acpicpufreq

acpicpufreq is a Linux kernel module that provides an interface for controlling CPU frequency scaling using the Advanced Configuration and Power Interface (ACPI) standard. It allows the operating system to dynamically adjust the CPU's clock speed and voltage based on system load and power management policies. This dynamic adjustment aims to improve power efficiency and reduce heat generation, especially on laptops and other mobile devices.

The acpicpufreq module interacts with the ACPI CPU object, which exposes the CPU's performance states. These states define various combinations of clock speed and voltage that the CPU can operate at. The module then exposes these performance states to userspace through the sysfs filesystem, typically under the /sys/devices/system/cpu/cpu*/cpufreq/ directory.

Users and system administrators can interact with these sysfs entries to monitor the current CPU frequency, available frequencies, and the current governor. The governor is a policy that dictates how the CPU frequency should be adjusted. Common governors include "performance" (keeps the CPU at its highest frequency), "powersave" (keeps the CPU at its lowest frequency), "ondemand" (switches frequency based on current load), and "conservative" (similar to ondemand but with a more gradual frequency increase).

The primary goal of acpicpufreq is to balance performance needs with power consumption. By reducing CPU speed when it's not fully utilized, systems can conserve energy, extend battery life, and operate more quietly due to less fan activity. Conversely, when demanding tasks are performed, acpicpufreq allows the CPU to ramp up to its maximum frequency to ensure responsiveness.