Why kernels android

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These patches can include: Backports and cherry-picks of upstream functionality needed for Android features Features ready for Android devices but still under development upstream for example, Energy Aware Scheduler task placement optimizations. Terms Here are some new terms used in this document to describe the Android common kernel policies.

Feature kernel Kernels that are enhanced with features for the latest Android platform release are called feature kernels. Launch kernel The designated launch kernels can be used for launching devices with a particular Android platform release. Legacy dessert kernel branches Legacy dessert kernels were created to guarantee that new feature development didn't interfere with merging from the Android common kernel. Android platform release Kernel Supported until Android 8.

Android platform release Launch kernels Feature kernels Android 9 android Figure 1. Creating common kernels from android-mainline kernel Notice that the new Android common kernel android Figure 2.

Development phase When it's created, a KMI branch enters the development phase dev in Figure 2 , and is open for feature contributions for the next Android platform release. Stabilization phase When the KMI branch is declared feature complete, it enters the stabilization phase , labeled as stab in Figure 2. Compatibility between kernels The compatibility requirements between kernels in the same LTS family are changing beginning with the new KMI kernels.

Compatibility matrix This table shows the kernel versions supported and tested with each Android platform release. Android platform release Supported kernels for upgrade Supported kernels for launch Android 9 android Common kernel testing The common kernels are tested with several CI systems in addition to downstream testing by vendors.

KernelCI testing KernelCI build-and-boot tests are initiated whenever a new patch is committed to a common kernel branch. Android presubmit and postsubmit testing Presubmit tests are used to prevent failures from being introduced into the common kernels.

But why the middle man? In very simple terms, it makes Android a lot more flexible. Google can worry about creating all of the functionality in Android, but not have to worry about how that is exactly executed on each device. Since there are so many devices that have all sorts of hardware, Google can't worry about providing compatibility and drivers with each device.

It's the manufacturer's job to create the kernel that has all the drivers necessary to make everything work on the device. The kernel, in this regard, is extremely customizable. Not only does the manufacturer have to plug in the necessary drivers to get all of the hardware to work correctly, but there are a lot of variables that they need to set.

They can mess with all sorts of things, such as:. That's great and all, but what can a custom kernel do for you? There are many different custom kernels for virtually every Android device in existence, so you'll have a lot of options to choose from. Depending on your needs, you can pick kernels that are optimized for performance, or ones that are optimized for power savings.

Others have a good balance of both. There are some developers who switch out some drivers with others for varying reasons , or develop their own patches for problems they identify. A lot of developers also try to include upstream Linux kernel patches, or use their own toolkits for compilation. For example, for my Nexus 5, there's one developer who uses his own toolkit, which includes the latest version of GCC, a Linaro toolchain with optimizations specifically for the CPU architecture used, and maximum optimization flags for the compiler.

Developers can even add some additional features from other kernels that don't officially exist for your device. For example, there are some kernels for the Nexus 5 that include the "double tap to wake" feature that first appeared on the LG G2.