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
Rafael J. Wysocki
parent
801e0f378f
commit
4e660759be
@ -111,82 +111,96 @@ directory.
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The CPUfreq governor "ondemand" sets the CPU depending on the
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current usage. To do this the CPU must have the capability to
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switch the frequency very quickly. There are a number of sysfs file
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accessible parameters:
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switch the frequency very quickly.
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sampling_rate: measured in uS (10^-6 seconds), this is how often you
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want the kernel to look at the CPU usage and to make decisions on
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what to do about the frequency. Typically this is set to values of
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around '10000' or more. It's default value is (cmp. with users-guide.txt):
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transition_latency * 1000
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Be aware that transition latency is in ns and sampling_rate is in us, so you
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get the same sysfs value by default.
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Sampling rate should always get adjusted considering the transition latency
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To set the sampling rate 750 times as high as the transition latency
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in the bash (as said, 1000 is default), do:
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echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) \
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>ondemand/sampling_rate
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Sysfs files:
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sampling_rate_min:
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The sampling rate is limited by the HW transition latency:
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transition_latency * 100
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Or by kernel restrictions:
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If CONFIG_NO_HZ_COMMON is set, the limit is 10ms fixed.
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If CONFIG_NO_HZ_COMMON is not set or nohz=off boot parameter is used, the
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limits depend on the CONFIG_HZ option:
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HZ=1000: min=20000us (20ms)
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HZ=250: min=80000us (80ms)
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HZ=100: min=200000us (200ms)
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The highest value of kernel and HW latency restrictions is shown and
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used as the minimum sampling rate.
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* sampling_rate:
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up_threshold: defines what the average CPU usage between the samplings
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of 'sampling_rate' needs to be for the kernel to make a decision on
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whether it should increase the frequency. For example when it is set
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to its default value of '95' it means that between the checking
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intervals the CPU needs to be on average more than 95% in use to then
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decide that the CPU frequency needs to be increased.
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Measured in uS (10^-6 seconds), this is how often you want the kernel
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to look at the CPU usage and to make decisions on what to do about the
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frequency. Typically this is set to values of around '10000' or more.
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It's default value is (cmp. with users-guide.txt): transition_latency
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* 1000. Be aware that transition latency is in ns and sampling_rate
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is in us, so you get the same sysfs value by default. Sampling rate
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should always get adjusted considering the transition latency to set
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the sampling rate 750 times as high as the transition latency in the
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bash (as said, 1000 is default), do:
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ignore_nice_load: this parameter takes a value of '0' or '1'. When
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set to '0' (its default), all processes are counted towards the
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'cpu utilisation' value. When set to '1', the processes that are
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run with a 'nice' value will not count (and thus be ignored) in the
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overall usage calculation. This is useful if you are running a CPU
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intensive calculation on your laptop that you do not care how long it
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takes to complete as you can 'nice' it and prevent it from taking part
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in the deciding process of whether to increase your CPU frequency.
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$ echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) > ondemand/sampling_rate
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sampling_down_factor: this parameter controls the rate at which the
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kernel makes a decision on when to decrease the frequency while running
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at top speed. When set to 1 (the default) decisions to reevaluate load
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are made at the same interval regardless of current clock speed. But
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when set to greater than 1 (e.g. 100) it acts as a multiplier for the
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scheduling interval for reevaluating load when the CPU is at its top
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speed due to high load. This improves performance by reducing the overhead
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of load evaluation and helping the CPU stay at its top speed when truly
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busy, rather than shifting back and forth in speed. This tunable has no
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effect on behavior at lower speeds/lower CPU loads.
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* sampling_rate_min:
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powersave_bias: this parameter takes a value between 0 to 1000. It
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defines the percentage (times 10) value of the target frequency that
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will be shaved off of the target. For example, when set to 100 -- 10%,
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when ondemand governor would have targeted 1000 MHz, it will target
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1000 MHz - (10% of 1000 MHz) = 900 MHz instead. This is set to 0
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(disabled) by default.
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When AMD frequency sensitivity powersave bias driver --
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drivers/cpufreq/amd_freq_sensitivity.c is loaded, this parameter
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defines the workload frequency sensitivity threshold in which a lower
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frequency is chosen instead of ondemand governor's original target.
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The frequency sensitivity is a hardware reported (on AMD Family 16h
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Processors and above) value between 0 to 100% that tells software how
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the performance of the workload running on a CPU will change when
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frequency changes. A workload with sensitivity of 0% (memory/IO-bound)
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will not perform any better on higher core frequency, whereas a
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workload with sensitivity of 100% (CPU-bound) will perform better
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higher the frequency. When the driver is loaded, this is set to 400
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by default -- for CPUs running workloads with sensitivity value below
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40%, a lower frequency is chosen. Unloading the driver or writing 0
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will disable this feature.
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The sampling rate is limited by the HW transition latency:
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transition_latency * 100
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Or by kernel restrictions:
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- If CONFIG_NO_HZ_COMMON is set, the limit is 10ms fixed.
