CPU frequency scaling

Related articles
Power saving
Laptop Mode Tools
Undervolting CPU
CPU performance scaling
enables the operating system to scale the CPU frequency up or down in order to save power or improve performance. Scaling can be done automatically in response to system load, adjust itself in response to ACPI events, or be manually changed by user space programs.
The Linux kernel offers CPU performance scaling via the
CPUFreq
subsystem, which defines two layers of abstraction:
Scaling governors
implement the algorithms to compute the desired CPU frequency, potentially based off of the system's needs.
Scaling drivers
interact with the CPU directly, enacting the desired frequencies that the current governor is requesting.
A default scaling driver and governor are selected automatically, but userspace tools like
cpupower
,
acpid
,
Laptop Mode Tools
, or GUI tools provided for your desktop environment, may still be used for advanced configuration.
Userspace tools
i7z
i7z
AUR
is an i7 (and now i3, i5, i7, i9) CPU reporting tool for Linux. It can be launched from a Terminal with the command
i7z
or as GUI with
i7z-gui
.
turbostat
turbostat
can display the frequency, power consumption, idle status and other statistics of the modern Intel and AMD CPUs.
cpupower
cpupower
is a set of userspace utilities designed to assist with CPU frequency scaling. The package is not required to use scaling, but is highly recommended because it provides useful command-line utilities and a
systemd
service to change the governor at boot.
The configuration file for
cpupower
is located in
/etc/default/cpupower-service.conf
. This configuration file is read by a bash script in
/usr/lib/systemd/scripts/cpupower
which is activated by
systemd
with
cpupower.service
. You may want to
enable
cpupower.service
to start at boot.
thermald
thermald
is a
Linux daemon
used to prevent the overheating of Intel CPUs. This daemon proactively controls thermal parameters using P-states, T-states, and the Intel power clamp driver. thermald can also be used for older Intel CPUs. If the latest drivers are not available, then the daemon will revert to x86 model specific registers and the Linux "cpufreq subsystem" to control system cooling.
By default, it monitors CPU temperature using available CPU digital temperature sensors and maintains CPU temperature under control, before hardware takes aggressive correction action. If there is a skin temperature sensor in thermal sysfs, then it tries to keep skin temperature under 45C.
On Tiger Lake laptops (e.g.
Dell Latitude 3420
), this daemon has been reported as
unlocking more performance
than what would be otherwise available.
The associated systemd unit is
thermald.service
, which should be
started
and
enabled
. See
thermald(8)
for more information.
power-profiles-daemon
The
powerprofilesctl
command-line tool from
power-profiles-daemon
handles power profiles (e.g. balanced, power-saver, performance) through the
power-profiles-daemon
service. GNOME and KDE also provide
graphical interfaces
for profile switching; see the following:
GNOME#Power modes
KDE#Power management
See the
project's README
for more information on usage, use cases, and comparisons with similar projects.
Start/enable
the
power-profiles-daemon
service. Note that when
powerprofilesctl
is launched, it also attempts to start the service (see the
unit status
of
dbus.service
).
Note
power-profiles-daemon
conflicts
with other power management services such as
TLP
,
tuned
and
system76-power
AUR
. To use one of the aforementioned services instead without
uninstalling
power-profiles-daemon
(due to its potential status as a dependency), disable the
power-profiles-daemon
service by
masking
it (see also
[1]
,
[2]
).
tuned
offers a
tuned-ppd
service compatibility layer for
power-profiles-daemon
since version 2.23.0.
TLP
also offers a complete compatibility replacement via the
tlp-pd
D-Bus
API since version 1.9.
tuned
tuned
is a daemon for monitoring and adaptive tuning of system devices. It can configure GPU power modes, PCIe power management, set sysctl settings, adjust kernel scheduling and more; a daemon that also configures out aspects of power management in the system.
