CPU frequency scaling (简体中文)
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- 1 cpupower
- 2 配置
- 2.1 CPU频率驱动
- 2.2 调速器
- 2.3 Daemon
- 2.4 Privilege Granting Under GNOME
- 2.5 Laptop Mode Tools
- 3 Troubleshooting
#守护进程）。是一组设计为辅助CPU frequency scaling的一组用户空间工具。为使用频率调整的功能，这个软件包并不是必须的，但强烈建议安装，因为它提供了方便的命令行工具和在启动时改变调速器的服务（参考下文
为使CPU频率调整正常工作，操作系统必须先知道CPU的频率限制。为达到这个目的，一个能够读取和管理CPU规格的内核模块将被加载。注意这些模块可能需要BIOS中的相关功能被打开。这些功能在BIOS中可能被描述为：Speedstep，Cool and Quiet，PowerNow!或ACPI。
powernow-k8（AMD K8/K10处理器，如Athlon 64, Opteron, and Phenom等）。这些模块同时支持32位和64位内核，所以即使你在64位硬件下运行32位内核，它们很可能仍然是你所需要的模块。
$ ls /lib/modules/$(uname -r)/kernel/drivers/cpufreq/
|acpi_cpufreq||支持ACPI Processor Performance States的CPUFreq驱动。该驱动也支持Intel Enhanced SpeedStep（之前由已过期的模块speedstep-centrino支持）。|
|speedstep-ich||支持部分移动Intel奔腾III (Coppermine)的CPUFreq驱动。该驱动支持所有具备Intel ICH2, ICH3 或 ICH4 南桥芯片的系统中的移动Intel奔腾III-M (Tualatin)和移动Intel奔腾4 P4-M。|
|speedstep-smi||支持部分移动Intel奔腾III (Coppermine)的CPUFreq驱动。该驱动支持所有具备Intel 440BX/ZX/MX南桥芯片系统中的移动Intel奔腾III-M (Tualatin) 。|
|cpufreq-nforce2||支持nForce2平台下外频调整的CPUFreq驱动（AMD K7, Socket A）|
|p4_clockmod|| 支持Intel奔腾4 / 至强 / 赛扬 处理器的CPUFreq驱动。生效时会通过skipping clocks技术降低CPU发热量。|
# modprobe acpi_cpufreq
FATAL: Error inserting acpi_cpufreq ([...]/acpi-cpufreq.ko): No such device
$ cpupower frequency-info
analyzing CPU 0: driver: acpi-cpufreq CPUs which run at the same hardware frequency: 0 1 2 3 CPUs which need to have their frequency coordinated by software: 0 maximum transition latency: 10.0 us. hardware limits: 1.20 GHz - 2.40 GHz available frequency steps: 2.40 GHz, 2.40 GHz, 2.27 GHz, 2.13 GHz, 2.00 GHz, 1.87 GHz, 1.73 GHz, 1.60 GHz, 1.47 GHz, 1.33 GHz, 1.20 GHz available cpufreq governors: ondemand, performance current policy: frequency should be within 1.20 GHz and 2.40 GHz. The governor "ondemand" may decide which speed to use within this range. current CPU frequency is 1.20 GHz. 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
# 加载cpufreq驱动 acpi_cpufreq
For Desktops and most systems, the ondemand governor can provide the best compromise between heat emission, power consumption, performance, and manageability. Since it is the default and built into the kernel, loading the CPU frequency driver should be sufficient to activate it. For Laptops or other mobile systems, the conservative governor can possibly provide significant savings in power consumption.
performance are built into the kernel and do not need to be loaded as modules. If you want to use one of the other governors, you have to load them with
modprobe. For example:
# modprobe cpufreq_powersave # modprobe cpufreq_userspace
Or, add a file specifying the desired governor(s) to
/etc/modules-load.d/ and reboot.
