cpu_notify(&timers_nb, (unsigned long)CPU_UP_PREPARE, (void *)(long)smp_processor_id()); init_timer_stats(); BUG_ON(err != NOTIFY_OK); register_cpu_notifier(&timers_nb); open_softirq(TIMER_SOFTIRQ, run_timer_softirq); }
如果是处于低分辨率模式,则会在周期性的 update_process_times-->run_local_timers-->hrtimer_run_queues-->__hrtimer_run_queues 来把这些高精度定时器回调来执行;
update_process_times 调用 run_local_timers 来触发TIMER_SOFTIRQ软中断,run_timer_softirq负责调用__run_timers处理 TIMER_SOFTIRQ软中断。
如果是处于高精度模式,则虽然周期性的 update_process_times-->run_local_timers-->hrtimer_run_queues 会执行,但不会调用 __hrtimer_run_queues ,而是在 hrtimer_interrupt
函数中调用 __hrtimer_run_queues->__run_hrtimer 来完成定时器的调用。
调用链如下:
hrtimer_interrupt-->__hrtimer_run_queues-->__run_hrtimer-->执行回调。
这点和网上的不一致,因为网上大多是2.6的内核描述,其实在哪处理不是很关键,主要是理解数据结构和调用。
总结一下:
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每个cpu有一个tvec_base结构;
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tvec_base结构管理着5个不同超时时间的数组,它采用的基准时间是jiffies。
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加入时间轮的时候,通过timer_list的超时时间,来指定它vec,
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时间轮,按到期时间进行处理,第一轮vec处理完毕,会在第二轮中取一个数组元素填充第一轮的256个到底的元素,
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它通过__run_timers来执行所有到期的低精度定时器
- 每个cpu有一个hrtimer_cpu_base结构;
- hrtimer_cpu_base结构管理着3种不同的时间基准系统的hrtimer,分别是:实时时间,启动时间和单调时间;它的基准时间是纳秒。
- 每种时间基准系统通过它的active字段(timerqueue_head结构指针),指向它们各自的红黑树;
- 红黑树上,按到期时间进行排序,最先到期的hrtimer位于最左下的节点,并被记录在active.next字段中;
- 3中时间基准的最先到期时间可能不同,所以,它们之中最先到期的时间被记录在hrtimer_cpu_base的expires_next字段中。
有一点需要注意,高精度定时器要生效,意味着我们要有高精度的时钟源,那么当没有这么高精度的时钟源的时候,高精度定时器的运转,则精度会降低。
说到时钟源:在我的机器上,3.10的内核,封装了一个结构,叫clocksource如下:
crash> list clocksource.list -H clocksource_list ffffffff81a273c0 ffffffff81a2bb40 ffffffff81aebb80 ffffffff81eb5980 ffffffff81a52c40 crash> clocksource ffffffff81a273c0 struct clocksource { read = 0xffffffff81032e20 <read_tsc>,-----------这个成员的位置放到第一个,因为它最频繁使用,和2.6.18系列版本不一样,大家定义结构的时候把最常使用的放前面,便于cache命中 cycle_last = 2592996216546832, mask = 18446744073709551615, mult = 4194304, shift = 23, max_idle_ns = 428122390528, maxadj = 461373, archdata = { vclock_mode = 1 }, name = 0xffffffff819217b4 "tsc", list = { next = 0xffffffff81a2bb78 <clocksource_hpet+56>, prev = 0xffffffff81a52c30 <clocksource_list> }, rating = 300,----------------精度最高 enable = 0x0, disable = 0x0, flags = 35, suspend = 0x0, resume = 0x0, owner = 0x0 } crash> clocksource ffffffff81a2bb40 struct clocksource { read = 0xffffffff81062430 <read_hpet>, cycle_last = 103666886, mask = 4294967295, mult = 2796202783, shift = 26, max_idle_ns = 69681373356, maxadj = 307582306, archdata = { vclock_mode = 2 }, name = 0xffffffff818ff927 "hpet", list = { next = 0xffffffff81aebbb8 <clocksource_acpi_pm+56>, prev = 0xffffffff81a273f8 <clocksource_tsc+56> }, rating = 250, enable = 