Linux 内核时间子系统分析文档
目录
1. 时间基础
1.1 Jiffies 和 HZ
源码位置: /Users/sphinx/github/linux/include/linux/jiffies.h
Jiffies 是内核中表示时间的基本单位,是一个全局变量,每经过一个时钟滴答(Tick)增加 1。
c
// include/linux/jiffies.h:85-86
extern u64 __cacheline_aligned_in_smp jiffies_64;
extern unsigned long volatile __cacheline_aligned_in_smp __jiffy_arch_data jiffies;HZ 是每秒时钟中断的次数,由架构决定:
| HZ 值 | 适用场景 |
|---|---|
| 100 | 通用服务器 |
| 250 | 桌面系统 |
| 300 | 某些特定架构 |
| 1000 | 高精度需求(嵌入式) |
c
// include/linux/jiffies.h:23-45
#if HZ >= 12 && HZ < 24
# define SHIFT_HZ 4
#elif HZ >= 24 && HZ < 48
# define SHIFT_HZ 5
// ... 更多HZ值定义
#endifTICK_USEC 计算每次tick的微秒数:
c
// include/linux/jiffies.h:64-65
#define TICK_USEC ((USEC_PER_SEC + HZ/2) / HZ)
#define USER_TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)时间比较宏:
c
// include/linux/jiffies.h:127-130
#define time_after(a,b) \
(typecheck(unsigned long, a) && \
typecheck(unsigned long, b) && \
((long)((b) - (a)) < 0))
#define time_before(a,b) time_after(b,a)1.2 时间结构体
struct timespec - 纳秒级精度:
c
// include/linux/time.h:36-56 (struct tm 定义)
// include/uapi/linux/time.h 中的实际定义:
// struct timespec {
// __kernel_time_t tv_sec; /* 秒 */
// long tv_nsec; /* 纳秒 */
// };struct timeval - 微秒级精度(较老):
c
// include/uapi/linux/time.h
// struct timeval {
// __kernel_time_t tv_sec; /* 秒 */
// __suseconds_t tv_usec; /* 微秒 */
// };ktime_t - 内核内部时间表示:
c
// include/linux/ktime.h
// 64位整数,直接存储纳秒值
typedef s64 ktime_t;时间转换关系:
CLOCK_REALTIME ←→ CLOCK_MONOTONIC
↑ ↑
wall_to_monotonic 偏移1.3 时间分辨率
| 组件 | 分辨率 | 源码位置 |
|---|---|---|
| jiffies | 1/HZ 秒 | jiffies.h |
| timespec | 1 纳秒 | time.h |
| timeval | 1 微秒 | time.h |
| ktime_t | 1 纳秒 | ktime.h |
| hrtimer | 1 纳秒(硬件支持) | hrtimer.c |
| TICK_NSEC | HZ对应的纳秒 | tick-internal.h |
c
// kernel/time/hrtimer.c:58
#define HIGH_RES_NSEC 12. Tick 设备
2.1 tick_handle_periodic()
源码位置: /Users/sphinx/github/linux/kernel/time/tick-common.c:108-146
这是周期 tick 的主要处理函数:
c
// tick-common.c:108-146
void tick_handle_periodic(struct clock_event_device *dev)
{
int cpu = smp_processor_id();
ktime_t next = dev->next_event;
tick_periodic(cpu); // 处理 tick 事件
// 检查是否转换到 HIGHRES 或 NOHZ 模式
if (IS_ENABLED(CONFIG_TICK_ONESHOT) && dev->event_handler != tick_handle_periodic)
return;
if (!clockevent_state_oneshot(dev))
return;
for (;;) {
// 设置下一个周期事件
next = ktime_add_ns(next, TICK_NSEC);
if (!clockevents_program_event(dev, next, false))
return;
// 在 oneshot 模式下循环调用 tick_periodic
if (timekeeping_valid_for_hres())
tick_periodic(cpu);
}
}tick_periodic() 处理具体事务:
c
// tick-common.c:86-103
static void tick_periodic(int cpu)
{
if (READ_ONCE(tick_do_timer_cpu) == cpu) {
raw_spin_lock(&jiffies_lock);
write_seqcount_begin(&jiffies_seq);
tick_next_period = ktime_add_ns(tick_next_period, TICK_NSEC);
do_timer(1); // 更新 jiffies
write_seqcount_end(&jiffies_seq);
raw_spin_unlock(&jiffies_lock);
update_wall_time(); // 更新墙上时间
}
update_process_times(user_mode(get_irq_regs()));
profile_tick(CPU_PROFILING);
}2.2 NO_HZ / Dynamic Tick
源码位置: /Users/sphinx/github/linux/kernel/time/tick-sched.c
NO_HZ(也称 dynamic tick)允许 CPU 在空闲时停止周期 tick 以节省功耗。
核心结构体 struct tick_sched:
