How are interrupts handled by dual processor machines?

Question

I have an idea of how interrupts are handled by a dual core CPU. I was wondering about how interrupt handling is implemented on a board with more than one physical processor.

Is any of the interrupt responsibility determined by the physical board's configuration? Each processor must be able to handle some types of interrupts, like disk I/O. Unless there is some circuitry to manage and dispatch interrupts to the appropriate processor? My guess is that the scheme must be processor neutral, so that any processor and core can run the interrupt handler.

If a core is waiting on a disk read, will that core be the one to run the interrupt handler when the disk is ready?

Answer 1

On x86 systems each CPU gets its own local APIC (Advanced Programmable Interrupt Controller) which are also wired to each other and to an I/O APIC that handles routing device interrupts to the local APICs.

The OS can program the APICs to determine which interrupts get routed to which CPUs (or to let the APICs make that decision).

I imagine that a multi-core CPU would have a local APIC for each core, but I'm honestly not certain about that.

See these links for more details:

• http://osdev.berlios.de/pic.html
• http://www.microsoft.com/whdc/archive/io-apic.mspx
• http://en.wikipedia.org/wiki/Intel_APIC_Architecture

Answer 2

What you're interested in is SMP Processor Affinity. Here is an excellent article about how it is handled in Linux. The Advanced Programmable Interrupt Controller (APIC) is how you manage this in a modern system. Basically, the default would be to all go to processor 0 unless you had an OS that utilized this interface to set things up properly. Also, you don't necessarily want the core that issued a command to wait on a particular interrupt. You want the less loaded cores to receive it.

Answer 3

I already asked this question a while back. Maybe it can offer you some insight :)

how do interrupts in multicore/multicpu machines work