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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def start(self, extra_args="", tag=""):
 """Starts iperf server on specified port. Args: extra_args: A string representing extra arguments to start iperf server with. tag: Appended to log file name to identify logs from different iperf runs. """

        if self.started:
            return
        utils.create_dir(self.log_path)
        if tag:
            tag = tag + ','
        out_file_name = "IPerfServer,{},{}{}.log".format(
            self.port, tag, len(self.log_files))
        full_out_path = os.path.join(self.log_path, out_file_name)
        cmd = '%s %s > %s' % (self.iperf_str, extra_args, full_out_path)
        self.iperf_process = utils.start_standing_subprocess(cmd, shell=True)
        self.log_files.append(full_out_path)
        self.started = True