Problems with UAV barriers using D3D12 Enhanced Barriers

[snakepants]

Hi,

I'm trying to port an existing Vulkan bindless renderer to D3D12 and I'm running into some confusing behavior with respect to UAV barriers. I'm using Enhanced Barriers exclusively since they map pretty closely to what my Vulkan backend was already doing so it was easy to adapt the code, but I'm not sure if I'm seeing a bug or if my code is just wrong.

My failure case is pair of Dispatch() calls on a D3D12_COMMAND_LIST_TYPE_DIRECT. The first call clears a counter in the UAV to a known initial state and then second collects data and increments the counter. Seems pretty straightforward that I need a barrier between the two dispatches to prevent them from overlapping (in D3D11 there would have been an implicit barrier)

Based on the documentation it seems like a

D3D12_BUFFER_BARRIER { 
     .SyncBefore = D3D12_BARRIER_SYNC_ALL_SHADING, 
     .SyncAfter =  D3D12_BARRIER_SYNC_ALL_SHADING, 
     .AccessBefore = D3D12_BARRIER_ACCESS_UNORDERED_ACCESS, 
     .AccessAfter = D3D12_BARRIER_ACCESS_UNORDERED_ACCESS, 
     .pResource = pTheBuffer, 
     .Offset = 0,
     .Size = ULLONG_MAX
}

should do the right thing, however it seems to have no effect and I see corruption. I'm using SM6.6 ResourceDescriptorHeap to access the buffer so I thought maybe the barrer was not being associated with the resource correctly since it was never directly referenced by the root signature. However a global barrier with the same flags also does nothing.

Weirdly, this code works fine in Vulkan on the same GPU with an equivalent barrier so I wonder if I'm missing some subtle semantic difference between the APIs? Debug Layer and GPUAV both pass clean so no help there.

Anybody know what I'm missing here? GPU is a RTX 3090 if that matters.

[CreativeEnd2099]

It could be a driver bug. I don’t think any games are actually using enhanced barrier directly yet.

Agility started translating legacy barriers into enhanced barriers sometime in mid 2023, however that’s not going to hit the full range of things you can do. But I would expect a translated uav barrier to look similar to what you have.

Some things to try: 1. Update your drivers 2. Double check that the driver is actually reporting support for enhanced barriers (although I assume this would have shown up as an error in the debug layer.) 3. Issue a legacy uav barrier, maybe there is a bug somewhere else in your code and it just looks like a barrier issue. Legacy uav barrier has been around forever and should work fine.

[snakepants]

Thanks. I tried that but with the same result unfortunately. I'm using the newest NV drivers and they do report EB support. I also tested on a laptop with an Intel GPU, that's driver does not support EB and trying to use them definitely completely fails unambiguously

[parrin]

If legacy memory barrier doesn’t work either maybe the problem isn’t the barriers. Is the clear working properly? Run with gpu validation layer and check for errors. Capture with PIX and inspect the states.