Bump map causes strange shading What is causing this strange shading when adding bump/normal maps?
This happens in the viewport and the final render.

See image below were the sun transitions into shadow.
It should be more smooth.

Blender v2.79
Cycles
HDRI lighting







Bump map close-up:


Also, it seems that adding subdivions increases quality but at a great cost of performance.
Given the image, and the fact that subdivisions help, I'm inclined to say that it's a terminator problem.
Sadly, it's a common problem on most ray/pathtracers, so your solutions are:


Increase subdivisions.
Increase light sizes. This will make shadows softer, and will mask the problem a bit.
Use a non-tracer renderer (like Blender Internal or, maybe Eevee), that doesn't have this problem.