Intel's ANV Vulkan Driver Gets An Important Performance Fix For Broadwell

If you are using Intel Broadwell graphics with Mesa's ANV Vulkan driver, the performance should be better for Dota 2 and potentially other workloads.

Back in January for the Intel IvyBridge/Haswell/Broadwell/Skylake OpenGL & Vulkan Benchmarks On Linux 4.10 + Mesa 13.1 article, the Vulkan performance on Broadwell was poor relative to the other generations/hardware. While the Core i7 5775C with Iris Pro graphics were much faster than the Core i5 6600K HD Graphics (Skylake) and others with OpenGL, under Vulkan it was barely faster than Skylake HD hardware. Fortunately, the underlying issue appears to have now been corrected.

Jason Ekstrand has landed a PMA stall workaround in the ANV driver today for Mesa 17.1-dev Git. This should help Dota 2 with Broadwell graphics hardware by 8~9%, according to Jason. Though with my aforelinked results from January, there's more than an 8~9% slowdown from where the i7-5775C should have been performing, so I guess I'll fire up Mesa Git on that Iris Pro box and see how the performance is now with Mesa 17.1-dev.

Details via this commit. The workaround is over 200 lines of new code and isn't CC'ed as a candidate for getting into Mesa 17.0 or older stable series. There is also a PMA optimization for Skylake but it doesn't appear to help the overall frame-rate by much.