Chapter 7. Bottom Halves and Deferring Work
The previous chapter looked at interrupt handlers as the kernel mechanism for dealing with interrupts. Interrupt handlers are a useful—indeed, required—part of any operating system kernel. Because of various limitations, however, interrupt handlers can form only the first half of the interrupt processing solution. The limitations include the following:
Interrupt handlers run asynchronously and thus interrupt other potentially important code, including other interrupt handlers. Therefore, to avoid stalling the interrupted code for too long, interrupt handlers need to run as quickly as possible.
Interrupt handlers run with the current interrupt level disabled at best (if
SA_INTERRUPTis unset), and at worst ...