Past exam of the mathematics course of the University of Cambridge / 2007 / ia / Paper 5 / 2 / c / Solution

First, suppressing kernel preemption simplifies protection of shared kernel data on a uniprocessor: another ordinary kernel execution cannot be scheduled in the middle of a short update which temporarily breaks an invariant. Fewer paths require preemption-specific locking and reentrancy handling, making the operating-system kernel easier to implement correctly.

Second, it avoids involuntary kernel context switches and their scheduler, register-save and cache-disruption costs, and can make the execution of short kernel operations more predictable. The tradeoff is greater scheduling latency if a kernel operation runs too long. Simpler synchronization and lower switching overhead are the two reasons. Non-preemptive kernel code can still receive interrupts or block voluntarily, and multiprocessor execution still requires synchronization; non-preemption is not a substitute for all locking.