vllm.distributed.kv_transfer.kv_connector.v1.lmcache_mp_connector ¶

class LMCacheMPConnector(KVConnectorBase_V1):
    """
    The connector for LMCache multi-process mode.

    Extra configs (kv_transfer_config.extra_config):
    - lmcache.mp.host: the host of the LMCache server.
    - lmcache.mp.port: the port of the LMCache server.
    """

    def __init__(
        self,
        vllm_config: "VllmConfig",
        role: KVConnectorRole,
        kv_cache_config: "KVCacheConfig | None" = None,
    ):
        super().__init__(vllm_config, role, kv_cache_config)

        assert vllm_config.kv_transfer_config is not None
        server_host = vllm_config.kv_transfer_config.get_from_extra_config(
            "lmcache.mp.host", "tcp://localhost"
        )
        server_port = vllm_config.kv_transfer_config.get_from_extra_config(
            "lmcache.mp.port", 5555
        )

        server_url = f"{server_host}:{server_port}"
        zmq_context = zmq.Context.instance()
        if self.role == KVConnectorRole.SCHEDULER:
            self.scheduler_adapter = create_scheduler_adapter(
                server_url, zmq_context, vllm_config
            )
            self.request_trackers: dict[str, LMCacheMPRequestTracker] = {}
        elif self.role == KVConnectorRole.WORKER:
            self.worker_adapter = create_worker_adapter(
                server_url, zmq_context, vllm_config
            )
        else:
            raise ValueError(f"Unknown KVConnectorRole: {self.role}")

        self.vllm_block_size = vllm_config.cache_config.block_size

    @property
    def role(self) -> KVConnectorRole:
        return self._role

    # ==============================
    # Worker-side methods
    # ==============================

    def _get_connector_metadata(self) -> KVConnectorMetadata:
        """Get the connector metadata.

        This function should only be called inside the connector.

        Returns:
            ConnectorMetadata: the connector metadata.
        """

        # Should only be called while set to valid metadata.
        assert self._connector_metadata is not None
        return self._connector_metadata

    def register_kv_caches(self, kv_caches: dict[str, torch.Tensor]):
        """
        Initialize with the KV caches. Useful for pre-registering the
        KV Caches in the KVConnector (e.g. for NIXL).

        Args:
            kv_caches: dictionary of layer names, kv cache
        """
        logger.info("Registering kv caches!")
        self.worker_adapter.register_kv_caches(kv_caches)
        return

    def start_load_kv(self, forward_context: "ForwardContext", **kwargs: Any) -> None:
        """
        Start loading the KV cache from the connector to vLLM's paged
        KV buffer. This is called from the forward context before the
        forward pass to enable async loading during model execution.

        Args:
            forward_context (ForwardContext): the forward context.
            **kwargs: additional arguments for the load operation

        Note:
            The number of elements in kv_caches and layer_names should be
            the same.

        """
        metadata = self._get_connector_metadata()
        assert isinstance(metadata, LMCacheMPConnectorMetadata)

        request_ids = []
        ops = []

        for meta in metadata.requests:
            if meta.direction != "RETRIEVE":
                continue
            request_ids.append(meta.request_id)
            ops.append(meta.op)

        if len(request_ids) == 0:
            return

        with torch.cuda.stream(torch.cuda.current_stream()):
            event = torch.cuda.Event(interprocess=True)
            event.record()

        self.worker_adapter.batched_submit_retrieve_requests(request_ids, ops, event)

    def wait_for_layer_load(self, layer_name: str) -> None:
        """
        Block until the KV for a specific layer is loaded into vLLM's
        paged buffer. This is called from within attention layer to ensure
        async copying from start_load_kv is complete.

        This interface will be useful for layer-by-layer pipelining.

        Args:
            layer_name: the name of that layer
        """
        return

    def save_kv_layer(
        self,
        layer_name: str,
        kv_layer: torch.Tensor,
        attn_metadata: AttentionMetadata,
        **kwargs: Any,
    ) -> None:
        """
        Start saving a layer of KV cache from vLLM's paged buffer
        to the connector. This is called from within attention layer to
        enable async copying during execution.

