On Fri, 29 Mar 2019 16:14:57 +0000, Jonathan Lemon wrote:
> 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.
I thought Ed Cree added something like that to ethtool - multiple RSS
contexts that is: commit 84a1d9c48200 ("net: ethtool: extend RXNFC API
to support RSS spreading of filter matches").
With Netronome NICs you could also program your RSS with offloaded BPF.
Unfortunately only Intel supports AF_XDP right now so that probably
doesn't help you :(
