Tiny Patch Gets AMD Per-Core Energy Monitoring For Linux's Perf

Exposed via Linux's very versatile perf subsystem has been per-package energy monitoring via the RAPL (Run-Time Average Power Limiting) counters. But AMD's counters also support per-core energy monitoring and now with a tiny kernel patch those sensors too will be exposed via perf.

AMD's Linux perf integration around the power reporting for their processors has mistakenly left out per-core energy monitoring support. With just reworking two lines of code, that power consumption information on a per-core basis will now be exposed to perf.

As with the other CPU power reporting, for security reasons it's limited to root/superviser mode perf execution.

This patch gets the per-core RAPL reporting working under perf with modern AMD Ryzen/EPYC processors.