Revision and Notes
Date | Owner | Revision | Notes |
|---|---|---|---|
| 1.0 | Initial release | |
Table of Contents | |||
Introduction
The Linux Kernel supports dynamic voltage and frequency switching (DVFS) in order to minimize power usage. Generally, the feature should remain enabled, however, if power consumption and heat dissipation aren't an issue and low latency is required, it might make sense to disable frequency scaling.
Maximum Frequency by SoMs
The maximum frequency to be used depends on the SoC present in the module, see the table below:
Module | Maximum frequency (Hz) |
|---|---|
i.mx6 | 792000 |
i.mx8m plus/mini (Industrial) | 1600000 |
i.mx8m plus/mini (Commercial) | 1800000 |
CPU Frequency
Please Note:
The operation below requires root access.
CPU frequency can be changed by using one of the following methods:
Changing the scaling governor
CPU governors can be viewed as preconfigured power settings for the CPU, for detailed information about governors consult this article.
Available governors can be seen through "scaling_available_governors" file:
root@sr-imx8:/home/debian# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors conservative powersave userspace ondemand performance schedutil
Execute the following command to see current scaling governor:
root@sr-imx8:/home/debian# cat /sys/devices/system/cpu/cpufreq/policy0/scaling_governor ondemand
Execute the following command to change the scaling governor:
echo performance > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
Where performance is the name of the scaling governor.
Changing CPU frequency
Please Note:
CPU frequency can be changed only when the scaling governor is set to userspace.
Available frequencies values can be seen through "scaling_available_frequencies" file:
root@sr-imx8:/home/debian# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies 1200000 1600000 1800000
Execute the following command to see current CPU frequency:
root@sr-imx8:/home/debian# cat /sys/devices/system/cpu/cpufreq/policy0/cpuinfo_cur_freq 1200000
Execute the following command to set CPU frequency:
echo frequency > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed
Where frequency is one of the available CPU frequencies.
Note:
The userspace governor must be set to change the frequency value.
The system will adjust to an appropriate voltage according to frequency. Please note that depending on the board/die temperature, thermal throttling might limit the current frequency in use.
CPUFreq Userspace Tools
The cpufreq userspace tools can be used to achieve the same results as above.
Check the current frequency information:
debian@sr-imx8:~$ cpufreq-info
cpufrequtils 008: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq@vger.kernel.org, please.
analyzing CPU 0:
driver: cpufreq-dt
CPUs which run at the same hardware frequency: 0 1 2 3
CPUs which need to have their frequency coordinated by software: 0 1 2 3
maximum transition latency: 150 us.
hardware limits: 1.20 GHz - 1.80 GHz
available frequency steps: 1.20 GHz, 1.60 GHz, 1.80 GHz
available cpufreq governors: conservative, powersave, userspace, ondemand, performance, schedutil
current policy: frequency should be within 1.20 GHz and 1.80 GHz.
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 1.20 GHz (asserted by call to hardware).
cpufreq stats: 1.20 GHz:98.03%, 1.60 GHz:0.63%, 1.80 GHz:1.34% (394)
analyzing CPU 1:
driver: cpufreq-dt
CPUs which run at the same hardware frequency: 0 1 2 3
CPUs which need to have their frequency coordinated by software: 0 1 2 3
maximum transition latency: 150 us.
hardware limits: 1.20 GHz - 1.80 GHz
available frequency steps: 1.20 GHz, 1.60 GHz, 1.80 GHz
available cpufreq governors: conservative, powersave, userspace, ondemand, performance, schedutil
current policy: frequency should be within 1.20 GHz and 1.80 GHz.
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 1.20 GHz (asserted by call to hardware).
cpufreq stats: 1.20 GHz:98.03%, 1.60 GHz:0.63%, 1.80 GHz:1.34% (394)
analyzing CPU 2:
driver: cpufreq-dt
CPUs which run at the same hardware frequency: 0 1 2 3
CPUs which need to have their frequency coordinated by software: 0 1 2 3
maximum transition latency: 150 us.
hardware limits: 1.20 GHz - 1.80 GHz
available frequency steps: 1.20 GHz, 1.60 GHz, 1.80 GHz
available cpufreq governors: conservative, powersave, userspace, ondemand, performance, schedutil
current policy: frequency should be within 1.20 GHz and 1.80 GHz.
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 1.20 GHz (asserted by call to hardware).
cpufreq stats: 1.20 GHz:98.03%, 1.60 GHz:0.63%, 1.80 GHz:1.34% (394)
analyzing CPU 3:
driver: cpufreq-dt
CPUs which run at the same hardware frequency: 0 1 2 3
CPUs which need to have their frequency coordinated by software: 0 1 2 3
maximum transition latency: 150 us.
hardware limits: 1.20 GHz - 1.80 GHz
available frequency steps: 1.20 GHz, 1.60 GHz, 1.80 GHz
available cpufreq governors: conservative, powersave, userspace, ondemand, performance, schedutil
current policy: frequency should be within 1.20 GHz and 1.80 GHz.
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 1.20 GHz (asserted by call to hardware).
cpufreq stats: 1.20 GHz:98.03%, 1.60 GHz:0.63%, 1.80 GHz:1.34% (394)
Change CPU frequency behavior to userspace:
cpufreq-set -g userspace
Change CPU frequency value by setting the CPU frequency explicitly:
cpufreq-set -f frequency
Where frequency is the desired frequency.
Enable/Disable CPU
Check the number of available CPUs/cores by simply running the following command and hit '1':
root@sr-imx8:/home/debian# top top - 08:57:45 up 18 min, 1 user, load average: 0.00, 0.00, 0.00 Tasks: 127 total, 1 running, 126 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.1 us, 0.1 sy, 0.0 ni, 99.8 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st MiB Mem : 2942.0 total, 2416.9 free, 338.5 used, 186.6 buff/cache MiB Swap: 0.0 total, 0.0 free, 0.0 used. 2530.3 avail Mem
Disable CPU
Directory path to see available CPU devices : /sys/devices/system/cpu
To disable CPU core, execute the following command:
echo 0 > /sys/devices/system/cpu/cpu3/online
Verify whether CPU has been disabled or not by executing TOP utility.
Choose on which one to work when using the previous command by checking the CPU core number:
debian@sr-imx8:~$ ls /sys/devices/system/cpu/ consumers cpu2 hotplug modalias possible smt vulnerabilities cpu0 cpu3 isolated offline power suppliers cpu1 cpufreq kernel_max online present uevent
Enable CPU
To enable CPU which have been disabled above, execute the following:
echo 1 > /sys/devices/system/cpu/cpu3/online
Check the status of enable CPUs by executing TOP utility.