[v0.18.0][bugfix]fixed block_size incorrect setting issue in dsv3.2 (#7630) (#7652)

### What this PR does / why we need it?
https://github.com/vllm-project/vllm/pull/35122 This PR in the vllm
community refactors the update mode of block_size. As a result, when the
user does not specify `--block-size`, dsv3.2 obtains an incorrect
block_size.

**The root cause of the problem is analyzed from the block_size update
process as follows:**
1. In NPUPlatform, `check_and_update_config` calls `refresh_block_size`
to set block_size to 128.
2. During Modelrunner initialization, the `self.block_size` parameter is
generated. At this time, block_size is still 128. This parameter will be
used for operations such as kvcache initialization.
3. `update_block_size_for_backend` updates block_size to the size set in
attn_backend. The reason why the DSV3.2 is faulty is that it has an
additional attn_backend `DeepseekV32IndexerBackend`, and this backend is
not rewritten. The block_size obtained from attn_backend is 64. In this
case, only `vllm_config.cache_config.block_size` is updated, and other
parts are not modified. As a result, the block_size on the entire
network is inconsistent.

**Modification solution:**
Skip `update_block_size_for_backend` and modify block_size only in the
`check_and_update_config` method.

In the future, the block_size update logic can be migrated to the
`update_block_size_for_backend` method. Ensure that all block_size
values on the entire network are updated.
### Does this PR introduce _any_ user-facing change? 
no
### How was this patch tested?

- vLLM version: v0.18.0
- vLLM main:
ed359c497a
---------

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Signed-off-by: Wang Kunpeng <1289706727@qq.com>

vllm_ascend/platform.py

@@ -224,17 +224,9 @@ class NPUPlatform(Platform):
 
     @classmethod
     def update_block_size_for_backend(cls, vllm_config: VllmConfig) -> None:
-        cache_config = vllm_config.cache_config
-        if cache_config.user_specified_block_size:
-            # User specified --block-size; keep it.
-            return
-        model_config = vllm_config.model_config
-        if model_config is not None and model_config.is_hybrid:
-            # Hybrid attention+mamba models rely on the model-specific sizing
-            # logic rather than the generic platform default.
-            return
-
-        super().update_block_size_for_backend(vllm_config)
+        # TODO: NPU still sets block_size in check_and_update_config.
+        # Move that logic here so block_size is chosen by the backend.
+        pass
 
     @classmethod
     def set_device(cls, device: torch.device):

vllm_ascend/utils.py

@@ -1101,12 +1101,12 @@ def refresh_block_size(vllm_config):
     if not scheduler_config or not model_config:
         return
 
-    # TODO(MengqingCao): Remove the model_type check, after resolving the hidden error in get_kv_cache_groups.
-    if (
-        "qwen3_next" not in model_config.hf_text_config.model_type
-        and "qwen3_5" not in model_config.hf_text_config.model_type
-        and cache_config.block_size != 128
-    ):
+    if model_config.is_hybrid:
+        # Hybrid attention+mamba models rely on the model-specific sizing
+        # logic rather than the generic platform default.
+        return
+
+    if cache_config.block_size != 128:
         if cache_config.enable_prefix_caching or scheduler_config.enable_chunked_prefill:
             logger.info("Block size is set to 128 if prefix cache or chunked prefill is enabled.")
             cache_config.block_size = 128