code: def benchmark_backward(self):
          
          try:
              self._benchmark_backward()
          except RuntimeError as e:
              # Seems like not implemented.
              print(e)
              self.mod_ext.synchronize(**self.ext_kwargs)
              self.backward_stat = None
docs: Benchmark backward execution.
  
          Note:
              If backward execution throws any exception,
              this benchmark system considers the error is because the function
              doesn't support backward operation, then set the benchmark
              ``None``.