The Nexus 9 has a very powerful processor – a 64-bit Nvidia K1 with 192 graphics cores. This power makes for great experiences, especially gaming, but the device does get warm in the top-left corner. The source code for the Nexus 6 kernel source is available from the AOSP repository, and a number of respected community developers have already released custom kernels which tweak settings to let the system run cooler without affecting performance. They also offer a number of other enhancements controlled by kernel companion apps. The kernel is flashed to a device as part of the boot image.
Get custom kernels
Nexus devices will generally have a selection of custom kernels available. The best place to look is the Original Android Development forum for your device at XDA-Developers.com. Look for kernels uploaded by respected developers such as faux123, flar2 or Franco. If you’re not sure where to start, for this tutorial we used this kernel from faux123.
Flash the custom kernels
Kernels are contained within a boot image and can either be flashed from bootloader using ‘fastboot flash boot filename.img’ or booted for a one-time try using ‘fastboot boot filename.img’. If you’ve decrypted your device, make sure you custom kernel is set to decrypted mode too!
Install the companion app
Many custom kernels have companion apps available from the Play Store, for instance, franco.Kernel updater for Franco’s kernels. Companion apps help you stay up to date with the latest releases and also tweak the settings of the kernel itself, giving a far greater degree of control.
Adjust CPU/GPU clocks
A good way to reduce the device temperature (which will also improve battery life) is by throttling the CPU and GPU clocks. This is best achieved using a kernel companion app if available. Change the values in small increments to find your own optimum settings.