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cpufreq: Documentation: Updates based on current code 

The cpufreq core has gone though lots of updates in recent times, but on
many occasions the documentation wasn't updated along with the code.
This patch tries to catchup the documentation with the code.

Also add Rafael and Viresh as the contributors to the documentation.

Based on a patch from Claudio Scordino.

Signed-off-by: Claudio Scordino <claudio@evidence.eu.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Viresh Kumar 2017-01-06 11:08:05 +05:30 committed by Rafael J. Wysocki
parent 4e660759be
commit 7de962c0c7
6 changed files with 230 additions and 191 deletions
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24
Documentation/cpu-freq/core.txt
View File

@ -8,6 +8,8 @@
Dominik Brodowski <linux@brodo.de>
David Kimdon <dwhedon@debian.org>
Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Viresh Kumar <viresh.kumar@linaro.org>
@ -36,10 +38,11 @@ speed limits (like LCD drivers on ARM architecture). Additionally, the
kernel "constant" loops_per_jiffy is updated on frequency changes
here.
Reference counting is done by cpufreq_get_cpu and cpufreq_put_cpu,
which make sure that the cpufreq processor driver is correctly
registered with the core, and will not be unloaded until
cpufreq_put_cpu is called.
Reference counting of the cpufreq policies is done by cpufreq_cpu_get
and cpufreq_cpu_put, which make sure that the cpufreq driver is
correctly registered with the core, and will not be unloaded until
cpufreq_put_cpu is called. That also ensures that the respective cpufreq
policy doesn't get freed while being used.
2. CPUFreq notifiers
====================
@ -69,18 +72,16 @@ CPUFreq policy notifier is called twice for a policy transition:
The phase is specified in the second argument to the notifier.
The third argument, a void *pointer, points to a struct cpufreq_policy
consisting of five values: cpu, min, max, policy and max_cpu_freq. min
and max are the lower and upper frequencies (in kHz) of the new
policy, policy the new policy, cpu the number of the affected CPU; and
max_cpu_freq the maximum supported CPU frequency. This value is given
for informational purposes only.
consisting of several values, including min, max (the lower and upper
frequencies (in kHz) of the new policy).
2.2 CPUFreq transition notifiers
--------------------------------
These are notified twice when the CPUfreq driver switches the CPU core
frequency and this change has any external implications.
These are notified twice for each online CPU in the policy, when the
CPUfreq driver switches the CPU core frequency and this change has no
any external implications.
The second argument specifies the phase - CPUFREQ_PRECHANGE or
CPUFREQ_POSTCHANGE.
@ -90,6 +91,7 @@ values:
cpu - number of the affected CPU
old - old frequency
new - new frequency
flags - flags of the cpufreq driver
3. CPUFreq Table Generation with Operating Performance Point (OPP)
==================================================================

