Debian testing, Nvidia GTX 780
Short description of error
2.78b became slower on render and more vram consuming in comparison to 2.78a
Exact steps for others to reproduce the error
Take any scene with textures and representative render time (not too small). I've tested it without motion blur, but with hair and sss shader.
Some other guys confirm that as well https://www.blendernation.com/2017/02/10/blender-2-78b-brings-10x-cycles-speedups/
I'm not sure if I should report it here or you already know this.