[perf] WebGPU metadata flush uploads full 256 KB padded buffer every frame (RenderingElement3D-WebGPU.cpp) #130

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opened 2026-06-17 21:18:55 +02:00 by jorijnvdgraaf · 0 comments

jorijnvdgraaf commented

2026-06-17 21:18:55 +02:00

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Found by an adversarially-verified performance audit (confirmed real after a skeptic pass).

Location: implementations/Crafter.Graphics-RenderingElement3D-WebGPU.cpp:162
Severity: medium · Effort: trivial · Category: memory

Problem

The metadata buffer is fixed at kNPadded = 65536 slots; only primitiveCount entries are live, but metadataBuffer.FlushDevice() wgpuWriteBuffers all 256 KB through the WASM→JS staging path every frame (~100-250× waste for a few-hundred-instance scene). The Vulkan parallel sizes to primitiveCount, so this is WebGPU-specific.

Fix

FlushDeviceRange(0, 0, primitiveCount * sizeof(uint32_t)) — the existing overload that the instanceBuffer loop directly above already uses.

Found by an adversarially-verified performance audit (confirmed real after a skeptic pass). **Location:** `implementations/Crafter.Graphics-RenderingElement3D-WebGPU.cpp:162` **Severity:** medium · **Effort:** trivial · **Category:** memory ### Problem The metadata buffer is fixed at `kNPadded = 65536` slots; only `primitiveCount` entries are live, but `metadataBuffer.FlushDevice()` `wgpuWriteBuffer`s all 256 KB through the WASM→JS staging path every frame (~100-250× waste for a few-hundred-instance scene). The Vulkan parallel sizes to `primitiveCount`, so this is WebGPU-specific. ### Fix `FlushDeviceRange(0, 0, primitiveCount * sizeof(uint32_t))` — the existing overload that the instanceBuffer loop directly above already uses.

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2026-06-18 15:48:41 +02:00