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TC Flower Offload

The TC Flower Classifier allows control of packets based on flows determined by matching of well-known packet fields and metadata. This is inspired by similar flow classification described by OpenFlow and implemented by Open vSwitch. Offload of the TC Flower classifier and related modules provides a powerful mechanism to both increase throughput and reduce CPU utilisation for users of such flow-based systems. This presentation will give an overview of the evolution of offload of the TC Flower classifier: where it came from, the current status and possible future directions.

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TC Flower Offload

  1. 1. © 2017 NETRONOME SYSTEMS, INC. Simon Horman Netdev 2.2, Seoul TC Flower Offload
  2. 2. © 2017 NETRONOME SYSTEMS, INC. 2 Match-Action Datapath ● Programmable datapaths are new and exciting ● Match-action tables are more static but widely used ● Packets traverse one or more table of match-action rules ○ Classifier seeds flow key ○ Flow key is optionally masked ○ Flow key is used to lookup rules of table ○ If a match is found the actions of the rule are executed ○ Otherwise some fall-through occurs Match Action
  3. 3. © 2017 NETRONOME SYSTEMS, INC. 3 Overview of TC Flower ● TC Flower classifier allows matching packets against pre-defined flow key fields: ○ Packet headers: f.e. IPv6 source address ○ Tunnel metadata: f.e. Tunnel Key ID ○ Metadata: Input port ● TC actions allow packet to be modified, forwarded, dropped, etc… ○ pedit: modify packet data ○ mirred: output packet ○ vlan: push, pop or modify VLAN ○ ...
  4. 4. © 2017 NETRONOME SYSTEMS, INC. 4 Example of TC Flower ● Filter packets recieved on eth0 ● Drop SCTP packets with destination port 80 # tc qdisc add dev eth0 ingress # tc filter add dev eth0 protocol ip parent ffff: flower ip_proto sctp dst_port 80 action drop
  5. 5. © 2017 NETRONOME SYSTEMS, INC. 5 Implementation ● TC Flower makes use of the flow dissector to perform classification ● Resulting flow key is masked ○ Only one mask allowed per priority ● Used to lookup flows ● If a match is found then TC actions of rule are executed ● If not packet processing proceeds to next classifier ○ Standard TC behaviour
  6. 6. © 2017 NETRONOME SYSTEMS, INC. 6 Motivation for Hardware Offload ● Provide greater throughput ● Increase CPU core efficiency and scalability
  7. 7. © 2017 NETRONOME SYSTEMS, INC. 7 History of TC Hardware Offload ● mqprio offload introduced in v2.6.39 ● Introduced ndo_setup_tc ● u32 Classifier offload introduced in v4.6 ● As of v4.15-rc4 BPF, flower and matchall classifier offload also supported ● Netronome NFP driver implements BPF and flower classifier offload ● Actions may be offloaded at discretion of driver
  8. 8. © 2017 NETRONOME SYSTEMS, INC. 8 Hardware Offload Policy ● per-netdev configuration ○ Allow disabling/enabling adding flows to hardware # ethtool -K eth0 hw-tc-offload on # ethtool -K eth0 hw-tc-offload off ● skip_hw and skip_sw flags ○ Allow users to influence placement of flows by kernel ○ Default is to add to hardware and try to add to software ● in_hw and not_in_hw flags ○ Allow kernel to report presence of flow in hardware
  9. 9. © 2017 NETRONOME SYSTEMS, INC. 9 Example of Setting Hardware Policy ● Add flow only to hardware # tc qdisc add dev eth0 ingress # tc filter add dev eth0 protocol ip parent ffff: flower skip_sw ip_proto sctp dst_port 80 action drop
  10. 10. © 2017 NETRONOME SYSTEMS, INC. 10 Example of Viewing Rule in Hardware ● Policy was to only add rule to hardware (skip_sw) ● Rule is present in hardware (in_hw) # tc filter show dev eth0 ingress filter parent ffff: protocol ip pref 49152 flower chain 0 handle 0x1 eth_type ipv4 ip_proto sctp dst_port 80 skip_sw in_hw ...
  11. 11. © 2017 NETRONOME SYSTEMS, INC. 11 Match Enhancements ● IPv6 label and neighbour discovery ● Maskable match of MPLS LSE fields ● GENEVE options
  12. 12. © 2017 NETRONOME SYSTEMS, INC. 12 Conntrack ● Aim would be to allow enhanced rules to be written ○ By taking into account Conntrack state ● Scheme implemented by Open vSwitch datapath is: ○ Conntrack action passes packet to conntrack subsystem ○ Packet is then classified for a second time; conntrack state may form part of flow key Match Action Match Action
  13. 13. © 2017 NETRONOME SYSTEMS, INC. Thank You

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