        Args:
            layer_name (str): the name of the layer.
            kv_layer (torch.Tensor): the paged KV buffer of the current
                layer in vLLM.
            attn_metadata (AttentionMetadata): the attention metadata.
            **kwargs: additional arguments for the save operation.
        """
        return

    def wait_for_save(self):
        """
        Block until all the save operations is done. This is called
        as the forward context exits to ensure that the async saving
        from save_kv_layer is complete before finishing the forward.

        This prevents overwrites of paged KV buffer before saving done.
        """
        metadata = self._get_connector_metadata()
        assert isinstance(metadata, LMCacheMPConnectorMetadata)

        request_ids = []
        ops = []
        for meta in metadata.requests:
            if meta.direction != "STORE":
                continue
            request_ids.append(meta.request_id)
            ops.append(meta.op)

        if len(request_ids) == 0:
            return

        with torch.cuda.stream(torch.cuda.current_stream()):
            event = torch.cuda.Event(interprocess=True)
            event.record()

        self.worker_adapter.batched_submit_store_requests(request_ids, ops, event)

    def get_finished(
        self, finished_req_ids: set[str]
    ) -> tuple[set[str] | None, set[str] | None]:
        """
        Notifies worker-side connector ids of requests that have
        finished generating tokens on the worker.
        The scheduler process (via the Executors) will use this output
        to track which workers are done.

        Returns:
            ids of requests that have finished asynchronous transfer
            (requests that previously returned True from request_finished()),
            tuple of (sending/saving ids, recving/loading ids).
            The finished saves/sends req ids must belong to a set provided in a
            call to this method (this call or a prior one).
        """
        val = self.worker_adapter.get_finished(finished_req_ids)
        # logger.error("Finished req ids: %s, %s", val[0], val[1])
        return val

    def get_block_ids_with_load_errors(self) -> set[int]:
        """
        Get the set of block IDs that failed to load.

        Returns:
            Set of block IDs that encountered load errors.
            Empty set if no load errors occurred.

        Notes:
            - Applies to both sync- and async-loading requests.
            - Async loading: failed blocks may be reported in any forward pass
              up to and including the pass where the request ID is returned by
              `get_finished()`. Even if failures occur, the request must still
              be reported via `get_finished()`, and the failed block IDs must
              appear here no later than that same pass.
            - Sync loading: failed blocks should be reported in the forward
              pass in which they are detected.
        """
        # TODO: add error tracking
        return set()

    def shutdown(self):
        """
        Shutdown the connector. This is called when the worker process
        is shutting down to ensure that all the async operations are
        completed and the connector is cleaned up properly.
        """
        if hasattr(self, "worker_adapter"):
            self.worker_adapter.shutdown()
        return None

    def get_kv_connector_stats(self) -> "KVConnectorStats | None":
        """
        Get the KV connector stats collected during the last interval.
        """
        return None

    # ==============================
    # Scheduler-side methods
    # ==============================

    def get_num_new_matched_tokens(
        self,
        request: "Request",
        num_computed_tokens: int,
    ) -> tuple[int | None, bool]:
        """
        Get number of new tokens that can be loaded from the
        external KV cache beyond the num_computed_tokens.

        Args:
            request (Request): the request object.
            num_computed_tokens (int): the number of locally
                computed tokens for this request

        Returns:
            A tuple with the following elements:
                - An optional number of tokens that can be loaded from the
                  external KV cache beyond what is already computed.
                  If None, it means that the connector needs more time to
                  determine the number of matched tokens, and the scheduler
                  should query for this request again later.
                - `True` if external KV cache tokens will be loaded
                  asynchronously (between scheduler steps). Must be
                  'False' if the first element is 0.

