Set Option “DRI” “3” in Xorg.conf

you can check DRI3 in Xorg.log

Set Option “DRI” “3” in Xorg.conf

for the HD 6000 series you may want enable Option “AccelMethod” “glamor” in your xorg.conf files for getting better performance

Look for DRI3 enabled in Xorg.log

The Radeon DDX was recently updated with vsync support with DRI3, so you should have no issues now.

DRI3 is enabled by default when using glamor as of nouveau DDX version 1.0.11, but it is buggy currently (imirkin)

this will work only for Mesa-3D with debug enabled OR libgl1-mesa-glx-dbg package on Ubuntu!

run glxgears or any simple application with gdb app_name

break dri3_swap_buffers will set a breakpoint in dri3_swap_buffers

Answer y to Function “dri3_swap_buffers” not defined.

run and it should stop at this function. If it doesn't, you're not using DRI3 OR you compiled with –disable-dri3 for VSync. If it's the latter, this is expected and everything should still work.