[Prefix Cache] Use LoRA name for consistent KV-cache block hashing (#27211)

Signed-off-by: Sage Ahrac <sagiahrak@gmail.com>

tests/v1/core/test_kv_cache_utils.py

@@ -8,6 +8,7 @@ import torch
 
 import vllm.v1.core.kv_cache_utils as kv_cache_utils
 from vllm.config import ModelConfig, SchedulerConfig, VllmConfig
+from vllm.lora.request import LoRARequest
 from vllm.multimodal.inputs import (
     MultiModalFeatureSpec,
     MultiModalKwargsItem,
@@ -449,6 +450,24 @@ def test_generate_block_hash_extra_keys_cache_salt():
     assert next_mm_idx == 1
 
 
+def test_generate_block_hash_extra_keys_lora():
+    request = make_request(
+        request_id="0",
+        prompt_token_ids=[_ for _ in range(6)],
+    )
+
+    request.lora_request = LoRARequest(
+        lora_name="test_lora_adapter", lora_int_id=1, lora_path="/path/to/lora"
+    )
+
+    extra_keys, _ = generate_block_hash_extra_keys(request, 0, 3, 0)
+    assert extra_keys == ("test_lora_adapter",)
+
+    request.lora_request = None
+    extra_keys, _ = generate_block_hash_extra_keys(request, 0, 3, 0)
+    assert extra_keys is None
+
+
 @pytest.mark.parametrize("hash_fn", [sha256, sha256_cbor])
 def test_hash_block_tokens(hash_fn):
     parent_block_hash = BlockHash(b"123")

vllm/v1/core/kv_cache_utils.py

@@ -373,7 +373,7 @@ def need_extra_keys(request: Request) -> bool:
     """
 
     # Multimodal requests need to include the MM hash.
-    # LoRA requests need to include the LoRA ID.
+    # LoRA requests need to include the LoRA name.
     # Request with provided cache salt need to include the salt.
     return (
         bool(request.mm_features)
@@ -446,26 +446,26 @@ def _gen_mm_extra_hash_keys(
     return extra_keys, curr_mm_idx
 
 
-def _gen_lora_extra_hash_keys(request: Request) -> list[int]:
+def _gen_lora_extra_hash_keys(request: Request) -> list[str]:
     """Generate extra keys related to LoRA for block hash computation.
 
     Args:
         request: The request object.
 
     Returns:
-        Return LoRA id of the request if it is a LoRA request. Return empty
+        Return LoRA name of the request if it is a LoRA request. Return empty
         list otherwise.
     """
     if not request.lora_request:
         return []
-    return [request.lora_request.lora_int_id]
+    return [request.lora_request.lora_name]
 
 
 def generate_block_hash_extra_keys(
     request: Request, start_token_idx: int, end_token_idx: int, start_mm_idx: int
 ) -> tuple[tuple[Any, ...] | None, int]:
     """Generate extra keys for the block hash. The extra keys can come from
-    the multi-modal inputs and request specific metadata (e.g., LoRA ID).
+    the multi-modal inputs and request specific metadata (e.g., LoRA name).
 
     Args:
         request: The request object.
@@ -480,7 +480,7 @@ def generate_block_hash_extra_keys(
     mm_extra_keys, new_start_mm_idx = _gen_mm_extra_hash_keys(
         request, start_token_idx, end_token_idx, start_mm_idx
     )
-    lora_extra_keys: list[int] = _gen_lora_extra_hash_keys(request)
+    lora_extra_keys: list[str] = _gen_lora_extra_hash_keys(request)
     cache_salt_keys: list[str] = (
         [request.cache_salt] if (start_token_idx == 0 and request.cache_salt) else []
     )