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[193.12.47.89]) by smtp.gmail.com with ESMTPSA id c18sm59140ljd.66.2021.04.26.10.04.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Apr 2021 10:04:46 -0700 (PDT) From: Tobias Waldekranz To: davem@davemloft.net, kuba@kernel.org Cc: andrew@lunn.ch, vivien.didelot@gmail.com, f.fainelli@gmail.com, olteanv@gmail.com, roopa@nvidia.com, nikolay@nvidia.com, jiri@resnulli.us, idosch@idosch.org, stephen@networkplumber.org, netdev@vger.kernel.org, bridge@lists.linux-foundation.org Subject: [RFC net-next 0/9] net: bridge: Forward offloading Date: Mon, 26 Apr 2021 19:04:02 +0200 Message-Id: <20210426170411.1789186-1-tobias@waldekranz.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Organization: Westermo Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org X-Patchwork-State: RFC ## Overview vlan1 vlan2 \ / .-----------. | br0 | '-----------' / / \ \ swp0 swp1 swp2 eth0 : : : (hwdom 1) Up to this point, switchdevs have been trusted with offloading forwarding between bridge ports, e.g. forwarding a unicast from swp0 to swp1 or flooding a broadcast from swp2 to swp1 and swp0. This series extends forward offloading to include some new classes of traffic: - Locally originating flows, i.e. packets that ingress on br0 that are to be forwarded to one or several of the ports swp{0,1,2}. Notably this also includes routed flows, e.g. a packet ingressing swp0 on VLAN 1 which is then routed over to VLAN 2 by the CPU and then forwarded to swp1 is "locally originating" from br0's point of view. - Flows originating from "foreign" interfaces, i.e. an interface that is not offloaded by a particular switchdev instance. This includes ports belonging to other switchdev instances. A typical example would be flows from eth0 towards swp{0,1,2}. The bridge still looks up its FDB/MDB as usual and then notifies the switchdev driver that a particular skb should be offloaded if it matches one of the classes above. It does so by using the _accel version of dev_queue_xmit, supplying its own netdev as the "subordinate" device. The driver can react to the presence of the subordinate in its .ndo_select_queue in what ever way it needs to make sure to forward the skb in much the same way that it would for packets ingressing on regular ports. Hardware domains to which a particular skb has been forwarded are recorded so that duplicates are avoided. The main performance benefit is thus seen on multicast flows. Imagine for example that: - An IP camera is connected to swp0 (VLAN 1) - The CPU is acting as a multicast router, routing the group from VLAN 1 to VLAN 2. - There are subscribers for the group in question behind both swp1 and swp2 (VLAN 2). With this offloading in place, the bridge need only send a single skb to the driver, which will send it to the hardware marked in such a way that the switch will perform the multicast replication according to the MDB configuration. Naturally, the number of saved skb_clones increase linearly with the number of subscribed ports. As an extra benefit, on mv88e6xxx, this also allows the switch to perform source address learning on these flows, which avoids having to sync dynamic FDB entries over slow configuration interfaces like MDIO to avoid flows directed towards the CPU being flooded as unknown unicast by the switch. ## RFC - In general, what do you think about this idea? - hwdom. What do you think about this terminology? Personally I feel that we had too many things called offload_fwd_mark, and that as the use of the bridge internal ID (nbp->offload_fwd_mark) expands, it might be useful to have a separate term for it. - .dfwd_{add,del}_station. Am I stretching this abstraction too far, and if so do you have any suggestion/preference on how to signal the offloading from the bridge down to the switchdev driver? - The way that flooding is implemented in br_forward.c (lazily cloning skbs) means that you have to mark the forwarding as completed very early (right after should_deliver in maybe_deliver) in order to avoid duplicates. Is there some way to move this decision point to a later stage that I am missing? - BR_MULTICAST_TO_UNICAST. Right now, I expect that this series is not compatible with unicast-to-multicast being used on a port. Then again, I think that this would also be broken for regular switchdev bridge offloading as this flag is not offloaded to the switchdev port, so there is no way for the driver to refuse it. Any ideas on how to handle this? ## mv88e6xxx Specifics Since we are now only receiving a single skb for both unicast and multicast flows, we can tag the packets with the FORWARD command instead of FROM_CPU. The swich(es) will then forward the packet in accordance with its ATU, VTU, STU, and PVT configuration - just like for packets ingressing on user ports. Crucially, FROM_CPU is still used for: - Ports in standalone mode. - Flows that are trapped to the CPU and software-forwarded by a bridge. Note that these flows match neither of the classes discussed in the overview. - Packets that are sent directly to a port netdev without going through the bridge, e.g. lldpd sending out PDU via an AF_PACKET socket. We thus have a pretty clean separation where the data plane uses FORWARDs and the control plane uses TO_/FROM_CPU. The barrier between different bridges is enforced by port based VLANs on mv88e6xxx, which in essence is a mapping from a source device/port pair to an allowed set of egress ports. In order to have a FORWARD frame (which carries a _source_ device/port) correctly mapped by the PVT, we must use a unique pair for each bridge. Fortunately, there is typically lots of unused address space in most switch trees. When was the last time you saw an mv88e6xxx product using more than 4 chips? Even if you found one with 16 (!) devices, you would still have room to allocate 16*16 virtual ports to software bridges. Therefore, the mv88e6xxx driver will allocate a virtual device/port pair to each bridge that it offloads. All members of the same bridge are then configured to allow packets from this virtual port in their PVTs. Tobias Waldekranz (9): net: dfwd: Constrain existing users to macvlan subordinates net: bridge: Disambiguate offload_fwd_mark net: bridge: switchdev: Recycle unused hwdoms net: bridge: switchdev: Forward offloading net: dsa: Track port PVIDs net: dsa: Forward offloading net: dsa: mv88e6xxx: Allocate a virtual DSA port for each bridge net: dsa: mv88e6xxx: Map virtual bridge port in PVT net: dsa: mv88e6xxx: Forward offloading MAINTAINERS | 1 + drivers/net/dsa/mv88e6xxx/Makefile | 1 + drivers/net/dsa/mv88e6xxx/chip.c | 61 ++++++- drivers/net/dsa/mv88e6xxx/dst.c | 160 ++++++++++++++++++ drivers/net/dsa/mv88e6xxx/dst.h | 14 ++ .../net/ethernet/intel/fm10k/fm10k_netdev.c | 3 + drivers/net/ethernet/intel/i40e/i40e_main.c | 3 + drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 3 + include/linux/dsa/mv88e6xxx.h | 13 ++ include/net/dsa.h | 13 ++ net/bridge/br_forward.c | 11 +- net/bridge/br_if.c | 4 +- net/bridge/br_private.h | 54 +++++- net/bridge/br_switchdev.c | 141 +++++++++++---- net/dsa/port.c | 16 +- net/dsa/slave.c | 36 +++- net/dsa/tag_dsa.c | 33 +++- 17 files changed, 510 insertions(+), 57 deletions(-) create mode 100644 drivers/net/dsa/mv88e6xxx/dst.c create mode 100644 drivers/net/dsa/mv88e6xxx/dst.h create mode 100644 include/linux/dsa/mv88e6xxx.h