[linux] 量測特定 process CPU ussage

Preparation

To calculate CPU usage for a specific process you'll need the following:

1. /proc/uptime
   • #1 uptime of the system (seconds)
2. /proc/[PID]/stat
   • #14 utime - CPU time spent in user code, measured in clock ticks
   • #15 stime - CPU time spent in kernel code, measured in clock ticks
   • #16 cutime - Waited-for children's CPU time spent in user code (in clock ticks)
   • #17 cstime - Waited-for children's CPU time spent in kernel code (in clock ticks)
   • #22 starttime - Time when the process started, measured in clock ticks
3. Hertz (number of clock ticks per second) of your system.
• In most cases, getconf CLK_TCK can be used to return the number of clock ticks.
• The sysconf(_SC_CLK_TCK) C function call may also be used to return the hertz value.

Calculation

First we determine the total time spent for the process:

total_time = utime + stime

We also have to decide whether we want to include the time from children processes. If we do, then we add those values to total_time:

total_time = total_time + cutime + cstime

Next we get the total elapsed time in seconds since the process started:

seconds = uptime - (starttime / Hertz)

Finally we calculate the CPU usage percentage:

cpu_usage = 100 * ((total_time / Hertz) / seconds)
















此例來說 bash 的 CPU usage 為
1.160880760010654




ref:
http://stackoverflow.com/questions/16726779/how-do-i-get-the-total-cpu-usage-of-an-application-from-proc-pid-stat