[PD] Release initial code (#4654)

Co-authored-by: SangBin Cho <rkooo567@gmail.com>
Co-authored-by: Ying1123 <sqy1415@gmail.com>
Co-authored-by: merrymercy <lianminzheng@gmail.com>
Co-authored-by: makro
Co-authored-by: dhou-xai

python/sglang/srt/disaggregation/conn.py

@@ -0,0 +1,81 @@
+from __future__ import annotations
+
+import logging
+from enum import Enum
+from typing import Optional
+
+import numpy as np
+import numpy.typing as npt
+
+logger = logging.getLogger(__name__)
+
+
+class KVArgs:
+    engine_rank: int
+    kv_data_ptrs: list[int]
+    kv_data_lens: list[int]
+    kv_item_lens: list[int]
+    aux_data_ptrs: list[int]
+    aux_data_lens: list[int]
+    aux_item_lens: list[int]
+    ib_device: str
+
+
+class KVManager:
+    def __init__(self, args: KVArgs): ...
+
+
+class KVPoll:
+    Failed = 0
+    Bootstrapping = 1
+    WaitingForInput = 2
+    Transferring = 3
+    Success = 4
+
+
+class KVSender:
+    def __init__(self, mgr: KVManager, bootstrap_addr: str, bootstrap_room: int):
+        self.has_sent = False
+
+    def init(self, num_kv_indices: int, aux_index: Optional[int] = None): ...
+
+    def send(self, kv_indices: npt.NDArray[np.int32]):
+        self.has_sent = True
+
+    def poll(self) -> KVPoll:
+        if self.has_sent is False:
+            # Assume handshake completed instantly
+            return KVPoll.WaitingForInput
+        else:
+            # Assume transfer completed instantly
+            return KVPoll.Success
+
+    def failure_exception(self):
+        raise Exception("Fake KVSender Exception")
+
+
+class KVReceiver:
+    def __init__(
+        self, mgr: KVManager, bootstrap_addr: str, bootstrap_room: Optional[int] = None
+    ):
+        self.has_init = False
+
+    def init(self, kv_indices: npt.NDArray[np.int32], aux_index: Optional[int] = None):
+        self.has_init = True
+
+    def poll(self) -> KVPoll:
+        if self.has_init is False:
+            # Assume handshake completed instantly
+            return KVPoll.WaitingForInput
+        else:
+            # Assume transfer completed instantly
+            return KVPoll.Success
+
+    def failure_exception(self):
+        raise Exception("Fake KVReceiver Exception")
+
+
+class KVBootstrapServer:
+    def __init__(self, port: int): ...
+
+    def poll(self) -> KVPoll: ...