171
Documentation/cpu-freq/cpu-drivers.txt
View File

@ -9,6 +9,8 @@
Dominik Brodowski <linux@brodo.de>
Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Viresh Kumar <viresh.kumar@linaro.org>
@ -49,49 +51,65 @@ using cpufreq_register_driver()
What shall this struct cpufreq_driver contain?
cpufreq_driver.name - The name of this driver.
.name - The name of this driver.
cpufreq_driver.init - A pointer to the per-CPU initialization
function.
.init - A pointer to the per-policy initialization function.
cpufreq_driver.verify - A pointer to a "verification" function.
.verify - A pointer to a "verification" function.
cpufreq_driver.setpolicy _or_
cpufreq_driver.target/
target_index - See below on the differences.
.setpolicy _or_ .fast_switch _or_ .target _or_ .target_index - See
below on the differences.
And optionally
cpufreq_driver.exit - A pointer to a per-CPU cleanup
function called during CPU_POST_DEAD
phase of cpu hotplug process.
.flags - Hints for the cpufreq core.
cpufreq_driver.stop_cpu - A pointer to a per-CPU stop function
called during CPU_DOWN_PREPARE phase of
cpu hotplug process.
.driver_data - cpufreq driver specific data.
cpufreq_driver.resume - A pointer to a per-CPU resume function
which is called with interrupts disabled
and _before_ the pre-suspend frequency
and/or policy is restored by a call to
->target/target_index or ->setpolicy.
.resolve_freq - Returns the most appropriate frequency for a target
frequency. Doesn't change the frequency though.
cpufreq_driver.attr - A pointer to a NULL-terminated list of
"struct freq_attr" which allow to
export values to sysfs.
.get_intermediate and target_intermediate - Used to switch to stable
frequency while changing CPU frequency.
cpufreq_driver.get_intermediate
and target_intermediate Used to switch to stable frequency while
changing CPU frequency.
.get - Returns current frequency of the CPU.
.bios_limit - Returns HW/BIOS max frequency limitations for the CPU.
.exit - A pointer to a per-policy cleanup function called during
CPU_POST_DEAD phase of cpu hotplug process.
.stop_cpu - A pointer to a per-policy stop function called during
CPU_DOWN_PREPARE phase of cpu hotplug process.
.suspend - A pointer to a per-policy suspend function which is called
with interrupts disabled and _after_ the governor is stopped for the
policy.
.resume - A pointer to a per-policy resume function which is called
with interrupts disabled and _before_ the governor is started again.
.ready - A pointer to a per-policy ready function which is called after
the policy is fully initialized.
.attr - A pointer to a NULL-terminated list of "struct freq_attr" which
allow to export values to sysfs.
.boost_enabled - If set, boost frequencies are enabled.
.set_boost - A pointer to a per-policy function to enable/disable boost
frequencies.
1.2 Per-CPU Initialization
--------------------------
Whenever a new CPU is registered with the device model, or after the
cpufreq driver registers itself, the per-CPU initialization function
cpufreq_driver.init is called. It takes a struct cpufreq_policy
*policy as argument. What to do now?
cpufreq driver registers itself, the per-policy initialization function
cpufreq_driver.init is called if no cpufreq policy existed for the CPU.
Note that the .init() and .exit() routines are called only once for the
policy and not for each CPU managed by the policy. It takes a struct
cpufreq_policy *policy as argument. What to do now?
If necessary, activate the CPUfreq support on your CPU.
@ -117,47 +135,45 @@ policy->governor must contain the "default policy" for
cpufreq_driver.setpolicy or
cpufreq_driver.target/target_index is called
with these values.
policy->cpus Update this with the masks of the
(online + offline) CPUs that do DVFS
along with this CPU (i.e. that share
clock/voltage rails with it).
For setting some of these values (cpuinfo.min[max]_freq, policy->min[max]), the
frequency table helpers might be helpful. See the section 2 for more information
on them.
SMP systems normally have same clock source for a group of cpus. For these the
.init() would be called only once for the first online cpu. Here the .init()
routine must initialize policy->cpus with mask of all possible cpus (Online +
Offline) that share the clock. Then the core would copy this mask onto
policy->related_cpus and will reset policy->cpus to carry only online cpus.
1.3 verify
------------
----------
When the user decides a new policy (consisting of
"policy,governor,min,max") shall be set, this policy must be validated
so that incompatible values can be corrected. For verifying these
values, a frequency table helper and/or the
cpufreq_verify_within_limits(struct cpufreq_policy *policy, unsigned
int min_freq, unsigned int max_freq) function might be helpful. See
section 2 for details on frequency table helpers.
values cpufreq_verify_within_limits(struct cpufreq_policy *policy,
unsigned int min_freq, unsigned int max_freq) function might be helpful.
See section 2 for details on frequency table helpers.
You need to make sure that at least one valid frequency (or operating
range) is within policy->min and policy->max. If necessary, increase
policy->max first, and only if this is no solution, decrease policy->min.
1.4 target/target_index or setpolicy?
----------------------------
