Background: With AF_XDP, packets are placed on queues which are serviced directly from an application running in user space, which promises greatly increased performance. However, not all incoming packets should be delivered to the application; there may be management traffic, or packets which should be handled by normal Linux networking applications.
Having the AF_XDP application handle the packets and return them to the kernel for processing is not ideal, nor is adding a bpf filter at the kernel level which performs the redirection. It would be nicer if the redirection was done in the NIC itself. Fortunately, there is a facility for this: the RX network flow classification. Unfortunately, the target of the classification is currently a single queue. Traffic arriving at a NIC which is not steered to a specific queue can be distributed across a set of queues through the RX flow hash redirection table (RSS steering). But being able to target a separate RSS object would allow arbitrary distribution of previously classified traffic. Ask: It would be nice to have more than one RSS table, which would be the target of a classifier or default packet stream. Queues would be attached to an RSS object, and flow classifiers could target the RSS object for further distribution. For example, something like: ethtool -X eth0 rss 0 queue 0-13 ethtool -X eth0 rss 1 queue 14-55 ethtool -N eth0 flow-type udp6 dst-port 4242 rss 1 This would set up a default RSS object (rss 0), which sprays traffic to 14 queues; this would be equivalent to "ethtool -X eth0 equal 14". At the same time, a second object (rss 1) is set up, distributing traffic across another set of queues. Is there interest in adding this type of feature? Having the ability to express this concept (not necessarily in ethtool) should facilitate having HW vendors add this to their products. I believe that some vendors have hardware which may be capable of this already. -- Jonathan
