AF_XDP Guide#

1. Background#

AF_XDP is an address family that is optimized for high-performance packet processing inside the kernel stack based on BPF and XDP. AF_XDP sockets enable XDP programs to redirect packets to a memory buffer in userspace. DPDK has built-in AF_XDP poll mode driver support. For details, please refer to https://www.kernel.org/doc/HTML/latest/networking/af_xdp.html and https://doc.dpdk.org/guides/nics/af_xdp.html.

By using AF_XDP, the Media Transport Library can leverage the full support of the Linux network stack. However, it’s worth noting that there is a slight performance discrepancy compared to the full DPDK user PMD.

2. DPDK build with AF_XDP PMD#

2.1. Install libxdp and libbpf#

Get latest source code release from libbpf/libbpf and xdp-project/xdp-tools, and follow the instructions to build and install from source. Use “pkg-config –libs libxdp” and “pkg-config –libs libbpf” to check if the packages are correctly installed.

2.2. Rebuild DPDK and and make sure af_xdp pmd driver is built#

Check DPDK/dpdk.

3. Setup#

Below is the command to assign an IP in case no DHCP support in your setup

sudo nmcli dev set enp175s0f0np0 managed no
sudo ifconfig enp175s0f0np0 192.168.108.101/24
sudo nmcli dev set enp175s0f1np1 managed no
sudo ifconfig enp175s0f1np1 192.168.108.102/24

Below is the tuned settings for performance.

echo 2 | sudo tee /sys/class/net/enp175s0f0np0/napi_defer_hard_irqs
echo 200000 | sudo tee /sys/class/net/enp175s0f0np0/gro_flush_timeout
echo 2 | sudo tee /sys/class/net/enp175s0f1np1/napi_defer_hard_irqs
echo 200000 | sudo tee /sys/class/net/enp175s0f1np1/gro_flush_timeout

You may need disable rp_filter for multicast report message.

sudo sysctl -w net.ipv4.conf.all.rp_filter=0

4. Run AF_XDP PMD with root user#

AF_XDP PMD rely on kernel AF_XDP support which need root access, and please refer to dpdk_af_xdp config for how to config the AF_XDP pmd in JSONs config.

Customize the kernel network interface name enp175s0f0np0 as your setup

    "interfaces": [
        {
            "name": "af_xdp:enp175s0f0np0",
        },
        {
            "name": "af_xdp:enp175s0f1np1",
        }
    ],

5. FAQs#

5.1. No IP assigned#

If you see below error while running RxTxApp with AF_XDP JSON, please assign an IP for the port.

st_app_parse_json, using json-c version: 0.13.1
ST: st_socket_get_if_ip, SIOCGIFADDR fail -1 for if enp175s0f0np0
ST: st_user_params_check, get ip fail, if enp175s0f0np0
ST: st_init, st_user_params_check fail -1
main, st_init fail

AF_XDP Guide

Contents