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3.2.3. Tuning CPUfreq Policy and Speed

Once you've chosen an appropriate CPUfreq governor, you can further tune the speed of each CPU using the tunables found in /sys/devices/system/cpu/[cpu ID]/cpufreq/. These tunables are:
  • cpuinfo_min_freq — Shows the CPU's available minimum operating frequency (in KHz).
  • cpuinfo_max_freq — Shows the CPU's available maximum operating frequency (in KHz).
  • scaling_driver — Shows what CPUfreq driver is used to set the frequency on this CPU.
  • scaling_available_governors — Shows the CPUfreq governors available in this kernel. If you wish to use a CPUfreq governor that is not listed in this file, refer to Procedure 3.2, “Enabling a CPUfreq Governor” in Section 3.2.2, “CPUfreq Setup” for instructions on how to do so.
  • scaling_governor — Shows what CPUfreq governor is currently in use. To use a different governor, simply use echo [governor] > /sys/devices/system/cpu/[cpu ID]/cpufreq/scaling_governor (refer to Procedure 3.2, “Enabling a CPUfreq Governor” in Section 3.2.2, “CPUfreq Setup” for more information).
  • cpuinfo_cur_freq — Shows the current speed of the CPU (in KHz).
  • scaling_available_frequencies — Lists available frequencies for the CPU, in KHz.
  • scaling_min_freq and scaling_max_freq — Sets the policy limits of the CPU, in KHz.


    When setting policy limits, you should set scaling_max_freq before scaling_min_freq.
  • affected_cpus — Lists CPUs that require frequency coordination software.
  • scaling_setspeed — Used to change the clock speed of the CPU, in KHz. You can only set a speed within the policy limits of the CPU (as per scaling_min_freq and scaling_max_freq).
To view the current value of each tunable, use cat [tunable]. For example, to view the current speed of cpu0 (in KHz), use:
cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq.
To change the value of each tunable, use echo [value] > /sys/devices/system/cpu/[cpu ID]/cpufreq/[tunable]. For example, to set the minimum clock speed of cpu0 to 360 KHz, use:
echo 360000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq

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