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Unity Raytracing - Does it use only CUDA cores, or only RT Cores, or both?

Discussion in 'HDRP Ray Tracing' started by newguy123, Oct 15, 2021.

  1. newguy123

    newguy123

    Joined:
    Aug 22, 2018
    Posts:
    1,248
    Hi guys

    I'm in the market for a new High End GPU and want maximum performance on average sized scenes for offline raytracing and sometimes pathtracing with Recorder or similar.

    Looking at the differences between a 3090 and A6000, then the A6000 slightly pulls ahead with a fraction more CUDA cores, however, the 3090 has a ton more RT cores. That makes me think the 3090 will beat the A6000 in the average scene, but only if Unity makes use of the RT cores and not just the CUDA cores.

    Also the 3090's texture fill rate is 556 GTexels, but the A6000 is 625 GTexels

    Could somebody with knowledge of this please let us know (I'm aware the A6000 has double the vram, but that only helps in much larger scenes)
     
    newguy123, Oct 15, 2021
    #1

  2. INedelcu

    INedelcu

    Unity Technologies

    Joined:
    Jul 14, 2015
    Posts:
    173
    Hi,

    Both CUDA cores and RT cores are used usually since there's no pure ray tracing execution. When a shader is executed, there are both compute instructions and ray tracing instructions. RT cores do acceleration structure traversal and ray triangle intersections and the rest of computation is done by compute units (e.g. lighting evaluation). These 2 types of computations can overlap. We don't specify how many CUDA cores and RT cores to use since it's handled by the GPU. For older GPUs from 10 series that don't have RT cores, ray tracing instructions are emulated in compute.

    Both GPUs that you mentioned are based on the same model GA102 so the specs should roughly be the same. The difference is that 3090 uses GDDR6X that has higher bandwidth than GDDR6. This might make a difference.

    I'm looking at the specs from here:
    https://www.techpowerup.com/gpu-specs/rtx-a6000.c3686
    https://www.techpowerup.com/gpu-specs/geforce-rtx-3090.c3622

    This site mentions that A6000 is 8% faster than 3090 but it really depends on what kind of benchmarks they are doing.
     
    INedelcu, Oct 15, 2021
    #2
    jeremedia, keeponshading, chap-unity and 1 other person like this.

  3. newguy123

    newguy123

    Joined:
    Aug 22, 2018
    Posts:
    1,248
    Thanks
     
    newguy123, Oct 15, 2021
    #3