python/sglang/srt/disaggregation/decode.py

@@ -0,0 +1,495 @@
+"""
+Life cycle of a request in the decode server
+
+1. PreallocQueue:
+    a. Initialize a receiver for each request
+    b. The request handshakes first, and pre-allocate kv once there is available kv.
+    c. Move the request to TransferQueue.
+
+2. TransferQueue:
+    a. Poll the receiver to check the transfer state
+    b. If the transfer has finished, move the request to waiting queue
+
+3. WaitingQueue:
+    a. Use the requests in the queue to construct a PrebuiltExtendBatch
+    b. Skip the prefill forward but only populate metadata
+
+4. RunningBatch:
+    a. Merge the resolved PrebuiltExtendBatch into running batch to run decoding
+"""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, List, Optional, Tuple
+
+import torch
+from torch.distributed import ProcessGroup
+
+from sglang.srt.disaggregation.conn import KVArgs, KVManager, KVPoll, KVReceiver
+from sglang.srt.disaggregation.utils import (
+    ReqToMetadataIdxAllocator,
+    poll_and_all_reduce,
+)
+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.sampling.sampling_batch_info import SamplingBatchInfo
+
+logger = logging.getLogger(__name__)
+
+if TYPE_CHECKING:
+    from sglang.srt.configs.model_config import ModelConfig
+    from sglang.srt.managers.schedule_batch import Req, ScheduleBatch
+    from sglang.srt.managers.scheduler import Scheduler
+    from sglang.srt.server_args import ServerArgs
+
+
+@dataclass
+class DecodeRequest:
+    req: Req
+    kv_receiver: KVReceiver
+    waiting_for_input: bool = False
+    metadata_buffer_index: int = -1
+
+
+class DecodePreallocQueue:
+    """
+    Store the requests that are preallocating.
+    """
+
+    def __init__(
+        self,
+        req_to_token_pool: ReqToTokenPool,
+        token_to_kv_pool_allocator: TokenToKVPoolAllocator,
+        req_to_metadata_buffer_idx_allocator: ReqToMetadataIdxAllocator,
+        metadata_buffers: List[torch.Tensor],
+        aux_dtype: torch.dtype,
+        scheduler: Scheduler,
+        transfer_queue: DecodeTransferQueue,
+        tree_cache: BasePrefixCache,
+        gloo_group: ProcessGroup,
+        tp_rank: int,
+        tp_size: int,
+        bootstrap_port: int,
+    ):
+        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.aux_dtype = aux_dtype
+        self.metadata_buffers = metadata_buffers
+        self.req_to_metadata_buffer_idx_allocator = req_to_metadata_buffer_idx_allocator
+        self.scheduler = scheduler
+        self.transfer_queue = transfer_queue
+        self.tree_cache = tree_cache  # this is always a chunk cache
+        self.gloo_group = gloo_group
+        self.tp_rank = tp_rank
+        self.tp_size = tp_size
+        self.bootstrap_port = bootstrap_port
+
+        self.num_reserved_decode_tokens = 512
+
+        # Queue for requests pending pre-allocation
+        self.queue: List[DecodeRequest] = []
+        self.kv_manager = self._init_kv_manager()
+
+    def _init_kv_manager(self) -> KVManager:
+        kv_args = KVArgs()
+        kv_args.engine_rank = self.tp_rank
+        kv_data_ptrs, kv_data_lens, kv_item_lens = (
+            self.token_to_kv_pool.get_contiguous_buf_infos()
+        )
+
+        kv_args.kv_data_ptrs = kv_data_ptrs
+        kv_args.kv_data_lens = kv_data_lens
+        kv_args.kv_item_lens = kv_item_lens
+
+        kv_args.aux_data_ptrs = [
+            output_id_tensor.data_ptr() for output_id_tensor in self.metadata_buffers
+        ]
+        kv_args.aux_data_lens = [
+            metadata_buffer.nbytes for metadata_buffer in self.metadata_buffers
+        ]
+        kv_args.aux_item_lens = [
+            metadata_buffer[0].nbytes for metadata_buffer in self.metadata_buffers
+        ]
+        kv_args.ib_device = "mock-ib-device"
+        kv_manager = KVManager(kv_args)
+        return kv_manager
+
+    def add(self, req: Req) -> None:
+        """Add a request to the pending queue."""
+
+        kv_receiver = KVReceiver(
+            mgr=self.kv_manager,
+            bootstrap_addr=f"{req.bootstrap_host}:{self.bootstrap_port}",
+            bootstrap_room=req.bootstrap_room,
+        )
+        self.queue.append(DecodeRequest(req=req, kv_receiver=kv_receiver))
+
+    def extend(self, reqs: List[Req]) -> None:
+        """Add a request to the pending queue."""
+        for req in reqs:
+            self.add(req)
+
+    def _update_handshake_waiters(self) -> None:
+        if not self.queue:
+            return
+
+        if all(decode_req.waiting_for_input for decode_req in self.queue):
+            return
+
+        polls = poll_and_all_reduce(
+            [decode_req.kv_receiver for decode_req in self.queue], self.gloo_group
+        )
+
+        for i, (decode_req, poll) in enumerate(zip(self.queue, polls)):
+            if poll == KVPoll.Bootstrapping:
+                pass
+            elif poll == KVPoll.WaitingForInput:
+                decode_req.waiting_for_input = True
+            elif poll == KVPoll.Failed:
+                raise Exception("Handshake failed")
+
+    def pop_preallocated(self) -> List[DecodeRequest]:
+        """Pop the preallocated requests from the pending queue (FIFO)."""
+        self._update_handshake_waiters()
+
+        preallocated_reqs = []
+        indices_to_remove = set()
+        allocatable_tokens = self._allocatable_tokens(count_retracted=True)
+
+        for i, decode_req in enumerate(self.queue):
+            if not decode_req.waiting_for_input:
+                continue
+
+            if self.req_to_token_pool.available_size() <= 0:
+                break
+
+            if self.req_to_metadata_buffer_idx_allocator.available_size() <= 0:
+                break
+
+            required_tokens_for_request = (
+                len(decode_req.req.origin_input_ids) + self.num_reserved_decode_tokens
+            )
+
+            if required_tokens_for_request > allocatable_tokens:
+                break
+
+            allocatable_tokens -= required_tokens_for_request
+            self._pre_alloc(decode_req.req)
+
+            kv_indices = (
+                self.req_to_token_pool.req_to_token[decode_req.req.req_pool_idx][
+                    : len(decode_req.req.origin_input_ids)
+                ]
+                .cpu()
+                .numpy()
+            )
+
+            decode_req.metadata_buffer_index = (
+                self.req_to_metadata_buffer_idx_allocator.alloc()
+            )
+            assert decode_req.metadata_buffer_index is not None
+            decode_req.kv_receiver.init(kv_indices, decode_req.metadata_buffer_index)
+            preallocated_reqs.append(decode_req)
+            indices_to_remove.add(i)
+
+        self.queue = [
+            entry for i, entry in enumerate(self.queue) if i not in indices_to_remove
+        ]
+
+        return preallocated_reqs
+
+    def _allocatable_tokens(self) -> int:
+        allocatable_tokens = (
+            self.token_to_kv_pool_allocator.available_size()
+            - self.num_reserved_decode_tokens
+            * (
+                len(self.scheduler.running_batch.reqs)
+                + len(self.transfer_queue.queue)
+                + len(self.scheduler.waiting_queue)
+            )
+        )
+
+        # Note: if the last fake extend just finishes, and we enter `pop_preallocated` immediately in the next iteration
+        #       the extend batch is not in any queue, so we need to explicitly add the tokens slots here
+        if (
+            self.scheduler.last_batch
+            and self.scheduler.last_batch.forward_mode.is_extend()
+        ):
+            allocatable_tokens -= self.num_reserved_decode_tokens * len(
+                self.scheduler.last_batch.reqs
+            )
+
+        return allocatable_tokens
+
+    def _pre_alloc(self, req: Req) -> torch.Tensor:
+        """Pre-allocate the memory for req_to_token and token_kv_pool"""
+        req_pool_indices = self.req_to_token_pool.alloc(1)
+
+        assert req_pool_indices is not None
+
+        req.req_pool_idx = req_pool_indices[0]
+        kv_loc = self.token_to_kv_pool_allocator.alloc(
+            len(req.origin_input_ids) + max(len(req.output_ids) - 1, 0)
+        )
+
+        assert kv_loc is not None
+
+        self.req_to_token_pool.write((req.req_pool_idx, slice(0, len(kv_loc))), kv_loc)
+
+        # populate metadata
+        req.fill_ids = req.origin_input_ids + req.output_ids
+        req.extend_input_len = len(req.origin_input_ids)
+
+        return kv_loc
+
+
+class DecodeTransferQueue:
+    """
+    Store the requests that is polling kv
+    """
+
+    def __init__(
+        self,
+        gloo_group: ProcessGroup,
+        req_to_metadata_buffer_idx_allocator: ReqToMetadataIdxAllocator,
+        metadata_buffers: torch.Tensor,
+    ):
+        self.queue: List[DecodeRequest] = []
+        self.gloo_group = gloo_group
+        self.req_to_metadata_buffer_idx_allocator = req_to_metadata_buffer_idx_allocator
+        self.metadata_buffers = metadata_buffers
+
+    def add(self, req_conn: DecodeRequest) -> None:
+        self.queue.append(req_conn)
+
+    def extend(self, req_conns) -> None:
