Benchmark window not showing up

[ghost]

Hi,

I was playing around with setting up Vulcan on my laptop. I'm running on Debian 9 "Stretch" and the OS is up-to-date. I managed to build and install vkmark and even run it trough primusrun.
The funny thing is i can see my GPU working and i even get the test results in the console but the actual render window is not showing up. I'm guessing it's the "DISPLAY=:8 " variable i use, but i can't get it to run without it.

I get this in the console:

tomislav@w230st:~$ DISPLAY=:8 optirun -b primus vkmark -p immediate
=======================================================
    vkmark 2017.08
=======================================================
    Vendor ID:      0x10DE
    Device ID:      0x11E2
    Device Name:    GeForce GTX 765M
    Driver Version: 1612742656
=======================================================
[vertex] device-local=true: FPS: 5221 FrameTime: 0.192 ms
[vertex] device-local=false: FPS: 4651 FrameTime: 0.215 ms
[texture] anisotropy=0: FPS: 4716 FrameTime: 0.212 ms
[texture] anisotropy=16: FPS: 4676 FrameTime: 0.214 ms
[shading] shading=gouraud: FPS: 4593 FrameTime: 0.218 ms
[shading] shading=blinn-phong-inf: FPS: 4593 FrameTime: 0.218 ms
[shading] shading=phong: FPS: 4589 FrameTime: 0.218 ms
[shading] shading=cel: FPS: 4584 FrameTime: 0.218 ms
[effect2d] kernel=edge: FPS: 5256 FrameTime: 0.190 ms
[effect2d] kernel=blur: FPS: 3898 FrameTime: 0.257 ms
[desktop] <default>: FPS: 3890 FrameTime: 0.257 ms
[cube] <default>: FPS: 6656 FrameTime: 0.150 ms
[clear] <default>: FPS: 6532 FrameTime: 0.153 ms
=======================================================
                                   vkmark Score: 4911
=======================================================

any idea what's going on?