Dominik Brodowski <linux@brodo.de>
+ some additions and corrections by Nico Golde <nico@ngolde.de>
2.1 Performance
2.2 Powersave
2.3 Userspace
+2.4 Ondemand
+2.5 Conservative
3. The Governor Interface in the CPUfreq Core
scaling_max_freq.
-2.1 Powersave
+2.2 Powersave
-------------
The CPUfreq governor "powersave" sets the CPU statically to the
scaling_max_freq.
-2.2 Userspace
+2.3 Userspace
-------------
The CPUfreq governor "userspace" allows the user, or any userspace
directory.
+2.4 Ondemand
+------------
+
+The CPUfreq govenor "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.
+
+show_sampling_rate_(min|max): the minimum and maximum sampling rates
+available that you may set 'sampling_rate' to.
+
+up_threshold: defines what the average CPU usaged 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 '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.
+
+sampling_down_factor: this parameter controls the rate that the CPU
+makes a decision on when to decrease the frequency. When set to its
+default value of '5' it means that at 1/5 the sampling_rate the kernel
+makes a decision to lower the frequency. Five "lower rate" decisions
+have to be made in a row before the CPU frequency is actually lower.
+If set to '1' then the frequency decreases as quickly as it increases,
+if set to '2' it decreases at half the rate of the increase.
+
+ignore_nice_load: this parameter takes a value of '0' or '1', when set
+to '0' (its default) then all processes are counted towards towards the
+'cpu utilisation' value. When set to '1' then processes that are
+run with a 'nice' value will not count (and thus be ignored) in the
+overal 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.
+
+
+2.5 Conservative
+----------------
+
+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:
+
+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.
3. The Governor Interface in the CPUfreq Core
=============================================
git://git.onelab.eu / linux-2.6.git / blobdiff