[Bugfix][KV-transfer] MoRIIO READ-mode completion notification ID

[chaeminlim-mb]

Purpose

Fix the MoRI-IO READ-mode completion-notification protocol between the
consumer (decode) and producer (prefill) connector workers. Today, the
ID the consumer sends back to acknowledge a finished KV read does not
match what the producer expects to look up, and KVConnectorWorker
fails a scheduler-side assertion when the notification arrives.

Specifically, the consumer was sending its internal connector
transfer_id, while the producer's bookkeeping was keyed on the
scheduler's request_id. The mismatch surfaced as:

AssertionError  at vllm/v1/core/sched/scheduler.py:2057

…inside the prefill engine's request-finished path.

Change

vllm/distributed/kv_transfer/kv_connector/v1/moriio/:

• Consumer (moriio_connector.py, moriio_engine.py): when reading
  is complete, send the scheduler request_id as the completion
  notification ID (matches the toy-proxy convention vLLM already uses
  elsewhere — this is the ID embedded in the router's request_id and
  surfaced through kv_transfer_params).
• Producer (moriio_connector.py): translate the incoming
  request_id to its local transfer_id before calling
  kv_transfer.notify_kv_block, resolving the
  scheduler.py:2057 assertion.

The previously-iterated paths (a brief detour through
"send transfer_id (not req_id)" and its revert) are dropped — only
the final correct protocol remains.

Backward compatibility

The toy-proxy reference server already passes request_id through to
both sides via kv_transfer_params, so no proxy change is required.
Existing producer code that called notify_kv_block with a local
transfer_id still works (the new translation step is keyed on the
incoming consumer ID, which is now the scheduler request_id).

Not a duplicate of

• Fix engine_id collision + MoRIIO robustness for multi-node disagg DP #39276 — DP engine_id collision + kv_transfer_params caching;
  doesn't touch READ-mode notify.
• [Bugfix][KVConnector][NIXL] Sync engine_id across nodes for headless multi-node deployments #42928 — NIXL engine_id sync; different connector.

Searched on 2026-05-19 for MoRIIO read mode, notify_kv_block,
scheduler.py:2057, kv_transfer notify request_id — nothing else
targets this assertion or the consumer/producer ID mismatch.

Test Plan

Lint

pre-commit run --files \
  vllm/distributed/kv_transfer/kv_connector/v1/moriio/moriio_connector.py \
  vllm/distributed/kv_transfer/kv_connector/v1/moriio/moriio_engine.py

Unit

.venv/bin/python -m pytest tests/v1/kv_connector/unit/test_moriio_connector.py -v

End-to-end (MoRI-IO 1P1D, READ mode)

# Proxy
python3 examples/disaggregated/disaggregated_serving/moriio_toy_proxy_server.py \
  --port 10001 &

# Prefill (kv_role=kv_producer)
python3 -m vllm.entrypoints.openai.api_server \
  --model meta-llama/Llama-3.1-8B-Instruct --served-model-name llama \
  --host 0.0.0.0 --port 8100 \
  --kv-transfer-config '{"kv_connector":"MoRIIOConnector","kv_role":"kv_producer","kv_connector_extra_config":{"proxy_ip":"127.0.0.1","proxy_port":36367,"proxy_ping_port":36367,"http_port":8100,"handshake_port":6301,"notify_port":61005}}' &

# Decode (kv_role=kv_consumer) — analogous, port 8200, separate proxy reg

# Drive enough requests to force more than one READ-mode KV transfer
.venv/bin/python -m vllm.entrypoints.openai.benchmark_serving \
  --backend openai-chat --base-url http://127.0.0.1:10001 \
  --endpoint /v1/chat/completions --model llama \
  --dataset-name random --random-input-len 1024 --random-output-len 128 \
  --num-prompts 200 --max-concurrency 8

Without this PR, the prefill engine asserts at
scheduler.py:2057 after the first read completes. With the PR, the
bench finishes 200/200.

Test Result

(To fill in before marking ready for review.)

• Lint: pre-commit → Passed locally (ruff / format / mypy clean).
• Unit: pytest tests/v1/kv_connector/unit/test_moriio_connector.py → …
• Repro: 200-prompt READ-mode bench finishes 200/200 (vs. assertion
  failure after a single transfer pre-fix). Engine log to attach.

AI assistance disclosure

This change was drafted with AI assistance (Claude Code). The diff is
~95 lines across 2 files. I (chaemin.lim@mangoboost.io) have reviewed
and defend each changed line; the consumer/producer ID convention
chosen matches the toy-proxy contract already documented in
examples/disaggregated/disaggregated_serving/moriio_toy_proxy_server.py,
not a new ad-hoc protocol.

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[gemini-code-assist]

Code Review

This pull request updates the MoRIIO connector to handle request ID translation between producers and consumers using a transfer_id, ensuring compatibility when internal request IDs differ. It also modifies the notification listener to accept any UTF-8 payload as a completion message. Feedback identifies two critical issues: a memory leak in the consumer-side mapping during READ mode because entries are never popped, and a potential crash of the notification listener thread if it receives non-UTF-8 data, as the error handling currently falls through to raise a fatal exception.

[gemini-code-assist]

In READ mode, the consumer-side mapping in transfer_id_to_request_id is never removed because _pop_done_transfers returns an empty set, which causes the translation and cleanup block in get_finished (lines 1288-1293) to be skipped. This results in a memory leak as the mapping grows indefinitely with every request. The entry should be popped here once the notification is successfully sent.

Suggested change

	self.moriio_wrapper.send_notify(
	req_id,
	transfer_id,
	self._recving_transfers_callback_addr[req_id][0],
	self._recving_transfers_callback_addr[req_id][1],
	)
	self.moriio_wrapper.send_notify(
	transfer_id,
	self._recving_transfers_callback_addr[req_id][0],
	self._recving_transfers_callback_addr[req_id][1],
	)
	self.transfer_id_to_request_id.pop(transfer_id, None)

[gemini-code-assist]

If a message cannot be decoded as UTF-8, a warning is logged but handled remains False. This causes the code to fall through and raise a MoRIIOError, which is caught in the listener loop and re-raised as a HandshakeError, ultimately terminating the notification listener thread. The function should return early after logging the warning to prevent the listener from crashing on malformed input.

Suggested change

	except UnicodeDecodeError:
	logger.warning("Received non-UTF8 message: %s", msg_str)
	logger.warning("Received non-UTF8 completion message of %d bytes", len(msg))
	except UnicodeDecodeError:
	logger.warning("Received non-UTF8 completion message of %d bytes", len(msg))
	return

[simondanielsson]

Think this might be a duplicate of #40344

[chaeminlim-mb]

Thanks @simondanielsson — you're right. #40344 covers the same scheduler.py:2057 assertion and addresses it as part of a broader high-concurrency MoRIIO hang fix that also handles Failed() transfers, busy-spin deadlines, the WRITE-mode race, and KV-block reaping. Closing this in favor of #40344. We'll cherry-pick that branch into our downstream image and report back on our 1P1D TP=16 workload.

[simondanielsson]

@chaeminlim-mb Sounds good - would you mind writing a comment on that PR to highlight that your team is also interested in having that PR merged? That would hopefully help getting it does more quickly 👍 Thanks