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- If CONFIG_NO_HZ_COMMON is not set or nohz=off boot parameter is
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used, the limits depend on the CONFIG_HZ option:
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HZ=1000: min=20000us (20ms)
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HZ=250: min=80000us (80ms)
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HZ=100: min=200000us (200ms)
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The highest value of kernel and HW latency restrictions is shown and
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used as the minimum sampling rate.
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* up_threshold:
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This defines what the average CPU usage between the samplings of
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'sampling_rate' needs to be for the kernel to make a decision on
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whether it should increase the frequency. For example when it is set
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to its default value of '95' it means that between the checking
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intervals the CPU needs to be on average more than 95% in use to then
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decide that the CPU frequency needs to be increased.
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* ignore_nice_load:
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This parameter takes a value of '0' or '1'. When set to '0' (its
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default), all processes are counted towards the 'cpu utilisation'
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value. When set to '1', the processes that are run with a 'nice'
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value will not count (and thus be ignored) in the overall usage
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calculation. This is useful if you are running a CPU intensive
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calculation on your laptop that you do not care how long it takes to
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complete as you can 'nice' it and prevent it from taking part in the
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deciding process of whether to increase your CPU frequency.
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* sampling_down_factor:
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This parameter controls the rate at which the kernel makes a decision
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on when to decrease the frequency while running at top speed. When set
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to 1 (the default) decisions to reevaluate load are made at the same
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interval regardless of current clock speed. But when set to greater
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than 1 (e.g. 100) it acts as a multiplier for the scheduling interval
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for reevaluating load when the CPU is at its top speed due to high
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load. This improves performance by reducing the overhead of load
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evaluation and helping the CPU stay at its top speed when truly busy,
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rather than shifting back and forth in speed. This tunable has no
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effect on behavior at lower speeds/lower CPU loads.
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* powersave_bias:
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This parameter takes a value between 0 to 1000. It defines the
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percentage (times 10) value of the target frequency that will be
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shaved off of the target. For example, when set to 100 -- 10%, when
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ondemand governor would have targeted 1000 MHz, it will target
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1000 MHz - (10% of 1000 MHz) = 900 MHz instead. This is set to 0
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(disabled) by default.
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When AMD frequency sensitivity powersave bias driver --
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drivers/cpufreq/amd_freq_sensitivity.c is loaded, this parameter
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defines the workload frequency sensitivity threshold in which a lower
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frequency is chosen instead of ondemand governor's original target.
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The frequency sensitivity is a hardware reported (on AMD Family 16h
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Processors and above) value between 0 to 100% that tells software how
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the performance of the workload running on a CPU will change when
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frequency changes. A workload with sensitivity of 0% (memory/IO-bound)
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will not perform any better on higher core frequency, whereas a
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workload with sensitivity of 100% (CPU-bound) will perform better
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higher the frequency. When the driver is loaded, this is set to 400 by
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default -- for CPUs running workloads with sensitivity value below
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40%, a lower frequency is chosen. Unloading the driver or writing 0
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will disable this feature.
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2.5 Conservative
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@ -200,23 +214,28 @@ CPU. This behaviour more suitable in a battery powered environment.
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The governor is tweaked in the same manner as the "ondemand" governor
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through sysfs with the addition of:
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freq_step: this describes what percentage steps the cpu freq should be
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increased and decreased smoothly by. By default the cpu frequency will
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increase in 5% chunks of your maximum cpu frequency. You can change this
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value to anywhere between 0 and 100 where '0' will effectively lock your
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CPU at a speed regardless of its load whilst '100' will, in theory, make
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it behave identically to the "ondemand" governor.
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* freq_step:
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down_threshold: same as the 'up_threshold' found for the "ondemand"
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governor but for the opposite direction. For example when set to its
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default value of '20' it means that if the CPU usage needs to be below
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20% between samples to have the frequency decreased.
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This describes what percentage steps the cpu freq should be increased
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and decreased smoothly by. By default the cpu frequency will increase
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in 5% chunks of your maximum cpu frequency. You can change this value
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to anywhere between 0 and 100 where '0' will effectively lock your CPU
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at a speed regardless of its load whilst '100' will, in theory, make
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it behave identically to the "ondemand" governor.
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sampling_down_factor: similar functionality as in "ondemand" governor.
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But in "conservative", it controls the rate at which the kernel makes
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a decision on when to decrease the frequency while running in any
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speed. Load for frequency increase is still evaluated every
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sampling rate.
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* down_threshold:
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Same as the 'up_threshold' found for the "ondemand" governor but for
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the opposite direction. For example when set to its default value of
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'20' it means that if the CPU usage needs to be below 20% between
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samples to have the frequency decreased.
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* sampling_down_factor:
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Similar functionality as in "ondemand" governor. But in
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"conservative", it controls the rate at which the kernel makes a
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decision on when to decrease the frequency while running in any speed.
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Load for frequency increase is still evaluated every sampling rate.
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3. The Governor Interface in the CPUfreq Core
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=============================================
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