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Jingya HUANG 863092ffec [core] Shard tensor-parallel checkpoints on load and save (#14544)
* [core] Shard tensor-parallel checkpoints on load and save

Stream each rank's slice of a tensor-parallel checkpoint straight off disk
instead of materializing the full checkpoint on every rank and resharding it
afterwards, and gather the shards back on save.

- `from_pretrained(..., parallel_config=TensorParallelConfig(...))` resolves
  the shard specs on the still-meta model, then slices each safetensors tensor
  before the dtype cast, so host memory peaks at ~1/tp_degree of the checkpoint.
- `save_pretrained` all-gathers the DTensors into an ordinary checkpoint, or
  writes a distributed checkpoint with `dcp=True` so no full tensor is ever
  formed. The writing `tp_degree` is recorded, since a packed weight's stored
  layout is interleaved by it.
- Factor the plan interpretation out of the Neuron pre-shard path into shared
  `TPShardSpec` / `resolve_tp_shard_specs` / `_local_shard` / `_hooks_only_styles`
  helpers, so both backends and both the load and save paths shard identically.

* Raise when tensor parallelism is combined with quantization, offloading or LoRA

Addresses the remaining two items of the review on #13718: tensor parallelism was rejected
alongside quantization and `device_map` only on the `from_pretrained` streaming path, while
`enable_parallelism` — which the quantization error message itself recommended — accepted a
quantized, offloaded or adapter-injected model and sharded it anyway.

- Add `_check_tp_model_state`, called from `apply_tensor_parallel`, the one chokepoint every TP
  entry point funnels through. It rejects a model that is quantized, group-offloaded, placed by
  accelerate (`device_map` or CPU offload), or has PEFT layers injected. Placed before the
  device-type check so the reported reason is the useful one.
- Guard the reverse order too: `enable_group_offload`, the two pipeline CPU-offload methods, and
  `load_lora_adapter` now refuse a tensor-parallel model.
- `save_pretrained` refuses a quantized tensor-parallel model. Previously the `dcp=True` branch
  returned before the quantizer's serialization step, writing shards with no quantization
  metadata and no error.
- The DCP load guard checked the `quantization_config` kwarg only, so a pre-quantized checkpoint
  directory loaded silently; check the config's own entry too, and add the missing `_tp_plan`
  check that otherwise surfaced as a raw `AttributeError`.
- Correct the `from_pretrained` message and the doc sentence that pointed at `enable_parallelism`
  as a way to shard a quantized model.

The new tests are the first tensor-parallel tests that need neither an accelerator nor more than
one rank: every case asserts a raise before any collective, so they run single-process on gloo.

* review: remove tp save/ dcp related

* review: add a new helper .

* review: moved the TP checks into enable_parallelism

* review: move the warning under caution block

* review: add loading time numbers

* review: move tp size dividende check

* review: delete test

* review: consolidate tp checks

* review: consolidate the tp checks, all in tensor_parallel.py

* review: improve conditionals

* review: debug info

* review: check weights format before instantiating the model

* review: restore duplicated _find_mismatched_keys since irrelevant

* revert: delete duplicated helper

* review: update doc for loading benchmark of flux2-dev

* review: improve the raising check

* review: add an args section

* Test tensor-parallel loading from sharded checkpoints

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
2026-10-01 10:16:29 +05:30
..
2025-06-19 07:46:01 +05:30
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2026-09-24 09:11:42 -07:00