Let me try this 4.0.4 rom in this long weekend!
wanna get rid of the high usage of Android OS!
There is no high usage. It is only being displayed as high usage in 4.0.3 due to a bug.
https://plus.google.com/105051985738280261832/posts/FV3LVtdVxPTDianne Hackborn said:Prior to 4.0, there were no wake locks computed for Android OS. It is now just the dumping ground for all of the time the device was awake that wasn't otherwise blamed on someone. So it is (total awake time) - (total app/system wake lock time) - (total screen on time).
There was also a bug that was my fault in 4.0.0-4.0.3 where this was computed incorrectly and would add the screen on time instead of subtract it.