As of
release 2.23.0
, the project ships with
tuned-ppd
, a compatibility layer for programs written for
power-profiles-daemon
, such as the following:
GNOME#Power modes
KDE#Power management
For reasons why tuned should be used instead of power-profiles-daemon, see Fedora's
proposal
to replace it with tuned. For opposite arguments, see
[3]
.
Start/enable
the
tuned
daemon service. For power-profiles-daemon compatibility, also
start/enable
the
tuned-ppd
service. To control tuned from the command line, use
tuned-adm
to view and set profiles.
Note
tuned-ppd
is configured at
/etc/tuned/ppd.conf
. To set which
tuned
profile is used whenever a program selects a
power-profiles-daemon
profile, edit the file, which includes all the power-profiles-daemon modes and battery detection.
cpupower-gui
cpupower-gui-git
AUR
is a graphical utility designed to assist with CPU frequency scaling. The GUI is based on
GTK
and is meant to provide the same options as
cpupower
.
cpupower-gui
can enable or disable cores and change the maximum/minimum CPU frequency and governor for each core. The application handles privilege granting through
polkit
and allows any logged-in user in the
wheel
user group
to change the frequency and governor. See
cpupower-gui systemd units
for more information on
cpupower-gui.service
and
cpupower-gui-user.service
.
gnome-shell-extension-cpupower
gnome-shell-extension-cpupower-git
AUR
is a
GNOME
shell extension that can alter minimum/maximum CPU frequencies and enable/disable frequency boosting.
auto-cpufreq
auto-cpufreq
AUR
is an automatic CPU speed and power optimizer for Linux based on active monitoring of laptop's battery state, CPU usage, CPU temperature and system load.
nvidia-powerd
The
nvidia-powerd
daemon provides support for
NVIDIA
's Dynamic Boost technology on supported laptop platforms. It acts as a system-wide power controller that dynamically redistributes power between the GPU and CPU based on workload demands, while maintaining the system's total thermal budget.
[4]
Start/enable
the
nvidia-powerd
service, which is provided by the
nvidia-utils
package.
Note
The prerequisites for
nvidia-powerd
are: NVIDIA Ampere (or newer) GPU, Intel Comet Lake (or newer) or AMD Renoir (or newer) chipset, and firmware-level Dynamic Boost support (verify with
nvidia-settings -q DynamicBoostSupport
( nvidia-settings relies on the X server exposing the GPU, and will not work properly under Xwayland or Wayland, so this verification is unreliable on Wayland)).
Scaling drivers
Scaling drivers implement controls over frequency scaling by interfacing with the CPU hardware. The driver is the hardware interface that communicates with the governor which dictates policy for generic frequency control.
However
intel_pstate
and
amd_pstate
(active mode) implement their own internal control logic, sometimes bypassing traditional governors.
The ACPI 2.0 standard introduced
power-performance states ("P-states")
), but can also have additional features (such as Hardware-based P-States, which allow the CPU to govern frequency autonomously).
[5]
Note
The kernel automatically selects the appropriate
CPUFreq
driver for the hardware at boot.
scaling_driver
Description
acpi_cpufreq
Utilizes
ACPI power-performance states (P-States)
. This driver also supports the Intel Enhanced SpeedStep (previously supported by the deprecated
speedstep_centrino
module). For AMD Ryzen, it only provides 3 frequency states.
amd_pstate
This driver has three modes corresponding to different degrees of autonomy from the CPU hardware: active, passive, and guided. Kernel 6.5 changed defaults to AMD P-State active (EPP) mode for supported Ryzen systems with CPPC support. However not all systems enable it automatically and server platforms may still default to
acpi_cpufreq
. See
#amd_pstate
for details.
amd_pstate_epp
EPP-based variant of the
amd_pstate
driver used in active mode.
cppc_cpufreq
Based on ACPI's newer CPPC system (see
#Collaborative processor performance control
). Common default on AArch64 systems. Works on modern x86 too, but the
intel_pstate
and
amd_pstate
drivers implement additional hardware-specific features.
intel_cpufreq
Reported
scaling_driver
when
intel_pstate
is in "passive mode"
[6]
.
