Scalable interrupts

A method comprising:

• receiving, by a first interrupt controller on a first integrated circuit (IC) from a second interrupt controller on a second IC that is co-packaged with the first IC, an interrupt from a particular interrupt source on the second IC;
• attempting, by the first interrupt controller, to deliver the interrupt to a first cluster interrupt controller on the first IC;
• and
• in response to receiving a non-acknowledge (NACK) response from the first cluster interrupt controller, attempting, by the first interrupt controller, to deliver the interrupt to a second cluster interrupt controller.

An apparatus comprising:

• a first integrated circuit (IC) including:
• a first plurality of cluster interrupt controllers, wherein a respective cluster interrupt controller of the first plurality of cluster interrupt controllers is associated with a first plurality of processors;
• and
• a first interrupt controller coupled to the first plurality of cluster interrupt controllers,
• a second IC, co-packaged with the first IC, and including a second interrupt controller configured to:
• in response to an interrupt from a particular interrupt source on the second IC, communicate the interrupt to the first interrupt controller;
• and
• wherein the first interrupt controller is configured to attempt to deliver the interrupt to the first plurality of cluster interrupt controllers.