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[TRTLLM-10657][fix] Resolve MIXED_PRECISION quant config for DeepSeek W4A8 MoE experts - #18393

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[TRTLLM-10657][fix] Resolve MIXED_PRECISION quant config for DeepSeek W4A8 MoE experts#18393
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Dev Engineer Review

  • Deepseekv3MoE now resolves per-expert quantization settings for MIXED_PRECISION.
  • The resolved configuration now selects the expert weight_loading_mode.
  • DeepseekV3DecoderLayer no longer rejects MIXED_PRECISION.
  • ConfigurableMoE now prioritizes _override_quant_config.
  • The changes address executor initialization failures caused by a global configuration that does not map to one QuantMode.
  • No configuration files or test-list files changed.

QA Engineer Review

  • Added CPU unit-test coverage for:
    • Per-expert W4A8-AWQ configuration resolution.
    • Global-configuration fallback.
    • W4A8_CUSTOM loading-mode selection.
    • _override_quant_config precedence.
    • Unquantized modules.
  • No matching tests/integration/test_lists/ coverage is reported for the new test.
  • Verdict: needs follow-up.

Description

DeepSeek-R1-W4AFP8 ships an hf_quant_config with quant_algo=MIXED_PRECISION. On the PyTorch backend, constructing DeepseekV3DecoderLayer hit a hard assertion (MIXED_PRECISION is ambiguous), so the 8-GPU TP8/EP8 quickstart_advanced run for this model aborted during executor initialization (surfacing to the caller as Executor worker returned error).

The global MIXED_PRECISION algo does not map to a single QuantMode; the per-module configs (W4A8_AWQ for the MoE experts, FP8 block scales for attention) must be resolved individually.

Changes:

  • Deepseekv3MoE: when the override quant config is MIXED_PRECISION, resolve the per-expert quant config via _get_experts_quant_config and pass it to create_moe (deriving weight_loading_mode from the resolved config).
  • DeepseekV3DecoderLayer: drop the assertion and set is_nvfp4 defensively for MIXED_PRECISION.
  • ConfigurableMoE._get_quant_config_dict: prefer the resolved per-module override over the global config.
  • Add CPU unit tests for the per-module quant-config resolution (tests/unittest/_torch/models/test_deepseekv3_mixed_precision_quant.py).

This supersedes #12149 (same fix, rebased onto current main). Once this merges, #12149 can be closed.

Fixes https://nvbugs/5836830

Note: weight_loading_mode on excluded layers

weight_loading_mode is now derived from the same resolved config that constructs the experts (expert_quant_config) instead of unconditionally from _get_experts_quant_config. On a layer excluded via is_module_excluded_from_quantization, both expert construction and the loading mode follow the stripped QuantConfig(quant_algo=None), i.e. VANILLA. Previously such a layer could be labeled W4A8_CUSTOM by a per-expert quant_config_dict entry while the module itself was built unquantized. The two modes load identically on the unquantized path, and that combination is not produced by examples/quantization/quantize_mixed_precision_moe.py (which emits no exclude_modules), so no reachable behavior changes; the new derivation keeps the mode consistent with the module. Intentional; see the review discussion.

Test Coverage

Covered by CPU unit tests in tests/unittest/_torch/models/test_deepseekv3_mixed_precision_quant.py (no GPU or weights required):

  • Deepseekv3MoE._get_experts_quant_config resolves the per-module W4A8_AWQ config for the experts under a MIXED_PRECISION global, and falls back to the global config for unlisted layers or when no per-module dict is present.
  • The resolved expert config selects the W4A8_CUSTOM loading mode (layer_quant_mode.is_int4_weight_only_per_group()), which the MIXED_PRECISION global does not.
  • ConfigurableMoE._get_quant_config_dict prefers the resolved _override_quant_config over the MIXED_PRECISION global, and falls back to the global config (or None) otherwise.

