My CPU clock speed is changing constantly. Is it normal?

Question

I am running Ubuntu 14.04 on my laptop, and whenever I run

cat /proc/cpuinfo | grep "MHz"

I get varying speeds. I thought that clockspeed is a fixed property, which can be under clocked or overclocked. But is this behaviour normal?

enter image description here

Run `sudo dmidecode | grep "Max Speed"`. But if CPU is overclocked, it won't show correct info. — Pilot6, Jun 19 '15 at 17:55
And please, do not post sceenshots of badly coloured text over transparent backgrounds. Just copy-paste it and save us all the trouble. — muru, Jun 19 '15 at 18:00
This is called "dynamic overclocking". An example is the [Intel® Turbo Boost Technology](https://en.wikipedia.org/wiki/Intel_Turbo_Boost) — Byte Commander, Jun 19 '15 at 18:01

score 3 · Accepted Answer · answered Jun 19 '15 at 17:58

This is what the CPU governor does - observe the usage and adjust frequency accordingly. CPU frequency scaling is a pretty standard technique for power saving. There are tools to manage frequency scaling, cpupower from linux-tools-common is one such.

To look at current governor settings, you can inspect the folders in /sys/devices/system/cpu/cpu*/cpufreq. For example, the available maximum frequency of my CPUs:

$ tail /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_max_freq 
==> /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq <==
3301000

==> /sys/devices/system/cpu/cpu1/cpufreq/cpuinfo_max_freq <==
3301000

==> /sys/devices/system/cpu/cpu2/cpufreq/cpuinfo_max_freq <==
3301000

==> /sys/devices/system/cpu/cpu3/cpufreq/cpuinfo_max_freq <==
3301000

The governor parameters might have a different (lower) maximum value, stored in the corresponding scaling_max_freq files.

My CPU clock speed is changing constantly. Is it normal?

1 Answers1