when setting the environment variable GL_SYNC_TO_VBLANK=1 using bash, i've seen two different suggestions.
Suggestion 1 is that at the command prompt:
$ export GL_SYNC_TO_VBLANK=1
and suggestion 2 is
$ export __GL_SYNC_TO_VBLANK=1.
Note that the suggestion 2 has the two underscores before the GL_SYNC..etc.
When I use suggestion one, there seems to be no difference in terms of sync with retrace, that is, tearing still occurs.
When I use suggestion two, my whole system freezes when staring an OpenGL application, and i have to reboot the whole system (I can't even logout of X).
My question is: which is the best method of setting the environment variable (GL_SYNC_TO_VBLANK), and if its the second method, why might my system freeze when i use it??