intel_pstate
Modern frequency scaling driver for Intel processors (Sandy Bridge and newer). It is used automatically for these processors instead of the other drivers below. This driver takes priority over other drivers and is built-in as opposed to being a module. By default,
intel_pstate
will select "Active Mode" if the processor supports hardware-managed P-States (HWP), called Speed Shift Technology (SST) by Intel (Skylake processors and newer). If the processor doesn't support HWP (or if using the
intel_pstate=no_hwp
parameter
) then
intel_pstate
will select "Passive Mode" and the reported
scaling_driver
string will be "
intel_cpufreq
". If you encounter a problem while using this driver, you can revert to
acpi_cpufreq
scaling driver by adding
intel_pstate=disable
to your
Kernel parameters
. See the
intel_pstate
documentation
for more details.
p4_clockmod
CPUFreq driver for Intel Pentium 4/Xeon/Celeron processors which lowers the CPU temperature by skipping clocks. (You probably want to use
speedstep_lib
instead, an internal helper library used by legacy Intel SpeedStep drivers.)
pcc_cpufreq
This driver supports Processor Clocking Control interface by Hewlett-Packard and Microsoft Corporation which is useful on some ProLiant servers.
powernow_k8
CPUFreq driver for K8/K10 Athlon 64/Opteron/Phenom processors. Since Linux 3.7, 'acpi_cpufreq' will automatically be used for more modern AMD CPUs.
speedstep_lib
CPUFreq driver for Intel SpeedStep-enabled processors (mostly Atoms and older Pentiums)
To see a full list of available modules, run:
$ ls /usr/lib/modules/$(uname -r)/kernel/drivers/cpufreq/
To view drivers built-in to the current kernel, query its config:
$ zgrep -E 'CONFIG_X86_(INTEL_PSTATE|AMD_PSTATE|ACPI_CPUFREQ|PCC_CPUFREQ|POWERNOW_K8|P4_CLOCKMOD)=[y]' /proc/config.gz
Load the appropriate module (see
Kernel modules
for details). Once the appropriate cpufreq driver is loaded, detailed information about the CPU(s) can be displayed by running
$ cpupower frequency-info
Setting maximum and minimum frequencies
In some cases, it may be necessary to manually set maximum and minimum frequencies.
To set the maximum clock frequency (
clock_freq
is a clock frequency with units: GHz, MHz):
# cpupower frequency-set -u
clock_freq
To set the minimum clock frequency:
# cpupower frequency-set -d
clock_freq
To set the CPU to run at a specified frequency:
# cpupower frequency-set -f
clock_freq
Note
To adjust for only a single CPU core, append
-c
core_number
.
The governor, maximum and minimum frequencies can be set in
/etc/default/cpupower
.
Alternatively, you can set the frequency manually:
# echo
value
| tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
The available values can be found in
/sys/devices/system/cpu/cpu*/cpufreq/scaling_available_frequencies
or similar.
[7]
Configuring frequency boosting
Some processors support raising their frequency above the normal maximum for a short burst of time, under appropriate thermal conditions. On Intel processors, this is called
Turbo Boost
, and on AMD processors this is called
Turbo-Core
.
Setting via sysfs (intel_pstate)
intel_pstate has a driver-specific interface for prohibiting the processor from entering turbo P-States:
# echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo
Setting via sysfs (other scaling drivers)
For scaling drivers other than
intel_pstate
, if the driver supports boosting, the
/sys/devices/system/cpu/cpufreq/boost
attribute will be present, and can be used to disable/enable boosting.
To disable boosting, run:
# echo 0 > /sys/devices/system/cpu/cpufreq/boost
To enable boosting, run:
# echo 1 > /sys/devices/system/cpu/cpufreq/boost
Setting via x86_energy_perf_policy
On Intel processors,
x86_energy_perf_policy
can also be used to configure Turbo Boost:
# x86_energy_perf_policy --turbo-enable 0
amd_pstate
amd_pstate
has three operation modes: CPPC autonomous (active) mode, CPPC non-autonomous (passive) mode and CPPC guided autonomous (guided) mode.
