2.2 Powersave
2.3 Userspace
2.4 Ondemand
+2.5 Conservative
3. The Governor Interface in the CPUfreq Core
Basically, it's the following flow graph:
-CPU can be set to switch independetly | CPU can only be set
+CPU can be set to switch independently | CPU can only be set
within specific "limits" | to specific frequencies
"CPUfreq policy"
2.4 Ondemand
------------
-The CPUfreq govenor "ondemand" sets the CPU depending on the
+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 fast.
-
-
+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
+
+show_sampling_rate_min:
+The sampling rate is limited by the HW transition latency:
+transition_latency * 100
+Or by kernel restrictions:
+If CONFIG_NO_HZ is set, the limit is 10ms fixed.
+If CONFIG_NO_HZ is not set or no_hz=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.
+
+show_sampling_rate_max: THIS INTERFACE IS DEPRECATED, DON'T USE IT.
+
+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.
+
+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.
+
+
+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
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