Overhead of the Driver

We found that when DrawCall used in the product becomes a lot, the API call overhead of the OpenGL ES of the CPU end will be high. This part should be the overhead of Driver. But we don't know what is expensive to overhead for a DrawCall. So we can only rebound through non-stop testing. Although we have tested some conclusions. But we are not very confirmed, they are correct. So, I want to ask a professional:

1.what is the main overhead of the Driver?

2.If you can do a proportion of overhead according to the type, what is the rough proportional situation? For example: Texture, FBO, Vertex, UBO, Uniform, Shader, TBO ... If sorted, what is the order?

3.Also, these overhead mentioned above is related to the specific parameters? Such as the size, number, etc.

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