[Core] Async Scheduling X Spec Decoding Compatibility (#24799)

Signed-off-by: Ronald1995 <ronaldautomobile@163.com>
Signed-off-by: Nick Hill <nhill@redhat.com>
Signed-off-by: Benjamin Chislett <chislett.ben@gmail.com>
Co-authored-by: Nick Hill <nhill@redhat.com>
Co-authored-by: Benjamin Chislett <chislett.ben@gmail.com>

tests/v1/e2e/test_async_scheduling.py

@@ -15,7 +15,7 @@ from ...conftest import VllmRunner
 from ...models.utils import check_outputs_equal
 
 MODEL = "Qwen/Qwen3-0.6B"
-MTP_MODEL = "XiaomiMiMo/MiMo-7B-Base"
+MTP_MODEL = "meta-llama/Llama-3.2-1B-Instruct"
 
 
 first_prompt = (
@@ -29,7 +29,8 @@ example_prompts = [first_prompt, "In one word, the capital of France is "] + [
 
 default_params = dict(
     temperature=0.0,  # greedy
-    max_tokens=20,
+    max_tokens=23,
+    min_tokens=18,
 )
 
 
@@ -69,15 +70,9 @@ def test_without_spec_decoding(
         (True, "uni", True, None, True),
     ]
 
-    run_tests(
-        monkeypatch,
-        MODEL,
-        test_configs,
-        test_sampling_params,
-    )
+    run_tests(monkeypatch, MODEL, test_configs, test_sampling_params)
 
 
-@pytest.mark.skip("MTP model too big to run in fp32 in CI")
 def test_with_spec_decoding(monkeypatch: pytest.MonkeyPatch):
     """Test consistency and acceptance rates with some different combos of
     preemption, executor, async scheduling, prefill chunking,
@@ -85,8 +80,9 @@ def test_with_spec_decoding(monkeypatch: pytest.MonkeyPatch):
     """
 
     spec_config = {
-        "method": "mtp",
+        "method": "eagle3",
         "num_speculative_tokens": 2,
+        "model": "nm-testing/Llama3_2_1B_speculator.eagle3",
     }
     spec_config_short = spec_config | {"max_model_len": 50}
 
@@ -106,12 +102,7 @@ def test_with_spec_decoding(monkeypatch: pytest.MonkeyPatch):
         (True, "uni", True, spec_config_short, True),
     ]
 
-    run_tests(
-        monkeypatch,
-        MTP_MODEL,
-        test_configs,
-        [{}],
-    )
+    run_tests(monkeypatch, MTP_MODEL, test_configs, [{}])
 
 
 @dynamo_config.patch(cache_size_limit=16)
@@ -182,15 +173,13 @@ def run_tests(
                     and test_acceptance_rate is not None
                 ):
                     if "spec_mml=None" in test_config:
-                        # because the acceptance rate can vary, we use a looser
-                        # tolerance here.
                         assert (
                             pytest.approx(test_acceptance_rate, rel=5e-2)
                             == base_acceptance_rate
                         )
                     else:
                         # Currently the reported acceptance rate is expected to be
-                        # lower when we skip drafting altogether.
+                        # lower when we sometimes skip drafting altogether.
                         assert test_acceptance_rate > 0.05
                 print(
                     f"PASSED: config=[{test_config}], params={params}"
@@ -220,6 +209,7 @@ def run_test(
 ):
     spec_decoding = spec_config is not None
     cache_arg: dict[str, Any] = (
+        # Force preemptions
         dict(num_gpu_blocks_override=32)
         if test_preemption
         else dict(gpu_memory_utilization=0.9)
@@ -238,6 +228,7 @@ def run_test(
         model,
         max_model_len=512,
         enable_chunked_prefill=test_prefill_chunking,
+        # Force prefill chunking
         max_num_batched_tokens=48 if test_prefill_chunking else None,
         # enforce_eager=True,
         async_scheduling=async_scheduling,
@@ -255,10 +246,7 @@ def run_test(
             results.append(
                 vllm_model.generate(
                     example_prompts,
-                    sampling_params=SamplingParams(
-                        **default_params,
-                        **override_params,
-                    ),
+                    sampling_params=SamplingParams(**default_params, **override_params),
                     return_logprobs=True,
                 )
             )
@@ -270,9 +258,7 @@ def run_test(
 
             if test_preemption:
                 preemptions = _get_count(
-                    metrics_before,
-                    metrics_after,
-                    "vllm:num_preemptions",
+                    metrics_before, metrics_after, "vllm:num_preemptions"
                 )
                 assert preemptions > 0, "preemption test had no preemptions"
 

vllm/config/speculative.py

@@ -3,7 +3,7 @@
 
 import ast
 import hashlib
-from typing import TYPE_CHECKING, Any, Literal
+from typing import TYPE_CHECKING, Any, Literal, get_args
 
 from pydantic import Field, SkipValidation, model_validator
 from pydantic.dataclasses import dataclass
@@ -29,31 +29,25 @@ else:
 
 logger = init_logger(__name__)
 
