Comment by dfox
3 years ago
It is almost certainly the other way around. Even 1000-base-T PHY is complex block of analog magic that draws significant power and adds measurable latency over direct SGMII/optical link. In comparison USB4 is even more directly connected to CPU than the whateverMII interface of PCIe NIC.
For a while at work I was trying to use ethernet for embedded stuff because it seemed more modern than CAN, i2c etc. I couldn't figure out why so few microcontrollers support it. It turns out just normal copper 100Mbps ethernet uses about 0.25W per port (0.5W for 1 point-point ethernet link) so it doesn't make sense for embedded applications. Gigbit uses more but I forget how much more.