Intel Performance Limit Reasons For Linux To Report Why Your CPU Is Downclocking

Intel Performance Limit Reasons (PLR) can indicate why your CPU is downclocking / limited to a lower performance limit for a given core or die. With some Windows utilities this information this Intel CPU feature has been available there while now Intel is bringing PLR support to Linux too.

Intel Performance Limit Reasons can report why the performance/power is being limited at the die level or for individual CPU cores within a die. With a new set of patches today to the Linux kernel mailing list, Intel PLR hardware performance event reporting is being wired up. The information is they conveyed to user-space via DebugFS for administrators to tap into directly or for other applications wanting to know why their CPU performance may be limited.

With the proposed Linux patches for Intel Performance Limit Reasons, the information is conveyed via /sys/kernel/debug/tpmi-*/plr/domain*/status. But as typical with DebugFS, "/sys/kernel/debug/" is typically restricted to software with root/administrator privileges.

With these patches there is a new "INTEL_PLR_TPMI" Kconfig option for gating this Intel PLR driver. Hopefully everything will be in shape for getting it mainlined in Linux v6.11. Those interested in the Intel PLR functionality can find the new driver patches for now on the kernel mailing list.