[HTC Sensation XL] Harbir:
This is not my work, i adjusted a bit (take several Governor out), so all credits go to droidphile.

i will myself accept THANKS :D

Explanation of Different Governors

1. GOVERNORS

These are the 9 governors we're talking about.

1) Ondemand

2) Ondemandx

3) Conservative

4) Interactive

5) SmartassV2

6) Intellidemand:

7) Lagfree

8) Userspacce

9) Performance

1) Ondemand:

Default governor in almost all stock kernels. One main goal of the ondemand governor is to switch to max frequency as soon as there is a CPU activity detected to ensure the responsiveness of the system. (You can change this behavior using smooth scaling parameters, refer Siyah tweaks at the end of 3rd post.) Effectively, it uses the CPU busy time as the answer to "how critical is performance right now" question. So Ondemand jumps to maximum frequency when CPU is busy and decreases the frequency gradually when CPU is less loaded/apporaching idle. Even though many of us consider this a reliable governor, it falls short on battery saving and performance on default settings. One potential reason for ondemand governor being not very power efficient is that the governor decide the next target frequency by instant requirement during sampling interval. The instant requirement can response quickly to workload change, but it does not usually reflect workload real CPU usage requirement in a small longer time and it possibly causes frequently change between highest and lowest frequency.

2) Ondemandx:

Basically an ondemand with suspend/wake profiles. This governor is supposed to be a battery friendly ondemand. When screen is off, max frequency is capped at 500 mhz. Even though ondemand is the default governor in many kernel and is considered safe/stable, the support for ondemand/ondemandX depends on CPU capability to do fast frequency switching which are very low latency frequency transitions. I have read somewhere that the performance of ondemand/ondemandx were significantly varying for different i/o schedulers. This is not true for most of the other governors. I personally feel ondemand/ondemandx goes best with SIO I/O scheduler.

3) Conservative:

A slower Ondemand which scales up slowly to save battery. The conservative governor is based on the ondemand governor. It functions like the Ondemand governor by dynamically adjusting frequencies based on processor utilization. However, the conservative governor increases and decreases CPU speed more gradually. Simply put, this governor increases the frequency step by step on CPU load and jumps to lowest frequency on CPU idle. Conservative governor aims to dynamically adjust the CPU frequency to current utilization, without jumping to max frequency. The sampling_down_factor value acts as a negative multiplier of sampling_rate to reduce the frequency that the scheduler samples the CPU utilization. For example, if sampling_rate equal to 20,000 and sampling_down_factor is 2, the governor samples the CPU utilization every 40,000 microseconds.

4) Interactive:

Can be considered a faster ondemand. So more snappier, less battery. Interactive is designed for latency-sensitive, interactive workloads. Instead of sampling at every interval like ondemand, it determines how to scale up when CPU comes out of idle. The governor has the following advantages: 1) More consistent ramping, because existing governors do their CPU load sampling in a workqueue context, but interactive governor does this in a timer context, which gives more consistent CPU load sampling. 2) Higher priority for CPU frequency increase, thus giving the remaining tasks the CPU performance benefit, unlike existing governors which schedule ramp-up work to occur after your performance starved tasks have completed. Interactive It's an intelligent Ondemand because of stability optimizations. Why??

Sampling the CPU load every X ms (like Ondemand) can lead to under-powering the CPU for X ms, leading to dropped frames, stuttering UI, etc. Instead of sampling the CPU at a specified rate, the interactive governor will check whether to scale the CPU frequency up soon after coming out of idle. When the CPU comes out of idle, a timer is configured to fire within 1-2 ticks. If the CPU is very busy between exiting idle and when the timer fires, then we assume the CPU is underpowered and ramp to max frequency.

5) SmartassV2:

Version 2 of the original smartass governor from Erasmux. Another favorite for many a people. The governor aim for an "ideal frequency", and ramp up more aggressively towards this freq and less aggressive after. It uses different ideal frequencies for screen on and screen off, namely awake_ideal_freq and sleep_ideal_freq. This governor scales down CPU very fast (to hit sleep_ideal_freq soon) while screen is off and scales up rapidly to awake_ideal_freq (500 mhz for GS2 by default) when screen is on. There's no upper limit for frequency while screen is off (unlike Smartass). So the entire frequency range is available for the governor to use during screen-on and screen-off state. The motto of this governor is a balance between performance and battery.

