SER pathtrace sample does nothing, SER doesn't appear to work on Vulkan

[BattleAxeVR]

Just wanted to add this here as well for visibility, since the issue affects both Path Tracing SDK (in Vulkan mode, DX12 works fine), and this repo as well.

Toggling the SER feature on/off has no effect on the framerate, nor the heatmap:

https://github.com/NVIDIAGameWorks/Path-Tracing-SDK/issues/2

I tried both game ready and latest beta drivers on my RTX 4090, in both code samples by Nvidia, and in both apps, the SER feature doesn't seem to work at all on Vulkan, only DX12 (in Path Tracing SDK). To enable it in that repo I had to add a couple lines, since it appears obviously that Vulkan is a second-class citizen compared to DX12.

[BattleAxeVR]

SER OFF:

[BattleAxeVR]

SER ON:

[NBickford-NV]

Looks like part of this is a silly bug in ser_pathtrace: the propagation of the specialization constant was accidentally removed 2 weeks ago in https://github.com/nvpro-samples/vk_mini_samples/commit/c5e5d6a550dd1ce96d6e1e62dfae2fdacdc51f9b#diff-6f12885eca6326d135a50a24e87c259021fad71cab5e5f23001e4f89020c78cbL557. (To reproduce, try modifying payload.nrm in the USE_SER branch of traceRay() in pathtrace.rgen.)

This fixes that:

    m_dutil->setObjectName(stages[eClosestHit].module, "Closest Hit");
#endif

+    stages[eRaygen].pSpecializationInfo = specialization.getSpecialization();

Could you try that on the 4090 and see if you see a difference now?

[BattleAxeVR]

YES! That fixed it. Thanks so much!

[NBickford-NV]

Awesome! I'll close this bug once the fix is in the public repo.

[BattleAxeVR]

[BattleAxeVR]

Awesome! I'll close this bug once the fix is in the public repo.

Any chance you could help me figure out why it's also broken in the Path Tracing SDK? I'd like to validate VK + DX12 have the same exact perf w/ SER enabled.

[BattleAxeVR]

I already got that repo to show the feature works / enumerated by adding it to the requested device extensions on VK, but the toggle isn't doing anything.

[mklefrancois]

Thanks for reporting, this commit should fix the issue. https://github.com/nvpro-samples/vk_mini_samples/commit/6b70af33aad8bf3c214f77b72357e2350dd02b1c

[NBickford-NV]

@BattleAxeVR For the Path Tracing SDK, let's follow up on the issue at https://github.com/NVIDIAGameWorks/Path-Tracing-SDK/issues/2#issuecomment-1920882049 .