RADV's Next-Gen Geometry Code Continues To Be Revised For Navi GPUs

The NGG (Next-Gen Geometry) support with Navi continues to be refined by the open-source AMD Linux graphics drivers with the RADV Vulkan driver seeing a fresh batch of fixes/clean-ups, inspired in part by the NGG code from the RadeonSI and AMDVLK drivers.

The latest batch of RADV NGG work comes via Valve open-source driver developer Samuel Pitoiset. Landing in Mesa 20.0-devel today is a performance optimization, support for the NGG passthrough mode, disabling of vertex grouping, and other tweaks.

Nothing too major itself but the latest in a long series of NGG activity for the open-source AMD Linux graphics drivers.

Lead RadeonSI developer Marek Olšák did review the patches and have some interesting comments and a recommendation for another possible optimization. He also made an interesting remark that NGG Stream-Out support will never be enabled by default. Marek wrote, "You could get more performance out of NGG by doing what radeonsi does in the latest MR: emit s_sendmsg and exp prim at the beginning of shaders and the rest should be just 1 branch for ES threads...Note that NGG streamout will never be enabled by default. We're deciding whether we'll need it for future chips."

The latest merged work can be found here.

Mesa 20.0 should be entering its feature freeze around the end of January so we'll see what else comes about for AMD Navi in the coming days. Mesa 20.0 should be released as stable around the end of February or early March.