webgpu-avoid-redundant-state-setting

Setting state multiple times can be a source of lost performance. There’s overhead in calling from JavaScript into the WebGPU api. There’s also no guarantee the implementation optimizes this stuff under the hood.

So, this is an attempt at

1. Trivially doing it for you

   In this case just add

   import 'https://greggman.github.io/webgpu-avoid-redundant-state-setting/webgpu-avoid-redundant-state-setting.js';
   

   or

   <script type="module" src="https://greggman.github.io/webgpu-avoid-redundant-state-setting/webgpu-avoid-redundant-state-setting.js"></script>
   

   To the top of your app and see if there is any perf difference.

   note: there is overhead in checking for redundant state calls, especially for setBindGroup with dynamic offsets as the library has to check each offset so there is some possibility perf will be worse with this library. Measure for yourself or use (2) below to check your own code.

2. Making it easy to check if you’re submitting redundant state

   This way you can optimize your code.

   In this case use

   import 'https://greggman.github.io/webgpu-avoid-redundant-state-setting/webgpu-check-redundant-state-setting.js';
   

   or

   <script type="module" src="https://greggman.github.io/webgpu-avoid-redundant-state-setting/webgpu-check-redundant-state-setting.js"></script>
   

   Then check the JavaScript console.

   Note: this assumes you’re using requestAnimationFrame to render. If you are using something else to render like requestVideoFrameCallback or setTimeout or other events, look at the source to see how to do this check for your specific situation.

   If you see lots of redundant state setting, refactor your code to avoid it. You can look at the source code of this library for some ideas. The easiest to avoid are redundant setVertexBuffer and setIndexBuffer calls. setBindGroup is harder if it has to check dynamic offsets.

   Important!

   You do NOT need to avoid setting all redundant state. Rather, this library is just meant to check if you’re setting 100s or 1000s of redundant state per pass.

Notes

There isn’t very much state in WebGPU. The most (all?) state comes in GPURenderPassEncoder and GPUComputePassEncoder. For example, you set bindGroups by calling setBindGroup and those are sticky until you end the pass encoder.

• compute and render pass state

  • pipeline: set via setPipeline
  • bindGroups: set via setBindGroup

• render pass state

  • vertexBuffers: set via setVertexBuffer
  • indexBuffer: set via setIndexBuffer
  • viewport: set via setViewport
  • scissor: set via setScissor
  • blendConstant: set via setBlendConstant
  • stencilReference: set via setStencilReference

The one exception is in a render pass, executeBundles resets some of the state, both before and after. The states reset are the bindGroups, vertexBuffers, indexBuffer, and pipeline.

Testing

Live Tests.

During dev, serve the repo as in npx servez . then open a page to http://locahost:8080/test/.

License

MIT

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