fa3 & trtllm_mha spec overlap #11874

JustinTong0323 · 2025-10-20T18:56:27Z

Motivation

Enable fa3 & trtllm_mha for spec_v2 (for gpt-oss on Hopper & Blackweel).

Modifications

Accuracy Tests

Test on gpt-oss and llama4, accuracy could match.

Detailed test result could be find here.

Benchmarking and Profiling

Checklist

Format your code according to the Format code with pre-commit.
Add unit tests according to the Run and add unit tests.
Update documentation according to Write documentations.
Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.

gemini-code-assist · 2025-10-20T18:56:49Z

Summary of Changes

Hello @JustinTong0323, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request, marked as a work-in-progress, introduces initial support for a new DRAFT_EXTEND_V2 forward mode, which appears to be an evolution or alternative to existing speculative decoding mechanisms. The changes primarily involve integrating this new mode into various attention backend components and updating internal ForwardMode classifications to properly recognize and handle it. This foundational work sets the stage for future enhancements related to speculative decoding within the system.

Highlights

Introduction of DRAFT_EXTEND_V2 Forward Mode: A new forward mode, DRAFT_EXTEND_V2, has been introduced, likely to support an updated speculative decoding mechanism. This mode is now recognized across various attention backend components.
Integration into Attention Backends: The DRAFT_EXTEND_V2 mode has been integrated into the logic of aiter_backend, flashattention_backend, flashmla_backend, trtllm_mha_backend, and trtllm_mla_backend, affecting how metadata is initialized and how forward_extend operations are handled under this new mode.
ForwardMode Utility Updates: The is_extend() and is_extend_or_draft_extend_or_mixed() utility methods in forward_batch_info.py have been updated to include and correctly classify the new DRAFT_EXTEND_V2 mode.
Temporary Bypass in Base Attention Backend: The update_verify_buffers_to_fill_after_draft method in base_attn_backend.py has had its NotImplementedError temporarily commented out and replaced with pass, indicating ongoing development for this specific functionality.
NSA Backend Compatibility: The NSA backend explicitly asserts that it does not support DRAFT_EXTEND_V2 (similar to DRAFT_EXTEND and TARGET_VERIFY), indicating that this mode is not compatible with the NSA attention mechanism.

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…xtend v2

JustinTong0323 · 2025-10-27T07:48:01Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a new parameter include_draft_extend_v2 to several methods related to forward mode in the sglang library. This parameter enables the inclusion of DRAFT_EXTEND_V2 in certain conditional checks, allowing for more flexible handling of different forward modes. The changes primarily affect flashattention_backend.py, trtllm_mha_backend.py, and forward_batch_info.py. The code has been reviewed and comments have been provided to address potential issues.

hnyls2002 · 2025-10-31T12:44:49Z

python/sglang/srt/speculative/eagle_worker_v2.py

    def draft_worker(self):
        return self._draft_worker

    def clear_cache_pool(self):


The API has already been defined here, and we actually do not need to clear the cache (cache is cleared in the scheduler).

Cool! Got it, as this PR is old so at that time this method is not introduced haha

python/sglang/srt/speculative/eagle_worker_v2.py

hnyls2002 · 2025-10-31T12:48:48Z

@JustinTong0323 Already approved, thanks for the support!

wip: fa3 spec overlap

ac59d1a

JustinTong0323 requested review from BBuf, Edwardf0t1, HaiShaw, Ying1123, ch-wan, hnyls2002, ispobock, kushanam, merrymercy and zhyncs as code owners October 20, 2025 18:56

sglang-bot added the run-ci label Oct 20, 2025

Merge branch 'main' into fa3-spec-overlap

0ab8131

JustinTong0323 marked this pull request as draft October 20, 2025 18:57

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add clear_cache_pool for eagle worker v2

746cfef

JustinTong0323 force-pushed the fa3-spec-overlap branch from 7f65515 to 746cfef Compare October 20, 2025 21:25

JustinTong0323 and others added 8 commits October 20, 2025 23:12

fix lint

04621dd

Merge branch 'main' into fa3-spec-overlap

38d1863

Merge branch 'main' into fa3-spec-overlap

9b8798c

Merge branch 'main' into fa3-spec-overlap

c72c3a5

Merge branch 'main' into fa3-spec-overlap

d7ec371

revert back other backend

463eee5

refactor forward_mode.is_extend

ccca63d

Merge branch 'main' into fa3-spec-overlap

bdf5def

JustinTong0323 changed the title ~~wip: fa3 spec overlap~~ wip: fa3 & trtllm_mha spec overlap Oct 27, 2025

JustinTong0323 changed the title ~~wip: fa3 & trtllm_mha spec overlap~~ fa3 & trtllm_mha spec overlap Oct 27, 2025

JustinTong0323 and others added 2 commits October 27, 2025 07:45

Refactor ForwardMode methods to include optional handling for draft e…

e908e5b

…xtend v2

Merge branch 'main' into fa3-spec-overlap

afcdbc2

JustinTong0323 marked this pull request as ready for review October 27, 2025 07:47

JustinTong0323 requested a review from kssteven418 as a code owner October 27, 2025 07:47

gemini-code-assist bot reviewed Oct 27, 2025

View reviewed changes

Merge branch 'main' into fa3-spec-overlap

8b06799

zhyncs assigned cicirori Oct 27, 2025

zhyncs added the high priority label Oct 27, 2025

JustinTong0323 added 2 commits October 27, 2025 16:32

Merge branch 'main' into fa3-spec-overlap

ef8b12a

Merge branch 'main' into fa3-spec-overlap

cf7d6c5

b8zhong mentioned this pull request Oct 29, 2025

Support overlap-spec-v2 with fa3 attention backend #12128

Closed

Merge branch 'main' into fa3-spec-overlap

46b55de

JustinTong0323 mentioned this pull request Oct 30, 2025

[Feature] Overlap Spec Support #11762

Open

26 tasks

Merge branch 'main' into fa3-spec-overlap

f835418

hnyls2002 approved these changes Oct 31, 2025

View reviewed changes

JustinTong0323 added 2 commits October 31, 2025 14:28

Update eagle_worker_v2.py

f491df8

Merge branch 'main' into fa3-spec-overlap

246b47d

Fridge003 mentioned this pull request Oct 31, 2025

chore: bump SGLang version to 0.5.4.post2 #12439

Merged

Fridge003 merged commit 0bfe1d1 into sgl-project:main Nov 1, 2025
81 of 102 checks passed

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fa3 & trtllm_mha spec overlap #11874

fa3 & trtllm_mha spec overlap #11874

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JustinTong0323 commented Oct 20, 2025 •

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fa3 & trtllm_mha spec overlap #11874

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JustinTong0323 commented Oct 20, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Motivation

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Accuracy Tests

Benchmarking and Profiling

Checklist

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gemini-code-assist bot commented Oct 20, 2025

Summary of Changes

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JustinTong0323 commented Oct 20, 2025 •

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