IEEE 802.1Qav

Overview

Credit-based shaping is an alternative scheduling algorithm used in network schedulers to achieve fairness when sharing a limited network resource. Zephyr has support for configuring a credit-based shaper described in the IEEE 802.1Qav-2009 standard. Zephyr does not implement the actual shaper; it only provides a way to configure the shaper implemented by the Ethernet device driver.

Enabling 802.1Qav

To enable 802.1Qav shaper, the Ethernet device driver must declare that it supports credit-based shaping. The Ethernet driver’s capability function must return ETHERNET_QAV value for this purpose. Typically also priority queues ETHERNET_PRIORITY_QUEUES need to be supported.

static enum ethernet_hw_caps eth_get_capabilities(const struct device *dev)
{
        ARG_UNUSED(dev);

        return ETHERNET_QAV | ETHERNET_PRIORITY_QUEUES |
               ETHERNET_HW_VLAN | ETHERNET_LINK_10BASE_T |
               ETHERNET_LINK_100BASE_T;
}

See sam-e70-xplained board Ethernet driver drivers/ethernet/eth_sam_gmac.c for an example.

Configuring 802.1Qav

The application can configure the credit-based shaper like this:

#include <zephyr/net/net_if.h>
#include <zephyr/net/ethernet.h>
#include <zephyr/net/ethernet_mgmt.h>

static void qav_set_status(struct net_if *iface,
                           int queue_id, bool enable)
{
        struct ethernet_req_params params;
        int ret;

        memset(&params, 0, sizeof(params));

        params.qav_param.queue_id = queue_id;
        params.qav_param.enabled = enable;
        params.qav_param.type = ETHERNET_QAV_PARAM_TYPE_STATUS;

        /* Disable or enable Qav for a queue */
        ret = net_mgmt(NET_REQUEST_ETHERNET_SET_QAV_PARAM,
                       iface, &params,
                       sizeof(struct ethernet_req_params));
        if (ret) {
                LOG_ERR("Cannot %s Qav for queue %d for interface %p",
                        enable ? "enable" : "disable",
                        queue_id, iface);
        }
}

static void qav_set_bandwidth_and_slope(struct net_if *iface,
                                        int queue_id,
                                        unsigned int bandwidth,
                                        unsigned int idle_slope)
{
        struct ethernet_req_params params;
        int ret;

        memset(&params, 0, sizeof(params));

        params.qav_param.queue_id = queue_id;
        params.qav_param.delta_bandwidth = bandwidth;
        params.qav_param.type = ETHERNET_QAV_PARAM_TYPE_DELTA_BANDWIDTH;

        ret = net_mgmt(NET_REQUEST_ETHERNET_SET_QAV_PARAM,
                       iface, &params,
                       sizeof(struct ethernet_req_params));
        if (ret) {
                LOG_ERR("Cannot set Qav delta bandwidth %u for "
                        "queue %d for interface %p",
                        bandwidth, queue_id, iface);
        }

        params.qav_param.idle_slope = idle_slope;
        params.qav_param.type = ETHERNET_QAV_PARAM_TYPE_IDLE_SLOPE;

        ret = net_mgmt(NET_REQUEST_ETHERNET_SET_QAV_PARAM,
                       iface, &params,
                       sizeof(struct ethernet_req_params));
        if (ret) {
                LOG_ERR("Cannot set Qav idle slope %u for "
                        "queue %d for interface %p",
                        idle_slope, queue_id, iface);
        }
}