[V1][Spec decode] Move drafter to model runner (#13363)

Signed-off-by: Woosuk Kwon <woosuk.kwon@berkeley.edu>

vllm/v1/engine/core.py

@@ -27,7 +27,6 @@ from vllm.v1.executor.abstract import Executor
 from vllm.v1.outputs import ModelRunnerOutput
 from vllm.v1.request import Request, RequestStatus
 from vllm.v1.serial_utils import MsgpackDecoder, MsgpackEncoder
-from vllm.v1.spec_decode.ngram_proposer import NgramProposer
 from vllm.version import __version__ as VLLM_VERSION
 
 logger = init_logger(__name__)
@@ -86,15 +85,6 @@ class EngineCore:
                         self.batch_queue_size)
             self.batch_queue = queue.Queue(self.batch_queue_size)
 
-        # Setup speculative decode.
-        # TODO: find a better way to check if we are using ngram.
-        self.use_spec_decode = False
-        if self.scheduler.speculative_config:
-            assert self.scheduler.speculative_config.ngram_prompt_lookup_min \
-                    , "Only ngram spec decode is supported in V1."
-            self.proposer = NgramProposer()
-            self.use_spec_decode = True
-
     def _initialize_kv_caches(self,
                               vllm_config: VllmConfig) -> Tuple[int, int]:
         start = time.time()
@@ -158,9 +148,6 @@ class EngineCore:
             return EngineCoreOutputs(
                 outputs=[], scheduler_stats=self.scheduler.make_stats())
 
-        if self.use_spec_decode:
-            self.propose_tokens()
-
         scheduler_output = self.scheduler.schedule()
         output = self.model_executor.execute_model(scheduler_output)
         engine_core_outputs = self.scheduler.update_from_output(
@@ -221,23 +208,6 @@ class EngineCore:
     def profile(self, is_start: bool = True):
         self.model_executor.profile(is_start)
 
-    def propose_tokens(self):
-        assert self.scheduler.speculative_config is not None
-        for req in self.scheduler.running:
-            # Ignore requests that are doing chunked prefill.
-            if req.num_computed_tokens < req.num_tokens - 1:
-                continue
-            # Ignore requests that already have spec tokens.
-            if req.spec_token_ids:
-                continue
-            spec_tokens = self.proposer.propose(
-                req.all_token_ids,
-                self.scheduler.speculative_config.ngram_prompt_lookup_min,
-                self.scheduler.speculative_config.num_speculative_tokens,
-            )
-            if spec_tokens:
-                req.append_spec_token_ids(spec_tokens)
-
     def reset_prefix_cache(self):
         self.scheduler.reset_prefix_cache()