50. Event Ethernet Rx Adapter Library

The DPDK Eventdev API allows the application to use an event driven programming model for packet processing. In this model, the application polls an event device port for receiving events that reference packets instead of polling Rx queues of ethdev ports. Packet transfer between ethdev and the event device can be supported in hardware or require a software thread to receive packets from the ethdev port using ethdev poll mode APIs and enqueue these as events to the event device using the eventdev API. Both transfer mechanisms may be present on the same platform depending on the particular combination of the ethdev and the event device.

The Event Ethernet Rx Adapter library is intended for the application code to configure both transfer mechanisms using a common API. A capability API allows the eventdev PMD to advertise features supported for a given ethdev and allows the application to perform configuration as per supported features.

50.1. API Walk-through

This section will introduce the reader to the adapter API. The application has to first instantiate an adapter which is associated with a single eventdev, next the adapter instance is configured with Rx queues that are either polled by a SW thread or linked using hardware support. Finally the adapter is started.

For SW based packet transfers from ethdev to eventdev, the adapter uses a DPDK service function and the application is also required to assign a core to the service function.

50.1.1. Creating an Adapter Instance

An adapter instance is created using rte_event_eth_rx_adapter_create(). This function is passed the event device to be associated with the adapter and port configuration for the adapter to setup an event port if the adapter needs to use a service function.

int err;
uint8_t dev_id;
struct rte_event_dev_info dev_info;
struct rte_event_port_conf rx_p_conf;

err = rte_event_dev_info_get(id, &dev_info);

rx_p_conf.new_event_threshold = dev_info.max_num_events;
rx_p_conf.dequeue_depth = dev_info.max_event_port_dequeue_depth;
rx_p_conf.enqueue_depth = dev_info.max_event_port_enqueue_depth;
err = rte_event_eth_rx_adapter_create(id, dev_id, &rx_p_conf);

If the application desires to have finer control of eventdev port allocation and setup, it can use the rte_event_eth_rx_adapter_create_ext() function. The rte_event_eth_rx_adapter_create_ext() function is passed a callback function. The callback function is invoked if the adapter needs to use a service function and needs to create an event port for it. The callback is expected to fill the struct rte_event_eth_rx_adapter_conf structure passed to it.

If the application desires to control the event buffer size at adapter level, it can use the rte_event_eth_rx_adapter_create_with_params() api. The event buffer size is specified using struct rte_event_eth_rx_adapter_params:: event_buf_size. To configure the event buffer size at queue level, the boolean flag struct rte_event_eth_rx_adapter_params::use_queue_event_buf need to be set to true. The function is passed the event device to be associated with the adapter and port configuration for the adapter to setup an event port if the adapter needs to use a service function.

50.1.2. Event device configuration for service based adapter

When rte_event_eth_rx_adapter_create() or rte_event_eth_rx_adapter_create_with_params() is used for creating adapter instance, rte_event_dev_config::nb_event_ports is automatically incremented and the event device is reconfigured with the additional event port during service initialization. This event device reconfigure logic also increments the rte_event_dev_config::nb_single_link_event_port_queues parameter if the adapter event port config is of type RTE_EVENT_PORT_CFG_SINGLE_LINK.

Application no longer needs to account for the rte_event_dev_config::nb_event_ports and rte_event_dev_config::nb_single_link_event_port_queues parameters required for eth Rx adapter in the event device configuration, when the adapter is created using the above-mentioned APIs.

