ps 和 top 的 CPU 占用率区别
一个常见现象：关掉包含 flash 的网页后，ps 显示它的 CPU 占用率仍然居高不下，而同时 top 显示的占用是 0。两者差异不是误差，而是统计口径不同。
man ps 的说明：
CPU usage is currently expressed as the percentage of time spent running during the entire lifetime of a process. This is not ideal, and it does not conform to the standards that ps otherwise conforms to. CPU usage is unlikely to add up to exactly 100%.
top 的说明：
%CPU — CPU usage: The task’s share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time. In a true SMP environment, if ‘Irix mode’ is Off, top will operate in ‘Solaris mode’ where a task’s cpu usage will be divided by the total number of CPUs.
由此可知：
- ps 从进程开始就统计，是整个生命周期的平均占用率。
- top 从上次刷新开始统计（一般几秒一刷），可视为即时占用率。
桌面系统通常更关注即时值，所以 top 的 CPU 占用率更符合需要。此外 top 默认 CPU 占用率之和不是 100% 而是「核数 × 100%」，因此单个进程占用超过 100% 是正常的。