---
id: pr-flash-attention-2497
repo: Dao-AILab/flash-attention
pr: 2497
title: '[FA4][hd256] Backward TMA bulk-store epilogue + LSE/dpsum coalesce'
author: Johnsonms
date: '2026-05-01'
url: https://github.com/Dao-AILab/flash-attention/pull/2497
source_category: upstream-code
architectures:
- sm100
tags:
- FA4
- arch_pipeline
- attention_kv
- blackwell
- compiler_runtime
- cute
- norm_elementwise
- scheduler_autotune
- sm100
- tma
- varlen
techniques:
- async-copy
- autotuning
- epilogue-fusion
- pipeline-stages
- tile-scheduling
- warp-specialization
hardware_features:
- blackwell
- tma
kernel_types:
- attention
- compiler
- norm
- runtime
- scheduler
languages:
- cuda-cpp
- cute-dsl
captured_at: '2026-05-16'
status: merged
merge_sha: 956366b9791645fc5250b9b4b16be26e48f8e399
inclusion_reason: 'Extract the architecture assumption first: SM target, TMA/WGMMA/tcgen path, cluster use, and pipeline stages.'
changed_paths:
- flash_attn/cute/sm100_hd256_2cta_fmha_backward_dkdvkernel.py
- flash_attn/cute/sm100_hd256_2cta_fmha_backward_dqkernel.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2497
head_ref_oid: 1e37d335b0619c4ceb6dcc6254c578bdb8f2b43f
---
# [FA4][hd256] Backward TMA bulk-store epilogue + LSE/dpsum coalesce

- Repository: `Dao-AILab/flash-attention`
- PR: [2497](https://github.com/Dao-AILab/flash-attention/pull/2497)
- Decision: `Extract the architecture assumption first: SM target, TMA/WGMMA/tcgen path, cluster use, and pipeline stages.`
- Reason: Extract the architecture assumption first: SM target, TMA/WGMMA/tcgen path, cluster use, and pipeline stages.

## Changed Paths

- `flash_attn/cute/sm100_hd256_2cta_fmha_backward_dkdvkernel.py`
- `flash_attn/cute/sm100_hd256_2cta_fmha_backward_dqkernel.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2497`
