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[https://nvbugs/5477730][fix] Fix the alltoall case when tp_size larger than ep_size by WeiHaocheng · Pull Request #7331 · NVIDIA/TensorRT-LLM · GitHub
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@WeiHaocheng WeiHaocheng commented Aug 28, 2025

…er than ep_size

Summary by CodeRabbit

  • Refactor
    • Migrated to MOE-oriented mapping fields for communicator composition and workspace sizing, improving consistency across MOE execution.
    • Introduced MOE topology attributes to better partition ranks in MOE setups.
    • Breaking: Renamed public mapping attributes to moe_ep_size/moe_ep_rank and added moe_tp_size/moe_tp_rank; update configurations and integrations accordingly.

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…er than ep_size

Signed-off-by: Fred Wei <20514172+WeiHaocheng@users.noreply.github.com>
@WeiHaocheng WeiHaocheng requested a review from dongxuy04 August 28, 2025 07:59
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📝 Walkthrough

Walkthrough

Shifts MOE-related logic from tensor-parallel (tp_) fields to new MOE endpoint (moe_ep_) and MOE topology (moe_tp_) fields. Updates communicator color/rank derivation, workspace sizing per rank, and workspace initialization to use moe_ep_ and moe_tp_* in tensorrt_llm/_mnnvl_utils.py. Adds/renames Mapping attributes accordingly.

Changes

Cohort / File(s) Summary
MOE utils: communicator and workspaces
tensorrt_llm/_mnnvl_utils.py
Replace tp_* with moe_ep_* for workspace sizing and initialization; introduce use of moe_tp_* for MPI color and rank composition; update get_moe_workspaces and get_moe_prepare_workspace to compute per-rank sizes via moe_ep_size and pass moe_ep_rank/moe_ep_size.
Mapping API updates
tensorrt_llm/mapping.py
Add attributes: moe_tp_size, moe_tp_rank. Rename attributes: tp_size → moe_ep_size, tp_rank → moe_ep_rank.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  participant Caller
  participant Mapping
  participant Communicator
  participant Workspace

  Note over Mapping,Workspace: New MOE-oriented fields (moe_ep_*, moe_tp_*)
  
  Caller->>Mapping: Read moe_ep_size, moe_ep_rank
  Caller->>Mapping: Read moe_tp_size, moe_tp_rank
  Mapping-->>Caller: Values

  Caller->>Communicator: compose_color(moe_tp_size, moe_tp_rank)
  Communicator-->>Caller: color, rank_in_color

  Caller->>Workspace: calc_size_per_rank(moe_ep_size)
  Workspace-->>Caller: workspace_size_per_rank

  Caller->>Workspace: init(moe_ep_rank, moe_ep_size)
  Workspace-->>Caller: init_ok

  Note right of Workspace: Sizing/initialization aligned to MOE endpoints
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🎯 4 (Complex) | ⏱️ ~60 minutes

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  • yuxianq
  • StudyingShao

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LGTM, thanks.

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Actionable comments posted: 0

🧹 Nitpick comments (1)
tensorrt_llm/_mnnvl_utils.py (1)

382-384: LGTM: prepare-workspace size per rank uses moe_ep_size

Consistent with the main workspace path; this should prevent over-allocation when tp_size > ep_size.

Optionally mirror a post-allocation barrier here (as done for the main workspace) if upstream users can race on first-touch of the prepare buffer.

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📥 Commits

Reviewing files that changed from the base of the PR and between 4541655 and b30e5c2.

