Deploy Google BBR on CentOS 7

Loong Chen發表於2018-06-07
GoCentOS

BBR (Bottleneck Bandwidth and RTT) is a new congestion control algorithm which is contributed to the Linux kernel TCP stack by Google. With BBR in place, a Linux server can get significantly increased throughput and reduced latency for connections. Besides, it's easy to deploy BBR because this algorithm requires only updates on the sender side, not in the network or on the receiver side.

In this article, I will show you how to deploy BBR on a CentOS 7 server instance.

Step 1: Upgrade the kernel using the ELRepo RPM repository

In order to use BBR, you need to upgrade the kernel of your CentOS 7 machine to atest kernel(≥4.9.0). You can easily get that done using the ELRepo RPM repository

  • Before the upgrade, you can take a look at the current kernel:

    uname -r
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    This command should output a string which resembles:

    kernel-3.10.0-862.el7.x86_64

    As you see, the current kernel is 3.10.0.

  • Install the ELRepo repo

    rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-3.el7.elrepo.noarch.rpm
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  • Install the latest kernel using the ELRepo repo:

    yum --enablerepo=elrepo-kernel install kernel-ml -y
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  • Confirm the result

    rpm -qa | grep kernel
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    If the installation is successful, you should see kernel-ml-4.17.0-1.el7.elrepo.x86_64 among the output list:

    kernel-3.10.0-862.el7.x86_64
    kernel-ml-4.17.0-1.el7.elrepo.x86_64
    kernel-tools-libs-3.10.0-862.3.2.el7.x86_64
    kernel-3.10.0-862.3.2.el7.x86_64
    kernel-tools-3.10.0-862.3.2.el7.x86_64

    Now, you need to enable the 4.17.0 kernel by setting up the default grub2 boot entry.

  • Show all entries in the grub2 menu

    awk -F\' '$1=="menuentry " {print i++ " : " $2}' /etc/grub2.cfg
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    The result should resemble:

    0 : CentOS Linux 7 Rescue 73af6d633b0a40ceab1e8326f2dd1726 (4.17.0-1.el7.elrepo.x86_64)
    1 : CentOS Linux (4.17.0-1.el7.elrepo.x86_64) 7 (Core)
    2 : CentOS Linux (3.10.0-862.3.2.el7.x86_64) 7 (Core)
    3 : CentOS Linux (3.10.0-862.el7.x86_64) 7 (Core)
    4 : CentOS Linux (0-rescue-f61a3aaf38e24555b5249a9aa4805773) 7 (Core)

    Since the line count starts at 0 and the 4.17.0 kernel entry is on the second line, set the default boot entry as 1:

    grub2-set-default 1
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    Reboot the system:

    reboot
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    You should see the result as below:

    4.17.0-1.el7.elrepo.x86_64

Step 2: Enable BBR

  • In order to enable the BBR algorithm, you need to modify the sysctl configuration as follows:

    echo 'net.core.default_qdisc=fq' | sudo tee -a /etc/sysctl.conf
echo 'net.ipv4.tcp_congestion_control=bbr' | sudo tee -a /etc/sysctl.conf
sudo sysctl -p
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    Now, you can use the following commands to confirm that BBR is enabled:

    sysctl net.ipv4.tcp_available_congestion_control
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    The output should resemble:

    net.ipv4.tcp_available_congestion_control = reno cubic bbr

    Next, verify with:

    sysctl -n net.ipv4.tcp_congestion_control
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    The output should be:

    bbr

    Finally, check that the kernel module was loaded:

    lsmod | grep bbr
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    The output will be similar to:

    tcp_bbr 20480 17

Step 3: Test the network performance enhancement.(optional)

In order to test BBR's network performance enhancement, you can create a file in the web server directory for download, and then test the download speed from a web browser on your desktop machine.

yum install httpd -y
systemctl start httpd.service
firewall-cmd --zone=public --permanent --add-service=http
firewall-cmd --reload
cd /var/www/html
dd if=/dev/zero of=500mb.zip bs=1024k count=500
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Finally, visit the URL http://[your-server-IP]/500mb.zip from a web browser on your desktop computer, and then evaluate download speed.

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