(In reply to Ilia Mirkin from comment #5)
> What GPU is this?
> 
> Check your xorg log. Are you using nouveau or modeset? If the latter, please
> use nouveau.

Do you mean this:

[    18.750] (==) Matched modesetting as autoconfigured driver 2
[    18.750] (II) LoadModule: "modesetting"
[    18.750] (II) Loading /usr/lib/xorg/modules/drivers/modesetting_drv.so
[    18.750] (II) Module modesetting: vendor="X.Org Foundation"
[    18.750] (==) Matched modesetting as autoconfigured driver 2
[    18.751] (II) LoadModule: "modesetting"
[    18.751] (II) Loading /usr/lib/xorg/modules/drivers/modesetting_drv.so
[    18.751] (II) Module modesetting: vendor="X.Org Foundation"
[    18.751] (II) UnloadModule: "modesetting"
[    18.751] (II) Unloading modesetting
[    18.751] (II) Failed to load module "modesetting" (already loaded, 0)
[    18.751] (II) modesetting: Driver for Modesetting Kernel Drivers: kms
[    18.751] (II) modeset(0): using drv /dev/dri/card0
[    18.751] (II) modeset(0): Creating default Display subsection in Screen
section

lspci:
01:00.0 VGA compatible controller: NVIDIA Corporation GP104M [GeForce GTX 1080
Mobile] (rev a1)
        Subsystem: Micro-Star International Co., Ltd. [MSI] GP104M [GeForce GTX
1080 Mobile]
        Kernel driver in use: nouveau
        Kernel modules: nvidiafb, nouveau