Linux 5.16's Smorgasbord Of Power Management Changes Land

Written by Michael Larabel in Hardware on 4 November 2021 at 12:00 AM EDT. 7 Comments
Sent in on Tuesday and since merged to the mainline Linux 5.16 code-base were the power management updates and accompanying ACPI and thermal changes.

Intel engineer Rafael Wysocki who oversees the power management / ACPI / thermal subsystem code for the Linux kernel has sent in all of the feature changes. There isn't any one overly exciting change this cycle but a diverse assortment of smaller changes. Below are some of the highlights.

The power management changes for Linux 5.16 include:

- The Energy Model and CPUFreq have gained awareness for inefficient operating performance points. This is an Arm-led change when working to optimize the power and performance of the Google Pixel 4 and discovering that some of the operating performance points (OPPs) were rather inefficient. As a result of removing the inefficient OPPs from the Energy Model, task placement on the efficient CPUs is made more appealing.

- A fix to avoid crashing the kernel by user-space when attempting to restore the system state from a swap partition in use.

A variety of other fixes and code improvements were also included as part of the power management pull. Note that with the Linux 5.16 PM changes nor the previously submitted scheduler changes, there are no items to report when it comes to Intel Alder Lake / hybrid architecture enhancements, particularly around Thread Director or other hybrid handling enhancements. So any further work won't come until at least 5.17 now.

Next up the ACPI updates for Linux 5.16 include:

- The change to avoid flushing caches before entering C3 idle states with AMD Zen CPUs.

- AMD's Mario Limonciello added support for the "Windows 2020" _OSI string that corresponds to Windows 10 version 2004.

- Disassembly support for the NHLT ACPI table.

The thermal changes include:

- Support for saving and restoring the TCC value within the Intel int340x driver for suspend/resume conditions.

- Including the current temperature in Netlink messages when hitting a trip point to avoid useless back-and-forth reading from user-space.

- A new Uniphier NX1 SoC temperature sensor driver.

- Support for changing the cooling device state from user-space has been deprecated along with the user-space governor.
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Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via

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