[Misc][Hybrid allocator + kv connector] Optionally enable hybrid allocator +...

[Misc][Hybrid allocator + kv connector] Optionally enable hybrid allocator + KV cache connector (#29805)
Signed-off-by: NickLucche <nlucches@redhat.com>

vllm/config/scheduler.py

@@ -122,10 +122,12 @@ class SchedulerConfig:
     the default scheduler. Can be a class directly or the path to a class of
     form "mod.custom_class"."""
 
-    disable_hybrid_kv_cache_manager: bool = False
+    disable_hybrid_kv_cache_manager: bool | None = None
     """If set to True, KV cache manager will allocate the same size of KV cache
     for all attention layers even if there are multiple type of attention layers
     like full attention and sliding window attention.
+    If set to None, the default value will be determined based on the environment
+    and starting configuration.
     """
 
     async_scheduling: bool = False

vllm/config/vllm.py

@@ -887,30 +887,21 @@ class VllmConfig:
         if not self.instance_id:
             self.instance_id = random_uuid()[:5]
 
-        if not self.scheduler_config.disable_hybrid_kv_cache_manager:
+        # Hybrid KV cache manager (HMA) runtime rules:
+        # - Explicit enable (--no-disable-kv-cache-manager): error if runtime
+        #   disables it
+        # - No preference: auto-disable for unsupported features (e.g. kv connector)
+        # - Explicit disable (--disable-kv-cache-manager): always respect it
+        need_disable_hybrid_kv_cache_manager = False
         # logger should only print warning message for hybrid models. As we
         # can't know whether the model is hybrid or not now, so we don't log
         # warning message here and will log it later.
         if not current_platform.support_hybrid_kv_cache():
             # Hybrid KV cache manager is not supported on non-GPU platforms.
-                self.scheduler_config.disable_hybrid_kv_cache_manager = True
-            if self.kv_transfer_config is not None:
-                # NOTE(Kuntai): turn HMA off for connector for now.
-                # TODO(Kuntai): have a more elegent solution to check and
-                # turn off HMA for connector that does not support HMA.
-                logger.warning(
-                    "Turning off hybrid kv cache manager because "
-                    "`--kv-transfer-config` is set. This will reduce the "
-                    "performance of vLLM on LLMs with sliding window attention "
-                    "or Mamba attention. If you are a developer of kv connector"
-                    ", please consider supporting hybrid kv cache manager for "
-                    "your connector by making sure your connector is a subclass"
-                    " of `SupportsHMA` defined in kv_connector/v1/base.py."
-                )
-                self.scheduler_config.disable_hybrid_kv_cache_manager = True
+            need_disable_hybrid_kv_cache_manager = True
         if self.kv_events_config is not None:
             # Hybrid KV cache manager is not compatible with KV events.
-                self.scheduler_config.disable_hybrid_kv_cache_manager = True
+            need_disable_hybrid_kv_cache_manager = True
         if (
             self.model_config is not None
             and self.model_config.attention_chunk_size is not None
@@ -921,7 +912,7 @@ class VllmConfig:
             ):
                 # Hybrid KV cache manager is not yet supported with chunked
                 # local attention + eagle.
-                    self.scheduler_config.disable_hybrid_kv_cache_manager = True
+                need_disable_hybrid_kv_cache_manager = True
             elif not envs.VLLM_ALLOW_CHUNKED_LOCAL_ATTN_WITH_HYBRID_KV_CACHE:
                 logger.warning(
                     "There is a latency regression when using chunked local"
@@ -931,7 +922,40 @@ class VllmConfig:
                 )
                 # Hybrid KV cache manager is not yet supported with chunked
                 # local attention.
-                    self.scheduler_config.disable_hybrid_kv_cache_manager = True
+                need_disable_hybrid_kv_cache_manager = True
+
+        if self.scheduler_config.disable_hybrid_kv_cache_manager is None:
+            # Default to disable HMA, but only if the user didn't express a preference.
+            if self.kv_transfer_config is not None:
+                # NOTE(Kuntai): turn HMA off for connector unless specifically enabled.
+                need_disable_hybrid_kv_cache_manager = True
+                logger.warning(
+                    "Turning off hybrid kv cache manager because "
+                    "`--kv-transfer-config` is set. This will reduce the "
+                    "performance of vLLM on LLMs with sliding window attention "
+                    "or Mamba attention. If you are a developer of kv connector"
+                    ", please consider supporting hybrid kv cache manager for "
+                    "your connector by making sure your connector is a subclass"
+                    " of `SupportsHMA` defined in kv_connector/v1/base.py and"
+                    " use --no-disable-hybrid-kv-cache-manager to start vLLM."
+                )
+            self.scheduler_config.disable_hybrid_kv_cache_manager = (
+                need_disable_hybrid_kv_cache_manager
+            )
+        elif (
+            self.scheduler_config.disable_hybrid_kv_cache_manager is False
+            and need_disable_hybrid_kv_cache_manager
+        ):
+            raise ValueError(
+                "Hybrid KV cache manager was explicitly enabled but is not "
+                "supported in this configuration. Consider omitting the "
+                "--no-disable-hybrid-kv-cache-manager flag to let vLLM decide"
+                " automatically."
+            )
+
+        if self.scheduler_config.disable_hybrid_kv_cache_manager is None:
+            # Default to enable HMA if not explicitly disabled by user or logic above.
+            self.scheduler_config.disable_hybrid_kv_cache_manager = False
 
         if self.compilation_config.debug_dump_path:
             self.compilation_config.debug_dump_path = (

vllm/engine/arg_utils.py

@@ -491,7 +491,7 @@ class EngineArgs:
     enable_chunked_prefill: bool | None = None
     disable_chunked_mm_input: bool = SchedulerConfig.disable_chunked_mm_input
 
-    disable_hybrid_kv_cache_manager: bool = (
+    disable_hybrid_kv_cache_manager: bool | None = (
         SchedulerConfig.disable_hybrid_kv_cache_manager
     )