+        self.queue.extend(req_conns)
+
+    def pop_transferred(self) -> List[Req]:
+        if not self.queue:
+            return []
+
+        polls = poll_and_all_reduce(
+            [decode_req.kv_receiver for decode_req in self.queue], self.gloo_group
+        )
+
+        transferred_reqs = []
+        indices_to_remove = set()
+        for i, (decode_req, poll) in enumerate(zip(self.queue, polls)):
+            if poll == KVPoll.Failed:
+                raise Exception("Transfer failed")
+            elif poll == KVPoll.Success:
+                # pop and push it to waiting queue
+                idx = decode_req.metadata_buffer_index
+                assert len(decode_req.req.output_ids) == 0
+                output_id_buffer = self.metadata_buffers[0]
+                # the last dimension is padded by the same values.
+                output_id = output_id_buffer[idx][0].item()
+                assert len(decode_req.req.output_ids) == 0
+                assert decode_req.req.transferred_output_id is None
+                decode_req.req.transferred_output_id = output_id
+                transferred_reqs.append(decode_req.req)
+                indices_to_remove.add(i)
+            elif poll in [
+                KVPoll.Bootstrapping,
+                KVPoll.WaitingForInput,
+                KVPoll.Transferring,
+            ]:
+                pass
+            else:
+                raise ValueError(f"Unexpected poll case: {poll}")
+
+        for i in indices_to_remove:
+            idx = self.queue[i].metadata_buffer_index
+            assert idx != -1
+            self.req_to_metadata_buffer_idx_allocator.free(idx)
+
+        self.queue = [
+            entry for i, entry in enumerate(self.queue) if i not in indices_to_remove
+        ]
+
+        return transferred_reqs
+
+
+class ScheduleBatchDisaggregationDecodeMixin:
+
+    def prepare_for_prebuilt_extend(self: ScheduleBatch):
+        """
+        Prepare a prebuilt extend by populate metadata
+        Adapted from .prepare_for_extend().
+        """
+
+        self.forward_mode = ForwardMode.EXTEND
+        reqs = self.reqs
+        input_ids = [r.fill_ids[len(r.prefix_indices) :] for r in reqs]
+        extend_num_tokens = sum(len(ids) for ids in input_ids)
+        seq_lens = []
+        pre_lens = []
+        req_pool_indices = []
+
+        # Pre-calculate total size
+        total_size = sum(req.extend_input_len for req in reqs)
+        out_cache_loc = torch.empty(total_size, dtype=torch.int64, device=self.device)
+
+        # Fill the tensor in one pass
+        offset = 0
+        for i, req in enumerate(reqs):
+            req_pool_indices.append(req.req_pool_idx)
+
+            chunk = self.req_to_token_pool.req_to_token[req.req_pool_idx][
+                : req.extend_input_len
+            ]
+            assert (
+                offset + req.extend_input_len <= total_size
+            ), f"Exceeds total size: offset={offset}, req.extend_input_len={req.extend_input_len}, total_size={total_size}"
+            out_cache_loc[offset : offset + req.extend_input_len] = chunk
+            offset += req.extend_input_len
+
+            pre_len = len(req.prefix_indices)
+            seq_len = len(req.origin_input_ids) + max(0, len(req.output_ids) - 1)
+            seq_lens.append(seq_len)
+            if len(req.output_ids) == 0:
+                assert (
+                    seq_len - pre_len == req.extend_input_len
+                ), f"seq_len={seq_len}, pre_len={pre_len}, req.extend_input_len={req.extend_input_len}"
+
+            req.cached_tokens += pre_len - req.already_computed
+            req.already_computed = seq_len
+            req.is_retracted = False
+            pre_lens.append(pre_len)
+            req.extend_logprob_start_len = 0
+
+        extend_input_logprob_token_ids = None
+
+        # Set fields
+        self.input_ids = torch.tensor(
+            sum(input_ids, []), dtype=torch.int32, device=self.device
+        )
+        self.req_pool_indices = torch.tensor(
+            req_pool_indices, dtype=torch.int64, device=self.device
+        )
+        self.seq_lens = torch.tensor(seq_lens, dtype=torch.int64, device=self.device)
+        self.out_cache_loc = out_cache_loc
+        self.seq_lens_sum = sum(seq_lens)
+        self.extend_num_tokens = extend_num_tokens
+        self.prefix_lens = [len(r.prefix_indices) for r in reqs]
+        self.extend_lens = [r.extend_input_len for r in reqs]
+        self.extend_logprob_start_lens = [r.extend_logprob_start_len for r in reqs]
+        self.extend_input_logprob_token_ids = extend_input_logprob_token_ids
+
+        # Build sampling info
+        self.sampling_info = SamplingBatchInfo.from_schedule_batch(
+            self,
+            self.model_config.vocab_size,
+        )
+
+    def process_prebuilt_extend(
+        self: ScheduleBatch, server_args: ServerArgs, model_config: ModelConfig
+    ):
+        """Assign the buffered last input id to schedule batch"""
+        self.output_ids = []
+        for req in self.reqs:
+            if req.output_ids and len(req.output_ids) > 0:
+                # resumed retracted req
+                self.output_ids.append(req.output_ids[-1])
+            else:
+                assert req.transferred_output_id is not None
+                req.output_ids.append(req.transferred_output_id)
+                self.output_ids.append(req.transferred_output_id)
+            self.tree_cache.cache_unfinished_req(req)
+        self.output_ids = torch.tensor(self.output_ids, device=self.device)
+
+
+class SchedulerDisaggregationDecodeMixin:
+
+    def get_next_disagg_decode_batch_to_run(
+        self: Scheduler,
+    ) -> Optional[Tuple[ScheduleBatch, bool]]:
+        """Create fake completed prefill if possible and merge with running batch"""
+        # Merge the prefill batch into the running batch
+        last_batch = self.last_batch
+        if last_batch and last_batch.forward_mode.is_extend():
+            # chunked prefill doesn't happen in decode instance.
+            assert self.chunked_req is None
+            # Filter finished batches.
+            last_batch.filter_batch()
+            if not last_batch.is_empty():
+                if self.running_batch.is_empty():
+                    self.running_batch = last_batch
+                else:
+                    # merge running_batch with prefill batch
+                    self.running_batch.merge_batch(last_batch)
+
+        new_prebuilt_batch = self.get_new_prebuilt_batch()
+
+        ret: Optional[ScheduleBatch] = None
+        if new_prebuilt_batch:
+            ret = new_prebuilt_batch
+        else:
+            if self.running_batch.is_empty():
+                ret = None
+            else:
+                self.running_batch = self.update_running_batch(self.running_batch)
+                ret = self.running_batch if not self.running_batch.is_empty() else None
+
+        return ret
+
+    def get_new_prebuilt_batch(self: Scheduler) -> Optional[ScheduleBatch]:
+        """Create a schedulebatch for fake completed prefill"""
+        if len(self.waiting_queue) == 0:
+            return None
+
+        curr_batch_size = self.running_batch.batch_size()
+
+        batch_size = min(self.req_to_token_pool.size, self.max_running_requests)
+
+        num_not_used_batch = batch_size - curr_batch_size
+
+        # pop req from waiting queue
+        can_run_list: List[Req] = []
+        waiting_queue: List[Req] = []
+
+        for i in range(len(self.waiting_queue)):
+            req = self.waiting_queue[i]
+            # we can only add at least `num_not_used_batch` new batch to the running queue
+            if i < num_not_used_batch:
+                can_run_list.append(req)
+                req.init_next_round_input(self.tree_cache)
+            else:
+                waiting_queue.append(req)
+
+        self.waiting_queue = waiting_queue
+        if len(can_run_list) == 0:
+            return None
+        # local import to avoid circular import
+        from sglang.srt.managers.schedule_batch import ScheduleBatch
+
+        # construct a schedule batch with those requests and mark as decode
+        new_batch = ScheduleBatch.init_new(
+            can_run_list,
+            self.req_to_token_pool,
+            self.token_to_kv_pool_allocator,
+            self.tree_cache,
+            self.model_config,
+            self.enable_overlap,
+            self.spec_algorithm,
+            self.server_args.enable_custom_logit_processor,
+        )
+
+        # construct fake completed prefill
+        new_batch.prepare_for_prebuilt_extend()
+        new_batch.process_prebuilt_extend(self.server_args, self.model_config)
+
+        return new_batch
+
+    def process_decode_queue(self: Scheduler):
+        req_conns = self.disagg_decode_prealloc_queue.pop_preallocated()
+        self.disagg_decode_transfer_queue.extend(req_conns)
+        alloc_reqs = (
+            self.disagg_decode_transfer_queue.pop_transferred()
+        )  # the requests which kv has arrived
+        self.waiting_queue.extend(alloc_reqs)

