Re:What is "preemtive" for ? (Score 2, Informative)

When a process starts a kernel call, it will not be context-swapped until it finishes executing the call. That is, the kernel will not change the executing process as long as it is kernel code that is in execution. There are many reasons for this. The patch makes it OK to to context swapping in the middle of kernel execution, helping all processes get an equal amount of CPU time.