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fix qwen3.5 397B converting error when enable expert parallel #1799

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Merged
zhuzilin merged 1 commit into from
Apr 3, 2026
Merged

fix qwen3.5 397B converting error when enable expert parallel #1799

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18 changes: 15 additions & 3 deletions slime_plugins/mbridge/qwen3_5.py
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Original file line number Diff line number Diff line change
Expand Up @@ -277,9 +277,21 @@ def _weight_to_mcore_format(
if "mlp.experts.linear_fc" in mcore_weights_name and len(hf_weights) == 1:
w = hf_weights[0]
if w.dim() == 3:
# Extract expert_id from name like "...linear_fc1.weight42"
expert_id = int(mcore_weights_name.split("weight")[-1])
expert_w = w[expert_id] # (out_features, in_features)
# Extract local expert_id from name like "...linear_fc1.weight42"
local_expert_id = int(mcore_weights_name.split("weight")[-1])
# When using Expert Parallelism (EP), the local expert_id is relative
# to this EP rank. We need to convert to global expert_id to index
# into the full HF fused tensor [num_experts, ...].
from megatron.core import mpu

ep_size = mpu.get_expert_model_parallel_world_size()
if ep_size > 1:
ep_rank = mpu.get_expert_model_parallel_rank()
num_local_experts = w.shape[0] // ep_size
global_expert_id = ep_rank * num_local_experts + local_expert_id
else:
global_expert_id = local_expert_id
expert_w = w[global_expert_id] # (out_features, in_features)
return expert_w.contiguous()

return super()._weight_to_mcore_format(mcore_weights_name, hf_weights)
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