python/sglang/srt/disaggregation/mini_lb.py

@@ -0,0 +1,285 @@
+"""
+Minimal HTTP load balancer for prefill and decode servers for testing purpose.
+"""
+
+import asyncio
+import random
+import urllib
+from itertools import chain
+
+import aiohttp
+import orjson
+import uvicorn
+from fastapi import FastAPI, HTTPException
+from fastapi.responses import ORJSONResponse, Response, StreamingResponse
+
+
+class MiniLoadBalancer:
+    def __init__(self, prefill_servers, decode_servers):
+        self.prefill_servers = prefill_servers
+        self.decode_servers = decode_servers
+
+    def select_pair(self):
+        return random.choice(self.prefill_servers), random.choice(self.decode_servers)
+
+    async def generate_request(self, request_data):
+        prefill_server, decode_server = self.select_pair()
+
+        # Parse and transform prefill_server
+        parsed_url = urllib.parse.urlparse(prefill_server)
+        hostname = parsed_url.hostname
+        bootstrap_host = f"{hostname}"
+
+        modified_request = request_data.copy()
+        modified_request.update(
+            {
+                "bootstrap_host": bootstrap_host,
+                "bootstrap_room": random.randint(0, 2**63 - 1),
+            }
+        )
+
+        async with aiohttp.ClientSession() as session:
+            # Create the tasks
+            tasks = [
+                session.post(f"{prefill_server}/generate", json=modified_request),
+                session.post(f"{decode_server}/generate", json=modified_request),
+            ]
+
+            prefill_response = None
+            decode_response = None
+
+            # Process responses as they arrive
+            for i, response in enumerate(asyncio.as_completed(tasks)):
+                response = await response
+                # Check if this is the prefill or decode response based on order created
+                if i == 0:  # First completed task
+                    if str(response.url).startswith(prefill_server):
+                        prefill_response = response
+                        if response.status != 200:
+                            raise HTTPException(
+                                status_code=response.status,
+                                detail=f"Prefill server error: Status {response.status} Details: {await response.text()}",
+                            )
+                    else:
+                        decode_response = response
+                        if response.status != 200:
+                            raise HTTPException(
+                                status_code=response.status,
+                                detail=f"Decode server error: Status {response.status} Details: {await response.text()}",
+                            )
+                else:  # Second completed task
+                    if str(response.url).startswith(prefill_server):
+                        prefill_response = response
+                    else:
+                        decode_response = response
+
+                    if response.status != 200:
+                        raise HTTPException(
+                            status_code=response.status,
+                            detail=f"{'Prefill' if str(response.url).startswith(prefill_server) else 'Decode'} server error: Status {response.status} Details: {await response.text()}",
+                        )
+
+            return await decode_response.json()
+
+
+app = FastAPI()
+load_balancer = None
+
+
+@app.get("/health")
+async def health_check():
+    return Response(status_code=200)
+
+
+@app.get("/health_generate")
+async def health_check():
+    prefill_servers, decode_servers = (
+        load_balancer.prefill_servers,
+        load_balancer.decode_servers,
+    )
+    async with aiohttp.ClientSession() as session:
+        # Create the tasks
+        tasks = []
+        for server in chain(prefill_servers, decode_servers):
+            tasks.append(session.post(f"{server}/health_generate"))
+        for i, response in enumerate(asyncio.as_completed(tasks)):
+            await response
+    return Response(status_code=200)
+
+
+@app.post("/flush_cache")
+async def flush_cache():
+    prefill_servers, decode_servers = (
+        load_balancer.prefill_servers,
+        load_balancer.decode_servers,
+    )
+    async with aiohttp.ClientSession() as session:
+        # Create the tasks
+        tasks = []
+        for server in chain(prefill_servers, decode_servers):
+            tasks.append(session.post(f"{server}/flush_cache"))
+        for i, response in enumerate(asyncio.as_completed(tasks)):
+            await response
+    return Response(status_code=200)
+
+
+@app.get("/get_server_info")
+async def get_server_info():
+    prefill_servers, decode_servers = (
+        load_balancer.prefill_servers,
+        load_balancer.decode_servers,
+    )
+    prefill_infos = []
+    decode_infos = []
+    async with aiohttp.ClientSession() as session:
+        for server in chain(prefill_servers):
+            server_info = await session.get(f"{server}/get_server_info")
+            prefill_infos.append(await server_info.json())
+        for server in chain(decode_servers):
+            server_info = await session.get(f"{server}/get_server_info")
+            decode_infos.append(await server_info.json())
+
+    return {"prefill": prefill_infos, "decode": decode_infos}
+
+
+@app.get("/get_model_info")
+async def get_model_info():
+    # Dummy model information
+    model_info = {
+        "model_path": "/path/to/dummy/model",
+        "tokenizer_path": "/path/to/dummy/tokenizer",
+        "is_generation": True,
+        "preferred_sampling_params": {"temperature": 0.7, "max_new_tokens": 128},
+    }
+    return ORJSONResponse(content=model_info)
+
+
+@app.post("/generate")
+async def handle_generate_request(request_data: dict):
+    prefill_server, decode_server = load_balancer.select_pair()
+
+    # Parse and transform prefill_server for bootstrap data
+    parsed_url = urllib.parse.urlparse(prefill_server)
+    hostname = parsed_url.hostname
+    modified_request = request_data.copy()
+    modified_request.update(
+        {
+            "bootstrap_host": hostname,
+            "bootstrap_room": random.randint(0, 2**63 - 1),
+        }
+    )
+
+    # Check if streaming is requested
+    if request_data.get("stream", False):
+
+        async def stream_results():
+            async with aiohttp.ClientSession(
+                timeout=aiohttp.ClientTimeout(total=3600)
+            ) as session:
+                try:
+                    # Create the tasks
+                    tasks = [
+                        session.post(
+                            f"{prefill_server}/generate", json=modified_request
+                        ),
+                        session.post(
+                            f"{decode_server}/generate", json=modified_request
+                        ),
+                    ]
+
+                    prefill_response = None
+                    decode_response = None
+
+                    # Process responses as they arrive
+                    for i, response_task in enumerate(asyncio.as_completed(tasks)):
+                        response = await response_task
+
+                        # Check the response immediately
+                        if str(response.url).startswith(prefill_server):
+                            prefill_response = response
+                            if response.status != 200:
+                                error_msg = {
+                                    "error": {
+                                        "message": f"Prefill server error: Status {response.status}, Details: {await response.text()}"
+                                    }
+                                }
+                                yield b"data: " + orjson.dumps(
+                                    error_msg, option=orjson.OPT_NON_STR_KEYS
+                                ) + b"\n\n"
+                                return
+                        else:
+                            decode_response = response
+                            if response.status != 200:
+                                error_msg = {
+                                    "error": {
+                                        "message": f"Decode server error: Status {response.status}"
+                                    }
+                                }
+                                yield b"data: " + orjson.dumps(
+                                    error_msg, option=orjson.OPT_NON_STR_KEYS
+                                ) + b"\n\n"
+                                return
+
+                    # Stream successful decode server response
+                    async for line in decode_response.content:
+                        yield line
+                    yield b"data: [DONE]\n\n"
+
+                except Exception as e:
+                    error_msg = {
+                        "error": {"message": f"Stream processing error: {str(e)}"}
+                    }
+                    yield b"data: " + orjson.dumps(
+                        error_msg, option=orjson.OPT_NON_STR_KEYS
+                    ) + b"\n\n"
+
+        return StreamingResponse(
+            stream_results(),
+            media_type="text/event-stream",
+        )
+
+    # Non-streaming case
+    result = await load_balancer.generate_request(request_data)
+    return ORJSONResponse(content=result)
+
+
+@app.get("/v1/models")
+async def get_models():
+    prefill_server = load_balancer.prefill_servers[0]  # Get the first prefill server
+    async with aiohttp.ClientSession() as session:
+        try:
+            response = await session.get(f"{prefill_server}/v1/models")
+            if response.status != 200:
+                raise HTTPException(
+                    status_code=response.status,
+                    detail=f"Prefill server error: Status {response.status}",
+                )
+            return ORJSONResponse(content=await response.json())
+        except Exception as e:
+            raise HTTPException(status_code=500, detail=str(e))
+
+
+def run(prefill_addrs, decode_addrs, host, port):
+    global load_balancer
+    load_balancer = MiniLoadBalancer(prefill_addrs, decode_addrs)
+    uvicorn.run(app, host=host, port=port)
+
+
+if __name__ == "__main__":
+    import argparse
+
+    parser = argparse.ArgumentParser(description="Mini Load Balancer Server")
+    parser.add_argument(
+        "--prefill", required=True, help="Comma-separated URLs for prefill servers"
+    )
+    parser.add_argument(
+        "--decode", required=True, help="Comma-separated URLs for decode servers"
+    )
+    parser.add_argument(
+        "--host", default="0.0.0.0", help="Host to bind the server (default: 0.0.0.0)"
+    )
+    parser.add_argument(
+        "--port", type=int, default=8000, help="Port to bind the server (default: 8000)"
+    )
+    args = parser.parse_args()
+    run(args.prefill.split(","), args.decode.split(","), args.host, args.port)

