[Spec] Route seq_lens through FutureMap; drop verify_done.wait (#25879)

python/sglang/srt/disaggregation/decode_schedule_batch_mixin.py

@@ -180,9 +180,8 @@ class ScheduleBatchDisaggregationDecodeMixin:
                 from sglang.srt.managers.overlap_utils import FutureIndices
 
                 spec_info.future_indices = FutureIndices(indices=self.req_pool_indices)
-                future_map.store_to_map_for_new_batch(
+                future_map.publish(spec_info.future_indices, spec_info.new_seq_lens)
-                    spec_info.future_indices, spec_info
+                future_map.stash(spec_info.future_indices, spec_info)
-                )
             self.spec_info = spec_info
         else:
             # Non-spec: input_ids feeds the next decode forward directly.

python/sglang/srt/managers/overlap_utils.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Optional
 
 import torch
 
@@ -10,7 +10,6 @@ from sglang.srt.utils import is_cuda, is_hip
 
 if TYPE_CHECKING:
     from sglang.srt.managers.schedule_batch import ScheduleBatch
-    from sglang.srt.managers.scheduler import GenerationBatchResult
     from sglang.srt.mem_cache.memory_pool import ReqToTokenPool
     from sglang.srt.speculative.eagle_info import EagleDraftInput
     from sglang.srt.speculative.spec_info import SpeculativeAlgorithm
@@ -57,21 +56,25 @@ class FutureMap:
         self.req_pool_size = req_to_token_pool.req_to_token.shape[0]
 
         if self.spec_algo.is_none():
-            self.buf_initialized = True
             self.token_ids_buf = torch.empty(
                 (self.req_pool_size,), dtype=torch.int64, device=self.device
             )
         else:
-            self.buf_initialized = False
+            # Schedule-consumed buf, eager fixed dtype.
+            self.new_seq_lens_buf = torch.empty(
+                (self.req_pool_size,), dtype=torch.int64, device=self.device
+            )
+            # Forward-only bufs are lazy (worker-dependent shape).
+            self._forward_buf_initialized = False
 
-    def _lazy_init_buf(self, draft_input: EagleDraftInput):
+        # Fences the schedule-consumed buf fields.
-        self.buf_initialized = True
+        self.publish_ready: Optional[torch.cuda.Event] = None
+
+    def _lazy_init_forward_buf(self, draft_input: EagleDraftInput):
+        self._forward_buf_initialized = True
 
         topk_p0 = draft_input.topk_p[0]
         topk_index0 = draft_input.topk_index[0]
-        bonus_token0 = draft_input.bonus_tokens[0]
-        new_seq_lens0 = draft_input.new_seq_lens[0]
-
         self.topk_p_buf = torch.empty(
             (self.req_pool_size, *topk_p0.shape),
             dtype=topk_p0.dtype,
@@ -83,16 +86,8 @@ class FutureMap:
             device=self.device,
         )
         self.bonus_tokens_buf = torch.empty(
-            (self.req_pool_size, *bonus_token0.shape),
+            (self.req_pool_size,), dtype=torch.int64, device=self.device
-            dtype=bonus_token0.dtype,
-            device=self.device,
         )
-        self.new_seq_lens_buf = torch.empty(
-            (self.req_pool_size, *new_seq_lens0.shape),
-            dtype=new_seq_lens0.dtype,
-            device=self.device,
-        )
-
         if spec_need_hidden_states():
             hidden_states0 = draft_input.hidden_states[0]
             self.hidden_states_buf = torch.empty(
@@ -118,51 +113,54 @@ class FutureMap:
             draft_input.topk_index = self.topk_index_buf[indices]
             draft_input.bonus_tokens = self.bonus_tokens_buf[indices]
             draft_input.new_seq_lens = self.new_seq_lens_buf[indices]
+            # Resolve seq_lens placeholder (-indices) to the post-verify view.
+            batch.seq_lens = draft_input.new_seq_lens
             if spec_need_hidden_states():
                 draft_input.hidden_states = self.hidden_states_buf[indices]
 
