Bug 924435 – AdminCD: Bad scaling on Intel P/E core Processors

• Product: Gentoo Release Media
• Status: UNCONFIRMED ---

[Description Rahul Sandhu 2024-02-13 17:21:46 UTC]

When using the Gentoo AdminCD (and the minimal InstallCD) with an Intel P/E core Processor from Tiger Lake or later, the kernel configuration causes processors to be placed at the maximum clock speed no matter what the system is doing. This is extremely concerning as in extreme cases (such as in mine), when compiling "heavy" packages such as sys-devel/gcc, the machine will have a *thermal event*, causing the machine to instantly shut off, and the UEFI warning about temperatures.

Reproducible: Always

Steps to Reproduce:
1. Use Gentoo Install/Admin CD on Tiger Lake or above Intel hardware.
Actual Results:  
The CPU's do not scale properly and are stuck to the maximum *turbo boost* clock speed (in my case about 5.6 Ghz)

Expected Results:  
The CPU's should scale up and down as appropriate, with the P (performance) cores clocking down to ~1100Mhz, and the E (efficiency) cores clocking down to ~800Mhz. Here is the output of a machine on idle with a working kernel configuration:
user@carbon ~ $ grep -i mhz /proc/cpuinfo
cpu MHz		: 1100.000
cpu MHz		: 800.000
cpu MHz		: 800.000
cpu MHz		: 800.000
cpu MHz		: 1098.729
cpu MHz		: 1101.113
cpu MHz		: 1100.527
cpu MHz		: 1100.058
cpu MHz		: 1100.000
cpu MHz		: 800.000
cpu MHz		: 1098.086
cpu MHz		: 1101.157
cpu MHz		: 1098.812
cpu MHz		: 800.000
cpu MHz		: 1101.257
cpu MHz		: 800.000
cpu MHz		: 801.190
cpu MHz		: 800.000
cpu MHz		: 800.523
cpu MHz		: 800.000
cpu MHz		: 800.000
cpu MHz		: 800.000
cpu MHz		: 800.000
cpu MHz		: 820.039
cpu MHz		: 800.612
cpu MHz		: 800.000
cpu MHz		: 800.000
cpu MHz		: 800.000
cpu MHz		: 799.621
cpu MHz		: 800.000
cpu MHz		: 800.000
cpu MHz		: 800.000

I do have a working kernel configuration to hand (see attached) that scales up and down properly. My suspicion is that schedutil and pstates are not configured properly for their kernels.

[Comment 1 Rahul Sandhu 2024-02-13 17:27:28 UTC]

Created attachment 884874 [details]
Working Kernel Config

Working kernel config for Linux 6.7.4

[Comment 2 Rahul Sandhu 2024-02-13 17:30:42 UTC]

For users looking to install, I'd advice turning off turbo boost temporarily while using the live media as not to damage your hardware. This can be accomplished with:
  echo 1 >/sys/devices/system/cpu/intel_pstate/no_turbo