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

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

Author: WoosukKwon

tests/v1/core/test_scheduler.py

@@ -203,6 +203,7 @@ def test_schedule_partial_requests():
         req_ids=[request.request_id for request in requests],
         req_id_to_index=req_to_index,
         sampled_token_ids=[[0] for _ in range(len(requests))],
+        spec_token_ids=None,
         logprobs=None,
         prompt_logprobs_dict={},
     )
@@ -259,6 +260,7 @@ def test_stop_via_update_from_output():
         sampled_token_ids=[[EOS_TOKEN_ID],
                            [10,
                             11]],  # First request hits EOS, second continues
+        spec_token_ids=None,
         logprobs=None,
         prompt_logprobs_dict={})
 
@@ -307,6 +309,7 @@ def test_stop_via_update_from_output():
         },
         sampled_token_ids=[[10, 42, 12],
                            [13, 14]],  # First request hits stop token
+        spec_token_ids=None,
         logprobs=None,
         prompt_logprobs_dict={})
 
@@ -354,6 +357,7 @@ def test_stop_via_update_from_output():
         },
         sampled_token_ids=[[10, 11, 12],
                            [13]],  # First request exceeds max_tokens
+        spec_token_ids=None,
         logprobs=None,
         prompt_logprobs_dict={})
 
@@ -394,6 +398,7 @@ def test_stop_via_update_from_output():
         req_ids=[requests[0].request_id],
         req_id_to_index={requests[0].request_id: 0},
         sampled_token_ids=[[EOS_TOKEN_ID, 10, 11]],
+        spec_token_ids=None,
         logprobs=None,
         prompt_logprobs_dict={})
 
@@ -434,6 +439,7 @@ def test_schedule_concurrent_batches():
         req_ids=[requests[0].request_id],
         req_id_to_index={requests[0].request_id: 0},
         sampled_token_ids=[[0]],
+        spec_token_ids=None,
         logprobs=None,
         prompt_logprobs_dict={},
     )
@@ -450,6 +456,7 @@ def test_schedule_concurrent_batches():
         req_ids=[requests[1].request_id],
         req_id_to_index={requests[1].request_id: 0},
         sampled_token_ids=[[0]],
+        spec_token_ids=None,
         logprobs=None,
         prompt_logprobs_dict={},
     )

vllm/v1/core/scheduler.py

@@ -474,6 +474,7 @@ def update_from_output(
         model_runner_output: "ModelRunnerOutput",
     ) -> EngineCoreOutputs:
         sampled_token_ids = model_runner_output.sampled_token_ids
+        spec_token_ids = model_runner_output.spec_token_ids
         logprobs = model_runner_output.logprobs
         prompt_logprobs_dict = model_runner_output.prompt_logprobs_dict
         num_scheduled_tokens = scheduler_output.num_scheduled_tokens
@@ -530,13 +531,9 @@ def update_from_output(
                         self.encoder_cache_manager.free_encoder_input(
                             request, input_id)
 
-            if request.num_computed_tokens >= request.num_tokens:
-                # Clear the spec tokens as the request has generated
-                # a new token. Here, We assume all spec tokens are verified
-                # if we perform speculative decoding for this request.
-                # Therefore, we can clear all spec tokens after
-                # the generation step.
-                request.clear_spec_tokens()
+            # Add newly generated spec token ids to the request.
+            if spec_token_ids is not None:
+                request.spec_token_ids = spec_token_ids[req_index]
 
             # Get prompt logprobs for this request.
             prompt_logprobs_tensors = prompt_logprobs_dict.get(req_id)

vllm/v1/engine/core.py

@@ -27,7 +27,6 @@
 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 @@ def __init__(
                         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 @@ def step(self) -> EngineCoreOutputs:
             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 @@ def shutdown(self):
     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()
 

vllm/v1/outputs.py

@@ -67,6 +67,9 @@ class ModelRunnerOutput:
     # each request due to speculative/jump decoding.
     sampled_token_ids: List[List[int]]
 
+    # num_reqs x num_spec_tokens
+    spec_token_ids: Optional[List[List[int]]]
+
     # [num_reqs, max_num_logprobs + 1]
     # [num_reqs, max_num_logprobs + 1]
     # [num_reqs]

vllm/v1/request.py

@@ -104,18 +104,6 @@ def append_output_token_ids(
         self._output_token_ids.extend(token_ids)
         self._all_token_ids.extend(token_ids)
 
