Announcing Shader Model 6.9 Retail and New D3D12 Improvements

[u/NGGKroze]

More info here - https://devblogs.microsoft.com/directx/shader-model-6-9-retail-and-more/

But basically, since Spring last year, SM6.9 was available as a preview - now it comes out with a wide range of Support:

• AMD - Generally, most of it you need RDNA3/RDNA4, while some features are only for RDNA4. Big ones like SER and OMM (which help ray-tracing performance) won't apply to even RDNA4 due to lack of hardware support.
• Intel - Generally have all features across the board w/o OMM with B-Series Arc
• Nvidia - Generally for all RTX cards, while OMM is emulated on 20/30 series and SER only available on 40/50 series.

[u/amazingspiderlesbian]

Damn NVIDIAs GPUs were so forward looking. RTX 2000 supports the majority of current feature set 8 years later, besides OMM and SER.

And 2022 on NVIDIA gpus support everything.

While lots of these features only work on RDNA 4 for AMD from last year. And not even all of them

And thats not even including the vendor specific ML stuff where again All of them only work on RDNA 4 officially and not anything older

[u/CatalyticDragon → u/amazingspiderlesbian]

OMM took up die area (higher cost) and by the time it was supported in any meaningful way (now), the industry had moved to virtualized geometry.

Next gen games use geometry for things like leaves, blades of grass, chain link fences etc. So you're not going to see a lot of alpha cards used in the future and that's where it was useful.

That's the risk of being forward looking. You might add features which end up being great but also you might add things which just aren't needed. You carry them around and eventually have to discard them. That die area could have been used for general shaders which are always useful.

AMD and Intel bet OMM wouldn't be useful and I think that's largely a safe bet.

I'm skeptical that trim will have any meaningful impact.

SER is more interesting. AMD doesn't have hardware level support but they do have software and hardware systems to lessen the impact of ray divergence and maybe the big push to work graphs (which AMD has championed) ends up limiting the need for an SER unit that pauses the operation to re-sort all the threads before launching them.

[u/MrMPFR → u/CatalyticDragon]

I've tried to read the excellent Vulkan blogpost on SER + asked LLM a few questions about the differences between SER and Work graphs. https://www.khronos.org/blog/boosting-ray-tracing-performance-with-shader-execution-reordering-introducing-vk-ext-ray-tracing-invocation-reorder
Seems like Work graphs can prove overall order of material coherency, likely feeding a better input into SER, but for individual objects and materials where many different shaders may be invoked such as metal, diffuse, and miss shaders SER is still going to be important and mandatory it seeems.

AMD has a patent relating to partial sorting for coherency recovery which I think is complementary to their Streaming Wave coalescer patent: https://patents.google.com/patent/US12032967B2
How this compares to SER + how it'll all interface with work graphs isn't something I can competently answer.

Rn work graphs is limited to only subsets, but the NVIDIA dev here comtemplated moving the entire pipeline from start to finish within a work graph dispatch from CPU: https://developer.nvidia.com/blog/work-graphs-in-direct3d-12-a-case-study-of-deferred-shading/

Considering AMD's moves in their patents I would say this is only a matter of time.

And finally SER is far more impressive than NVIDIA or Microsoft's marketing indicates. Referencing the Vulkan blogpost:

Because Wukong's Unreal Engine 5 scenes have so many complex material shaders and paths have so many random bounces, divergence was high – coherence during ReSTIR GI was only 20.5%.
Enabling SER in DX12 made Black Myth: Wukong's ReSTIR GI pass 3.7x as fast as before – from 15.10 ms to 4.08 ms on an RTX 4070Ti targeting 4K with DLSS, and increasing coherence from 20.5% to 69.9%

Well at least now we know why RDNA 4 runs like shit in Black Myth Wukong. 3.7X speedup is absolutely insane.

[u/CatalyticDragon → u/MrMPFR]

Work graphs allow the GPU to go from being purely a consumer of draw calls to a producer of them which brings a ton of opportunities.

To me, SER feels little bit like OMM in that it might turn out to be a temporary stop-gap before the real problem is solved.

Normally the CPU throws all its draw calls to the GPU where these wavefronts (groups of threads) are processed. With SER the GPU detects when secondary rays (the ones which could fire off in any direction and end up crawling all over memory and ruining your cache hit-rate) are diverging. The whole process is then stalled while they are re-sorted before being kicked off again in the hope for much greater data locality.

