[Misc] [Core] Implement RFC "Augment BaseExecutor interfaces to enable hardware-agnostic speculative decoding" (#3837)

vllm/worker/worker_base.py

@@ -0,0 +1,83 @@
+from abc import ABC, abstractmethod
+from typing import Dict, List
+
+from vllm.lora.request import LoRARequest
+from vllm.sequence import SamplerOutput, SequenceGroupMetadata
+
+
+class WorkerBase(ABC):
+    """Worker interface that allows vLLM to cleanly separate implementations for
+    different hardware.
+    """
+
+    @abstractmethod
+    def init_device(self) -> None:
+        """Initialize device state, such as loading the model or other on-device
+        memory allocations.
+        """
+        raise NotImplementedError
+
+    @abstractmethod
+    def determine_num_available_blocks(self) -> tuple[int, int]:
+        """Determine the number of available blocks for the GPU KV cache and
+        swappable CPU KV cache.
+
+        The implementation may run profiling or other heuristics to determine
+        the size of caches.
+
+        Returns a tuple[num_gpu_blocks, num_cpu_blocks], where num_gpu_blocks
+        are blocks that are "active" on the device and can be appended to.
+        num_cpu_blocks refers to "swapped" blocks in CPU memory and cannot be
+        appended to.
+        """
+        raise NotImplementedError
+
+    @abstractmethod
+    def initialize_cache(self, num_gpu_blocks: int,
+                         num_cpu_blocks: int) -> None:
+        """Initialize the KV cache with the given size in blocks.
+        """
+        raise NotImplementedError
+
+    @abstractmethod
+    def execute_model(self,
+                      seq_group_metadata_list: List[SequenceGroupMetadata],
+                      blocks_to_swap_in: Dict[int, int],
+                      blocks_to_swap_out: Dict[int, int],
+                      blocks_to_copy: Dict[int, List[int]]) -> SamplerOutput:
+        """Executes one model step on the given sequences."""
+        raise NotImplementedError
+
+    @abstractmethod
+    def get_cache_block_size_bytes() -> int:
+        """Return the size of a single cache block, in bytes. Used in
+        speculative decoding.
+        """
+        raise NotImplementedError
+
+    @abstractmethod
+    def add_lora(self, lora_request: LoRARequest) -> bool:
+        raise NotImplementedError
+
+    @abstractmethod
+    def remove_lora(self, lora_id: int) -> bool:
+        raise NotImplementedError
+
+    @abstractmethod
+    def list_loras(self) -> List[int]:
+        raise NotImplementedError
+
+
+class LoraNotSupportedWorkerBase(WorkerBase):
+    """Partial implementation of WorkerBase that raises exceptions when LoRA
+    methods are invoked.
+    """
+
+    def add_lora(self, lora_request: LoRARequest) -> bool:
+        raise ValueError(f"{type(self)} does not support LoRA")
+
+    def remove_lora(self, lora_id: int) -> bool:
+        raise ValueError(f"{type(self)} does not support LoRA")
+
+    def list_loras(self) -> List[int]:
+        raise ValueError(f"{type(self)} does not support LoRA")