View source for Receive Side Scaling

Receive Side Scaling (RSS) is a method of directing incoming traffic to different CPUs. It requires support in the bus (MSI-X), NIC hardware (such hardware is commonly referred to as "multi-queue") and driver. In the absence of hardware support, Linux implements Receive Packet Steering in software, but it is higher in the stack.

<tt>irqbalance</tt> works by identifying large interrupt sources, and binding their handlers to different processors. Under this scheme, a single NIC's traffic will only be handled on a single CPU. With sufficiently high loads, we need handling on multiple CPUs. RSS is typically configured so that all packets of a given flow go to a single CPU, and different flows are randomly distributed across CPUs. Each receive queue gets its own IRQ, which can then be directed to a set of CPUs via standard processes. <tt>irqbalance</tt> can conflict with manual RSS configurations.