CUTLASS 4.2.0

[hwu36]

CuTe DSL

• More Python versions are now supported for both x86-64 and aarch64, including
  • Python 3.10, 3.11, 3.12, and 3.13
• Added new example and updated notebook to get started with CuTe DSL
  • Call kernels with dlpack bypassed
  • Updates on TensorSSA demonstration
    • Added a section for introducing the broadcast
• API updates
  • Please refer to DSL API changelog for details
• Bug fixings and improvements
  • Fixed cute.print_tensor for coordinate tensor
  • Fixed cute.print for tuple of layouts
  • Fixed frozen object is not properly updated after fully assigned in dynamic control flow
  • Fixed assign tuple/list element in a dynamic control flow may cause compilation failure
  • Improved error message when CUDA context is not initialized
  • Improved docstring of congruent and weakly_congruent

CUTLASS C++

• Support for Blackwell SM103 kernels for B300 GPUs.
  • Collective mainloop codes: Blockscaled datatypes with support for dense GEMM mainloop
  • New GEMM and epilogue dispatch policies for collectives, kernel layers, and builders.
  • Kernel codes: Blockscaled datatypes with support for dense GEMM kernel.
• Set of examples that demonstrate the usage of the 3.x API for targeting Blackwell SM103 architecture:
  • Blockscaled ultra fp4 dense GEMM.
  • Blockscaled ultra fp4 dense grouped GEMM.
• Set of unit tests that demonstrate the usage of Blackwell SM103 blockscaled GEMM
  • Unit test files with prefix name of sm103_ under GEMM device unit tests.
• Support for Blackwell SM121 kernels for DGX Spark GPUs.
  • Share the major codes with Blackwell SM120 kernels.
• Add support for heuristics-based kernel filtering and autotuning using nvidia-matmul-heuristics to find the best kernels for a given scenario.
  • Details please refer to heuristics doc.
• Further enhance Blackwell SM100 Attention kernels in example 77.
  • Add fused reduction kernel support for cutlass MLA.
  • Add softmax skip correction.
  • Support for GQA in FMHA backward kernel.
  • Fix an issue where get_unmasked_trip_count may return a negative value.
  • Fix an issue where mbarriers are initialized with a zero arrival count.
  • Fix a corner case issue where the sequence length of q is not a multiple of tile_q.
  • Remove tma padding for forward kernel inputs.
• Add Blackwell SM100 kernels for MoEs (focusing on Low-Latency inference performance): example 92. It uses TMA (for weights) and CPASYNC (for tokens) to load input matrices and allow only one problem dimension to vary across groups/experts, unlike general Grouped GEMMs. Note: further API simplifications and kernel improvements are upcoming. Any feedback on API is welcome.
• Further enhance blockwise and groupwise GEMMs on Hopper and Blackwell
  • On Blackwell SM120, a blockwise gemm kernel is added: example 87.
  • On Hopper, add K major scale factor support for SM90 blockwise kernels.
  • On Hopper, relax the restriction that the k dimension of the problem size has to be the multiple of the k dimension of the tile size.
  • On Hopper, grouped version supports the case when k = 0.
• Support for Blackwell SM100 fp4 gemv kernels.
  • Kernel codes: Gemv kernel.
  • Example codes: example 91
• Support for Blackwell SM100 legacy mixed input GEMM kernels.
  • Collective mainloop codes: Mixed input mainloop.
  • Kernel codes: Mixed input kernel.
  • Example codes: example 86.
• Support for Blackwell SM100 cpasync kernel.
  • Collective mainloop codes: cpasync mainloop.
  • Kernel codes: cpasync kernel.
• Support Blackwell SM120 mixed input blockscaled grouped GEMM.
• Instantiating more Blackwell kernels in profiler.
  • Blackwell SM100 and SM103 kernels support CUTLASS_LIBRARY_INSTANTIATION_LEVEL to instantiate all possible combinations.
  • To use this feature, CUTLASS_LIBRARY_KERNELS must be non-empty. Profiler will combine CUTLASS_LIBRARY_KERNELS and CUTLASS_LIBRARY_INSTANTIATION_LEVEL to instantiate specific kernels.
  • Details please check Profiler Doc.
• Fix some profiler issues:
  • Modify default cluster callback values to none 0 to avoid profiler failure when these values are not set in command line.
  • Fix some no output and timeout issues.
  • Fix Pingpong Blockwise Hopper library generation.
• From CUDA 13.0, the Blackwell SM101 for Thor GPUs is renamed to SM110.
  • For CUDA toolkit version < 13.0, SM101 is still used for Thor GPUs.
  • For CUDA toolkit version >= 13.0, SM110 is used for Thor GPUs and SM101 is no longer valid.
• Rename legacy Python API package from cutlass to cutlass_cppgen and add Blackwell EVT support to legacy Python interface.
  • Restructuring the C++ Blackwell SM100 Collective Epilogue Builder to work with the Python interface's EpilogueDescriptors.
  • Added Blackwell SM100 EVT Emitter on the Python side and routed most emission through Hopper SM90 Emitter.
  • Added some support for running SM100 kernels via the Python interface.
• CuTe changes:
  • Fix inaccurate GridDim calculation under CuTe tutorial.
  • Add movmatrix support.
  • Fix smallest MMA-N allowed for Blackwell fp8 and fp16 gemm kernels.
  • Support fp16 accmulator for sm89 fp8 mma.
  • Shorten nullspace implementation.
  • Isolate and comment on cosize hacks.
  • Important documentation correction: E<0,1> == 1@0@1.
• Fix some kernel issues:
  • Fix Hopper SM90 group gemm kernel to only use the commit group and wait group instead of also waiting on mbarriers.
  • Fix a tiny bug when K is large for Blackwell SM103 fp4 grouped GEMM kernel.
• Add following unit tests:
  • fp16 accmulator for sm89 fp8 mma
  • movmatrix test
  • fp8 narrow mma n and fp16 narrow mma n
• Various improvements and fixes from the community and CUTLASS team. Thanks to everyone who submitted PRs!
• Optimal code generation with CUDA toolkit versions 13.0U1.

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This discussion was created from the release CUTLASS 4.2.0.