Mark the benchmark as erroneous, e.g., because the benchmarking tool crashed.
        The message is intended as explanation for the user.

def set_error(self, msg, runSet=None):
        """
        Mark the benchmark as erroneous, e.g., because the benchmarking tool crashed.
        The message is intended as explanation for the user.
        """
        self.xml_header.set('error', msg if msg else 'unknown error')
        if runSet:
            runSet.xml.set('error', msg if msg else 'unknown error')