Browser WebGPU?

[mighdoll]

Is support for WebGPU development on your radar?

[miguel-petersen]

Hi Mighdoll.

At this moment WebGPU is not being considered for support.

[miguel-petersen]

To clarify, we are currently not seeking official support.

However, if WebGPU translates down to either DX12 or Vulkan (apologies, I am not too familiar), then GPU Reshape is able to hook into it.

[mighdoll]

Yep, I think there'd be hope that GPU-Reshape could hook in when running a browser on the the right platform. In WebGPU land, we're eager for GPU tool support!

Here's a bit about chrome: https://chromium.googlesource.com/chromium/src/+/main/docs/security/research/graphics/webgpu_technical_report.md
and firefox: https://github.com/gfx-rs/wgpu

[miguel-petersen]

I took a quick look, and I am able to "attach" if I launch from Reshape, though no other chrome instances may be running before.

Specifically, I launch from Reshape with (provided by an AMD fellow!):
--disable-gpu-sandbox --disable-direct-composition -enable-dawn-features=emit_hlsl_debug_symbols,disable_symbol_renaming

However, something is broken in the rendering. I don't think it's actually presenting, particularly also because during presents some data is sent back to the app, and I get nothing.

[miguel-petersen]

One thing about Chrome is that sub-processes are spawned with process mitigation policies.
https://github.com/chromium/chromium/blob/b119cd4f3bf59a6b58553420741713a88b5325eb/sandbox/win/src/process_mitigations.cc#L460

Which I check against here.
https://github.com/GPUOpen-Tools/GPU-Reshape/blob/main/Source/Backends/DX12/Bootstrapper/Source/DLL.cpp#L795

Chrome's sandboxing enables it. If a process enables either mitigation policy, I cannot inject my bootstrapper. I wonder how PIX (I heard it can do it?) handles it, I could tamper with the creation parameters, but I'm not sure if that's the right way forward, and could be seen as malicious, maybe.

Chrome does have a --no-sandbox parameter which avoids it, but then Reshape fails to discover any device on newly spawned tabs (new processes). Strange lands.

[miguel-petersen]

As a repro case, this is what I'm doing.

Reshape launch parameters:
App: C:\Program Files (x86)\Google\Chrome\Application\chrome.exe
Cwd: C:\Program Files (x86)\Google\Chrome\Application
Args: --disable-gpu-sandbox --disable-direct-composition -enable-dawn-features=emit_hlsl_debug_symbols,disable_symbol_renaming --no-sandbox https://webgpu.github.io/webgpu-samples/samples/helloTriangle

It does launch, and connect to a device, but something breaks somewhere. This'll be an interesting one to debug!

[miguel-petersen]

From a brief investigation it appears that a command list is failing to close, likely indicating a validation error somewhere.

It'd be nice if it's a quick fix.

[mighdoll]

I posted a ref to this bug over on: https://matrix.to/#/#webgpu-dawn:matrix.org. I recommend dropping in over there if you have questions about Chrome/Dawn!

[miguel-petersen]

I joined the room 🙂

Managed to get this validation error out of Dawn with Reshape, probably what's causing the command list to fault.
D3D12 ERROR: ID3D12GraphicsCommandList::CopyBufferRegion: Invalid Command List method (CopyBufferRegion) called within a Render Pass. [ EXECUTION ERROR #1203: RENDER_PASS_DISALLOWED_API_CALLED]

[kainino0x]

GPU work in chrome is all done in a single GPU subprocess. That process definitely needs sandboxing disabled to debug it.
Here are instructions on how to get it working with PIX:
https://gist.github.com/Popov72/41f71cbf8d55f2cb8cae93f439eee347
(The flags are the same as the ones you mentioned.)

That's likely the best option but if any problems are caused by launching multiple processes, there are other options:
https://chromium.googlesource.com/chromium/src/+/main/docs/gpu/debugging_gpu_related_code.md#debugging-in-the-gpu-process

• There is a flag called --gpu-launcher which prepends some arguments (i.e. a debugger or profiler) to the GPU process launch:
  https://peter.sh/experiments/chromium-command-line-switches/#gpu-launcher
• And another one called --gpu-startup-dialog which pauses GPU process startup before it starts doing anything, so you can attach a debugger and continue:
  https://peter.sh/experiments/chromium-command-line-switches/#gpu-startup-dialog

Another option to incrementally investigate this would be to try debugging Dawn samples, though unfortunately you would have to build them from Dawn. If that error is coming from the D3D12 debug layer - both Chrome and Dawn should run cleanly against it, but Chrome has a lot more going on, so running just Dawn would narrow down where it's coming from. There are also ways to enable the D3D12 debug layer for Dawn (I think the flags are: when launching chrome, --enable-dawn-backend-validation; when launching dawn samples/tests, --enable-backend-validation; but tell me if those don't work)

[miguel-petersen]

As of d46430d it seems to render properly, however, does not send any data back yet.

Please note that the change is incomplete as I need to carefully manage the before / after access states of each render target and depth stencil, something I need a little more time to think about. Currently it just blindly reconstructs the render pass, which is incorrect.

[miguel-petersen]

@kainino0x Absolute pleasure to have a direct contributor here, thanks for the wealth of information!

Regarding D3D11On12, would you know how (Chrome) WebGPU utilizes it? Reshape does support hooking D3D11On12, however, it currently doesn't do much with it. Is it somehow involved with presentation?

Particularly on presentation, Reshape doesn't seem to hit hit any hooks, so I'm very much curious how that happens.

[miguel-petersen]

The issue is definitely regarding presentation. Currently Reshape sends data back during presentation, as I'm not hitting that hook nothing ever gets sent.

If I add a dummy thread to pump out data manually, I can get Reshape communicating. This is a change I've been meaning to do anyway, so I'll track it here.

Instrumentation seems to do its job as well. Though I am having troubles getting debug sources working. 🤔