When is cli() needed?
• (ADB) cli() is a kernel wide function that disables maskable interrupts, whereas sti() is the equivalent function that enables maskable interrupts. Some routines must be run with interrupts disabled, because some peripherals need a guaranteed access sequence, or because the routine is not reentrant and could be reentered from an interrupt, etc. You should never use cli() in a user space program/daemon. • (REW) The use of cli() is no longer encouraged. On a single processor, this simply clears an internal CPU flag, which is ANDed with the Maskable Interrupt Request pin. On SMP systems it is quite troublesome to keep ALL processors from servicing interrupts if one processor wants to do something uninterrupted. Currently we try to do locking on a much finer scale. For example, you should put a spinlock on the record that describes THIS INSTANCE of the device that needs the handling without accesses to other registers (e.g. from the interrupt routine). Besides preventing the overhead of