-    def store_to_map(
+    def resolve_seq_lens_cpu(self, batch: ScheduleBatch) -> None:
-        self, future_indices: FutureIndices, batch_result: GenerationBatchResult
+        fi = batch.spec_info.future_indices if batch.spec_info is not None else None
-    ):
+        if fi is None:
-        if self.spec_algo.is_none():
+            return
-            indices = future_indices.indices
+        if self.publish_ready is not None:
-            if indices.shape[0] == 0:
+            self.publish_ready.wait()
-                # DP attention idle rank: indices is empty but next_token_ids
+        batch.seq_lens_cpu = self.new_seq_lens_buf[fi.indices].cpu()
-                # may carry padded values from sibling ranks. Nothing to store
+        batch.seq_lens_sum = int(batch.seq_lens_cpu.sum())
-                # for this rank.
-                return
-            # next_token_ids is int32; buf is int64. Slice assignment used to
-            # cast implicitly, but advanced indexing requires an explicit match.
-            self.token_ids_buf[indices] = batch_result.next_token_ids.to(torch.int64)
-        else:
-            draft_input: EagleDraftInput = batch_result.next_draft_input
-            self.store_to_map_for_new_batch(future_indices, draft_input)
 
-    def store_to_map_for_new_batch(
+    def publish(
-        self, future_indices: FutureIndices, draft_input: EagleDraftInput
+        self, future_indices: FutureIndices, new_seq_lens: torch.Tensor
-    ):
+    ) -> None:
+        """Store schedule-consumed fields and signal publish_ready."""
+        if self.spec_algo.is_none():
+            return
         indices = future_indices.indices
         if indices.shape[0] == 0:
-            # DP idle rank: draft_input fields are empty stubs without a usable
+            return  # DP idle
-            # shape, so _lazy_init_buf's shape peek (draft_input.topk_p[0])
+        self.new_seq_lens_buf[indices] = new_seq_lens.to(self.new_seq_lens_buf.dtype)
-            # would IndexError. Defer init until a real batch arrives.
+        if self.publish_ready is None:
+            self.publish_ready = torch.get_device_module(self.device).Event()
+        self.publish_ready.record()
+
+    def stash(self, future_indices: FutureIndices, payload) -> None:
+        """Store forward-only fields for the next forward batch to pick up."""
+        indices = future_indices.indices
+        if indices.shape[0] == 0:
+            return  # DP idle
+        if self.spec_algo.is_none():
+            # next_token_ids is int32; buf is int64. Advanced indexing requires
+            # an explicit cast.
+            self.token_ids_buf[indices] = payload.to(torch.int64)
             return
 
-        if not self.buf_initialized:
+        draft_input: EagleDraftInput = payload
-            self._lazy_init_buf(draft_input)
+        if not self._forward_buf_initialized:
-
+            self._lazy_init_forward_buf(draft_input)
-        # Slice assignment used to coerce src dtype to buf dtype implicitly;
-        # advanced index requires an explicit cast. bonus_tokens / new_seq_lens
-        # in particular differ across disagg (int64) and forward (int32) paths.
-        self.topk_p_buf[indices] = draft_input.topk_p.to(self.topk_p_buf.dtype)
-        self.topk_index_buf[indices] = draft_input.topk_index.to(
-            self.topk_index_buf.dtype
-        )
         self.bonus_tokens_buf[indices] = draft_input.bonus_tokens.to(
             self.bonus_tokens_buf.dtype
         )
-        self.new_seq_lens_buf[indices] = draft_input.new_seq_lens.to(
+        self.topk_p_buf[indices] = draft_input.topk_p.to(self.topk_p_buf.dtype)
-            self.new_seq_lens_buf.dtype
+        self.topk_index_buf[indices] = draft_input.topk_index.to(
+            self.topk_index_buf.dtype
         )
         if spec_need_hidden_states():
             self.hidden_states_buf[indices] = draft_input.hidden_states.to(

python/sglang/srt/managers/schedule_batch.py

@@ -2420,8 +2420,7 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
             self.seq_lens.add_(1)
             self.seq_lens_cpu.add_(1)
             self.orig_seq_lens.add_(1)
-        # Defer compute to refresh_seq_lens_cpu (either pre-forward in scheduler.py
+        # Sum is recomputed lazily by ForwardBatch.init_new.
-        # or lazily in ForwardBatch.init_new).
         self.seq_lens_sum = None
 
         if self.hisparse_coordinator is not None:
@@ -2447,25 +2446,6 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
                 .to(device=self.device, non_blocking=True)
             )
 