0x0, disable = 0x0, flags = 33, suspend = 0x0, resume = 0xffffffff810619e0 <hpet_resume_counter>, owner = 0x0 } crash> clocksource ffffffff81aebb80 struct clocksource { read = 0xffffffff8153cb10 <acpi_pm_read>, cycle_last = 0, mask = 16777215, mult = 2343484437, shift = 23, max_idle_ns = 3649976793, maxadj = 257783288, archdata = { vclock_mode = 0 }, name = 0xffffffff8191e0b6 "acpi_pm", list = { next = 0xffffffff81eb59b8 <refined_jiffies+56>, prev = 0xffffffff81a2bb78 <clocksource_hpet+56> }, rating = 200, enable = 0x0, disable = 0x0, flags = 33, suspend = 0x0, resume = 0x0, owner = 0x0 } crash> clocksource ffffffff81eb5980 struct clocksource { read = 0xffffffff810f3290 <jiffies_read>, cycle_last = 0, mask = 4294967295, mult = 255961088, shift = 8, max_idle_ns = 3344197395684985, maxadj = 28155719, archdata = { vclock_mode = 0 }, name = 0xffffffff8191e0fb "refined-jiffies", list = { next = 0xffffffff81a52c78 <clocksource_jiffies+56>, prev = 0xffffffff81aebbb8 <clocksource_acpi_pm+56> }, rating = 2,------------------------精度最低 enable = 0x0, disable = 0x0, flags = 0, suspend = 0x0, resume = 0x0, owner = 0x0 } crash> clocksource ffffffff81a52c40 struct clocksource { read = 0xffffffff810f3290 <jiffies_read>, cycle_last = 4294669298, mask = 4294967295, mult = 256000000, shift = 8, max_idle_ns = 3344705780981250, maxadj = 28160000, archdata = { vclock_mode = 0 }, name = 0xffffffff8191e103 "jiffies", list = { next = 0xffffffff81a52c30 <clocksource_list>, prev = 0xffffffff81eb59b8 <refined_jiffies+56> }, rating = 1, enable = 0x0, disable = 0x0, flags = 0, suspend = 0x0, resume = 0x0, owner = 0x0 }
用户可以通过 手工来切换clocksource,比如我的环境上有tsc,hpet,acpi_pm三个可用的clocksource(这个比crash中列的少一些)
cat /sys/devices/system/clocksource/clocksource0/available_clocksource tsc hpet acpi_pm [root@localhost ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource tsc [root@localhost ~]# cat /sys/devices/system/clocksource/clocksource0/unbind_clocksource cat: /sys/devices/system/clocksource/clocksource0/unbind_clocksource: Permission denied [root@localhost ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource tsc [root@localhost ~]# ls -alrt /sys/devices/system/clocksource/clocksource0/current_clocksource -rw-r--r-- 1 root root 4096 Oct 30 09:52 /sys/devices/system/clocksource/clocksource0/current_clocksource [root@localhost ~]# echo hpet > /sys/devices/system/clocksource/clocksource0/current_clocksource [root@localhost ~]# cat /sys/devices/system/clocksource/clocksource0/current_clocksource hpet [root@localhost ~]# echo tsc > /sys/devices/system/clocksource/clocksource0/current_clocksource切换之后会有打印,有时候也可以在message中看到内核自动切换的打印。
[44890.290544] Switched to clocksource hpet
[44902.121090] Switched to clocksource tsc
介绍完时钟源的定义和使用,有必要介绍下一个重要概念,时钟事件设备。
