linux内核timer_interrupt()源码

以下是Linux内核4.19版本中timer_interrupt()函数的源码实现：

asmlinkage __visible void __weak timer_interrupt(struct pt_regs *regs)
{
    struct cpu_data *cpu = get_cpu_ptr(smp_processor_id());
    struct clock_event_device *evt = cpu->evtdev;
    unsigned long next_jiffies = jiffies + 1;

    if (unlikely(time_after_eq(next_jiffies, cpu->last_jiffies + TICK_NSEC))) {
        /*
         * Some of this is really subtle. If we're in the middle of a tick
         * already, we don't want to update the tick count - that could
         * confuse the heck out of anyone trying to do timing. So make sure
         * we don't update the tick until after the tick period has
         * expired.
         */
        if (time_after(next_jiffies, cpu->last_jiffies + TICK_NSEC)) {
            int clock_was_set = 0;

            while (time_after_eq(next_jiffies, cpu->last_jiffies + TICK_NSEC)) {
                cpu->last_jiffies += TICK_NSEC;
                update_wall_time();
                clock_was_set = tick_nohz_update_jiffies(&cpu->tick_dep_mask);
                if (cpu_is_offline(smp_processor_id()))
                    return;
            }
            if (clock_was_set)
                tick_program_event(evt, cpu->next_timer_interrupt);
        }

        /*
         * We must make sure that the jiffies update is visible
         * before we test time_after_eq().
         */
        smp_wmb();
        if (time_after_eq(next_jiffies, READ_ONCE(jiffies)))
            __generic_touch_nmi_watchdog();

        if (unlikely(in_nmi()))
            return;

        /*
         * If we missed any timer interrupts, correct this now
         * by advancing the local timer and updating wall time
         * again.
         */
        while (time_after_eq(next_jiffies, READ_ONCE(jiffies))) {
            cpu->last_jiffies += TICK_NSEC;
            update_wall_time();
            tick_nohz_idle_enter();
        }
    }

    evt->event_handler(evt);
}

timer_interrupt()函数是中断处理程序，用于处理定时器中断。该函数首先获取当前CPU的事件设备指针，然后计算出下一次中断的时间，如果下一次中断的时间已经到了，则更新 jiffies 值并调用事件处理函数。如果下一次中断的时间还没有到，则继续等待下一次中断。函数中还包含了一些调用其他函数的代码块，用于更新时间值、设置时钟事件等。