Comment # 2 on bug 98874 from Matthias Nagel

@Michel: How and where do I set the environment variable
GALLIUM_DDEBUG="pipelined 2000" such that it is passed to the execution
environment of the Xorg process or compositor? I use systemd as my init system
and the active service file is sddm.service. Presumably, I need to modify some
unit files but offhand I do not have an idea which one.