ARM Engineer Used LLMs to Find and Fix Major Single-Threaded Bottlenecks, Cutting Linux Kernel Build Times Dramatically

# What happened An ARM Linux engineer, Lorenzo Stoakes, posted a 23-patch series aiming to speed up Linux kernel builds by removing or reducing single-threaded bottlenecks. He used an unnamed large language model to find where the build system got stuck, to propose fixes, and to help run and analyze builds. Stoakes personally audited, heavily edited, and rewrote much of the code the LLM generated before posting the patches.

# Why it matters Kernel builds can be slow because parts of the build system run serially. By parallelizing those hotspots, overall developer iteration time drops. The reported results are substantial: a kernel build with all modules enabled was about 36% faster, incremental builds saw up to 70% speedups, and noop builds improved by roughly 90%.

# What was changed The patch series targets multiple build-system components and tools rather than a single area. Notable targets listed in the announcement are:

• Kbuild (the core kernel build system)
• kallsyms (symbol table generation)
• modpost (post-processing of modules)
• objtool (object-file checks and transformations)
• mksysmap (system map generation)
• Rust build steps (Rust integration in the kernel build)

Each area involved converting or reworking single-threaded stages to allow greater task parallelization and better resource use during builds.

# was validated Stoakes described the LLM as a tool that first identified bottlenecks and then proposed ways to address them. The model produced a large volume of code—"a lot of code, much of it hideous," in Stoakes' words. He audited the outputs, extensively rewrote generated code, and edited commit messages, the cover letter, and comments. The LLM also helped orchestrate build runs, testing, debugging, and analysis, but final correctness and performance verification were done manually.

Because the LLM contributed substantially, each commit in the series carries an Assisted-by tag.

# Results and next steps

The next practical step is review by the wider kernel community. If maintainers accept the changes and they pass review, the patches could be merged into mainline Linux and deliver faster builds to developers across kernels and distributions.

# Practical takeaways for kernel developers and integrators

• Expect shorter iteration cycles on machines that frequently rebuild kernels, especially for incremental and noop compilations.
• Build-system maintainers should examine the 23-patch series for approaches to parallelize other serial phases.
• Review and testing remain essential: generated suggestions still require careful human audit and rewriting before being accepted into the tree.

# Where to find more detail The patch series and its benchmark-linked pages contain the technical details and per-configuration results. Stoakes' public post notes manual correctness checks on both build outputs and running kernels built with the series applied.