Comment # 10 on bug 1016402 from Patrik Jakobsson

The modesetting driver doesn't tell in the Xorg log if DRI3 is loaded.

With modesetting DRI3 is loaded by default. Here's my config:

Section "Device"
   Identifier  "Intel Graphics"
   Driver      "modesetting"
EndSection

Try running: LIBGL_DEBUG=verbose glxgears

That should tell you if DRI3 is actually available or not. I tested this on a
Kabylake with Tumbleweed and DOTA2 runs fine with Vulkan.