你能解释一下"用户CPU时间"和"系统CPU时间"吗？ 我读了很多，但我听不清楚。

不同之处在于时间是花在用户空间还是内核空间上。 用户CPU时间是运行程序代码(或库中的代码)的处理器所花费的时间; 系统CPU时间是代表程序在操作系统内核中运行代码所花费的时间。

术语"用户CPU时间"起初可能有点误导。 需要明确的是，总时间(实际CPU时间)是CPU为程序执行某些操作所花费的时间量与CPU为代表程序执行内核系统调用所花费的时间量的组合。 当程序循环遍历数组时，它会累积用户CPU时间。 相反，当程序执行系统调用(如exec或fork)时，它会累积系统CPU时间。

User CPU Time: Amount of time the processor worked on the specific program.

System CPU Time: Amount of time the processor worked on operating system's functions connected to that specific program.

基于维基百科：

• User time is the amount of time the CPU was busy executing code in user space.
• System time is the amount of time the CPU was busy executing code in kernel space. If this value is reported for a thread or
  process, then it represents the amount of time the kernel was doing
  work on behalf of the executing context, for example, after a thread
  issued a system call.