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[Qwen3.5] mamba slice fix (Prefill TP != Decode TP & decode TP size>1) #20655

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Merged
ShangmingCai merged 2 commits into from
Mar 17, 2026
Merged

[Qwen3.5] mamba slice fix (Prefill TP != Decode TP & decode TP size>1) #20655

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4451395
mamba slice fix
YAMY1234 Mar 16, 2026
91ddc44
Merge branch 'main' into mamba_slice_fix
ShangmingCai Mar 17, 2026
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4 changes: 3 additions & 1 deletion python/sglang/srt/disaggregation/mooncake/conn.py
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Original file line number Diff line number Diff line change
Expand Up @@ -726,7 +726,9 @@ def _send_mamba_state_slice(
# Each prefill sends all its dims to the appropriate offset in decode
src_dim_start = 0
num_dims_to_send = src_dim
dst_dim_start = local_tp_rank_in_group * src_dim
writers_per_decode = self.attn_tp_size // dst_attn_tp_size
local_writer_idx = local_tp_rank_in_group % writers_per_decode
dst_dim_start = local_writer_idx * src_dim
else:
# 1 prefill rank sends to multiple decode ranks
# Prefill sends a slice of its dims to each decode rank
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