Performance issue in /image/data.py

[DLPerf]

Hello! I've found a performance issue in /image/data.py: dataset = dataset.batch(per_core_bsz, drop_remainder=True)(here) should be called before dataset = dataset.map(parser, num_parallel_calls=32)(here), which would make your program more efficient.

Here is the tensorflow document to support it.

Besides, you need to check the function parser(here) called in dataset.map() whether to be affected or not to make the changed code work properly. For example, if parser needs data with shape (x, y, z) as its input before fix, it would require data with shape (batch_size, x, y, z).

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~