What is the correct way to view your CPU speed on Linux?

Question

I found two commands to output information about my CPU: cat /proc/cpuinfo and lscpu. /proc/cpuinfo shows that my CPU speed is 2.1 Ghz, whereas lspcu says it is 3167 Mhz. Which one is correct?

This is my exact output from cat /proc/cpuinfo about my processor speed:

model name  : Intel(R) Core(TM) i7-4600U CPU @ 2.10GHz

And this is from lscpu:

CPU MHz:               3225.234

(For some reason, lscpu outputs differently every time, varying between 3100 and 3300 MHz)

Answer 1

To see the current speed of each core I do this:

watch -n.1 "grep \"^[c]pu MHz\" /proc/cpuinfo"

Notes:

This does not work on server CPUs such as the Intel Xeon series. On such machines it will show the base frequency only. To show the turbo frequency, you'll need cpupower or turbostat. See @Maxim Egorushkin's answer.

If your watch command does not work with intervals smaller than one second, modify the interval like so:

watch -n1 "grep \"^[c]pu MHz\" /proc/cpuinfo"

This displays the cpu speed of each core in real time.

By running the following command, one or more times, from another terminal one can see the speed change with the above watch command, assuming SpeedStep is enabled (Cool'n'Quiet for AMD).

echo "scale=10000; 4*a(1)" | bc -l &

(This command uses bc to calculate pi to 10000 places.)

Answer 2

For intel i3, i5 and i7 based cpus there is a dedicated tool called i7z that shows current speed for all cpu cores.

From man page (description):

i7z runs the i7z, ncurses based, program without any options. i7z will print out the C-states and temperature for i3, i5 and i7 based Core processors from Intel (including Nehalems, Sandy Bridge and Ivy Bridge).

For ubuntu-based distributions you can install it by issuing this command:

sudo apt-get install i7z

then just run it (tool needs to be run with sudo):

sudo i7z

Answer 3

The Intel Core i7-4600U Processor supports Turbo Boost technology. It has a base frequency of 2.10GHz and a Max Turbo Frequency of 3.30GHz. That means that,

• If you disable the Turbo Boost (in the BIOS setup menu), the CPU will work at 2.10GHz all the time.
• When Turbo Boost is enabled and only one of the cores is working, the CPU will work at a maximum of 3.30GHz.
• If Turbo Boost is enabled and all the cores are working, the CPU will work at 2.10GHz.

Obtaining current frequency

To determine if the Turbo Boost is activated and which is the current frequency, you can use cpupower frequency-info. For instance, for an old Intel Core i5-660 with Turbo Boost enabled, you will get the following.

$ cpupower frequency-info
analyzing CPU 0:
  driver: acpi-cpufreq
  CPUs which run at the same hardware frequency: 0
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency: 10.0 us.
  hardware limits: 1.20 GHz - 3.47 GHz
  available frequency steps: 3.47 GHz, 3.33 GHz, 2.53 GHz, 1.87 GHz, 1.20 GHz
  available cpufreq governors: conservative, ondemand, userspace, powersave, performance
  current policy: frequency should be within 1.20 GHz and 3.47 GHz.
              The governor "ondemand" may decide which speed to use
              within this range.
  current CPU frequency is 1.87 GHz.
  cpufreq stats: 3.47 GHz:82,67%, 3.33 GHz:0,00%, 2.53 GHz:0,00%, 1.87 GHz:0,06%, 1.20 GHz:17,28%  (3)
  boost state support:
    Supported: yes
    Active: yes
    25500 MHz max turbo 4 active cores
    25500 MHz max turbo 3 active cores
    25500 MHz max turbo 2 active cores
    25500 MHz max turbo 1 active cores

Note that the information states the hardware limits (1.20 GHz - 3.47 GHz), the possible frequencies (3.47 GHz, 3.33 GHz, 2.53 GHz, 1.87 GHz, 1.20 GHz) and the current frequency (1.87 GHz). You may find the technical information of these frequencies at the Intel website.

Frequency when TurboBoost is disabled

Note the difference when you run the same command with Turbo Boost disabled: In the boost state support section, the values for Supported and Active are no. Here, the CPU will be at the nominal/minimal value (1.20Ghz) all the time.

$ cpupower frequency-info
analyzing CPU 0:
  driver: acpi-cpufreq
  CPUs which run at the same hardware frequency: 0
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency: 10.0 us.
  hardware limits: 1.20 GHz - 3.47 GHz
  available frequency steps: 3.47 GHz, 3.33 GHz, 2.53 GHz, 1.87 GHz, 1.20 GHz
  available cpufreq governors: conservative, ondemand, userspace, powersave, performance
  current policy: frequency should be within 1.20 GHz and 3.47 GHz.
                  The governor "ondemand" may decide which speed to use
                  within this range.
  current CPU frequency is 1.20 GHz.
  cpufreq stats: 3.47 GHz:40,86%, 3.33 GHz:0,01%, 2.53 GHz:0,06%, 1.87 GHz:0,22%, 1.20 GHz:58,85%  (493)
  boost state support:
    Supported: no
    Active: no
    25500 MHz max turbo 4 active cores
    25500 MHz max turbo 3 active cores
    25500 MHz max turbo 2 active cores
    25500 MHz max turbo 1 active cores

You can disable the Turbo Boost using the BIOS or some Linux options/commands. The kernel support can be enabled/disabled using the /sys/devices/system/cpu/cpufreq/boost file.

