docs: def get_docker_cpu(self, container_id, all_stats):
          """Return the container CPU usage.
  
          Input: id is the full container id
                 all_stats is the output of the stats method of the Docker API
          Output: a dict {'total': 1.49}
          """
          cpu_new = {}
          ret = {'total': 0.0}
  
          # Read the stats
          # For each container, you will find a pseudo-file cpuacct.stat,
          # containing the CPU usage accumulated by the processes of the container.
          # Those times are expressed in ticks of 1/USER_HZ of a second.
          # On x86 systems, USER_HZ is 100.
          try:
              cpu_new['total'] = all_stats['cpu_stats']['cpu_usage']['total_usage']
              cpu_new['system'] = all_stats['cpu_stats']['system_cpu_usage']
              cpu_new['nb_core'] = len(all_stats['cpu_stats']['cpu_usage']['percpu_usage'] or [])
          except KeyError as e:
              # all_stats do not have CPU information
              logger.debug("docker plugin - Cannot grab CPU usage for container {} ({})".format(container_id, e))
              logger.debug(all_stats)
          else:
              # Previous CPU stats stored in the cpu_old variable
              if not hasattr(self, 'cpu_old'):
                  # First call, we init the cpu_old variable
                  self.cpu_old = {}
                  try:
                      self.cpu_old[container_id] = cpu_new
                  except (IOError, UnboundLocalError):
                      pass
  
              if container_id not in self.cpu_old:
                  try:
                      self.cpu_old[container_id] = cpu_new
                  except (IOError, UnboundLocalError):
                      pass
              else:
                  #
                  cpu_delta = float(cpu_new['total'] - self.cpu_old[container_id]['total'])
                  system_delta = float(cpu_new['system'] - self.cpu_old[container_id]['system'])
                  if cpu_delta > 0.0 and system_delta > 0.0:
                      ret['total'] = (cpu_delta / system_delta) * float(cpu_new['nb_core']) * 100
  
                  # Save stats to compute next stats
                  self.cpu_old[container_id] = cpu_new
  
          # Return the stats
          return ret