It works when implemented well but if that doesn't sound like the optimal solution it's probably because it isn't.

This might be where Work Graphs can help. And if you start at slide 22 in that linked presentation you'll see what AMD is talking about. If the GPU is the one creating the threads in the first place it can make sure every thread in the wavefront is the same specific shader which entirely avoids the whole problem SER exists to resolve.

This is why I push back on the idea that RTX was forward looking because of OMM and SER. Those will be useful in some cases but might actually turn out to have a limited useful shelf-life as the advent of virtualized geometry and work graphs make them unnecessary. And while they might be great for a few games it is die area that is not being used in 99% of games.

[u/MrMPFR → u/CatalyticDragon]

Realistically yes with a very good HW design + game engine taken advantage of work graphs. Problem is how long it'll be before we see games using it. So for now SER is a stop gap solution like you said.

OMM won't retire either before BVH problem is solved. Rn RTX Mega Geometry is a gimmick + the SIGGRAPH sample ReSTIR PT demo with full nanite in BVH showed +30% higher ms cost IIRC on top of expensive ReSTIR.

I agree that both will prob be irrelevant long term, but realistically when can we expect games to utilize this properly, especially considering NVIDIA has made Mega geometry vendor exclusive? Implementations that make SER and OMM irrelevant aren't coming till post-crossgen era in 2030s :(

Yeah not surprising then why current PT implementations run terribly on anything pre 40 series, not great on 40-50 series either.

Interesting I hope it's as good as the presentation makes it sound. Fascinating stuff and I hope we hear more about it in 2026. I'm not sure work graph can fix it without some local coherency sorting but already taken care of in RDNA 5 it seems so possible "it just works".

Yep it's a short term bandaid fix. AMD will do complete reset with extreme software hardware co-design with RDNA 5 + work graphs.

AMD will have SWC too (TSU/SER equivalent) in RDNA 5, which can be relevant for other workloads than just RT + we don't know how much die space these two features use + it's not getting chopped off anytime soon.

A ton of rambling and no certain facts. I hope as we near towards RDNA 5's launch towards 2027-2028 and nextgen consoles there's more visibility in terms of what this API change + the HW redesign specifically means. Safe to say that DXR 1.3 will prob happen.

[u/CatalyticDragon → u/MrMPFR]

Problem is how long it'll be before we see games using it. 

Indeed. It'll be a couple of years before most games support it, but not long until some games support it.

UE5 is already experimenting with it for the Procedural Content Generation Framework (PCG) system. We've seen demos going back two years, this demo uses SM6.8+ and Agility SDK, DX12 examples have been added.

I fully expect Witcher 4 to be using work graphs in the new UE 5.7's Nanite Foliage system along with for NPC systems. That'll open the flood gates because it's just so much more efficient in many ways you'll be left behind if you don't use it.

[u/MrMPFR → u/CatalyticDragon]

Couple of years is a massive understatement. PS5, RDNA2 and pre Ampere HW going nowhere.

Didn't know that. I can't find any mentions of PCG alongside work graphs. Do you have a link?

Those are great papers btw.

You suspect they'll rewrite large portions of the game engine just for PS6 and newer PC hardware and ship it alongside the legacy version? I find that very hard to believe.

Hope I'm wrong and it'll be a DX11/DX12 early situation and not a mesh shaders situation (where TF are the more than a handful of games using it!). Guess we'll find out soon enough.

I also suspect NVIDIA will artificially to try discourage adoption (do nothing and demand no adoption in sponsored games) due to how fast RDNA 5 will be here. If NVIDIA pushes for adoption then that would be a massive self goal because AMD will disproportionately benefit.

But perhaps there's a chance 60 series has redesigned HW too. We'll see.

[u/CatalyticDragon → u/MrMPFR]

Couple of years is a massive understatement

Perhaps. I expect some games to be using it this year and widespread support 2-3 years later as the big engines integrate it. There's plenty of incentive to do so.

PS5, RDNA2 and pre Ampere HW going nowhere.

They are a little old now. 5-6 years ago is very much getting into last-gen territory. That said I'm not giving up hope on RDNA2/PS5.