1.4 target or target_index or setpolicy or fast_switch?
-------------------------------------------------------
Most cpufreq drivers or even most cpu frequency scaling algorithms
only allow the CPU to be set to one frequency. For these, you use the
->target/target_index call.
only allow the CPU frequency to be set to predefined fixed values. For
these, you use the ->target(), ->target_index() or ->fast_switch()
callbacks.
Some cpufreq-capable processors switch the frequency between certain
limits on their own. These shall use the ->setpolicy call
Some cpufreq capable processors switch the frequency between certain
limits on their own. These shall use the ->setpolicy() callback.
1.5. target/target_index
-------------
------------------------
The target_index call has two arguments: struct cpufreq_policy *policy,
and unsigned int index (into the exposed frequency table).
@ -186,9 +202,20 @@ actual frequency must be determined using the following rules:
Here again the frequency table helper might assist you - see section 2
for details.
1.6. fast_switch
----------------
1.6 setpolicy
---------------
This function is used for frequency switching from scheduler's context.
Not all drivers are expected to implement it, as sleeping from within
this callback isn't allowed. This callback must be highly optimized to
do switching as fast as possible.
This function has two arguments: struct cpufreq_policy *policy and
unsigned int target_frequency.
1.7 setpolicy
-------------
The setpolicy call only takes a struct cpufreq_policy *policy as
argument. You need to set the lower limit of the in-processor or
@ -198,7 +225,7 @@ setting when policy->policy is CPUFREQ_POLICY_PERFORMANCE, and a
powersaving-oriented setting when CPUFREQ_POLICY_POWERSAVE. Also check
the reference implementation in drivers/cpufreq/longrun.c
1.7 get_intermediate and target_intermediate
1.8 get_intermediate and target_intermediate
--------------------------------------------
Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION unset.
@ -222,42 +249,36 @@ failures as core would send notifications for that.
As most cpufreq processors only allow for being set to a few specific
frequencies, a "frequency table" with some functions might assist in
some work of the processor driver. Such a "frequency table" consists
of an array of struct cpufreq_frequency_table entries, with any value in
"driver_data" you want to use, and the corresponding frequency in
"frequency". At the end of the table, you need to add a
cpufreq_frequency_table entry with frequency set to CPUFREQ_TABLE_END. And
if you want to skip one entry in the table, set the frequency to
CPUFREQ_ENTRY_INVALID. The entries don't need to be in ascending
order.
some work of the processor driver. Such a "frequency table" consists of
an array of struct cpufreq_frequency_table entries, with driver specific
values in "driver_data", the corresponding frequency in "frequency" and
flags set. At the end of the table, you need to add a
cpufreq_frequency_table entry with frequency set to CPUFREQ_TABLE_END.
And if you want to skip one entry in the table, set the frequency to
CPUFREQ_ENTRY_INVALID. The entries don't need to be in sorted in any
particular order, but if they are cpufreq core will do DVFS a bit
quickly for them as search for best match is faster.
By calling cpufreq_table_validate_and_show(struct cpufreq_policy *policy,
struct cpufreq_frequency_table *table);
the cpuinfo.min_freq and cpuinfo.max_freq values are detected, and
policy->min and policy->max are set to the same values. This is
helpful for the per-CPU initialization stage.
By calling cpufreq_table_validate_and_show(), the cpuinfo.min_freq and
cpuinfo.max_freq values are detected, and policy->min and policy->max
are set to the same values. This is helpful for the per-CPU
initialization stage.
int cpufreq_frequency_table_verify(struct cpufreq_policy *policy,
struct cpufreq_frequency_table *table);
assures that at least one valid frequency is within policy->min and
policy->max, and all other criteria are met. This is helpful for the
->verify call.
cpufreq_frequency_table_verify() assures that at least one valid
frequency is within policy->min and policy->max, and all other criteria
are met. This is helpful for the ->verify call.
int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
unsigned int target_freq,
unsigned int relation);
is the corresponding frequency table helper for the ->target
stage. Just pass the values to this function, and this function
returns the number of the frequency table entry which contains
the frequency the CPU shall be set to.
cpufreq_frequency_table_target() is the corresponding frequency table
helper for the ->target stage. Just pass the values to this function,
and this function returns the of the frequency table entry which
contains the frequency the CPU shall be set to.
The following macros can be used as iterators over cpufreq_frequency_table:
cpufreq_for_each_entry(pos, table) - iterates over all entries of frequency
table.
cpufreq-for_each_valid_entry(pos, table) - iterates over all entries,
cpufreq_for_each_valid_entry(pos, table) - iterates over all entries,
excluding CPUFREQ_ENTRY_INVALID frequencies.
Use arguments "pos" - a cpufreq_frequency_table * as a loop cursor and
"table" - the cpufreq_frequency_table * you want to iterate over.

