[PD] support spec decode (#6507)

Co-authored-by: SangBin Cho <rkooo567@gmail.com>

python/sglang/srt/disaggregation/decode.py

@@ -47,7 +47,7 @@ from sglang.srt.disaggregation.utils import (
 from sglang.srt.managers.schedule_batch import FINISH_ABORT
 from sglang.srt.mem_cache.base_prefix_cache import BasePrefixCache
 from sglang.srt.mem_cache.memory_pool import ReqToTokenPool, TokenToKVPoolAllocator
-from sglang.srt.model_executor.forward_batch_info import ForwardMode
+from sglang.srt.model_executor.forward_batch_info import CaptureHiddenMode, ForwardMode
 from sglang.srt.sampling.sampling_batch_info import SamplingBatchInfo
 
 logger = logging.getLogger(__name__)
@@ -76,6 +76,7 @@ class DecodePreallocQueue:
         self,
         req_to_token_pool: ReqToTokenPool,
         token_to_kv_pool_allocator: TokenToKVPoolAllocator,
+        draft_token_to_kv_pool: Optional[KVCache],
         req_to_metadata_buffer_idx_allocator: ReqToMetadataIdxAllocator,
         metadata_buffers: List[torch.Tensor],
         aux_dtype: torch.dtype,
@@ -91,6 +92,7 @@ class DecodePreallocQueue:
         self.req_to_token_pool = req_to_token_pool
         self.token_to_kv_pool_allocator = token_to_kv_pool_allocator
         self.token_to_kv_pool = token_to_kv_pool_allocator.get_kvcache()
+        self.draft_token_to_kv_pool = draft_token_to_kv_pool
         self.is_mla_backend = is_mla_backend(self.token_to_kv_pool)
         self.aux_dtype = aux_dtype
         self.metadata_buffers = metadata_buffers
@@ -119,6 +121,14 @@ class DecodePreallocQueue:
             self.token_to_kv_pool.get_contiguous_buf_infos()
         )
 
+        if self.draft_token_to_kv_pool is not None:
+            draft_kv_data_ptrs, draft_kv_data_lens, draft_kv_item_lens = (
+                self.draft_token_to_kv_pool.get_contiguous_buf_infos()
+            )
+            kv_data_ptrs += draft_kv_data_ptrs
+            kv_data_lens += draft_kv_data_lens
+            kv_item_lens += draft_kv_item_lens
+
         kv_args.kv_data_ptrs = kv_data_ptrs
         kv_args.kv_data_lens = kv_data_lens
         kv_args.kv_item_lens = kv_item_lens

python/sglang/srt/disaggregation/mooncake/conn.py

@@ -51,6 +51,7 @@ def group_concurrent_contiguous(
     return src_groups, dst_groups
 
 
+# prefill
 @dataclasses.dataclass
 class TransferKVChunk:
     room: int
@@ -60,6 +61,7 @@ class TransferKVChunk:
     prefill_aux_index: Optional[int]
 
 
+# decode
 @dataclasses.dataclass
 class TransferInfo:
     room: int
@@ -93,6 +95,7 @@ class TransferInfo:
         )
 
 
+# decode
 @dataclasses.dataclass
 class KVArgsRegisterInfo:
     room: str

python/sglang/srt/disaggregation/mooncake/transfer_engine.py

@@ -61,7 +61,8 @@ class MooncakeTransferEngine:
         self, session_id: str, buffer: int, peer_buffer_address: int, length: int
     ) -> int:
         """Synchronously transfer data to the specified address."""
-
+        # the first time: based on session_id (which contains remote_ip) to construct a queue pair, and cache the queue pair
+        # later: based on the cached queue pair to send data
         ret = self.engine.transfer_sync_write(
             session_id, buffer, peer_buffer_address, length
         )

python/sglang/srt/disaggregation/prefill.py

@@ -61,6 +61,7 @@ class PrefillBootstrapQueue:
     def __init__(
         self,
         token_to_kv_pool: KVCache,
+        draft_token_to_kv_pool: Optional[KVCache],
         req_to_metadata_buffer_idx_allocator: ReqToMetadataIdxAllocator,
         metadata_buffers: List[torch.Tensor],
         aux_dtype: torch.dtype,
@@ -72,6 +73,8 @@ class PrefillBootstrapQueue:
         scheduler: Scheduler,
     ):
         self.token_to_kv_pool = token_to_kv_pool
+        self.draft_token_to_kv_pool = draft_token_to_kv_pool
+
         self.is_mla_backend = is_mla_backend(token_to_kv_pool)
         self.aux_dtype = aux_dtype
 
@@ -98,6 +101,16 @@ class PrefillBootstrapQueue:
             self.token_to_kv_pool.get_contiguous_buf_infos()
         )
 
+        if self.draft_token_to_kv_pool is not None:
+            # We should also transfer draft model kv cache. The indices are
+            # always shared with a target model.
+            draft_kv_data_ptrs, draft_kv_data_lens, draft_kv_item_lens = (
+                self.draft_token_to_kv_pool.get_contiguous_buf_infos()
+            )
+            kv_data_ptrs += draft_kv_data_ptrs
+            kv_data_lens += draft_kv_data_lens
+            kv_item_lens += draft_kv_item_lens
+
         kv_args.kv_data_ptrs = kv_data_ptrs
         kv_args.kv_data_lens = kv_data_lens
         kv_args.kv_item_lens = kv_item_lens

python/sglang/srt/managers/scheduler.py

@@ -591,6 +591,11 @@ class Scheduler(
             self.disagg_decode_prealloc_queue = DecodePreallocQueue(
                 req_to_token_pool=self.req_to_token_pool,
                 token_to_kv_pool_allocator=self.token_to_kv_pool_allocator,
+                draft_token_to_kv_pool=(
+                    None
+                    if self.draft_worker is None
+                    else self.draft_worker.model_runner.token_to_kv_pool
+                ),
                 req_to_metadata_buffer_idx_allocator=req_to_metadata_buffer_idx_allocator,
                 metadata_buffers=metadata_buffers,
                 aux_dtype=aux_dtype,
@@ -624,6 +629,11 @@ class Scheduler(
 
             self.disagg_prefill_bootstrap_queue = PrefillBootstrapQueue(
                 token_to_kv_pool=self.token_to_kv_pool_allocator.get_kvcache(),
+                draft_token_to_kv_pool=(
+                    None
+                    if self.draft_worker is None
+                    else self.draft_worker.model_runner.token_to_kv_pool
+                ),
                 req_to_metadata_buffer_idx_allocator=req_to_metadata_buffer_idx_allocator,
                 metadata_buffers=metadata_buffers,
                 aux_dtype=aux_dtype,
@@ -1409,6 +1419,13 @@ class Scheduler(
                 self.running_batch.batch_is_full = True
                 break
 
+            if self.disaggregation_mode == DisaggregationMode.PREFILL:
+                # In prefill mode, prealloc queue and transfer queue can also take memory,
+                # so we need to check if the available size for the actual available size.
+                if len(adder.can_run_list) >= self.req_to_token_pool.available_size():
+                    self.running_batch.batch_is_full = True
+                    break
+
             req.init_next_round_input(
                 None if prefix_computed else self.tree_cache,
                 self.enable_hierarchical_cache,