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[Metrics] Add KV events publishing (#6098)

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This commit is contained in:
Trevor Morris
2025-05-19 14:19:54 -07:00
committed by GitHub
parent 299fd22f9e
commit 7adf245ba2
7 changed files with 686 additions and 1 deletions
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python/sglang/srt/disaggregation/kv_events.py Normal file
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"""
Copyright 2025 SGLang Team
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""
"""
KV caching events
"""
import atexit
import logging
import queue
import threading
import time
from abc import ABC, abstractmethod
from collections import deque
from itertools import count
from queue import Queue
from typing import Any, Callable, Optional, Union
import msgspec
import zmq
from pydantic import BaseModel
logger = logging.getLogger(__name__)
class EventBatch(
msgspec.Struct,
array_like=True, # type: ignore[call-arg]
omit_defaults=True, # type: ignore[call-arg]
gc=False, # type: ignore[call-arg]
):
ts: float
events: list[Any]
class KVCacheEvent(
msgspec.Struct,
array_like=True, # type: ignore[call-arg]
omit_defaults=True, # type: ignore[call-arg]
gc=False, # type: ignore[call-arg]
tag=True,
):
"""Base class for all KV cache-related events"""
class BlockStored(KVCacheEvent):
block_hashes: list[int]
parent_block_hash: Optional[int]
token_ids: list[int]
block_size: int
lora_id: Optional[int]
class BlockRemoved(KVCacheEvent):
block_hashes: list[int]
class AllBlocksCleared(KVCacheEvent):
pass
class KVEventBatch(EventBatch):
events: list[Union[BlockStored, BlockRemoved, AllBlocksCleared]]
class EventPublisher(ABC):
"""Lightweight publisher for EventBatch batches."""
@abstractmethod
def publish(self, events: EventBatch) -> None:
"""Emit events in order.
Implementations should guarantee at-least-once delivery and
monotonic ordering (e.g., via sequence numbers).
"""
@abstractmethod
def shutdown(self) -> None:
"""Shutdown the publisher."""
class NullEventPublisher(EventPublisher):
"""No-op implementation (default when disabled)."""
def publish(self, events) -> None:
return
def shutdown(self) -> None:
return
class ZmqEventPublisher(EventPublisher):
"""Reliable PUB/ROUTER publisher with an in-memory replay buffer.
Spawns a separate thread to handle publishing from a queue.
Parameters
----------
endpoint:
PUB address. Use ``tcp://*:5557`` to bind or ``tcp://host:5557`` to
connect.
replay_endpoint:
Optional ROUTER address for replay requests. When given, subscribers can
request missed batches by sending the starting sequence number as an
8-byte big-endian integer.
buffer_steps:
Number of past batches to keep for replay.
hwm:
ZeroMQ high-water-mark for PUB socket.
max_queue_size:
Maximum number of events to buffer in memory.
topic:
Topic to publish events to.
"""
SHUTDOWN_TIMEOUT: float = 1.0
END_SEQ = (-1).to_bytes(8, "big", signed=True)
def __init__(
self,
endpoint: str = "tcp://*:5557",
replay_endpoint: Optional[str] = None,
buffer_steps: int = 10_000,
hwm: int = 100_000,
max_queue_size: int = 100_000,
topic: str = "",
) -> None:
# Storage
self._event_queue = Queue[Optional[EventBatch]](maxsize=max_queue_size)
self._buffer = deque[tuple[int, bytes]](maxlen=buffer_steps)
# ZMQ sockets
self._ctx = zmq.Context.instance()
self._pub: Optional[zmq.Socket] = None
self._replay: Optional[zmq.Socket] = None
self._endpoint = endpoint
self._replay_endpoint = replay_endpoint
self._hwm = hwm
self._socket_setup()
# Payload
self._seq_gen = count()
self._topic_bytes = topic.encode("utf-8")
# Thread
self._running = True
logger.info("Starting ZMQ publisher thread")
self._thread = threading.Thread(
target=self._publisher_thread, daemon=True, name="zmq-publisher"
)
self._thread.start()
atexit.register(self.shutdown)
def publish(self, events: EventBatch) -> None:
if not self._running:
raise RuntimeError("Publisher is closed")
self._event_queue.put(events)
def shutdown(self) -> None:
"""Stop the publisher thread and clean up resources."""
