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

As usual when the Linux 5.15 merge window began wrapping up, I set out to dive into its performance to see what is in store for this next version of the kernel and whether there was any regressions or other performance changes worth noting. Linux 5.15 overall has been in good shape for the "-rc1" state except noticing that code compilation workloads were taking longer on multiple Linux 5.15-rc1-running systems than Linux 5.14 or prior. Seeing it across multiple systems and a very real-world regression, it was worth bisecting and looking closer so here are the details.