[Bugfix][ROCm][P/D][MoRIIO] Read-mode KV-release + best_of_n fixes

[crazyguitar]

Summary

Fixes two MoRIIO XGMI READ-mode P/D bugs that hit under parallel sampling (n > 1) and high concurrency:

1. FIX(best_of-1many) — n best_of siblings share ONE transfer_id (the proxy mints one per prompt; vLLM fans n into siblings 0_..k_). transfer_id_to_request_id was a 1:1 dict that clobbered all but the last sibling, so the single write-completion released only one and the other n − 1 hung Deferred forever on the decode.
2. FIX(read-release) — on read-complete the decode notified the prefill with its LOCAL req_id (with a -N-XXXX suffix the prefill doesn't own), so the prefill couldn't match and free the held KV → prefill GPU KV cache pins ~100% and the engine hangs. The fix sends the SHARED transfer_id instead and gates the release on vLLM's finished_req_ids (is_finished-safe; avoids tripping the scheduler's assert req_id in self.requests).

Validated end-to-end on AMD MI3xx, MoRIIO XGMI READ, Qwen2.5-7B fp8, best_of_n=8: 1p3d (TP=1 × 4) and 1p1d_2tp (homogeneous TP=2) — no leaks, no engine hangs, KV drains between batches.

Why this is not duplicating an existing PR

Searched open / merged PRs for MoRIIO best_of, MoRIIO parallel sampling, MoRIIO KV leak, MoriioConnector READ, moriio_connector get_finished, transfer_id_to_request_id. Closest matches:

• [ROCm] Add XGMI backend for MoRI Connector #41753 (merged) adds the XGMI backend selection this PR builds on top of. Does not touch the release / best_of paths.
• [Bugfix][NIXL] Fix best_of_n KV leak and early-notification race in P/D #43509 same root cause (siblings sharing one transfer_id) on the NIXL connector. This PR is the MoRIIO analog with a different fix shape (1:many scheduler map + finished-gated worker release, since MoRIIO uses a different release protocol).
• [Fix][MoRI] Align MoRI-IO message format with P2pNcclConnector and vllm-router #39565 (merged) different layer (zmq wire format).
• fix(mooncake): resolve HBM leak from stuck WAITING_FOR_REMOTE_KVS requests #36014 same leak pattern, different connector.

No existing PR covers the MoRIIO best_of_n fan-out or the READ-mode release protocol.

Purpose

Two related bug fixes to the MoRIIO XGMI READ-mode P/D release path that together resolve an engine hang under parallel sampling (n > 1 / best_of_n > 1) and a prefill KV leak from un-matched read-complete notifications.

1. FIX(best_of-1many) — n > 1 decode hang

Under parallel sampling vLLM expands one prompt into n sibling requests f"{i}_{parent}" (vllm/v1/engine/parallel_sampling.py:92). All n siblings share the SAME transfer_id (the proxy mints exactly one per client prompt). MoRIIOConnectorScheduler.map_request_id was a plain 1:1 dict assignment, so siblings clobbered each other and only the last survived in transfer_id_to_request_id. The single write-completion per transfer_id then released only that one sibling; the other n − 1 stayed Deferred on the decode forever (Running 0 / Waiting n−1 → hang).

Before:

  PREFILL                                   DECODE (n=8)
  ┌──────────────────────────┐              ┌──────────────────────────┐
  │ map_request_id called    │              │ scheduler maps siblings  │
  │  8 times with shared tid │              │  to the same shared tid; │
  │  tx-d1f3 → CLOBBERED to  │              │  decode pulls KV for one │
  │  the LAST sibling only   │ ───KV────►   │  sibling (others served  │
  │                          │              │  by prefix cache)        │
  │ on write-complete:       │ ◄──notif:    │ send read-complete       │
  │  get_finished returns    │  tx-d1f3 ────│                          │
  │  ONLY the last sibling   │              └──────────────────────────┘
  │                          │
  │ other 7 siblings stuck   │
  │ Deferred → prefill KV    │
  │ ~100% → engine hangs     │
  └──────────────────────────┘

After:

  PREFILL                                   DECODE (n=8)
  ┌──────────────────────────┐              ┌──────────────────────────┐
  │ map_request_id appends   │              │ pull KV (one shared      │
  │  each sibling under the  │ ───KV────►   │  prompt write serves     │
  │  shared tx-d1f3:         │              │  all n siblings)         │
  │  {0_,1_,...,7_}_cmpl...  │ ◄──notif:    │                          │
  │                          │  tx-d1f3 ────│                          │
  │ on write-complete:       │              └──────────────────────────┘
  │  one tid → release ALL   │
  │  its siblings; KV drains │
  └──────────────────────────┘

unmap_request_id drops one sibling at a time and only removes the transfer_id key when its last sibling is gone.

2. FIX(read-release) — prefill held-KV leak in READ mode

In MoRIIO XGMI READ mode the decode pulls the KV from the prefill (vs WRITE mode where the prefill pushes). On read-complete the decode needs to notify the prefill so it can free the held KV. Stock code sent the decode's LOCAL request_id (e.g. 0_cmpl-...-N-XXXX with the per-sibling suffix the prefill never owned). The prefill received an id it couldn't match against any local req → the held KV stayed pinned until the connector's expiry timer fired, capping concurrency and eventually pinning prefill GPU KV cache at ~100%.

