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[PATCH] cpufreq: documentation for 'ondemand' and 'conservative'

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Added a more verbose entry for the 'ondemend' governor and an entry for the
'conservative' governor to the documentation.

Signed-off-by: Alexander Clouter <alex-kernel@digriz.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Dave Jones <davej@redhat.com>
This commit is contained in:
Alexander Clouter 2005-12-01 01:09:23 -08:00 committed by Dave Jones
parent 001893cda2
commit 537208c807
1 changed files with 57 additions and 1 deletions
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58
Documentation/cpu-freq/governors.txt
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@ -27,6 +27,7 @@ Contents:
2.2 Powersave
2.3 Userspace
2.4 Ondemand
2.5 Conservative
3. The Governor Interface in the CPUfreq Core
@ -110,9 +111,64 @@ directory.
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 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.
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
=============================================