RSS (Receive Side Scaling) Receive Side Scaling
The network card's way of spreading incoming packets across several receive queues, so that one CPU core doesn't have to handle every interrupt.
Without it, all inbound traffic lands in one queue with an interrupt bound to a single core, and that core saturates long before the card does — which is why a ten-gigabit server sometimes tops out at a couple. The card instead hashes each packet's address and port combination and places it in one of several queues, each tied to its own core. That the hash is over the flow rather than random is deliberate: every packet of a connection lands on the same core, preserving ordering and keeping that connection's state warm in cache. The distribution table can be adjusted with ethtool -X. For cards without the feature, RPS and RFS provide software equivalents.