Intel P-State Getting Energy Efficiency Knob, EPB Knob Change

Intel's P-State CPU frequency scaling driver for Linux systems has been seeing a number of refinements lately including some major changes like shifting towards the "Schedutil" scheduler utilization governor by default. Further tuning with new/changed knobs is also on the way for giving users more control over their CPU power / performance preferences.

One of the new patches sent out on Monday allows for enabling/disabling the "Energy Efficiency Optimization" found on Kaby Lake / Coffee Lake CPUs. The P-State driver to date has been setting the relevant MSR for ensuring the maximum performance potential in hitting the highest performance states. But now P-State is set to offer a "energy_efficiency_enable" node on sysfs that can be enabled to force the more energy efficient CPU mode. Enabling the "Energy Efficiency" mode will help lower power usage and in turn lower heat output and lower power usage, but with the CPU not likely to be running in its highest performance state when needed.

A second patch to P-State changes the "energy_performance_preference" behavior to allow more fine-grained Energy-Performance Preference (EPP) handling. Basically it allows picking between the existing modes with more control than previously possible. It seems this work was driven at least in part for optimizing the Google Chromebook power/performance experience. See the commit message for more details.

If the review on these patches go well, they could see mainline with Linux 5.9.