        Notes:
            The connector should only consider the largest prefix of prompt-
            tokens for which KV cache is actually available at the time of the
            call. If the cache cannot be loaded for some tokens (e.g., due to
            connectivity issues or eviction), those tokens must not be taken
            into account.
        """
        tracker = self._get_or_create_request_tracker(request)
        # TODO: support loading KV for preempted requests in the future
        if request.status == RequestStatus.PREEMPTED:
            return 0, False

        self.scheduler_adapter.maybe_submit_lookup_request(
            request.request_id,
            token_ids=list(request.all_token_ids),
        )

        ret = self.scheduler_adapter.check_lookup_result(request.request_id)
        if ret is None:
            return None, True

        if ret == 0:
            return 0, False

        assert (
            ret % (self.scheduler_adapter.num_blocks_per_chunk() * self.vllm_block_size)
            == 0
        )

        # Update num stored blocks for the tracker
        num_vllm_blocks = num_computed_tokens // self.vllm_block_size
        num_lmcache_blocks = ret // self.vllm_block_size
        tracker.increase_num_stored_blocks(num_lmcache_blocks)

        # Save the vllm and lmcache hit tokens
        tracker.num_vllm_hit_blocks = num_vllm_blocks
        tracker.num_lmcache_hit_blocks = num_lmcache_blocks

        need_to_load = max(0, ret - num_computed_tokens)
        logger.debug(
            "vLLM hit is: %d, Need to load is %d", num_computed_tokens, need_to_load
        )
        return need_to_load, need_to_load > 0

    def update_state_after_alloc(
        self, request: "Request", blocks: "KVCacheBlocks", num_external_tokens: int
    ):
        """
        Update KVConnector state after block allocation.

        If get_num_new_matched_tokens previously returned True for a
        request, this function may be called twice for that same request -
        first when blocks are allocated for the connector tokens to be
        asynchronously loaded into, and second when any additional blocks
        are allocated, after the load/transfer is complete.

        Args:
            request (Request): the request object.
            blocks (KVCacheBlocks): the blocks allocated for the request.
            num_external_tokens (int): the number of tokens that will be
                loaded from the external KV cache.
        """
        # NOTE: `blocks` comes from kv_cache_manager.get_blocks(request_id),
        # which returns ALL blocks for the request (not just newly allocated).
        # This function may be called twice for async-load requests:
        #   1st call: blocks = initial allocation (APC + fresh)
        #   2nd call: blocks = all blocks
        #  (initial + newly allocated for remaining tokens)
        # We must only append the NEW blocks beyond what's already tracked
        # to avoid duplication, which would corrupt the store path's block indexing.
        tracker = self._get_request_tracker(request.request_id)
        block_ids = reformat_block_ids(blocks.get_block_ids())

        # Only append blocks beyond what's already tracked
        existing_count = len(tracker.allocated_block_ids)
        new_block_ids = block_ids[existing_count:]
        if new_block_ids:
            tracker.append_block_ids(new_block_ids)

        # Update the state of the tracker
        condition = tracker.needs_retrieve()
        if tracker.state == LMCacheMPRequestState.PREFETCHING:
            # If need to retrieve, change to WAITING_FOR_LOAD
            # Otherwise, change to READY
            tracker.state = (
                LMCacheMPRequestState.WAITING_FOR_LOAD
                if condition
                else LMCacheMPRequestState.READY
            )
            # Clean up lookup future in scheduler adapter
            self.scheduler_adapter.cleanup_lookup_result(request.request_id)

            # Free locks on chunks that vLLM already computed and won't
            # retrieve from LMCache.
            if tracker.num_lmcache_hit_blocks > 0:
                if not condition:
                    # No retrieve needed — free ALL locked chunks
                    free_end = tracker.num_lmcache_hit_blocks * self.vllm_block_size
                else:
                    # Note(Roy): Boundary misalignment between vLLM blocks and LMCache
                    # blocks is handled in free_lookup_locks. It makes sure that if
                    # the last vLLM computed block ends in the middle of a LMCache
                    # block, the end LMCache block is not freed (i.e., floor division)
                    # since it will still be needed by vLLM and such block's lock will
                    # be freed by vLLM's retrieve.
                    free_end = tracker.num_vllm_hit_blocks * self.vllm_block_size

