In fact, in Linux, we can generalize that each processor is doing exactly one of three things at any given moment:a) In user-space, executing user code in a processb) In kernel-space, in process context, executing on behalf of a specific processc) In kernel-space, in interrupt context, not associated with a process, handling aninterrupt在Linux中，任何时候，CPU都在做下面三件事中的一件：a）运行进程的用户空间代码；b）运行进程的内核空间代码；c）处理中断（也是工作在内核空间，但不与任何进程关联）。