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Enable PREEMPT_RT

This guide covers how to enable PREEMPT_RT on the Jetson Orin Nano, transforming it into a real-time operating system (RTOS) ready for low-latency robotics applications.

Note

These notes are based on the official NVIDIA Jetson Linux Developer Guide R36.5 - Kernel Customization.

Watch the following video for a complete walkthrough of the process: [YouTube Video Link] (xxx)

1. Verify system performance

Before we jump into the build, let's establish a performance baseline. This helps us see the actual real-time improvement later on.

Check the current kernel

First, let's verify the kernel version and variant currently running on the device.

$ uname -a
# Linux ubuntu 5.15.136-tegra #1 SMP PREEMPT Tue Jan 13 01:23:45 UTC 2026 aarch64 aarch64 aarch64 GNU/Linux

Install stress-test tools

Install the necessary utilities for real-time performance measurement and system stressing.

$ sudo apt update
$ sudo apt upgrade -y

# Install RT and stress testing tools
$ sudo apt install -y rt-tests stress-ng

Run latency tests

To measure the baseline latency, run a stress test in one terminal and the cyclic test in another.

  1. Terminal 1: Start the CPU and I/O stress: 

    $ sudo stress-ng --cpu 8 --io 4 --vm 2 --vm-bytes 1G --timeout 30s

  2. Terminal 2: Run the latency measurement: 

    $ sudo cyclictest --mlockall --smp --priority=80 --interval=200 --duration=10m

Example Output

Latency Test Results

2. Prerequisites

Make sure to have the source code and packages ready before moving forward. Check out Get Ready!

3. Build and enable PREEMPT_RT

Now for the fun part --> building and enabling the patch! We'll use a helper repository to streamline the process.

Download the helper repository and run the script.

Clone the helper repository

$ git clone git@github.com:rylanpeng/jetson-orin-nano-preempt-rt.git

Run the build script

$ cd jetson-orin-nano-preempt-rt
$ ./build-preempt-rt.sh <install-path>

Note

The <install-path> should point to the root directory where the source code was extracted. The script will look for files within <install-path>/Linux_for_Tegra/source/.

4. Verify the installation

Once the script finishes, it's a good idea to double-check that everything was installed correctly.

Inspect the /boot directory

We should see Image.backup and initrd.backup files created alongside the new kernel image.

$ ls /boot
# Image  Image.backup  initrd  initrd.backup  ...

Inspect kernel modules

Check /lib/modules to ensure both the standard and RT versions of the kernel modules are present.

$ ls /lib/modules
# 5.15.136-tegra  5.15.136-rt-tegra

5. Add a fallback boot entry

Edit extlinux.conf

Open the boot configuration file with vim or preferred text editor.

$ sudo vim /boot/extlinux/extlinux.conf

Add the backup entry

Modify the configuration to include a fallback option:

  1. Uncomment the backup section.
  2. Copy the APPEND line from the current default section to the backup section.
  3. Update the INITRD path to point to /boot/initrd.backup.

Example Configuration

LABEL backup
    MENU LABEL backup kernel
    LINUX /boot/Image.backup
    INITRD /boot/initrd.backup
    APPEND ${cbootargs} root=PARTUUID=cb24a353-d890-4252-9751-21d939088c7c rw rootwait rootfstype=ext4 mminit_loglevel=4 console=ttyTCU0,115200 firmware_class.path=/etc/firmware fbcon=map:0 video=efifb:off console=tty0 efi=runtime pci=pcie_bus_perf nvme.use_threaded_interrupts=1 nv-auto-config

6. Reboot

$ sudo reboot

7. Verify the boot selection

During the boot process, we will be presented with the boot menu.

Select the backup entry if you ever need to roll back to the original kernel; otherwise, the system will boot using the new PREEMPT_RT image by default.

8. Verify the results

Check the RT kernel variant

Run uname -a again, and you should see the PREEMPT_RT identifier!

$ uname -a
# Linux ubuntu 5.15.136-rt-tegra #1 SMP PREEMPT_RT Tue Jan 13 01:23:45 UTC 2026 aarch64 aarch64 aarch64 GNU/Linux

Re-run latency tests

Perform the stress test and cyclictest again to observe the improvement in latency.

Example Output

Latency Test Results (RT)

Optimizing performance (Optional)

You can boost performance even further by increasing the kernel timer frequency (CONFIG_HZ).

1. Open defconfig

$ vim Linux_for_Tegra/source/kernel/kernel-jammy-src/arch/arm64/configs/defconfig

2. Update configuration

CONFIG_HZ_1000=y

3. Build and install again

Restore original images

Restore the original Image and initrd before rebuilding. This ensures the script's backup step saves the non-RT kernel as the fallback, not the RT kernel currently in /boot.

$ sudo cp /boot/Image.backup /boot/Image
$ sudo cp /boot/initrd.backup /boot/initrd

Re-run the build script

$ ./build-preempt-rt.sh <install-path>

5. Reboot

Finally, reboot the system to apply the changes.

sudo reboot