Answer 4

CPU frequencies are kept in the kernel but they can be a little "off". You can see them using:

$ cd /sys/devices/system/cpu
$ paste <(cat cpu*/cpufreq/affected_cpus) <(cat cpu*/cpufreq/scaling_cur_freq) | column -s $'\t' -t
0  833914
1  800021
2  800086
3  800029
4  800036
5  800460
6  800118
7  800141

If you don't need to know the CPU #'s a shorter method is simply using:

$ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq
1396354
800058
800050
800024
800005
800017
800001
1392006

Answer 5

To get informations about your CPU type the following command:

dmidecode -t processor | grep -i mhz

Answer 6

cpupower application measures average CPU frequency over specified time intervals (1 second by default).

Average values differ from current instantaneous values from /proc/cpuinfo. Instantaneous values can show the minimum and maximum CPU frequency values, which are quite useful for CPU performance tuning. Average values rarely reach minimum and maximum extremes due to process scheduler migrating threads/processes to other CPU cores to spread heat and wear evenly across all CPU cores (unless threads are pinned to specific cores); they are useful for examining sustained CPU frequencies during long-running (30+ minutes) full loads.

For example, during a workload utilizing half of available CPU cores at 100%, instantaneous core frequencies are everywhere between minimum and maximum, whereas average frequencies are similar and slightly below maximum for all cores. This is the workload used in the examples below.

The following command continuously displays average CPU core frequencies over last 2 seconds (-i2 option):

$ sudo watch -n0 cpupower monitor -i2

Every 0.1s: cpupower monitor -i2    supernova2: Sun Jul 30 01:05:07 2023

    | Mperf              || Idle_Stats
 CPU| C0   | Cx   | Freq  || POLL | C1   | C2   | C3
   0| 60.27| 39.73|  2295||  0.00|  0.00|  0.07| 39.71
   1| 40.35| 59.65|  2295||  0.00|  0.00|  0.00| 59.73
   2| 84.22| 15.78|  2297||  0.00|  0.00|  0.07| 15.71
   3| 16.74| 83.26|  2286||  0.00|  0.00|  0.06| 83.24
   4| 21.42| 78.58|  2286||  0.00|  0.00|  0.00| 78.59
   5| 78.70| 21.30|  2298||  0.00|  0.00|  0.03| 21.27
   6| 99.98|  0.02|  2295||  0.00|  0.00|  0.00|  0.00
   7|  0.47| 99.53|  2262||  0.00|  0.00|  0.06| 99.48
   8| 84.02| 15.98|  2294||  0.00|  0.00|  0.00| 15.97
   9| 16.23| 83.77|  2299||  0.00|  0.00|  0.05| 83.74
  10| 99.98|  0.02|  2295||  0.00|  0.00|  0.00|  0.00
  11|  0.58| 99.42|  2278||  0.00|  0.00|  0.85| 98.55
  12| 99.98|  0.02|  2295||  0.00|  0.00|  0.00|  0.00
  13|  0.15| 99.85|  2278||  0.00|  0.00|  0.01| 99.84
  14| 10.87| 89.13|  2292||  0.00|  0.00|  0.08| 89.06
  15| 89.30| 10.70|  2296||  0.00|  0.00|  0.00| 10.70

instantaneous CPU core frequencies for comparison:

watch -n2 fgrep MHz /proc/cpuinfo

Every 2.0s: fgrep MHz /proc/cpuinfo    supernova2: Sun Jul 30 01:05:33 2023

cpu MHz         : 1600.000
cpu MHz         : 2305.026
cpu MHz         : 2294.830
cpu MHz         : 2305.022
cpu MHz         : 1600.000
cpu MHz         : 2305.033
cpu MHz         : 2305.035
cpu MHz         : 1600.000
cpu MHz         : 2305.026
cpu MHz         : 2318.834
cpu MHz         : 2305.038
cpu MHz         : 2309.039
cpu MHz         : 2000.000
cpu MHz         : 2305.027
cpu MHz         : 1600.000
cpu MHz         : 2305.026

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cpupower application package name depends on Linux distribution (from comments):

• linux-tools-$(uname -r) in Ubuntu.
• kernel-tools in Red Hat.
• linux-cpupower in Debian.

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htop since version 3 displays instantaneous CPU frequency next to CPU utilization at the top. (Open the image in the new tab to view it at 100% scale, if it displays too small.)