-    def append_spec_token_ids(
-        self,
-        token_ids: Union[int, List[int]],
-    ) -> None:
-        if isinstance(token_ids, int):
-            self.spec_token_ids.append(token_ids)
-        else:
-            self.spec_token_ids.extend(token_ids)
-
-    def clear_spec_tokens(self) -> None:
-        self.spec_token_ids.clear()
-
     @property
     def num_tokens(self) -> int:
         return len(self._all_token_ids)

vllm/v1/spec_decode/ngram_proposer.py

@@ -1,16 +1,20 @@
 # SPDX-License-Identifier: Apache-2.0
 from typing import List, Optional
 
-from vllm.v1.utils import ConstantList
+import numpy as np
 
 
 class NgramProposer:
 
     def __init__(self):
         pass
 
-    def propose(self, context_token_ids: ConstantList[int], n: int,
-                k: int) -> Optional[List[int]]:
+    def propose(
+        self,
+        context_token_ids: np.ndarray,
+        n: int,
+        k: int,
+    ) -> Optional[np.ndarray]:
         """Proposes the next sequence of tokens based on n-gram pattern 
         matching in the context. The function finds matches of the last n 
         tokens in the previous context, and returns k tokens that followed 
@@ -25,8 +29,8 @@ def propose(self, context_token_ids: ConstantList[int], n: int,
                the maximum amount of tokens until the end.
         
         Returns:
-            List[int]: The sequence of tokens that followed 
-                       the matched n-gram in the context.
+            np.ndarray: The sequence of tokens that followed 
+                        the matched n-gram in the context.
             None: If no matching n-gram pattern is found.
         
         Example:
@@ -66,9 +70,12 @@ def _kmp_lps_array(pattern: List[int]) -> List[int]:
         return lps
 
     @staticmethod
-    def _find_subarray_kmp(context_token_ids: ConstantList[int], n: int,
-                           k: int) -> Optional[List[int]]:
-        context_len = len(context_token_ids)
+    def _find_subarray_kmp(
+        context_token_ids: np.ndarray,
+        n: int,
+        k: int,
+    ) -> Optional[np.ndarray]:
+        context_len = context_token_ids.shape[0]
         assert n > 0
 
         pattern = context_token_ids[-n:]

vllm/v1/worker/gpu_input_batch.py

@@ -78,6 +78,7 @@ def __init__(
         )
         self.token_ids_cpu = self.token_ids_cpu_tensor.numpy()
         self.num_tokens = np.zeros(max_num_reqs, dtype=np.int32)
+        self.num_tokens_no_spec = np.zeros(max_num_reqs, dtype=np.int32)
         self.num_prompt_tokens = np.zeros(max_num_reqs, dtype=np.int32)
         self.num_computed_tokens_cpu = np.empty(max_num_reqs, dtype=np.int32)
 
@@ -217,7 +218,11 @@ def add_request(
         end_idx = start_idx + len(request.output_token_ids)
         self.token_ids_cpu[req_index,
                            start_idx:end_idx] = request.output_token_ids
+        # Number of token ids in token_ids_cpu.
+        # NOTE(woosuk): This may include spec decode tokens.
         self.num_tokens[req_index] = request.num_tokens
+        # Number of tokens without spec decode tokens.
+        self.num_tokens_no_spec[req_index] = request.num_tokens
 
         self.num_computed_tokens_cpu[req_index] = request.num_computed_tokens
         self.block_table.add_row(req_index, request.block_ids)
@@ -356,6 +361,8 @@ def condense(self, empty_req_indices: List[int]) -> None:
             self.token_ids_cpu[empty_index, :num_tokens] = self.token_ids_cpu[
                 last_req_index, :num_tokens]
             self.num_tokens[empty_index] = num_tokens
+            self.num_tokens_no_spec[empty_index] = self.num_tokens_no_spec[
+                last_req_index]
             self.num_prompt_tokens[empty_index] = self.num_prompt_tokens[
                 last_req_index]
             self.num_computed_tokens_cpu[