-SpeculativeMethod = Literal[
-    "ngram",
-    "eagle",
-    "eagle3",
-    "medusa",
-    "mlp_speculator",
-    "draft_model",
-    "deepseek_mtp",
-    "ernie_mtp",
-    "qwen3_next_mtp",
-    "mimo_mtp",
-    "longcat_flash_mtp",
-    "pangu_ultra_moe_mtp",
-    "mtp",
-    "suffix",
-]
-MTP_MODEL_TYPES = (
+MTPModelTypes = Literal[
     "deepseek_mtp",
     "mimo_mtp",
     "glm4_moe_mtp",
     "ernie_mtp",
     "qwen3_next_mtp",
     "longcat_flash_mtp",
+    "mtp",
     "pangu_ultra_moe_mtp",
-)
+]
+EagleModelTypes = Literal["eagle", "eagle3", MTPModelTypes]
+SpeculativeMethod = Literal[
+    "ngram",
+    "medusa",
+    "mlp_speculator",
+    "draft_model",
+    "suffix",
+    EagleModelTypes,
+]
 
 
 @config
@@ -244,7 +238,7 @@ class SpeculativeConfig:
         # can not be detected, it will be considered as the "draft_model" by
         # default.
 
-        if self.method in MTP_MODEL_TYPES:
+        if self.method in get_args(MTPModelTypes) and self.method != "mtp":
             logger.warning(
                 "method `%s` is deprecated and replaced with mtp.", self.method
             )
@@ -361,7 +355,9 @@ class SpeculativeConfig:
                     self.method = "medusa"
                 elif self.draft_model_config.hf_config.model_type == "mlp_speculator":
                     self.method = "mlp_speculator"
-                elif self.draft_model_config.hf_config.model_type in MTP_MODEL_TYPES:
+                elif self.draft_model_config.hf_config.model_type in get_args(
+                    MTPModelTypes
+                ):
                     self.method = "mtp"
                     if self.num_speculative_tokens > 1:
                         logger.warning(

vllm/config/vllm.py

@@ -14,13 +14,14 @@ from dataclasses import replace
 from datetime import datetime
 from functools import lru_cache
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, TypeVar
+from typing import TYPE_CHECKING, Any, TypeVar, get_args
 
 import torch
 from pydantic import ConfigDict, Field, model_validator
 from pydantic.dataclasses import dataclass
 
 import vllm.envs as envs
+from vllm.config.speculative import EagleModelTypes
 from vllm.logger import enable_trace_function_call, init_logger
 from vllm.transformers_utils.runai_utils import is_runai_obj_uri
 from vllm.utils import random_uuid
@@ -374,10 +375,22 @@ class VllmConfig:
                     "Async scheduling is not yet compatible with "
                     "pipeline_parallel_size > 1."
                 )
+            # Currently, async scheduling only support eagle speculative
+            # decoding.
             if self.speculative_config is not None:
-                raise ValueError(
-                    "Async scheduling is not yet compatible with speculative decoding."
-                )
+                if self.speculative_config.method not in get_args(EagleModelTypes):
+                    raise ValueError(
+                        "Currently, async scheduling is only supported "
+                        "with EAGLE/MTP kind of speculative decoding"
+                    )
+                if self.speculative_config.disable_padded_drafter_batch:
+                    raise ValueError(
+                        "async scheduling for EAGLE/MTP kind of speculative "
+                        "decoding is enabled, but disable_padded_drafter_batch=True "
+                        "disable_padded_drafter_batch=True is not supported for "
+                        "this situation now. please set "
+                        "disable_padded_drafter_batch=Fasle"
+                    )
             if not executor_supports_async_sched:
                 raise ValueError(
                     "Currently, async scheduling only supports `mp`, `uni`, or "

vllm/v1/core/sched/async_scheduler.py

@@ -16,18 +16,25 @@ class AsyncScheduler(Scheduler):
     ) -> None:
         super()._update_after_schedule(scheduler_output)
         pending_structured_output_tokens = False
+        spec_decode_tokens = scheduler_output.scheduled_spec_decode_tokens
         for req_id in scheduler_output.num_scheduled_tokens:
             request = self.requests[req_id]
             pending_structured_output_tokens |= (
                 request.use_structured_output and request.num_output_placeholders > 0
             )
+            cur_num_spec_tokens = len(spec_decode_tokens.get(req_id, ()))
             if (
                 request.num_computed_tokens
-                == request.num_tokens + request.num_output_placeholders
+                == request.num_tokens
+                + request.num_output_placeholders
+                + cur_num_spec_tokens
             ):
-                # The request will generate a new token in this scheduling step.
-                # TODO(woosuk): Support speculative decoding.
-                request.num_output_placeholders += 1
+                # The request will generate a new token plus num_spec_tokens
+                # in this scheduling step.
+                request.num_output_placeholders += 1 + cur_num_spec_tokens
+                # Add placeholders for the new tokens in spec_token_ids.
+                # Wwe will update the actual spec token ids in the worker process.
+                request.spec_token_ids = [-1] * self.num_spec_tokens
 
         scheduler_output.pending_structured_output_tokens = (
             pending_structured_output_tokens

