TCP Segmentation Offload (or TCP Large Send) is when buffer's much larger than the supported maximum transmission unit (MTU) of a given medium are passed through the bus to the network interface card. The work of dividing the much larger packets into smaller packets is thus offloaded to the NIC. More specifically, the e1000 driver is passing 64k packets to the network card, which then divides these into proper MTU-sized 1500 byte packets.

Alexey Kuznetsov added TSO support into the stack, noting that as of yet, "the implementation in tcp is still at [the] level of a toy". Be that as it may, it's a good start, and before long other TSO capable devices will likely also be supported.

Read more: Linux: TCP Segmentation Offload (TSO) | KernelTrap