code: def _init_runtime(self):
          
          if self.idx != 0:
              from tensorpack.models.registry import disable_layer_logging
              disable_layer_logging()
          self.predictor = OfflinePredictor(self.config)
          if self.idx == 0:
              with self.predictor.graph.as_default():
                  describe_trainable_vars()
docs: Call _init_runtime under different CUDA_VISIBLE_DEVICES, you'll
              have workers that run on multiGPUs