UM0851 datasheet(236/245 Pages) STMICROELECTRONICS

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Power management section

UM0851

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Doc ID 16604 Rev 2

$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors

$ conservative ondemand userspace powersave performance

Ondemand governor

●

sampling_rate - This is measured in microseconds (one millionth of a second). 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. If you wanted to set the sampling rate to 1 second you would

set it to 1000000 like in the following example.

echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

echo 1000000 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/sampling_rate

●

show_sampling_rate_(min|max) - These are the available minimum and maximum

sampling rates that you may set 'sampling_rate' to. To see both just do the following.

cat /sys/devices/system/cpu/cpu0/cpufreq/ondemand/sampling_rate_min

125000

cat /sys/devices/system/cpu/cpu0/cpufreq/ondemand/sampling_rate_max

125000000

●

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 or not it

should increase the frequency. For example when it is set to its default value of '80' it

means that between the checking intervals the CPU needs to be on average more than

80% in use to then decide that the CPU frequency needs to be increased. To set this to

something lower like 20% you would do the following

echo 20 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/up_threshold

●

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 utilization' 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

that you do not care how long it takes to complete. You can 'nice' it and prevent it from

taking part in the deciding process of whether to increase your CPU frequency. To turn

this on do the following.

echo 1 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load

Conservative governor

Conservative governor - CPU frequency is scaled based on the current load of the system. It

is similar to ondemand. The difference is 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

would be best used in a battery powered environment.

Conservative governor configuration options

●

freq_step - This describes what percentage steps the CPU freq should be increased

and decreased smoothly by. By default the CPU frequency is increased in 5% chunks

of your maximum CPU frequency. You can change this value to anywhere between 0

and 100 where '0' effectively locks your CPU at a speed regardless of its load whilst

'100' , in theory, makes it behave identically to the "ondemand" governor. For example

to have it step up and down in increments of 10% you would do the following.

echo conservative > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

echo 10 > /sys/devices/system/cpu/cpu0/cpufreq/conservative/freq_step

●

down_threshold - This is same as the 'up_threshold' found in the "ondemand" governor

but for the opposite direction. For example when set to its default value of '20' it means

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