[Enhance]: make total loss at the end of all losses (#369)

mmengine/model/base_model/base_model.py

@@ -159,20 +159,23 @@ class BaseModel(BaseModule):
             all losses, and the second is log_vars which will be sent to the
             logger.
         """
-        log_vars = OrderedDict()
+        log_vars = []
         for loss_name, loss_value in losses.items():
             if isinstance(loss_value, torch.Tensor):
-                log_vars[loss_name] = loss_value.mean()
+                log_vars.append([loss_name, loss_value.mean()])
             elif is_list_of(loss_value, torch.Tensor):
-                log_vars[loss_name] = sum(_loss.mean() for _loss in loss_value)
+                log_vars.append(
+                    [loss_name,
+                     sum(_loss.mean() for _loss in loss_value)])
             else:
                 raise TypeError(
                     f'{loss_name} is not a tensor or list of tensors')
 
-        loss = sum(value for key, value in log_vars.items() if 'loss' in key)
-        log_vars['loss'] = loss
+        loss = sum(value for key, value in log_vars if 'loss' in key)
+        log_vars.insert(0, ['loss', loss])
+        log_vars = OrderedDict(log_vars)  # type: ignore
 
-        return loss, log_vars
+        return loss, log_vars  # type: ignore
 
     def to(self,
            device: Optional[Union[int, str, torch.device]] = None,