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The Qualcomm® Linux RT kernel is built using the same Yocto toolchain as the standard kernel. The meta-qcom layer provides a dedicated Bitbake recipe that fetches the LTS RT kernel sources, applies the PREEMPT_RT patch set, and enables the required Kconfig options automatically.

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Choose the correct RT recipe

Two RT recipes are available depending on the target branch:
RecipeKernel trackUse when
linux-qcom-rt_6.18.bbLTS 6.18.xBuilding for a QLI release (stable, production-ready)
linux-qcom-next-rt_git.bbqcom-nextBuilding from the latest development tree
Both recipes are in meta-qcom/recipes-kernel/linux/. The LTS recipe is used for all examples on this page.

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Build the RT kernel image

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1. Sync the workspace

Clone meta-qcom at a release tag and sync all Qualcomm Linux meta layers before building. For workspace setup instructions, see Build the kernel with Yocto.

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2. Open the kas shell for the RT kernel

kas shell meta-qcom/ci/qcs6490-rb3gen2-core-kit.yml:meta-qcom/ci/linux-qcom-rt-6.18.yml:meta-qcom/ci/qcom-distro-kvm.yml
Replace qcs6490-rb3gen2-core-kit.yml with the kas machine file for your target board.

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3. Build the image

bitbake qcom-multimedia-image
Build output is in: 
build/tmp/deploy/images/<Machine>/<Image>-*.rootfs.qcomflash/

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4. Flash to the device

cd build/tmp/deploy/images/<Machine>/<Image>-*.rootfs.qcomflash/
fastboot flash efi efi.bin
fastboot flash dtb_a dtb.bin
fastboot reboot

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Customise the RT kernel

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Add a patch

  1. Place the patch file in recipes-kernel/linux/linux-qcom-6.18/: 
    meta-qcom/recipes-kernel/linux/linux-qcom-6.18/your_patch.patch
  2. Append it to SRC_URI in linux-qcom-rt_6.18.bb: 
    SRC_URI += " \
    file://your_patch.patch \
"

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Add a Kconfig configuration fragment

  1. Create a .cfg file with the required CONFIG_* symbols: 
    meta-qcom/recipes-kernel/linux/linux-qcom-6.18/configs/qcom_rt_custom.cfg
    Example contents: 
    CONFIG_CPU_ISOLATION=y
CONFIG_HZ_1000=y
# CONFIG_TRANSPARENT_HUGEPAGE is not set
  2. Append it to SRC_URI in linux-qcom-rt_6.18.bb: 
    SRC_URI += " \
    file://configs/qcom_rt_custom.cfg \
"

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Modify the kernel command line

Add or override command-line parameters in meta-qcom/ci/base.yml using the KERNEL_CMDLINE_EXTRA variable: 
KERNEL_CMDLINE_EXTRA:append: " isolcpus=7 nohz_full=7 rcu_nocbs=7"
For platform-specific command-line tuning variables, set them in meta-qcom/conf/machine/<machine-name>.conf: 
QCOM_RT_CPU        = "7"
QCOM_IRQAFF        = "0-6"
QCOM_RCU_NOCBS     = "7"
QCOM_RCU_EXPEDITED = "1"
QCOM_CPUIDLE_OFF   = "1"
These variables configure the RT core isolation, IRQ affinity, and RCU callback exclusion on the platform kernel command line.

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Verify the RT kernel is installed

After flashing and rebooting, confirm the RT kernel is active: 
uname -r
# Expected: a version string with the -rt suffix, e.g. 6.18.0-rt1+

zcat /proc/config.gz | grep CONFIG_PREEMPT_RT
# Expected: CONFIG_PREEMPT_RT=y
For latency validation after installation, see RT validation and known limitations.