[erezzarum]

Description

Problem

Removing the RDMA packages bundled in NGC PyTorch images and relying on NIXL's system lookup leaves these containers without a usable LIBFABRIC plugin.

Solution

• Preserve the bundled RDMA packages and select EFA at /opt/amazon/efa when its development header and link library are present.
• Discover hwloc through /usr/local/mpi, the default HPC-X Open MPI installation in NGC PyTorch images. Preserve the existing pkg-config search path and retain optional system detection when bundled dependencies are absent.
• Document plugin setup, correct NIXL_PLUGIN_DIR, and describe the known KV cache V2 limitation. The NIXL UCX backend remains the default; this change does not switch the KV cache manager.

The build uses unpatched NIXL 1.4.0 and the bundled EFA installation. It does not rebuild libfabric or backport either dependency. Rocky Linux and SBSA Ubuntu retain system detection; plugin availability there depends on compatible development packages.

Known limitation: Two-node B300 testing with NGC PyTorch 26.09, unmodified NIXL 1.4.0 and AWS libfabric 2.4.0amzn5.0 exposed two failures when using KV cache V2 with the NIXL LIBFABRIC backend over EFA RDM: NIXL allocation-context handling and libfabric CUDA VMM synchronization. A diagnostic build containing the libfabric fixes alone still failed NIXL's context check. With the same fixed libfabric and unmodified NIXL, setting NIXL_DISABLE_CUDA_ADDR_WA=1 allowed 3/3 requests to complete. This is a workaround for the tested configuration, not a fix for the bundled libfabric or a default container setting. The intended dependency update path is an upstream NIXL resolution and a validated official EFA Installer package; this PR backports neither dependency.

Test Coverage

Validation

At e0b4d06ff81a5ab41b99dc72574ac1a4a7633243, rebased onto main a77de9e3bfa7b0e885e4da6d637d5f38c2e78b61:

• All 40 mocked installer cases pass, covering complete, partial and missing EFA/hwloc development files and preservation of the existing pkg-config path. They validate build arguments and environment, not compilation or communication. The test runs through the existing CPU CI unittest/scripts entry.
• Shell syntax, whitespace, applicable pre-commit checks and all 16 commit sign-offs pass.
• CI image references temporarily match the main baseline. Fresh unpatched staging-image, runtime regression and full L0 validation for the post-revert revision have not been established by the diagnostic tests below.

Documentation follow-up 85f73b1c5df37dce53e9354d91fd55c7b8a2115b changes only the disaggregated-serving README; applicable pre-commit checks, DCO and whitespace checks pass.

Historical evidence: an unpatched Qwen3-0.6B TP1/PP1 KV cache V1 control completed 3/3 requests; this does not establish support for other configurations. Earlier KV cache V2 over EFA successes used the now-reverted dependency patches and do not validate this revision. The full L0 run at 574d402 failed in both single-GPU suites and blocked multi-GPU execution; those failures have not yet been diagnosed.

Additional dependency-isolation evidence (2026-10-15): Qwen3-0.6B, TP1/PP1, two B300 nodes, TRT-LLM eac0f787e1aab5b1d8757909345b26acd1854adb. The libfabric-only and libfabric-plus-env comparison used the same unmodified NIXL 1.4.0 binaries. Worker logs confirmed KVCacheManagerV2 and the KV cache V2 transceiver with the NIXL LIBFABRIC backend and EFA RDM; loaded libraries and environment were checked. The libfabric fix was a diagnostic backport, not an official EFA Installer release. These results isolate the dependency failures and do not validate PR HEAD 85f73b1c5df37dce53e9354d91fd55c7b8a2115b.

PR Checklist

Please review the following before submitting your PR:

• PR description clearly explains what and why. If using CodeRabbit's summary, please make sure it makes sense.

• PR Follows TRT-LLM CODING GUIDELINES to the best of your knowledge.