c
// kernel/time/tick-sched.h:64-103
struct tick_sched {
/* 通用标志 */
unsigned long flags;
/* Tick 处理: jiffies 停滞检查 */
unsigned int stalled_jiffies;
unsigned long last_tick_jiffies;
/* Tick 处理 */
struct hrtimer sched_timer; // 调度定时器
ktime_t last_tick; // 上一次 tick
ktime_t next_tick; // 下一次 tick
unsigned long idle_jiffies;
ktime_t idle_waketime;
unsigned int got_idle_tick;
/* 空闲入口 */
seqcount_t idle_sleeptime_seq;
ktime_t idle_entrytime;
/* Tick 停止 */
unsigned long last_jiffies;
u64 timer_expires_base;
u64 timer_expires;
u64 next_timer;
ktime_t idle_expires;
unsigned long idle_calls;
unsigned long idle_sleeps;
/* 空闲退出 */
ktime_t idle_exittime;
ktime_t idle_sleeptime;
ktime_t iowait_sleeptime;
/* 全动态 tick 处理 */
atomic_t tick_dep_mask;
/* 时钟源变化通知 */
unsigned long check_clocks;
};Tick 标志位:
c
// tick-sched.h:17-31
#define TS_FLAG_INIDLE BIT(0) // CPU 处于 tick 空闲模式
#define TS_FLAG_STOPPED BIT(1) // 空闲 tick 已停止
#define TS_FLAG_IDLE_ACTIVE BIT(2) // 空闲 tick 正在执行
#define TS_FLAG_DO_TIMER_LAST BIT(3) // CPU 是最后一个执行 do_timer 的
#define TS_FLAG_NOHZ BIT(4) // NO_HZ 已启用
#define TS_FLAG_HIGHRES BIT(5) // 高精度 tick 模式NO_HZ 核心函数 - tick_nohz_handler():
c
// kernel/time/tick-sched.c:306-334
static enum hrtimer_restart tick_nohz_handler(struct hrtimer *timer)
{
struct tick_sched *ts = container_of(timer, struct tick_sched, sched_timer);
struct pt_regs *regs = get_irq_regs();
ktime_t now = ktime_get();
tick_sched_do_timer(ts, now); // 处理计时器
if (regs)
tick_sched_handle(ts, regs); // 更新进程时间
else
ts->next_tick = 0;
// 如果 tick 已停止则不重启
if (unlikely(tick_sched_flag_test(ts, TS_FLAG_STOPPED)))
return HRTIMER_NORESTART;
hrtimer_forward(timer, now, TICK_NSEC); // 转发到下一个 tick
return HRTIMER_RESTART;
}2.3 Tick 设备管理
struct tick_device - 每个 CPU 的 tick 设备:
c
// kernel/time/tick-sched.h:12-15
struct tick_device {
struct clock_event_device *evtdev; // 事件设备
enum tick_device_mode mode; // PERODIC 或 ONESHOT
};
enum tick_device_mode {
TICKDEV_MODE_PERIODIC,
TICKDEV_MODE_ONESHOT,
};tick_do_timer_cpu - 负责更新 jiffies 的 CPU:
c
// tick-common.c:51
int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;3. 高精度定时器 hrtimer
3.1 hrtimer 结构体
源码位置: /Users/sphinx/github/linux/include/linux/hrtimer_types.h:39-48
c
struct hrtimer {
struct timerqueue_node node; // 定时器队列节点
ktime_t _softexpires; // 软过期时间
enum hrtimer_restart (*__private function)(struct hrtimer *); // 回调函数
struct hrtimer_clock_base *base; // 所属时钟基准
u8 state; // 状态 (ENQUEUED, INACTIVE)
u8 is_rel; // 是否为相对时间
u8 is_soft; // 是否在软中断上下文执行
u8 is_hard; // 是否在硬中断上下文执行
};hrtimer_clock_base - 每个 CPU 每种时钟的基础结构:
c
// include/linux/hrtimer_defs.h:26-34
struct hrtimer_clock_base {
struct hrtimer_cpu_base *cpu_base; // 指向 per-CPU 基准
unsigned int index; // 基准索引
clockid_t clockid; // 时钟 ID
seqcount_raw_spinlock_t seq; // seqcount 保护
struct hrtimer *running; // 当前运行的定时器
struct timerqueue_head active; // 活跃定时器红黑树
ktime_t offset; // 到单调时钟的偏移
};hrtimer_cpu_base - per-CPU 的 hrtimer 基准:
c
// include/linux/hrtimer_defs.h:81-107
struct hrtimer_cpu_base {
raw_spinlock_t lock;
unsigned int cpu;
unsigned int active_bases; // 活跃基准位图
