Linux 6.15: An energy surprise for some systems

A notable decline in energy performance in Linux 6.15: implications for the open source community

The release of Linux kernel version 6.15 in 2025 has raised high expectations among both developers and end users. However, this milestone has been accompanied by a crucial issue: an unexpected decline in energy performance on some systems. Despite the incremental improvements brought by this update, a bug that occurred late in the development cycle complicated effective power management. These failures particularly affect configurations equipped with specific processors or using certain power management types. Adding to this is the technical complexity reinforced by the diversity of architectures and distributions, such as Ubuntu, Debian, Fedora, and Arch Linux, which all adopt different approaches to optimization. The open source community thus faces the additional challenge of balancing innovation and stability. Discover the improvements made in version 6.15 of our performance regression tool, optimizing data analysis and ensuring more accurate and faster results for your projects.

The technical causes behind the energy regression in Linux 6.15

The causes of this energy regression lie in a recent change made to the Linux kernel, more specifically in x86 processor management. The removal of a key function,

mwait_play_dead_cpuid_hint() , introduced in Linux 6.16, was intended to optimize CPU sleep state management on some Intel systems. However, this operation created a side effect: a substantial increase in the current consumed by processors in idle mode.This phenomenon has been exacerbated on architectures using “nosmt” systems, where CPU core paralysis management is not optimized, resulting in higher permanent energy consumption. The degradation in energy performance is also amplified on platforms like Raspberry Pi, where energy efficiency is a major priority. The decline has manifested itself in an increase of up to 50% in standby power consumption, hampering battery life, particularly on low-power laptops or servers. Factor

Description

Removal of mwait_play_dead_cpuid_hint()	Impact on sleep state management reserved for Intel processors
“nosmt” systems	Inefficient management of CPU cores, increased power consumption
https://www.youtube.com/watch?v=uTFfUaT7chA	This case illustrates the delicate balance between optimization and stability, as every change aimed at improving performance can paradoxically harm power consumption. It also highlights the importance of a thorough testing phase, particularly for integration into various distributions such as Fedora or Manjaro, which often prioritize early testing to avoid negative repercussions.

Concrete consequences for users and system administrators

The repercussions of this regression are palpable in both professional and home environments. Linux users, particularly those using Ubuntu or Debian for their stability and compatibility, have noticed an increase in power consumption without any hardware modifications. Servers hosting websites or databases running Linux have seen their operating costs increase, directly impacting their profitability.

In this context, system administrators must implement corrective measures, including downgrading to an earlier version of the Linux kernel or applying temporary patches. The situation is even more critical for those using solutions like CentOS or OpenSUSE, which play a key role in managing large-scale IT assets.

Temporarily downgrade to Linux 6.14 or earlier

Manually optimize power management using tools like powertop or tlp

Monitor the impact of each update on power consumption
Apply patches available in the upcoming Linux 6.16 patch or later
Consider migrating to modifiable distributions like Arch Linux or Manjaro, which quickly adapt their kernels
It should also be noted that this situation highlights an often underestimated issue in the world of open source software: the balance between raw performance and resource consumption. As energy becomes an increasingly precious resource, development teams are called upon to strengthen their controls and test even the smallest changes.
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Application solutions and current fixes to restore energy performance

Faced with the severity of this regression, the Linux community reacted quickly. The first step is to deploy a patch in Linux 6.16, without any missteps, to regain energy stability. Rafael Wysocki, a power management engineer at Intel, led this task by reverting the problematic commit. This process allows for restoring energy consumption to acceptable levels, particularly for systems using Intel Sierra Forest processors and other affected architectures.

In addition, parallel work is underway to integrate new abstractions into future Rust code, allowing for more precise management of CPU frequency, performance management, and energy consumption. The goal is also to develop adaptive strategies that can automatically reduce power consumption based on running tasks, similar to what some distributions like Fedora or Manjaro offer. Fix

Description

Revert of commit 96040f7273e2

Removal of the function causing the regression, restoration of energy behavior	Introduction of Rust abstractions
Better management of CPUFreq, OPP, and Cpumasks, aimed at dynamic optimization	These solutions illustrate the strength of Linux as an adaptable platform, capable of quickly fixing major bugs such as energy management. The active contribution of developers, particularly through small teams in distributions such as OpenSUSE or community initiatives on GitHub, accelerates the correction process.
https://www.youtube.com/watch?v=hC425RvNMd4	It is also encouraged that users of Raspberry Pi or small, low-power machines stay alert for updates, as they often incorporate tweaks to preserve their energy efficiency. Collaboration between manufacturers, distributors and developers remains crucial in this context of rapid modernization.

Future Outlook: How to Avoid Future Energy Regressions in Linux in 2025

As Linux continues to evolve at a breakneck pace, particularly with the arrival of new ARM, RISC-V or other types of exotic processor architectures, the question of energy stability becomes essential. The technical community must strengthen its testing methods by integrating consumption analysis during QA phases, and not just raw performance.

Performance analysis tools must also evolve to provide accurate monitoring of consumption in real time, helping to quickly detect any drift. For example, the integration of tools like

Linux scheduler fixes

or real-time monitoring of energy states would make it possible to anticipate these problems.

Strategy Description Intensive energy testing in CI/CD

To quickly detect any consumption drift during new versions	Inclusion of consumer analytics
To identify energy anomalies upstream on various architectures such as those of Ubuntu or Fedora	Adoption of modular and scalable distributions
Allowing specific fixes to be quickly integrated depending on the hardware used	Innovation in dynamic energy management
Via advanced abstractions in Rust or C to predict and reduce consumption in real time	In conclusion, the decline in energy performance in Linux 6.15, although short-lived thanks to community efforts, highlights the need to systematically integrate energy management into all phases of kernel development. The rise of devices such as the Raspberry Pi, as well as high-density servers, requires Linux to demonstrate exemplary adaptability to remain the preferred platform for engineers and tech hobbyists in 2025.