Here is some information regarding kernels that I've collected from people off of this forum and the internet. This work is not mine, I just reworded it to make it fit. I thought I'd compile it for future users that have questions.
** There are two main styles of kernels, those being CFS and BFS.
CFS = Completely Fair Scheduler
CFS kernels tend to focus on the system as a whole, and CFS is the default in the mainline linux kernel
. CFS's are efficient for lighter or standard tasks, think texting and web browsing here. The stock kernels that we run from HTC are CFS kernels. The CFS kernels typically give you the best battery life as well. Though it's worth pointing out that while CFS does attempt to be more fair with respect to all running processes, the mainline kernel
devs have implemented some ideas that originated with BFS into CFS.
Here is more information on CFS: http://en.wikipedia.org/wiki/Completely_Fair_Scheduler
BFS= Brain **** Scheduler
BFS kernels tend to focus on whatever app is running in the foreground, think a 3d gaming here. So a BFS kernel
may give you better Quadrant scores, which shouldn't be the end all for someone choosing a kernel
. The BFS is a 3rd party scheduler that the dev's have to patch into a CFS kernel
( which in turn makes it into a BFS kernel
) . These kernels can tend to be laggy at times too.
Here is more information on BFS : http://en.wikipedia.org/wiki/Brain_****_Scheduler
** Then there are sub-styles of these CFS and BFS kernels. Those being No-HAVS, HAVS, Static Undervolting, SBC and smartass governors.
HAVS = Hybrid Adaptive Voltage Scaling
Non-HAVS = Non Hybrid Adaptive Voltage Scaling AKA Static Voltage Scaling
HAVS built kernels, both less aggressive and more aggressive builds, are based on the idea by allowing a range of variable voltage levels at each speed setting. Which basically means the amount of current the system draws from the battery fluctuates according to what it needs ( based off of the process at hand ). HAVS dynamically scales the voltage supplied to the CPU at any given speed, erring on the side of lowest power draw, in an effort to enhance power saving. The theory is that if the load isn't significant enough, it may be possible to lower the voltage more than the static setting, and in terms saving that much more battery. But also it can raise it higher than the static setting if it sees fit.
For an example in a More Aggressive HAVS kernel
the speed of 245mhz has a range of voltage values that can be used. The ranges are from 900-950mV. So if the load is low enough, instead of sending 925mV to the CPU only 900mV will be sent ( saving battery ). Now if the load is big enough to call for more juice than 925mV (which is the static setting), the HAVS ( inside of the kernel
) can send up to 950mV to the CPU at that 245mhz speed. The voltage of 950mV is the max HAVS can send at a 245mhz speed. ( Keep in mind these voltages are not the same for all forms of HAVS, so the voltages will vary between devs and which kernel
your looking into. This was just an example from Netarchy's More HAVS table )
No-HAVS built kernels use Static voltage scaling and do not use undervolting. These will not alter the amount of current at one set CPU speed. So no matter what process is being ran, it's still going to provide that dead set amount of current to the CPU.Thus burning battery life for smaller tasks, as it would use the same amount of battery for heavier tasks.
Not all EVOs can run a HAVS built kernel
. Most should try out the More Aggressive HAVS kernels, and if your phone acts funny ( Force closing, Camera issues, if it doesn't reboot etc ) then you should try the Less Aggressive HAVS kernels. And if still you're in the same boat, then last resort is to use a Non-HAVS kernel
. Then you can run something like SetCPU to help out to throttle down the CPU at times.
Remember how I said that HAVS can fluctuate how much power it draws based on CPU load and battery temperature? Well when the kernel
is not using HAVS, it is going to use Static Undervolting. Static Undervolting is when each frequency uses less mV then it normally would call for, but those numbers are set in stone. They will not fluctuate like HAVS would to save battery life. For example, the stock default voltage for the 998mhz setting is 1300mV.If the static voltage table is altered so that the setting for 998mhz is 1275mV ( this is what a Statis Undervolting kernel
does ) . Then whenever the cpu scales to 998mhz on the phone, the power supplied will be 1275mV instead of 1300mV. So basically each frequency is guaranteed to always draw less power than normal ( In this case the CPU will pull 35 LESS mV every time the phone's CPU hits 998mhz ) .
So in Static Undervolting kernel
, the frequency of 245mhz has a voltage setting of 925mV assigned to it. So whenever the cpu is at 245mhz, it will be getting 925mV at all times. Regardless of the process at hand. ( Again these numbers used above are for Netarchy's Kernel
. It will vary from dev to dev and kernel
SBC=Superior Battery Charging
SBC is a type of "trickle" charging. It's a full, slow, complete charge and it prevents the 10% drop that most users get when pulling the phone off the charger. This kernel
performs best with an overnight charge. Some users asked questions on the safety of the SBC charging method. Ms79723 states that it slowly pushes mV into the battery and thus keeps the battery cool. SBC kernels push the battery past their normal 100% charged point, to a TRUE 100% charged battery. These kernels also charge extended batteries to their maximum and show true "on charger" voltages, which would deem these to be more accurate for checking voltages on your battery. There was and still are concerns of the SBC kernels destroying your battery, but to most people now these dont pose much concern anymore.
The issues people were bring up is that the Li-Ion batteries are charged to the point HTC set them to was for safety of the battery. Li-Ion's can be unstable at times, but Ms79723 programmed safety temperature and voltage "stops" to kill the charging is they get too high. Bad things can start to form, I said can not will, if the temperature gets above 140f and voltage gets to or past 4230mV. If the mV gets to 4230mV it can causes issues. If it gets to 4300 mV it can cause plating. People are also speculating that the SBC kernels are going to kill your battery and or shorten the life. With the price of eBay batteries now days, if the SBC kernels give you drastically ( which has been seen ) more battery life, then why not? The highest seem on the SBC kernels is 4210mV, which is under both values for issues to start.
This is an integrated process that basically does something like SetCPU does but smarter. What Smartass does is it learns from how you use the system ( the system being your phone ). So SetCPU has its "profiles" to determine how it will set the CPU ( for lack of better terms ), smartass will automatically distribute power as needed. And again this is determined by how you use the phone. Its more of an Intelligent SetCPU. This process is not in every kernel
, so if you are interested look for it in the features.
There are other governors that are available as well. Those being conservative, ondemand, powersave, etc. which those are more self explanatory.
If anything needs to be added or altered PM me and I'll edit the post. If it helps, dont forgot to click the thanks button in the bottom right, instead of posting thanks.