python/sglang/srt/disaggregation/prefill.py

@@ -0,0 +1,249 @@
+"""
+Life cycle of a request in the prefill server
+
+1. Bootstrap Queue
+    a. Initialize a sender for each request
+    b. Use the queue to store requests whose bootstrap (handshake and preallocation) has not finished
+    c. Poll senders to check bootstrap state
+    d. Once bootstrap is complete, move request to Waiting Queue
+
+2. Waiting Queue
+    a. Use PrefillAdder to pop requests
+    b. Run forward
+    c. Add the request to Infight Queue
+
+3. Infight Queue
+    a. Poll (non-blocking) the sender of the request
+    b. Once the transfer has finished, return the request
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import TYPE_CHECKING, List, Optional
+
+import torch
+
+from sglang.srt.disaggregation.conn import KVArgs, KVManager, KVPoll, KVSender
+from sglang.srt.disaggregation.utils import (
+    ReqToMetadataIdxAllocator,
+    poll_and_all_reduce,
+)
+from sglang.srt.managers.schedule_batch import FINISH_LENGTH, Req, ScheduleBatch
+
+if TYPE_CHECKING:
+    from torch.distributed import ProcessGroup
+
+    from sglang.srt.managers.scheduler import GenerationBatchResult, Scheduler
+    from sglang.srt.mem_cache.memory_pool import KVCache
+
+logger = logging.getLogger(__name__)
+
+
+class PrefillBootstrapQueue:
+    """
+    Store the requests in bootstrapping
+    """
+
+    def __init__(
+        self,
+        token_to_kv_pool: KVCache,
+        req_to_metadata_buffer_idx_allocator: ReqToMetadataIdxAllocator,
+        metadata_buffers: List[torch.Tensor],
+        aux_dtype: torch.dtype,
+        tp_rank: int,
+        tp_size: int,
+        bootstrap_port: int,
+        gloo_group: ProcessGroup,
+    ):
+        self.token_to_kv_pool = token_to_kv_pool
+        self.aux_dtype = aux_dtype
+
+        self.metadata_buffers = metadata_buffers
+        self.req_to_metadata_buffer_idx_allocator = req_to_metadata_buffer_idx_allocator
+        self.tp_rank = tp_rank
+        self.tp_size = tp_size
+        self.kv_manager = self._init_kv_manager()
+        self.queue: List[Req] = []
+        self.gloo_group = gloo_group
+        self.bootstrap_port = bootstrap_port
+
+    def allocate_token_id(self, idx: int, token_id: int):
+        assert token_id >= 0, f"token_id: {token_id} is negative"
+        output_id_buffer = self.metadata_buffers[0]
+        output_id_buffer[idx] = token_id
+
+    def _init_kv_manager(self) -> KVManager:
+        kv_args = KVArgs()
+        kv_args.engine_rank = self.tp_rank
+        kv_data_ptrs, kv_data_lens, kv_item_lens = (
+            self.token_to_kv_pool.get_contiguous_buf_infos()
+        )
+
+        kv_args.kv_data_ptrs = kv_data_ptrs
+        kv_args.kv_data_lens = kv_data_lens
+        kv_args.kv_item_lens = kv_item_lens
+
+        # Define req -> input ids buffer
+        kv_args.aux_data_ptrs = [
+            metadata_buffer.data_ptr() for metadata_buffer in self.metadata_buffers
+        ]
+        kv_args.aux_data_lens = [
+            metadata_buffer.nbytes for metadata_buffer in self.metadata_buffers
+        ]
+        kv_args.aux_item_lens = [
+            metadata_buffer[0].nbytes for metadata_buffer in self.metadata_buffers
+        ]
+        kv_args.ib_device = "mock-ib-device"
+        kv_manager = KVManager(kv_args)
+        return kv_manager
+
+    def add(self, req: Req) -> None:
+        req.disagg_kv_sender = KVSender(
+            mgr=self.kv_manager,
+            bootstrap_addr=f"{req.bootstrap_host}:{self.bootstrap_port}",
+            bootstrap_room=req.bootstrap_room,
+        )
+        self._process_req(req)
+        self.queue.append(req)
+
+    def _process_req(self, req: Req) -> None:
+        """
+        Set max_new_tokens = 1, so PrefillAdder memory estimation is accurate
+        """
+        req.sampling_params.max_new_tokens = 1
+
+    def pop_bootstrapped(self) -> List[Req]:
+        """pop the reqs which has finished bootstrapping"""
+        bootstrapped_reqs = []
+        indices_to_remove = set()
+
+        if len(self.queue) == 0:
+            return []
+
+        polls = poll_and_all_reduce(
+            [req.disagg_kv_sender for req in self.queue], self.gloo_group
+        )
+
+        for i, (req, poll) in enumerate(zip(self.queue, polls)):
+            if poll == KVPoll.Bootstrapping:
+                continue
+            elif poll == KVPoll.Failed:
+                raise Exception("Bootstrap failed")
+
+            # KV.WaitingForInput - init here
+            num_kv_indices = len(req.origin_input_ids)
+            if self.req_to_metadata_buffer_idx_allocator.available_size() == 0:
+                break
+
+            req.metadata_buffer_index = (
+                self.req_to_metadata_buffer_idx_allocator.alloc()
+            )
+            assert req.metadata_buffer_index is not None
+            req.disagg_kv_sender.init(num_kv_indices, req.metadata_buffer_index)
+
+            bootstrapped_reqs.append(req)
+            indices_to_remove.add(i)
+
+        self.queue = [
+            entry for i, entry in enumerate(self.queue) if i not in indices_to_remove
+        ]
+
+        return bootstrapped_reqs
+
+
+class SchedulerDisaggregationPrefillMixin:
+    """
+    Mixin for Scheduler to handle disaggregation prefill
+    """
+
+    def process_batch_result_disagg_prefill(
+        self: Scheduler, batch: ScheduleBatch, result: GenerationBatchResult
+    ) -> None:
+        """
+        Transfer kv for prefill completed requests and add it into disagg_prefill_infight_queue
+        Adapted from process_batch_result_prefill
+        """
+
+        next_token_ids = result.next_token_ids.tolist()
+
+        for req, next_token_id in zip(batch.reqs, next_token_ids, strict=True):
+            req: Req
+            if req.is_chunked <= 0:
+                # There is no output_ids for prefill
+                req.output_ids.append(next_token_id)
+                self.tree_cache.cache_unfinished_req(req)  # update the tree and lock
+                self.send_kv_chunk(req, token_id=next_token_id)
+                self.disagg_prefill_infight_queue.append(req)
+            else:
+                # being chunked reqs' prefill is not finished
+                req.is_chunked -= 1
+
+        # TODO: Not sure if this is necessary
+        if batch.next_batch_sampling_info:
+            batch.next_batch_sampling_info.update_regex_vocab_mask()
+            # We need to remove this for overlap schedule.
+            self.current_stream.synchronize()
+            batch.next_batch_sampling_info.sampling_info_done.set()
+
+    def process_disagg_prefill_infight_queue(self: Scheduler) -> None:
+        """
+        Poll the requests in the middle of transfer. If done, return the request.
+        """
+        assert len(self.disagg_prefill_infight_queue) > 0
+
+        done_reqs = []
+
+        polls = poll_and_all_reduce(
+            [req.disagg_kv_sender for req in self.disagg_prefill_infight_queue],
+            self.tp_worker.get_tp_cpu_group(),
+        )
+
+        undone_reqs: List[Req] = []
+        # Check .poll() for the reqs in disagg_prefill_infight_queue. If Success, respond to the client and remove it from the queue
+        for req, poll in zip(self.disagg_prefill_infight_queue, polls):
+            if poll in [KVPoll.WaitingForInput, KVPoll.Transferring]:
+                undone_reqs.append(req)
+            elif poll == KVPoll.Success:  # transfer done
+                self.tree_cache.cache_finished_req(req)  # unlock the tree
+                req.finished_reason = FINISH_LENGTH(length=0)
+                done_reqs.append(req)
+            elif poll == KVPoll.Failed:
+                raise Exception("Transferring failed")
+
+        # Stream requests which have finished transfer
+        self.stream_output(done_reqs, False, None)
+
+        self.disagg_prefill_infight_queue = undone_reqs
+
+    def process_prefill_chunk(self: Scheduler) -> None:
+        if self.last_batch and self.last_batch.forward_mode.is_extend():
+            if self.chunked_req:
+                # Move the chunked request out of the batch so that we can merge
+                # only finished requests to running_batch.
+                self.last_batch.filter_batch(chunked_req_to_exclude=self.chunked_req)
+                self.tree_cache.cache_unfinished_req(self.chunked_req)
+                self.send_kv_chunk(self.chunked_req)
+                # chunked request keeps its rid but will get a new req_pool_idx
+                self.req_to_token_pool.free(self.chunked_req.req_pool_idx)
+                self.running_batch.batch_is_full = False
+
+    def send_kv_chunk(
+        self: Scheduler, req: Req, token_id: Optional[int] = None
+    ) -> None:
+        """
+        Send a prefilled chunk to the decode server
+        """
+        start_idx = req.start_send_idx
+        end_idx = min(len(req.fill_ids), len(req.origin_input_ids))
+        kv_indices = (
+            self.req_to_token_pool.req_to_token[req.req_pool_idx][start_idx:end_idx]
+            .cpu()
+            .numpy()
+        )
+        req.start_send_idx = end_idx
+        if token_id is not None:
+            self.disagg_prefill_pending_queue.allocate_token_id(
+                req.metadata_buffer_index, token_id
+            )
+        req.disagg_kv_sender.send(kv_indices)

