On 26/01/2022 14:50, Toke Høiland-Jørgensen wrote: > Nikolay Aleksandrov <nikolay@xxxxxxxxxx> writes: > >> On 26/01/2022 13:27, Lorenzo Bianconi wrote: >>>> On 24/01/2022 19:20, Lorenzo Bianconi wrote: >>>>> Similar to bpf_xdp_ct_lookup routine, introduce >>>>> br_fdb_find_port_from_ifindex unstable helper in order to accelerate >>>>> linux bridge with XDP. br_fdb_find_port_from_ifindex will perform a >>>>> lookup in the associated bridge fdb table and it will return the >>>>> output ifindex if the destination address is associated to a bridge >>>>> port or -ENODEV for BOM traffic or if lookup fails. >>>>> >>>>> Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx> >>>>> --- >>>>> net/bridge/br.c | 21 +++++++++++++ >>>>> net/bridge/br_fdb.c | 67 +++++++++++++++++++++++++++++++++++------ >>>>> net/bridge/br_private.h | 12 ++++++++ >>>>> 3 files changed, 91 insertions(+), 9 deletions(-) >>>>> >>>> >>>> Hi Lorenzo, >>> >>> Hi Nikolay, >>> >>> thx for the review. >>> >>>> Please CC bridge maintainers for bridge-related patches, I've added Roopa and the >>>> bridge mailing list as well. Aside from that, the change is certainly interesting, I've been >>>> thinking about a similar helper for some time now, few comments below. >>> >>> yes, sorry for that. I figured it out after sending the series out. >>> >>>> >>>> Have you thought about the egress path and if by the current bridge state the packet would >>>> be allowed to egress through the found port from the lookup? I'd guess you have to keep updating >>>> the active ports list based on netlink events, but there's a lot of egress bridge logic that >>>> either have to be duplicated or somehow synced. Check should_deliver() (br_forward.c) and later >>>> egress stages, but I see how this is a good first step and perhaps we can build upon it. >>>> There are a few possible solutions, but I haven't tried anything yet, most obvious being >>>> yet another helper. :) >>> >>> ack, right but I am bit worried about adding too much logic and slow down xdp >>> performances. I guess we can investigate first the approach proposed by Alexei >>> and then revaluate. Agree? >>> >> >> Sure, that approach sounds very interesting, but my point was that >> bypassing the ingress and egress logic defeats most of the bridge >> features. You just get an fdb hash table which you can build today >> with ebpf without any changes to the kernel. :) You have multiple >> states, flags and options for each port and each vlan which can change >> dynamically based on external events (e.g. STP, config changes etc) >> and they can affect forwarding even if the fdbs remain in the table. > > To me, leveraging all this is precisely the reason to have BPF helpers > instead of just replicating state in BPF maps: it's very easy to do that > and show a nice speedup, and then once you get all the corner cases > covered that the in-kernel code already deals with, you've chipped away > at that speedup and spent a lot of time essentially re-writing the > battle-tested code already in the kernel. > > So I think figuring out how to do the state sync is the right thing to > do; a second helper would be fine for this, IMO, but I'm not really > familiar enough with the bridge code to really have a qualified opinion. > > -Toke > Right, sounds good to me. IMO it should be required in order to get a meaningful bridge speedup, otherwise the solution is incomplete and you just do simple lookups that ignore all of the state that could impact the forwarding decision. Cheers, Nik