unsigned int clock_was_set_seq; // 时钟设置序列
unsigned int hres_active : 1; // 高精度模式活跃
unsigned int in_hrtirq : 1; // hrtimer 中断中
unsigned int hang_detected : 1; // 检测到挂起
unsigned int softirq_activated : 1;
unsigned int online : 1;
ktime_t expires_next; // 下一个过期时间
struct hrtimer *next_timer; // 下一个定时器
ktime_t softirq_expires_next;
struct hrtimer *softirq_next_timer;
struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES];
call_single_data_t csd;
};时钟基准类型枚举:
c
// include/linux/hrtimer_defs.h:36-46
enum hrtimer_base_type {
HRTIMER_BASE_MONOTONIC, // 单调时钟
HRTIMER_BASE_REALTIME, // 实时时钟
HRTIMER_BASE_BOOTTIME, // 启动时间
HRTIMER_BASE_TAI, // TAI 国际原子时
HRTIMER_BASE_MONOTONIC_SOFT, // 软中断版本
HRTIMER_BASE_REALTIME_SOFT,
HRTIMER_BASE_BOOTTIME_SOFT,
HRTIMER_BASE_TAI_SOFT,
HRTIMER_MAX_CLOCK_BASES,
};per-CPU hrtimer 基准初始化:
c
// kernel/time/hrtimer.c:80-119
DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
{
.lock = __RAW_SPIN_LOCK_UNLOCKED(hrtimer_bases.lock),
.clock_base = {
{ .index = HRTIMER_BASE_MONOTONIC, .clockid = CLOCK_MONOTONIC, },
{ .index = HRTIMER_BASE_REALTIME, .clockid = CLOCK_REALTIME, },
{ .index = HRTIMER_BASE_BOOTTIME, .clockid = CLOCK_BOOTTIME, },
{ .index = HRTIMER_BASE_TAI, .clockid = CLOCK_TAI, },
{ .index = HRTIMER_BASE_MONOTONIC_SOFT, .clockid = CLOCK_MONOTONIC, },
{ .index = HRTIMER_BASE_REALTIME_SOFT, .clockid = CLOCK_REALTIME, },
{ .index = HRTIMER_BASE_BOOTTIME_SOFT, .clockid = CLOCK_BOOTTIME, },
{ .index = HRTIMER_BASE_TAI_SOFT, .clockid = CLOCK_TAI, },
},
.csd = CSD_INIT(retrigger_next_event, NULL)
};3.2 hrtimer_start() 启动定时器
源码位置: /Users/sphinx/github/linux/kernel/time/hrtimer.c:1312-1335
c
// hrtimer.c:1312-1335
void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
u64 delta_ns, const enum hrtimer_mode mode)
{
struct hrtimer_clock_base *base;
unsigned long flags;
// 检查 SOFT/HARD 模式匹配
if (!IS_ENABLED(CONFIG_PREEMPT_RT))
WARN_ON_ONCE(!(mode & HRTIMER_MODE_SOFT) ^ !timer->is_soft);
else
WARN_ON_ONCE(!(mode & HRTIMER_MODE_HARD) ^ !timer->is_hard);
base = lock_hrtimer_base(timer, &flags);
if (__hrtimer_start_range_ns(timer, tim, delta_ns, mode, base))
hrtimer_reprogram(timer, true); // 重新编程硬件
unlock_hrtimer_base(timer, &flags);
}
EXPORT_SYMBOL_GPL(hrtimer_start_range_ns);内部函数 __hrtimer_start_range_ns():
c
// hrtimer.c:1218-1301
static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
u64 delta_ns, const enum hrtimer_mode mode,
struct hrtimer_clock_base *base)
{
struct hrtimer_cpu_base *this_cpu_base = this_cpu_ptr(&hrtimer_bases);
struct hrtimer_clock_base *new_base;
bool force_local, first;
// 决定是否强制本地执行
force_local = base->cpu_base == this_cpu_base;
force_local &= base->cpu_base->next_timer == timer;
force_local &= this_cpu_base->online;
// 移除已存在的定时器
remove_hrtimer(timer, base, true, force_local);
// 处理相对时间
if (mode & HRTIMER_MODE_REL)
tim = ktime_add_safe(tim, __hrtimer_cb_get_time(base->clockid));
tim = hrtimer_update_lowres(timer, tim, mode);
hrtimer_set_expires_range_ns(timer, tim, delta_ns);
// 切换定时器基准(如需要)
if (!force_local) {
new_base = switch_hrtimer_base(timer, base,
mode & HRTIMER_MODE_PINNED);
