test(sglang): exercise NIXL in embedding cache E/PD test

[pskiran1]

Overview:

Update the existing SGLang cache-enabled E/PD video test to use nixl-read instead of the local embedding-transfer mode. This makes the test exercise the real NIXL embedding-transfer and remote-metadata path inside the SGLang runtime container, providing meaningful regression coverage for #12558.

Details:

The existing video_e_pd_qwen scenario:

• Launches separate encode and PD workers on one GPU.
• Enables the multimodal embedding cache.
• Sends an initial cache-miss video request.
• Repeats the request and verifies an embedding-cache hit.

Previously, the test used the local transfer mode and therefore bypassed NIXL. Switching it to nixl-read ensures both requests exercise the real NIXL sender, receiver, and remote-agent metadata exchange.

Current GitHub GPU CI runs this test on x86. It does not reproduce the ARM-specific GB200 environment today, but the same test will provide that coverage when ARM GPU CI becomes available.

Validation:

• Validated using a locally built SGLang runtime/test container on an A100 GPU:

pytest -p no:codeblocks tests/serve/test_sglang.py -v -k "video_e_pd_qwen and not nvdec"

tests/serve/test_sglang.py::test_sglang_deployment[video_e_pd_qwen-4] PASSED                                                                                             [100%]
 1 passed, 29 deselected in 55.23s 

• Validated the targeted video_e_pd_qwen SGLang test using the PR-built multi-architecture runtime on an ARM64 NVIDIA GB200. The NIXL-read E/PD video path completed successfully, including the embedding-cache-hit and NIXL-agent-initialization assertions. 1 passed, 29 deselected in 73.28s.

Related Issues

🔗 This PR is linked to an issue:

• Closes OPS-8449

Summary by CodeRabbit

• Tests
  • Updated the video_e_pd_qwen test to use the nixl-read embedding transfer mode instead of local.

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[pskiran1]

/ok to test e1f46c8

[coderabbitai]

Walkthrough

The video_e_pd_qwen test now sets DYN_SGL_EMBEDDING_TRANSFER_MODE to nixl-write instead of local.

Changes

SGLang transfer mode coverage

Layer / File(s)	Summary
Video embedding transfer configuration tests/serve/test_sglang.py	The video_e_pd_qwen test now uses NIXL-write embedding transfer.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: 🔵 Low · up to 59210

The video E/PD test may not run reliably or provide valid NIXL coverage, while a separate localized test-helper concern remains unresolved. Both issues are low-scope but should be addressed before merge.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 78.26% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the main change: updating the SGLang embedding-cache E/PD test to exercise NIXL.
Description check	✅ Passed	The description explains the change, test behavior, validation results, and related issue. It omits the requested “Where should the reviewer start?” section, but the description is otherwise complete …

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Actionable comments posted: 1

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Inline comments:
In `@tests/dependencies/test_sglang_nixl_ucx_layout.py`:
- Line 50: Replace runtime-validation assertions in _load_discovery_module and
the installer partitioning flow with explicit failures. Validate the installer
marker before partition() returns helpers, and validate spec and spec.loader
before loading the discovery module; raise a clear exception when either
condition is missing so behavior is preserved under python -O.

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🤖 Completed: Fix pre-merge checks in PR #14795 — View commit 338c2d2

[pskiran1]

/ok to test 59210e4

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Actionable comments posted: 1

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Inline comments:
In `@tests/serve/test_sglang.py`:
- Line 851: Update the DYN_SGL_EMBEDDING_TRANSFER_MODE override in the E/PD test
to use nixl-read, matching multimodal_epd.sh and the launcher’s compatible
NIXL/UCX setup; do not retain nixl-write unless the backend configuration is
also changed accordingly.

