AFXDP-rs

This module provides a Rust interface for AF_XDP built on libbpf-sys (https://github.com/alexforster/libbpf-sys).

Author: Dan Siemon dan@coverfire.com

AF_XDP:

• https://www.kernel.org/doc/html/latest/networking/af_xdp.html
• https://lwn.net/Articles/750845/

The goals of this crate, in order, are:

1. Correctness
2. Performance
3. Ease of use

Current Status

The API works for my current use cases but I expect it will change to achieve higher performance and better usability.

If you have knowledge of Rust FFI and general Rust unsafe things I would greatly appreciate some help auditing this crate as my experience in this area is limited.

Sample Programs

There are two sample programs in src/bin/:

l2fwd-1link: Receives frames on a single link/queue, swaps the MAC and writes back to the same link/queue. This is roughly like the kernel xdpsock_user.c sample program in l2fwd mode.

l2fwd-2link: Receives frames from two link/queue pairs (separate devices) and forwards the frames to the opposite link.

Performance

Test System:

• Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz
• Single X710 (4 physical 10G ports) (i40e)
• Kernel: 5.4.2-300.fc31.x86_64
• Kernel boot args: skewtick=1 mitigations=off selinux=0 isolcpus=4-27 nohzfull=4-27 rcunobcs=4-27 defaulthugepagesz=1G hugepagesz=1G hugepages=4

Traffic Generator:

• Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz
• Single X710 (4 physical 10G ports) (i40e)
• Traffic goes from one port, through test system and to second port on the same X710
• T-Rex traffic generator (https://trex-tgn.cisco.com/) (DPDK)
• 64-byte UDP packets

Scenario 1: l2fwd-2link on a single core running userspace and NAPI

Small amounts of packet loss starts at about 6.5M PPS unidirectional and 6.0M PPS bi-directionally (3M each direction).

Little effort has been put into optimizing this so I expect there are some easy performance wins.

AF_XDP Features

• HUGE TLB flag: Optional (command line arg in the sample programs)
• ZEROCOPY flag: Optional (command line arg in the sample programs)
• Only the chunked memory mode is supported
• Need wakeup flag is required which implies Linux >= 5.4

To Do

• Currently this module is not 'safe' because Bufs can outlive the memory pool they are associated with. I believe fixing this will require adding an Arc to each Buf. I have not had the time yet to determine the performance impact of this and would appreciate any other ideas.
• Allow more configurability of AF XDP features
• All interactions with the Tx, Rx, fill and completion queues are done with C functions that wrap the inline functions in libbpf. I believe this means that these hot functions cannot be inlined in Rust. In the medium term we should build pure Rust functions so they can be inlined.