} else {
new_base = base;
}
first = enqueue_hrtimer(timer, new_base, mode);
if (!force_local) {
if (hrtimer_base_is_online(this_cpu_base))
return first;
if (first) {
smp_call_function_single_async(new_cpu_base->cpu, &new_cpu_base->csd);
}
return 0;
}
hrtimer_force_reprogram(new_base->cpu_base, 1);
return 0;
}3.3 hrtimer_run_pending() hrtimer 调度
源码位置: /Users/sphinx/github/linux/kernel/time/hrtimer.c (实际调用在 tick-sched.c)
hrtimer 通过 tick 调度,在以下流程中被调用:
tick_nohz_handler() 或 tick_periodic()
└── hrtimer_run_queues()
└── __hrtimer_run_queues()
└── 遍历所有过期的 hrtimer 并执行回调__hrtimer_run_queues() 处理过期定时器:
c
// hrtimer.c 中的实现,核心逻辑:
// 遍历所有活跃的 clock_base
// 对每个 base 的红黑树中的过期定时器调用其回调函数定时器重新编程:
c
// hrtimer.c:660-687
static void __hrtimer_reprogram(struct hrtimer_cpu_base *cpu_base,
struct hrtimer *next_timer,
ktime_t expires_next)
{
cpu_base->expires_next = expires_next;
if (!hrtimer_hres_active(cpu_base) || cpu_base->hang_detected)
return;
tick_program_event(expires_next, 1); // 编程下一个事件
}4. Posix Timers
4.1 timer_create() 系统调用
源码位置: /Users/sphinx/github/linux/kernel/time/posix-timers.c
k_itimer 结构体 - 内核中的 POSIX 定时器:
c
// 实际定义在 posix-timers.c 中,核心字段:
struct k_itimer {
struct list_head list; // 链表头
spinlock_t it_lock; // 保护此结构
clockid_t it_clock; // 时钟类型
timer_t it_id; // 定时器 ID
int it_status; // 状态
s64 it_overrun; // 超限计数
s64 it_overrun_last; // 上次超限
union { // 定时器类型联合
struct {
struct hrtimer timer;
} real;
struct { ... } cpu;
struct { ... } sig;
} it;
struct callback_head futex_state;
// ...
};do_timer_create() 实现:
c
// posix-timers.c:458-510
static int do_timer_create(clockid_t which_clock, struct sigevent *event,
timer_t __user *created_timer_id)
{
const struct k_clock *kc = clockid_to_kclock(which_clock);
// ... 参数验证 ...
new_timer = alloc_posix_timer();
// ... 初始化 ...
new_timer_id = posix_timer_add(new_timer, req_id);
if (new_timer_id < 0) {
posixtimer_free_timer(new_timer);
return new_timer_id;
}
new_timer->it_clock = which_clock;
new_timer->kclock = kc;
// ...
if (event->sigev_notify != SIGEV_NONE) {
// 设置信号处理
}
return new_timer_id;
}时钟类型到 k_clock 的映射:
c
// posix-timers.c:57
static const struct k_clock * const posix_clocks[];
static const struct k_clock clock_realtime, clock_monotonic;k_clock 操作接口:
c
// kernel/time/posix-timers.h:10-37
struct k_clock {
int (*clock_getres)(const clockid_t which_clock, struct timespec64 *tp);
int (*clock_set)(const clockid_t which_clock, const struct timespec64 *tp);
int (*clock_get_timespec)(const clockid_t which_clock, struct timespec64 *tp);
ktime_t (*clock_get_ktime)(const clockid_t which_clock);
int (*clock_adj)(const clockid_t which_clock, struct __kernel_timex *tx);
int (*timer_create)(struct k_itimer *timer);
int (*nsleep)(const clockid_t which_clock, int flags, const struct timespec64 *);
int (*timer_set)(struct k_itimer *timr, int flags,
struct itimerspec64 *new_setting,
struct itimerspec64 *old_setting);
int (*timer_del)(struct k_itimer *timr);
void (*timer_get)(struct k_itimer *timr, struct itimerspec64 *cur_setting);
void (*timer_rearm)(struct k_itimer *timr);
// ...
