不看代码，先操作一下
docs/kernel/sysfs-irq.md
此外 irqstat 工具来分析 /proc/interrupts
qemu hmp
info lapic
(qemu) info lapic
dumping local APIC state for CPU 0
LVT0 0x00010700 active-hi edge masked ExtINT (vec 0)
LVT1 0x00000400 active-hi edge NMI
LVTPC 0x00010000 active-hi edge masked Fixed (vec 0)
LVTERR 0x000000fe active-hi edge Fixed (vec 254)
LVTTHMR 0x00010000 active-hi edge masked Fixed (vec 0)
LVTT 0x000400ec active-hi edge tsc-deadline Fixed (vec 236)
Timer DCR=0x0 (divide by 2) initial_count = 0 current_count = 0
SPIV 0x000001ff APIC enabled, focus=off, spurious vec 255
ICR 0x000000fd physical edge de-assert no-shorthand
ICR2 0x01000000 cpu 16777216 (X2APIC ID)
ESR 0x00000000
ISR (none)
IRR (none)
APR 0x00 TPR 0x10 DFR 0x0f LDR 0x00 PPR 0x10
aarch64 有类似的机制吗，例如 info gic 之类的
info pic
(qemu) info pic
ioapic0: ver=0x11 id=0x00 sel=0x22 (redir[9])
pin 0 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 1 0x0000000000000021 dest=0 vec=33 active-hi edge fixed physical
pin 2 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 3 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 4 0x0100000000000021 dest=1 vec=33 active-hi edge fixed physical
pin 5 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 6 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 7 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 8 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 9 0x0100000000008025 dest=1 vec=37 active-hi level fixed physical
pin 10 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 11 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 12 0x0100000000000020 dest=1 vec=32 active-hi edge fixed physical
pin 13 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 14 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 15 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 16 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 17 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 18 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 19 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 20 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 21 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 22 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
pin 23 0x0000000000010000 dest=0 vec=0 active-hi edge masked fixed physical
IRR (none)
Remote IRR (none)
pic0: irr=13 imr=ff isr=00 hprio=0 irq_base=30 rr_sel=0 elcr=00 fnm=0
pic1: irr=12 imr=ff isr=00 hprio=0 irq_base=38 rr_sel=0 elcr=0c fnm=0
既然所有的中断都是在内核，那么就不该有人来调用 kvm_set_irq ，让系统是安静的时候
在 console 中执行 dmesg ，然后
sudo perf top -e kvm:kvm_set_irq
Samples: 672K of event 'kvm:kvm_set_irq', 1 Hz, Event count (approx.): 38414 lost: 0/0 drop: 0/0
Overhead Trace output
82.65% gsi 0 level 0 source 0
9.01% gsi 4 level 0 source 0
8.34% gsi 4 level 1 source 0
以上内容说明:
- Vector domain 中 hwirq 的内容和 kvm:kvm_set_irq 中观测到的 gsi 是一个东西.
这里推测 gsi 就是 ioapic 或者 pic 的引脚。
@[
kvm_pic_set_irq+313
kvm_pic_set_irq+313
kvm_set_irq+192
kvm_vm_ioctl_irq_line+39
kvm_vm_ioctl+719
__x64_sys_ioctl+148
do_syscall_64+183
entry_SYSCALL_64_after_hwframe+119
]: 45408
- kvm_check_and_inject_events
- kvm_cpu_has_injectable_intr
- kvm_cpu_get_interrupt
在 kvm_cpu_get_interrupt 中，这里的判断都是需要 检查两次，是 pic 和 lpaic 都需要考虑的。
类似的:
int kvm_apic_accept_pic_intr(struct kvm_vcpu *vcpu)
{
u32 lvt0 = kvm_lapic_get_reg(vcpu->arch.apic, APIC_LVT0);
if (!kvm_apic_hw_enabled(vcpu->arch.apic))
return 1;
if ((lvt0 & APIC_LVT_MASKED) == 0 &&
GET_APIC_DELIVERY_MODE(lvt0) == APIC_MODE_EXTINT)
return 1;
return 0;
}
物理机中设置的位置: disconnect_bsp_APIC
对应 sdm 11.1 中的: Locally connected I/O devices — These interrupts originate as an edge or level asserted by an I/O device that is connected directly to the processor’s local interrupt pins (LINT0 and LINT1). The I/O devices may also be connected to an 8259-type interrupt controller that is in turn connected to the processor through one of the local interrupt pins.
8259-type 现在也可以作为一个 APIC 的来源。
setup_local_APIC 中看，默认是打开的
if (!cpu && (pic_mode || !value || ioapic_is_disabled)) {
value = APIC_DM_EXTINT;
apic_printk(APIC_VERBOSE, "enabled ExtINT on CPU#%d\n", cpu);
} else {
value = APIC_DM_EXTINT | APIC_LVT_MASKED;
apic_printk(APIC_VERBOSE, "masked ExtINT on CPU#%d\n", cpu);
}
总结: PIC 在 kvm 中模拟的场景，首先模拟，然后通过 apic 的 ExtINT 注入进去。
ioapic 还是可以工作的，为什么 irq routing 将 pic 忽视了
@[
vmx_deliver_interrupt+320
__apic_accept_irq+244
kvm_irq_delivery_to_apic_fast+320
kvm_irq_delivery_to_apic+103
ioapic_service+311
ioapic_set_irq+308
kvm_ioapic_set_irq+101
kvm_set_irq+192
kvm_vm_ioctl_irq_line+39
kvm_vm_ioctl+719
__x64_sys_ioctl+148
do_syscall_64+183
entry_SYSCALL_64_after_hwframe+119
]: 3222
因为 pic 的注入需要 apicv 没有打开，但是 ioapic 是可以忽视这个。
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