Learning DPDK : Symmetric RSS

rss diagram (1)

Overview

Receive side scaling (RSS) is a technology that enables the distribution of received packets between multiple RX queues using a predefined hash function. It enabled multicore CPU to process packets from different queues on different cores.

Symmetric RSS promise is to populate two-way packets from the same TCP connection to the same RX queue. As a result statistics on the different connections could be stored in the per-queue data structures avoiding any need for locking.

System

Recently I had a chance to test symmetric RSS on two NICs from Intel, namely XL710 40G and 82599 10G. 

The approach to configuring symmetric RSS in XL710 is different from the standard DPDK approach. Thus i40e driver offers specific API for this purpose.

DPDK 18.05.1 was used for testing.

82599 solution

To make symmetric RSS work a default hash key has to be replaced with a custom one.

XL710 solution

To enable symmetric RSS i40e driver provides API to setup hardware registers.

References

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