-    def maybe_wait_verify_done(self):
-        # Use event.wait() (stream-level wait) instead of .synchronize()
-        # (CPU block). Schedule-stream prep ops following this call get
-        # ordered after the forward-stream verify via the wait; CPU is not
-        # blocked. Subsequent .cpu()/.item() naturally sync the stream.
-        if self.is_spec_v2:
-            draft_input: EagleDraftInput = self.spec_info
-            if draft_input.verify_done is not None:
-                draft_input.verify_done.wait()
-
-    def refresh_seq_lens_cpu(self, sync: bool = True):
-        # sync=True: D2H from seq_lens (needed when seq_lens_cpu is stale
-        # relative to seq_lens, i.e. spec v2's mid-forward GPU rebind).
-        # sync=False: caller asserts seq_lens_cpu already fresh — skip D2H,
-        # only recompute the cached sum.
-        if sync and self.is_spec_v2:
-            self.seq_lens_cpu = self.seq_lens.cpu()
-        self.seq_lens_sum = int(self.seq_lens_cpu.sum())
-
     def filter_batch(
         self,
         chunked_req_to_exclude: Optional[Union[Req, List[Req]]] = None,
@@ -2473,10 +2453,6 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
         # FIXME(lsyin): deprecate this API after spec v1 is deprecated
         v1_spec_info_filtered: Optional[bool] = False,
     ):
-        # FIXME(lsyin): used here to get the correct seq_lens
-        # The batch has been launched but we need it verified to get correct next batch info
-        self.maybe_wait_verify_done()
-
         if keep_indices is None:
             if isinstance(chunked_req_to_exclude, Req):
                 chunked_req_to_exclude = [chunked_req_to_exclude]
@@ -2516,8 +2492,7 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
         self.seq_lens_cpu = self.seq_lens_cpu[keep_indices]
         self.orig_seq_lens = self.orig_seq_lens[keep_indices_device]
         self.out_cache_loc = None
-        # Defer compute to refresh_seq_lens_cpu (either pre-forward in scheduler.py
+        # Sum is recomputed lazily by ForwardBatch.init_new.
-        # or lazily in ForwardBatch.init_new).
         self.seq_lens_sum = None
 
         if self.input_ids is not None:
@@ -2553,15 +2528,6 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
             )
 
     def merge_batch(self, other: "ScheduleBatch"):
-        # In the regular scheduler path:
-        # 1) self is always prefill, whose seq_lens is not a future
-        # 2) other is always decode, which is finished in previous step
-        # so verify_done is already synced and this is a no-op.
-        # In disagg decode + overlap, merge_batch can be called before
-        # filter_batch, so running_batch.seq_lens may still be a forward_stream
-        # future. Synchronize here to avoid a cross-stream data race.
-        self.maybe_wait_verify_done()
-
         # Penalizer orchestrator must be merged before Batch.reqs is merged. This is because
         # orchestrator.merge() depends on Batch.reqs during preparation of each penalizers, so it
         # needs to be called with pre-merged Batch.reqs.
@@ -2578,8 +2544,7 @@ class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
         self.seq_lens_cpu = torch.cat([self.seq_lens_cpu, other.seq_lens_cpu])
         self.orig_seq_lens = torch.cat([self.orig_seq_lens, other.orig_seq_lens])
         self.out_cache_loc = None
-        # Defer compute to refresh_seq_lens_cpu (either pre-forward in scheduler.py
+        # Sum is recomputed lazily by ForwardBatch.init_new.
-        # or lazily in ForwardBatch.init_new).
         self.seq_lens_sum = None
         if self.input_ids is not None:
             self.input_ids = torch.cat([self.input_ids, other.input_ids])

python/sglang/srt/managers/scheduler.py

@@ -22,6 +22,7 @@ import sys
 import time
 from collections import deque
 from contextlib import contextmanager, nullcontext
+from functools import partial
 from http import HTTPStatus
 from typing import Any, Deque, Dict, List, Optional, Tuple, Union
 