Officially supported kernels
are built with
CONFIG_X86_AMD_PSTATE_DEFAULT_MODE=3
which means the default for them is the active mode. This can be changed with the
kernel parameter
amd_pstate=active
,
amd_pstate=passive
or
amd_pstate=guided
. To revert to the
acpi_cpufreq
driver, set
amd_pstate=disable
instead.
Active mode
The
active
mode is implemented by
amd_pstate_epp
(Energy Performance Preference) driver. In this mode, the
amd_pstate_epp
driver provides a hint to the hardware when software wants to bias the CPPC firmware towards performance (0x0) or power efficiency (0xff).
Passive mode
The
passive
mode is implemented by the
amd_pstate
driver. In this mode, the driver defines a desired performance based on the current workload, and specifically how much performance degradation can be tolerated without affecting quality of life.
Guided mode
The
guided
mode is implemented by the
amd_pstate
driver. In this mode, the
amd_pstate
driver requests minimum and maximum performance level and the platform autonomously selects a performance level in this range and appropriate to the current workload.
Note
Some motherboards might not enable the required setting in their firmware, leading to a
the _CPC object is not present in SBIOS or ACPI disabled
error. Change
Enable CPPC
, usually found in the
AMD CBS > NBIO > SMU > CPPC
, from
Auto
to
Enabled
, or any similar settings in your UEFI. If they are not present, consult the vendor website for an update, or check if the motherboard has a hidden way to show advanced UEFI options.
Scaling governors
Scaling governors are power schemes determining the desired frequency for the CPU. Some request a constant frequency, others implement algorithms to dynamically adjust according to the system load. The governors included in the kernel are:
Note
Each governor is compatible with any scaling driver, with the exceptions of
intel_pstate
and
amd_pstate
in active mode, which provide pseudo-governors in the form of
powersave
and
performance
. See
#Autonomous frequency scaling
below.
Governor
Description
performance
Run the CPU at the maximum frequency, obtained from
/sys/devices/system/cpu/cpu
X
/cpufreq/scaling_max_freq
.
powersave
Run the CPU at the minimum frequency, obtained from
/sys/devices/system/cpu/cpu
X
/cpufreq/scaling_min_freq
.
userspace
Run the CPU at user specified frequencies, configurable via
/sys/devices/system/cpu/cpu
X
/cpufreq/scaling_setspeed
.
ondemand
Scales the frequency dynamically according to current load. Jumps to the highest frequency and then possibly back off as the idle time increases.
conservative
Scales the frequency dynamically according to current load. Scales the frequency more gradually than ondemand.
schedutil
Scheduler-driven CPU frequency selection
[8]
,
[9]
.
Depending on the scaling driver, one of these governors will be loaded by default:
schedutil
since
Linux 4.9.5
the internal
powersave
governor for Intel and AMD CPUs using the
intel_pstate
and
amd_pstate
driver respectively (see the note above, it is equivalent to
schedutil
).
Warning
Use CPU monitoring tools (for temperatures, voltage, etc.) when changing the default governor.
To activate a particular governor, run:
# cpupower frequency-set -g
governor
Note
To adjust for only a single CPU core, append
-c
core_number
to the command above.
Activating a governor requires that specific
kernel module
(named
cpufreq_
governor
) is loaded. As of kernel 3.4, these modules are loaded automatically.
Alternatively, you can activate a governor on every available CPU manually:
# echo
governor
| tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
Tip
To monitor cpu speed in real time, run:
$ watch cat /sys/devices/system/cpu/cpu[0-9]*/cpufreq/scaling_cur_freq
Tuning the ondemand governor
See the
kernel documentation
for details.
