Direct3D feature levels discussion

Discussion in 'Rendering Technology and APIs' started by DmitryKo, Feb 20, 2015.

  1. Kaotik

    Kaotik Drunk Member
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    FP16 is supposed to be available on Polaris (same speed as FP32) and Vega (twice the speed via RPM). R9 380X is GCN3
     
  2. CarstenS

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    According to Anandtech, even first-iteration Tonga (R9 285) had FP16-instructions. No mention though, to what extend. The slide says "New 16 bit floating point and integer instructions for low power GPU compute and media processing."
    https://www.anandtech.com/show/8460/amd-radeon-r9-285-review/2
    The slide in question:
    https://images.anandtech.com/doci/8460/GCN12ISA.png

    I need to dig up my older DXDiag-logs, but IIRC, there were drivers which reported back "16/32 Bit" for minimum precision query even on GCN1.2/GCN gen 3 (which is the same, depending on where you start to count) Tonga and Fiji. Not 2× speed of course.
     
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  3. CSI PC

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    #903 CSI PC, May 1, 2018
    Last edited: May 1, 2018
  4. willardjuice

    willardjuice super willyjuice
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    GCN3/GCN4 FP16 was useful for register pressure even though it was the same rate as FP32 (you could pack two FP16 elements into a register). I think they also lacked some of the FP conversion instructions Vega supports too (I can't recall and I'm too lazy to check the ISA) which further limited their usefulness in situations involving mixed precision. All in all, I think in practical terms the "FP16 support" on those cards weren't useful. The planets really had to align to show a benefit for GCN3/4. It's probably why amd "retired" support in drivers, more trouble than it was worth.
     
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  5. DmitryKo

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    It looks like barycentric intrinsincs are not enabled by default in the Catalyst driver - you have to use AMD GPU Services library to enable video driver extensions then check for AGS_DX12_EXTENSION_INTRINSIC_BARYCENTRICS:

    https://github.com/GPUOpen-LibrariesAndSDKs/Barycentrics12
    https://gpuopen-librariesandsdks.github.io/ags/amd__ags_8h.html
    https://github.com/GPUOpen-LibrariesAndSDKs/AGS_SDK
     
    #905 DmitryKo, May 27, 2018
    Last edited: May 28, 2018
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  6. donjulio

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    I don't know if it makes sense, but I couldn't find a the data for on Intel Core with Radeon RX Vega M Graphics. So here we go:

     
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  7. Malo

    Malo YakTribe.games
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    Definitely doesn't seem to be Vega ISA thereby confirming it's based on Polaris?
     
  8. donjulio

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    That’s why I did run this in the first place as soon as I got in touch with that CPU. But I’m still not sure if this can confirm anything.
     
  9. Ryan Smith

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    We've previously been able to work out that the graphics core is Polaris based on AMD's Linux driver commits. It's using the gfx8 family branch, which is Tonga/Fiji/Polaris. Vega is gfx9.
     
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