How to view the CPU frequency scaling policy in Linux

In Linux, understanding your CPU's frequency scaling policy is important for monitoring how your system balances performance and power consumption. The frequency scaling policy determines how your CPU adjusts its clock speed in response to system demand, affecting everything from battery life on a laptop to the performance of high-demand applications on a server.

While there are dedicated tools like cpufreq for managing and viewing CPU frequency scaling, you can also access this information directly through the sysfs interface. The sysfs interface allows users to interact directly with kernel parameters related to CPU performance, providing detailed insights into the current CPU frequency, active scaling governor, and the range of frequencies your CPU can operate within.

This article will guide you through the steps to view the CPU frequency scaling policy on a Linux system using the sysfs interface. This method provides a clear way to monitor and understand how your CPU is configured to manage its speed under different workloads.

1. Ensure the cpufreq driver is loaded by checking available drivers.

   $ lsmod | grep cpufreq
   acpi_cpufreq           20480  0
   intel_pstate           20480  0
   cpufreq_stats          16384  0

   If the output lists drivers like acpi_cpufreq or intel_pstate, the cpufreq driver is loaded and ready for use.

2. Ensure the sysfs interface is accessible.

   $ ls /sys/devices/system/cpu/cpu*/cpufreq/
     /sys/devices/system/cpu/cpu0/cpufreq/
     /sys/devices/system/cpu/cpu1/cpufreq/
     /sys/devices/system/cpu/cpu2/cpufreq/
     /sys/devices/system/cpu/cpu3/cpufreq/

   If the output lists files like scaling_governor and scaling_cur_freq, the interface is available and ready for use.

3. View the active governor for each CPU core.

   $ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
   ondemand
   ondemand
   ondemand
   ondemand

   This command displays the active governor for each CPU core, indicating how the CPU manages its frequency scaling.

4. Check the current CPU frequency.

   $ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq
   1500000
   1500000
   1500000
   1500000

   This command shows the current frequency of each CPU core in kilohertz (kHz), providing real-time insight into the CPU's performance.

5. View the minimum and maximum frequency limits set by the system.

   $ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_min_freq
   1200000
   1200000
   1200000
   1200000
   
   $ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
   3000000
   3000000
   3000000
   3000000

   These commands reveal the range within which the CPU can scale its frequency, helping you understand the boundaries of your CPU's performance capabilities.