These exercise the exact resolution the fix adds; the previous behavior (using the ambiguous global) fails them. The 8-GPU test_ptp_quickstart_advanced_deepseek_r1_w4afp8_8gpus end-to-end test stays waived rather than being enabled, to avoid adding an 8-GPU post-merge case for the fixed logic that the unit tests already cover.

PR Checklist

Please review the following before submitting your PR:

  • PR description clearly explains what and why.

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

  • Test cases are provided for new code paths (see test instructions)

  • No API changes (internal quantization-config resolution only).

  • Please check this after reviewing the above items as appropriate for this PR.

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Walkthrough

DeepSeekV3 now resolves mixed-precision quantization per expert, prioritizes explicit MoE overrides, selects W4A8 loading from resolved settings, and permits mixed precision during decoder-layer initialization. CPU tests cover resolution and flag behavior.

Changes

DeepSeekV3 mixed-precision quantization

Layer / File(s) Summary
Expert quantization resolution
tensorrt_llm/_torch/moe/fused_moe/configurable_moe.py, tensorrt_llm/_torch/models/modeling_deepseekv3.py, tests/unittest/_torch/models/test_deepseekv3_mixed_precision_quant.py
ConfigurableMoE prefers an explicit override over the model-wide configuration. Deepseekv3MoE resolves per-expert settings before expert creation and uses the resolved mode for W4A8 loading. Tests cover per-expert resolution and fallback behavior.
Decoder support and flag validation
tensorrt_llm/_torch/models/modeling_deepseekv3.py, tests/unittest/_torch/models/test_deepseekv3_mixed_precision_quant.py
Decoder initialization accepts MIXED_PRECISION and disables the layer-level NVFP4 flag for that mode. Tests cover override precedence, global FP8 fallback, and unquantized behavior.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: 🔵 Low · up to 60a15

This change enables mixed-precision DeepSeek expert initialization, but its new W4A8 custom-loading selection is not directly covered by the added unit tests. Add a CPU test for Deepseekv3MoE loading-mode selection before merge to prevent initialization regressions.

Suggested reviewers: bowenfu

Sequence Diagram(s)

sequenceDiagram
  participant Deepseekv3DecoderLayer
  participant Deepseekv3MoE
  participant ConfigurableMoE
  participant Expert
  Deepseekv3DecoderLayer->>Deepseekv3MoE: initialize mixed-precision layer
  Deepseekv3MoE->>ConfigurableMoE: resolve override or model quantization
  ConfigurableMoE-->>Deepseekv3MoE: return quantization configuration
  Deepseekv3MoE->>Expert: create expert with resolved configuration
  Deepseekv3MoE->>Expert: apply W4A8 loading when configured
Loading
🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name Status Explanation Resolution
Docstring Coverage ⚠️ Warning Docstring coverage is 14.29% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 14 functions across 4 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.
Description check ✅ Passed The description clearly explains the MIXED_PRECISION failure, the implementation changes, the test coverage, and the lack of API changes. It includes the required Description, Test Coverage, and PR Ch…
Title check ✅ Passed The title clearly identifies the ticket, fix type, and primary change: resolving MIXED_PRECISION configuration for DeepSeek W4A8 MoE experts.
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🧹 Nitpick comments (1)
tests/integration/test_lists/test-db/l0_dgx_h200.yml (1)

49-49: 📐 Maintainability & Code Quality | 🔵 Trivial

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Test coverage summary: needs follow-up.

The change adds test_e2e.py::test_ptp_quickstart_advanced_deepseek_r1_w4afp8_8gpus[...] to tests/integration/test_lists/test-db/l0_dgx_h200.yml. No test-code files or entries are removed. No cbts_touchmap.sqlite or CBTS coverage report is available. Provide one to confirm the impacted scope before merge.

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Nitpick comments:
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- Line 49: Provide CBTS scope evidence for the added test entry
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brnguyen2 force-pushed the fix-deepseek-w4a8-mixed-precision-moe branch from 2eb817b to 4259b22 Compare August 31, 2026 15:44
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Signed-off-by: Brian Nguyen <brnguyen@nvidia.com>
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LGTM

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