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[Megatron Lite] Fix qwen3_moe BSHD forward under context parallelism (#5617) #5661

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[Megatron Lite] Fix qwen3_moe BSHD forward under context parallelism (#5617) #5661

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18 changes: 16 additions & 2 deletions experimental/lite/megatron/lite/model/qwen3_moe/lite/protocol.py
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,8 @@
normalize_lora_config,
trainable_param_stats,
)
from megatron.lite.primitive.parallel import ParallelState, init_parallel
from megatron.lite.primitive.parallel import ParallelState, init_parallel, zigzag_slice_for_cp
from megatron.lite.primitive.parallel.thd import parallel_state_from_model
from megatron.lite.primitive.recompute import apply_recompute, parse_recompute_spec
from megatron.lite.runtime.contracts import OptimizerConfig, ParallelConfig
from megatron.lite.runtime.contracts.data import PackedBatch
Expand Down Expand Up @@ -133,8 +134,21 @@ def _forward_step(model: nn.Module, batch: PackedBatch) -> dict:


def _forward_step_bshd(model: nn.Module, batch: PackedBatch) -> dict:
ps = parallel_state_from_model(model) or ParallelState()
input_ids = batch.input_ids.reshape(1, -1)
labels = batch.labels.reshape(1, -1) if batch.labels is not None else None
return model(input_ids=batch.input_ids.reshape(1, -1), labels=labels, packed_seq_params=None)
loss_mask = batch.loss_mask.reshape(1, -1) if batch.loss_mask is not None else None
if ps.cp_size > 1:
# GQAttention's non-THD branch expects CP-zigzag-sharded inputs, and
# unpack_forward_output() reconstructs zigzag-CP outputs; match both.
input_ids = zigzag_slice_for_cp(input_ids, ps.cp_rank, ps.cp_size, seq_dim=1)
if labels is not None:
labels = zigzag_slice_for_cp(labels, ps.cp_rank, ps.cp_size, seq_dim=1)
if loss_mask is not None:
loss_mask = zigzag_slice_for_cp(loss_mask, ps.cp_rank, ps.cp_size, seq_dim=1)
return model(
input_ids=input_ids, labels=labels, loss_mask=loss_mask, packed_seq_params=None
)


def unpack_forward_output(model: nn.Module, batch: PackedBatch, output) -> Any:
Expand Down