We are the Android LLVM toolchain team. One of our top priorities is to improve Android performance through optimization techniques in the LLVM ecosystem. We are constantly searching for ways to make Android faster, smoother, and more efficient. While much of our optimization work happens in userspace, the kernel remains the heart of the system. Today, we’re excited to share how we are bringing Automatic Feedback-Directed Optimization (AutoFDO) to the Android kernel to deliver significant performance wins for users.

What is AutoFDO?

During a standard software build, the compiler makes thousands of small decisions, such as whether to inline a function and which branch of a conditional is likely to be taken, based on static code hints.While these heuristics are useful, they don't always accurately predict code execution during real-world phone usage.

AutoFDO changes this by using real-world execution patterns to guide the compiler. These patterns represent the most common instruction execution paths the code takes during actual use, captured by recording the CPU's branching history. While this data can be collected from fleet devices, for the kernel we synthesize it in a lab environment using representative workloads, such as running the top 100 most popular apps. We use a sampling profiler to capture this data, identifying which parts of the code are 'hot' (frequently used) and which are 'cold'. When we rebuild the kernel with these profiles, the compiler can make much smarter optimization decisions tailored to actual Android workloads.

To understand the impact of this optimization, consider these key facts:

• On Android, the kernel accounts for about 40% of CPU time.
• We are already using AutoFDO to optimize native executables and libraries in the userspace, achieving about 4% cold app launch improvement and a 1% boot time reduction.

Real-World Performance Wins

We have seen impressive improvements across key Android metrics by leveraging profiles from controlled lab environments. These profiles were collected using app crawling and launching, and measured on Pixel devices across the 6.1, 6.6, and 6.12 kernels.

The most noticeable improvements are listed below. Details on the AutoFDO profiles for these kernel versions can be found in the respective Android kernel repositories for