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✅ Coding task complete — no changes needed

[dmitry-tokarev-nv]

Reviewed at 59210e4c. Verified by execution rather than by reading: RTX 6000 Ada, AMD64, the repo's …-sglang-runtime-test image (CUDA 13.0), this PR's worktree mounted at /workspace, eight runs of tests/serve/test_sglang.py -k "video_e_pd_qwen and not nvdec" across three transfer modes.

The change does what it claims. In nixl-write both launcher workers bring up a real NIXL agent — sender_… in the encode worker, receiver_… in the PD worker — and the existing cache-hit assertion still holds. Two runs exactly as merged: 49.2 s and 46.9 s, against 45.5 s for the local tree it replaces. No startup or transfer failure in any nixl-write run.

Two points, both P2, neither blocking:

• a new thread on line 851 — the mode is exercised but not pinned; the test passes identically on local, nixl-write and nixl-read.
• a reply on the existing line-851 thread — I agree with nixl-read but for different reasons than the ones given there, and the breakage premise did not reproduce.

P3, description only: the Related Issues section still carries both template branches — Closes OPS-8449 and a ticked Confirmed — no related issue — along with the "delete the other" instruction comment. Worth trimming to whichever applies.

CI triage, not a finding: sglang-runtime / Test cuda13.0, amd64 is red on this test's decord2 install failing inside the runner, ~2 s in, before any worker starts — unrelated to the diff, and decord2>=3.4.0,<4 installs cleanly from that same image on my box. Recording it only because of what it implies: no CI run has yet exercised this change. The green sglang-runtime job on e1f46c80 predates the one-line edit, which landed later.

[dmitry-tokarev-nv]

Approving at 59210e4c. The change is correct and does what the description says — I confirmed it by execution rather than by reading, on an RTX 6000 Ada in the repo's …-sglang-runtime-test image (AMD64, CUDA 13.0) with this PR's worktree mounted at /workspace:

• nixl-write brings up both NIXL agents through the launcher — sender_… in the encode worker, receiver_… in the PD worker — where the local tree it replaces brings up none. Two runs exactly as merged: PASSED at 49.2 s and 46.9 s, versus 45.5 s for local. No startup or transfer failure in any run.
• The cache-hit assertion still holds on the second request in every mode.
• The red sglang-runtime / Test cuda13.0, amd64 is this test's decord2 install failing inside the runner ~2 s in, before any worker starts — unrelated to the diff; that spec installs cleanly from the same image on my box. It does mean CI has not itself exercised this change yet.

Three items left open, all non-blocking and all the author's call:

• P2 (new thread, line 851) — the mode is exercised but not pinned: the test passes identically on local, nixl-write and nixl-read. One expected_log entry closes it; I mutation-tested the patch in both directions.
• P2 (reply on the existing line-851 thread) — nixl-read is the better mode here, though not for the reason originally given: the breakage premise did not reproduce, but multimodal_epd.sh forces nixl-read for any NIXL backend, so nixl-write pins a mode no deployment of this launcher runs, and it costs a measured 8.06 GiB of resident host memory at PD-worker start. I verified the alternative passes before recommending it.
• P3 — the description's Related Issues section still carries both template branches plus the "delete the other" instruction comment.

Deliberately not raised: video_e_pd_qwen_nvdec and multimodal_e_pd_fd_qwen stay on local, which their own comments justify, and neither is in scope here.

[pskiran1]

Thanks, @dmitry-tokarev-nv. I have switched the test to nixl-read to match the mode used by multimodal_epd.sh and added Initialized NIXL agent to the expected logs, ensuring the test cannot silently pass in local mode. I also updated the description to accurately reflect the related Issues section. I will provide the new test results soon.

[pskiran1]

/ok to test 9ec47a7

[pskiran1]

Validated the targeted video_e_pd_qwen SGLang test using the PR-built multi-architecture runtime on an ARM64 NVIDIA GB200. The NIXL-read E/PD video path completed successfully, including the embedding-cache-hit and NIXL-agent-initialization assertions.
I have updated the validation section in the PR description with the latest test results.