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

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>

1 files changed, 59 insertions, 3 deletions

diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt
index 933fae7..f4b8dc4 100644
--- a/Documentation/cpu-freq/governors.txt
+++ b/Documentation/cpu-freq/governors.txt
@@ -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
 =============================================