python/sglang/srt/disaggregation/utils.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+from collections import deque
+from enum import Enum
+from typing import List
+
+import torch
+import torch.distributed as dist
+
+
+class DisaggregationMode(Enum):
+    NULL = "null"
+    PREFILL = "prefill"
+    DECODE = "decode"
+
+
+def poll_and_all_reduce(pollers, gloo_group):
+    polls = [int(poller.poll()) for poller in pollers]
+    tensor_to_reduce = torch.tensor(polls, dtype=torch.uint8, device="cpu")
+    dist.all_reduce(tensor_to_reduce, op=dist.ReduceOp.MIN, group=gloo_group)
+    return tensor_to_reduce.tolist()
+
+
+class ReqToMetadataIdxAllocator:
+    """A memory pool that maps a request to its first output token location."""
+
+    def __init__(
+        self,
+        size: int,
+    ):
+        self.size = size
+        self.free_slots = deque(list(range(size)))
+
+    def available_size(self):
+        return len(self.free_slots)
+
+    def alloc(self) -> List[int]:
+        if len(self.free_slots) == 0:
+            return None
+
+        return self.free_slots.popleft()
+
+    def free(self, free_index: int):
+        self.free_slots.append(free_index)

python/sglang/srt/managers/schedule_batch.py

@@ -42,6 +42,8 @@ import triton.language as tl
 from sglang.global_config import global_config
 from sglang.srt.configs.model_config import ModelConfig
 from sglang.srt.constrained.base_grammar_backend import BaseGrammarObject
+from sglang.srt.disaggregation.conn import KVSender
+from sglang.srt.disaggregation.decode import ScheduleBatchDisaggregationDecodeMixin
 from sglang.srt.mem_cache.base_prefix_cache import BasePrefixCache
 from sglang.srt.mem_cache.chunk_cache import ChunkCache
 from sglang.srt.mem_cache.memory_pool import ReqToTokenPool, TokenToKVPoolAllocator
@@ -396,6 +398,24 @@ class Req:
         self.spec_verify_ct = 0
         self.lora_path = lora_path
 
+        # For disaggregation
+        self.bootstrap_host: str = "0.0.0.0"
+        self.bootstrap_room: Optional[int] = None
+        self.disagg_kv_sender: Optional[KVSender] = None
+
+        # used for warmup because we don't have a pair yet when init
+        self.skip_kv_transfer: bool = False
+        # the start index of the sent kv cache
+        # We want to send it chunk by chunk for chunked prefill.
+        # After every chunk forward, we do the following:
+        # kv_send(req.input_ids[req.start_send_idx:len(req.fill_ids)])
+        # start_send_idx = len(req.fill_ids)
+        self.start_send_idx: int = 0
+
+        self.metadata_buffer_index: int = -1
+        # The first output_id transferred from prefill instance.
+        self.transferred_output_id: Optional[int] = None
+
     @property
     def seqlen(self):
         return len(self.origin_input_ids) + len(self.output_ids)
@@ -531,7 +551,7 @@ bid = 0
 
 
 @dataclasses.dataclass
-class ScheduleBatch:
+class ScheduleBatch(ScheduleBatchDisaggregationDecodeMixin):
     """Store all information of a batch on the scheduler."""
 
