I have a Samsung Galaxy S5 with Android Lollipop. My phone was feeling sluggish. Using an app called "OS Monitor", I see that the "System" process (not to be confused with "Android System") is using a lot of CPU time. The CPU percentage goes as high as 50% on a quad-core processor.
I looked at the Battery screen in settings and it says the "System" process is using the most of the battery. How do I figure out what inside "System" is consuming so much CPU time? What app will reveal what is going on inside?
Rebooting the phone temporarily fixes the problem.
Note: The app or solution has to work on a non-rooted phone.