The 8 sec is not the first batch, it is on average.
The batch size for tensorflow is 1024. There are four parallel convolutional layers for my tensorflow model, the kernel sizes are  1X250, 3X250, 4X250, 5X250. And then some hidden layers. That is a much larger graph than the example I showed above.
Sorry, the tensorflow code has too many dependencies, I don’t think I can simply show it here.
Thank you very much!