code: func joinCpuset(c *configs.Cgroup, pid int) error {
  	path, err := getSubsystemPath(c, "cpuset")
  	if err != nil && !cgroups.IsNotFound(err) {
  		return err
  	}
  
  	s := &fs.CpusetGroup{}
  
  	return s.ApplyDir(path, c, pid)
  }
docs: // systemd does not atm set up the cpuset controller, so we must manually
  // join it. Additionally that is a very finicky controller where each
  // level must have a full setup as the default for a new directory is "no cpus"