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• CODEOWNERS updated if ownership changes

• Documentation updated as needed

• Update tava architecture diagram if there is a significant design change in PR.

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Walkthrough

The NIXL installer detects bundled EFA libfabric files and uses the EFA prefix when both required files exist. It adds MPI's pkg-config directory when the required hwloc files are present. The disaggregated guide describes bundled and custom setup paths.

Changes

EFA libfabric setup

Layer / File(s)	Summary
NIXL dependency detection and configuration docker/common/install_base.sh, docker/common/install_nixl.sh, tests/unittest/scripts/test_install_nixl.py	The Ubuntu package workaround for ibverbs-providers, libibverbs1, and libibverbs-dev is removed. The installer passes the detected EFA prefix to Meson when both required files exist. It prepends MPI's pkg-config directory when the EFA files and all required hwloc files are present. Parameterized tests cover these file-presence and PKG_CONFIG_PATH conditions.
Bundled and custom setup guidance examples/disaggregated/README.md	The guide describes bundled EFA support, prerequisites, conditional installation and rebuild steps, and troubleshooting checks for plugin availability, EFA devices, and libfabric compatibility.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant install_nixl.sh
  participant EFA_files
  participant MPI_hwloc_files
  participant Meson
  install_nixl.sh->>EFA_files: Check for the fabric header and library
  install_nixl.sh->>MPI_hwloc_files: Check for the hwloc header, library, and pkg-config file
  install_nixl.sh->>Meson: Pass detected libfabric prefix

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Suggested reviewers: chzblych, weiminwang-nv

Merge Risk: ⚪ Minimal · up to b7d38

No confirmed issue blocks merging. Plugin compilation and EFA/non-EFA runtime behavior remain unverified.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly and concisely describes the main change: enabling the NIXL LIBFABRIC plugin in NGC PyTorch images.
Description check		The description includes the problem, solution, detailed test coverage, known limitations, dependency context, and the required checklist. It is complete and directly related to the changes.

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Actionable comments posted: 1

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Inline comments:
Review comments at @examples/disaggregated/README.md:
- Line 90: Move the inline comment in the meson setup command out of the
continued argument line so the trailing backslash directly precedes the newline;
retain the AWS EFA path explanation as a standalone comment.

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[juney-nvidia]

Approved from OSS compliance and doc perspectives.

[tburt-nv]

Once the changes are ready, we can generate containers and test them in CI.

[github-actions]

Automatically added "ci: full pre-merge approved" because this PR has satisfied the required GitHub review approvals. Unresolved review conversations and other required checks remain independent merge requirements.

[EmmaQiaoCh]

/bot run --stage-list "Build-Docker-Images" --disable-fail-fast

[tensorrt-cicd]

PR_Github #77457 [ run ] triggered by Bot. Commit: f9f897c Link to invocation

[chzblych]

/bot kill

[tensorrt-cicd]

PR_Github #77464 [ kill ] triggered by Bot. Commit: 80cb869 Link to invocation

[tensorrt-cicd]

PR_Github #77825 [ run ] triggered by Bot. Commit: 27399f8 Link to invocation

[chzblych]

/bot run --add-multi-gpu-test --disable-fail-fast

[tensorrt-cicd]

PR_Github #77838 [ run ] triggered by Bot. Commit: 574d402 Link to invocation

[tensorrt-cicd]

PR_Github #77825 [ run ] completed with state ABORTED. Commit: 27399f8

Link to invocation

[tensorrt-cicd]

PR_Github #77838 [ run ] completed with state SUCCESS. Commit: 574d402
/LLM/main/L0_MergeRequest_PR pipeline #64167 completed with status: 'FAILURE'

CI Report

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CI Agent Failure Analysis

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[chzblych]

Dependency-isolation follow-up (2026-10-15)