vllm/v1/worker/gpu_model_runner.py

@@ -33,6 +33,7 @@
 from vllm.v1.outputs import LogprobsTensors, ModelRunnerOutput
 from vllm.v1.sample.metadata import SamplingMetadata
 from vllm.v1.sample.rejection_sampler import INVALID_TOKEN_ID
+from vllm.v1.spec_decode.ngram_proposer import NgramProposer
 from vllm.v1.utils import bind_kv_cache
 from vllm.v1.worker.gpu_input_batch import CachedRequestState, InputBatch
 from vllm.v1.worker.lora_model_runner_mixin import LoRAModelRunnerMixin
@@ -117,6 +118,15 @@ def __init__(
         # req_id -> (input_id -> encoder_output)
         self.encoder_cache: Dict[str, Dict[int, torch.Tensor]] = {}
 
+        # Set up speculative decoding.
+        self.use_spec_decode = False
+        if self.speculative_config:
+            # TODO: find a better way to check if we are using ngram.
+            assert self.speculative_config.ngram_prompt_lookup_min, \
+                    "Currently, only ngram spec decode is supported in V1."
+            self.drafter = NgramProposer()
+            self.use_spec_decode = True
+
         # Request states.
         self.requests: Dict[str, CachedRequestState] = {}
         # Persistent batch.
@@ -367,6 +377,7 @@ def _update_states(self, scheduler_output: "SchedulerOutput") -> bool:
             self.input_batch.token_ids_cpu[
                 req_index,
                 start_token_index:end_token_index] = req_data.new_token_ids
+            self.input_batch.num_tokens_no_spec[req_index] = end_token_index
             # Add spec_token_ids to token_ids_cpu.
             spec_token_ids = scheduler_output.scheduled_spec_decode_tokens.get(
                 req_id, [])
@@ -1009,15 +1020,51 @@ def execute_model(
                 for seq in sampled_token_ids[valid_mask].split(gen_lens)
             ]
 
+        if not self.use_spec_decode:
+            spec_token_ids = None
+        else:
+            spec_token_ids = self.generate_draft_token_ids(
+                valid_sampled_token_ids)
+
         model_runner_output = ModelRunnerOutput(
             req_ids=req_ids,
             req_id_to_index=self.input_batch.req_id_to_index,
             sampled_token_ids=valid_sampled_token_ids,
+            spec_token_ids=spec_token_ids,
             logprobs=logprobs_lists,
             prompt_logprobs_dict=prompt_logprobs_dict,
         )
         return model_runner_output
 
+    def generate_draft_token_ids(
+        self,
+        sampled_token_ids: List[List[int]],
+    ) -> List[List[int]]:
+        # TODO(woosuk): Optimize.
+        num_reqs = len(sampled_token_ids)
+        draft_token_ids: List[List[int]] = []
+        for i in range(num_reqs):
+            if len(sampled_token_ids[i]) == 0:
+                # Skip speculative decoding.
+                draft_token_ids.append([])
+                continue
+
+            # Add sampled_token_ids to token_ids_cpu.
+            start_idx = self.input_batch.num_tokens_no_spec[i]
+            end_idx = start_idx + len(sampled_token_ids[i])
+            self.input_batch.token_ids_cpu[
+                i, start_idx:end_idx] = sampled_token_ids[i]
+            drafter_output = self.drafter.propose(
+                self.input_batch.token_ids_cpu[i, :end_idx],
+                self.speculative_config.ngram_prompt_lookup_min,
+                self.speculative_config.num_speculative_tokens,
+            )
+            if drafter_output is None or len(drafter_output) == 0:
+                draft_token_ids.append([])
+            else:
+                draft_token_ids.append(drafter_output.tolist())
+        return draft_token_ids
+
     def load_model(self) -> None:
         logger.info("Starting to load model %s...", self.model_config.model)
         with DeviceMemoryProfiler() as m:  # noqa: SIM117

vllm/v1/worker/tpu_model_runner.py

@@ -718,6 +718,7 @@ def execute_model(
             req_ids=all_req_ids,
             req_id_to_index=self.input_batch.req_id_to_index,
             sampled_token_ids=[[token_id] for token_id in sampled_token_ids],
+            spec_token_ids=None,
             logprobs=None,
             prompt_logprobs_dict=prompt_logprobs_dict,  # type: ignore[arg-type]
         )