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cpufreq(4)

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 differ-
     ent settings into a single interface of all possible levels.  Users can
     access this interface directly via sysctl(8) or by indicating to
     power_profile(8) that it should switch settings when the AC line state
     changes via rc.conf(5).

SYSCTLS

     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.

     dev.cpu.%d.freq
	     Current active CPU frequency in MHz.

     dev.cpu.%d.freq_levels
	     Currently available levels for the CPU frequency and power usage
	     for each.	Values are in units of MHz and milliwatts.

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(4)  ACPI CPU performance states
     est(4)	   Intel Enhanced SpeedStep
     ichss(4)	   Intel SpeedStep for ICH
     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
     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 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.

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().  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-
     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), sysctl(8)

AUTHORS

     Nate Lawson

BUGS

     The following drivers have not yet been converted to the cpufreq inter-
     face: longrun(4), p4tcc(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 5.4		       February 20, 2005		   FreeBSD 5.4

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