[GitHub] [tvm] masahi edited a comment on pull request #7056: [TOPI] GPU scatter 1D via sorting based approach

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masahi edited a comment on pull request #7056:
URL: https://github.com/apache/tvm/pull/7056#issuecomment-740919507


   > As a larger conversation, I don't love how much we're depending on thrust for functionality, I'd kind of like to fix the issues in topi around sort so we don't have to lean on thrust so much. We're depending on the nomially cuda topi kernels for a lot of other GPUs, so this trend makes it harder to support more diverse hardware.
   
   @mbrookhart @zhiics While I fully agree with this generally, for fundamental, low level GPU primitives such as sorting, scan etc, I think it would be really hard for generic implementations to match or outperform platform specific libraries. These libraries have years of development behind it and use platform specific intrinsics to maximize performance. This also applies to cuDNN, but unlike convolution op, I don't think AutoTVM or Ansor would help generate efficient sort or scan ops.
   
   Sooner or later, I think we will introduce `cumsum` op to TVM. On CUDA, `cumsum` can be implemented very efficiently via thrust or cub's `inclusive_scan`. But without it, we have to roll our own GPU scan implementation that can compete with vender-provided one, which I think would be a formidable or near impossible task.
   
   So my opinion is, while native TVM solution is always what we should strive for, if there is a platform specific library, we should embrace it. Sort, scan etc are standard enough that there is a good chance platform specific library is available. For example, rocm has their implementation of thrust, on OpenCL there is Boost.compute.


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