};4.2 itimer 间隔定时器
源码位置: /Users/sphinx/github/linux/kernel/time/itimer.c
itimer 是传统的间隔定时器实现,与 POSIX timers 共享底层机制:
c
// itimer.c:29-45
static struct timespec64 itimer_get_remtime(struct hrtimer *timer)
{
ktime_t rem = __hrtimer_get_remaining(timer, true);
if (hrtimer_active(timer)) {
if (rem <= 0)
rem = NSEC_PER_USEC;
} else
rem = 0;
return ktime_to_timespec64(rem);
}ITIMER 类型:
c
// itimer.c:81-86
switch (which) {
case ITIMER_REAL: // 真实时间,发送 SIGALRM
case ITIMER_VIRTUAL: // 虚拟时间(用户 CPU 时间),发送 SIGVTALRM
case ITIMER_PROF: // 剖析时间(用户+系统 CPU),发送 SIGPROF
}do_setitimer() 设置定时器:
c
// itimer.c:225-269
static int do_setitimer(int which, struct itimerspec64 *value,
struct itimerspec64 *ovalue)
{
// ITIMER_REAL 使用 hrtimer 实现
case ITIMER_REAL:
timer = &tsk->signal->real_timer;
// 启动 hrtimer
hrtimer_start(timer, expires, HRTIMER_MODE_REL);
break;
// ITIMER_VIRTUAL/PROF 使用 CPU 定时器
}4.3 clock_* 系统调用
源码位置: /Users/sphinx/github/linux/kernel/time/posix-timers.c
clock_gettime():
c
// posix-timers.c:187-196
static int posix_get_realtime_timespec(clockid_t which_clock, struct timespec64 *tp)
{
ktime_get_real_ts64(tp);
return 0;
}
static ktime_t posix_get_realtime_ktime(clockid_t which_clock)
{
return ktime_get_real();
}clock_settime():
c
// posix-timers.c:198-202
static int posix_clock_realtime_set(const clockid_t which_clock,
const struct timespec64 *tp)
{
return do_sys_settimeofday64(tp, NULL);
}clock_getres():
c
// posix-timers.c:272-277
static int posix_get_hrtimer_res(clockid_t which_clock, struct timespec64 *tp)
{
tp->tv_sec = 0;
tp->tv_nsec = hrtimer_resolution; // 通常为 1ns
return 0;
}5. Timekeeping 时间追踪
5.1 struct tk_core 时间追踪核心
源码位置: /Users/sphinx/github/linux/kernel/time/timekeeping.c
tk_data 结构体:
c
// timekeeping.c:52-57
struct tk_data {
seqcount_raw_spinlock_t seq;
struct timekeeper timekeeper;
struct timekeeper shadow_timekeeper;
raw_spinlock_t lock;
} ____cacheline_aligned;
static struct tk_data timekeeper_data[TIMEKEEPERS_MAX];
// 核心时间追踪器
#define tk_core (timekeeper_data[TIMEKEEPER_CORE])5.2 struct timekeeper
源码位置: /Users/sphinx/github/linux/include/linux/timekeeper_internal.h:140-183
c
struct timekeeper {
/* Cacheline 0 (与 seqcount 一起): */
struct tk_read_base tkr_mono; // CLOCK_MONOTONIC 读取基准
/* Cacheline 1: */
u64 xtime_sec; // CLOCK_REALTIME 秒数
unsigned long ktime_sec; // CLOCK_MONOTONIC 秒数
struct timespec64 wall_to_monotonic; // 实时到单调的偏移
ktime_t offs_real; // 单调到实时的偏移
ktime_t offs_boot; // 单调到启动的偏移
union { ktime_t offs_tai; ktime_t offs_aux; };
u32 coarse_nsec; // 粗粒度纳秒
enum timekeeper_ids id; // 时间追踪器 ID
/* Cacheline 2: */
struct tk_read_base tkr_raw; // 原始时钟读取基准
u64 raw_sec; // 原始时钟秒数
/* Cacheline 3-4 (内部变量): */
unsigned int clock_was_set_seq;
u8 cs_was_changed_seq;
u8 clock_valid;
union { struct timespec64 monotonic_to_boot; struct timespec64 monotonic_to_aux; };
u64 cycle_interval; // 一个 NTP 周期的时钟周期数
u64 xtime_interval; // 一个 NTP 周期的纳秒数
s64 xtime_remainder; // 剩余纳秒
u64 raw_interval; // 原始周期
ktime_t next_leap_ktime; // 下一次闰秒时间
u64 ntp_tick; // NTP tick 长度
s64 ntp_error; // NTP 误差
u32 ntp_error_shift; // NTP 误差位移
u32 ntp_err_mult; // NTP 误差乘数
u32 skip_second_overflow;
s32 tai_offset; // UTC 到 TAI 的偏移
};tk_read_base - NMI 安全的快速读取结构:
c
// include/linux/timekeeper_internal.h:50-59
struct tk_read_base {
struct clocksource *clock; // 当前使用的时钟源
u64 mask; // 位掩码
u64 cycle_last; // 上次读取的周期值
u32 mult; // NTP 调整后的乘数
u32 shift; // 位移值
u64 xtime_nsec; // 移位后的纳秒偏移
ktime_t base; // 基准时间
u64 base_real; // 实时基准
};5.3 update_wall_time() 更新墙上时间
源码位置: /Users/sphinx/github/linux/kernel/time/timekeeping.c
timekeeping_forward_now() - 将时间推进到当前:
c
// timekeeping.c:765-785