📒 Files selected for processing (1)
  • tensorrt_llm/_mnnvl_utils.py (3 hunks)
🧰 Additional context used
🧠 Learnings (1)
📓 Common learnings
Learnt from: djns99
PR: NVIDIA/TensorRT-LLM#6915
File: cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_kernels.cu:4616-4626
Timestamp: 2025-08-19T03:35:20.866Z
Learning: In the MOE profiler TMA workspace preparation (cpp/tensorrt_llm/kernels/cutlass_kernels/moe_gemm/moe_kernels.cu), the overlapping of TMA WS regions for NONE and FINALIZE variants is deliberate design to save memory space, as confirmed by djns99. The comment "reuse the same pointers to save space" reflects this intentional behavior.
🧬 Code graph analysis (1)
tensorrt_llm/_mnnvl_utils.py (2)
tensorrt_llm/_torch/distributed/communicator.py (1)
  • cp_size (38-39)
tensorrt_llm/mapping.py (2)
  • moe_tp_rank (352-353)
  • moe_ep_rank (360-361)
⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (1)
  • GitHub Check: Pre-commit Check
🔇 Additional comments (2)
tensorrt_llm/_mnnvl_utils.py (2)

366-373: LGTM: workspace sizing/initialization now correctly keyed to moe_ep_{size,rank}

Switching from tp_* to moe_ep_* aligns the workspace with the EP dimension and fixes the tp_size > ep_size case.

Consider adding an E2E test with tp_size=8, moe_ep_size=4 validating that moe_commworkspace_size_per_rank and moe_initialize_workspace don’t depend on tp_size.


107-110: Use mapping.moe_ep_rank as Split key to align communicator ranks with ep_rank
In tensorrt_llm/_mnnvl_utils.py, replace

comm = mpi_comm().Split(
    (mapping.pp_rank * mapping.cp_size + mapping.cp_rank) * mapping.moe_tp_size
    + mapping.moe_tp_rank,
    mapping.tp_rank,
)

with

color = (mapping.pp_rank * mapping.cp_size + mapping.cp_rank) * mapping.moe_tp_size \
        + mapping.moe_tp_rank
key   = mapping.moe_ep_rank
comm  = mpi_comm().Split(color, key)
assert comm.Get_size() == mapping.moe_ep_size, \
    f"Unexpected comm size: {comm.Get_size()} vs moe_ep_size={mapping.moe_ep_size}"

Then verify at runtime:

assert MnnvlMemory.get_comm(mapping).Get_rank() == mapping.moe_ep_rank

[tag: verify_review_comment]

@dongxuy04 dongxuy04 changed the title [https://nvbugs/5477730][fix] Fix the alltoall case when tp_size larg… [TRTLLM-7456][fix] Fix the alltoall case when tp_size larg… Aug 28, 2025
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PR_Github #16821 [ run ] triggered by Bot

@dongxuy04 dongxuy04 changed the title [TRTLLM-7456][fix] Fix the alltoall case when tp_size larg… [https://nvbugs/5477730][fix] Fix the alltoall case when tp_size larg… Aug 28, 2025
@dongxuy04 dongxuy04 changed the title [https://nvbugs/5477730][fix] Fix the alltoall case when tp_size larg… [https://nvbugs/5477730][fix] Fix the alltoall case when tp_size larger than ep_size Aug 28, 2025
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PR_Github #16821 [ run ] completed with state SUCCESS
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/bot run --disable-fail-fast

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PR_Github #16848 [ run ] completed with state SUCCESS
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/bot run --disable-fail-fast

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/bot run --disable-fail-fast

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PR_Github #17275 [ run ] completed with state SUCCESS
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PR_Github #17329 [ run ] completed with state SUCCESS
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/bot run --post-merge

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PR_Github #17525 [ run ] triggered by Bot

@WeiHaocheng WeiHaocheng enabled auto-merge (squash) September 3, 2025 14:49
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PR_Github #17525 [ run ] completed with state SUCCESS
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/bot run --post-merge --disable-fail-fast

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PR_Github #17594 [ run ] completed with state SUCCESS
/LLM/main/L0_MergeRequest_PR pipeline #13228 completed with status: 'SUCCESS'

@WeiHaocheng WeiHaocheng merged commit 5bcda75 into NVIDIA:main Sep 4, 2025
13 of 19 checks passed
Wong4j pushed a commit to Wong4j/TensorRT-LLM that referenced this pull request Sep 20, 2025
…er than ep_size (NVIDIA#7331)

Signed-off-by: Fred Wei <20514172+WeiHaocheng@users.noreply.github.com>
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