The Linux kernel, the core of Linux systems and distributions worldwide, has encountered a significant hiccup with its latest stable release, version 6.15.

Reports have surfaced of a power regression affecting certain systems, an issue that slipped through the cracks during the final stages of development. This glitch, tied to the “nosmt” (no Simultaneous Multithreading) boot parameter, has raised eyebrows among system administrators and developers who rely on Linux for energy-efficient operations in data centers and personal devices.

According to Phoronix, the Linux 6.15 kernel, which hit stable status recently, inadvertently shipped with a flaw that causes increased power consumption on some hardware configurations. The problem stems from a misstep in handling the nosmt parameter, which disables hyper-threading to mitigate security vulnerabilities or improve performance in specific workloads. When enabled, it appears to disrupt expected power-saving behaviors, leading to higher energy draw than intended.

Unpacking the Technical Misstep

A deeper look into the kernel’s commit history reveals the root of the issue. A specific commit, documented on the official Linux kernel Git repository at git.kernel.org, introduced changes that inadvertently altered how the nosmt parameter interacts with CPU power states. The commit, identified as 70523f335734b0b42f97647556d331edf684c7dc, aimed to refine CPU topology handling but seems to have triggered unintended side effects on power management logic. This has left some systems unable to enter lower power states effectively when hyper-threading is disabled.

This isn’t the first time a Linux kernel update has stumbled over power management. Historically, regressions in this area have sparked heated discussions in the community, as energy efficiency is critical for everything from mobile devices to sprawling server farms. The current issue with Linux 6.15 echoes past challenges, where seemingly minor changes rippled into significant real-world impacts.

Community Response and Fixes in Motion

The Linux community, known for its rapid response to such issues, is already mobilizing. Developers are dissecting the problematic commit to pinpoint where the power management logic went awry. Phoronix notes that early patches are under discussion on mailing lists, with maintainers working to restore expected behavior without compromising the security or performance benefits of the nosmt option.

Meanwhile, system administrators are advised to test the kernel update thoroughly on their hardware before deployment, especially if power efficiency is a priority. For those already affected, reverting to an earlier kernel version or applying temporary workarounds, such as avoiding the nosmt parameter, may be necessary until a stable fix lands.

Broader Implications for Linux Development

This incident underscores the complexity of maintaining a kernel that supports an immense variety of hardware and use cases. Each update, while bringing new features and security enhancements, carries the risk of regressions that can only be caught through extensive testing across diverse environments. The Linux 6.15 power regression serves as a reminder of the delicate balance developers must strike.

As the community works toward a resolution, this episode will likely inform future testing protocols and patch review processes. For now, the focus remains on delivering a corrected kernel build, ensuring that Linux continues to be the reliable, efficient foundation that millions depend on daily.