code: def run_iperf_client(self, server_host, extra_args=''):
          
          out = self.adb.shell('iperf3 -c %s %s' % (server_host, extra_args))
          clean_out = new_str(out, 'utf-8').strip().split('\n')
          if 'error' in clean_out[0].lower():
              return False, clean_out
          return True, clean_out
docs: Start iperf client on the device.
  
          Return status as true if iperf client start successfully.
          And data flow information as results.
  
          Args:
              server_host: Address of the iperf server.
              extra_args: A string representing extra arguments for iperf client,
                  e.g. '-i 1 -t 30'.
  
          Returns:
              status: true if iperf client start successfully.
              results: results have data flow information