Question about nvidia-smi

I am using nvidia-smi to find out the exact gpu resources used by a program (in my case opencl - nvidia0smi supports opencl processes).

I am using accounting mode:
nvidia-smi --accounting-mode=1
nvidia-smi --query-accounted-apps=pid,gpu_util --format=csv

My question is the gpu_util in percentage %, is the average percentage of the used SMs of my gpu or something else like?

Additionally, is there any better way to print exact used resources by a process especially in OpenCL?

I am courious about nvidia-smi as well.

I observe that nvidia-smi --query-accounted-apps=pid,gpu_util --format=csv
gives me either 0% or 99% for an application which shows in a real time observation of the gpu resources utiliation a percentage arround 40% (Volatil-GPU Util. when I type “whatch nvidia-smi”).

What really happens?