Linux 6.16 RC2 will fix the power regression!
Linux 5.15 was mistakenly shipped with code that caused power regression for non-SMT systems. That is, the systems that boot with the nosmt
option. Since then, this code has been reverted as it could cause serious damage to the computers that use that option, starting from Linux 6.16 RC1 and 6.15.
Now, the patch has been re-introduced to Linux 6.16 RC2. This time, it’s implemented properly to prevent this power regression on non-SMT systems to avoid damages caused by this regression. The code has been fixed, and the below explanation has been provided:
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 by taking them online and back offline when a proper cpuidle driver for the platform has been registered
During initialization, the ACPI processor code needs to rescan the “dead” SMT siblings in a way that prevents leaving them in C1 after initialization. This is by taking those siblings online temporarily while waiting for a proper CPU idle driver to register itself before taking them back off.
Linux 6.16 RC2 will be released today at 9 PM GMT!
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