R300 Open-Source Gallium3D Driver Sees New Optimization For Two Decade Old ATI GPUs

Written by Michael Larabel in Radeon on 21 August 2022 at 07:25 AM EDT. 10 Comments
Thanks to being open-source, the Mesa R300 Gallium3D driver that is used for supporting OpenGL on the ATI Radeon 9500/9600/9700/9800 series up through the Radeon X1000 "R500" series has seen a new set of performance optimization work twenty years after the R300 GPUs first shipped.

Independent Mesa contributor Pavel Ondra─Źka recently took to working on R300g optimizations around merging ALU instructions writing different channels of the same destination using the constant swizzles.

With the R300g optimization work Pavel has got the Lightsmark benchmark to break 30 FPS. It's just going from 29 to breaking 30 while at least the old Unigine Sanctuary Tech demo also sees a tiny increase too. Nearly 300 lines of code was written for this latest R300g optimization work.
total instructions in shared programs: 155488 -> 149176 (-4.06%)
instructions in affected programs: 126672 -> 120360 (-4.98%)
helped: 1530
HURT: 123

total presub in shared programs: 8226 -> 7983 (-2.95%)
presub in affected programs: 970 -> 727 (-25.05%)
helped: 25
HURT: 13

total temps in shared programs: 20841 -> 20617 (-1.07%)
temps in affected programs: 3492 -> 3268 (-6.41%)
helped: 207
HURT: 65

total lits in shared programs: 4328 -> 4196 (-3.05%)
lits in affected programs: 558 -> 426 (-23.66%)
helped: 39
HURT: 30

The ShaderDB stats are looking good for affected shader programs by this work that was merged today to Mesa 22.3-devel.

See this merge request for more details. There still is the potential for more optimizations should interested developers be willing to work on this GPU support for hardware approaching two decades of existence.
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