removed auto val reduce (#2462)

pytorch_lightning/trainer/evaluation_loop.py

@@ -341,11 +341,6 @@ def _evaluate(
             elif self.is_overridden('validation_epoch_end', model=model):
                 eval_results = model.validation_epoch_end(outputs)
 
-        # aggregate ddp stats across
-        has_content = eval_results is not None and len(eval_results) > 0
-        if has_content and (self.use_ddp or self.use_ddp2):
-            self.reduce_eval_ddp(eval_results)
-
         # enable train mode again
         model.train()
 
@@ -354,19 +349,6 @@ def _evaluate(
 
         return eval_results
 
-    def reduce_eval_ddp(self, eval_results):
-        # ignore bad inputs
-        if eval_results is None or len(eval_results) == 0:
-            return
-
-        for k, v in eval_results.items():
-            if isinstance(v, dict):
-                self.reduce_eval_ddp(v)
-            elif isinstance(v, torch.Tensor):
-                dist.all_reduce(v, op=dist.reduce_op.SUM)
-                v = v / self.world_size
-                eval_results[k] = v
-
     def run_evaluation(self, test_mode: bool = False):
         # hook
         model = self.get_model()