AFXDP-rs

This module provides a Rust interface for AF_XDP which wraps libbpf built on libbpf-sys.

Author: Dan Siemon <dan@coverfire.com>

AF_XDP (XSK):

• 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 several programs in examples/:

• 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.
• l2fwd-2link-multicore: Multi-core/multi-queue version of l2fwd-2link.
• dump: Receives frames on a single link/queue, parses with Pnet and prints packet.
• rxdrop: Receives packets on one or more links and queues and drops then while counting and printing the packet rate.

You can run with cargo run --release --example <example_name> -- [example options] to see a list of options run cargo run --release --example <example_name> -- --help

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: skew_tick=1 mitigations=off selinux=0 isolcpus=4-27 nohz_full=4-27 rcu_nobcs=4-27 default_hugepagesz=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.

Supported Features

• HUGE TLB flag to mmap area: Optional (command line arg in the sample programs)

Required AF_XDP Features

• Need wakeup flag (implies Linux >= 5.4)
• Aligned chunk mode

Supported AF_XDP Features

• ZEROCOPY flag: Optional (command line arg in the sample programs)
• Aligned chunk mode

Unsupported AF_XDP Features (for now)

• Unaligned chunk mode
• Shared Umem (new in Linux 5.10)
• Busy poll (coming in Linux 5.11)
• Non-zero headroom

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.
• 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.
• A more idiomatic Rust interface could be built by talking directly to the kernel vs. wrapping libbpf functions.
• Investigate if it makes sense to have a non-busy loop interface. This could be useful for tcpdump like applications where it is not ideal to dedicate a core/thread.