added single node distdataparallel

pytorch_lightning/models/trainer.py

@@ -282,6 +282,7 @@ class Trainer(TrainerIO):
         # when GPU is called, spawn off a single worker for each gpu
         if self.on_gpu:
             rank = 0
+            pdb.set_trace()
             mp.spawn(self.__dp_train, nprocs=len(self.data_parallel_device_ids), args=(rank, model ))
         else:
             self.__run_pretrain_routine(model)