cpufreq: Documentation: Minor reformatting

This patch doesn't change the content of the documentation, but rather
reformat it to make it more readable.

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 11:08:04 +05:30 committed by Rafael J. Wysocki
parent 801e0f378f
commit 4e660759be
1 changed files with 104 additions and 85 deletions

View File

@ -111,82 +111,96 @@ directory.
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:
switch the frequency very quickly.
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
Sysfs files:
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:
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.
* 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
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.
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:
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.
$ echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) > ondemand/sampling_rate
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.
* sampling_rate_min:
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 is chosen instead of ondemand governor's original target.
The frequency sensitivity is a hardware reported (on AMD Family 16h
Processors and above) value between 0 to 100% that tells software how
the performance of the workload running on a CPU will change when
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
40%, a lower frequency is chosen. Unloading the driver or writing 0
will disable this feature.
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:
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:
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
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
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 is chosen instead of ondemand governor's original target.
The frequency sensitivity is a hardware reported (on AMD Family 16h
Processors and above) value between 0 to 100% that tells software how
the performance of the workload running on a CPU will change when
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
40%, a lower frequency is chosen. Unloading the driver or writing 0
will disable this feature.
2.5 Conservative
@ -200,23 +214,28 @@ 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:
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.
* freq_step:
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.
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.
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.
* 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:
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
=============================================