arch/x86/kvm/i8254.c

ps -elf | grep kvm

1 I root     2488068       2  0  60 -20 -     0 -      12:10 ?        00:00:00 [kvm]
1 S root     2488069       2  0  80   0 -     0 -      12:10 ?        00:00:00 [kvm-nx-lpage-recovery-2488065]
1 S root     2488079       2  0  80   0 -     0 -      12:10 ?        00:00:00 [kvm-pit/2488065]

但是使用 pit_do_work ，开机一共就使用几次而已:

sudo bpftrace -e "kprobe:pit_do_work { print("hit kprobe:pit_do_work") }"

感觉没啥用途，只是为了模拟一个绝对 legacy 的设备而已。

但是，qemu 中也是有 pit 的啊!

timer 中断

/*
 * Default timer interrupt handler for PIT/HPET
 */
static irqreturn_t timer_interrupt(int irq, void *dev_id)
{
    global_clock_event->event_handler(global_clock_event);
    return IRQ_HANDLED;
}

static void __init setup_default_timer_irq(void)
{
    unsigned long flags = IRQF_NOBALANCING | IRQF_IRQPOLL | IRQF_TIMER;

    /*
     * Unconditionally register the legacy timer interrupt; even
     * without legacy PIC/PIT we need this for the HPET0 in legacy
     * replacement mode.
     */
    if (request_irq(0, timer_interrupt, flags, "timer", NULL))
        pr_info("Failed to register legacy timer interrupt\n");
}

就对应的，这里把名称 timer 换成了 gg

🧀  cat /proc/interrupts
           CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       CPU6       CPU7
  0:         34          0          0          0          0          0          0          0  IO-APIC   2-edge      gg

实际上就是开机的时候有用的，之后不会触发了

现在看，tsc 就是事实，为什么这里还写了这么多废话?

• PSA: If your clocksource is HPET rather than TSC you may see severely crippled performance in games (DX11 especially)
• Misconceptions about timers (HPET, TSC, PMT…)
• the industry shift back toward favouring TSC. - https://www.anandtech.com/show/12678/a-timely-discovery-examining-amd-2nd-gen-ryzen-results

pit 会导致 nmi 中断注入

https://unix.stackexchange.com/questions/216925/nmi-received-for-unknown-reason-20-do-you-have-a-strange-power-saving-mode-ena

这个让现在内核无需检查: commit c8c4076723da (“x86/timer: Skip PIT initialization on modern chipsets”)

这里真的让人感觉乱七八糟的

看看 acpi_pm ，的确是一个时钟源的

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