5. AF_XDP Poll Mode Driver

AF_XDP is an address family that is optimized for high performance packet processing. AF_XDP sockets enable the possibility for XDP program to redirect packets to a memory buffer in userspace.

For the full details behind AF_XDP socket, you can refer to AF_XDP documentation in the Kernel.

This Linux-specific PMD driver creates the AF_XDP socket and binds it to a specific netdev queue, it allows a DPDK application to send and receive raw packets through the socket which would bypass the kernel network stack. Current implementation only supports single queue, multi-queues feature will be added later.

Note that MTU of AF_XDP PMD is limited due to XDP lacks support for fragmentation.

AF_XDP PMD enables need_wakeup flag by default if it is supported. This need_wakeup feature is used to support executing application and driver on the same core efficiently. This feature not only has a large positive performance impact for the one core case, but also does not degrade 2 core performance and actually improves it for Tx heavy workloads.

5.1. Options

The following options can be provided to set up an af_xdp port in DPDK.

• iface - name of the Kernel interface to attach to (required);
• start_queue - starting netdev queue id (optional, default 0);
• queue_count - total netdev queue number (optional, default 1);
• pmd_zero_copy - enable zero copy or not (optional, default 0);

5.2. Prerequisites

This is a Linux-specific PMD, thus the following prerequisites apply:

• A Linux Kernel (version > v4.18) with XDP sockets configuration enabled;
• libbpf (within kernel version > v5.1-rc4) with latest af_xdp support installed, User can install libbpf via make install_lib && make install_headers in <kernel src tree>/tools/lib/bpf;
• A Kernel bound interface to attach to;
• For need_wakeup feature, it requires kernel version later than v5.3-rc1;

5.3. Set up an af_xdp interface

The following example will set up an af_xdp interface in DPDK:

--vdev net_af_xdp,iface=ens786f1