XB1/PS4 Polygon pushing power

Discussion in 'Console Technology' started by MBDF, Dec 7, 2013.

  1. MBDF

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    I was just wondering from a somewhat newb perspective; how is the polygon pushing power of these machines. First off I know that the X1 gpu was likely upgraded from one to having two geometry engines? This was of course to keep some parity with PS4 as it also has two geometry engines (vert setup?)

    The question I'm asking though is this: Does the extra compute power in PS4 (those extra CU's) allow for a higher polygonal ceiling in real world scenarios? I'm assuming yes, as the CU's can be dedicated to vertex shading.. is this true?
     
  2. scently

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    Xbox One always had 2 geometry engines.
     
  3. MBDF

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    Yeah, but the chipset it's GPU was based off of only had one I believe.. Was it Bonaire?


    But anyways the more important question is... is the ceiling afforded by two geometry engines easily obtainable by both APU's in a real game scenario (as in.. is it limiting?) or does the extra shader grunt of the PS4 APU allow it to get closer to that ceiling?
     
  4. AlBran

    AlBran Ferro-Fibrous
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    Bonaire has 2.
     
  5. Grall

    Grall Invisible Member
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    I believe it's a mistake to believe either of the APUs in the new consoles are "based" on any existing thing in particular, they're custom order jobbies designed for either company that ordered them.
     
  6. shredenvain

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    Well I dont know if having a higher cu count would effect the poly count. Clockrate does though.
    The xbox one because of the gpu clock increase is capable of 1.7 billion polys a second. The Ps4 is at 1.6 billion
     
  7. fellix

    fellix Hey, You!
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    GCN doesn't distribute the geometry workload across the multiprocessors (CUs) like what Nvidia does, so there shouldn't be disparity between PS4 and XBO setup rates -- just the clock-rate difference.
     
  8. MBDF

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    I know Xbox has a higher setup rate. I am wondering though if becasue PS4 has more shaders available, can it push more polygons, all else being equal.
     
  9. ultragpu

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    Pushing more polygons means more shading, more texturing, more shadowing, more collision detection etc..which I don't think the Bone could afford to even if it could theoretically push more polys. So in the real world I think PS4 should be able to render more polygons anyway since it's more balanced to do so.
     
  10. Grall

    Grall Invisible Member
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    Furthermore, adding more polys would require different art (which has a production cost impact, often a big one) - unless you're simply just tesselating, and AMD chips have traditionally not excelled at this so I don't know how common tesselation will be in this console gen.
     
  11. Rangers

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    He's just asking about polygons, not anything else. And there's no "even if it could theoretically" . It can.
     
  12. steveOrino

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    No he didn't, he asked:

    Yes.

    Triangle setup is a pointless metric by itself because it depends on so many variables.

    How complicated is the vertex shader?
    How many verts shaded per triangle?
    How many of those tris are culled?
    How many fragments are there?
    How complex are the fragments?

    So if we are talking meaningful real-world polygon pushing potential then yes, the PS4's GPU has the higher ceiling.

    Once these machines are rooted we could probably get real numbers from benchmarking.

    Anyways, I think fill rate would be the more meaningful performance metric.
     
  13. Steve Dave Part Deux

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    There are way too many variables to get at answer to that question. Designing a shader that would create max throughput at any part of the pipeline wouldn't be of any practical use. The difference is negligible in either direction.
     
  14. MBDF

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    So wait.. I'm confused... do the geometry engines in PS4's GPU take over the task that was one relegated to shaders on say... Xenos? Because I remember a chart showing that if Xenos dedicated all it's shading to verts it could push an obscene amount of geometry (limited only by it's setup rate). Am I mistakenly thinking that the PS4 (or Xbox One) could do this as well(dedicate all of it's shaders to verts)?

    Because if so, PS4 would have more vert proccessing power available given it has more shaders it could allocate to verts.

    Correct me if I'm wrong.
     
    #14 MBDF, Dec 9, 2013
    Last edited by a moderator: Dec 9, 2013
  15. sebbbi

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    Agreed, but you can think it in an inverse way :)

    Every shader is bound by some bottleneck, and thus maximizes the throughput of that part of the GPU. Shadow mapping for example is either bound by the primitive rate or the fill rate (ROPs) (not by BW since depth compression solves that). The large objects (low triangle density) are ROP bound and the small objects (high triangle density) are primitive bound (in general).

    Every developer tries to balance the GPU usage. Deliberately hitting a bottleneck (maximizing throughput of only one part of the hardware while other parts are idling) is of course a stupid design decision :)
     
  16. MBDF

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    My next question is what does a geometry engine do exactly?

    Isn't it just setup?

    Like for instance Xenos could setup, I believe, 500 million polygons per second.

    Xenos could generate much more than that though, correct?
     
  17. 3dcgi

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    I don't know why people don't think geometry work is distributed across the CUs. Geometry related shading can execute on any CU.

    Geometry engine is a marketing name encompassing all fixed function hardware related to geometry processing. This includes vertex reuse checking, tessellation, index fetching, clipping, setup, etc.

    Xenos peaked at 1 triangle or 1 vertex per clock and vertex reuse determined which limited performance. At some point there could be too many ALUs in the VS or too many memory fetches and peak rate would not be maintained.

    More CUs potentially means you can execute longer vertex shaders, but you would need to run benchmarks to know if it really makes a difference.
     
  18. MBDF

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    Thanks for the info!
     
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