RadeonSI Lands Zen CCX/Thread Optimization For GLThread Mode

After the AMD Zen tuning for RadeonSI was dropped earlier this month, a revised implementation has now landed in Mesa 19.0-devel.

The revised patch that was merged overnight pins driver threads to a fixed core complex (CCX) when glthread is enabled. Glthread is the tunable for enabling OpenGL threading and can be done on a per-game basis with whitelisting that is handled by the DRI configuration file. The current list of whitelisted games can be seen here for where this glthread behavior is enabled by default.

That patch explains that the RadeonSI Gallium3D driver's three threads -- glthread, Gallium, and Winsys -- will be pinned to a random CCX. The belief is this should be the optimal approach for getting the best gaming performance on AMD Ryzen processors.

Separately, there was other glthread work merged. The immediate mode is now enabled and then Talos Principle was whitelisted. With a Radeon RX Vega 56, enabling glthread for this game led to about a 4% increase in frame-rates.