50.1.3. Adding Rx Queues to the Adapter Instance

Ethdev Rx queues are added to the instance using the rte_event_eth_rx_adapter_queue_add() function. Configuration for the Rx queue is passed in using a struct rte_event_eth_rx_adapter_queue_conf parameter. Event information for packets from this Rx queue is encoded in the ev field of struct rte_event_eth_rx_adapter_queue_conf. The servicing_weight member of the struct rte_event_eth_rx_adapter_queue_conf is the relative polling frequency of the Rx queue and is applicable when the adapter uses a service core function. The applications can configure queue event buffer size in struct rte_event_eth_rx_adapter_queue_conf::event_buf_size parameter.

ev.queue_id = 0;
ev.sched_type = RTE_SCHED_TYPE_ATOMIC;
ev.priority = 0;

queue_config.rx_queue_flags = 0;
queue_config.ev = ev;
queue_config.servicing_weight = 1;
queue_config.event_buf_size = 1024;

err = rte_event_eth_rx_adapter_queue_add(id,
                                        eth_dev_id,
                                        0, &queue_config);

50.1.4. Querying Adapter Capabilities

The rte_event_eth_rx_adapter_caps_get() function allows the application to query the adapter capabilities for an eventdev and ethdev combination. For e.g, if the RTE_EVENT_ETH_RX_ADAPTER_CAP_OVERRIDE_FLOW_ID is set, the application can override the adapter generated flow ID in the event using rx_queue_flags field in struct rte_event_eth_rx_adapter_queue_conf which is passed as a parameter to the rte_event_eth_rx_adapter_queue_add() function.

err = rte_event_eth_rx_adapter_caps_get(dev_id, eth_dev_id, &cap);

queue_config.rx_queue_flags = 0;
if (cap & RTE_EVENT_ETH_RX_ADAPTER_CAP_OVERRIDE_FLOW_ID) {
        ev.flow_id = 1;
        queue_config.rx_queue_flags =
                RTE_EVENT_ETH_RX_ADAPTER_QUEUE_FLOW_ID_VALID;
}

50.1.5. Configuring the Service Function

If the adapter uses a service function, the application is required to assign a service core to the service function as show below.

uint32_t service_id;

if (rte_event_eth_rx_adapter_service_id_get(0, &service_id) == 0)
        rte_service_map_lcore_set(service_id, RX_CORE_ID);

50.1.6. Starting the Adapter Instance

The application calls rte_event_eth_rx_adapter_start() to start the adapter. This function calls the start callbacks of the eventdev PMDs for hardware based eventdev-ethdev connections and rte_service_run_state_set() to enable the service function if one exists.

Note

The eventdev to which the event_eth_rx_adapter is connected needs to be started before calling rte_event_eth_rx_adapter_start().

50.1.7. Getting Adapter Statistics

The rte_event_eth_rx_adapter_stats_get() function reports counters defined in struct rte_event_eth_rx_adapter_stats. The received packet and enqueued event counts are a sum of the counts from the eventdev PMD callbacks if the callback is supported, and the counts maintained by the service function, if one exists. The service function also maintains a count of cycles for which it was not able to enqueue to the event device.

50.1.8. Getting Adapter queue config

The rte_event_eth_rx_adapter_queue_conf_get() function reports flags for handling received packets, event queue identifier, scheduler type, event priority, polling frequency of the receive queue and flow identifier in struct rte_event_eth_rx_adapter_queue_conf.

50.1.9. Set/Get adapter runtime configuration parameters

The runtime configuration parameters of adapter can be set/get using rte_event_eth_rx_adapter_runtime_params_set() and rte_event_eth_rx_adapter_runtime_params_get() respectively. The parameters that can be set/get are defined in struct rte_event_eth_rx_adapter_runtime_params.

50.1.10. Getting and resetting Adapter queue stats

The rte_event_eth_rx_adapter_queue_stats_get() function reports adapter queue counters defined in struct rte_event_eth_rx_adapter_queue_stats. This function reports queue level stats only when queue level event buffer is used otherwise it returns -EINVAL.

The rte_event_eth_rx_adapter_queue_stats_reset function can be used to reset queue level stats when queue level event buffer is in use.

50.1.11. Getting Adapter Instance ID

The rte_event_eth_rx_adapter_instance_get() function reports Rx adapter instance ID for a specified ethernet device ID and Rx queue index.

50.1.12. Interrupt Based Rx Queues

The service core function is typically set up to poll ethernet Rx queues for packets. Certain queues may have low packet rates and it would be more efficient to enable the Rx queue interrupt and read packets after receiving the interrupt.

