What are Multi-queue NICs⌗

RX queue was used to pass packets between hardware and kernel. Now days NICs support multiple RX queues: Each RX queue is pinned to a separate CPU.

Multi-queue hashing algorithms⌗

Use a hash from packet to decide the RX queue number. The hash is usually counted from a tuple (src IP, dst IP, src port, dst port). This guarantees that packets for a single flow will always end up on exactly the same RX queue, and reordering of packets within a single flow can’t happen.

The hash algorithm is configurable with ethtool

receiver$ ethtool -n eth2 rx-flow-hash udp4
UDP over IPV4 flows use these fields for computing Hash flow key:
IP SA
IP DA

Reads as

RX_queue_number = hash('192.168.254.30', '192.168.254.1') % number_of_queues