Page "Interrupt latency" Paragraph 3

Maximum interrupt latency is largely determined by the methods an OS uses for interrupt handling.

For example, most processors allow programs to disable interrupts, putting off the execution of interrupt handlers, in order to protect critical sections of code.

During the execution of such a critical section, all interrupt handlers that cannot execute safely within a critical section are blocked ( they save the minimum amount of information required to restart the interrupt handler after all critical sections have exited ).

So the interrupt latency for a blocked interrupt is extended to the end of the critical section, plus any interrupts with equal and higher priority that arrived while the block was in place.