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0 pointsjms552y ago0 comments

The actual issue is not CPU-side. The issue is GPU-side.

The CPU feeds commands (CommandBuffers) telling the GPU what to do over a Queue.

WebGPU/wgpu/dawn only have a single general purpose queue. Meaning any data upload commands (copyBufferToBuffer) you send on the queue block rendering commands from starting.

The solution is multiple queues. Modern GPUs have a dedicated transfer/copy queue separate from the main general purpose queue.

WebGPU/wgpu/dawn would need to add support for additional queues: https://github.com/gpuweb/gpuweb/issues?q=is%3Aopen+is%3Aiss...

There's also ReBAR/SMA, and unified memory (UMA) platforms to consider, but that gets even more complex.

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6 comments · 2 top-level

Animats2y ago· 3 in thread

> The solution is multiple queues. Modern GPUs have a dedicated transfer/copy queue separate from the main general purpose queue.

Yes. This is the big performance advantage of Vulkan over OpenGL. You can get the bulk copying of textures and meshes out of the render thread. So asset loading can be done concurrently with rendering.

None of this matters until you're rendering something really big. Then it dominates the problem.

Ono-Sendai2y ago

I believe you can do loading texture data onto the GPU from another thread with OpenGL with pixel buffer objects: https://www.khronos.org/opengl/wiki/Pixel_Buffer_Object

I haven't tried it yet, but will try soon for my open-source metaverse Substrata: https://substrata.info/.

exDM692y ago

It is possible but managing asynchronous transfers in OpenGL is quite tricky.

You either need to use OpenGL sync objects very carefully or accept the risk of unintended GPU stalls.

Ono-Sendai2y ago

Yeah you need to make sure the upload has completed before you try and use the texture, right?

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dc4432y ago· 1 in thread

Thank you. I hope to see progress in these areas when I visit later. I was hoping to be able to go all in on wgpu but if there are still legitimate reasons like this one to build a native app, then so be it.

jms55OP2y ago

It depends on your requirements and experience level. Using WebGPU is _much_ easier than Vulkan, so if you don't have a lot of prior experience with all of computer graphics theory / graphics APIs / engine design, I would definitely start with WebGPU. You can still get very far with it, and it's way easier.

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