> Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx> writes: > > > On Nov 28, Toke Høiland-Jørgensen wrote: > >> Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx> writes: > >> > >> >> Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx> 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? Regards, Lorenzo > > -Toke
