Linux 6.15 faced a critical power regression affecting systems using "nosmt" to disable Hyper-Threading. Discover how Intel engineer Rafael Wysocki resolved the issue in Linux 6.15.2 and 6.16-rc2, optimizing idle power efficiency for enterprise and high-performance computing.
A significant idle power regression was discovered in Linux kernel 6.15, particularly impacting systems using the "nosmt" boot option to disable Simultaneous Multi-Threading (SMT) or Hyper-Threading (HT).
This issue, caused by a problematic patch, led to higher power consumption in idle states—an unacceptable drawback for data centers, cloud servers, and energy-conscious enterprises.
The regression was quickly addressed in two ways:
Linux 6.15.2 – Reverted the faulty patch as an emergency fix.
Linux 6.16 Git (pre-rc2) – Implemented a proper long-term solution with refined CPU power management.
How Intel & Linux Developers Resolved the Issue
Rafael Wysocki, Intel engineer and Linux power management subsystem maintainer, led the fix by:
Re-engineering CPU idle handling to prevent "dead" SMT siblings from lingering in C1 state.
Modifying the Intel Idle driver and ACPI processor code to properly rescan inactive CPU threads.
Ensuring stable power efficiency while maintaining SMT-disabled functionality.
"Eliminate mwait_play_dead_cpuid_hint() again after reverting its elimination during the 6.16 merge window due to a problem with handling 'dead' SMT siblings, but this time prevent leaving them in C1 after initialization."
– Rafael Wysocki
This fix not only restores power efficiency but also optimizes enterprise server performance—critical for cloud computing, virtualization, and high-performance computing (HPC).
Why This Fix Matters for Enterprise & High-CPC Niches
This update is crucial for:
✔ Data Centers – Reduced idle power = lower operational costs.
✔ Cloud Hosting Providers – Better SMT-disabled performance for security-focused workloads.
✔ Linux SysAdmins – Avoid unexpected power spikes in production environments.
Final Verdict: A Win for Power Efficiency
The Linux 6.15.2 and 6.16-rc2 updates demonstrate the rapid response of the open-source community to critical performance issues. For businesses relying on Linux-based infrastructure, this fix ensures optimal power management without sacrificing security or performance.
🔍 Want deeper insights? Check the official Linux kernel pull request for full technical details.
FAQ Section (For Additional SEO & Engagement)
Q: Does this affect consumer PCs or just servers?
A: Primarily impacts servers and workstations using "nosmt," but all users should update for stability.
Q: Will this fix improve gaming performance on Linux?
A: Unlikely—this targets idle power efficiency, not active workload performance.
Q: How soon will distros like Ubuntu & RHEL include this patch?
A: Expect backports in stable kernel updates within weeks.
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