static void timekeeping_forward_now(struct timekeeper *tk)
{
u64 cycle_now, delta;
cycle_now = tk_clock_read(&tk->tkr_mono);
delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last,
tk->tkr_mono.mask, tk->tkr_mono.clock->max_raw_delta);
tk->tkr_mono.cycle_last = cycle_now;
tk->tkr_raw.cycle_last = cycle_now;
// 更新 xtime_nsec
while (delta > 0) {
u64 max = tk->tkr_mono.clock->max_cycles;
u64 incr = delta < max ? delta : max;
tk->tkr_mono.xtime_nsec += incr * tk->tkr_mono.mult;
tk->tkr_raw.xtime_nsec += incr * tk->tkr_raw.mult;
tk_normalize_xtime(tk);
delta -= incr;
}
tk_update_coarse_nsecs(tk);
}tk_normalize_xtime() - 规范化 xtime:
c
// timekeeping.c:190-200
static inline void tk_normalize_xtime(struct timekeeper *tk)
{
while (tk->tkr_mono.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr_mono.shift)) {
tk->tkr_mono.xtime_nsec -= (u64)NSEC_PER_SEC << tk->tkr_mono.shift;
tk->xtime_sec++;
}
// 同样处理 raw
}快速时间获取函数:
c
// timekeeping.c:490-494
u64 ktime_get_mono_fast_ns(void)
{
return __ktime_get_fast_ns(&tk_fast_mono);
}
EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);
// timekeeping.c:502-505
u64 ktime_get_raw_fast_ns(void)
{
return __ktime_get_fast_ns(&tk_fast_raw);
}5.4 时钟源 (Clocksource)
源码位置: /Users/sphinx/github/linux/kernel/time/clocksource.c
时钟源是提供精确定时的时间源设备:
c
// include/linux/clocksource.h 中的结构体
struct clocksource {
u64 (*read)(struct clocksource *cs); // 读取函数
u64 mask; // 位掩码
u32 mult; // 乘数 (cycles to ns)
u32 shift; // 位移 (ns to cycles)
u64 max_idle_ns; // 最大空闲时间
u64 max_cycles; // 最大周期数
const char *name; // 名称
struct list_head list; // 链表
u64 cs_last; // 上次读取值
u64 raw_time; // 原始时间
// ...
};6. 时区处理
6.1 sys_tz 时区结构
源码位置: /Users/sphinx/github/linux/kernel/time/time.c
c
// time.c:50
struct timezone sys_tz;
EXPORT_SYMBOL(sys_tz);struct timezone 定义:
c
// include/linux/time.h
struct timezone {
int tz_minuteswest; // 相对于 UTC 西部的分钟数
int tz_dsttime; // 夏令时类型
};6.2 do_sys_timezone() 获取时区
源码位置: /Users/sphinx/github/linux/kernel/time/time.c
实际上,时区通过 gettimeofday 系统调用获取:
c
// time.c:140-156
SYSCALL_DEFINE2(gettimeofday, struct __kernel_old_timeval __user *, tv,
struct timezone __user *, tz)
{
if (likely(tv != NULL)) {
struct timespec64 ts;
ktime_get_real_ts64(&ts);
if (put_user(ts.tv_sec, &tv->tv_sec) ||
put_user(ts.tv_nsec / 1000, &tv->tv_usec))
return -EFAULT;
}
if (unlikely(tz != NULL)) {
if (copy_to_user(tz, &sys_tz, sizeof(sys_tz)))
return -EFAULT;
}
return 0;
}6.3 settimeofday 设置时间和时区
源码位置: /Users/sphinx/github/linux/kernel/time/time.c:169-197
c
int do_sys_settimeofday64(const struct timespec64 *tv, const struct timezone *tz)
{
static int firsttime = 1;
int error = 0;
if (tv && !timespec64_valid_settod(tv))
return -EINVAL;
error = security_settime64(tv, tz);
if (error)
return error;
if (tz) {
// 验证时区范围
if (tz->tz_minuteswest > 15*60 || tz->tz_minuteswest < -15*60)
return -EINVAL;
sys_tz = *tz; // 更新系统时区
update_vsyscall_tz(); // 更新 vsyscall
if (firsttime) {
firsttime = 0;
if (!tv)
timekeeping_warp_clock();
}
}
if (tv)
return do_settimeofday64(tv);
return 0;
}7. 架构图
7.1 时间子系统整体架构
+------------------------------------------------------------------+
| 用户空间 |
+------------------------------------------------------------------+
| clock_gettime() | timer_create() | gettimeofday() | alarm()|
+------------------------------------------------------------------+
|
v
+------------------------------------------------------------------+
| 系统调用接口 (syscalls) |
| sys_clock_gettime | sys_timer_create | sys_gettimeofday | etc |
+------------------------------------------------------------------+
|
v
+------------------------------------------------------------------+
