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CPUFREQ(4)             FreeBSD Kernel Interfaces Manual             CPUFREQ(4)

     cpufreq -- CPU frequency control framework

     device cpufreq

     #include <sys/cpu.h>

     cpufreq_levels(device_t dev, struct cf_level *levels, int *count);

     cpufreq_set(device_t dev, const struct cf_level *level, int priority);

     cpufreq_get(device_t dev, struct cf_level *level);

     cpufreq_drv_settings(device_t dev, struct cf_setting *sets, int *count);

     cpufreq_drv_type(device_t dev, int *type);

     cpufreq_drv_set(device_t dev, const struct cf_setting *set);

     cpufreq_drv_get(device_t dev, struct cf_setting *set);

     The cpufreq driver provides a unified kernel and user interface to CPU
     frequency control drivers.  It combines multiple drivers offering differ-
     ent 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).

     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 return EPERM.

     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.

             Current active CPU frequency in MHz.

             Currently available levels for the CPU (frequency/power usage).
             Values are in units of MHz and milliwatts.

             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.

             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 sys-

             Print verbose messages.  This setting is also accessible via a
             tunable with the same name.

     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

     The following device drivers offer relative frequency control and have an
     additive effect:

     acpi_throttle  ACPI CPU throttling
     p4tcc          Pentium 4 Thermal Control Circuitry

     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, check-
     ing 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 fre-
     quency and power for this level.  Unknown or irrelevant values are set to

     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 over-
     ridden 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.

     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().  Addition-
     ally, 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 to CPUFREQ_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. */

     On entry to this method, count contains the number of settings that can
     be returned.  On successful completion, the driver sets it to the actual
     number of settings returned.  If the driver offers more settings than
     count will allow, it should return 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 pro-
     vides 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

     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

     acpi(4), sysctl(8)

     Nate Lawson
     Bruno Ducrot contributed the powernow driver.

     The following drivers have not yet been converted to the cpufreq inter-
     face: longrun(4).

     Notification of CPU and bus frequency changes is not implemented yet.

     When multiple CPUs offer frequency control, they cannot be set to differ-
     ent levels and must all offer the same frequency settings.

FreeBSD 6.2                     March 03, 2006                     FreeBSD 6.2


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