cpufreq: Documentation: Minor reformatting

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.  There are a number of sysfs file

accessible parameters:

sampling_rate: measured in uS (10^-6 seconds), this is how often you

want the kernel to look at the CPU usage and to make decisions on

what to do about the frequency.  Typically this is set to values of

around '10000' or more. It's default value is (cmp. with users-guide.txt):

transition_latency * 1000

Be aware that transition latency is in ns and sampling_rate is in us, so you

get the same sysfs value by default.

Sampling rate should always get adjusted considering the transition latency

To set the sampling rate 750 times as high as the transition latency

in the bash (as said, 1000 is default), do:

echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) \

    >ondemand/sampling_rate

sampling_rate_min:

switch the frequency very quickly.

Sysfs files:

* sampling_rate:

  Measured in uS (10^-6 seconds), this is how often you want the kernel

  to look at the CPU usage and to make decisions on what to do about the

  frequency.  Typically this is set to values of around '10000' or more.

  It's default value is (cmp. with users-guide.txt): transition_latency

  * 1000.  Be aware that transition latency is in ns and sampling_rate

  is in us, so you get the same sysfs value by default.  Sampling rate

  should always get adjusted considering the transition latency to set

  the sampling rate 750 times as high as the transition latency in the

  bash (as said, 1000 is default), do:

  $ echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) > ondemand/sampling_rate

* sampling_rate_min:

  The sampling rate is limited by the HW transition latency:

  transition_latency * 100

  Or by kernel restrictions:

If CONFIG_NO_HZ_COMMON is set, the limit is 10ms fixed.

If CONFIG_NO_HZ_COMMON is not set or nohz=off boot parameter is used, the

limits depend on the CONFIG_HZ option:

  - If CONFIG_NO_HZ_COMMON is set, the limit is 10ms fixed.

  - If CONFIG_NO_HZ_COMMON is not set or nohz=off boot parameter is

    used, the limits depend on the CONFIG_HZ option:

    HZ=1000: min=20000us  (20ms)

    HZ=250:  min=80000us  (80ms)

    HZ=100:  min=200000us (200ms)

  The highest value of kernel and HW latency restrictions is shown and

  used as the minimum sampling rate.

up_threshold: defines what the average CPU usage between the samplings

of 'sampling_rate' needs to be for the kernel to make a decision on

* up_threshold:

  This defines what the average CPU usage between the samplings of

  'sampling_rate' needs to be for the kernel to make a decision on

  whether it should increase the frequency.  For example when it is set

  to its default value of '95' it means that between the checking

  intervals the CPU needs to be on average more than 95% in use to then

  decide that the CPU frequency needs to be increased.

ignore_nice_load: this parameter takes a value of '0' or '1'. When

set to '0' (its default), all processes are counted towards the

'cpu utilisation' value.  When set to '1', the processes that are

run with a 'nice' value will not count (and thus be ignored) in the

overall usage calculation.  This is useful if you are running a CPU

intensive calculation on your laptop that you do not care how long it

takes to complete as you can 'nice' it and prevent it from taking part

in the deciding process of whether to increase your CPU frequency.

sampling_down_factor: this parameter controls the rate at which the

kernel makes a decision on when to decrease the frequency while running

at top speed. When set to 1 (the default) decisions to reevaluate load

are made at the same interval regardless of current clock speed. But

when set to greater than 1 (e.g. 100) it acts as a multiplier for the

scheduling interval for reevaluating load when the CPU is at its top

speed due to high load. This improves performance by reducing the overhead

of load evaluation and helping the CPU stay at its top speed when truly

busy, rather than shifting back and forth in speed. This tunable has no

* ignore_nice_load:

  This parameter takes a value of '0' or '1'. When set to '0' (its

  default), all processes are counted towards the 'cpu utilisation'

  value.  When set to '1', the processes that are run with a 'nice'

  value will not count (and thus be ignored) in the overall usage

  calculation.  This is useful if you are running a CPU intensive

  calculation on your laptop that you do not care how long it takes to

  complete as you can 'nice' it and prevent it from taking part in the

  deciding process of whether to increase your CPU frequency.