     # Request, memory pool, and cache

python/sglang/srt/managers/scheduler.py

@@ -37,6 +37,19 @@ from torch.distributed import barrier
 from sglang.global_config import global_config
 from sglang.srt.configs.model_config import ModelConfig
 from sglang.srt.constrained.base_grammar_backend import create_grammar_backend
+from sglang.srt.disaggregation.decode import (
+    DecodePreallocQueue,
+    DecodeTransferQueue,
+    SchedulerDisaggregationDecodeMixin,
+)
+from sglang.srt.disaggregation.prefill import (
+    PrefillBootstrapQueue,
+    SchedulerDisaggregationPrefillMixin,
+)
+from sglang.srt.disaggregation.utils import (
+    DisaggregationMode,
+    ReqToMetadataIdxAllocator,
+)
 from sglang.srt.hf_transformers_utils import get_processor, get_tokenizer
 from sglang.srt.layers.dp_attention import compute_dp_attention_world_info
 from sglang.srt.layers.logits_processor import LogitsProcessorOutput
@@ -137,7 +150,11 @@ class EmbeddingBatchResult:
     bid: int
 
 
-class Scheduler(SchedulerOutputProcessorMixin):
+class Scheduler(
+    SchedulerOutputProcessorMixin,
+    SchedulerDisaggregationDecodeMixin,
+    SchedulerDisaggregationPrefillMixin,
+):
     """A scheduler that manages a tensor parallel GPU worker."""
 
     def __init__(
@@ -389,6 +406,11 @@ class Scheduler(SchedulerOutputProcessorMixin):
             ]
         )
 
+        self.disaggregation_mode = DisaggregationMode(
+            self.server_args.disaggregation_mode
+        )
+        self.init_disaggregation()
+
     def init_tokenizer(self):
         server_args = self.server_args
 
@@ -489,6 +511,73 @@ class Scheduler(SchedulerOutputProcessorMixin):
                 },
             )
 
+    def init_disaggregation(self):
+        if (
+            self.disaggregation_mode == DisaggregationMode.DECODE
+        ):  # *2 for the headroom.
+            buffer_size = (self.req_to_token_pool.size) * 2
+            req_to_metadata_buffer_idx_allocator = ReqToMetadataIdxAllocator(
+                buffer_size
+            )
+            aux_dtype = torch.int32
+            # A list of metadata buffers. The shape is (b, metadata_size) where
+            # b corresponds to a max running requests. The last shape * dtype.itemsize
+            # should be larger than 64 bytes to work with RDMA, so we pad it.
+            output_id_buffer = torch.zeros(
+                (buffer_size, 16), dtype=aux_dtype, device="cpu"
+            )
+            metadata_buffers = [output_id_buffer]
+
+            # The decode requests polling kv cache
+            self.disagg_decode_transfer_queue = DecodeTransferQueue(
+                gloo_group=self.tp_worker.get_attention_tp_cpu_group(),
+                req_to_metadata_buffer_idx_allocator=req_to_metadata_buffer_idx_allocator,
+                metadata_buffers=metadata_buffers,
+            )
+
+            # The decode requests pending for pre-allocation
+            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,
+                req_to_metadata_buffer_idx_allocator=req_to_metadata_buffer_idx_allocator,
+                metadata_buffers=metadata_buffers,
+                aux_dtype=aux_dtype,
+                scheduler=self,
+                transfer_queue=self.disagg_decode_transfer_queue,
+                tree_cache=self.tree_cache,
+                gloo_group=self.tp_worker.get_attention_tp_cpu_group(),
+                tp_rank=self.tp_rank,
+                tp_size=self.tp_size,
+                bootstrap_port=self.server_args.disaggregation_bootstrap_port,
+            )
+        elif self.disaggregation_mode == DisaggregationMode.PREFILL:
+            # *2 for the headroom.
+            buffer_size = self.max_running_requests * 2
+            req_to_metadata_buffer_idx_allocator = ReqToMetadataIdxAllocator(
+                buffer_size
+            )
+            aux_dtype = torch.int32
+            # A list of metadata buffers. The shape is (b, metadata_size) where
+            # b corresponds to a max running requests. The last shape * dtype.itemsize
+            # should be larger than 64 bytes to work with RDMA, so we pad it.
+            output_id_buffer = torch.zeros(
+                (buffer_size, 16), dtype=aux_dtype, device="cpu"
+            )
+            metadata_buffers = [output_id_buffer]
+
+            self.disagg_prefill_pending_queue = PrefillBootstrapQueue(
+                token_to_kv_pool=self.token_to_kv_pool_allocator.get_kvcache(),
+                req_to_metadata_buffer_idx_allocator=req_to_metadata_buffer_idx_allocator,
+                metadata_buffers=metadata_buffers,
+                aux_dtype=aux_dtype,
+                tp_rank=self.tp_rank,
+                tp_size=self.tp_size,
+                bootstrap_port=self.server_args.disaggregation_bootstrap_port,
+                gloo_group=self.tp_worker.get_attention_tp_cpu_group(),
+            )
+            # The prefill requests that are in the middle of kv sending
+            self.disagg_prefill_infight_queue: List[Req] = []
+
     @DynamicGradMode()
     def event_loop_normal(self):
         """A normal scheduler loop."""
@@ -549,6 +638,70 @@ class Scheduler(SchedulerOutputProcessorMixin):
 
             self.last_batch = batch
 
+    @torch.no_grad()
+    def event_loop_normal_disagg_prefill(self):
+        """A normal scheduler loop for prefill worker in disaggregation mode."""
+
+        while True:
+            recv_reqs = self.recv_requests()
+            self.process_input_requests(recv_reqs)
+            self.waiting_queue.extend(
+                self.disagg_prefill_pending_queue.pop_bootstrapped()
+            )
+            self.process_prefill_chunk()
+            batch = self.get_new_batch_prefill()
+            self.cur_batch = batch
+
+            if batch:
+                result = self.run_batch(batch)
+                self.process_batch_result_disagg_prefill(batch, result)
+
+            if len(self.disagg_prefill_infight_queue) > 0:
+                self.process_disagg_prefill_infight_queue()
+
+            if batch is None and len(self.disagg_prefill_infight_queue) == 0:
+                self.check_memory()
+                self.new_token_ratio = self.init_new_token_ratio
+
+            self.last_batch = batch
+            # HACK (byronhsu): reset the batch_is_full flag because we never enter update_running_batch which resets it
+            # Otherwise, it hangs under high concurrency
+            self.running_batch.batch_is_full = False
+
+    @torch.no_grad()
+    def event_loop_normal_disagg_decode(self):
+        """A normal scheduler loop for decode worker in disaggregation mode."""
+
+        while True:
+            recv_reqs = self.recv_requests()
+            self.process_input_requests(recv_reqs)
+            # polling and allocating kv cache
+            self.process_decode_queue()
+            batch = self.get_next_disagg_decode_batch_to_run()
+            self.cur_batch = batch
+
+            if batch:
+                # Generate fake extend output.
+                if batch.forward_mode.is_extend():
+                    # Note: Logprobs should be handled on the prefill engine.
+                    self.stream_output(
+                        batch.reqs, [False for _ in range(len(batch.reqs))]
+                    )
+                else:
+                    result = self.run_batch(batch)
+                    self.process_batch_result(batch, result)
+
+            if batch is None and (
+                len(self.disagg_decode_transfer_queue.queue)
+                + len(self.disagg_decode_prealloc_queue.queue)
+                == 0
+            ):
+                # When the server is idle, do self-check and re-init some states
+                self.check_memory()
+                self.new_token_ratio = self.init_new_token_ratio
+
+            self.last_batch = batch
+
     def recv_requests(self) -> List[Req]:
         """Receive results at tp_rank = 0 and broadcast it to all other TP ranks."""
         if self.attn_tp_rank == 0:
@@ -778,10 +931,20 @@ class Scheduler(SchedulerOutputProcessorMixin):
             self._add_request_to_queue(req)
 
