kernel_cwnd

An eBPF program that modifies the kernel's congestion window (cwnd) based on a user-space-provided value stored in an eBPF map. The modification occurs only if a fallback flag, stored in another eBPF map, is set to true. The user-space program updates these maps using the bpftool map update command.

Getting Started

• make: Build vmlinux.h and the program.
• make load_kernel_cwnd: Attach the hooks and load the program.
• make map.update MAP=CwndMap VAL=00: Update the CwndMap for testing the loaded eBPF program.
• make map.dump MAP=CwndMap: Dump the contents of CwndMap to stdout.
• make unload_kernel_cwnd: Detach the hooks and unload the program.

log_tcp_cwnd

An eBPF program that logs the kernel's congestion window (cwnd) value to the trace pipe whenever a TCP connection is used for an HTTPS request.

Getting Started

• make: Build vmlinux.h and the program.
• make load_log_tcp_cwnd: Attach to the tracepoint and load the program.
• make trace_log_tcp_cwnd: Flush the trace pipe and store new logs in log_tcp_cwnd.log.
• make log_tcp_cwnd.csv: Process log_tcp_cwnd.log and create a CSV file.
• make unload_log_tcp_cwnd: Detach the hooks and unload the program.
• make read_cwnd_map: Demo to read the value of CwndMap in user-space program.

always_update_cwnd

An eBPF program that modifies the kernel's congestion window (cwnd) based on a user-space-provided value stored in an eBPF map. Unlike kernel_cwnd.bpf.c, the update occurs every time. The user-space program updates these maps using the bpftool map update command.

Getting Started

• make: Build vmlinux.h and the program.
• make load_always_update_cwnd: Attach the hooks and load the program.
• make map.update MAP=CwndMap VAL=00: Update the CwndMap for testing the loaded eBPF program.
• make map.dump MAP=CwndMap: Dump the contents of CwndMap to stdout.
• make unload_always_update_cwnd: Detach the hooks and unload the program.

Important Unloading the program is crucial; otherwise, the program and map will persist until the system restarts.

Installation

git clone https://github.com/hyouteki/cwndebpf --depth=1
cd cwndebpf
make setup
git clone --recurse-submodules https://github.com/libbpf/bpftool
cd bpftool/src
make

Dependency

• libbpf-dev
• bpftool
• Clang and LLVM

References

• Learning eBPF - lizrice
• BPF helpers - man