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| -rw-r--r-- | Documentation/cpu-freq/governors.txt | 62 |
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diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt index 933fae74c33..f4b8dc4237e 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 ============================================= |