About (context switch) on Android Traceview

Question

I'm starting to learn Android Traceview to improve Android apps performance, There is a concept that makes me confused! After tracing a method until the deepest level, in list of children methods, I see a (context switch) taking most of CPU time.

My question is: What is it mean? Why we cannot tracing further more into it?

Let's take a look at this example

Answer 1

Looking at com/android/traceview/Call.java, context switch means only that MethodData.mId == -1, i.e. some method which id cannot be determined, e.g. belongs to other process.