| Posix Timers 层 |
| +------------------+ +------------------+ +------------------+ |
| | clock_realtime | | clock_monotonic | | clock_tai | |
| +------------------+ +------------------+ +------------------+ |
| | k_itimer (定时器) | | k_itimer (CPU) | | k_itimer (进程) | |
| +------------------+ +------------------+ +------------------+ |
+------------------------------------------------------------------+
|
v
+------------------------------------------------------------------+
| hrtimer 层 |
| +------------------------------------------------------------+ |
| | struct hrtimer_cpu_base (per-CPU) | |
| | +-------------------------------------------------------+| |
| | | clock_base[HRTIMER_BASE_MONOTONIC] -> 红黑树 || |
| | | clock_base[HRTIMER_BASE_REALTIME] -> 红黑树 || |
| | | clock_base[HRTIMER_BASE_BOOTTIME] -> 红黑树 || |
| | | clock_base[HRTIMER_BASE_TAI] -> 红黑树 || |
| | +-------------------------------------------------------+| |
| +------------------------------------------------------------+ |
+------------------------------------------------------------------+
|
v
+------------------------------------------------------------------+
| Timekeeping 层 |
| +------------------------------------------------------------+ |
| | struct timekeeper (核心时间追踪) | |
| | +------------------------------------------------------+ | |
| | | tkr_mono: CLOCK_MONOTONIC 读取基准 | | |
| | | tkr_raw: CLOCK_MONOTONIC_RAW 读取基准 | | |
| | | xtime_sec: 墙上时间(秒) | | |
| | | wall_to_monotonic: 实时到单调的偏移 | | |
| | +------------------------------------------------------+ | |
| +------------------------------------------------------------+ |
+------------------------------------------------------------------+
|
v
+------------------------------------------------------------------+
| Tick 设备层 |
| +------------------------------------------------------------+ |
| | struct tick_device (per-CPU) | |
| | +------------------------------------------------------+ | |
| | | evtdev: clock_event_device (硬件事件设备) | | |
| | | mode: TICKDEV_MODE_PERIODIC / TICKDEV_MODE_ONESHOT | | |
| | +------------------------------------------------------+ | |
| +------------------------------------------------------------+ |
| +------------------------------------------------------------+ |
| | struct tick_sched (per-CPU) | |
| | +------------------------------------------------------+ | |
| | | sched_timer: hrtimer (调度 tick) | | |
| | | flags: TS_FLAG_STOPPED, TS_FLAG_NOHZ, TS_FLAG_HIGHRES| | |
| | +------------------------------------------------------+ | |
| +------------------------------------------------------------+ |
+------------------------------------------------------------------+
|
v
+------------------------------------------------------------------+
| 硬件/时钟源层 |
| +------------------------------------------------------------+ |
| | clock_event_device (per-CPU) | |
| | +------------------------------------------------------+ | |
| | | Local APIC / Global Timer / HPET / etc | | |
| | +------------------------------------------------------+ | |
| +------------------------------------------------------------+ |
| +------------------------------------------------------------+ |
| | clocksource (全局) | |
| | +------------------------------------------------------+ | |
| | | TSC / jiffies / clocksource_msm / etc | | |
| | +------------------------------------------------------+ | |
| +------------------------------------------------------------+ |
+------------------------------------------------------------------+7.2 hrtimer 调度流程
定时器过期
|
v
+---------------------------+
