colabfold-legacy-kernels

Prebuilt CUDA kernels to make ColabFold fast on Volta and Turing NVIDIA GPUs. This package has three kernels that replace the Ampere+ Pallas/Triton kernels: Attention, layer norm and the gated dual projection.

import colabfold_legacy_kernels as clk
clk.available(cc=70)                  # True if the wheel has kernels for sm_70
clk.library_path("attention", cc=70)  # path of the shared library
clk.symbol("attention", cc=70)        # XLA FFI target name to register

The attention kernel also has a backward pass on both architectures, so a model can be trained or designed against it. It returns dQ, dK, dV and dBias. MSA attention takes q, k and v from the MSA and the pair representation only as that bias, so dBias is the one path a gradient has back to the pair trunk.

clk.symbol("attention_bwd", cc=75)  # VoltaMmaBwd   dq, dk, dv, dbias
clk.symbol("attention_bwd", cc=70)  # VoltaWmmaBwd  the same, with wmma

The backward rebuilds the softmax from lse, the second result of the forward. Pass want_lse=False and a one element buffer for it when only inferring, and want_dbias=False when the bias takes no gradient.

To build the kernels, run the build script. It needs nvcc and the XLA FFI headers, and fetches CUTLASS itself.

NVCC=/usr/local/cuda-12.9/bin/nvcc scripts/build_all.sh   # sm_70 and sm_75
ARCH=75 scripts/build_kernels.sh                          # one architecture