Re: XDP packet queueing and scheduling capabilities

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Alexandre Cassen <acassen@gmail.com> writes:

> Hi Toke,
>
> here is a target with lot of interest for it : www.gtp-guard.org

Ah, seems like a cool project; thanks for the pointer!

> When dealing with mobile network data-plane, at some point you have
> ordering issues and shaping needs, so queuing is truly needed.
> Alternatively ones can implement PIFO or others built on AF_XDP but if
> dedicated bpf map covers the use-case, would be nice.

Right, I'm kinda thinking about the map type that is part of the XDP
queueing series as a general-purpose packet buffer that will enable all
kinds of features, not just queueing for forwarding. Whether it'll end
up being the PIFO map type, or a simpler one, I'm less certain about.
The PIFO abstraction may end up being too special-purpose. Opinions
welcome!

> Watching at your LPC 2022 presentation, at the end, discussions where
> made around using existing Qdisc kernel framework and find a way to
> share the path between XDP and netstack. Is it a target for adding
> PIFO, or more generally getting queuing support for XDP ?

I don't personally consider it feasible to have forwarded XDP frames
share the qdisc path. The presence of an sk_buff is too simply too
fundamentally baked into the qdisc layer. I'm hoping that the addition
of an eBPF-based qdisc will instead make it feasible to share queueing
algorithm code between the two layers (and even build forwarding paths
that can handle both by having the different BPF implementations
cooperate). And of course co-existence between XDP and stack forwarding
is important to avoid starvation, but that is already an issue for XDP
forwarding today.

-Toke