Recently, veteran kernel developer Ingo Molnar submitted a huge patch set of 2,297 patches, and named it "Fast Kernel Headers". He said that he started the project at the end of 2020, which is a complete redesign of the Linux kernel's header file hierarchy and header file dependencies, aiming to speed up Linux build times and solve the "dependency hell" problem.
What is "dependency hell"?
Molnar wrote in the patch letter: "Most kernel developers know that there are about 10,000 main .h header files in the Linux kernel, in the include/ and arch/*/include/ levels. Over the past 30+ years , they have grown into a complex and painful set of cross-dependencies that we affectionately call "dependency hell".
This huge patchset decouples many high-level headers from other files, removes unnecessary functions, decouples types and API headers, automatically handles header dependencies, and various other changes, so it's not the same as the current kernel. In comparison, kernel builds with the "Fast Kernel Headers" patch enabled may see a 78% improvement per hour. On supported architectures, absolute kernel build performance is likely to improve by 50-80%.
So far, "Fast Kernel Headers" have been tested on x86/x86_64, SPARC, MIPS and ARM64 architectures.
This huge set of patches covers most of the Linux kernel codebase and speeds up Linux kernel compilation (both clean and incremental builds). It was originally issued as a "comment for comment", and with such a wide range of capabilities for kernel build time improvements, many developers hope that this patchset will make its way into the kernel after it is somehow reviewed in the not too distant future main line.
For more information, please see: https://lkml.org/lkml/2022/1/2/187