Performance issue in src/eval.py (by P3)

[DLPerf]

Hello! I've found a performance issue in src/eval.py: with tf.Session(config=tf.ConfigProto(allow_soft_placement=True)) as sess:(line 52) is defined in the function eval_once(line 48) which is repeatedly called in a loop while True:(line 214).

tf.Session being defined repeatedly could lead to incremental overhead. If you define tf.Session out of the loop and pass tf.Session as a parameter to the loop, your program would be much more efficient.

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~