### What this PR does / why we need it? The current MatmulReduceScatter operator experiences performance degradation in small-shape scenarios, so it determines whether to use this operator by judging the size of the shape. ### Does this PR introduce _any_ user-facing change? ### How was this patch tested? - vLLM version: v0.11.0rc3 - vLLM main: https://github.com/vllm-project/vllm/commit/releases/v0.11.1 --------- Signed-off-by: ZYang6263 <zy626375@gmail.com>