[Mesa-dev] [PATCH RFC 0/4] Don't lose speed with dri3 on virtual drivers

[Thomas Hellstrom]

With dri3 and certain levels of dri2, the glx-dri layer automatically turn
on some GLX extensions whose functionality is mostly emulated on virtual
drivers. This causes a performance loss and increased latency.
Two such examples are GLX_EXT_buffer_age and GLX_OML_sync_control.
We'd like the ability to turn those off on a per-application and per-driver
basis to avoid the performance loss.

Now, dri-glx only looks for options in the "dri2" driver which firstly plays
badly with driconf, and secondly doesn't allow us to turn the extensions off
on a per-driver basis. So have dri-glx also check the driver options on
gallium drivers, preferring the driver options if there is a clash.

We implement the new options for all gallium drivers with a default
not to disable those GLX extensions.

Finally for the default drirc, turn those extensions off for the
gnome-shell on vmwgfx combination. That might be modified in the future to
also cover other compositors.