How to get precise cpu_usage() from process?

help
1

Hi everyone. I am trying to get the CPU usage of processes belonging to Docker containers. My attempt is as follows:

fn update_cpu_process_info(system_info: &mut SysInfo) {
let mut system = System::new_all();

std::thread::sleep(Duration::from_millis(200));

system.refresh_processes_specifics(
    ProcessesToUpdate::All,
    ProcessRefreshKind::new().with_cpu());

std::thread::sleep(Duration::from_millis(200));

for proc in &mut system_info.processes {   
         
    let pid : Pid = Pid::from_u32(proc.pid);        

    if let Some(docker_proc) = system.process(pid) {    
        println!("PID: {}", docker_proc.pid());
        println!("{}", docker_proc.cpu_usage());        
    }        
}

}

I have the PIDs of the Docker container processes stored in the SysInfo struct in the processes field. It should be noted that I have verified that the processes are running and correspond to the containers.

The problem is that for the cpu_usage field I get a value of 0 for all processes. I can access all other fields like mem_usage without problems and get a reasonable value, but cpu_usage is always 0. What could be happening? What is the correct way to get that value?

Any help is appreciated.

2

I am trying to get the CPU usage of processes belonging to Docker containers.

Each docker container has its own cgroup. So find the cgroup belonging to the container (via /proc/<pid>/cgroup) and then read the stats from <path_to_cgroup>/cpu.stat (assuming cgroup v2).

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