docs: clarify LoRA is not supported with --use_fp8_rowwise in Fp8RowwiseAttention (see #2603)

[ssam18]

Improved the error message in Fp8RowwiseAttention to clearly state that LoRA is not supported with use_fp8_rowwise, suggest alternatives, and reference the related GitHub issue #2603. This helps users quickly understand the limitation and how to proceed.

Summary by CodeRabbit

• Documentation
  • Improved error messages for LoRA compatibility issues to provide clearer guidance on alternative quantization approaches and troubleshooting resources.

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📝 Walkthrough

Walkthrough

Updated two LoRA-related assertion error messages in the quantization layers module to provide more explicit information about FP8 rowwise quantization incompatibility, including references to alternative attention implementations and a GitHub issue link.

Changes

Cohort / File(s)	Summary
Error message enhancements tensorrt_llm/quantization/layers.py	Two LoRA assertion messages expanded to clarify incompatibility with use_fp8_rowwise quantization, reference alternative attention methods (fp16, int8), and include GitHub issue link for context.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Pre-merge checks and finishing touches

❌ 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%.	You can run @coderabbitai generate docstrings to improve docstring coverage.
Description check	❓ Inconclusive	The description explains the purpose of the change but does not follow the required template structure with Description, Test Coverage, and PR Checklist sections.	Use the repository's PR template structure including Description, Test Coverage, and PR Checklist sections to provide complete context.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly indicates a documentation change regarding LoRA incompatibility with FP8 rowwise quantization and references the related GitHub issue.

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Actionable comments posted: 1

📜 Review details

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Review profile: CHILL

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📥 Commits

Reviewing files that changed from the base of the PR and between 270be80 and 5b4cbe8.

📒 Files selected for processing (1)

• tensorrt_llm/quantization/layers.py

🧰 Additional context used

📓 Path-based instructions (2)

**/*.py

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Files:

• tensorrt_llm/quantization/layers.py

**/*.{cpp,h,cu,cuh,py}

📄 CodeRabbit inference engine (CODING_GUIDELINES.md)

All TensorRT-LLM Open Source Software code should contain an NVIDIA copyright header that includes the year of its latest meaningful modification

Files:

• tensorrt_llm/quantization/layers.py

🧠 Learnings (9)

📓 Common learnings

Learnt from: amitz-nv
Repo: NVIDIA/TensorRT-LLM PR: 8063
File: tensorrt_llm/lora_manager.py:1080-1112
Timestamp: 2025-09-29T15:14:28.503Z
Learning: In tensorrt_llm/lora_manager.py, when calculating part_sizes for attn_qkv fused LoRA modules, the sizes are correctly multiplied by tp_size because model_config.num_heads and model_config.num_kv_heads are already divided by tp_size (per-TP-rank values), so multiplication is needed to get the original full concatenated dimension size. The interleave_fused_lora_weights_for_tp function provides proper validation with asserts for total size and TP divisibility.

Learnt from: amitz-nv
Repo: NVIDIA/TensorRT-LLM PR: 8063
File: tensorrt_llm/lora_manager.py:1080-1112
Timestamp: 2025-09-29T15:14:28.503Z
Learning: In tensorrt_llm/lora_manager.py, when calculating part_sizes for attn_qkv fused LoRA modules, the sizes are correctly multiplied by tp_size because model_config.num_heads and model_config.num_kv_heads are already divided by tp_size (per-TP-rank values), so multiplication is needed to get the original full concatenated dimension size. The interleave_fused_lora_weights_for_tp function provides proper validation.

Learnt from: amitz-nv
Repo: NVIDIA/TensorRT-LLM PR: 8063
File: tensorrt_llm/lora_manager.py:1080-1112
Timestamp: 2025-09-29T15:14:28.503Z
Learning: In tensorrt_llm/lora_manager.py, when calculating part_sizes for attn_qkv fused LoRA modules, the sizes are correctly multiplied by tp_size because model_config.num_heads and model_config.num_kv_heads are already divided by tp_size (per-TP-rank values), so multiplication is needed to get the original full concatenated dimension size. The interleave_fused_lora_weights_for_tp function provides proper validation.

📚 Learning: 2025-09-29T15:14:28.503Z

Learnt from: amitz-nv
Repo: NVIDIA/TensorRT-LLM PR: 8063
File: tensorrt_llm/lora_manager.py:1080-1112
Timestamp: 2025-09-29T15:14:28.503Z
Learning: In tensorrt_llm/lora_manager.py, when calculating part_sizes for attn_qkv fused LoRA modules, the sizes are correctly multiplied by tp_size because model_config.num_heads and model_config.num_kv_heads are already divided by tp_size (per-TP-rank values), so multiplication is needed to get the original full concatenated dimension size. The interleave_fused_lora_weights_for_tp function provides proper validation with asserts for total size and TP divisibility.

