Last I remember as of at least 7 years ago Google et al were using custom NIC firmware to avoid having the kernel get involved in general (I think they managed to do a lot of Maglev directly on the NICs) because latency is so dang important at high speed networking speeds that letting anything context switch and need to wait on the kernel is a big performance hit. Not a lot of room for latency when you're working at 100 Gbps.