| tick_handle_periodic() |
| 或 tick_nohz_handler() |
+---------------------------+
|
v
+---------------------------+
| hrtimer_interrupt() |
| (硬件中断处理) |
+---------------------------+
|
v
+---------------------------+
| __hrtimer_run_queues() |
+---------------------------+
|
+-------------+-------------+
| | |
v v v
+-----------+ +-----------+ +-----------+
| MONOTONIC | | REALTIME | | BOOTTIME |
| 红黑树 | | 红黑树 | | 红黑树 |
+-----------+ +-----------+ +-----------+
| | |
v v v
+-----------------------------------------+
| 对每个过期的 hrtimer: |
| timer->function(timer) |
| 返回 HRTIMER_RESTART 或 HRTIMER_NORESTART |
+-----------------------------------------+
|
v
+---------------------------+
| hrtimer_reprogram() |
| (如果需要,重编硬件) |
+---------------------------+7.3 NTP 调整流程
+------------------+
| second_overflow |
| (每秒调用一次) |
+------------------+
|
v
+------------------+
| ntp_update_ |
| frequency() |
+------------------+
|
v
+------------------+ +------------------+
| 调整 tick_length | --> | 更新 time_freq |
| (tick 长度调整) | | (频率偏移) |
+------------------+ +------------------+
|
v
+------------------+
| timekeeping_ |
| update_tai() |
+------------------+
|
v
+------------------+
| updateWallTime |
| (应用调整到 xtime)|
+------------------+附录: 关键数据结构关系图
jiffies_64 ─────────────────────────────────────> 基础时间单位
│
│ tick_next_period (ktime)
│
▼
tick_periodic() ────────────────────────────────> do_timer(1)
│ │
│ v
│ jiffies_64++
│
v
update_wall_time() ─────────────────────────────> struct timekeeper
│ │
│ tkr_mono (tk_read_base) │
│ ├── clock->read() ──────────────────────> clocksource
│ ├── cycle_last │
│ ├── mult, shift │
│ └── xtime_nsec │
│ │
│ xtime_sec │
│ wall_to_monotonic ─────────────────────────> CLOCK_MONOTONIC
│ │
│ offs_real ─────────────────────────────────> CLOCK_REALTIME
│ offs_boot ────────────────────────────────> CLOCK_BOOTTIME
│ offs_tai ─────────────────────────────────> CLOCK_TAI
│
v
struct tick_sched ───────────────────────────────> NO_HZ 控制
│
├── sched_timer (hrtimer)
│ │
│ v
│ tick_nohz_handler()
│
└── flags: TS_FLAG_STOPPED, TS_FLAG_NOHZ, TS_FLAG_HIGHRES
hrtimer_cpu_base (per-CPU) ────────────────────> 高精度定时器
│
├── lock
├── clock_base[8]
│ │
│ ├── MONOTONIC ────> 红黑树 (active timers)
│ ├── REALTIME
│ ├── BOOTTIME
│ ├── TAI
│ └── _SOFT 变体
│
└── expires_next ────────────────────────────> 下一个过期时间参考源码路径
| 组件 | 路径 |
|---|---|
| 核心时间追踪 | /Users/sphinx/github/linux/kernel/time/timekeeping.c |
| 时间追踪头文件 | /Users/sphinx/github/linux/include/linux/timekeeper_internal.h |
| hrtimer 实现 | /Users/sphinx/github/linux/kernel/time/hrtimer.c |
| hrtimer 类型 | /Users/sphinx/github/linux/include/linux/hrtimer_defs.h |
| hrtimer 类型 | /Users/sphinx/github/linux/include/linux/hrtimer_types.h |
| Tick 调度 | /Users/sphinx/github/linux/kernel/time/tick-sched.c |
| Tick 调度头文件 | /Users/sphinx/github/linux/kernel/time/tick-sched.h |
| Tick 通用 | /Users/sphinx/github/linux/kernel/time/tick-common.c |
| Tick 内部 | /Users/sphinx/github/linux/kernel/time/tick-internal.h |
| POSIX 定时器 | /Users/sphinx/github/linux/kernel/time/posix-timers.c |
| POSIX 定时器头 | /Users/sphinx/github/linux/kernel/time/posix-timers.h |
| itimer | /Users/sphinx/github/linux/kernel/time/itimer.c |
| 系统时间调用 | /Users/sphinx/github/linux/kernel/time/time.c |
| NTP | /Users/sphinx/github/linux/kernel/time/ntp.c |
| NTP 内部 | /Users/sphinx/github/linux/kernel/time/ntp_internal.h |
| 时钟源 | /Users/sphinx/github/linux/kernel/time/clocksource.c |
| jiffies | /Users/sphinx/github/linux/include/linux/jiffies.h |
| 时间头文件 | /Users/sphinx/github/linux/include/linux/time.h |
文档生成日期: 2026-04-26内核版本: Linux kernel master branch