D5 does not seems to be utilizing Graphics card at all

When photos are rendered, D5 render does not seems to be utilizing the graphics card (or even CPU much) when checked with task manager. and render time is usually higher than Lum even for photos, is there any option that i have to turn on to use the graphics card or is it utilizing it without task manager knowing or is this a bug? I have a GTX 1080Ti and CPU as i7-7700

Thanks in Advance!