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Loop unrolling makes a Blender compute shader up to 10 times faster

aras-p.info by aras-p.info via calvin 8 min read Editor score 7/10

Unrolling a loop sped up a Kuwahara filter shader by 10× on one GPU and 2× on another. The result is a useful reminder to benchmark compiler assumptions against real hardware when optimizing GPU workloads.

What

Loop unrolling made a Blender compute shader for the anisotropic Kuwahara filter up to 10 times faster on one GPU and twice as fast on another.

How

Profiling found the shader used 192 registers, spilled 64 bytes, and had 28% occupancy on the examined Apple GPU.

Why it matters

The result shows why engineers should profile GPU workloads rather than assume the compiler's loop choice is always best.

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