Webgpu Impl Performance

WebGPU Performance

Optimize WebGPU by minimizing CPU-side command-submission cost and GPU state churn. Most WebGPU apps are CPU-bound, so the levers below target per-frame JavaScript work.

Quick Reference

All values target WebGPU 1.0-stable (Chrome 113+, Safari 26+, Firefox 141+).

Decision Tree

Should I use render bundles?

• Scene draws the SAME command sequence unchanged across frames → ALWAYS use a render bundle. Encode once, replay every frame.
• Same geometry drawn multiple times per frame (VR per-eye, cascaded shadow maps) → ALWAYS use a render bundle.
• Draw list changes every frame (objects added/removed each frame) → NEVER use a render bundle. Encode directly into the render pass instead.
• Draw list is fixed but per-object data (matrices, colors) changes → use a render bundle. Update the uniform/storage buffers between replays; the bundle stays valid.
• Draw COUNT must change per frame → keep the bundle, drive variation with indirect draws whose argument buffer a compute pass writes.

How do I size a compute workgroup?

• Pick @workgroup_size(x, y, z) so x * y * z is a multiple of the hardware subgroup width (32 on most NVIDIA/Intel, 64 on most AMD).
• ALWAYS use 64 as the portable default when unsure: @workgroup_size(64).
• 2D image work → @workgroup_size(8, 8) (product 64). 3D → @workgroup_size(4, 4, 4).
• NEVER let x * y * z exceed maxComputeInvocationsPerWorkgroup (default 256).
• NEVER pick a product that is not a multiple of 32 (for example 100): partial subgroups waste GPU lanes.

Core Patterns

ALWAYS create pipelines and bind groups once

GPURenderPipeline, GPUComputePipeline, and GPUBindGroup are immutable and expensive to build. Create them at load time, store the references, reuse them every frame.

// Load time (once)
const pipeline = device.createRenderPipeline({ label: "scene", layout, vertex, fragment });
const bindGroup = device.createBindGroup({ label: "scene-bg", layout: bgl, entries });

// Frame loop (reuse)
function frame() {
  pass.setPipeline(pipeline);
  pass.setBindGroup(0, bindGroup);
  // ...
}

NEVER call createRenderPipeline or createBindGroup inside the frame loop.

ALWAYS reuse one render bundle for static draws

device.createRenderBundleEncoder records a command subset once. finish() yields a GPURenderBundle that passEncoder.executeBundles([bundle]) replays. Validation and native translation happen at encode time, so replay costs far less CPU work.

// Load time (once)
const bundleEncoder = device.createRenderBundleEncoder({
  label: "static-scene",
  colorFormats: [presentationFormat],
  depthStencilFormat: "depth24plus",
  sampleCount: 1,
});
bundleEncoder.setPipeline(pipeline);
for (const obj of staticObjects) {
  bundleEncoder.setBindGroup(0, obj.bindGroup);
  bundleEncoder.setVertexBuffer(0, obj.vertexBuffer);
  bundleEncoder.draw(obj.vertexCount);
}
const bundle = bundleEncoder.finish();

// Frame loop (replay)
pass.executeBundles([bundle]);

NEVER rebuild the bundle inside the frame loop. Update buffers, replay the same bundle.

ALWAYS sort draws by pipeline then bind group

State changes (setPipeline, setBindGroup) are the dominant per-draw cost. Sort the draw list by pipeline first, then by bind group, then issue draws. This collapses redundant state switches.

draws.sort((a, b) => a.pipelineId - b.pipelineId || a.bindGroupId - b.bindGroupId);

ALWAYS pack small uniforms into one buffer with dynamic offsets

Allocating one GPUBuffer per object multiplies allocation and binding cost. Pack all per-object uniform structs into a single buffer and select one with a dynamic offset.

// Layout entry must declare hasDynamicOffset
const bgl = device.createBindGroupLayout({
  entries: [{ binding: 0, visibility: GPUShaderStage.VERTEX,
    buffer: { type: "uniform", hasDynamicOffset: true } }],
});
// Each dynamic offset MUST be a multiple of minUniformBufferOffsetAlignment (256)
pass.setBindGroup(0, bindGroup, [objectIndex * 256]);

The per-object struct stride MUST be padded to 256 bytes. See webgpu-impl-buffer-upload for the upload side.

ALWAYS profile passes with timestamp queries (feature-gated)

The timestamp-query feature plus a GPUQuerySet of type "timestamp" measure real GPU pass duration. timestampWrites on a render or compute pass records a start and end timestamp; resolveQuerySet copies them into a buffer.

// Gate the feature at device creation
const device = await adapter.requestDevice({
  requiredFeatures: adapter.features.has("timestamp-query") ? ["timestamp-query"] : [],
});

See references/methods.md for the full query-set setup and references/examples.md for the resolve-and-read code.

NEVER block the frame on GPU readback

await mapAsync(...) or await queue.onSubmittedWorkDone() inside the render path forces a full CPU-GPU sync that collapses frame pipelining. Read GPU results one or two frames late from a rotating staging buffer instead. See webgpu-impl-async-patterns.

Common Anti-Patterns

1. Rebuilding render bundles every frame. Encoding a bundle still pays the full validation cost. Rebuilding it each frame negates the only benefit, cheap replay. The bundle stays valid when the draw list is fixed: update buffers, replay unchanged.

2. Recreating pipelines or bind groups per frame. Both are immutable and expensive to build. Per-frame creation adds allocation, validation, and shader-translation cost to every frame. Build once at load, reuse.

3. Synchronously blocking on mapAsync each frame for readback. Awaiting the map promise stalls the CPU until the GPU drains, destroying the frame pipeline. Use a rotating staging buffer and accept results one or two frames late.

Critical Warnings

• NEVER call createRenderPipeline, createComputePipeline, or createBindGroup inside the frame loop.
• NEVER rebuild a GPURenderBundle per frame when the draw list is unchanged.
• NEVER pass a dynamic offset that is not a multiple of 256 (minUniformBufferOffsetAlignment / minStorageBufferOffsetAlignment).
• NEVER pick a compute @workgroup_size product that is not a multiple of 32 or 64.
• NEVER let @workgroup_size product exceed maxComputeInvocationsPerWorkgroup (default 256).
• NEVER use a GPUQuerySet of type "timestamp" or timestampWrites without first confirming adapter.features.has("timestamp-query") and adding it to requiredFeatures. Requesting the feature unconditionally makes requestDevice reject on browsers that lack it.
• NEVER await mapAsync or await onSubmittedWorkDone inside the per-frame render path.

Reference Files

• references/methods.md — render bundle API, caching strategy, workgroup-size tuning, timestamp-query profiling setup.
• references/examples.md — verified code: render bundle encode and replay, timestamp query profiling, dynamic-offset sub-allocation.
• references/anti-patterns.md — performance mistakes with WHY-it-fails explanations.

Related Skills

• webgpu-syntax-command-encoder — command encoder and render pass basics.
• webgpu-core-pipeline-architecture — pipeline and bind-group layout design.
• webgpu-impl-buffer-upload — writeBuffer versus staging-ring upload strategy.
• webgpu-impl-async-patterns — non-blocking readback, mapAsync, onSubmittedWorkDone.
• webgpu-wgsl-compute-shaders — @workgroup_size, compute dispatch in WGSL.