* sampling_down_factor:

  This parameter controls the rate at which the kernel makes a decision

  on when to decrease the frequency while running at top speed. When set

  to 1 (the default) decisions to reevaluate load are made at the same

  interval regardless of current clock speed. But when set to greater

  than 1 (e.g. 100) it acts as a multiplier for the scheduling interval

  for reevaluating load when the CPU is at its top speed due to high

  load. This improves performance by reducing the overhead of load

  evaluation and helping the CPU stay at its top speed when truly busy,

  rather than shifting back and forth in speed. This tunable has no

  effect on behavior at lower speeds/lower CPU loads.

powersave_bias: this parameter takes a value between 0 to 1000. It

defines the percentage (times 10) value of the target frequency that

will be shaved off of the target. For example, when set to 100 -- 10%,

when ondemand governor would have targeted 1000 MHz, it will target

* powersave_bias:

  This parameter takes a value between 0 to 1000. It defines the

  percentage (times 10) value of the target frequency that will be

  shaved off of the target. For example, when set to 100 -- 10%, when

  ondemand governor would have targeted 1000 MHz, it will target

  1000 MHz - (10% of 1000 MHz) = 900 MHz instead. This is set to 0

  (disabled) by default.

  When AMD frequency sensitivity powersave bias driver --

  drivers/cpufreq/amd_freq_sensitivity.c is loaded, this parameter

  defines the workload frequency sensitivity threshold in which a lower

  frequency changes. A workload with sensitivity of 0% (memory/IO-bound)

  will not perform any better on higher core frequency, whereas a

  workload with sensitivity of 100% (CPU-bound) will perform better

higher the frequency. When the driver is loaded, this is set to 400

by default -- for CPUs running workloads with sensitivity value below

  higher the frequency. When the driver is loaded, this is set to 400 by

  default -- for CPUs running workloads with sensitivity value below

  40%, a lower frequency is chosen. Unloading the driver or writing 0

  will disable this feature.

The governor is tweaked in the same manner as the "ondemand" governor

through sysfs with the addition of:

freq_step: this describes what percentage steps the cpu freq should be

increased and decreased smoothly by.  By default the cpu frequency will

increase in 5% chunks of your maximum cpu frequency.  You can change this

value to anywhere between 0 and 100 where '0' will effectively lock your

CPU at a speed regardless of its load whilst '100' will, in theory, make

* freq_step:

  This describes what percentage steps the cpu freq should be increased

  and decreased smoothly by.  By default the cpu frequency will increase

  in 5% chunks of your maximum cpu frequency.  You can change this value

  to anywhere between 0 and 100 where '0' will effectively lock your CPU

  at a speed regardless of its load whilst '100' will, in theory, make

  it behave identically to the "ondemand" governor.

down_threshold: same as the 'up_threshold' found for the "ondemand"

governor but for the opposite direction.  For example when set to its

default value of '20' it means that if the CPU usage needs to be below

20% between samples to have the frequency decreased.

* down_threshold:

  Same as the 'up_threshold' found for the "ondemand" governor but for

  the opposite direction.  For example when set to its default value of

  '20' it means that if the CPU usage needs to be below 20% between

  samples to have the frequency decreased.

* sampling_down_factor:

sampling_down_factor: similar functionality as in "ondemand" governor.

But in "conservative", it controls the rate at which the kernel makes

a decision on when to decrease the frequency while running in any

speed. Load for frequency increase is still evaluated every

sampling rate.

  Similar functionality as in "ondemand" governor.  But in

  "conservative", it controls the rate at which the kernel makes a

  decision on when to decrease the frequency while running in any speed.

  Load for frequency increase is still evaluated every sampling rate.

3. The Governor Interface in the CPUfreq Core

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