This repository contains the compiled, modified and built Raspberry Pi Linux kernels for use in this project. Both kernels have multi-core scheduler support enabled, however, one features a fully real-time (preemptable) kernel using the RT patch.
The latest version of Raspberry Pi OS Lite at the time of writing (2024-03-15) uses the 6.6.20 Linux kernel (commit id: 6f16847710cc0502450788b9f12f0a14d3429668). I will be using this kernel along with the RT patch version 6.6.20-rt25 for the RT kernel.
On an Ubuntu VM, install the build dependencies.
sudo apt install git bc bison flex libssl-dev make libc6-dev libncurses5-dev crossbuild-essential-arm64
Download Raspberry Pi Linux sources for 6.6.20, unzip the download, and finally, rename for readability.
wget https://github.com/raspberrypi/linux/archive/6f16847710cc0502450788b9f12f0a14d3429668.zip
unzip 6f16847710cc0502450788b9f12f0a14d3429668.zip
mv linux-6f16847710cc0502450788b9f12f0a14d3429668/ linux/
Apply the default configuration for the Pi 5 (64-bit).
cd linux
KERNEL=kernel_2712
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bcm2712_defconfig
From inside the linux directory, download and apply the RT kernel patch (version 6.6.25 to match the exact kernel version, and only applying to the rt-kernel)
wget https://mirrors.edge.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patch-6.6.20-rt25.patch.gz
gunzip patch-6.6.20-rt25.patch.gz
cat patch-6.6.20-rt25.patch | patch -p1
Build with configs for 64-bit. This step might produce a prompt asking for the preemption type if due to the patch, select the fully preemptable option and enable RCU priority boosting with a 500ms delay boosting (only for fully RT kernel).
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- Image modules dtbs
Kernel configurations using menuconfig on 64-bit.
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
In the menuconfig screen, select the Kernel Features option from the list to open this page, from there enable the Multi-core scheduler support option.
Next, build and install the kernel for 64-bit.
sudo env PATH=$PATH make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- INSTALL_MOD_PATH=. modules_install
Copy all the files from the build directory into the repository directory. Assuming that the build directory is called pi5-kernel-std and the repository directory is on the same level.
sudo cp -n pi5-kernel-std/linux/arch/arm64/boot/Image rpi-kernels/fat32/$KERNEL.img
sudo cp -n pi5-kernel-std/linux/arch/arm64/boot/dts/broadcom/*.dtb rpi-kernels/fat32/
sudo cp -n pi5-kernel-std/linux/arch/arm64/boot/dts/overlays/*.dtb* rpi-kernels/fat32/overlays/
sudo cp -n pi5-kernel-std/linux/arch/arm64/boot/dts/overlays/README rpi-kernels/fat32/overlays/
sudo cp -r -n pi5-kernel-std/linux/lib/* rpi-kernels/ext4/lib/
Before starting the following steps, make note of the Pi's kernel details.
sid@sidpi5:/boot/firmware $ uname -a
Linux sidpi5 6.6.20+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.6.20-1+rpt1 (2024-03-07) aarch64 GNU/Linux
Copy the new kernel files recursively without clobbering so that directories are also copied without overwriting existing files.
sudo cp -r -n rpi-kernels/fat32/* /boot/firmware/
Backup the existing kernel.
sudo cp /boot/firmware/kernel_2712.img /boot/firmware/kernel_2712.img.bkup
Overwrite the existing kernel with the newly built one. Make sure it has been backed up first (complete previous step).
sudo cp rpi-kernels/fat32/kernel_2712.img /boot/firmware/
Copy in the kernel modules recursively and without clobbering existing files.
sudo cp -r -n rpi-kernels/ext4/lib/* /lib/
Update config.txt to select the kernel to boot into.
sid@sidpi5:~ $ sudo nano /boot/firmware/config.txt
# —> at the bottom, add the following: kernel=kernel_2712.img
# —> or for the real-time kernel: kernel=kernel_2712-rt.img
Reboot the Pi and verify that the kernel has been correctly booted.
# Non-RT:
sid@sidpi5:~ $ sudo uname -a
Linux sidpi5 6.6.20-v8-16k #1 SMP PREEMPT Sun Apr 21 18:59:14 BST 2024 aarch64 GNU/Linux
# RT:
sid@sidpi5:~ $ sudo uname -a
Linux sidpi5 6.6.20-rt25-v8-16k #1 SMP PREEMPT_RT Sun Apr 21 17:37:59 BST 2024 aarch64 GNU/Linux