6) Intellidemand:

Intellidemand aka Intelligent Ondemand from Faux is yet another governor that's based on ondemand. Unlike what some users believe, this governor is not the replacement for OC Daemon (Having different governors for sleep and awake). The original intellidemand behaves differently according to GPU usage. When GPU is really busy (gaming, maps, benchmarking, etc) intellidemand behaves like ondemand. When GPU is 'idling' (or moderately busy), intellidemand limits max frequency to a step depending on frequencies available in your device/kernel for saving battery. This is called browsing mode. We can see some 'traces' of interactive governor here. Frequency scale-up decision is made based on idling time of CPU. Lower idling time (<20%) causes CPU to scale-up from current frequency. Frequency scale-down happens at steps=5% of max frequency. (This parameter is tunable only in conservative, among the popular governors )

To sum up, this is an intelligent ondemand that enters browsing mode to limit max frequency when GPU is idling, and (exits browsing mode) behaves like ondemand when GPU is busy; to deliver performance for gaming and such. Intellidemand does not jump to highest frequency when screen is off.

7) Lagfree:

Lagfree is similar to ondemand. Main difference is it's optimization to become more battery friendly. Frequency is gracefully decreased and increased, unlike ondemand which jumps to 100% too often. Lagfree does not skip any frequency step while scaling up or down. Remember that if there's a requirement for sudden burst of power, lagfree can not satisfy that since it has to raise cpu through each higher frequency step from current. Some users report that video playback using lagfree stutters a little.

8) Userspace:

Instead of automatically determining frequencies, lets user set frequencies.

9) Performance:

Sets min frequency as max frequency. Use this while benchmarking!

So, Governors can be categorized into 3/4 on a high level:

1.a) Ondemand Based:

Works on "ramp-up on high load" principle. CPU busy-time is taken into consideration for scaling decisions. Members: Ondemand, OndemandX, Intellidemand, Lagfree.

1.b) Conservative Based:

Members: Conservative,

2) Interactive Based:

Works on "make scaling decision when CPU comes out of idle-loop" principle. Members: Interactive, InteractiveX, Smartass, SmartassV2,

3) Weird Category:

Members: Userspace, Performance.

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II) QUESTION TIME

Q. "Ok. Enough of explanations. Tell me which governor is for performance and which one is for battery life."

A. Tough question! smartassV2 for a balance between performance and battery. For light weight tasks. To get maximum performance, use a tweaked ondemand or conservative, but never complain about battery. NOTE: If you don't know how exactly to do it, stay away from it or you will end up complaining about battery drain!

Q. "Hey, almost forgot. How do i change governors?"

A. Best way is to use apps such as system tuner,android tuner,kernel tuner etc.

Q. "How do i know which governor is best for me?"

A. It depends on what you need and your daily usage pattern. Performance or battery. Better choose a governor that's balanced for battery/performance. Or tweak a governor to give performance an upper-hand as compared to battery. We can always re-charge the phone: In car when off to work, or overnight. But we can not recharge performance!

Q. "I can feel slight lags here and there with a governor. For ex: while scrolling through app drawer/vertically scrolling browser, etc. I really love this governor and don't tell me to use another governor. Can i diminish this lag?"

A. Hmm well, you can. Basically what we have to do is make the governor "poll" less often to scale-down cpu. Increase down-sampling-time of your governor (whichever parameter that corresponds to), so that the cpu will stay longer on a frequency before scaling down. This should eliminate the lag.

Q. "Even though i don't have too much uv/oc, once in a while; may be once in two weeks, i experience a freeze/lock/reboot. I'm using governor X. How do i solve this?"

A. Well, a random reboot/freeze once in a while signifies that we're android/ enthusiast. If everything go smooth as silk, what's the fun? We could use stock rom/kernel/governor and be happy. A rare reboot or freeze is nothing to worry about. Just restart the phone.

Q. "OK. I want to tweak these governors according to my usage pattern, because i'm not happy with the default behavior of these governors".

A. You can tweak the governors using an init.d script to echo suitable values into:

/sys/devices/system/cpu/cpufreq/name-of-active-governor/name-of-the-paramater-to-tweak

screen-on will not drain too much battery like you think!

HIT THE THANKS IF THIS INFORMATION WAS HELPFULL;)