CPU settings. How to change the frequency of the processor without utilities and reboot in Linux

Well, what is it for? Maybe you want to save resources. In my case, I use this setting to reduce CPU heat. The maximum frequency on my processor is 2.3 GHz. The minimum allowable frequency is 2.0 GHz. Therefore, I made every core of my processor work within the 2 GHz range. Everything works as before. I don’t feel the difference in speed at all.

We can change our processor settings on the fly!

No reboot required!

Utilities are not required!

Utilities that control the speed of the processor – abstractions that are needed to simplify.

How many cores does your processor have?

We can change the settings for each of our cores! … Individually!

Now where are our settings located? Let’s get a look. Use these commands:

cd /sys/devices/system/cpu/
ls -a
...
.  ..  cpu0  cpu1  cpu2  cpu3  cpufreq  cpuidle  hotplug  isolated  kernel_max  microcode  modalias  offline  online  possible  power  present  smt  uevent  vulnerabilities

I have a four core processor. Therefore, I have four directories: cpu0, cpu1, cpu2, cpu3. As you guessed, these are the directories for each of the cores. Their numbering starts from zero. So, if you have 2 cores, your directories will be called cpu0, cpu1.

There is a lot of information here. There is even about thermal throttling. This thing reduces the performance of your processor when it starts to overheat, thereby protecting it.

We can read about all information files in the technical documentation of the Linux kernel.

Information about the processor, as well as about each of the cores can be viewed through this command:

cat /proc/cpuinfo 

You can see the real-time frequency of the processor cores by this command.

cat /proc/cpuinfo | grep -i mhz
...
cpu MHz		: 1999.788
cpu MHz		: 1999.759
cpu MHz		: 1999.830
cpu MHz		: 1999.759

Try to enter it several times and you will see it.

Now, how can we change the frequency of the cores? Let’s go here:

cd /sys/devices/system/cpu/cpu0/cpufreq/

This is our first core. Let’s see what is in this directory.

ls -a
...
.   affected_cpus  cpuinfo_max_freq  cpuinfo_transition_latency  related_cpus                   scaling_available_governors  scaling_driver    scaling_max_freq  scaling_setspeed
..  bios_limit     cpuinfo_min_freq  freqdomain_cpus             scaling_available_frequencies  scaling_cur_freq             scaling_governor  scaling_min_freq  stats

Let’s first see what frequencies we can set for the first core (and for all the others):

cat scaling_available_frequencies
...
2333000 2000000

This means that my cores support only these frequencies. So, I can choose from two.

There are also these two files that act as limits:

cat cpuinfo_max_freq
...
2333000
_____________________
cat cpuinfo_min_freq
...
2000000

This command allows us to view the frequency on the core in real time:

cat scaling_cur_freq
...
1999835

These files allow us to set our core frequency:

scaling_max_freq
scaling_min_freq

Attention! Here we can choose the options that are in the file scaling_available_frequencies. If you enter something else, it will not work.

Also there is a file:

bios_limit

Probably the Linux kernel takes this information straight from BIOS. So, if you are interested in CPU overclocking, this may be what you need.

Now let’s change the frequency of our core!

echo 2000000 | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq 
echo 2000000 | sudo tee /sys/devices/system/cpu/cpu1/cpufreq/scaling_max_freq 
echo 2000000 | sudo tee /sys/devices/system/cpu/cpu2/cpufreq/scaling_max_freq 
echo 2000000 | sudo tee /sys/devices/system/cpu/cpu3/cpufreq/scaling_max_freq 

This command allows me to set the frequency for all four cores.

Attention! These configuration files are in RAM, so after a reboot, our configuration will disappear!

Therefore, you need to make sure that every time the system boots, this setting takes effect.

How to make settings work on every boot

So, there are many ways, but I did it that way.

  1. I wrote a script:
#!/bin/sh -e
echo 2000000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
echo 2000000 > /sys/devices/system/cpu/cpu1/cpufreq/scaling_max_freq
echo 2000000 > /sys/devices/system/cpu/cpu2/cpufreq/scaling_max_freq
echo 2000000 > /sys/devices/system/cpu/cpu3/cpufreq/scaling_max_freq
exit 0

2. Then i named it as frequencies and put it here:

/usr/sbin/frequencies

3. Then i launched crontab -e as root(it is important):

sudo crontab -e

4. And put there this line:

@reboot /usr/sbin/frequencies

And it works.

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