This is a minor issue, but I’m completely flummoxed.
Here’s a quick step by step.
My GPU option is greyed out upon opening Blender.
I open User preferences>System. My GPU box is already checked under the CUDA section.
I close the User Preferences window.
Suddenly GPU is no longer greyed out and works perfectly.
I tried on both 2.79 and 2.78. Same thing.
I tried running Blender from the terminal and get no error message.
This is with Manjaro Linux, Threadripper 1950x, GTX1070
Anyone with a similar issue or ideas to clear up the mystery?