vllm/v1/core/sched/scheduler.py

@@ -348,7 +348,10 @@ class Scheduler(SchedulerInterface):
             # Speculative decode related.
             if request.spec_token_ids:
                 num_scheduled_spec_tokens = (
-                    num_new_tokens + request.num_computed_tokens - request.num_tokens
+                    num_new_tokens
+                    + request.num_computed_tokens
+                    - request.num_tokens
+                    - request.num_output_placeholders
                 )
                 if num_scheduled_spec_tokens > 0:
                     # Trim spec_token_ids list to num_scheduled_spec_tokens.
@@ -1024,7 +1027,12 @@ class Scheduler(SchedulerInterface):
                 # tokens and rejections. If some tokens are rejected,
                 # num_computed_tokens is decreased by the number of rejected
                 # tokens.
-                request.num_computed_tokens -= num_rejected
+                if request.num_computed_tokens > 0:
+                    request.num_computed_tokens -= num_rejected
+                # If async scheduling, num_output_placeholders also includes
+                # the scheduled spec tokens count and so is similarly adjusted.
+                if request.num_output_placeholders > 0:
+                    request.num_output_placeholders -= num_rejected
                 spec_decoding_stats = self.make_spec_decoding_stats(
                     spec_decoding_stats,
                     num_draft_tokens=num_draft_tokens,

vllm/v1/engine/core.py

@@ -198,6 +198,7 @@ class EngineCore:
         self.step_fn = (
             self.step if self.batch_queue is None else self.step_with_batch_queue
         )
+        self.async_scheduling = vllm_config.scheduler_config.async_scheduling
 
         # Mark the startup heap as static so that it's ignored by GC.
         # Reduces pause times of oldest generation collections.
@@ -341,7 +342,10 @@ class EngineCore:
         return engine_core_outputs, scheduler_output.total_num_scheduled_tokens > 0
 
     def post_step(self, model_executed: bool) -> None:
-        if self.use_spec_decode and model_executed:
+        # When using async scheduling we can't get draft token ids in advance,
+        # so we update draft token ids in the worker process and don't
+        # need to update draft token ids here.
+        if not self.async_scheduling and self.use_spec_decode and model_executed:
             # Take the draft token ids.
             draft_token_ids = self.model_executor.take_draft_token_ids()
             if draft_token_ids is not None:

vllm/v1/engine/processor.py

@@ -150,6 +150,23 @@ class Processor:
             raise ValueError(
                 "vLLM V1 does not support per request user provided logits processors."
             )
+        # Async scheduling + spec decode currently incompatible with some
+        # sampling parameters.
+        if (
+            self.vllm_config.speculative_config is not None
+            and self.vllm_config.scheduler_config.async_scheduling
+            and (
+                params.frequency_penalty != 0.0
+                or params.presence_penalty != 0.0
+                or params.repetition_penalty != 1.0
+                or params.bad_words_token_ids
+                or params.structured_outputs
+            )
+        ):
+            raise ValueError(
+                "async scheduling with spec decoding doesn't yet support "
+                "penalties, bad words or structured outputs in sampling parameters."
+            )
 
     def _validate_params(
         self,

vllm/v1/sample/logits_processor/__init__.py

@@ -41,7 +41,7 @@ STR_POOLING_REJECTS_LOGITSPROCS = (
 # Error message when the user tries to initialize vLLM with a speculative
 # decoding enabled and custom logitsproces
 STR_SPEC_DEC_REJECTS_LOGITSPROCS = (
-    "Custom logits processors are not supportedwhen speculative decoding is enabled."
+    "Custom logits processors are not supported when speculative decoding is enabled."
 )
 
 LOGITSPROCS_GROUP = "vllm.logits_processors"

vllm/v1/spec_decode/eagle.py

@@ -397,10 +397,13 @@ class EagleProposer:
                 positions += 1
                 exceeds_max_model_len = positions >= self.max_model_len
                 clamped_positions = torch.where(exceeds_max_model_len, 0, positions)
-
+            # For data integrity when async scheduling, we shouldn't use in place
+            # operations in case they are modified in next step's `prepare_input`
+            # of main model.
             # Increment the sequence lengths.
             common_attn_metadata.seq_lens += 1
-            common_attn_metadata.seq_lens_cpu += 1
+            # This is an out-of-place operation to avoid modifying the original tensor.
+            common_attn_metadata.seq_lens_cpu = common_attn_metadata.seq_lens_cpu + 1
             # For the requests that exceed the max model length, we set the
             # sequence length to 1 to minimize their overheads in attention.
 

vllm/v1/worker/gpu_input_batch.py

@@ -46,6 +46,9 @@ class CachedRequestState:
     lora_request: LoRARequest | None = None
     prompt_embeds: torch.Tensor | None = None
 
+    # Used when both async_scheduling and spec_decode are enabled.
+    prev_num_draft_len: int = 0
+
     def __post_init__(self):
         self.num_prompt_tokens = length_from_prompt_token_ids_or_embeds(
             self.prompt_token_ids, self.prompt_embeds