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Advanced usage: Deploy Google BBR congestion control algorithm

Google BBR is a congestion control algorithm that could significantly increase server throughput and reduce latency.

Google BBR has been built into Linux kernel 4.9 and higher, but needs to be manually turned on.

To learn more about the Google BBR algorithm, see this official blog or this official repository.

Prepare

You can check the current Linux kernel version with the command uname -r. When the version is greater than or equal to 4.9, you can deploy BBR directly by referring to the instructions below.

Generally speaking, the kernel versions of Ubuntu 18.04+, Debian 10+, CentOS 8+ and RHEL 8+ are greater than 4.9. But for CentOS 7 or Amazon Linux 2, you need to update the kernel in the following ways before deploying Google BBR.

Amazon Linux 2

Amazon Linux 2 provides newer versions of the verified Linux kernel, which can be installed from the Extras repository.

  1. Install kernel-ng from the Extras repository 
    sudo amazon-linux-extras install kernel-ng
  2. Update packages 
    sudo yum update
  3. Restart the system 
    sudo reboot
  4. Check the Linux kernel version 
    uname -r

CentOS 7

When using CentOS 7, a newer Linux kernel provided by the ELRepo Project needs to be installed. More information about the Linux kernels provided by the ELRepo Project can be found at this page.

Refer to the installation instructions below.

  1. Import ELRepo Project's public key. 
    sudo rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
  2. Install ELRepo for RHEL-7, SL-7 or CentOS-7. 
    sudo yum install https://www.elrepo.org/elrepo-release-7.el7.elrepo.noarch.rpm
  3. Install kernel-ml. 
    sudo yum --enablerepo=elrepo-kernel install kernel-ml
  4. Confirm the result. 
    rpm -qa | grep kernel
    You should see kernel-ml-xxx in output.
  5. Show all entries in the grub2 menu and setup kernel-ml. 
    sudo egrep ^menuentry /etc/grub2.cfg | cut -f 2 -d \'
    Indexing starts at 0.
    For example, when the kernel-ml is located at 1, use the command below to activate kernel-ml. 
    sudo grub2-set-default 1
  6. Reboot. 
    sudo reboot
  7. Check Linux kernel version. 
    uname -r

Deploy Google BBR

In this section, we will start Google BBR by modifying the configuration file.

  1. Backup /etc/sysctl.conf 
    sudo cp /etc/sysctl.conf /etc/sysctl.conf.backup
  2. Modify /etc/sysctl.conf 
    sudo vim /etc/sysctl.conf
    Add the following lines to the file 
    net.core.default_qdisc = fq
net.ipv4.tcp_congestion_control = bbr
  3. Enable Google BBR
    First, check your server's kernel version using uname -r.
    For kernel versions >= 4.20, apply sysctl settings: 
    sudo sysctl -p
    For kernel versions < 4.20, you must reboot the server: 
    sudo reboot
  4. Check Google BBR status 
    sudo sysctl net.ipv4.tcp_available_congestion_control
# net.ipv4.tcp_available_congestion_control = reno cubic bbr
sudo sysctl -n net.ipv4.tcp_congestion_control
# bbr
lsmod | grep bbr
# tcp_bbr  16384  0

Document author

Copyright (C) 2022 Leo Liu
Translated by Lin Song