Linux APIC interrupts priority

Question

What does process assigned to particular interrupt do? For example part of my FF processes on rt kernel is:

98  FF     95 135   - [irq/23-ehci_hcd]
96  FF     85 125   - [irq/16-uhci_hcd]
94  FF     85 125   - [irq/20-ehci_hcd]
8  FF      1  41   - [rcu_preempt]
56  FF     99 139   - [irq/8-rtc0]

is it an interrupt handlers? According to this thread, How to give highest priority to ethernet interrupt in linux linux kernel doesn't prioritize APIC interrupts. But what if two interrupt occurs simultaneously? How processor knows what handler to execute, if on APIC level all interrupts are same priority?

In thread link above one guy propose to write kernel module get the ability set up APIC interrupt priorities. Will it be useful tweak for rt-audio processing, or just setting timer and audiocard interrupts to higher priority will do the same work?

Answer 1

Interrupt priorities matter only when two differents interrupts are pending, and the CPU has to decide which one to handle.

With interrupt handlers being very short, and with multiple cores available, it is unlikely that priorities will have any noticeable effect.

(And the RTC is not used for anything audio-related.)