Repository: huggingface/transformers
Pull request: log: Add logging when using split_batches and per_device_train_batch_size

# What does this PR do?
Adds logger warning when user uses `split_batches=True` in `accelerator_config` arg of Trainer. 

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Fixes # (issue)
When using `split_batches=True` in `accelerator_config` arg of Trainer, all batches are split equally across all processes. 
Hence, `per_device_train_batch_size` value is actually the aggregate sum of batch size split across all processes. 

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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    - https://github.com/huggingface/transformers/issues/38484#issue-3101907511
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## Who can review?

@SunMarc 

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Changed files:
filename: src/transformers/training_args.py
patch: @@ -1753,6 +1753,11 @@ def __post_init__(self):
                     )
                 else:
                     self.accelerator_config = AcceleratorConfig.from_json_file(self.accelerator_config)
+            if self.accelerator_config.split_batches:
+                logger.info(
+                    "Using `split_batches=True` in `accelerator_config` will override the `per_device_train_batch_size` "
+                    "Batches will be split across all processes equally when using `split_batches=True`."
+                )
 
         # Initialize device before we proceed
         if self.framework == "pt" and is_torch_available():