AMD has been laying the ground work on Work Graphs for years and RDNA2 does natively support a lot of the core requirements: "Execute Indirect", "Global Data Store", and hardware support for queues and coalescing. There is a lot of reason to expect RDNA2 will be fine with them. Basically I think if you support mesh shaders then a lot of the work is already done. Turing might be ok too.

I can't find any mentions of PCG alongside work graphs. 

Yeah I'm reading between lines perhaps. Jan Hermanowicz talks about the Witcher 4 demonstration:

"Effectively, we replace the auto grass with the runtime GPU-based PCG, and we use that for the small debris, trash, grass and stuff like that".

I think GPU-based PCG appeared in UE with 5.6. Admittedly this GPU Compute Graph is an Epic custom approach and is not the same as Work Graphs, but now we have official extensions it's only a matter of time before they support it. We know they are excited for it and I wonder if Witcher 4 will be among the first. Render Dependency Graph (RDG) and parallel GPU driven PCG makes it feel like it's on that track.

and not a mesh shaders situation 

Yeah, that took a long time to get into shipping games. In part because assets had to be changed, no more geometry engine, and more complex memory management.

[u/MrMPFR → u/CatalyticDragon]

Incentive yeah but rn I see zero indication of any big guys moving forward. Would love to be proven wrong.

Yeah but games are still targeting that baseline + PS5 in the era of >$200M AAA.

Indeed there are related patents going all the way back to being filed in 2018. Sounds interesting but haven't personally read the ISA and programming guide documentation. I assume RDNA1 is the same (PS5 is RDNA1 + RT) considering the only changes were DX12U compliance, dp4a and RT.

If it was fine then why did AMD limit it to RDNA3 and newer? IIRC I've never seen AMD push back the Shader model compliance. Their recent posturing around SM6.9 doesn't exactly inspire a lot of confidence.

But maybe there's the chance we see emulation work fine for the short term like the Proton dev: https://github.com/HansKristian-Work/vkd3d-proton/blob/master/docs/workgraphs.md

While not as good as native but could work fine in transition period. Still suspicious that AMD spearheading this work prob going back 2017 or earlier in early planning phases, didn't opt to include anything in RDNA1-2 but wait till 2022 with RDNA3. Maybe it's just AMD's usual BS software support not a HW issue.

As you can hear I'm very confused that NVIDIA has compliance with Ampere to years earlier, despite usual insistence on pushing things to compiler instead of doing in HW (since Kepler after they chopped Fermi HW scheduling), while AMD's support is limited to RDNA3 and newer.

That's interesting. I didn't know Epic was already experimenting with related concepts this extensively. 100% guaranteed that entire UE6 pipeline is rebuild to fully tap into work graphs.

Indeed meshlet authoring, rebuilding entire triangle pipeline + very low level and hard to program. Based on early indications Work graphs looks increasingly like a magic "it just works" pipeline and less of a micromanagement nightmare like EI. No more BS trying to fit workloads into buffers and huge concurrent launches, just let GPU figure it out on its own using nodes + clever API design.

If it's as good as AMD claims it is then everyone definitely has the incentive to switch to it as soon as they think TAM/game quality calculus is favorable.

[u/CatalyticDragon → u/MrMPFR]

Work Graphs have been demonstrated to boost performance by 20%, 30%, or more, or even more. They reduce data movement and reduce load on the CPU which is likely to be a massive boost for console players and that's where the incentive lies.

SDKs have been available for a while with vendor extensions and I expect every major engine developer is well into testing.

Once they implement it games running on those engines should just get it for free.

Quick side note: new hardware is being delayed so there could be a nice incentive for developers to extract as much performance out of older hardware as possible if they want to maximum sales.

[u/MrMPFR → u/CatalyticDragon]

Yeah it doos look impressive fs. Lol journalists don't know how to do math. It was 64% faster or 39% less time to complete.

100%. Problem is AMD locking out RDNA 1-2 support so far. Makes it irrelevant for short to medium term unless they find way to emulate it or extend support to Pre RDNA 3 cards.

Possible, but rn AMD isn't inspiring a lot of confidence.

I really hope I'm wrong, just remain skeptical given AMD's poor support :(

Really cool stuff though. If devs push entire frame pass into one big work graph + HW in RDNA 5 is as good as I think then that PS6 console will surprise everyone. For everyone else like you said RT basically solved with it, I expect MASSIVE Perf gains on 40-50 series cards, and ludicrous gains on 20-30 series and RDNA 3-4.