@@ -2841,18 +2842,36 @@ class Scheduler(
         # Run forward
         if self.is_generation:
             if self.enable_overlap:
-                # Refresh BEFORE _overlap_forward_isolation so snapshot
+                # Spec v2 pre-isolation CPU mirror prep: D2H new_seq_lens_buf
-                # captures fresh values and restore preserves them.
+                # into batch.seq_lens_cpu + set seq_lens_sum. For non-spec_v2,
-                batch.refresh_seq_lens_cpu()
+                # ForwardBatch.init_new lazily computes the sum.
+                if batch.is_spec_v2:
+                    # FIXME: make this optional to different backends.
+                    self.future_map.resolve_seq_lens_cpu(batch)
 
                 with self._overlap_forward_isolation(batch):
                     future_indices = FutureIndices(indices=batch.req_pool_indices)
 
+                    # Spec_v2 worker fires this between sample-end and
+                    # draft_extend; publish moves the fence to verify-end so
+                    # schedule prep can overlap with draft_extend.
+                    fwd_kwargs = (
+                        {
+                            "on_verify_complete": partial(
+                                self.future_map.publish, future_indices
+                            )
+                        }
+                        if batch.is_spec_v2
+                        else {}
+                    )
+
                     with self.forward_stream_ctx:
                         self.forward_stream.wait_stream(self.schedule_stream)
                         self.future_map.resolve_future(batch)
                         # FIXME: pp is not compatible with overlap
-                        batch_result = self.model_worker.forward_batch_generation(batch)
+                        batch_result = self.model_worker.forward_batch_generation(
+                            batch, **fwd_kwargs
+                        )
                         # Park any refs the worker wants kept alive 2 iters
                         # (cross-stream tensor lifetime; pinned in the same
                         # ring slot as the SB attr snapshot).
@@ -2863,7 +2882,12 @@ class Scheduler(
                         # FIXME(lsyin): maybe move this to forward_batch_generation
                         batch_result.copy_done = self.device_module.Event()
                         if batch_result.delay_sample_func is None:
-                            self.future_map.store_to_map(future_indices, batch_result)
+                            stash_payload = (
+                                batch_result.next_draft_input
+                                if batch.is_spec_v2
+                                else batch_result.next_token_ids
+                            )
+                            self.future_map.stash(future_indices, stash_payload)
                             batch_result.copy_to_cpu(
                                 return_logprob=batch.return_logprob,
                                 return_hidden_states=batch.return_hidden_states,
@@ -2876,15 +2900,11 @@ class Scheduler(
                 batch.input_ids = -future_indices.indices
 
                 if batch.is_spec_v2:
-                    # FIXME(lsyin): tmp code for spec v2
-                    # We only keep future indices for next draft input
-
                     batch.spec_info = batch_result.next_draft_input
                     batch.spec_info.future_indices = future_indices
-
+                    # Schedule-stream sentinel between iters; next iter's
-                    # The future value, usually for next batch preparation
+                    # resolve_future reassigns batch.seq_lens from new_seq_lens_buf.
-                    # Current implementation strictly synchronizes the seq_lens
+                    batch.seq_lens = -future_indices.indices
-                    batch.seq_lens = batch_result.next_draft_input.new_seq_lens
             elif self.enable_pdmux and batch.forward_mode.is_split_prefill():
                 batch_result = self.tp_worker.forward_batch_split_prefill(batch)
                 if isinstance(batch_result.next_token_ids, torch.Tensor):
@@ -2968,7 +2988,10 @@ class Scheduler(
             self.forward_stream.wait_stream(self.schedule_stream)
             _batch_result = batch_result.delay_sample_func()
             assert _batch_result is batch_result
-            self.future_map.store_to_map(batch_result.future_indices, batch_result)
+            # Delay-sample is non-spec only; stash takes next_token_ids tensor.
+            self.future_map.stash(
+                batch_result.future_indices, batch_result.next_token_ids
+            )
             batch_result.copy_to_cpu(
                 return_logprob=self.cur_batch.return_logprob,
                 return_hidden_states=self.cur_batch.return_hidden_states,

