text: 
  
  TITLE
  [trainer] --model_parallel hasn't been implemented for most models
  
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  Apparently we unleashed `--model_parallel` in trainer w/o checking if the model supports MP (most don't). This PR:
  
  * [x] checks whether the model supports MP and asserts otherwise
  * [x] fixes the cl arg help to note that the flag will only work if the model supports MP 
  
  As we are gradually starting to build MP-support a cleaner solution will be made in the future, but for now this is good enough to prevent misleading false expectations as reported in https://github.com/huggingface/transformers/issues/9336
  
  (Also for the future, I'm not sure whether it'd be better to check `model.config.architectures`, which would be more precise than checking `model_type` since it's the `architectures` that may or may not support MP within the same `model_type` - but that's a different discussion).
  
  Fixes: #9336
  
  @patrickvonplaten, @sgugger 
  