[Kernel] Savaged-zen for HTC EVO 4G

Thrax

Continuing along with posting great kernels for popular devices, the Savaged-zen kernel for the HTC EVO 4G is easily one of the best. This kernel should only be used with AOSP-based ROMs, such as CyanogenMod or Savaged-zen. I recommend 1-1.3GHz with the InteractiveX (preferred) or Conservative governor.

When paired with one of these firmwares and the above settings, primary improvements include improved device responsiveness, and substantially better battery life.

http://mirror.savaged-zen.com/?filter=Kernel&scheduler=BFS -- newest version at the top.

Kwitko

Great kernel. I've used it before. I'd also like to give a mention to Tiamat kernel. It has HAVS, so you can change voltage, and comes in SBC (supper battery charge) and non-SBC. It's my current kernel. Like Savaged-Zen, it is only designed for AOSP firmware.

You can download it here.

fatcat

curious to what each CPU governer means

I have:

SavagedZen
smartass
interactive
conservative
ondemand
userspace
powersave
interactiveX
performance

and then cpu frequency between 128mhz-1190mhz

Thrax

Each governor is a different way of controlling how and when the CPU ramps up its clockspeed in response to whatever you're doing.

For example, conservative is very pro-battery life because it prefers the minimum clockspeed to smoothly accomplish whatever task you're doing. Performance locks the CPU at maximum clockspeed. OnDemand very rapidly ramps the clockspeed up to maximum--a brute force way of getting performance. InteractiveX is somewhat like OnDemand, except it locks the CPU at the lowest frequency when the screen is turned off.

So on and so forth.

I prefer conservative.

fatcat

any clue what the "smartass" governor might be

Thrax

Smartass is a reprogram of the interactive governor. After coming out of sleep, the interactive governor polls the CPU to see if it's been 100% active in the last few microseconds (as a result of user actions coming out of sleep). If it has been that active, the CPU is bumped to the maximum clockspeed and slowly lowered over time. If the user does something that continues to demand power, the "downclock the CPU" timer is continuously reset until user activity ceases, at which point the downclock function resumes. If the CPU was not 100% active out of sleep, it settles at the average clockspeed needed for smooth performance as an average of the last 50 milliseconds.

Now that you know what interactive does, we can explain smartass. Smartass is a complete rewrite of the interactive governor to be more responsive and potentially deliver more performance as a result. It also locks the CPU frequency at 352MHz when the screen is off.

InteractiveX is identical to interactive, except the lowest CPU frequency you set is what the CPU is locked at when the display is off, rather than 352MHz with Smartass.

I like the conservative for battery life reasons, but for performance, it's your choice: Smartass vs. InteractiveX. Smartass will give better performance at the cost of higher battery drain during screen off (352MHz idle). InteractiveX will give slightly (perhaps imperceptibly small) less performance, but better battery life (your 128MHz CPU idle).

IdleTime

Thanks, Thrax for the thorough explanation. Yours is the only one that is understandable and complete that I've come across.

Question: re "screen off". What happens when the screen goes off, yet an app is still running, such as a music/media is still playing a song? Would the governor consider the phone "sleeping"? If so, using a governor that locks the CPU frequency at a low setting when screen is off might cause problems as some media player requires higher frequency than what is set by "smartass" or interactive x. I listen to music a lot on my phone.

Any input would be appreciated. Tx again!

Thrax

A phone is capable of playing music with a CPU frequency as low as 180MHz on most devices made in the last two years. If the screen is off, an application may keep the device awake, but the governor will still lock the CPU to minimum frequency if you're using one of the governors that does that.

IdleTime

Thank you! 180! That explains why my Winamp player kinda "stutters" when the screen goes off b/c I have my lowest frequency locked at 128. I will follow your advice and use "conservative" and create a "screen off" profile locked at 245?

Also, how do "powersave" and "userspace" poll the CPU?

Thrax

Powersave uses the lowest possible frequency at all times. I've never used the userspace governor.

ardichoke

The userspace governor allows any user space application to set the CPU frequency however it wants. Other than that, I don't think it actually manages the CPU frequency on it's own at all (last time I checked anyway). Unless you want to manually control your CPU frequency at all times, don't use it.

That governor is essentially made for desktop/laptop systems where you want to be able to select your frequency on the fly using an application. Very useful on laptops if you're doing something intensive and want to stick it in performance mode without opening a root session. I'd argue that it's not at all useful for phones though.

IdleTime

Thanks, guys! I keep hearing everyone saying not to use "userspace", but never really understood why and kept wondering why do they have it there just for us not to use it. Now I get it.

One last question: In SetCPU there's a profile named "In Call". Is that profile as obvious as its name, when you're on a phone call? Or does it mean something else? Tx!

Thrax

It's as obvious as its name.