# Load cpufreq governors cpufreq_powersave cpufreq_userspace
To see which governors have been loaded and which frequencies are supported:
# cpupower frequency-info
Manually set the governor by running the
cpupower command (as root). For example:
# cpupower frequency-set -g performance
Additional options such as upper and lower frequency bounds used by the governor can optionally be set by using the
-d options. For example, to set the second core's upper frequency bound as 2.00GHz and its lower bound as 1.00 GHz:
# cpupower -c 1 frequency-set -g ondemand -u 2.00Ghz -d 1.00Ghz
To manually set a processor to a specific frequency the userspace governor is used. For example, to set core 0 to 2.50Ghz and core 1 to 800Mhz:
# cpupower -c 0 frequency-set -f 2.50Ghz # cpupower -c 1 frequency-set -f 800Mhz
cpupower --help or
man cpupower for more information.
For those who would like a GUI for setting governors or frequency there is trayfreq, a GTK+ application that sits in the system tray.
The monitoring of CPU clock in real-time is accomplished by running:
$ watch grep \"cpu MHz\" /proc/cpuinfo
Improving on-demand performance
With the out-of-the-box configuration, the ondemand governor will result in a slight but measurable and noticeable loss of performance. It will not clock up the CPU when it is at lower than 95% usage, and will sample the usage at the fastest possible frequency when at full clock speeds in order to clock back down as soon as possible.
Tuning the governor for your needs can reduce the performance loss to the point where it is negligible/non-existent if you are willing to lose a lot of the power savings. If you just want to save power while idle, lowering the up_threshold to 11% and raising the sample_down_factor by an order of magnitude can accomplish this.
Tunables are available in
/sys/devices/system/cpu/cpufreq/ondemand/ once the governor is loaded and selected and can be preserved at reboot using
/etc/tmpfiles.d. For example:
w /sys/devices/system/cpu/cpufreq/ondemand/up_threshold - - - - 25
Changing the on-demand governor's threshold
To change when the
ondemand governor switches to a higher multiplier, one can manipulate
/sys/devices/system/cpu/cpufreq/ondemand/up_threshold. Determine the current setting by issuing the following command as root:
# cat /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
The value returned should be
95, the default setting as of kernel version 3.0. This means that the
ondemand governor currently increases the clock rate if a core reaches 95% utilization. This can be changed, for example:
# echo -n 15 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
On-demand governor sampling_down_factor
sampling_down_factor is another global ondemand global tunable.
sampling_down_factor set to
1 makes no changes from existing behavior, but having
sampling_down_factor set to a value greater than 1 (e.g. 100) causes it to act as a multiplier for the scheduling interval for re-evaluating load when the CPU is at its highest clock frequency due to high load. This improves performance by reducing the overhead of load evaluation and helping the CPU stay at its highest clock frequency when it is truly busy, rather than shifting back and forth in speed. This tunable has no effect on behavior at lower frequencies/lower CPU loads.
Read the value (default: 1):
# cat /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor
Set the value:
# echo -n 10 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor
Tuning conservative governor
While the conservative governor switches smoothly and utilizes all of the available frequencies, users may want to tune it further. Out-of-the-box it will clock the CPU up when load reaches 75% and clock down when load drops to 20%. As with the on-demand governor, decreasing the
up_threshold may improve performance and responsiveness.
Tunables are available in
/sys/devices/system/cpu/cpufreq/conservative/. Refer to the #Improving ondemand performance section for important advice regarding making this changes permanent, and potential daemon loading issues.
Changing the conservative governor's thresholds
Determine the current
up_threshold setting by issuing the following command as root:
# cat /sys/devices/system/cpu/cpufreq/conservative/up_threshold
The value returned should be
75, the default setting as of kernel version 3.0. This means that the
conservative governor currently increases the clock rate to the next highest speed if a core reaches 75% utilization. The can be changed, for example:
# echo -n 40 > /sys/devices/system/cpu/cpufreq/conservative/up_threshold
down_threshold value can be read and modified via
/sys/devices/system/cpu/cpufreq/conservative/down_threshold. The default value should be
20 as of kernel version 3.0. This means that the
conservative governor decreases the clock rate to the next lowest speed if a core falls to 20% utilization, which is a sensible default.
