Re: [RFC 0/5] add XDP support to mt76x2e/mt76x0e drivers

["Michał Kazior" <kazikcz@gmail.com>]

On Wed, 28 Nov 2018 at 13:39, Toke Høiland-Jørgensen <toke@toke.dk> wrote:[...]
> > This is an early stage implementation, at this point I would collect
> > other people opinions/concerns about using bpf/xdp directly on 802.11
> > frames.
>
> Thanks for looking into this!

I'm really hyped up with this especially when I think this could be
maybe offloaded to wlan cpu's for e.g. deep powersaving (allow host
system to suspend) without relying on blackbox logic you get today, or
802.11 -> 802.3 conversion (to offload host cpu).


> I have two concerns with running XDP on 802.11 frames:
>
> 1. It makes it more difficult to add other XDP actions (such as
>    REDIRECT), as the XDP program would then have to make sure that the
>    outer packet headers are removed before, say, redirecting the packet
>    out of an ethernet interface. Also, if we do add redirect, we would
>    be bypassing mac80211 entirely; to what extent would that mess up
>    internal state?
>
> 2. UI consistency; suddenly, the user needs to know which kind of
>    frames to expect, and XDP program reuse becomes more difficult. This
>    may be unavoidable given the nature of XDP, but some thought needs to
>    go into this. Especially since we wouldn't necessarily be consistent
>    between WiFi drivers (there are fullmac devices that remove 802.11
>    headers before sending up the frame, right?).

Yep - you can expect 802.3 frames or amsdu subframes (DA+SA+length)
too. In some cases you could also expect internal events (broadcom if
I understand their fullmac arch).


Michał