                if free_end > 0:
                    self.scheduler_adapter.free_lookup_locks(
                        token_ids=list(tracker.all_token_ids),
                        start=0,
                        end=free_end,
                        request_id=request.request_id,
                    )
                    logger.debug(
                        "Free locks of tokens %d-%d since it is cached by vLLM.",
                        0,
                        free_end,
                    )

    def build_connector_meta(
        self, scheduler_output: SchedulerOutput
    ) -> KVConnectorMetadata:
        """
        Build the connector metadata for this step.

        This function should NOT modify fields in the scheduler_output.
        Also, calling this function will reset the state of the connector.

        Args:
            scheduler_output (SchedulerOutput): the scheduler output object.
        """
        metadata = LMCacheMPConnectorMetadata()

        self._process_retrieve_requests(metadata)
        self._process_new_requests(scheduler_output, metadata)
        self._process_cached_requests(scheduler_output, metadata)

        if len(metadata) > 0:
            logger.debug("Final connector metadata: %s", metadata)

        return metadata

    def update_connector_output(self, connector_output: KVConnectorOutput):
        """
        Update KVConnector state from worker-side connectors output.

        Args:
            connector_output (KVConnectorOutput): the worker-side
                connectors output.
        """
        return

    def request_finished(
        self,
        request: "Request",
        block_ids: list[int],
    ) -> tuple[bool, dict[str, Any] | None]:
        """
        Called exactly once when a request has finished, before its blocks are
        freed.

        The connector may assumes responsibility for freeing the blocks
        asynchronously by returning True.

        Returns:
            True if the request is being saved/sent asynchronously and blocks
            should not be freed until the request_id is returned from
            get_finished().
            Optional KVTransferParams to be included in the request outputs
            returned by the engine.
        """
        # Clean up request tracker to prevent memory leak
        self._cleanup_request_tracker(request.request_id)
        # Notify LMCache to end the session for this request
        self.scheduler_adapter.end_session(request.request_id)

        return True, None

    def take_events(self) -> Iterable["KVCacheEvent"]:
        """
        Take the KV cache events from the connector.

        Yields:
            New KV cache events since the last call.
        """
        return ()

    @classmethod
    def get_required_kvcache_layout(cls, vllm_config: "VllmConfig") -> str | None:
        """
        Get the required KV cache layout for this connector.
        Args:
            vllm_config (VllmConfig): the vllm config.

        Returns:
            str: the required KV cache layout. e.g. HND, or NHD.
            None if the connector does not require a specific layout.
        """

        if cls is KVConnectorBase_V1:
            raise TypeError(
                "get_required_kvcache_layout should not be called "
                "on the abstract base class"
            )
        return None

    def get_finished_count(self) -> int | None:
        """
        Get the count of requests expected to complete send/receive operations
        via this connector. This method is used to initialize the
        KVOutputAggregator, overwriting the default world_size.

        Returns:
            int: expected sending or receiving completion count.
        """
        return None

    @classmethod
    def build_kv_connector_stats(
        cls, data: dict[str, Any] | None = None
    ) -> "KVConnectorStats | None":
        """
        KVConnectorStats resolution method. This method allows dynamically
        registered connectors to return their own KVConnectorStats object,
        which can implement custom aggregation logic on the data dict.
        """
        return None

    @classmethod
    def build_prom_metrics(
        cls,
        vllm_config: "VllmConfig",
        metric_types: dict[type["PromMetric"], type["PromMetricT"]],
        labelnames: list[str],
        per_engine_labelvalues: dict[int, list[object]],
    ) -> "KVConnectorPromMetrics | None":
        """
        Create a KVConnectorPromMetrics subclass which should register
        per-connector Prometheus metrics and implement observe() to
        expose connector transfer stats via Prometheus.
        """
        return None