时间事件设备允许注册一个事件,在未来一个指定的时间点上发生,但与定时器实现相比,它只能存储一个事件。
举一个clock_event_device 的例子:
clock_event_device ffff8827dcf11140 struct clock_event_device { event_handler = 0xffffffff810b9890 <hrtimer_interrupt>, set_next_event = 0xffffffff81053df0 <lapic_next_deadline>, set_next_ktime = 0x0, next_event = { tv64 = 62900678796701 }, max_delta_ns = 2199023255551, min_delta_ns = 1000, mult = 8388608, shift = 27, mode = CLOCK_EVT_MODE_ONESHOT, features = 2,-------------------------------------------属性,为2说明是oneshot模式 retries = 19117, broadcast = 0xffffffff81053e30 <lapic_timer_broadcast>, set_mode = 0xffffffff81054620 <lapic_timer_setup>, suspend = 0x0, resume = 0x0, min_delta_ticks = 15, max_delta_ticks = 18446744073709551615, name = 0xffffffff818fefdd "lapic",------------------事件设备的名称 rating = 150, irq = -1, bound_on = 0, cpumask = 0xffffffff816e7c60 <cpu_bit_bitmap+26240>, list = { next = 0xffff8857bc2d11d8, prev = 0xffff8827dcf511d8 }, owner = 0x0 }
/* * Clock event features */ #define CLOCK_EVT_FEAT_PERIODIC 0x000001 #define CLOCK_EVT_FEAT_ONESHOT 0x000002 #define CLOCK_EVT_FEAT_KTIME 0x000004 /* * x86(64) specific misfeatures: * * - Clockevent source stops in C3 State and needs broadcast support. * - Local APIC timer is used as a dummy device. */ #define CLOCK_EVT_FEAT_C3STOP 0x000008 #define CLOCK_EVT_FEAT_DUMMY 0x000010 /* * Core shall set the interrupt affinity dynamically in broadcast mode */ #define CLOCK_EVT_FEAT_DYNIRQ 0x000020 /* * Clockevent device is based on a hrtimer for broadcast */ #define CLOCK_EVT_FEAT_HRTIMER 0x000080
每个时钟硬件设备注册一个时钟设备tick_device 和一个时钟事件设备。
为了精度,系统兼容了两套定时器,一套是时间轮的低精度定时器,一种是高精度的hrtimer。定时器软中断调用 hrtimer_run_queues 来处理高分辨率定时器队列,哪怕底层时钟事件设备只提供了低分辨率,也是如此。这使得可以使用现存的框架,而无需关注时钟的分辨率。
为了节能,系统又引入了tickless模型,也就是nohz模型,其实就是将原来周期性的tick,变为按需触发,对于需要模拟tick的周期性函数,则由相应的cpu来完成,其他cpu如果没事可以
休息。
nohz_mode目前包含三种模式,一种是未开启nohz,一种是系统工作于低分辨率模式下的动态时钟,一种是系统工作于高精度模式下的动态时钟。
struct tick_sched { struct hrtimer sched_timer;---用于高分辨率模式下,模拟周期时钟的一个timer unsigned long check_clocks; enum tick_nohz_mode nohz_mode;---包含三种模式, ktime_t last_tick; ktime_t next_tick; int inidle; int tick_stopped; unsigned long idle_jiffies; unsigned long idle_calls; unsigned long idle_sleeps; int idle_active; ktime_t idle_entrytime; ktime_t idle_waketime; ktime_t idle_exittime; ktime_t idle_sleeptime; ktime_t iowait_sleeptime; ktime_t sleep_length; unsigned long last_jiffies; u64 next_timer; ktime_t idle_expires; int do_timer_last; };
crash> tick_sched struct tick_sched { struct hrtimer sched_timer; unsigned long check_clocks; enum tick_nohz_mode nohz_mode; ktime_t last_tick; ktime_t next_tick; int inidle; int tick_stopped; unsigned long idle_jiffies; unsigned long idle_calls; unsigned long idle_sleeps; int idle_active; ktime_t idle_entrytime; ktime_t idle_waketime; ktime_t idle_exittime; ktime_t idle_sleeptime; ktime_t iowait_sleeptime; ktime_t sleep_length; unsigned long last_jiffies; u64 next_timer; ktime_t idle_expires; int do_timer_last; }
