Originally Posted by Chalnoth
If the environment variable __GL_SYNC_TO_VBLANK=1 is to have any effect, it has to be set before XGL starts. This means you would have to place it in one of the system init scripts (typically rc.local).
Edit: By the way, you can see all of the environment variable settings in Appendix E of the readme:
but it works in xorg and not in xgl.