Intel's i965 Mesa Driver Now Supports Threaded OpenGL

While Intel may be developing the Iris Gallium3D driver as their future OpenGL driver, they haven't given up all work on their existing "i965" classic Mesa driver. Hitting Mesa 19.1's development code this morning is support for threaded OpenGL with this existing and widely-used driver on Linux systems.

For ages now the Mesa Gallium3D drivers have supported "mesa_glthread=true" mode for turning on threaded OpenGL where more work can be punted off to separate CPU threads. This same treatment is now available to Intel's current (non-Gallium) OpenGL driver. We've done many tests on this mesa_glthread functionality since it came about two to three years back.

The Intel enablement work has been available for a year on the mailing list while finally today made it to Git master.

The Gallium3D threaded OpenGL support has been a big win in select OpenGL games and they've been expanding their .drirc white-list for managing what games/applications benefit from this optimization. As for the benefits in Intel's case:

According to Markus (degasus), the Citra emulator now runs ~30% faster. Emmanuel (linkmauve) also reported that the Dolphin emulator improved by 2.8x on one game. (Both of those still need to be added to drirc.)

An Intel Mesa CI run with mesa_glthread=true appears to be happy.

Bioshock Infinite's benchmark mode seems to be around 15-20% faster on my Skylake GT4 at 1920x1080.

I'll be running some Intel mesa_glthread benchmarks shortly; coming up later today are some fresh i965 vs. Iris driver benchmarks from the Git state as of a few days ago, though the numbers still remain very much relevant with the GL threading only being relevant for select cases. If you want to give it a go, upgrade to the newest Mesa 19.1-devel driver code and set the mesa_glthread=true environment variable to override the default behavior.