Switching threshold
To set the threshold for stepping up to another frequency:
# echo -n
percent
> /sys/devices/system/cpu/cpufreq/
governor
/up_threshold
To set the threshold for stepping down to another frequency:
# echo -n
percent
> /sys/devices/system/cpu/cpufreq/
governor
/down_threshold
Sampling rate
The sampling rate determines how frequently the governor checks to tune the CPU.
sampling_down_factor
is a tunable that multiplies the sampling rate when the CPU is at its highest clock frequency, thereby delaying load evaluation and improving performance. Allowed values for
sampling_down_factor
are 1 to 100000.  This tunable has no effect on behavior at lower CPU frequencies/loads.
To read the value (default = 1), run:
$ cat /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor
To set the value, run:
# echo -n
value
> /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor
Make changes permanent
Since Linux 5.9, it is possible to set the
cpufreq.default_governor
kernel option.
[10]
To set the desired scaling parameters at boot, configure the
cpupower
utility and enable its systemd service. Alternatively,
systemd-tmpfiles
or
udev
rules can be used.
Autonomous frequency scaling
Both Intel and AMD define a way to have the CPU decide its own speed based on (1) a performance range from the system and (2) a performance/power hint specifying the preference. The fully-autonomous mode is activated when:
amd_pstate
is set to "active"—requires CPPC support in both the CPU
and
BIOS,
intel_pstate
is set to "active"
and
hardware P-state (HWP) is available (i.e. Sandy Bridge and newer)—works out-of-the-box.
The most important feature of active governing is that only two governors appear available,
powersave
and
performance
. They do not work
at all
like their normal counterpart, however: these levels are translated into an
Energy Performance Preference
hint for the CPU's internal governor. As a result, they both provide dynamic scaling, similar to the
schedutil
or
ondemand
generic governors respectively, differing mostly in latency. The
performance
algorithm
should give better power saving functionality than the old ondemand governor
for Intel HWP.
Intel active, non-HWP
The intel-pstate driver has, confusingly, an "active" mode that works without the CPU's active decision. This mode turns on when kernel cmdline forces an "active" mode but HWP is unavailable or disabled. It will still only provide
powersave
and
performance
, but the driver itself does the governing in a way similar to
schedutil
and
performance
(i.e. it stays at the maximum P-state). There is no real benefit to this mode compared to passive intel-pstate.
Setting the EPP
It is possible to select in-between hints with the sysfs interfaces available. The interface is identical between AMD and Intel, where the files
/sys/devices/system/cpu/cpu*/cpufreq/energy_performance_preference
describe the current preference and
/sys/devices/system/cpu/cpu*/cpufreq/energy_performance_available_preferences
providing a list of available preferences. One can also pass a number between 0 (favor performance) and 255 (favor power). A fallback implementation is provided for Intel CPUs without EPP, translating strings to EPB levels (described in next section) but failing on numbers.
x86_energy_perf_policy
supports configuration of EPP hints via the
--hwp-epp
switch on Intel CPUs
only
. It works via direct access of machine-specific registers (MSRs) which differ between Intel and AMD. The program can also restrict the range of HWP frequencies using a range of frequency multipliers.
To enable hardware P-States with
x86_energy_perf_policy(8)
:
# x86_energy_perf_policy -H 1
# x86_energy_perf_policy -U 1
Collaborative processor performance control
The power consumption of modern CPUs is no longer simply dependent on the frequency or voltage setting, as there are modules that can be switched on as needed. Collaborative processor performance control (CPPC) is the P-state replacement provided by ACPI 5.0. Instead of defining a table of static frequency levels, the processor provides many abstract
performance levels
and the operating system selects from these levels. There are two advantages:
There is no longer a limit of 16 P-state entries; a typical CPU provides hundreds of levels to choose from.
The CPU can provide a higher frequency (e.g. boost) for a performance level when certain parts (e.g. vector FPU) is not used.
On the other hand, the flexible frequency breaks frequency-invariant utilization tracking, which is important for fast frequency changes by
schedutil
. A number of vendor-specific methods have been used to make the frequency static under CPPC, with most successes coming from arm64.
cppc_cpufreq
is the generic CPPC scaling driver.
amd_pstate
also uses ACPI CPPC to manage the CPU frequency when the Zen 3 MSR is unavailable – this method, also called "shared memory", has higher latency than MSR.
