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WarrierRajeev · 2026-09-29T04:19:03Z

Purpose

The ModelOpt docs say that for W4A16_NVFP4 checkpoints, auto "currently selects Marlin". That isn't what the code does. #53014 added this sentence together with the logic that makes auto pick the FlashInfer CuTe-DSL kernel on SM100/SM103, which the v0.30.0 release notes list under "New defaults".

ModelOpt W4A16 layers go through select_linear_kernel → init_nvfp4_linear_kernel(use_a16=True):

elif linear_backend == "auto" and use_a16:
    ...
    # Weight-only: prefer FlashInfer CuTe-DSL W4A16 on SM100/103,
    # otherwise Marlin.
    cutedsl_ok, _ = FlashInferCuteDslNvFp4W4A16LinearKernel.is_supported(
        compute_capability
    )
    if compute_capability in (100, 103) and cutedsl_ok:
        force_kernel = FlashInferCuteDslNvFp4W4A16LinearKernel
    else:
        force_kernel = MarlinNvFp4LinearKernel

What changed:

docs/features/quantization/modelopt.md: the paragraph now says auto picks CuTe-DSL on SM100/SM103 when FlashInfer's BF16 x FP4 GEMM is available, and Marlin otherwise. It also notes that CuTe-DSL only handles BF16 activations, so FP16 models on SM100/SM103 need --linear-backend marlin. The existing sentence about explicitly selecting CuTe-DSL is unchanged.
vllm/model_executor/layers/quantization/modelopt.py: fixed the comment in select_linear_kernel. It said use_a16=True defaults to Marlin and referred to ModelOptNvFp4W4A16LinearMethod, which [ModelOpt] Redesign the LinearMethod classes using the generic QuantKey-driven method #49381 removed; it now points to [Quantization] Honor --linear-backend for ModelOpt W4A16 #50273.

Docs and comments only, no functional changes.

I checked the open PRs touching modelopt.md or NVFP4 W4A16 selection (#48782, #44672, #55405, #48360); none change this text.

I used Claude Code to find the mismatch and trace the selection path, and reviewed every changed line myself.

Test Plan

Docs and a comment only.
I have run pre-commit on the files and ran:
grep -rn ModelOptNvFp4W4A16LinearMethod vllm/

Test Result

All pre-commit hooks pass. The grep finds no remaining references to ModelOptNvFp4W4A16LinearMethod.

Essential Elements of an Effective PR Description Checklist

The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
The test plan, such as providing test command.
The test results, such as pasting the results comparison before and after, or e2e results
(Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Signed-off-by: Rajeev Warrier <warrier.rajeev.95@gmail.com>

claude

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

mergify · 2026-09-29T04:19:38Z

github-actions · 2026-09-29T04:33:36Z

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hmellor · 2026-09-29T11:39:41Z

The test in https://github.com/vllm-project/vllm/pull/53014/changes#diff-baf85e0f1106cd3e76d320f20396e53f6474a8c13544f90a154ab34895ac6d0a seems to indicate that auto is meant to resolve to Marlin? Does this test fail?

WarrierRajeev · 2026-09-29T15:59:12Z

The test in https://github.com/vllm-project/vllm/pull/53014/changes#diff-baf85e0f1106cd3e76d320f20396e53f6474a8c13544f90a154ab34895ac6d0a seems to indicate that auto is meant to resolve to Marlin? Does this test fail?

Yes @hmellor the test fails with B200 (SM100):

tests/quantization/test_modelopt.py::test_modelopt_w4a16_respects_linear_backend[auto-MarlinNvFp4LinearKernel] FAILED
>       assert isinstance(kernel, kernel_cls)
E       AssertionError: assert False
E        +  where False = isinstance(<vllm.model_executor.kernels.linear.nvfp4.flashinfer.FlashInferCuteDslNvFp4W4A16LinearKernel object at 0x2af915ed5160>, <class 'vllm.model_executor.kernels.linear.nvfp4.marlin.MarlinNvFp4LinearKernel'>)
================ 1 failed, 39 deselected, 15 warnings in 4.24s =================

Signed-off-by: Rajeev Warrier <warrier.rajeev.95@gmail.com>

mgoin

Can we just remove the backend-specific docs references? The important note is that we are running without activation quantization, which I think is self-obvious from the "ALGO" name imo

Signed-off-by: Rajeev Warrier <warrier.rajeev.95@gmail.com>

WarrierRajeev · 2026-10-02T05:29:01Z

Can we just remove the backend-specific docs references? The important note is that we are running without activation quantization, which I think is self-obvious from the "ALGO" name imo

@mgoin Yeah, makes sense. The choice made by auto is anyway logged at model load time. I've removed the references from docs.