24
Documentation/cpu-freq/cpufreq-stats.txt
View File

@ -34,10 +34,10 @@ cpufreq stats provides following statistics (explained in detail below).
- total_trans
- trans_table
All the statistics will be from the time the stats driver has been inserted
to the time when a read of a particular statistic is done. Obviously, stats
driver will not have any information about the frequency transitions before
the stats driver insertion.
All the statistics will be from the time the stats driver has been inserted
(or the time the stats were reset) to the time when a read of a particular
statistic is done. Obviously, stats driver will not have any information
about the frequency transitions before the stats driver insertion.
--------------------------------------------------------------------------------
<mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l
@ -110,25 +110,13 @@ Config Main Menu
CPU Frequency scaling --->
[*] CPU Frequency scaling
[*] CPU frequency translation statistics
[*] CPU frequency translation statistics details
"CPU Frequency scaling" (CONFIG_CPU_FREQ) should be enabled to configure
cpufreq-stats.
"CPU frequency translation statistics" (CONFIG_CPU_FREQ_STAT) provides the
basic statistics which includes time_in_state and total_trans.
statistics which includes time_in_state, total_trans and trans_table.
"CPU frequency translation statistics details" (CONFIG_CPU_FREQ_STAT_DETAILS)
provides fine grained cpufreq stats by trans_table. The reason for having a
separate config option for trans_table is:
- trans_table goes against the traditional /sysfs rule of one value per
interface. It provides a whole bunch of value in a 2 dimensional matrix
form.
Once these two options are enabled and your CPU supports cpufrequency, you
Once this option is enabled and your CPU supports cpufrequency, you
will be able to see the CPU frequency statistics in /sysfs.

