Docker Container CPU Usage

Question

I am using the docker remote API to retrieve stats of my running containers. For CPU usage I get for example this:

"cpu_stats": {
    "cpu_usage": {
      "total_usage": 13039191340,
      "percpu_usage": [
        13039191340
      ],
      "usage_in_kernelmode": 420000000,
      "usage_in_usermode": 10480000000
    },
    "system_cpu_usage": 8.8930204e+14,
    "throttling_data": {
      "periods": 0,
      "throttled_periods": 0,
      "throttled_time": 0
    }
  }

How can I calculate the CPU usage in percent? When I divide "usage_in_kernelmode" with "total_usage" I get a similar result as the docker stats command, but is this the right way to do it?

Thank you :)

Answer 1

Ultimately, it comes down to what CPU usage you want to measure.

The usage states are in cycles. User cycles are those spent in executing applications, including system applications (like daemons) executing in user space. Kernel cycles are those spent in executing fundamental OS or driver functions. Non-fundamental OS functions execute in user space. The unaccounted for cycles are probably idle cycles, those spent doing nothing useful.

So total CPU percent usage is (kernel+user)/(idle+kernel+user)*100. User CPU usage is (user))/(idle+kernel+user)*100. And you can guess the equation for system % usage.

system_cpu_usage puzzles me. If it, instead of total_usage, refers to total cycles, then replace (idle+kernel+user) with that. What puzzles me is if system_cpu_usage is total usage, then what the heck is total_usage?