eBPF Congestion Control

Note: This repository is considered legacy. All current work will be done in the 'trafik' repository.

Dependencies

The provided Vagrantfile should provide everything except for cargo and libbpf-sys. Make sure vmlinux is supported on your kernel version.

Architecture

This project originally stemmed from efforts to implement the CCP project in eBPF by re-implementing libccp in eBPF, though this proved infeasible with verifier restrictions.

Previous attempts have used a userspace libccp hooked to an eBPF program which implemented struct_ops updates, but required a full userspace libccp running process throughout. This implementation removes that layer of indirection, and also implements a generic datapath program that can support a variety of algorithms.

Components

1. eBPF Datapath (ebpf/datapath.bpf.c): Kernel-space BPF program that:

   • Registers as a TCP congestion control algorithm via struct_ops
   • Hooks into TCP stack callbacks
   • Sends measurements and flow events to userspace via ring buffers
   • Receives cwnd updates from userspace via BPF hash map

2. Rust Userspace Daemon (src/main.rs, src/bpf.rs):

   • Loads and attaches the eBPF program using libbpf-rs
   • Polls ring buffers for measurements and flow events
   • Runs CUBIC algorithm logic per-flow
   • Sends cwnd updates back to kernel via BPF maps

3. Algorithm Implementations (src/algorithms):

   • Implement a generic algorithm/runner trait that act as userspace policy.

Running

Note

PLEASE DO NOT RUN THIS OUTSIDE OF A VIRTUAL MACHINE! IT CAN AND MIGHT BREAK YOUR KERNEL IN WAYS I REALLY DON'T WANT TO BE HELD RESPONSIBLE FOR, OKEY?

Once you've got your VM up and running (I built on Ubuntu 24.04) and have all your dependencies satisfied, you can run make all to build both the eBPF and userspace Rust component.

There are three different configurations for testing functionality.

make test-register # Run registration test, succeeds if ebpf-cubic hooks into struct_ops
make test/test-quick # 3-second iperf test
make test-full # 10 second iperf test w/ packet drops

Note

YOU MUST RUN WITH SUDO. IF THE MAKEFILE DOESN'T WORK FOR YOU, RUN THE SCRIPT MANUALLY UNDER SUDO

Troubleshooting

"File exists" error when running tests

make cleanup

Test targets automatically cleanup ebpf daemon on run

Manual cleanup

If the automated cleanup fails, you can manually stop the daemon:

# Find and kill the daemon process
sudo pkill -f ebpf-ccp-cubic

# Verify ebpf_cubic is unregistered
sysctl net.ipv4.tcp_available_congestion_control

Can't build because of cargo stuff

Solution:

rm -rf ~/.cargo/git
rm -rf ~/.cargo/registry

Can't halt VM

Solution:

Still trying to fix this one. I just power the VM off, pray, then restart

This repo was created and written by Alex Khosrowshahi (Brown '27) for research under Professor Akshay Narayan as part of the CCP project. A large part of the code is taken from the ccp-project/generic-cong-avoid repository.