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TCP BBR Quick-Start: Building and Running TCP BBR on Google Compute Engine

Google recently contributed BBR ("Bottleneck Bandwidth and RTT"), a new congestion control algorithm, to the the Linux kernel TCP stack. The commit description in the Linux TCP BBR commit describes the background, motivation, design, and example performance results for BBR.

This tutorial shows how to download, compile, configure, and install a Linux kernel running TCP BBR on Google Compute Engine.

Prerequisites:

Create a Ubuntu LTS 16.04 VM

Let's start by declaring some shell variables relating to your GCE environment:

typeset -x PROJECT="make-tcp-fast"    # A GCE project name
typeset -x ZONE="us-west1-a"          # A GCE Zone

Next, we can create a VM to build the kernel with BBR. This will create a Google Cloud instance to compile our kernel:

gcloud compute \
  instances create "bbrtest1" \
  --project ${PROJECT} --zone ${ZONE} \
  --machine-type "n1-standard-8" \
  --network "default" \
  --maintenance-policy "MIGRATE" \
  --boot-disk-type "pd-standard" \
  --boot-disk-device-name "bbrtest1" \
  --image "/ubuntu-os-cloud/ubuntu-1604-xenial-v20160922" \
  --boot-disk-size "20" \
  --scopes default="https://www.googleapis.com/auth/devstorage.read_only","https://www.googleapis.com/auth/logging.write","https://www.googleapis.com/auth/monitoring.write","https://www.googleapis.com/auth/servicecontrol","https://www.googleapis.com/auth/service.management.readonly"

After creating the instance; log in:

gcloud compute ssh --project ${PROJECT} --zone ${ZONE} bbrtest1

Then, on your GCE instance, use apt(8) to install the packages necessary to build a kernel (answer Y and press Enter when prompted by apt-get):

sudo apt-get update
sudo apt-get build-dep linux
sudo apt-get upgrade

Obtain kernel sources with TCP BBR

TCP BBR is in Linux v4.9 and beyond. However, we recommend compiling from the latest sources, from the networking development branch. In particular, the davem/net-next networking development branch (and Linux v4.20 and beyond) support TCP-level pacing. This means that there is no longer a strict requirement to install the "fq" qdisc to use BBR. Any qdisc will work, though "fq" performs better for highly-loaded servers. (Note that TCP-level pacing was added in v4.13-rc1 but did not work well for BBR until a fix was added in 4.20.)

For this guide, we'll grab the Linux networking development branch davem/net-next from git.kernel.org.

On your GCE instance, use git to clone the Linux sources into /usr/src/net-next and do the configuration and compliation as a mortal (non-root) user:

# Make /usr/src writeable/sticky like /tmp:
cd /usr/src && sudo chmod 1777 .
# Clone a copy of the kernel sources:
git clone git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git
cd /usr/src/net-next

Configure the kernel

If you do not yet have a Linux kernel config for GCE, you can try the config included in this tutorial. On your GCE instance you can download that kernel config and then update that config to select the defaults for any new config options added recently:

cd /usr/src/net-next
wget -O .config https://raw.githubusercontent.com/google/bbr/master/Documentation/config.gce
make olddefconfig

Compile the kernel

Compile the kernel, on your GCE instance:

cd /usr/src/net-next
make prepare
make -j`nproc`
make -j`nproc` modules

Install the kernel and reboot

On your GCE instance, install the newly-compiled kernel and reboot:

cd /usr/src/net-next
sudo make -j`nproc` modules_install install
sudo reboot now

Verify the kernel and configuration

On your GCE instance, confirm that it has booted the kernel we compiled:

uname -a

That should show something like the following, except with a version number and build timestamp matching the kernel you compiled above:

Linux bbrtest1 4.8.0-rc7+ #1 SMP Thu Sep 29 20:06:31 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Finally, on your GCE instance, confirm that BBR is being used:

sysctl net.ipv4.tcp_congestion_control

Enjoy!

Further reading

If you already have a kernel config for GCE, then you can just enable BBR, rebuild, and reboot. On your GCE instance, check that if you run:

cd /usr/src/net-next
egrep '(_BBR)' .config

then you see exactly the following lines:

CONFIG_TCP_CONG_BBR=y
CONFIG_DEFAULT_BBR=y

If you want to create your own .config, then just remember to include those two lines, and follow the kernel/image requirements for GCE.

If you have questions about BBR, check the BBR FAQ.