117
Documentation/cpu-freq/governors.txt
View File

@ -10,6 +10,8 @@
Dominik Brodowski <linux@brodo.de>
some additions and corrections by Nico Golde <nico@ngolde.de>
Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Viresh Kumar <viresh.kumar@linaro.org>
@ -28,32 +30,27 @@ Contents:
2.3 Userspace
2.4 Ondemand
2.5 Conservative
2.6 Schedutil
3. The Governor Interface in the CPUfreq Core
4. References
1. What Is A CPUFreq Governor?
==============================
Most cpufreq drivers (except the intel_pstate and longrun) or even most
cpu frequency scaling algorithms only offer the CPU to be set to one
frequency. In order to offer dynamic frequency scaling, the cpufreq
core must be able to tell these drivers of a "target frequency". So
these specific drivers will be transformed to offer a "->target/target_index"
call instead of the existing "->setpolicy" call. For "longrun", all
stays the same, though.
cpu frequency scaling algorithms only allow the CPU frequency to be set
to predefined fixed values. In order to offer dynamic frequency
scaling, the cpufreq core must be able to tell these drivers of a
"target frequency". So these specific drivers will be transformed to
offer a "->target/target_index/fast_switch()" call instead of the
"->setpolicy()" call. For set_policy drivers, all stays the same,
though.
How to decide what frequency within the CPUfreq policy should be used?
That's done using "cpufreq governors". Two are already in this patch
-- they're the already existing "powersave" and "performance" which
set the frequency statically to the lowest or highest frequency,
respectively. At least two more such governors will be ready for
addition in the near future, but likely many more as there are various
different theories and models about dynamic frequency scaling
around. Using such a generic interface as cpufreq offers to scaling
governors, these can be tested extensively, and the best one can be
selected for each specific use.
That's done using "cpufreq governors".
Basically, it's the following flow graph:
@ -71,7 +68,7 @@ CPU can be set to switch independently | CPU can only be set
/ the limits of policy->{min,max}
/ \
/ \
Using the ->setpolicy call, Using the ->target/target_index call,
Using the ->setpolicy call, Using the ->target/target_index/fast_switch call,
the limits and the the frequency closest
"policy" is set. to target_freq is set.
It is assured that it
@ -109,9 +106,12 @@ directory.
2.4 Ondemand
------------
The CPUfreq governor "ondemand" sets the CPU depending on the
current usage. To do this the CPU must have the capability to
switch the frequency very quickly.
The CPUfreq governor "ondemand" sets the CPU frequency depending on the
current system load. Load estimation is triggered by the scheduler
through the update_util_data->func hook; when triggered, cpufreq checks
the CPU-usage statistics over the last period and the governor sets the
CPU accordingly. The CPU must have the capability to switch the
frequency very quickly.
Sysfs files:
@ -207,12 +207,12 @@ Sysfs files:
----------------
The CPUfreq governor "conservative", much like the "ondemand"
governor, sets the CPU depending on the current usage. It differs in
behaviour in that it gracefully increases and decreases the CPU speed
rather than jumping to max speed the moment there is any load on the
CPU. This behaviour more suitable in a battery powered environment.
The governor is tweaked in the same manner as the "ondemand" governor
through sysfs with the addition of:
governor, sets the CPU frequency depending on the current usage. It
differs in behaviour in that it gracefully increases and decreases the
CPU speed rather than jumping to max speed the moment there is any load
on the CPU. This behaviour is more suitable in a battery powered
environment. The governor is tweaked in the same manner as the
"ondemand" governor through sysfs with the addition of:
* freq_step:
@ -237,6 +237,29 @@ through sysfs with the addition of:
decision on when to decrease the frequency while running in any speed.
Load for frequency increase is still evaluated every sampling rate.
2.6 Schedutil
-------------
The "schedutil" governor aims at better integration with the Linux
kernel scheduler. Load estimation is achieved through the scheduler's
Per-Entity Load Tracking (PELT) mechanism, which also provides
information about the recent load [1]. This governor currently does
load based DVFS only for tasks managed by CFS. RT and DL scheduler tasks
are always run at the highest frequency. Unlike all the other
governors, the code is located under the kernel/sched/ directory.
Sysfs files:
* rate_limit_us:
This contains a value in microseconds. The governor waits for
rate_limit_us time before reevaluating the load again, after it has
evaluated the load once.
For an in-depth comparison with the other governors refer to [2].
3. The Governor Interface in the CPUfreq Core
=============================================
@ -244,26 +267,10 @@ A new governor must register itself with the CPUfreq core using
"cpufreq_register_governor". The struct cpufreq_governor, which has to
be passed to that function, must contain the following values:
governor->name - A unique name for this governor
governor->governor - The governor callback function
governor->owner - .THIS_MODULE for the governor module (if
appropriate)
The governor->governor callback is called with the current (or to-be-set)
cpufreq_policy struct for that CPU, and an unsigned int event. The
following events are currently defined:
CPUFREQ_GOV_START: This governor shall start its duty for the CPU
policy->cpu
CPUFREQ_GOV_STOP: This governor shall end its duty for the CPU
policy->cpu
CPUFREQ_GOV_LIMITS: The limits for CPU policy->cpu have changed to
policy->min and policy->max.
If you need other "events" externally of your driver, _only_ use the
cpufreq_governor_l(unsigned int cpu, unsigned int event) call to the
CPUfreq core to ensure proper locking.
governor->name - A unique name for this governor.
governor->owner - .THIS_MODULE for the governor module (if appropriate).
plus a set of hooks to the functions implementing the governor's logic.
The CPUfreq governor may call the CPU processor driver using one of
these two functions:
@ -277,12 +284,18 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,
unsigned int relation);
target_freq must be within policy->min and policy->max, of course.
What's the difference between these two functions? When your governor
still is in a direct code path of a call to governor->governor, the
per-CPU cpufreq lock is still held in the cpufreq core, and there's
no need to lock it again (in fact, this would cause a deadlock). So
use __cpufreq_driver_target only in these cases. In all other cases
(for example, when there's a "daemonized" function that wakes up
every second), use cpufreq_driver_target to lock the cpufreq per-CPU
lock before the command is passed to the cpufreq processor driver.
What's the difference between these two functions? When your governor is
in a direct code path of a call to governor callbacks, like
governor->start(), the policy->rwsem is still held in the cpufreq core,
and there's no need to lock it again (in fact, this would cause a
deadlock). So use __cpufreq_driver_target only in these cases. In all
other cases (for example, when there's a "daemonized" function that
wakes up every second), use cpufreq_driver_target to take policy->rwsem
before the command is passed to the cpufreq driver.
4. References
=============
[1] Per-entity load tracking: https://lwn.net/Articles/531853/
[2] Improvements in CPU frequency management: https://lwn.net/Articles/682391/

25
Documentation/cpu-freq/index.txt
View File

@ -18,16 +18,29 @@
Documents in this directory:
----------------------------
core.txt - General description of the CPUFreq core and
of CPUFreq notifiers
cpu-drivers.txt - How to implement a new cpufreq processor driver
amd-powernow.txt - AMD powernow driver specific file.
boost.txt - Frequency boosting support.
core.txt - General description of the CPUFreq core and
of CPUFreq notifiers.
cpu-drivers.txt - How to implement a new cpufreq processor driver.
cpufreq-nforce2.txt - nVidia nForce2 platform specific file.
cpufreq-stats.txt - General description of sysfs cpufreq stats.
governors.txt - What are cpufreq governors and how to
implement them?
index.txt - File index, Mailing list and Links (this document)
intel-pstate.txt - Intel pstate cpufreq driver specific file.
pcc-cpufreq.txt - PCC cpufreq driver specific file.
user-guide.txt - User Guide to CPUFreq
@ -35,9 +48,7 @@ Mailing List
------------
There is a CPU frequency changing CVS commit and general list where
you can report bugs, problems or submit patches. To post a message,
send an email to linux-pm@vger.kernel.org, to subscribe go to
http://vger.kernel.org/vger-lists.html#linux-pm and follow the
instructions there.
send an email to linux-pm@vger.kernel.org.
Links
-----
@ -48,7 +59,7 @@ how to access the CVS repository:
* http://cvs.arm.linux.org.uk/
the CPUFreq Mailing list:
* http://vger.kernel.org/vger-lists.html#cpufreq
* http://vger.kernel.org/vger-lists.html#linux-pm
Clock and voltage scaling for the SA-1100:
* http://www.lartmaker.nl/projects/scaling

