Performance issue in tensorflow/vision/model/input_fn.py (by P3)

[DLPerf]

Hello! I've found a performance issue in input_fn.py: batch() should be called before map(), which could make your program more efficient. Here is the tensorflow document to support it.

Detailed description is listed below:

• tensorflow/vision/model/input_fn.py: .batch(params.batch_size)(here) should be called before .map(parse_fn, num_parallel_calls=params.num_parallel_calls)(here).
• tensorflow/vision/model/input_fn.py: .batch(params.batch_size)(here) should be called before .map(parse_fn)(here).

Besides, you need to check the function called in map()(e.g., parse_fn called in .map(parse_fn)) whether to be affected or not to make the changed code work properly. For example, if parse_fn 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~