18. Traffic Metering and Policing API

18.1. Overview

This is the generic API for the Quality of Service (QoS) Traffic Metering and Policing (MTR) of Ethernet devices. This API is agnostic of the underlying HW, SW or mixed HW-SW implementation.

The main features are:

  • Part of DPDK rte_ethdev API
  • Capability query API
  • Metering algorithms: RFC 2697 Single Rate Three Color Marker (srTCM), RFC 2698 and RFC 4115 Two Rate Three Color Marker (trTCM)
  • Policer actions (per meter output color): recolor, drop
  • Statistics (per policer output color)
  • Chaining multiple meter objects
  • Protocol based input color selection

18.2. Configuration steps

The metering and policing stage typically sits on top of flow classification, which is why the MTR objects are enabled through a special “meter” action.

The MTR objects are created and updated in their own name space (rte_mtr) within the librte_ethdev library. Whether an MTR object is private to a flow or potentially shared by several flows has to be specified at its creation time.

Once successfully created, an MTR object is hooked into the RX processing path of the Ethernet device by linking it to one or several flows through the dedicated “meter” flow action. One or several “meter” actions can be registered for the same flow. An MTR object can only be destroyed if there are no flows using it.

18.3. Run-time processing

Traffic metering determines the color for the current packet (green, yellow, red) based on the previous history for this flow as maintained by the MTR object. The policer can do nothing, override the color the packet or drop the packet. Statistics counters are maintained for MTR object, as configured.

The processing done for each input packet hitting an MTR object is:

  • Traffic metering: The packet is assigned a color (the meter output color) based on the previous traffic history reflected in the current state of the MTR object, according to the specific traffic metering algorithm. The traffic metering algorithm can typically work in color aware mode, in which case the input packet already has an initial color (the input color), or in color blind mode, which is equivalent to considering all input packets initially colored as green.
  • There is a meter policy API to manage pre-defined policies for meter. Any rte_flow action list can be configured per color for each policy. A meter object configured with a policy executes the actions per packet according to the packet color.
  • Statistics: The set of counters maintained for each MTR object is configurable and subject to the implementation support. This set includes the number of packets and bytes dropped or passed for each output color.

18.4. API walk-through


Fig. 18.1 Meter components

This section will introduce the reader to the critical APIs to use the traffic meter and policing library.

In general, the application performs the following steps to configure the traffic meter and policing library.

  1. Application gets the meter driver capabilities using rte_mtr_capabilities_get().
  2. The application creates the required meter profiles by using the rte_mtr_meter_profile_add() API function.
  3. The application creates the required meter policies by using the rte_mtr_meter_policy_add() API function.
  4. The application creates a meter object using the rte_mtr_create() API function. One of the previously created meter profile (struct rte_mtr_params::meter_profile_id) and meter policy (struct rte_mtr_params::meter_policy_id) are provided as arguments at this step.
  5. The application enables the meter object execution as part of the flow action processing by calling the rte_flow_create() API function with one of the flow action set to RTE_FLOW_ACTION_TYPE_METER and the associated meter object ID set to this meter object.
  6. The API allows chaining the meter objects to create complex metering topology by the following methods.
    • Adding multiple flow actions of the type RTE_FLOW_ACTION_TYPE_METER to the same flow. Each of the meter action typically refers to a different meter object.
    • Adding one (or multiple) actions of the type RTE_FLOW_ACTION_TYPE_METER to the list of meter actions (struct rte_mtr_meter_policy_params::actions) specified per color as show in Fig. 18.1.
  7. The rte_mtr_meter_profile_get() and rte_mtr_meter_policy_get() API functions are available for getting the object pointers directly. These pointers allow quick access to profile/policy objects and are required by the RTE_FLOW_ACTION_TYPE_METER_MARK action. This action may omit the policy definition to provide flexibility to match a color later with the RTE_FLOW_ITEM_TYPE_METER_COLOR item.

18.5. Protocol based input color selection

The API supports selecting the input color based on the packet content. Following is the API usage model for the same.

  1. Probe the protocol based input color selection device capabilities using the following parameters with rte_mtr_capabilities_get() API.
    • struct rte_mtr_capabilities::input_color_proto_mask;
    • struct rte_mtr_capabilities::separate_input_color_table_per_port
  2. When creating the meter object using rte_mtr_create(), configure relevant input color selection parameters such as
    • Fill the tables struct rte_mtr_params::dscp_table, struct rte_mtr_params::vlan_table based on input color selected.
    • Update the struct rte_mtr_params::default_input_color to determine the default input color in case the input packet does not match the input color method.
  3. Use the following APIs to configure the meter object
    • Select the input protocol color with rte_mtr_color_in_protocol_set() API.
    • If needed, update the input color table at runtime using rte_mtr_meter_vlan_table_update() and rte_mtr_meter_dscp_table_update() APIs.
    • Application can query the configured input color protocol and its associated priority using rte_mtr_color_in_protocol_get() and rte_mtr_color_in_protocol_priority_get() APIs.