self._running = False
self._event_queue.put_nowait(None)
start = time.time()
pending_items = True
while pending_items and (time.time() - start < self.SHUTDOWN_TIMEOUT):
pending_items = not self._event_queue.empty()
if pending_items:
time.sleep(0.1)
if pending_items:
logger.warning(
"Warning: Queue still has %s items after %s seconds timeout",
self._event_queue.qsize(),
self.SHUTDOWN_TIMEOUT,
)
if self._thread.is_alive():
self._thread.join(timeout=self.SHUTDOWN_TIMEOUT)
# Clean up ZMQ resources
try:
if self._pub is not None:
self._pub.close(linger=0)
if self._replay is not None:
self._replay.close(linger=0)
finally:
pass # Do not terminate context; other sockets may use it
def _socket_setup(self) -> None:
"""Initialize sockets
https://pyzmq.readthedocs.io/en/v19.0.0/morethanbindings.html#thread-safety
"""
if self._pub is None:
self._pub = self._ctx.socket(zmq.PUB)
self._pub.set_hwm(self._hwm)
# Heuristic: bind if wildcard / * present, else connect.
# bind stable, connect volatile convention
if (
"*" in self._endpoint
or "::" in self._endpoint
or self._endpoint.startswith("ipc://")
or self._endpoint.startswith("inproc://")
):
self._pub.bind(self._endpoint)
else:
self._pub.connect(self._endpoint)
# Set up replay socket: use ROUTER
# 1) handles multiple REQ clients (identities)
# 2) lets us send back one request → many replies (streamed events)
# 3) works in our non‑blocking poll loop alongside PUB
if self._replay_endpoint is not None:
self._replay = self._ctx.socket(zmq.ROUTER)
self._replay.bind(self._replay_endpoint)
def _publisher_thread(self) -> None:
"""Background thread that processes the event queue."""
self._pack = msgspec.msgpack.Encoder()
assert self._pub is not None # narrows type for mypy
while self._running or self._event_queue.qsize() > 0:
# --- replay (non-critical) ---------------------------------
if self._replay is not None and self._replay.poll(0):
try:
self._service_replay()
except Exception as e:
logger.exception("Error in replay: %s", e)
# --- main queue (critical) ---------------------------------
try:
event = self._event_queue.get(timeout=0.1)
if event is None:
break # Sentinel received, exit thread
except queue.Empty:
continue
try:
seq = next(self._seq_gen)
payload = self._pack.encode(event)
seq_bytes = seq.to_bytes(8, "big")
self._pub.send_multipart((self._topic_bytes, seq_bytes, payload))
self._buffer.append((seq, payload))
self._event_queue.task_done()
except Exception as e:
# Publishing failed; back-off a bit to avoid a tight error loop
logger.exception("Error in publisher thread: %s", e)
time.sleep(0.1)
def _service_replay(self) -> None:
"""If a replay request is waiting, send buffered batches."""
assert self._replay is not None # narrows type for mypy
frame = self._replay.recv_multipart()
if len(frame) != 3:
logger.warning("Invalid replay request: %s", frame)
return
client_id, _, start_seq_bytes = frame
start_seq = int.from_bytes(start_seq_bytes, "big")
for seq, buf in self._buffer:
if seq >= start_seq:
# [identity, empty_delim, seq_bytes, payload]
# (identity, empty_delim) are stripped off by the router
# receiving payload is (seq_bytes, payload)
self._replay.send_multipart(
(client_id, b"", seq.to_bytes(8, "big"), buf)
)
# Send end of sequence marker
# receiving payload is (-1, b""")
self._replay.send_multipart((client_id, b"", self.END_SEQ, b""))
class KVEventsConfig(BaseModel):
"""Configuration for KV event publishing."""
publisher: str = "null"
"""The publisher to use for publishing kv events. Can be "null", "zmq".
"""
endpoint: str = "tcp://*:5557"
"""The zmq endpoint to use for publishing kv events.
"""
replay_endpoint: Optional[str] = None
"""The zmq endpoint to use for replaying kv events.
"""
buffer_steps: int = 10_000
"""The number of steps to cache for replay endpoint. Will only save
events from the last N steps for the replay endpoint.
"""
hwm: int = 100_000
"""The zmq high water mark for the event publisher. After queueing N events,
events will start dropping if the consumer is not keeping up.
"""
max_queue_size: int = 100_000
"""The maximum number of events to queue while waiting for publishing.
"""
topic: str = ""
"""The topic to use for the event publisher. Consumers can subscribe to
this topic to receive events.
"""
@classmethod
def from_cli(cls, cli_value: str) -> "KVEventsConfig":
"""Parse the CLI value for the event publisher config."""
return KVEventsConfig.model_validate_json(cli_value)
class EventPublisherFactory:
_registry: dict[str, Callable[..., EventPublisher]] = {
"null": NullEventPublisher,
"zmq": ZmqEventPublisher,
}
@classmethod
def register_publisher(cls, name: str, ctor: Callable[..., EventPublisher]) -> None:
if name in cls._registry:
raise KeyError(f"publisher '{name}' already registered")
cls._registry[name] = ctor
@classmethod
def create(cls, config: Optional[str]) -> EventPublisher:
"""Create publisher from a config mapping."""
if not config:
return NullEventPublisher()
config = KVEventsConfig.from_cli(config)
config_dict = config.model_dump()
kind = config_dict.pop("publisher", "null")
try:
constructor = cls._registry[kind]
except KeyError as exc:
raise ValueError(f"Unknown event publisher '{kind}'") from exc
return constructor(**config_dict)