Sensors, CPU & Fans Control: Difference between revisions

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= CPU Control =
= 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 =
= Potential important kernel modules =

Revision as of 10:04, 18 March 2022

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. 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?).