Performance issue in /datasets/dataloader.py (by P3)

[DLPerf]

Hello! I've found a performance issue in /datasets/dataloader.py: dataset.batch(self.config['batch_size'])(here) should be calle before dataset.map(transform_fn, num_parallel_calls=self.config['prefetch_threads'])(here), which could make your program more efficient.

Here is the tensorflow document to support it.

Besides, you need to check the function transform_fn called in dataset.map(transform_fn, num_parallel_calls=self.config['prefetch_threads']) whether to be affected or not to make the changed code work properly. For example, if transform_fn needs data with shape (x, y, z) as its input before fix, it would require data with shape (batch_size, x, y, z) after fix.

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.

[DLPerf]

Hello, I'm looking forward to your reply~