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AFXDP-rs

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

Author: Dan Siemon <dan@coverfire.com>

docs.rs

AF_XDP (XSK):

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.