AMD VLIW4 GPUs and fp64

Discussion in 'GPGPU Technology & Programming' started by codedivine, Jul 26, 2013.

  1. codedivine

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    Hi folks. I am wondering if the AMD's VLIW4 based GPUs (6900 series and Trinity/Richland) support fp64 under any API. Various media outlets had mentioned the support for fp64 in both the 6900 series launch articles as well as Trinity.

    But the API support is .. odd. I have documented some observations here: http://codedivine.org/2013/07/26/amd-vliw4-gpus-and-double-precision-floating-point-fp64/

    Can anyone clarify the situation? Also, can someone with a 6900 series (and/or Trinity/Richland) verify the double precision DirectCompute support using something like DX Caps Viewer?
     
  2. Davros

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    tell me where to get it
    without me having to download the full directx sdk
     
  3. codedivine

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    Not sure. I hacked up a small command-line tool that you can use. This will list all the GPUs installed in the system and list their double-precision capabilities. As a bonus, I added a query for driver's DX11 multithreading capabilities as well.

    EXE: http://www.rgbench.com/testfp64_win7.exe
    Source code: http://www.rgbench.com/testfp64_win7.cpp

    Compatible with Windows 7 or higher. 32-bit exe that should work everywhere.
     
  4. Priyadarshi

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    AFAIR, the HD 5800 series supported FP64 in OpenCL and they have VLIW4 SIMD units.
     
  5. codedivine

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    Nope. Radeon 5800 series (the only ones to support fp64 under OpenCL in the 5000 series) are VLIW5 and not VLIW4.
     
  6. swaaye

    swaaye Entirely Suboptimal
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    I saw someone say on the TR forum that Fp64 support in VLIW4 chips had been dropped in recent drivers. I just went digging for that post and realized it was you! ;)
     
  7. Sinistar

    Sinistar I LIVE
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    AMD Radeon HD 6900 Series
    Feature level 11.0
    Successfully opened device
    Supports doubles? Yes
    Supports concurrent resource creation? Yes
    Supports driver command list? No
     
  8. codedivine

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    Thanks a lot! Looks like 6900 series supports fp64 under DirectCompute at least. From other B3D threads, we know it supports the non-standard cl_amd_fp64 but not the standard cl_khr_fp64.
     
  9. Priyadarshi

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    Oh yes, I meant the 5800 series and they are VLIW5! My guess would be the transcendentals on VLIW4 don't conform to DP requirements by Khronos.
     
  10. codedivine

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    Btw can you also post which OS and driver version you are running? Thanks a lot for your help :grin:
     
  11. Sinistar

    Sinistar I LIVE
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  12. codedivine

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  13. Davros

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    win 7 x64
    6950 cats 13.4




    C:\Temp>testfp64_win7
    AMD Radeon HD 6900 Series
    Feature level 11.0
    Successfully opened device
    Supports doubles? Yes
    Supports concurrent resource creation? Yes
    Supports driver command lists? No
     
  14. OpenGL guy

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    HD6900 series supports both. I think you are confused because doubles are a part of the OpenCL 1.2 core spec and not an extension.
     
  15. codedivine

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    Well thanks for the 6900 series clarification. I guess 6900 series seems fine then. Also, my understanding of the spec is that you are still supposed to provide cl_khr_fp64 if you support double precison under OpenCL 1.2 for backwards compatibility. Anyway, I will keep this in mind and add both tests (cl_khr_fp64 for v1.1 and the GetDeviceInfo property for v1.2) to my codepaths in the future.

    But I think the Trinity/Richland situation is still not clear. On my 8650G, I see no support for double-precision under Direct3D and only support for cl_amd_fp64 under OpenCL but no cl_khr_fp64. The property CL_DEVICE_DOUBLE_FP_CONFIG also indicates that no fp64 support is present, thus I guess Trinity GPU is not really a compliant fp64 part.

    edit: I have also edited my blogpost to say that the 6900 series seems fine but Trinity/Richland not. Thanks for the replies.
     
  16. 3dcgi

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    AMD A10-4655M (Trinity)
    AMD Radeon HD 7620G
    Feature level 11.0
    Successfully opened device
    Supports doubles? No
    Supports concurrent resource creation? Yes
    Supports driver command lists? No
     
  17. OpenGL guy

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    That's correct. We don't expose doubles for the GPU device on Trinity/Richland aside from cl_amd_fp64.
     
  18. Davros

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    whats the difference between cl_khr_fp64. and cl_amd_fp64
     
  19. Dade

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    cl_amd_fp64 inludes the support only for few basic math operators (like *, /, +, - and not very much more). It was introduced to expose the limited double support of HD5xxx family.
     
  20. OpenGL guy

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    Not true as HD5800 chips support full double precision support in OpenCL. The rest of the HD5xxx family had no double precision support at all.
     
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