Building kernel with BBRv2 on VMs

[Shiva Ketabi]

Hi,

I'm trying to build a kernel with BBR-v2 and I have a related question. I started with building on a VM (on KVM), but eventually I should build it on real servers. I was not able to build it successfully on the VM. So I was reading the BBR-dev forum and it seems the .config file may not work for VMs. Is this the case? Does the .config file work for a linux server or is it specifically for GCE?

Best regards,

Shiva Ketabi

[Neal Cardwell]

In my experience the kernel config in the v2alpha distribution works for Google Cloud VMs and Linode VMs, but it may or may not work on other cloud platforms, depending on the exact details.

If you want to build a kernel from the BBR v2alpha branch that supports particular hardware, I would recommend something like the following:

(1) Find the kernel config for the kernel currently running on the hardware in question, using:

cp /boot/config-`uname -r` ~/kernel_src_dir/.config

Then you can transform that into a kernel config that builds BBRv2 and sets it as the default by doing the following:

(2) In the .config file remove the two lines that say:

CONFIG_DEFAULT_CUBIC=y
CONFIG_DEFAULT_TCP_CONG="cubic"

(3) Then in the .config file add lines that say:

CONFIG_TCP_CONG_BBR2=y
# CONFIG_DEFAULT_CUBIC is not set
CONFIG_DEFAULT_BBR2=y
CONFIG_DEFAULT_TCP_CONG="bbr2"

Then you can try building and booting the kernel.

best regards,
neal

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