Fix save error for multi-gpu

utils/torch_utils.py

@@ -201,5 +201,5 @@ class ModelEMA:
     def update_attr(self, model):
         # Update EMA attributes
         for k, v in model.__dict__.items():
-            if not k.startswith('_') and k != 'module':
+            if not k.startswith('_') and k not in ["module", "process_group", "reducer"]:
                 setattr(self.ema, k, v)