     def _add_request_to_queue(self, req: Req):
-        self.waiting_queue.append(req)
+        if self.disaggregation_mode == DisaggregationMode.PREFILL:
+            self.disagg_prefill_pending_queue.add(req)
 
-    def _extend_requests_to_queue(self, reqs: List[Req]):
-        self.waiting_queue.extend(reqs)
+        elif self.disaggregation_mode == DisaggregationMode.DECODE:
+            self.disagg_decode_prealloc_queue.add(req)
+
+        else:
+            self.waiting_queue.append(req)
+
+    def _extend_requests_to_queue(self, reqs: List[Req], is_retracted: bool = False):
+        if self.disaggregation_mode == DisaggregationMode.DECODE:
+            self.disagg_decode_prealloc_queue.extend(reqs)
+        else:
+            self.waiting_queue.extend(reqs)
 
     def handle_embedding_request(
         self,
@@ -1814,10 +1977,18 @@ def run_scheduler_process(
                 "max_req_input_len": scheduler.max_req_input_len,
             }
         )
-        if scheduler.enable_overlap:
-            scheduler.event_loop_overlap()
-        else:
-            scheduler.event_loop_normal()
+        disaggregation_mode: DisaggregationMode = scheduler.disaggregation_mode
+
+        if disaggregation_mode == DisaggregationMode.NULL:
+            if scheduler.enable_overlap:
+                scheduler.event_loop_overlap()
+            else:
+                scheduler.event_loop_normal()
+        elif disaggregation_mode == DisaggregationMode.PREFILL:
+            scheduler.event_loop_normal_disagg_prefill()
+        elif disaggregation_mode == DisaggregationMode.DECODE:
+            scheduler.event_loop_normal_disagg_decode()
+
     except Exception:
         traceback = get_exception_traceback()
         logger.error(f"Scheduler hit an exception: {traceback}")

python/sglang/srt/managers/tokenizer_manager.py

@@ -49,6 +49,8 @@ from fastapi import BackgroundTasks
 
 from sglang.srt.aio_rwlock import RWLock
 from sglang.srt.configs.model_config import ModelConfig
+from sglang.srt.disaggregation.conn import KVBootstrapServer
+from sglang.srt.disaggregation.utils import DisaggregationMode
 from sglang.srt.hf_transformers_utils import get_processor, get_tokenizer
 from sglang.srt.managers.image_processor import (
     get_dummy_image_processor,
@@ -313,6 +315,16 @@ class TokenizerManager:
             ]
         )
 
+        self.disaggregation_mode = DisaggregationMode(
+            self.server_args.disaggregation_mode
+        )
+        # for disaggregtion, start kv boostrap server on prefill
+        if self.disaggregation_mode == DisaggregationMode.PREFILL:
+            # only start bootstrap server on prefill tm
+            self.bootstrap_server = KVBootstrapServer(
+                self.server_args.disaggregation_bootstrap_port
+            )
+
     async def generate_request(
         self,
         obj: Union[GenerateReqInput, EmbeddingReqInput],

python/sglang/srt/mem_cache/memory_pool.py

@@ -271,6 +271,19 @@ class MHATokenToKVPool(KVCache):
             v_size_bytes += np.prod(v_cache.shape) * v_cache.dtype.itemsize
         return k_size_bytes, v_size_bytes
 
+    # for disagg
+    def get_contiguous_buf_infos(self):
+        kv_data_ptrs = [
+            self.get_key_buffer(i).data_ptr() for i in range(self.layer_num)
+        ] + [self.get_value_buffer(i).data_ptr() for i in range(self.layer_num)]
+        kv_data_lens = [
+            self.get_key_buffer(i).nbytes for i in range(self.layer_num)
+        ] + [self.get_value_buffer(i).nbytes for i in range(self.layer_num)]
+        kv_item_lens = [
+            self.get_key_buffer(i)[0].nbytes for i in range(self.layer_num)
+        ] + [self.get_value_buffer(i)[0].nbytes for i in range(self.layer_num)]
+        return kv_data_ptrs, kv_data_lens, kv_item_lens
+
     # Todo: different memory layout
     def get_flat_data(self, indices):
         # prepare a large chunk of contiguous data for efficient transfer

python/sglang/srt/server_args.py

@@ -185,6 +185,10 @@ class ServerArgs:
     debug_tensor_dump_input_file: Optional[str] = None
     debug_tensor_dump_inject: bool = False
 
+    # For PD disaggregation: can be "null" (not disaggregated), "prefill" (prefill-only), or "decode" (decode-only)
+    disaggregation_mode: str = "null"
+    disaggregation_bootstrap_port: int = 8998
+
     def __post_init__(self):
         # Set missing default values
         if self.tokenizer_path is None:
@@ -325,6 +329,18 @@ class ServerArgs:
         if is_hip():
             self.triton_attention_num_kv_splits = 16
 
+        # PD disaggregation
+        if self.disaggregation_mode == "prefill":
+            self.disable_cuda_graph = True
+            logger.warning("KV cache is forced as chunk cache for decode server")
+            self.disable_overlap_schedule = True
+            logger.warning("Overlap scheduler is disabled for prefill server")
+        elif self.disaggregation_mode == "decode":
+            self.disable_radix_cache = True
+            logger.warning("Cuda graph is disabled for prefill server")
+            self.disable_overlap_schedule = True
+            logger.warning("Overlap scheduler is disabled for decode server")
+
     @staticmethod
     def add_cli_args(parser: argparse.ArgumentParser):
         # Model and port args
@@ -1063,6 +1079,21 @@ class ServerArgs:
             help="Inject the outputs from jax as the input of every layer.",
         )
 
+        # Disaggregation
+        parser.add_argument(
+            "--disaggregation-mode",
+            type=str,
+            default="null",
+            choices=["null", "prefill", "decode"],
+            help='Only used for PD disaggregation. "prefill" for prefill-only server, and "decode" for decode-only server. If not specified, it is not PD disaggregated',
+        )
+        parser.add_argument(
+            "--disaggregation-bootstrap-port",
+            type=int,
+            default=ServerArgs.disaggregation_bootstrap_port,
+            help="Bootstrap server port on the prefill server. Default is 8998.",
+        )
+
     @classmethod
     def from_cli_args(cls, args: argparse.Namespace):
         args.tp_size = args.tensor_parallel_size