New AMD P-State Driver Headlines The Power Management Updates For Linux 5.17

Written by Michael Larabel in Linux Kernel on 11 January 2022 at 06:00 AM EST. 29 Comments
The power management subsystem updates were sent out yesterday and already mainlined for the in-development Linux 5.17 kernel. Most notable with the power management changes for this new version of the Linux kernel is the introduction of the AMD P-State driver developed in cooperation with Valve for the Steam Deck but stands to help CPU/SoC power efficiency across Zen 2 and newer hardware.

Linux PM/ACPI maintainer Rafael Wysocki of Intel sent in the power management updates yesterday to which Linus Torvalds has already merged them.

By far the most notable change is the new AMD P-State driver as the optional replacement to AMD's longstanding usage of the ACPI CPUFreq driver. For AMD Zen 2 and newer systems having ACPI Collaborative Processor Performance Controls (CPPC) support exposed, AMD P-State can lead to better power efficiency due to more fine grained controls and more informed decision making. Due to depending on CPPC, this driver cannot and will not support older pre-Zen2 processors and the motherboard must also have CPPC support enabled. AMD P-State is most promising for modern AMD mobile and desktop systems including the likes of the Steam Deck. I'll be running some fresh AMD P-State benchmarks in the days ahead for showing how this now-mature driver (prior testing was mixed) compared to ACPI CPUFreq across various systems and with the different frequency scaling governors.

On the Intel side, the power management updates have an important update for Alder Lake mobile to Intel's P-State driver for proper Energy Performance Preference (EPP) handling.

There are also a variety of other fixes and improvements as outlined in the PM pull request.

Rafael also sent in the ACPI updates at the same time. This includes shipping the latest ACPICA code, avoiding of unnecessary or redundant CPU cache flushes during system power management transitions, and a variety of other ACPI related fixes.
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