According to Phoronix, a new patch for the Linux kernel is coming soon that deals with core prioritization problems on Alder Lake CPUs. The issue stems from enabling XMP memory profiles in the UEFI or manually overclocking Alder Lake chips. Doing either of the two causes Linux to put improper workloads on the wrong cores, reducing system performance.
More specifically, it appears that Intel Turbo Boost Max Technology is the main culprit. Linux requires functional Turbo Boost Max code to enable proper core prioritization. However, this code can easily be disabled automatically by the motherboard if it uses an XMP mode or the user enters a custom core overclock.
When Turbo Boost Max is disabled, the ACPI CPPC's highest performance state is applied to all cores. Unfortunately, this causes the operating system to think all cores have the same performance value, leading to performance degradation.
This is a significant problem on Alder Lake chips due to their hybrid architecture that relies on high-performance cores and power efficiency cores to get work done efficiently. When the operating system puts critical tasks on the efficiency cores and light workloads on the performance cores, it'll lead to significant losses in overall performance.
Thankfully a new Linux kernel patch is already being tested to fix these issues. Once released, overclocking Alder Lake CPUs will no longer cause the OS's core prioritization to bug out.