tick_sched 中收集的统计信息通过/proc/timer_list 导出到用户层。
crash> tick_cpu_sched PER-CPU DATA TYPE: struct tick_sched tick_cpu_sched; PER-CPU ADDRESSES: [0]: ffff8827dca13f20 [1]: ffff8827dca53f20 [2]: ffff8827dca93f20 [3]: ffff8827dcad3f20 。。。。。。。。。。。。。 crash> p tick_cpu_sched:0 per_cpu(tick_cpu_sched, 0) = $18 = { sched_timer = { node = { node = { __rb_parent_color = 18446612303169076872, rb_right = 0x0, rb_left = 0x0 }, expires = { tv64 = 579956705000000 } }, _softexpires = { tv64 = 579956705000000 }, function = 0xffffffff810f9170 <tick_sched_timer>, base = 0xffff8827dca139a0, state = 1, start_pid = 0, start_site = 0xffffffff810f95c2 <tick_nohz_stop_sched_tick+690>, start_comm = "swapper/0\000\000\000\000\000\000" }, check_clocks = 1, nohz_mode = NOHZ_MODE_HIGHRES, last_tick = { tv64 = 579956549000000 }, next_tick = { tv64 = 579956705000000 }, inidle = 1, tick_stopped = 1, idle_jiffies = 4874623845, idle_calls = 2616662184, idle_sleeps = 2409217702, idle_active = 1, idle_entrytime = { tv64 = 579956548218826 }, idle_waketime = { tv64 = 579956548210360 }, idle_exittime = { tv64 = 579956548213511 }, idle_sleeptime = { tv64 = 548323643001010 }, iowait_sleeptime = { tv64 = 53588522970 }, sleep_length = { tv64 = 515114 }, last_jiffies = 4874623845, next_timer = 579956705000000, idle_expires = { tv64 = 579956705000000 }, do_timer_last = 0 }
对时钟的禁用是按cpu指定的,一般来说,所有cpu都空闲的概率还是比较低的。
crash> p tick_next_period tick_next_period = $19 = { tv64 = 580792669000000 } crash> p tick_next_period tick_next_period = $20 = { tv64 = 580794124000000 } crash> p tick_next_period tick_next_period = $21 = { tv64 = 580795263000000 } crash> p tick_next_period tick_next_period = $22 = { tv64 = 580796247000000 } crash> p last_jiffies_update last_jiffies_update = $23 = { tv64 = 580801981000000 } crash> p last_jiffies_update last_jiffies_update = $24 = { tv64 = 580802792000000 } crash> p last_jiffies_update last_jiffies_update = $25 = { tv64 = 580803530000000 }
时间相关系统调用及外部设置:
adjtimex 系统调用,NTP设置,
内核的工作模式:
-
没有动态时钟的低分辨率系统,总是用周期时钟。这时不会支持单触发模式
-
启用了动态时钟的低分辨率系统,将以单触发模式是用时钟设备
-
高分辨率系统总是用单触发模式,无论是否启用了动态时钟特性
- 高分辨率时钟系统,每个cpu会使用一个hrtimer来模拟周期时钟,提供tick,毕竟精度高的要模拟精度低的比较容易,同时又能纳入自己的高分辨率框架。模拟的函数为:tick_sched_timer
非广播时最终的处理函数:
高分辨率动态时钟:hrtimer_interrupt
高分辨率周期时钟:hrtimer_interrupt
低分辨率动态时钟:tick_nohz_handler
低分辨率周期时钟:tick_handle_periodic
广播时最终的处理函数:
高分辨率动态时钟:tick_handle_oneshot_broadcast
高分辨率周期时钟:tick_handle_oneshot_broadcast
低分辨率动态时钟:tick_handle_oneshot_broadcast
低分辨率周期时钟:tick_handle_periodic_broadcast
参考资料:
linux 3.10内核源码
原文:https://blog.csdn.net/goodluckwhh/article/details/9048565
来源:https://www.cnblogs.com/10087622blog/p/9854619.html