NVIDIA / NVIDIA/cutlass

[QST] why the implementation of f16xs8 mixed gemm is different between TRT-LLM and native cutlass mixed gemm example?

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Description

What is your question?
Dear cutlass team,

lets consider sm80 and f16s8, the example of f16s8 TN mixed gemm shown here is different from TRT-LLM implementation, specifically, to my knowledge, the TRT-LLM one added the dequantization scale, but the cutlass one did not. Then my questions are:

  1. Is the performance or accuracy of TRT-LLM adding dequantization scale better than cutlass native one in LLM linear cases?
  2. from here, I see the TRT-LLM one seems load operand B(s8) using LDS not LDSM, but I can't find the f16s8 LDS specialization in MmaTensorOpMultiplicandTileIterator, only find LDS specialization for TF32, which make me confused with the “LDS". Am I missing something?

Thanks your time!

cc @manishucsd @alexsamardzic @hwu36

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Research direction

Compare the native CUTLASS f16s8 TN mixed GEMM example linked from PR 1084 with TensorRT-LLM's fpA_intB_gemm_template.h and dq_mma_pipelined_finegrained.h. Trace the referenced MmaTensorOpMultiplicandTileIterator implementation for the sm80 path. Done means documenting the dequantization-scale and LDS/LDSM differences and answering their performance, accuracy, and specialization questions.

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Assessment

Tech stack
cpp
Domain
hpc, machine-learning
Issue type
Documentation
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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