CPU utilization

During the home screen, you can press 'c' to get CPU utilization chart:

CPU utilization metrics are read from /proc/stat file:

$ cat /proc/stat
cpu  69329351 1546 2133140 1777137470 701736 266457 200025 0 0 0
cpu0 1381282 4 75089 16197830 12424 6417 107331 0 0 0
cpu1 1368760 13 67306 16310343 9995 6896 19434 0 0 0
......

After Linux 2.6, every CPU row has 10 items: user, nice, system, idle, iowait, irq, softirq, steal, guest and guest_nice (For the meaning of every metric, please refer /proc document), and the value is measured in units of USER_HZ. The first row is the total statistics of the system, and followings are the information of every CPU. In the screen, User% consists of user and nice, Sys% is composed of system, irq and softirq, etc. Please refer nomon code:

        ......
        cpu_user = RAW(user) + RAW(nice);
        cpu_sys =
        RAW(sys) + RAW(irq) + RAW(softirq); 
        /* + RAW(guest) + RAW(guest_nice); these are in addition to the 100% */
        cpu_wait = RAW(wait);
        cpu_idle = RAW(idle);
        cpu_steal = RAW(steal);

        cpu_sum =
        cpu_idle + cpu_user + cpu_sys + cpu_wait +
        cpu_steal; 
        ......

BTW, press 'l' can display CPU utilization in long-term format, which can help you get the overview of system better in real time: