[HTC One X] Meltus:
YOU MUST BE ROOTED TO ATTEMPT ANYTHING IN THIS THREAD

I don't take full credit for this, someone posted information about the file I listen to but I can't for the life of me find the post. If someone locates it let me know so I can give credit where it's due!

Detecting the Companion Core

The 5th Core (Companion Core/Low Power - LP - Core) is invisible to the android system and cannot be controlled at the moment. However, the kernel can see the 5th core and can detect whether it's running or not.

This is a simple demonstration of this, nothing particularly interesting or useful yet! :p

Results with screen ON

Results with screen OFF

So yeah, this is why we get such great screen-off battery life!

I know pretty much everything written here is already known I just thought it would be nice to see some proof!

For those of you that want to try this out yourself, make a service that runs in the background that reads from: "/sys/kernel/cluster/active". It will be either "G" or "LP" (G meaning it's running from the normal cores, LP is the Low Power core.)

Interestingly, while the screen is on but nothing much is happening on the device it will constantly switch between G and LP (like in the first screenshot) but when doing CPU intensive tasks it runs as G constantly. When the screen is off, it never switches to G which is giving us the insane screen-off battery life.

Disabling 4 Cores and just running the LP Core!

NOTE: This may not be the case. The phone kinda gets a bit screwy and reports different things. I'm pretty sure this is just the throttle that happens when the CPU hits 90°c but I'm not sure (it's hard to make it hit 90°c!). If anyone knows what else it does please let me know!

WARNING: This can, and most probably will, crash your phone after a while. When running CM9 I even had to reflash the ROM (This hasn't happened on Android Revolution yet). Basically PLEASE make a backup and don't blame me if you mess anything up!

This is a strange one. If you navigate to "/sys/kernel/debug/cpu-tegra" there's a file called 'Throttling'. Changing this file to '1' makes the system throttle CPU usage drastically.

Interestingly though, it also makes the "sys/kernel/cluster/active" file report nothing but 'LP' even when doing tasks, indicating that it's running solely off the LP Core. However, I'm using TegraStats to monitor what's active and what isn't and when throttling is enabled it reports that 'cpu0' is also active, contrary to what the "sys/kernel/cluster/active" file says.

If you apply this mod you will instantly see why I think it's running soley off the LP Core: It makes the phone almost unusable and I wouldn't recommend doing it for any great length of time!

Another wierd thing is that TegraStats also reports that CPU1 activates at random points while the phone stays as slow as ever.

Of course, CPU1 could indeed be active and just throttled to a low clock speed (102mhz is pretty much the average when doing anything. It can go as high as 304 though) but it still doesn't explain the LP Core results.

So, if this is running off only the companion core, what does it mean? Well, you could ultimately gain massive battery improvements. The only problem is, the mod renders the phone unusable as it stands. The throttle would probably need to be modified from kernel source to not be quite as aggressive or something, so not useful at the moment but it has potential :D

I hope you found this interesting! :)