python/sglang/srt/model_executor/forward_batch_info.py

@@ -502,7 +502,7 @@ class ForwardBatch(ForwardBatchDeepSeekMHAMixin):
             seq_lens_cpu = batch.seq_lens_cpu
 
         if batch.seq_lens_sum is None:
-            batch.refresh_seq_lens_cpu(sync=False)
+            batch.seq_lens_sum = int(batch.seq_lens_cpu.sum())
 
         ret = cls(
             forward_mode=batch.forward_mode,

python/sglang/srt/speculative/eagle_info.py

@@ -696,7 +696,6 @@ class EagleDraftInput(SpecInput, EagleDraftInputV2Mixin):
     # V2 overlap worker only
     future_indices: Optional[FutureIndices] = None
     new_seq_lens: Optional[torch.Tensor] = None
-    verify_done: Optional[torch.cuda.Event] = None
     # V2 reuses `EagleDraftInput` across phases (V1 has a separate
     # `EagleDraftExtendInput` for these). Set during V2's draft-extend.
     num_correct_drafts: Optional[torch.Tensor] = None

python/sglang/srt/speculative/eagle_info_v2.py

@@ -96,9 +96,6 @@ class EagleDraftInputV2Mixin:
 
         bs = batch.batch_size()
 
-        # Now seq_lens is correct
-        batch.maybe_wait_verify_done()
-
         # Accumulate penalty
         # This is a relaxed version of penalties for speculative decoding.
         if batch.sampling_info.penalizer_orchestrator.is_required:
@@ -231,9 +228,7 @@ class EagleDraftInputV2Mixin:
         batch.input_ids = predict
         batch.seq_lens = batch.seq_lens + num_draft_tokens
         batch.seq_lens_cpu = batch.seq_lens_cpu + num_draft_tokens
-        # seq_lens_cpu was just CPU-updated in tandem — sync=False avoids
+        batch.seq_lens_sum = int(batch.seq_lens_cpu.sum())
-        # a redundant D2H on the draft hot path.
-        batch.refresh_seq_lens_cpu(sync=False)
         batch.extend_lens = [num_draft_tokens for _ in range(len(batch.seq_lens))]
         batch.prefix_lens = seq_lens_cpu_.tolist()
         batch.extend_num_tokens = extend_num_tokens

python/sglang/srt/speculative/eagle_worker_v2.py

@@ -756,7 +756,7 @@ class EAGLEWorkerV2(BaseSpecWorker):
         # allocator and kv cache pool are shared with target worker, which are cleared in scheduler
         pass
 
-    def forward_batch_generation(self, batch: ScheduleBatch):
+    def forward_batch_generation(self, batch: ScheduleBatch, on_verify_complete=None):
         if batch.forward_mode.is_extend() or batch.is_extend_in_batch:
             # Target prefill
             target_capture_mode = (
@@ -767,6 +767,10 @@ class EAGLEWorkerV2(BaseSpecWorker):
             batch.capture_hidden_mode = target_capture_mode
             batch_output = self.target_worker.forward_batch_generation(batch)
 
+            # Publish before draft_extend so the fence is at target-end.
+            if on_verify_complete is not None:
+                on_verify_complete(batch.seq_lens)
+
             # Draft prefill
             with (
                 self.draft_worker.draft_tp_context(
@@ -809,6 +813,9 @@ class EAGLEWorkerV2(BaseSpecWorker):
             assert verify_input.is_verify_input()
             batch.spec_info = verify_input
             batch_output = self.verify(batch)
+            # Publish before draft_extend so the fence is at verify-end.
+            if on_verify_complete is not None:
+                on_verify_complete(batch_output.next_draft_input.new_seq_lens)
             with (
                 self.draft_worker.draft_tp_context(
                     self.draft_worker.draft_runner.tp_group
@@ -1068,9 +1075,6 @@ class EAGLEWorkerV2(BaseSpecWorker):
                 batch, verify_input, accept_lens, accept_index, bs
             )
 
