Running Linux 5.15-rc1 Causing A New Slowdown... Here's A Look

This build speed regression on Linux 5.15 wasn't found to be an Intel-specific issue. On AMD hardware I am also seeing it taking longer in build tests. Below was just some of the further confirmation with a Ryzen 9 5950X. (In those tests it's Linux 5.13 vs. 5.15-rc1 due to a segmentation fault sneaking into Linux 5.14 on this system.)

Slowing down by a few percent isn't good news for developers frequently compiling code and especially for build farms / build servers.

On the "build farm" front, I've also been testing Linux 5.15-rc1 with the AMD EPYC 7763 2P flagship server configuration. Sure enough, even on that server with 256 threads this regression reproduced:

Linux 5.15 on this AMD EPYC 7763 2P server was also showing compilation tests generally taking up to a few percent hit when Linux 5.15 is at play....

Across a wide range of code-bases this regression was seen. Normally within a few percent one might just think it's noise, but the trend was forming for software compilation workloads near universally seeing them all trend lower on Linux 5.15-rc1.

Besides the many C/C++ code-bases tested with various build systems, surprisingly even with compiling the Rust-based Wasmer project for WASM was also seeing Linux 5.15 taking longer.