Configuration: TRT-LLM eac0f787e1aab5b1d8757909345b26acd1854adb, NGC PyTorch 26.09, unmodified NIXL 1.4.0, Qwen3-0.6B, TP1/PP1, two B300 nodes with one GPU each. KV cache V2, the Python transceiver, the NIXL LIBFABRIC backend and EFA RDM were confirmed in the worker logs.

libfabric	NIXL_DISABLE_CUDA_ADDR_WA	Result
Bundled AWS libfabric 2.4.0amzn5.0	unset	Ordinary inference passed; first disaggregated request failed NIXL's CUDA context guard.
Diagnostic libfabric with the VMM fixes	unset	Same NIXL guard failure; zero disaggregated requests completed. Reproduced in both allocations.
Same diagnostic libfabric	1	3/3 disaggregated requests completed; the first greedy response matched the ordinary-inference reference.

The diagnostic library contains 2c7d11a and 790f0fb, from libfabric #12918. It is a saved diagnostic backport, not an official EFA Installer release.

The fixed-library comparison was completed in one allocation with 128 GiB host memory per node, restarting both containers between cases. Both cases used the same original NIXL plugin and the same fixed libfabric binary, verified through the workers' mapped libraries and SHA-256 hashes. The workaround was absent in the failing case and set to 1 in the passing case; no LD_PRELOAD or NIXL_PLUGIN_DIR override was used. A preceding attempt at the positive control was OOM-killed during startup with a 64 GiB limit and is excluded from the functional result.

Conclusion: the tested libfabric fix alone does not resolve the NIXL context guard. A NIXL-side resolution or the tested environment workaround is still needed in this configuration. This does not show that one particular NIXL source patch is the only solution.

Earlier pointer observations found a valid, mapped KV cache V2 VMM allocation with a valid device ordinal and a null allocation-associated context, while the submitting thread had a non-null current context. A separate control using KV cache V2 with the NIXL UCX backend completed 3/3 requests with KVCacheManagerV2 confirmed and no KV cache V1 fallback. That NIXL UCX backend control used UCX_TLS=^ib,gdr_copy; it is not EFA transport or performance evidence. The NIXL UCX backend must not be confused with TRT-LLM's direct UCX backend.

Clarification of the NULL context origin: The NIXL LIBFABRIC backend obtains the NULL value by querying CU_POINTER_ATTRIBUTE_CONTEXT from the CUDA pointer; TRT-LLM does not pass it a NULL CUcontext argument. A standalone CUDA-only program reproduced a NULL allocation-associated context for valid, mapped cuMemCreate/cuMemMap allocations while the thread's current context was non-null and memory read/write checks passed, without TRT-LLM, NIXL or libfabric. This is consistent with CUDA's documented context-independent allocation semantics; the evidence does not indicate that TRT-LLM or libfabric lost a context. The observed failure is in NIXL's handling of the query result, separate from libfabric's SYNC_MEMOPS failure. The NIXL evidence comment includes the standalone reproducer and build command. This clarifies the existing investigation; it is not a new test run.

This supports the scoped limitation tracked in NIXL #2425 and libfabric #12853. TRT-LLM #19783 remains a container/plugin enablement change with neither dependency patched. These diagnostic runs do not validate TRT-LLM PR HEAD 85f73b1c5df37dce53e9354d91fd55c7b8a2115b or the official replacement EFA package.

[chzblych]

/bot run --stage-list "Build-Docker-Images" --disable-fail-fast

[tensorrt-cicd]

PR_Github #78112 [ run ] triggered by Bot. Commit: 85f73b1 Link to invocation

[tensorrt-cicd]

PR_Github #78112 [ run ] completed with state FAILURE. Commit: 85f73b1
/LLM/main/L0_MergeRequest_PR pipeline #64383 (Partly Tested) completed with status: 'FAILURE'

CI Report

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[chzblych]

Put this PR in draft until a new EFA installer compatible with TRT-LLM KV cache manager V2 is available for testing.