CPU-frequency scaling on Slackware
ѕубликувана от admin на December 28 2015 10:46:34
Overview: CPU frequency scaling is carried out by the kernel, but requires that the relevant UEFI/BIOS options be enabled, such as Intel (Enhanced) Speedstep. Slackware comes with all requirements necessary to use this feature.



Kernel Config Requirements

The kernel options for CPU frequency scaling are as follows. You need both a governor (one set to default) and a driver. The Slackware default governor is 'userspace'.

Power management and ACPI options
CPU Frequency scaling
CPU Frequency scaling (CPU_FREQ [=y])
'performance' governor (CONFIG_CPU_FREQ_GOV_PERFORMANCE)
This sets CPU frequency to the maximum available.
'powersave' governor (CONFIG_CPU_FREQ_GOV_POWERSAVE)
This sets CPU frequency to the minimum available.
'userspace' governor for userspace frequency scaling
(CONFIG_CPU_FREQ_GOV_USERSPACE)
This allows userspace programs to set the CPU frequency.
'ondemand' cpufreq policy governor (CONFIG_CPU_FREQ_GOV_ONDEMAND)
This governor is recommended for desktops.
'conservative' cpufreq governor (CONFIG_CPU_FREQ_GOV_CONSERVATIVE)
This governor is recommended for laptops/netbooks. Although similar to the 'ondemand'
governor, frequency is gracefully increased and decreased rather than jumping to 100%
when speed is required.
x86 CPU frequency scaling drivers
Intel P state control (X86_INTEL_PSTATE [=n])
This driver is mutually exclusive with CONFIG_X86_ACPI_CPUFREQ. It is a newer
driver for Sandy Bridge processors and may cause problems.
Processor Clocking Control interface driver (CONFIG_X86_PCC_CPUFREQ)
This is only required for HP ProLiant servers, which use this interface. Otherwise,
disable it.
ACPI Processor P-States driver (CONFIG_X86_ACPI_CPUFREQ [=y])
This is the recommended driver for newer CPUs Intel (Enhanced) Speedstep enabled
and AMD K10 and newer.
AMD Opteron/Athlon64 PowerNow! (CONFIG_X86_POWERNOW_K8)
This is for K8/early Opteron/Athlon64 processors.
Intel Enhanced SpeedStep (deprecated) (CONFIG_X86_SPEEDSTEP_CENTRINO [=n])
This is a deprecated option that has been superseded by CONFIG_X86_ACPI_CPUFREQ,
so leave this disabled.
Intel Pentium 4 clock modulation (CONFIG_X86_P4_CLOCKMOD [=n])
This is a hack for Pentium 4s that may cause severe slowdowns and noticeable latencies,
so disable it.


It is recommended that the drivers be built-in to the kernel. If they are not, they may load
automatically or you may have to load them yourself.


Checking the CPU frequency settings Slackware comes with the cpufrequtils package which helps to configure frequency scaling in an appropriate manner. You can check the settings on your system with the command

cpufreq-info

Or if you don't have the package installed:

cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

cat /proc/cpuinfo

where Уcpu*Ф is the CPU you want the info on, for example cpu0.



Setting the CPU frequency settings


The cpufreq-set command can be used to set the appropriate governor.
Adding the following to the /etc/rc.d/rc.local file

# CPU-frequency scaling

cpufreq-set --cpu 0 --governor conservative
cpufreq-set --cpu 1 --governor conservative

will set the governor to 'conservative' on each boot.

The same can be done using sysfs:

echo "conservative" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo "conservative" > /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor

If you have Turbo Boost enabled in the UEFI/BIOS, you can turn boost on (1) or off (0) by running:

echo 1 > /sys/devices/system/cpu/cpufreq/boost

as long as the interface exists.


cpufreq.pdf