@hmellor I've fixed the test in #59598. It expected auto to resolve to Marlin, but now auto prefers CuTe-DSL on SM100/SM103, so it failed on B200.

hmellor · 2026-10-02T09:49:35Z

/ci run --allow-stale

github-actions · 2026-10-02T09:49:57Z

✅ Triggered Buildkite CI #92596 for commit 31a7802921ab.

⚠️ This PR is 255 commits behind upstream main. Running CI at your own risk because --allow-stale was requested; outdated CI configuration may cause failures. Before merging, merge or rebase onto the latest main, then rerun /ci run on the latest PR commit.

hmellor · 2026-10-02T09:53:10Z

/ci run

github-actions · 2026-10-02T09:53:53Z

✅ Triggered Buildkite CI #92598 for commit 378b8d357774.

vllm-agent · 2026-10-02T11:10:12Z

CI selector (shadow): 0 test steps (0 jobs) instead of 70 (94 jobs)

Shadow mode: this changes nothing about what CI runs. It shows what the evidence-based selector would pick for this PR, next to today's rules. How it works.

Feedback welcome: reply here if it would skip a step this change needs, or runs something unrelated.

steps (jobs)	Today's rules	Selector	Would skip	Would add
NVIDIA, CPU and others	70 (94)	0 (0)	70 (94)	0 (0)
AMD mirrors	77 (115)	0 (0)	77 (115)	0 (0)

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v1-metrics-lmeval
v1-sample
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AMD mirrors: would skip (77)

async-engine-inputs-utils-worker
basic-correctness ×2
basic-correctness-cpu-offload
basic-correctness-cumem
basic-correctness-prefetch-offload
basic-correctness-sleep-mode
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kernels-root-misc-test-b200
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multi-modal-models-standard-2-qwen3-gemma
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multi-modal-models-standard-4-other-whisper
multi-modal-processor ×4
openai-api-correctness
pipeline-context-parallelism-4-gpus
platform-tests
pytorch-compilation-dynamic-shapes
pytorch-compilation-passes-unit-tests
pytorch-compilation-unit-tests
pytorch-compilation-unit-tests-h100
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quantized-fusions
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v1-metrics-lmeval
v1-sample
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AMD mirrors: would add (0)

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_{2 changed files · base 8e58ac22af · head 378b8d3577 · Python record: build 92561 at 4056c8ac1f · kernel record: table 4056c8a (build 92561), map 4056c8a · not counted: 10 build steps, 5 A100 steps the generator no longer emits, 0 optional steps the selector would also run}

WarrierRajeev · 2026-10-02T11:38:05Z

/ci retry

github-actions · 2026-10-02T11:38:23Z

✅ No failed, timed-out, or expired jobs need retrying: https://buildkite.com/vllm/ci/builds/92598

hmellor · 2026-10-02T11:39:48Z

…oject#59135) Signed-off-by: Rajeev Warrier <warrier.rajeev.95@gmail.com> Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

[Docs] Fix stale W4A16 NVFP4 default kernel in ModelOpt docs

f4f489d

Signed-off-by: Rajeev Warrier <warrier.rajeev.95@gmail.com>

WarrierRajeev requested review from mgoin, pavanimajety, robertgshaw2-redhat, tlrmchlsmth, yewentao256 and zyongye as code owners September 29, 2026 04:19

claude Bot reviewed Sep 29, 2026

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mergify Bot added documentation Improvements or additions to documentation quantization labels Sep 29, 2026

eopXD reviewed Sep 29, 2026

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Comment thread vllm/model_executor/layers/quantization/modelopt.py Outdated

update modelopt.py comment as per review

abf03f9

Signed-off-by: Rajeev Warrier <warrier.rajeev.95@gmail.com>

WarrierRajeev requested a review from eopXD September 29, 2026 19:03

WarrierRajeev mentioned this pull request Oct 1, 2026

[Test][Quantization] Fix W4A16 NVFP4 auto kernel selection test #59598

Open

mgoin reviewed Oct 1, 2026

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[Docs] Drop backend-specific NVFP4 notes from ModelOpt docs

31a7802

Signed-off-by: Rajeev Warrier <warrier.rajeev.95@gmail.com>

hmellor approved these changes Oct 2, 2026

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hmellor enabled auto-merge (squash) October 2, 2026 09:48

github-actions Bot added the ready ONLY add when PR is ready to merge/full CI is needed label Oct 2, 2026

Merge branch 'main' into modelopt-doc

378b8d3

hmellor disabled auto-merge October 2, 2026 12:14

hmellor enabled auto-merge (squash) October 2, 2026 12:15

hmellor merged commit 30e956f into vllm-project:main Oct 2, 2026
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