Lorenzo Bianconi <[email protected]> writes: >> Lorenzo Bianconi <[email protected]> writes: >> >> > On Nov 28, Toke Høiland-Jørgensen wrote: >> >> Lorenzo Bianconi <[email protected]> writes: >> >> >> >> >> Lorenzo Bianconi <[email protected]> writes: >> >> >> >> >> >> >> >> > This series is intended as a playground to start >> >> >> >> >> > experimenting/developing >> >> >> >> >> > with XDP/eBPF over WiFi and collect ideas/concerns about it. >> >> >> >> >> > Introduce XDP support to mt76x2e/mt76x0e drivers. Currently >> >> >> >> >> > supported >> >> >> >> >> > actions are: >> >> >> >> >> > - XDP_PASS >> >> >> >> >> > - XDP_ABORTED >> >> >> >> >> > - XDP_DROP >> >> >> >> >> > Introduce ndo_bpf mac80211 callback in order to to load a bpf >> >> >> >> >> > program into low level driver XDP rx hook. >> >> >> >> >> > This series has been tested through a simple bpf program >> >> >> >> >> > (available here: >> >> >> >> >> > https://github.com/LorenzoBianconi/bpf-workspace/tree/master/mt76_xdp_stats) >> >> >> >> >> > used to count frame types received by the device. >> >> >> >> >> > Possible eBPF use cases could be: >> >> >> >> >> > - implement new statistics through bpf maps >> >> >> >> >> > - implement fast packet filtering (e.g in monitor mode) >> >> >> >> >> > - ... >> >> >> >> > >> >> >> >> > Hi Kalle, >> >> >> >> > >> >> >> >> >> >> >> >> >> >> This is most likely a stupid question, but why do this in the >> >> >> >> >> driver and >> >> >> >> >> not in mac80211 so that all drivers could benefit from it? I >> >> >> >> >> guess there >> >> >> >> >> are reasons for that, I just can't figure that out. >> >> >> >> >> >> >> >> XDP achieves its speedup by running the eBPF program inside the >> >> >> >> driver >> >> >> >> NAPI loop, before the kernel even touches the data in any other >> >> >> >> capacity >> >> >> >> (and in particular, before it allocates an SKB). Which kinda means >> >> >> >> the >> >> >> >> hook needs to be in the driver... Could be a fallback in mac80211, >> >> >> >> though; although we'd have to figure out how that interacts with >> >> >> >> Generic >> >> >> >> XDP. >> >> >> >> >> >> >> >> > 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! >> >> >> > >> >> >> > Hi Toke, >> >> >> > >> >> >> >> >> >> >> >> 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? >> >> >> >> >> >> >> > >> >> >> > You are right, my assumption here is the logic/complexity is moved to >> >> >> > the bpf program that needs to take care of all possible issues that >> >> >> > can be introduced. More or less it is the same if a bpf program mess >> >> >> > up with TCP segments on a wired connection, isn't it? >> >> >> >> >> >> No, I guess not; except here it potentially applies to all packets >> >> >> (things like BAW tracking), and it is *in addition* to TCP. >> >> > >> >> > Yes, here it is a little bit harder, but I was meaning that the bpf >> >> > program >> >> > has to be very careful when dropping a packet :) >> >> >> >> Yeah. What kind of filtering were you thinking you would use this for in >> >> the short term? >> >> >> > >> > When I started working on XDP for mt76 I was thinking about BSSID >> > filtering but I was looking for a more general solution respect to add >> > that feature in the driver. Moreover we could use bpf for fast packet >> > filtering when you add an interface in monitor mode. >> >> Yup, both of these make sense. >> >> > Nevertheless I guess there could be other use cases not limited to >> > frame filtering. My primary goal with this series is to collect >> > ideas/concerns on WiFi XDP/eBPF possible uses cases. >> >> Well, Michał's idea about offloading is cool if it is possible to get >> vendors to implement it. >> > > Yep, would be very cool :) > >> Other than that, if we can solve the issues with differences between >> 802.11 and plain Ethernet frames, I see no reason why it wouldn't be >> possible to implement an XDP fast-path for WiFi-to-Ethernet forwarding, >> which might be useful in an access point, especially as WiFi speeds >> increase. >> > > Agree > >> The other direction will probably be more difficult, at least if 802.11 >> frames need to be built in software. It *might* be possible with the XDP >> egress hook we are planning (with a suitable set of helpers, the eBPF >> program could build the 802.11 frames), but I'm not really sure if that >> is worth doing as I'm quite sure there are some hairy edge cases >> there... > > The possible issue with XDP_DROP action you are referring to here is > A-MPDU reordering on rx side, right? If so I guess the issue will be > fixed by tid_agg_rx->reorder_timer. Are you referring to other > possible edge cases?
I'm not sure, which is why I was being deliberately vague... ;) Just something to be aware of when going beyond proof of concept, I guess: here be dragons. -Toke
