CPUFREQ(9) BSD Kernel Developer's Manual CPUFREQ(9)NAME
cpufreq, cpufreq_register, cpufreq_deregister, cpufreq_suspend,
cpufreq_resume, cpufreq_get, cpufreq_get_backend, cpufreq_get_state,
cpufreq_get_state_index, cpufreq_set, cpufreq_set_all — interface for CPU
frequency scaling
SYNOPSIS
#include <sys/cpufreq.h>
int
cpufreq_register(struct cpufreq *cf);
void
cpufreq_deregister(void);
void
cpufreq_suspend(struct cpu_info *ci);
void
cpufreq_resume(struct cpu_info *ci);
uint32_t
cpufreq_get(struct cpu_info *ci);
int
cpufreq_get_backend(struct cpufreq *cf);
int
cpufreq_get_state(uint32_t freq, struct cpufreq_state *cfs);
int
cpufreq_get_state_index(uint32_t index, struct cpufreq_state *cfs);
void
cpufreq_set(struct cpu_info *ci, uint32_t freq);
void
cpufreq_set_all(uint32_t freq);
DESCRIPTION
The machine-independent cpufreq interface provides a framework for CPU
frequency scaling done by a machine-dependent backend implementation.
User space control is available via cpuctl(8).
The cpufreq interface is a per-CPU framework. It is implicitly assumed
that the frequency can be set independently for all processors in the
system. However, cpufreq does not imply any restrictions upon whether
this information is utilized by the actual machine-dependent implementa‐
tion. It is possible to use cpufreq with frequency scaling implemented
via pci(4). In addition, it assumed that the available frequency levels
are shared uniformly by all processors in the system, even when it is
possible to control the frequency of individual processors.
It should be noted that the cpufreq interface is generally stateless.
This implies for instance that possible caching should be done in the
machine-dependent backend. The cpufreq_suspend() and cpufreq_resume()
functions are exceptions. These can be integrated with pmf(9).
FUNCTIONScpufreq_register(cf)
The cpufreq_register() function initializes the interface by
associating a machine-dependent backend with the framework.
Only one backend can be registered. Upon successful completion,
cpufreq_register() returns 0 and sets the frequency of all pro‐
cessors to the maximum available level. Note that the registra‐
tion can be done only after interrupts have been enabled; cf.
config_interrupts(9).
The following elements in struct cpufreq should be filled prior
to the call:
char cf_name[CPUFREQ_NAME_MAX];
struct cpufreq_state cf_state[CPUFREQ_STATE_MAX];
uint32_t cf_state_count;
bool cf_mp;
void *cf_cookie;
xcfunc_t cf_get_freq;
xcfunc_t cf_set_freq;
· The name of the backend should be given in cf_name.
· The cpufreq_state structure conveys descriptive information
about the frequency states. The following fields can be
used for the registration:
uint32_t cfs_freq;
uint32_t cfs_power;
From these cfs_freq (the clock frequency in MHz) is manda‐
tory, whereas the optional cfs_power can be filled to
describe the power consumption (in mW) of each state. The
cf_state array must be filled in descending order, that is,
the highest frequency should be at the zero index.
If the backend operates with a simple boolean switch without
knowing the clock frequencies, the cfs_freq field should be
set to CPUFREQ_STATE_ENABLED or CPUFREQ_STATE_DISABLED. The
first constant should precede the latter one in cf_state.
· The cf_state_count field defines the number of states that
the backend has filled in the cf_state array.
· The cf_mp boolean should be set to false if it is known that
the backend can not handle per-CPU frequency states; changes
should always be propagated to all processors in the system.
· The cf_cookie field is an opaque pointer passed to the back‐
end when cpufreq_get(), cpufreq_set(), or cpufreq_set_all()
is called.
· The cf_get_freq and cf_set_freq are function pointers that
should be associated with the machine-dependent functions to
get and set a frequency, respectively. The xcfunc_t type is
part of xcall(9). When the function pointers are invoked by
cpufreq, the first parameter is always the cf_cookie and the
second parameter is the frequency, defined as uint32_t *.
cpufreq_deregister()
Deregisters any possible backend in use.
cpufreq_suspend(ci)
The cpufreq_suspend() can be called when the processor suspends.
The function saves the current frequency of ci and sets the min‐
imum available frequency.
cpufreq_resume(ci)
Resumes the frequency of ci that was used before suspend.
cpufreq_get(ci)
Returns the current frequency of the processor ci. A value zero
is returned upon failure.
cpufreq_get_backend(cf)
Upon successful completion, cpufreq_get_backend() returns 0 and
fills cf with the data related to the currently used backend.
cpufreq_get_state(freq, cfs)
The cpufreq_get_state() function looks for the given frequency
from the array of known frequency states. If freq is not found,
the closest match is returned. Upon successful completion, the
function returns zero and stores the state information to cfs.
cpufreq_get_state_index(index, cfs)
Stores the frequency state with the given index to cfs, return‐
ing zero upon successful completion.
cpufreq_set(ci, freq)
The cpufreq_set() function sets the frequency of ci to freq.
cpufreq_set_all(freq)
Sets freq for all processors in the system.
The three functions cpufreq_get(), cpufreq_set(), and cpufreq_set_all()
guarantee that the call will be made in curcpu(9). The interface holds a
mutex(9) while calling the functions. This, and the use of xcall(9),
implies that no memory can be allocated in the backend during the calls.
Nor should the functions be called from interrupt context.
CODE REFERENCES
The cpufreq interface is implemented within sys/kern/subr_cpufreq.c.
SEE ALSOcpuctl(8), pmf(9), xcall(9)
Venkatesh Pallipadi and Alexey Starikovskiy, The Ondemand Governor. Past,
Present, and Future, Intel Open Source Technology Center,
http://www.kernel.org/doc/ols/2006/ols2006v2-pages-223-238.pdf, July,
2006, Proceedings of the Linux Symposium.
HISTORY
The cpufreq interface first appeared in NetBSD 6.0.
AUTHORS
Jukka Ruohonen ⟨jruohonen@iki.fi⟩
BUGS
The interface does not support different “governors” and policies.
BSD October 27, 2011 BSD