The servicing_weight member of struct rte_event_eth_rx_adapter_queue_conf is applicable when the adapter uses a service core function. The application has to enable Rx queue interrupts when configuring the ethernet device using the rte_eth_dev_configure() function and then use a servicing_weight of zero when adding the Rx queue to the adapter.

The adapter creates a thread blocked on the interrupt, on an interrupt this thread enqueues the port id and the queue id to a ring buffer. The adapter service function dequeues the port id and queue id from the ring buffer, invokes the rte_eth_rx_burst() to receive packets on the queue and converts the received packets to events in the same manner as packets received on a polled Rx queue. The interrupt thread is affinitized to the same CPUs as the lcores of the Rx adapter service function, if the Rx adapter service function has not been mapped to any lcores, the interrupt thread is mapped to the main lcore.

50.1.13. Rx Callback for SW Rx Adapter

For SW based packet transfers, i.e., when the RTE_EVENT_ETH_RX_ADAPTER_CAP_INTERNAL_PORT is not set in the adapter’s capabilities flags for a particular ethernet device, the service function temporarily enqueues mbufs to an event buffer before batch enqueuing these to the event device. If the buffer fills up, the service function stops dequeuing packets from the ethernet device. The application may want to monitor the buffer fill level and instruct the service function to selectively enqueue packets to the event device. The application may also use some other criteria to decide which packets should enter the event device even when the event buffer fill level is low. The rte_event_eth_rx_adapter_cb_register() function allow the application to register a callback that selects which packets to enqueue to the event device.

50.1.14. Rx event vectorization

The event devices, ethernet device pairs which support the capability RTE_EVENT_ETH_RX_ADAPTER_CAP_EVENT_VECTOR can aggregate packets based on flow characteristics and generate a rte_event containing rte_event_vector whose event type is either RTE_EVENT_TYPE_ETHDEV_VECTOR or RTE_EVENT_TYPE_ETH_RX_ADAPTER_VECTOR. The maximum, minimum vector sizes and timeouts vary based on the device capability and can be queried using rte_event_eth_rx_adapter_vector_limits_get. The Rx adapter additionally might include useful data such as ethernet device port and queue identifier in the rte_event_vector::port and rte_event_vector::queue and mark rte_event_vector::attr_valid as true. The aggregation size and timeout are configurable at a queue level by setting rte_event_eth_rx_adapter_queue_conf::vector_sz, rte_event_eth_rx_adapter_queue_conf::vector_timeout_ns and rte_event_eth_rx_adapter_queue_conf::vector_mp when adding queues using rte_event_eth_rx_adapter_queue_add.

A loop processing rte_event_vector containing mbufs is shown below.

event = rte_event_dequeue_burst(event_dev, event_port, &event,
                                1, 0);
if (!event)
        continue;

switch (ev.event_type) {
case RTE_EVENT_TYPE_ETH_RX_ADAPTER_VECTOR:
case RTE_EVENT_TYPE_ETHDEV_VECTOR:
        struct rte_mbufs **mbufs;

        mbufs = (struct rte_mbufs **)ev[i].vec->mbufs;
        for (i = 0; i < ev.vec->nb_elem; i++) {
                /* Process each mbuf. */
        }
break;
case default:
        /* Handle other event_types. */
}

50.1.15. Rx event vectorization for SW Rx adapter

For SW based event vectorization, i.e., when the RTE_EVENT_ETH_RX_ADAPTER_CAP_INTERNAL_PORT is not set in the adapter’s capabilities flags for a particular ethernet device, the service function creates a single event vector flow for all the mbufs arriving on the given Rx queue. The 20-bit event flow identifier is set to 12-bits of Rx queue identifier and 8-bits of ethernet device identifier. Flow identifier is formatted as follows:

19      12,11            0
+---------+--------------+
| port_id |   queue_id   |
+---------+--------------+