AMD Radeon RDNA2 Navi (RX 6800, 6800 XT, 6900 XT) [2020-10-28]

Discussion in 'Architecture and Products' started by BRiT, Oct 28, 2020.

  1. JoeJ

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    IIRC, research on advanced reordering in GPU HW gave a speed up of about 2 for incoherent test cases. As long as we are interested mostly in coherent rays (shadows, sharp reflections), i think that's not worth it yet. But as time moves on we might get it and then inline tracing becomes deprecated.

    However, the really interesting thought about this "AMD prefers inline tracing", and the assumption "inline tracing has been added for AMD / consoles" is this:
    It fits the TMU patent where traversal outer loop is handled from regular shader cores. And if that's what they have finally used, traversal shaders would be possible.
    So my hope AMD exposes it with extensions is not totally dead yet.
     
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  2. Cyan

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    if that's a 6800XT or similar, is much smaller than I thought

     
  3. Kaotik

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    The card on the table next to Igor? Nah, that's Radeon R9 290X, you can recognize the rear end
     
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  4. nAo

    nAo Nutella Nutellae
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  5. JoeJ

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    This is very limited. The ray has to select LOD at launch, but here we don't know the distance it travels until it hits something. Can't remember precisely, but my conclusion was this is usable e.g. for characters, but can't be extended to full scene.
    What we want is to switch LOD after the ray has passed some distance to the camera. The ray is still in air and traversal, so there is no callback or shader stage where we could do this.
    To fully emulate stochastic LOD like in the Intel paper, we could only divide the ray into segments, requiring to restart a full trace at each boundary.
    Traversal shaders would solve this, but they still lack the option to share upper BVH levels across discrete LODs which might be interesting too.
    Lacking any idea what else Traversal Shaders would be good for, implementing such LOD switches in HW instead could be enough and faster.
     
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  6. Jawed

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    If you place "transparent quads" as "LOD curtains" in a scene, you get a distance query. Or a transparent LOD sphere? Or nested transparent LOD spheres?
     
  7. JoeJ

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    Just thought about that same idea :) But then realized it's the same as dividing the ray into segments upfornt :/
     
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  8. Jawed

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    I'm thinking LOD curtains in a moderately dense grid are statically placed. This means coarser levels of the TLAS don't need to keep being updated to move the curtains with the camera. Instead there's simply "too many" curtains. The ray payload doesn't change in size as it traverses curtains, but obviously there's increased latency for the entire time of flight for a ray, much of which will be cached.

    So the payback for using curtains is low-density meshes (or billboards?) in distant, finer, levels of TLAS. Presumably it's possible to keep the BVH's size approximately constant while supporting a low rate of BVH LOD update.

    I don't know how the update for selected "distant" BVH nodes works, in order to keep dense distant meshes at "low quality", but improve meshes as they get closer to the camera (and the converse for meshes that move away from the camera). I'm struggling to find any meaningful content on BVH update strategies.

    It sounds like a fun optimisation problem. Console devs are going to have a great time exploring this stuff (PS5, mostly, assuming PC is something they can ignore).
     
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  9. Krteq

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  10. pjbliverpool

    pjbliverpool B3D Scallywag
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  11. Flappy Pannus

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    They 'target' 4k and 30fps with ray tracing. No PC vendor is going to promote their GPU with a resolution target that can only be achieved at 30fps with ray tracing.
     
  12. Subtlesnake

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    I don't really see the difference between this and Nvidia pushing DLSS instead of native 4K. (Presumably AMD's Super Resolution technology is designed to scale from 1440p to 4K)
     
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  13. Silent_Buddha

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    I found this little bit more interesting.

    That was accompanied by a slide showing >10x bandwidth density. If that somehow translates into 10x (or more) the interchip bandwidth that they can currently get, would that make multi-GPU chiplets more feasible? Obviously this is more likely related to an upcoming Zen CPU or possibly a Zen CPU paired up with a discrete GPU chip, but would it be enough to allow them to start thinking about GPU chiplets?

    Regards,
    SB
     
  14. Ext3h

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    No need to "guess" what AMD has to offer in terms of software support:

    For upscaling:
    https://www.amd.com/en/technologies/radeon-software-fidelityfx#CONTRAST-ADAPTIVE-SHARPENING
    https://github.com/GPUOpen-Effects/FidelityFX-CAS

    No surprise here, the contrast adaptive sharpening is just the quality we are used to, and not really suitable to target a higher resolution. Single frame in and out, no temporal accumulation, no integration with MSAA resolve, no integration with TAA, no depth buffer for better distinction.

    As a result, visual quality is as limited as ever. It's just nowhere near to what NVidia can do with their fully integrated DLSS 2.0 solution, it simply doesn't have enough input to achieve the same IQ in (almost) still scenes.
    Still, 1440p to 4k is still reasonable according to comments in the code. Just don't expect anything surpassing the original DLSS 1.0, with all the quirks that one had.


    For the denoiser:
    https://www.amd.com/en/technologies/radeon-software-fidelityfx#DENOISER
    The example looks like something around 1-2 samples per pixel on the input side, and then used for global illumination only, reconstructed with full G-buffer.

    No public source code yet, but the quality doesn't exactly appear to surpass the first iteration of what NVidia had to offer either.
    Keep in mind that NVidia only achieved a proper IQ in combination with DLSS, a denoiser with only a single frame worth of input can only do so much.

    All in all, not bad, but still about a man-year behind in R&D on the software end. And doesn't exactly appear to much manpower behind it either, TBH.
     
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  15. no-X

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    Why not? CAS offered better IQ than DLSS 1.0 according to almost every review.
     
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  16. Malo

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    AMD mentioned their Super Resolution as separate to their FidelityFX CAS technology. Likely it's an evolution of the tech but it's probably more than just CAS.
     
  17. Scott_Arm

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    It sounds like directml stuff. CAS is just slightly improved image sharpening. I doubt it'll be competitive with this new trained upscaling.
     
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  18. Kaotik

    Kaotik Drunk Member
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    Holy crap on a cracker :confused:

    Look at that LED-matrix behind the GPU. Also is that backplate-display built-in or something we can buy separately :runaway:
    (around 4:45 if you dont't want to watch the whole thing)


    edit: it's a pico-projector he built into the rig
     
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  19. sonen

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    woow that is the nicest thing I've seen this whole year
     
  20. ToTTenTranz

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    Navi 23:





    Weren't there some rumors claiming that Navi 23 was a "low-power premium" GPU that uses HBM?
     
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