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CPU cores

There are two ways to disable/enable CPU cores:

  1. Add 'maxcpus=n' (n being the number of cores you wish to activate), to the kernel command line (the bootargs from U-Boot). E.g. Assuming you are using our latest U-Boot, stop at the U-Boot command line and enter:
=> setenv kernelargs maxcpus=2
  1. To disable/enable cores at kernel runtime: Disable core X:
echo 0 > /sys/devices/system/cpu/cpuX/online

Enable core X:

echo 1 > /sys/devices/system/cpu/cpuX/online

X being the core number you want to enable/disable, and can range from '1' to '(number of actual CPU cores)-1' (cpu0 is always enabled).

To see the active cores, run:

cat /proc/cpuinfo

CPU frequencies

Governors: There are several frequency governors which determine the frequency policy. The default frequency governor is "ondemand", which sets the CPU frequency depending on the current system load. (Note: the default governor is selected in the kernel defconfig. You can choose a different default governor using menuconfig before building the kernel - to reach this setting, go to: CPU Power Management -> CPU Frequency scaling -> Default CPUFreq governor)

To list all available governors:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors

To read about the different governors, see the following page from the Linux documentation: https://github.com/varigit/linux-imx/blob/5.4-2.1.x-imx_var01/Documentation/admin-guide/pm/cpufreq.rst

To set the current governor:

echo GOVERNOR > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

(GOVERNOR being one of the available governors)

Useful commands: To see the available CPU frequencies:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies

To see the current CPU frequency:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq

Common scenarios: 1. Use the default "ondemand" governor and limit the maximum allowed CPU freq. using the following commands:

To see the current maximum allowed CPU frequency:

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq

To set the maximum allowed CPU frequency:

echo FREQ > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq

(FREQ being one of the available CPU frequencies)

  1. Use the "userspace" governor and set the CPU to a specific frequency using the following command:
echo FREQ > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed

(FREQ being one of the available CPU frequencies)