::interrupts output in mdb
Years ago, 8259 was extensively adopted by single CPU PC and the IRQ and vector number was clear to OS. Now, we have APICs in Intel multiple processor systems. It is quite confusing how the IRQ numbers are assigned to OS. Here is the output of "::interrupts" output in mdb.
::interrupts
IRQ Vect IPL Bus Trg Type CPU Share APIC/INT# ISR(s)
4 0xb0 12 ISA Edg Fixed 3 1 0x0/0x4 asyintr
9 0x81 9 PCI Lvl Fixed 1 1 0x0/0x9 acpi_wrapper_isr
14 0x41 5 ISA Edg Fixed 7 1 0x0/0xe ata_intr
20 0x20 1 PCI Lvl Fixed 4 1 0x0/0x14 ehci_intr
21 0x21 1 PCI Lvl Fixed 5 1 0x0/0x15 ohci_intr
48 0x60 6 PCI Lvl Fixed 6 1 0x1/0x0 e1000g_intr <--- first pin of second IOAPIC
49 0x61 6 PCI Lvl Fixed 6 1 0x1/0x1 e1000g_intr
50 0x62 6 PCI Lvl Fixed 6 1 0x1/0x2 e1000g_intr
51 0x63 6 PCI Lvl Fixed 6 1 0x1/0x3 e1000g_intr
63 0x40 5 PCI Edg MSI 2 1 - mpt_intr
....
We have IRQ numbers from 4 to 63 here. But how they are assigned? Before we understand it, we should firstly look into IOAPIC. Usually, Intel IOAPIC have 24 interrupt pins. The interrupt pins of PCI devices will be routed to these pins hierarchically. And the routing paths are almost harden into the motherboard, though PCI devices may have two selectable pins for some flexibility. The first interrupt input pin of first IOAPIC will be assigned IRQ 0, while the forth pin will be assigned IRQ4 in this example, and so on. If the system have two more IOAPICs, the first IRQ number will start from the multiples of 24, 48 in the example above. Now, we know the IRQ numbers are from the input pins of IOAPICs. IRQ numbers are not necessary bundled with the vector numbers in APICs, because the vector numbers can be re-programmable. To some degrees, IRQ numbers are the hardware level layout of interrupt lines and vector numbers are in software level and more meaningful to OS.
As to the MSI interrupt, IOAPIC is no longer required to deliver the interrupt. For, MSI message can target the host bridge address as other IO transactions. So such format will be printed for MSI devices:
24 0x61 6 PCIe Edg MSI 0 1 - e1000g`e1000g_intr_pciexpress
^
|-------- no ioapic listed
