My point is that to receive a single packet, you have an external interrupt, you go through the device driver, the ip stack, etc. And in all that you are lookin

My point is that to receive a single packet, you have an external interrupt, you go through the device driver, the ip stack, etc. And in all that you are looking for a difference of a single cycle. That won't work. Even with a zero latency network. There is just too much code involved. You can measure differences of thousands or maybe even hundreds of cycles, but not single cycles. That's below the noise level of a modern computer.