NAME

     cpufreq — CPU frequency control framework

SYNOPSIS

     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
     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.

     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

     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 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 to CPUFREQ_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 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 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), est(4), timecounters(4), powerd(8), sysctl(8)

AUTHORS

     Nate Lawson
     Bruno 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.