Applied to files:

• tensorrt_llm/quantization/layers.py

📚 Learning: 2025-09-29T15:14:28.503Z

Learnt from: amitz-nv
Repo: NVIDIA/TensorRT-LLM PR: 8063
File: tensorrt_llm/lora_manager.py:1080-1112
Timestamp: 2025-09-29T15:14:28.503Z
Learning: In tensorrt_llm/lora_manager.py, when calculating part_sizes for attn_qkv fused LoRA modules, the sizes are correctly multiplied by tp_size because model_config.num_heads and model_config.num_kv_heads are already divided by tp_size (per-TP-rank values), so multiplication is needed to get the original full concatenated dimension size. The interleave_fused_lora_weights_for_tp function provides proper validation.

Applied to files:

• tensorrt_llm/quantization/layers.py

📚 Learning: 2025-08-26T06:07:02.166Z

Learnt from: shaharmor98
Repo: NVIDIA/TensorRT-LLM PR: 7231
File: tensorrt_llm/_torch/pyexecutor/_util.py:504-509
Timestamp: 2025-08-26T06:07:02.166Z
Learning: In tensorrt_llm/_torch/pyexecutor/_util.py, when calling model_engine.set_lora_model_config(), pass model_binding_config.mlp_hidden_size directly without multiplying by mapping.tp_size, as the mlp_hidden_size from get_bindings_model_config() is already the per-TP rank value needed for LoRA weight packaging.

Applied to files:

• tensorrt_llm/quantization/layers.py

📚 Learning: 2025-08-19T12:45:11.997Z

Learnt from: amitz-nv
Repo: NVIDIA/TensorRT-LLM PR: 7033
File: tensorrt_llm/_torch/pyexecutor/model_engine.py:0-0
Timestamp: 2025-08-19T12:45:11.997Z
Learning: In tensorrt_llm/_torch/pyexecutor/model_engine.py, DoRA (Delta Orthogonal Rank Adaptation) functionality was removed from the PyTorch flow to eliminate issues with inverted DoRA detection logic. The original is_dora condition was checking if scaling_vec_pointer == 0, which was potentially incorrect.

Applied to files:

• tensorrt_llm/quantization/layers.py

📚 Learning: 2025-12-19T06:31:54.973Z

Learnt from: nvyocox
Repo: NVIDIA/TensorRT-LLM PR: 10117
File: tensorrt_llm/_torch/auto_deploy/transform/library/fuse_rope_attention.py:336-339
Timestamp: 2025-12-19T06:31:54.973Z
Learning: In tensorrt_llm/_torch/auto_deploy/transform/library/fuse_rope_attention.py, the cast to torch.float16 for qkv_node before creating the AttentionPlugin is intentional and required because DriveOS LLM expects float16 dtype specifically. This should not be changed to preserve original dtype or made configurable for bfloat16 models in the DriveOS LLM ONNX export path.

Applied to files:

• tensorrt_llm/quantization/layers.py

📚 Learning: 2025-08-21T00:16:56.457Z

Learnt from: farshadghodsian
Repo: NVIDIA/TensorRT-LLM PR: 7101
File: docs/source/blogs/tech_blog/blog9_Deploying_GPT_OSS_on_TRTLLM.md:36-36
Timestamp: 2025-08-21T00:16:56.457Z
Learning: TensorRT-LLM container release tags in documentation should only reference published NGC container images. The README badge version may be ahead of the actual published container versions.

Applied to files:

• tensorrt_llm/quantization/layers.py

📚 Learning: 2025-09-19T21:28:13.751Z

Learnt from: jhaotingc
Repo: NVIDIA/TensorRT-LLM PR: 7856
File: cpp/tensorrt_llm/thop/fp8BlockScaleMoe.cpp:159-166
Timestamp: 2025-09-19T21:28:13.751Z
Learning: In TensorRT-LLM blockScaleMoe routing (cpp/tensorrt_llm/kernels/trtllmGenKernels/blockScaleMoe/runner.cu), the DeepSeek routing method performs reinterpret_cast<float*>(routingLogits) at line 89, which could cause issues if routing_logits are BF16. However, Qwen3-FP8 models use RenormalizeNaive routing method and are not affected by this dtype casting issue.

Applied to files:

• tensorrt_llm/quantization/layers.py

📚 Learning: 2025-07-17T09:01:27.402Z

Learnt from: amitz-nv
Repo: NVIDIA/TensorRT-LLM PR: 5616
File: tensorrt_llm/executor/worker.py:375-384
Timestamp: 2025-07-17T09:01:27.402Z
Learning: In tensorrt_llm/executor/worker.py, the LoRA adapter cache optimization logic that checks `is_adapter_in_cpu_cache()` and conditionally passes None for weights/config has a known race condition issue that cannot be solved with simple error handling or verification checks. This is a known limitation that requires a more comprehensive solution.

Applied to files:

• tensorrt_llm/quantization/layers.py