 Performance issues in the program
Hello,I found a performance issue in the definition of `convert_dataset_for_tensorflow` ,
examples/tensorflow/text-classification/run_glue.py,
[tf_dataset = tf_dataset.batch(batch_size=batch_size, drop_remainder=drop_remainder).map](https://github.com/huggingface/transformers/blob/439a43b6b403205eeda2d62645fc16c93627d30d/examples/tensorflow/text-classification/run_glue.py#L83) was called without **num_parallel_calls**.
I think it will increase the efficiency of your program if you add this.

The same issues also exist in [tf_dataset.batch(batch_size=batch_size, drop_remainder=drop_remainder).map](https://github.com/huggingface/transformers/blob/439a43b6b403205eeda2d62645fc16c93627d30d/examples/tensorflow/text-classification/run_text_classification.py#L98) ,
[.map(densify_ragged_batch)](https://github.com/huggingface/transformers/blob/439a43b6b403205eeda2d62645fc16c93627d30d/examples/tensorflow/multiple-choice/run_swag.py#L109) and [tf_dataset.batch(batch_size=batch_size, drop_remainder=drop_remainder).map](https://github.com/huggingface/transformers/blob/439a43b6b403205eeda2d62645fc16c93627d30d/examples/tensorflow/question-answering/run_qa.py#L253)

Here is [the documemtation of tensorflow](https://tensorflow.google.cn/api_docs/python/tf/data/Dataset?hl=en#map) to support this thing.

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.
Hi @DLPerf, thanks for the warning! We're actually in the process of refactoring our Datasets to automatically support conversion to TF Datasets, at which point I'll be removing this part of our examples and replacing it with a call to the conversion method.

However, if you have any insights for how we can improve the performance of our conversion methods there, that would be very helpful! You can review the code at https://github.com/huggingface/datasets/pull/2731 and leave suggestions as comments on that PR.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.