---
id: pr-flash-attention-1893
repo: Dao-AILab/flash-attention
pr: 1893
title: Improve causal backward determinism perf with SPT schedule
author: jayhshah
date: '2025-09-17'
url: https://github.com/Dao-AILab/flash-attention/pull/1893
source_category: upstream-code
architectures:
- sm90
tags:
- FA3
- arch_pipeline
- attention_kv
- benchmark_test
- hopper
- norm_elementwise
- scheduler_autotune
techniques:
- async-copy
- autotuning
- epilogue-fusion
- pipeline-stages
- tile-scheduling
hardware_features:
- hopper
- tma
kernel_types:
- attention
- norm
- runtime
- scheduler
languages:
- cuda-cpp
captured_at: '2026-05-16'
status: merged
merge_sha: 5c1627a7a1cda9c32cb9b937a053564e663f81bc
inclusion_reason: 'Extract the architecture assumption first: SM target, TMA/WGMMA/tcgen path, cluster use, and pipeline stages.'
changed_paths:
- hopper/epilogue_bwd.hpp
- hopper/flash_api.cpp
- hopper/flash_api_stable.cpp
- hopper/flash_bwd_launch_template.h
- hopper/mainloop_bwd_sm90_tma_gmma_ws.hpp
- hopper/test_flash_attn_bwd_determinism.py
- hopper/tile_scheduler.hpp
artifact_dir: evidence/pull-bundles/flash-attention/gh-1893
head_ref_oid: 35f6eb37344d0bae73db1185c703f25c970087d0
---
# Improve causal backward determinism perf with SPT schedule

- Repository: `Dao-AILab/flash-attention`
- PR: [1893](https://github.com/Dao-AILab/flash-attention/pull/1893)
- 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

- `hopper/epilogue_bwd.hpp`
- `hopper/flash_api.cpp`
- `hopper/flash_api_stable.cpp`
- `hopper/flash_bwd_launch_template.h`
- `hopper/mainloop_bwd_sm90_tma_gmma_ws.hpp`
- `hopper/test_flash_attn_bwd_determinism.py`
- `hopper/tile_scheduler.hpp`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-1893`