Intel performance and energy bias hint
The
Intel performance and energy bias hint (EPB)
is an interface provided by Intel CPUs to allow for user space to specify the desired power-performance tradeoff, on a scale of 0 (highest performance) to 15 (highest energy savings). The EPB register is another layer of performance management functioning independently from frequency scaling. It influences how aggressive P-state and C-state selection will be, and informs internal model-specific decision making that affects energy consumption.
Common values and their aliases, as recognized by sysfs and
x86_energy_perf_policy(8)
are:
EPB value
String
0
performance
4
balance-performance
6
normal, default
8
balance-power
15
power
Setting via sysfs
The EPB can be set using a sysfs attribute:
# echo
epb
| tee /sys/devices/system/cpu/cpu*/power/energy_perf_bias
Setting via x86_energy_perf_policy
With
x86_energy_perf_policy
:
# x86_energy_perf_policy --epb
epb
Setting via cpupower
With
cpupower
:
# cpupower set -b
epb_value
Warning
cpupower does not support the string aliases. If given a string, it will silently set the EPB to 0, corresponding to max performance.
Interaction with ACPI events
Users may configure scaling governors to switch automatically based on different ACPI events such as connecting the AC adapter or closing a laptop lid. A quick example is given below; however, it may be worth reading full article on
acpid
.
Events are defined in
/etc/acpi/handler.sh
. If the
acpid
package is installed, the file should already exist and be executable. For example, to change the scaling governor from
performance
to
conservative
when the AC adapter is disconnected and change it back if reconnected:
/etc/acpi/handler.sh
[...]

ac_adapter)
    case "$2" in
        AC*)
            case "$4" in
                00000000)
                    echo "conservative" >/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor    
                    echo -n $minspeed >$setspeed
                    #/etc/laptop-mode/laptop-mode start
                ;;
                00000001)
                    echo "performance" >/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
                    echo -n $maxspeed >$setspeed
                    #/etc/laptop-mode/laptop-mode stop
                ;;
            esac
        ;;
        *) logger "ACPI action undefined: $2" ;;
    esac
;;

[...]
Troubleshooting
BIOS frequency limitation
Some CPU and BIOS configurations are unable to reach their maximum frequency or scale to higher frequencies at all. This is most likely caused by BIOS events telling the OS to limit the frequency resulting in
/sys/devices/system/cpu/cpu0/cpufreq/bios_limit
set to a lower value.
Before blaming the BIOS implementation, verify you have not manually set the CPU frequency limits, thermal management preferences, or other relevant options in the BIOS Setup Utility.
On some devices (e.g. IBM/Lenovo Thinkpads), usage with a failing battery (or it removed) coupled with an undersized AC adapter may trigger a BIOS-enforced CPU frequency limit. See
ThinkWiki
.
Warning
CPU frequency limitation is a safety feature of your BIOS and should not need to be bypassed in most cases.
This can seriously damage your hardware: use at your own risk.
[11]
You can tell the kernel to ignore the limitations: set the
processor.ignore_ppc=1
kernel parameter
. For trying this temporarily, change the value in
/sys/module/processor/parameters/ignore_ppc
from
0
to
1
.
Some systems use a different mechanism to limit the CPU frequency when running without battery or an unofficial power adapter. On Intel CPUs, you can manipulate the BD PROCHOT bit in Intel CPUs as explained in
Lenovo ThinkPad T480#CPU stuck at minimum frequency
and
Dell XPS 15 (9560)#General slowness & stuttering
. These steps may also apply to other devices, like Intel-based MacBooks running at the minimum CPU frequency without a battery.
See also
Linux CPUFreq - kernel documentation
Reddit post talking about pstate
Processor boosting control
intel_pstate kernel documentation
amd_pstate kernel documentation
intel_pstate/intel_cpufreq documentation kernel 5.7+