[Core] Add xxHash as a high-performance hash option for accelerating prefix caching (#29163)

Signed-off-by: LuminolT <lumischen01@gmail.com>
Signed-off-by: Lumis Chen <lumischen01@gmail.com>
Co-authored-by: Russell Bryant <rbryant@redhat.com>

vllm/v1/core/kv_cache_utils.py

@@ -12,7 +12,7 @@ from typing import Any, NewType, TypeAlias, overload
 from vllm import envs
 from vllm.config import VllmConfig
 from vllm.logger import init_logger
-from vllm.utils.hashing import sha256_cbor
+from vllm.utils.hashing import sha256_cbor, xxhash_cbor
 from vllm.utils.math_utils import cdiv
 from vllm.utils.mem_constants import GiB_bytes
 from vllm.v1.kv_cache_interface import (
@@ -83,18 +83,19 @@ logger = init_logger(__name__)
 #
 # The function `init_none_hash` initializes this variable globally.
 NONE_HASH: BlockHash
+_CBOR_HASH_FUNCTIONS = frozenset({sha256_cbor, xxhash_cbor})
 
 
 def init_none_hash(hash_fn: Callable[[Any], bytes]):
     global NONE_HASH
 
     hash_seed = os.getenv("PYTHONHASHSEED")
-    if hash_seed is None and hash_fn is sha256_cbor:
+    if hash_seed is None and hash_fn in _CBOR_HASH_FUNCTIONS:
         logger.warning(
             "PYTHONHASHSEED is not set. This will lead to non-reproducible "
-            "block-hashes when using sha256_cbor as the hash function."
-            "Consider setting PYTHONHASHSEED to a fixed value for "
-            "reproducibility."
+            "block-hashes when using CBOR-based hash functions such as "
+            "sha256_cbor or xxhash_cbor. Consider setting PYTHONHASHSEED to a "
+            "fixed value for reproducibility."
         )
 
     if hash_seed is None: