Performance issues in 11.TFRecord/read_cifar10.py(P2)

[DLPerf]

Hello,I found a performance issue in 11.TFRecord/read_cifar10.py , dataset=dataset.map(map_func=_parse_data) 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 dataset=dataset.map(map_func=_parse_data) , parsed_dataset = dataset.map, parsed_dataset = dataset.map,parsed_dataset = dataset.map ,parsed_dataset = dataset.map and dataset=dataset.map

Here is the documemtation of tensorflow 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.