https://bugs.freedesktop.org/show_bug.cgi?id=110214
--- Comment #65 from Diego Viola diego.viola@gmail.com --- Just to make it a bit more clear:
If I set that environment variable while I'm already on X:
export MESA_EXTENSION_OVERRIDE="-GL_NV_texture_barrier"
It has no effect on Xephyr (from current git master), i.e. xterm still shows the bug.
However, if I set before `startx`.
It works with both, X and Xephyr (from git master), i.e. xterm works fine.