-        verify_done = torch.get_device_module(self.device).Event()
-        verify_done.record()
-
         if not batch.forward_mode.is_idle():
             accept_tokens = predict[accept_index]
             bonus_tokens = torch.empty_like(accept_lens, dtype=torch.int32)
@@ -1089,15 +1093,12 @@ class EAGLEWorkerV2(BaseSpecWorker):
             )
 
         next_draft_input = EagleDraftInput(
-            bonus_tokens=bonus_tokens,
+            bonus_tokens=bonus_tokens, new_seq_lens=new_seq_lens
-            new_seq_lens=new_seq_lens,
-            verify_done=verify_done,
         )
 
         # verify_forward_batch transitively holds verify-time GPU tensors
         # (draft_token / out_cache_loc / ...) that must outlive the imminent
-        # batch.input_ids rebind in prepare_for_extend_to_fill_draft_kvcache,
+        # batch.input_ids rebind in prepare_for_extend_to_fill_draft_kvcache.
-        # until the next iter's verify_done.synchronize() in filter_batch.
         # Scheduler pins it in batch_record_buf for the 2-iter window.
         return GenerationBatchResult(
             logits_output=logits_output,

python/sglang/srt/speculative/multi_layer_eagle_worker_v2.py

@@ -669,7 +669,7 @@ class MultiLayerEagleWorkerV2(BaseSpecWorker):
         # allocator and kv cache pool are shared with target worker, which are cleared in scheduler
         pass
 
-    def forward_batch_generation(self, batch: ScheduleBatch):
+    def forward_batch_generation(self, batch: ScheduleBatch, on_verify_complete=None):
         if batch.forward_mode.is_extend() or batch.is_extend_in_batch:
             # Target prefill
             target_capture_mode = (
@@ -680,6 +680,10 @@ class MultiLayerEagleWorkerV2(BaseSpecWorker):
             batch.capture_hidden_mode = target_capture_mode
             batch_output = self.target_worker.forward_batch_generation(batch)
 
+            # Publish before draft_extend so the fence is at target-end.
+            if on_verify_complete is not None:
+                on_verify_complete(batch.seq_lens)
+
             # Chain-style MTP needs FULL to get all-token hidden states;
             # non-chain only needs LAST (the target model's hidden states).
             batch_output.next_draft_input = self.draft_worker._draft_extend_for_prefill(
@@ -706,6 +710,9 @@ class MultiLayerEagleWorkerV2(BaseSpecWorker):
             assert verify_input.is_verify_input()
             batch.spec_info = verify_input
             batch_output = self.verify(batch)
+            # Publish before draft_extend so the fence is at verify-end.
+            if on_verify_complete is not None:
+                on_verify_complete(batch_output.next_draft_input.new_seq_lens)
             self.draft_worker._draft_extend_for_decode(batch, batch_output)
             return batch_output
 
@@ -767,8 +774,6 @@ class MultiLayerEagleWorkerV2(BaseSpecWorker):
             accept_index,
         ) = verify_input.sample(batch, logits_output)
         new_seq_lens = batch.seq_lens + accept_lens
-        verify_done = torch.get_device_module(self.device).Event()
-        verify_done.record()
 
         if not batch.forward_mode.is_idle():
             accept_tokens = predict[accept_index]
@@ -790,7 +795,6 @@ class MultiLayerEagleWorkerV2(BaseSpecWorker):
         next_draft_input = EagleDraftInput(
             bonus_tokens=bonus_tokens,
             new_seq_lens=new_seq_lens,
-            verify_done=verify_done,
         )
         # verify_forward_batch transitively holds verify-time GPU tensors that
         # must outlive the imminent batch.input_ids rebind; scheduler pins it