Linux 6.15.2 significantly fixes a potentially dangerous idle power regression

A critical update to Linux 6.15.2 addresses a regression in idle power

The latest version of Linux, 6.15.2, marks a key milestone in the stability and security of the open-source operating system. The subject of technical debate for several months, this update primarily addresses a regression in idle power that, in certain contexts, could pose a risk to device security and power consumption. In professional or industrial settings, where every watt counts, understanding the implications of this fix is ​​essential. The issue particularly concerns an unexpected increase in power consumption on systems equipped with complex CPU configurations. The fix implemented in Linux 6.15.2 isn’t just a matter of optimization: it becomes strategic to ensure system stability and reliability from the moment it’s updated.

Since the introduction of Linux 6.15, several users and system administrators have noticed a specific anomaly: on certain devices, particularly those with a Simultaneous Multithreading (SMT) configuration, power consumption in idle mode has increased significantly. This phenomenon was initially detected during systematic testing by industry professionals, who alerted the open source community. The regression directly affects the Linux kernel’s power management subsystem, which controls the sleep mode of processor cores to reduce power consumption during periods of inactivity. If this mechanism is compromised, not only does power consumption skyrocket, but it can also open the door to risks of overheating or hardware failure, particularly in critical environments.

Here are some key causes of this regression:

A change to the CPU sleep state manager code, introduced in version 6.15, which reportedly disrupted the power state hierarchy. A problematic interaction with the SMT configuration, particularly on systems booted with the “nosmt” option enabled, which instead forces the CPU to remain in active mode.

• Poor management of the C1 and C10 states, which are essential for achieving minimum idle power consumption, but which are now compromised by this anomaly.
• Main FactorsImpactsModification of the power manager
• Increased idle power consumption

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An expansion of support for configuration options

1. nosmt”, in order to guarantee better management in complex scenarios.Intensive tests, particularly in critical environments, to ensure that power consumption returns to initial expectations.
2. Better documentation and a stricter validation process to avoid the reoccurrence of such regressions in the future.Technical aspectImpact
3. Reverse of problematic commit
4. Immediate reduction in consumption at rest

Security risks must also be considered. Excessive power consumption can lead to overheating, which could damage hardware or compromise the physical security of servers or industrial infrastructure. In an industrial context, where Linux is at the heart of many critical solutions (Industry 4.0, embedded systems, etc.), this issue is becoming a top priority. It is no longer simply a matter of optimizing raw performance, but also of ensuring overall integrity, including energy management.

Update management strategies to avoid reintroducing power regressions

Proactive update management represents the best response to the challenges posed by this regression. The Linux community, with its many contributors, has implemented several key strategies to ensure the long-term stability and security of the operating system. These include:

Automated testing processes, integrating load and power consumption scenarios, ensure complete validation before deployment.

Particular attention to compatibility with various architectures, notably by maintaining a wide range of configuration options, such as “nosmt” mode.

Increased collaboration with hardware stakeholders and suppliers to anticipate power management in different system configurations.

Integration of security measures to quickly detect any anomalies, thereby preventing the propagation of critical bugs in production.

• Management Practices
• ObjectivesTest automationEarly identification of energy performance regressions
• Extensive architecture support
• Prevent risks associated with various hardware configurations