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Sequence packing and long-context training in Megatron Bridge. Use when the user asks about packed sequences, sequence packing, long context training, PackedSequenceSpecs, pack_sequences_in_batch, or CP with packing.
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SOC 職業分類に基づく
Guide for adding support for new LLM or VLM models in Megatron-Bridge. Covers bridge, provider, recipe, tests, docs, and examples. Use when the user asks to add, support, onboard, or integrate a new model, or when creating bridges, providers, or recipes for a new model family.
Convert single-node scripts to multi-node Slurm sbatch jobs and debug common multi-node failures. Covers srun-native vs uv run torch.distributed approaches, container setup, NCCL timeouts, OOM sizing for MoE models, and interactive allocation. Use when creating Slurm scripts, scaling to multi-node, or debugging multi-node job failures.
Developer environment setup, CI/CD workflows, and CI failure debugging for Megatron Bridge. Covers container-based development, uv package management, pre-commit hooks, running tests, CI failure investigation, and common pitfalls. Use when onboarding, setting up a dev environment, troubleshooting build issues, or investigating CI failures.
Code style and quality guidelines for Megatron Bridge. Covers naming, type hints, ruff enforcement, keyword-arg safety, copyright headers, logging, and common anti-patterns. Auto-invoked during code review and when writing new code.
Structured framework for verifying numerical parity of HF<->MCore weight conversions. References existing tools and the add-model-support skill. Use when debugging weight mismatches, verifying checkpoint round-trips, or choosing which verification tool to run.
Validate and use MoE expert-parallel communication overlap in Megatron-Bridge, including overlap_moe_expert_parallel_comm, delay_wgrad_compute, and flex dispatcher backends such as DeepEP and HybridEP.
| name | packed-sequences-long-context |
| description | Sequence packing and long-context training in Megatron Bridge. Use when the user asks about packed sequences, sequence packing, long context training, PackedSequenceSpecs, pack_sequences_in_batch, or CP with packing. |
For what packed sequences are, the three packing paths, and when to use them, see:
docs/training/packed-sequences.mdcard.yaml (co-located)cfg.train.micro_batch_size = 1
cfg.dataset.dataset_kwargs.pad_to_max_length = True
cfg.dataset.packed_sequence_specs.packed_sequence_size = 8192 # match seq_length
cfg.dataset.pack_sequences_in_batch = True
cfg.train.micro_batch_size = 4 # must be > 1
cfg.model.context_parallel_size = 4
cfg.model.calculate_per_token_loss = True
cfg.ddp.average_in_collective = False
cfg.dataset.packed_sequence_specs.pad_seq_to_mult = 2 * 4 # 2 * CP
# If sequence_parallel is also enabled, pad_seq_to_mult must include TP:
# cfg.dataset.packed_sequence_specs.pad_seq_to_mult = 2 * CP * TP
src/megatron/bridge/data/datasets/packed_sequence.pysrc/megatron/bridge/data/datasets/sft.pysrc/megatron/bridge/training/utils/packed_seq_utils.pysrc/megatron/bridge/training/gpt_step.pysrc/megatron/bridge/training/vlm_step.pysrc/megatron/bridge/recipes/utils/finetune_utils.pytests/functional_tests/training/test_seqpacking_cp_example.pyMBS constraint: Offline packed SFT requires micro_batch_size == 1.
VLM in-batch packing requires micro_batch_size > 1. Mixing these up
produces silent data corruption.
CP divisibility: seq_length must be divisible by 2 * context_parallel_size.
When sequence parallelism (SP) is also enabled, the divisor becomes
2 * CP * TP. Violations cause assertion errors during initialization.
Per-token loss with CP: Finetuning with CP > 1 requires
calculate_per_token_loss=True and average_in_collective=False.
Without these, loss scaling is wrong across CP ranks.
MTP incompatibility: Sequence packing for finetuning is documented as unsupported with multi-token prediction.
Model-family opt-outs: Several model families explicitly disable packing: Qwen3-Next SFT, GLM-4.5 SFT/PEFT, Qwen3.5-VL. Check model-specific recipes before assuming packing is available.
For offline packed SFT, verify that cu_seqlens and seq_offsets are
present in the batch dict during the forward pass. For CP + packing, look for
the pad_seq_to_mult validation message during config setup.