update default block_size

vllm/config.py

@@ -1464,7 +1464,7 @@ PrefixCachingHashAlgo = Literal["builtin", "sha256"]
 class CacheConfig:
     """Configuration for the KV cache."""
 
-    block_size: SkipValidation[BlockSize] = None  # type: ignore
+    block_size: SkipValidation[BlockSize] = 64  # type: ignore
     """Size of a contiguous cache block in number of tokens. This is ignored on
     neuron devices and set to `--max-model-len`. On CUDA devices, only block
     sizes up to 32 are supported. On HPU devices, block size defaults to 128.