While the down sampling rate can also be adjusted for the
conservative governor, increasing it may only help with occasional low usage CPU spikes during high usage applications, as the
down_threshold is a much more direct control for down scaling which does not exist on the
Be aware that setting
down_threshold too close to
up_threshold may result in constant CPU switching, which might be something desirable for certain users and not for others. Setting
up_threshold too low may result in the CPU being clocked higher than it needs sacrificing power saving for performance, and setting
up_threshold too high may result in decreased performance, but reduced power consumption. Experiment to find the optimal values for your system and your needs.
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 package is installed, the file should already exist and be executable. For example, to change the scaling governor from
conservative when the AC adapter is disconnected and change it back if reconnected:
[...] 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 ;; [...]
includes a daemon which allows users to set the desired scaling governor and min/max clock speeds for all processor cores at boot-time.
Before starting the daemon, edit
/etc/conf.d/cpupower as root, selecting the desired governor and setting the min/max speed for your CPU(s).
With the appropriate configuration, start the daemon with the following command:
# systemctl start cpupower
To start the daemon automatically at startup:
# systemctl enable cpupower
Privilege Granting Under GNOME
GNOME has a nice applet to change the governor on the fly. To use it without the need to enter the root password, simply create
/var/lib/polkit-1/localauthority/50-local.d/org.gnome.cpufreqselector.pkla and populate it with the following:
[org.gnome.cpufreqselector] Identity=unix-user:USER Action=org.gnome.cpufreqselector ResultAny=no ResultInactive=no ResultActive=yes0
Where the word
USER is replaced with the username of interest.
Laptop Mode Tools
If you are already using or plan to use Laptop Mode Tools for other power saving solutions, then you may want to let it also manage CPU frequency scaling. To do so, you just have to insert the appropriate frequency driver to the
/etc/modules.d/ directory. (see #CPU frequency driver above) and then go through the
/etc/laptop-mode/conf.d/cpufreq.conf file to define governors, frequencies and policies. You will not need to load other modules and daemons or to set up scaling governors and interaction with ACPI events. Please refer to Laptop Mode Tools for more details.
- Some applications, like ntop, do not respond well to automatic frequency scaling. In the case of ntop it can result in segmentation faults and lots of lost information as even the
on-demandgovernor cannot change the frequency quickly enough when a lot of packets suddenly arrive at the monitored network interface that cannot be handled by the current processor speed.
- Some CPU's may suffer from poor performance with the default settings of the
on-demandgovernor (e.g. flash videos not playing smoothly or stuttering window animations). Instead of completely disabling frequency scaling to resolve these issues, the aggressiveness of frequency scaling can be increased by lowering the up_threshold sysctl variable for each CPU. See #Changing the on-demand governor's threshold.
- Sometimes the on-demand governor may not throttle to the maximum frequency but one step below. This can be solved by setting max_freq value slightly higher than the real maximum. For example, if frequency range of the CPU is from 2.00 GHz to 3.00 GHz, setting max_freq to 3.01 GHz can be a good idea.
- Some combinations of ALSA drivers and sound chips may cause audio skipping as the governor changes between frequencies, switching back to a non-changing governor seems to stop the audio skipping.
BIOS frequency limitation
Some CPU/BIOS configurations may have difficulties to scale to the 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.
Either you just made a specific Setting in the BIOS Setup Utility, (Frequency, Thermal Management, etc.) you can blame a buggy/outdated BIOS or the BIOS might have a serious reason for throttling the CPU on it's own.
Reasons like that can be (assuming your machine's a notebook) that the battery is removed (or near death) so you're on AC-power only. In this case a weak AC-source might not supply enough electricity to fulfill extreme peak demands by the overall system and as there is no battery to assist this could lead to data loss, data corruption or in worst case even hardware damage!
Not all BIOS'es limit the CPU-Frequency in this case, but for example most IBM/Lenove Thinkpads do. Refer to thinkwiki for more thinkpad related info on this topic.
If you checked there's not just an odd BIOS setting and you know what you're doing you can make the Kernel ignore these BIOS-limitations.
A special parameter has to be passed to the processor module.
For trying this temporarily change the value in
For setting it permanent refer to Kernel modules or just read on.
processor.ignore_ppc=1 to your kernel boot line or create
# If the frequency of your machine gets wrongly limited by BIOS, this should help options processor ignore_ppc=1