padding valid
50000/50000 [==============================] - 99s - loss: 1.9688 - acc: 0.2727 - val_loss: 2.2398 - val_acc: 0.2541
padding same
50000/50000 [==============================] - 160s - loss: 1.7978 - acc: 0.3541 - val_loss: 2.0574 - val_acc: 0.3463
如果训练的图片非常小，padding最好用same。