60
Documentation/cpu-freq/user-guide.txt
View File

@ -18,7 +18,7 @@
Contents:
---------
1. Supported Architectures and Processors
1.1 ARM
1.1 ARM and ARM64
1.2 x86
1.3 sparc64
1.4 ppc
@ -37,16 +37,10 @@ Contents:
1. Supported Architectures and Processors
=========================================
1.1 ARM
-------
The following ARM processors are supported by cpufreq:
ARM Integrator
ARM-SA1100
ARM-SA1110
Intel PXA
1.1 ARM and ARM64
-----------------
Almost all ARM and ARM64 platforms support CPU frequency scaling.
1.2 x86
-------
@ -69,6 +63,7 @@ Transmeta Crusoe
Transmeta Efficeon
VIA Cyrix 3 / C3
various processors on some ACPI 2.0-compatible systems [*]
And many more
[*] Only if "ACPI Processor Performance States" are available
to the ACPI<->BIOS interface.
@ -147,10 +142,19 @@ mounted it at /sys, the cpufreq interface is located in a subdirectory
"cpufreq" within the cpu-device directory
(e.g. /sys/devices/system/cpu/cpu0/cpufreq/ for the first CPU).
affected_cpus : List of Online CPUs that require software
coordination of frequency.
cpuinfo_cur_freq : Current frequency of the CPU as obtained from
the hardware, in KHz. This is the frequency
the CPU actually runs at.
cpuinfo_min_freq : this file shows the minimum operating
frequency the processor can run at(in kHz)
cpuinfo_max_freq : this file shows the maximum operating
frequency the processor can run at(in kHz)
cpuinfo_transition_latency The time it takes on this CPU to
switch between two frequencies in nano
seconds. If unknown or known to be
@ -163,25 +167,30 @@ cpuinfo_transition_latency The time it takes on this CPU to
userspace daemon. Make sure to not
switch the frequency too often
resulting in performance loss.
scaling_driver : this file shows what cpufreq driver is
used to set the frequency on this CPU
related_cpus : List of Online + Offline CPUs that need software
coordination of frequency.
scaling_available_frequencies : List of available frequencies, in KHz.
scaling_available_governors : this file shows the CPUfreq governors
available in this kernel. You can see the
currently activated governor in
scaling_cur_freq : Current frequency of the CPU as determined by
the governor and cpufreq core, in KHz. This is
the frequency the kernel thinks the CPU runs
at.
scaling_driver : this file shows what cpufreq driver is
used to set the frequency on this CPU
scaling_governor, and by "echoing" the name of another
governor you can change it. Please note
that some governors won't load - they only
work on some specific architectures or
processors.
cpuinfo_cur_freq : Current frequency of the CPU as obtained from
the hardware, in KHz. This is the frequency
the CPU actually runs at.
scaling_available_frequencies : List of available frequencies, in KHz.
scaling_min_freq and
scaling_max_freq show the current "policy limits" (in
kHz). By echoing new values into these
@ -190,16 +199,11 @@ scaling_max_freq show the current "policy limits" (in
first set scaling_max_freq, then
scaling_min_freq.
affected_cpus : List of Online CPUs that require software
coordination of frequency.
related_cpus : List of Online + Offline CPUs that need software
coordination of frequency.
scaling_cur_freq : Current frequency of the CPU as determined by
the governor and cpufreq core, in KHz. This is
the frequency the kernel thinks the CPU runs
at.
scaling_setspeed This can be read to get the currently programmed
value by the governor. This can be written to
change the current frequency for a group of
CPUs, represented by a policy. This is supported
currently only by the userspace governor.
bios_limit : If the BIOS tells the OS to limit a CPU to
lower frequencies, the user can read out the