| 6.3 Updating the Time and Date | |||||||||
| //kernel/timer.c | |||||||||
| /* | |||||||||
| * Called by the timer interrupt. xtime_lock must already be taken | |||||||||
| * by the timer IRQ! | |||||||||
| */ | |||||||||
| static inline void update_times(void) | |||||||||
| { | |||||||||
| unsigned long ticks; | |||||||||
| ticks = jiffies - wall_jiffies; | |||||||||
| if (ticks) { | |||||||||
| wall_jiffies += ticks; | |||||||||
| update_wall_time(ticks); | |||||||||
| } | |||||||||
| calc_load(ticks); | |||||||||
| } | |||||||||
| /* | |||||||||
| * Using a loop looks inefficient, but "ticks" is | |||||||||
| * usually just one (we shouldn't be losing ticks, | |||||||||
| * we're doing this this way mainly for interrupt | |||||||||
| * latency reasons, not because we think we'll | |||||||||
| * have lots of lost timer ticks | |||||||||
| */ | |||||||||
| static void update_wall_time(unsigned long ticks) | |||||||||
| { | |||||||||
| do { | |||||||||
| ticks--; | |||||||||
| update_wall_time_one_tick(); | |||||||||
| if (xtime.tv_nsec >= 1000000000) { | |||||||||
| xtime.tv_nsec -= 1000000000; | |||||||||
| xtime.tv_sec++; | |||||||||
| second_overflow(); | |||||||||
| } | |||||||||
| } while (ticks); | |||||||||
| } | |||||||||
| /* | |||||||||
| * calc_load - given tick count, update the avenrun load estimates. | |||||||||
| * This is called while holding a write_lock on xtime_lock. | |||||||||
| */ | |||||||||
| static inline void calc_load(unsigned long ticks) | |||||||||
| { | |||||||||
| unsigned long active_tasks; /* fixed-point */ | |||||||||
| static int count = LOAD_FREQ; | |||||||||
| count -= ticks; | |||||||||
| if (count < 0) { | |||||||||
| count += LOAD_FREQ; | |||||||||
| active_tasks = count_active_tasks(); | |||||||||
| CALC_LOAD(avenrun[0], EXP_1, active_tasks); | |||||||||
| CALC_LOAD(avenrun[1], EXP_5, active_tasks); | |||||||||
| CALC_LOAD(avenrun[2], EXP_15, active_tasks); | |||||||||
| } | |||||||||
| } | |||||||||
| 6.4 Updating System Statistics | |||||||||
| The kernel, among the other time-related duties, must periodically collect various data used for: | |||||||||
| · Checking the CPU resource limit of the running processes | |||||||||
| · Updating statistics about the local CPU workload | |||||||||
| · Computing the average system load | |||||||||
| · Profiling the kernel code | |||||||||
| · Updating Local CPU Statistics | |||||||||
| /* | |||||||||
| * Called from the timer interrupt handler to charge one tick to the current | |||||||||
| * process. user_tick is 1 if the tick is user time, 0 for system. | |||||||||
| */ | |||||||||
| void update_process_times(int user_tick) | |||||||||
| { | |||||||||
| struct task_struct *p = current; | |||||||||
| int cpu = smp_processor_id(); | |||||||||
| /* Note: this timer irq context must be accounted for as well. */ | |||||||||
| if (user_tick) | |||||||||
| account_user_time(p, jiffies_to_cputime(1)); | |||||||||
| else | |||||||||
| account_system_time(p, HARDIRQ_OFFSET, jiffies_to_cputime(1)); | |||||||||
| run_local_timers(); | |||||||||
| if (rcu_pending(cpu)) | |||||||||
| rcu_check_callbacks(cpu, user_tick); | |||||||||
| scheduler_tick(); | |||||||||
| } | |||||||||
| This function performs the following steps: | |||||||||
