---
id: pr-flash-attention-2150
repo: Dao-AILab/flash-attention
pr: 2150
title: '[Cute, Bwd, Sm100] Add varlen for sm100 bwd'
author: jayhshah
date: '2026-01-09'
url: https://github.com/Dao-AILab/flash-attention/pull/2150
source_category: upstream-code
architectures:
- sm100
tags:
- benchmark kernel
- blackwell
- tma
techniques:
- async-copy
hardware_features:
- blackwell
- tma
kernel_types:
- attention
languages:
- cuda-cpp
- cute-dsl
captured_at: '2026-05-16'
status: merged
merge_sha: ed6a82f050200b89a0228e6b38ad5406784d9d16
inclusion_reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.
changed_paths:
- benchmarks/benchmark_attn.py
- flash_attn/cute/cute_dsl_utils.py
- flash_attn/cute/flash_bwd_postprocess.py
- flash_attn/cute/flash_bwd_preprocess.py
- flash_attn/cute/flash_bwd_sm100.py
- flash_attn/cute/interface.py
- flash_attn/cute/seqlen_info.py
- flash_attn/cute/testing.py
- flash_attn/cute/tile_scheduler.py
- tests/cute/test_flash_attn.py
- tests/cute/test_flash_attn_race_condition.py
- tests/cute/test_flash_attn_varlen.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2150
head_ref_oid: 92744ce4b70f169c569d589d9002fb60b55214fa
---
# [Cute, Bwd, Sm100] Add varlen for sm100 bwd

- Repository: `Dao-AILab/flash-attention`
- PR: [2150](https://github.com/Dao-AILab/flash-attention/pull/2150)
- Decision: `Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.`
- Reason: Search-matched CUDA kernel optimization PR; materialize diff/source before synthesis.

## Changed Paths

- `benchmarks/benchmark_attn.py`
- `flash_attn/cute/cute_dsl_utils.py`
- `flash_attn/cute/flash_bwd_postprocess.py`
- `flash_attn/cute/flash_bwd_preprocess.py`
- `flash_attn/cute/flash_bwd_sm100.py`
- `flash_attn/cute/interface.py`
- `flash_attn/cute/seqlen_info.py`
- `flash_attn/cute/testing.py`
- `flash_attn/cute/tile_scheduler.py`
- `tests/cute/test_flash_attn.py`
- `tests/cute/test_flash_attn_race_condition.py`
- `tests/cute/test_flash_attn_varlen.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2150`
