GSO / TSO
Generic Segmentation Offload + TCP Segmentation Offload — Linux + NIC features where a large send buffer (64KB) is split into MTU-sized packets as late as possible in path (NIC = TSO, kernel = GSO). Massive CPU saving for 10GbE+.
Without TSO: kernel builds 1500-byte packets each, 7 frames per 10KB send, 7x syscall overhead. With TSO: kernel sends a 64KB buffer + offset, NIC segments in hardware. Linux ethtool -K eth0 tso on gso on. Mirrored: LRO/GRO (Large/Generic Receive Offload) bundles incoming small frames into large chunks. Modern hot-path optimization. Classic debug: virt-NIC (virtio) with GSO disabled → throughput tanks. Recommended on by default; off only in edge cases (firewall that DPIs every packet).