| 1. Checks how long the current process has been running. | |||||||||
| in User Mode or in Kernel Mode when the timer interrupt occurred, | |||||||||
| invokes either account_user_time( ) or account_system_time( ). | |||||||||
| 2. Invokes raise_softirq( ) to activate the TIMER_SOFTIRQ tasklet on the local CPU | |||||||||
| 3. If some old version of an RCU-protected data structure has to be reclaimed, | |||||||||
| checks whether the local CPU has gone through a quiescent state and invokes | |||||||||
| tasklet_schedule( ) to activate the rcu_tasklet tasklet of the local CPU . | |||||||||
| 4. Invokes the scheduler_tick( ) function, which decreases the time slice counter of | |||||||||
| the current process, and checks whether its quantum is exhausted. | |||||||||
| · Keeping Track of System Load | |||||||||
| At every tick, update_times( ) invokes the calc_load( ) function, | |||||||||
| which counts the number of processes in the TASK_RUNNING or TASK_UNINTERRUPTIBLE | |||||||||
| state and uses this number to update the average system load | |||||||||
| · Profiling the Kernel Code | |||||||||
| void profile_tick(int type, struct pt_regs *regs) | |||||||||
| { | |||||||||
| if (type == CPU_PROFILING && timer_hook) | |||||||||
| timer_hook(regs); | |||||||||
| if (!user_mode(regs) && cpu_isset(smp_processor_id(), prof_cpu_mask)) | |||||||||
| profile_hit(type, (void *)profile_pc(regs)); | |||||||||
| } | |||||||||
| The profile_tick( ) function collects the data for the code profiler. | |||||||||
| It is invoked either by the do_timer_interrupt( ) function in uniprocessor systems | |||||||||
| or by the smp_local_timer_interrupt( ) function in multiprocessor systems | |||||||||
| · Checking the NMI Watchdogs | |||||||||
| static void default_do_nmi(struct pt_regs * regs) | |||||||||
| { | |||||||||
| unsigned char reason = 0; | |||||||||
| /* Only the BSP gets external NMIs from the system. */ | |||||||||
| if (!smp_processor_id()) | |||||||||
| reason = get_nmi_reason(); | |||||||||
| if (!(reason & 0xc0)) { | |||||||||
| if (notify_die(DIE_NMI_IPI, "nmi_ipi", regs, reason, 0, SIGINT) | |||||||||
| == NOTIFY_STOP) | |||||||||
| return; | |||||||||
| #ifdef CONFIG_X86_LOCAL_APIC | |||||||||
| /* | |||||||||
| * Ok, so this is none of the documented NMI sources, | |||||||||
| * so it must be the NMI watchdog. | |||||||||
| */ | |||||||||
| if (nmi_watchdog) { | |||||||||
| nmi_watchdog_tick(regs); | |||||||||
| return; | |||||||||
| } | |||||||||
| #endif | |||||||||
| unknown_nmi_error(reason, regs); | |||||||||
| return; | |||||||||
| } | |||||||||
| if (notify_die(DIE_NMI, "nmi", regs, reason, 0, SIGINT) == NOTIFY_STOP) | |||||||||
| return; | |||||||||
| if (reason & 0x80) | |||||||||
| mem_parity_error(reason, regs); | |||||||||
| if (reason & 0x40) | |||||||||
| io_check_error(reason, regs); | |||||||||
| /* | |||||||||
| * Reassert NMI in case it became active meanwhile | |||||||||
| * as it's edge-triggered. | |||||||||
| */ | |||||||||
| reassert_nmi(); | |||||||||
| } | |||||||||
Understanding the linux kernel-ch6-Timing Measurements
最新推荐文章于 2022-02-07 12:46:24 发布
本文详细介绍了Linux内核中时间更新机制的实现，包括时间与日期的更新、系统统计信息的更新等核心过程。此外，还涉及了如何跟踪系统负载、内核代码剖析以及非屏蔽中断(NMI)看门狗的检查等内容。
扫一扫
1492
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
