table of contents
CPUFREQ(4) | Device Drivers Manual | CPUFREQ(4) |
NAME¶
cpufreq — CPU frequency control frameworkSYNOPSIS¶
device cpufreq#include <sys/cpu.h> int
cpufreq_levels(device_t dev, struct cf_level *levels, int *count); int
cpufreq_set(device_t dev, const struct cf_level *level, int priority); int
cpufreq_get(device_t dev, struct cf_level *level); int
cpufreq_drv_settings(device_t dev, struct cf_setting *sets, int *count); int
cpufreq_drv_type(device_t dev, int *type); int
cpufreq_drv_set(device_t dev, const struct cf_setting *set); int
cpufreq_drv_get(device_t dev, struct cf_setting *set);
DESCRIPTION¶
The cpufreq driver provides a unified kernel and user interface to CPU frequency control drivers. It combines multiple drivers offering different settings into a single interface of all possible levels. Users can access this interface directly via sysctl(8) or by indicating to /etc/rc.d/power_profile that it should switch settings when the AC line state changes via rc.conf(5).SYSCTL VARIABLES¶
These settings may be overridden by kernel drivers requesting alternate settings. If this occurs, the original values will be restored once the condition has passed (e.g., the system has cooled sufficiently). If a sysctl cannot be set due to an override condition, it will returnEPERM
.
The frequency cannot be changed if TSC is in use as the timecounter. This is
because the timecounter system needs to use a source that has a constant rate.
The timecounter source can be changed with the
kern.timecounter.hardware sysctl. Available modes are in
kern.timecounter.choice sysctl entry.
- dev.cpu.%d.freq
- Current active CPU frequency in MHz.
- dev.cpu.%d.freq_levels
- Currently available levels for the CPU (frequency/power usage). Values are in units of MHz and milliwatts.
- dev.DEVICE.%d.freq_settings
- Currently available settings for the driver (frequency/power usage). Values are in units of MHz and milliwatts. This is helpful for understanding which settings are offered by which driver for debugging purposes.
- debug.cpufreq.lowest
- Lowest CPU frequency in MHz to offer to users. This setting is also accessible via a tunable with the same name. This can be used to disable very low levels that may be unusable on some systems.
- debug.cpufreq.verbose
- Print verbose messages. This setting is also accessible via a tunable with the same name.
SUPPORTED DRIVERS¶
The following device drivers offer absolute frequency control via the cpufreq interface. Usually, only one of these can be active at a time.- acpi_perf
- ACPI CPU performance states
- est
- Intel Enhanced SpeedStep
- ichss
- Intel SpeedStep for ICH
- powernow
- AMD PowerNow! and Cool'n'Quiet for K7 and K8
- smist
- Intel SMI-based SpeedStep for PIIX4
- acpi_throttle
- ACPI CPU throttling
- p4tcc
- Pentium 4 Thermal Control Circuitry
KERNEL INTERFACE¶
Kernel components can query and set CPU frequencies through the cpufreq kernel interface. This involves obtaining a cpufreq device, calling cpufreq_levels() to get the currently available frequency levels, checking the current level with cpufreq_get(), and setting a new one from the list with cpufreq_set(). Each level may actually reference more than one cpufreq driver but kernel components do not need to be aware of this. The total_set element of struct cf_level provides a summary of the frequency and power for this level. Unknown or irrelevant values are set toCPUFREQ_VAL_UNKNOWN
.
The cpufreq_levels() method takes a cpufreq
device and an empty array of levels. The
count value should be set to the number of levels
available and after the function completes, will be set to the actual number
of levels returned. If there are more levels than count
will allow, it should return E2BIG
.
The cpufreq_get() method takes a pointer to space to store a
level. After successful completion, the output will be
the current active level and is equal to one of the levels returned by
cpufreq_levels().
The cpufreq_set() method takes a pointer a
level and attempts to activate it. The
priority (i.e.,
CPUFREQ_PRIO_KERN
) tells cpufreq
whether to override previous settings while activating this level. If
priority is higher than the current active level, that
level will be saved and overridden with the new level. If a level is already
saved, the new level is set without overwriting the older saved level. If
cpufreq_set() is called with a NULL
level, the saved level will be restored. If there is no
saved level, cpufreq_set() will return
ENXIO
. If priority is lower than
the current active level's priority, this method returns
EPERM
.
DRIVER INTERFACE¶
Kernel drivers offering hardware-specific CPU frequency control export their individual settings through the cpufreq driver interface. This involves implementing these methods: cpufreq_drv_settings(), cpufreq_drv_type(), cpufreq_drv_set(), and cpufreq_drv_get(). Additionally, the driver must attach a device as a child of a CPU device so that these methods can be called by the cpufreq framework. The cpufreq_drv_settings() method returns an array of currently available settings, each of type struct cf_setting. The driver should set unknown or irrelevant values toCPUFREQ_VAL_UNKNOWN
. All the following elements for
each setting should be returned:
struct cf_setting { int freq; /* CPU clock in MHz or 100ths of a percent. */ int volts; /* Voltage in mV. */ int power; /* Power consumed in mW. */ int lat; /* Transition latency in us. */ device_t dev; /* Driver providing this setting. */ };
E2BIG
.
The cpufreq_drv_type() method indicates the type of settings
it offers, either CPUFREQ_TYPE_ABSOLUTE
or
CPUFREQ_TYPE_RELATIVE
. Additionally, the driver may
set the CPUFREQ_FLAG_INFO_ONLY
flag if the settings it
provides are information for other drivers only and cannot be passed to
cpufreq_drv_set() to activate them.
The cpufreq_drv_set() method takes a driver setting and makes
it active. If the setting is invalid or not currently available, it should
return EINVAL
.
The cpufreq_drv_get() method returns the currently-active
driver setting. The struct cf_setting returned must be
valid for passing to cpufreq_drv_set(), including all
elements being filled out correctly. If the driver cannot infer the current
setting (even by estimating it with cpu_est_clockrate())
then it should set all elements to
CPUFREQ_VAL_UNKNOWN
.
SEE ALSO¶
acpi(4), powerd(8), sysctl(8)AUTHORS¶
Nate LawsonBruno Ducrot contributed the powernow driver.
BUGS¶
The following drivers have not yet been converted to the cpufreq interface: longrun(4). Notification of CPU and bus frequency changes is not implemented yet. When multiple CPUs offer frequency control, they cannot be set to different levels and must all offer the same frequency settings.March 3, 2006 | Debian |