Clang AutoFDO + Propeller Optimization Support Merged For Linux 6.13

Last night when writing about the Clang AutoFDO and Propeller optimization patches sent in for Linux 6.13 I had wondered whether Linus Torvalds would go through with the pull request given some of his past commentary around aggressive compiler optimizations... But to much delight, this evening Linus Torvalds has merged the Kbuild pull request that introduces Clang-based AutoFDO and Propeller compiler optimization support for allowing greater kernel performance out of tailored (profiled) workloads.

Several times Linus Torvalds has expressed reservations around introducing new kernel options for more aggressive compiler optimizations on the basis of producing potentially unsafe code and/or the performance benefits not matching expectations. Like two years ago when Torvalds expressed his latest criticism to -O3 optimizing the Linux kernel. But thankfully he expressed no objections to merging the Clang AutoFDO and Propeller support: the code is now merged via the Kbuild PR for Linux 6.13.

This merge is what now presents the Clang Propeller profile-guided optimizations and Clang Auto Feedback Directed Optimization support.

The Propeller + AutoFDO use does mandate collecting an accurate profile of the intended workloads for the system(s) but the performance benefits can be compelling. As noted yesterday, Google engineers have reported around a 10% uplift to micro-benchmarks or around 5% to larger more realistic workloads.

In any case this Clang Propeller + AutoFDO compiler optimization support is now merged ahead of the Linux 6.13-rc1 kernel release expected tomorrow, 1 December.