[https://nvbugs/5829097][fix] Disaggregated serving: Only send finished context requests to the KV cache transceiver

[Funatiq]

Summary by CodeRabbit

Bug Fixes

• Improved KV cache transfer efficiency in pipeline parallel distributed serving by synchronizing cache block transfers with completed context requests instead of ongoing requests.

Tests

• Enhanced disaggregated serving test suite with new chunked prefill test scenarios supporting flexible configurations including pipeline parallel, tensor parallel sizes, and multiple concurrent instances.

Description

Fix for bug introduced in #9308.

Test Coverage

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[Funatiq]

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[tensorrt-cicd]

PR_Github #35183 [ run ] triggered by Bot. Commit: 48478e9

[tensorrt-cicd]

PR_Github #35183 [ run ] completed with state SUCCESS. Commit: 48478e9
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[Funatiq]

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[coderabbitai]

📝 Walkthrough

Walkthrough

The changes update KV cache transfer logic in the PP executor to use finished context requests instead of scheduled ones, and refactor the disaggregated serving test infrastructure to use keyword-only arguments with expanded configuration options for chunked prefill scenarios.

Changes

Cohort / File(s)	Summary
Executor KV Cache Logic tensorrt_llm/_torch/pyexecutor/py_executor.py	Changed KV cache transfer to source from finished_ctx_reqs instead of scheduled_ctx_reqs when signaling the KV cache path in the PP executor loop.
Test Method Refactoring tests/integration/defs/accuracy/test_disaggregated_serving.py	Refactored run_parallel_test() to use keyword-only arguments with expanded parameters (ctx_pp, ctx_tp, gen_pp, gen_tp, ctx_instances, gen_instances, test_sets, optional ctx_model/gen_model). Added helper method _test_chunked_prefill_helper() and new test methods test_chunked_prefill and test_chunked_prefill_ctx_pp2 with corresponding test setup configurations.
Test Configuration tests/integration/test_lists/test-db/l0_dgx_h100.yml	Added new test case accuracy/test_disaggregated_serving.py::TestQwen3_8B::test_chunked_prefill_ctx_pp2 to the l0_dgx_h100 configuration.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 1 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check	❓ Inconclusive	The description provides minimal detail—only stating 'Fix for bug introduced in #9308'—without explaining what the bug was, how it manifests, or why the fix works. The Test Coverage section is empty, leaving uncertainty about validation.	Expand the description to explain the specific bug (e.g., why scheduled_ctx_reqs was incorrect and why finished_ctx_reqs is correct) and explicitly list which test(s) validate the fix (e.g., test_chunked_prefill_ctx_pp2).

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and clearly describes the main fix: ensuring only finished context requests are sent to KV cache, which directly aligns with the primary code change in py_executor.py and the bug referenced in PR #9308.

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