    ##############################
    # Helper functions
    ##############################
    def _process_retrieve_requests(
        self,
        metadata: LMCacheMPConnectorMetadata,
    ) -> None:
        blocks_per_chunk = self.scheduler_adapter.num_blocks_per_chunk()

        for request_tracker in self.request_trackers.values():
            if request_tracker.state != LMCacheMPRequestState.WAITING_FOR_LOAD:
                continue
            r_metadata = LMCacheMPRequestMetadata.GetRetrieveMetadata(
                request_tracker,
                blocks_per_chunk,
                vllm_block_size=self.vllm_block_size,
            )
            if r_metadata is not None:
                metadata.add_request_metadata(r_metadata)
            request_tracker.state = LMCacheMPRequestState.READY

    def _process_new_requests(
        self,
        scheduler_output: SchedulerOutput,
        metadata: LMCacheMPConnectorMetadata,
    ) -> None:
        blocks_per_chunk = self.scheduler_adapter.num_blocks_per_chunk()

        for new_request in scheduler_output.scheduled_new_reqs:
            request_tracker = self._get_request_tracker(new_request.req_id)

            num_new_tokens = scheduler_output.num_scheduled_tokens[new_request.req_id]
            request_tracker.increase_num_scheduled_tokens(num_new_tokens)

            r_meta = LMCacheMPRequestMetadata.GetStoreMetadata(
                request_tracker, blocks_per_chunk, self.vllm_block_size
            )
            if r_meta is not None:
                metadata.add_request_metadata(r_meta)

    def _process_cached_requests(
        self,
        scheduler_output: SchedulerOutput,
        metadata: LMCacheMPConnectorMetadata,
    ) -> None:
        blocks_per_chunk = self.scheduler_adapter.num_blocks_per_chunk()

        cached_reqs = scheduler_output.scheduled_cached_reqs
        for idx, request_id in enumerate(cached_reqs.req_ids):
            request_tracker = self._get_request_tracker(request_id)

            # Update block ids
            new_block_ids = reformat_block_ids(cached_reqs.new_block_ids[idx])
            if request_id not in cached_reqs.resumed_req_ids:
                request_tracker.append_block_ids(new_block_ids)

            # Update new scheduled tokens
            num_new_tokens = cached_reqs.num_computed_tokens[idx]
            request_tracker.increase_num_scheduled_tokens(num_new_tokens)

            r_meta = LMCacheMPRequestMetadata.GetStoreMetadata(
                request_tracker, blocks_per_chunk, self.vllm_block_size
            )

            if r_meta is not None:
                metadata.add_request_metadata(r_meta)

    def _get_request_tracker(self, request_id: str) -> LMCacheMPRequestTracker:
        assert request_id in self.request_trackers, (
            f"Request tracker for request_id {request_id} not found. "
        )
        return self.request_trackers[request_id]

    def _get_or_create_request_tracker(
        self, request: "Request"
    ) -> LMCacheMPRequestTracker:
        request_id = request.request_id
        # Remove the old trackers that is created before the preemption
        if (
            request.status == RequestStatus.PREEMPTED
            and request_id in self.request_trackers
        ):
            tracker = self.request_trackers[request_id]

            # NOTE: since this function may be called multiple times
            # for a single request (because get_num_new_matched_tokens
            # may be called multiple times) for the same request, we
            # will only do the remove if the tracker is not in the "fresh"
            # state, i.e., PREFETCHING
            if tracker.state != LMCacheMPRequestState.PREFETCHING:
                self.request_trackers.pop(request_id)

        if request_id not in self.request_trackers:
            new_tracker = LMCacheMPRequestTracker(request)
            self.request_trackers[request_id] = new_tracker
        return self.request_trackers[request_id]

    def _cleanup_request_tracker(self, request_id: str) -> None:
        """
        Clean up request tracker and associated lookup future for a request.
        This should be called when a request is finished to prevent memory leak.
        """
        # Clean up request tracker
        if self.request_trackers.pop(request_id, None):
            logger.debug(
                "[KVConnector] Cleaned up request_tracker for request %s",
                request_id,
            )