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Nemo Mbridge Perf Tp Dp Comm Overlap

NVIDIAOfficialPublished by NVIDIA

  • Skill
  • Tool integration
  • Software development
  • Apache-2.0
  • Medium risk
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From the author

Operational guide for enabling TP, DP, and PP communication overlap in Megatron-Bridge, including config knobs, code anchors, pitfalls, and verification.
— the description by NVIDIA

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a comprehensive guide for enabling and tuning communication overlap (TP, DP, and PP) within the Megatron-Bridge framework. It covers essential configuration knobs, code-level gating mechanisms, common pitfalls to avoid, and verification procedures to ensure optimal performance during large-scale model training.

What it does

  • Provides configuration templates for enabling TP, DP, and PP communication overlap.
  • Identifies key code anchors that control overlap gating and P2P communication logic.
  • Highlights common pitfalls regarding sequence parallelism, Transformer Engine dependencies, and bucket sizing.
  • Details environment variable tuning for launch-time performance optimization.
  • Outlines verification steps using unit tests to confirm overlap configuration success.

When to use it

  • When configuring communication overlap for Megatron-Bridge training jobs.
  • When investigating throughput regressions related to communication overlap settings.
  • When troubleshooting why TP or PP overlap features are not activating as expected.
  • When tuning environment variables like CUDA_DEVICE_MAX_CONNECTIONS for performance.

Advantages

  • Centralizes configuration knowledge for complex parallel training setups.
  • Provides clear guidance on the interaction between model parallelism and overlap features.
  • Includes specific verification commands to validate configuration integrity.
  • Warns against common misconfigurations in mixed precision and environment settings.

Usage examples

“How do I enable TP communication overlap in my Megatron-Bridge config?”
The skill provides the CommOverlapConfig snippet to set tp_comm_overlap=True and notes the requirement for sequence_parallel=True and Transformer Engine availability.
“Why is my PP overlap not working?”
The guide explains that PP overlap is only auto-selected when pipeline_model_parallel_size > 1 and virtual_pipeline_model_parallel_size > 1.

Install

  1. Download the skill as a ZIP:

    https://mp-staging.autogineer.com/agent-skills/nvidia/nemo-mbridge-perf-tp-dp-comm-overlap/download

  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip nemo-mbridge-perf-tp-dp-comm-overlap.zip -d .agents/skills

Documentation by NVIDIA

TP / DP / PP Communication Overlap Skill

For stable background and recommendation level, see:

  • @docs/training/communication-overlap.md

Enablement

Minimal Bridge override:

from megatron.bridge.training.comm_overlap import CommOverlapConfig

cfg.model.tensor_model_parallel_size = 4
cfg.model.sequence_parallel = True
cfg.model.pipeline_model_parallel_size = 4
cfg.model.virtual_pipeline_model_parallel_size = 2

cfg.comm_overlap = CommOverlapConfig(
    tp_comm_overlap=True,
)

cfg.ddp.use_distributed_optimizer = True
cfg.ddp.overlap_grad_reduce = True
cfg.ddp.overlap_param_gather = True

Optional TP preset:

from megatron.bridge.training.comm_overlap import userbuffers_bf16_h100_h12288_tp4_mbs1_seqlen2048

cfg.comm_overlap.tp_comm_overlap_cfg = userbuffers_bf16_h100_h12288_tp4_mbs1_seqlen2048

Precision knobs belong to mixed precision:

cfg.mixed_precision.grad_reduce_in_fp32 = False
cfg.mixed_precision.fp8_param_gather = False

Code Anchors

Bridge overlap gating:

if self.user_comm_overlap_cfg.tp_comm_overlap is True:
    if model_cfg.tensor_model_parallel_size < 2:
        ...
    elif not model_cfg.sequence_parallel:
        ...
    elif not HAVE_TE:
        ...

PP overlap selection:

if model_cfg.pipeline_model_parallel_size > 1:
    if vp_size > 1:
        comm_overlap_cfg.overlap_p2p_comm = True
        comm_overlap_cfg.batch_p2p_comm = False
    else:
        comm_overlap_cfg.overlap_p2p_comm = False
        comm_overlap_cfg.batch_p2p_comm = True

DP overlap defaults:

if self.data_parallel_size > 1:
    comm_overlap_cfg.bucket_size = 128 * 1024 * 1024
    comm_overlap_cfg.overlap_grad_reduce = True
    comm_overlap_cfg.overlap_param_gather = True

Launch-time env tuning:

executor.env_vars["CUDA_DEVICE_MAX_CONNECTIONS"] = str(cuda_device_max_connections)
...
executor.env_vars["NVTE_FWD_LAYERNORM_SM_MARGIN"] = str(self.layernorm_sm_margin)
executor.env_vars["NVTE_BWD_LAYERNORM_SM_MARGIN"] = str(self.layernorm_sm_margin)

Pitfalls

  1. TP overlap silently disables itself if sequence_parallel=False or Transformer Engine is unavailable.

  2. PP overlap is not enabled for all PP cases. Bridge only auto-selects overlap_p2p_comm=True when PP > 1 and VPP > 1.

  3. bucket_size is a parameter-count knob, not a byte-size knob.

  4. grad_reduce_in_fp32 and fp8_param_gather should be set through mixed precision, not as standalone DDP tuning first.

  5. CUDA_DEVICE_MAX_CONNECTIONS and LayerNorm SM margin are launch-time plugin settings, not CommOverlapConfig fields.

Verification

Use the checked-in overlap unit coverage first:

uv run python -m pytest tests/unit_tests/training/test_comm_overlap.py -q

Optional second check if nemo_run is available:

uv run python -m pytest tests/unit_tests/recipes/test_run_plugins.py -q

Success criteria:

  • first command reports 26 passed

  • second command validates plugin-owned env wiring when not skipped

Files

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Requirements and compatibility

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Attribution and licence

Published by
NVIDIA
Publisher
NVIDIA (Official)
Source
NVIDIA/skills · skills/nemo-mbridge-perf-tp-dp-comm-overlap · commit fce3cca
Licence
Apache License 2.0 (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE-APACHE)
  • ATTRIBUTION.md (written by AutoGineer)
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Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download nemo-mbridge-perf-tp-dp-comm-overlap.zip