View source for Sensors, CPU & Fans Control

= Sensors =

== CPU temperature ==

* To get CPU temperature, kernel modules are needed. I2C support in particular is generally required (compile '''I2C_CHARDEV''').
* In addition, the correct modules corresponding to your chip should be added in the Hardware Monitoring support and I2C sections. One good technique is to compile everything available, then run '''sensors-detect''', which will find the correct module. Then you can delete all the other modules and rebuild the kernel.
* For a recent Intel Core CPU, compile in the '''SENSORS_CORETEMP''' module (Device Drivers -> Hardware Monitoring support).
* In user space, you need to emerge lm-sensors.
* A KDE widget (plasmoid) is available to display current CPU temperature. You need to emerge ksysguard with the lm_sensors USE flag in order for it to work. It's not very beautiful but functional.

== Fan metrics ==

* lm-sensors is also needed, along with some kernel modules (same procedure as for CPU temperature above).
* You may need to add the '''acpi_enforce_resources=lax''' command-line kernel boot parameter for some ASUS motherboards (like the ROG Strix Z590-I).
* You can then get the current fan RPM by running the '''sensors''' program.

== Asus ==

* On some ASUS motherboards you may need to build the Asus atk0110 ACPI module. You don't need anything else but this module is not detected by sensors-detect; you must load it manually in the configuration file, see below.
* If you use the Asus atk0110 module, enter the following in /etc/conf.d/lm_sensors:

 MODULE_0=asus_atk0110

= Fan Control =

* Fan control is better done in the BIOS. Normally it will allow you to set a fan profile, which associates a given CPU temperature with a given rotation speed. Usually you will want to keep rotation speed low to minimize noise, even if the CPU gets hot. In particular, running the fan at full speed produces a lot of noise at least on Noctua fans.
* CPU temperature should be less than 45 degrees while idling, 75 degrees under normal load, and 95 degrees under heavy load (gaming).

== Pulse-Width Modulation ==

* Modern fans implement this interface, and in theory this makes it possible to control the fan speed from the OS rather than the BIOS. In practice, I think it's hard to do so and I was not able to even obtain metrics via PWM.
* Kernel modules that might be needed for this include Device Drivers -> Pulse-Width Modulation and Device Drivers -> Hardware Monitoring support -> PWM fan.

= CPU Control =

* Modern CPUs implement frequency scaling, which means they run at higher clocks under load and run slower when idle or under light load.
* In the Linux kernel, software support is implemented in the Power management and ACPI options -> CPU frequency scaling sections.

== Intel processors ==

* Modern Intel CPUs (recent Core models) use the P-state driver. [https://www.kernel.org/doc/html/v5.16/admin-guide/pm/intel_pstate.html Documentation is available here.]
* This driver only support two governors: performance and powersave. Building other governors into the kernel is useless, they won't be used.
* The performance governor produces high CPU temperatures that generally send the fans to high speeds, while powersave produces temperatures lower than 50 degrees.
* You can switch the current used governor by using the cpupower program:
 cpupower frequency-set -g powersave
* You can obtain the currently running frequency and used governor by running:
 cat /sys/devices/system/cpu/cpufreq/policy*/scaling_cur_freq
 cat /sys/devices/system/cpu/cpufreq/policy*/scaling_governor

= Potential important kernel modules =

* Some modules in the ACPI section (mostly for CPU frequency scaling).
* Some modules in Device Drivers -> Multifunction device drivers (in particular the Intel LPSS modules?).
* Some modules in Device Drivers -> X86 Platform specific drivers (Intel ones?).