---
id: pr-flash-attention-2488
repo: Dao-AILab/flash-attention
pr: 2488
title: '[hd256] Improve forward kernel with exp2 FMA emulation (3% to 9% performance gain)'
author: Johnsonms
date: '2026-04-28'
url: https://github.com/Dao-AILab/flash-attention/pull/2488
source_category: upstream-code
architectures:
- sm100
tags:
- arch_pipeline
- attention_kv
- benchmark_test
- compiler_runtime
- scheduler_autotune
- sm100
- softmax
techniques:
- async-copy
- autotuning
- pipeline-stages
- tile-scheduling
hardware_features:
- blackwell
- tma
kernel_types:
- attention
- compiler
- runtime
- scheduler
- softmax
languages:
- cuda-cpp
- cute-dsl
captured_at: '2026-05-16'
status: merged
merge_sha: 6c73fb506fa84424c3fa04880f85c789b4a498e2
inclusion_reason: Preserve page/KV/layout and plan-run contracts; profile memory traffic separately from math utilization.
changed_paths:
- flash_attn/cute/flash_fwd_sm100.py
- flash_attn/cute/sm100_hd256_2cta_fmha_forward.py
artifact_dir: evidence/pull-bundles/flash-attention/gh-2488
head_ref_oid: 80fb1ec4a3086a25774c1f636eea9b6a1b505b2c
---
# [hd256] Improve forward kernel with exp2 FMA emulation (3% to 9% performance gain)

- Repository: `Dao-AILab/flash-attention`
- PR: [2488](https://github.com/Dao-AILab/flash-attention/pull/2488)
- Decision: `Preserve page/KV/layout and plan-run contracts; profile memory traffic separately from math utilization.`
- Reason: Preserve page/KV/layout and plan-run contracts; profile memory traffic separately from math utilization.

## Changed Paths

- `flash_attn/cute/flash_fwd_sm100.py`
- `flash_attn/cute/sm100_hd256_2cta_fmha_forward.py`

## Evidence Bundle

`evidence/pull-bundles/flash-attention/gh-2488`