Two complications make the fix non-trivial:

• The scheduler calls unmap_request_id in request_finished BEFORE the decode's read-complete notify arrives, so by the time we try to look up the sibling's transfer_id it's already gone. We capture sibling → transfer_id proactively in start_load_kv (BEFORE any unmap) into a worker-persistent _read_req_tid.
• Releasing siblings the moment a read-complete notify arrives trips the scheduler's assert req_id in self.requests in _update_from_kv_xfer_finished on reqs that have already been freed (delay_free=False) or never delay-freed. We gate the release on vLLM's finished_req_ids (the is_finished signal) and persist accumulated done-tids + finished-seen so late-finishing siblings free on a later step.

Before:

  PREFILL                                   DECODE
  ┌──────────────────────────┐              ┌──────────────────────────┐
  │ scheduler unmaps         │              │ pull KV for              │
  │  0_cmpl-...-N-XXXX at    │ ◄──notif:    │  0_cmpl-...-N-XXXX       │
  │  request_finished        │  0_cmpl-... ─│                          │
  │                          │              │                          │
  │ get_finished: bare       │              │                          │
  │  req_id can't be mapped  │              │                          │
  │  back to a held req →    │              │                          │
  │  no free → KV stranded   │              └──────────────────────────┘
  │  until expiry, prefill   │
  │  pins ~100% → hang       │
  └──────────────────────────┘

After:

  PREFILL                                   DECODE
  ┌──────────────────────────┐              ┌──────────────────────────┐
  │ start_load_kv: capture   │              │ at read setup, capture   │
  │  sibling → tid into      │              │  shared tid (tx-d1f3)    │
  │  _read_req_tid BEFORE    │              │  into _recving_transfer  │
  │  unmap; promote into     │              │  _id[req]                │
  │  _read_sibs on delay-    │              │                          │
  │  free                    │              │                          │
  │                          │              │ on read-complete:        │
  │ get_finished READ:       │ ◄──notif:    │  send SHARED tid (not    │
  │  receive shared tid,     │  tx-d1f3 ────│  local req_id)           │
  │  release siblings gated  │              │                          │
  │  on vLLM finished signal │              └──────────────────────────┘
  │  → KV drains             │
  └──────────────────────────┘

Consumer READ-mode done_recving is intentionally discarded: MoRIIO READ is synchronous (get_num_new_matched_tokens returns load_kv_async=False) so reqs never enter WAITING_FOR_REMOTE_KVS. The internal _pop_done_transfers return is consumed to drive send_notify; passing it on to the scheduler trips _update_from_kv_xfer_finished's assert is_finished(req.status) on reqs that are still RUNNING.

Test Plan

Unit tests

5 new tests in tests/v1/kv_connector/unit/test_moriio_connector.py that isolate the new behavior using MoRIIOConnectorWorker.__new__ + MagicMock (no real network, no real MoRIIO/XGMI session needed):

• test_best_of_n_map_accumulates_siblings
• test_consumer_write_mode_fans_out_completion
• test_consumer_read_mode_discards_done_recving
• test_producer_read_mode_finished_gated_release
• test_pop_done_transfers_sends_shared_transfer_id

Skipped on non-ROCm / no-mori platforms (matches the file's existing pytestmark).

pytest tests/v1/kv_connector/unit/test_moriio_connector.py -v

End-to-end

End-to-end validation on AMD MI3xx, MoRIIO over XGMI in READ mode, Qwen2.5-7B fp8, best_of_n=8, --no-enable-prefix-caching on serving workers (required for MoRIIO READ-mode P/D — a prefill served from its prefix cache produces no remote blocks for the decode to pull). Topologies:

• 1p3d (TP=1 × 4) — 1 prefill + 3 decode; exercises the best_of fan-out + read-release paths at TP=1.
• 1p1d_2tp (homogeneous TP=2) — prefill TP=2 + decode TP=2; exercises per-rank notify wiring and cross-rank _read_sibs accounting.

Repro scripts (1p3d/run.sh)

#!/usr/bin/env bash
# 1p3d (AMD MI3xx, MoRIIOConnector / XGMI, READ mode) — 1 toy proxy + 1 prefill + 3 decode.
set -o pipefail

cd "$(dirname "${BASH_SOURCE[0]}")"
mkdir -p logs && rm -f logs/*.log
touch logs/proxy.log logs/prefill_0.log logs/decode_{0,1,2}.log

PIDS=()
trap 'echo; echo "[run] stopping..."; kill "${PIDS[@]:-}" 2>/dev/null; pkill -P $$ 2>/dev/null; wait 2>/dev/null; exit' INT TERM

PROXY=$(find /vllm-workspace /app /workspace /opt /usr/local /code /root -maxdepth 8 \
    -name 'moriio_toy_proxy_server.py' -print -quit 2>/dev/null || true)
[ -f "$PROXY" ] || { echo "ERROR: moriio_toy_proxy_server.py not found." >&2; exit 1; }

export VLLM_ROCM_USE_AITER=1 MORI_IO_ENABLE_NOTIFICATION=0 VLLM_MORIIO_CONNECTOR_READ_MODE=1
export VLLM_USE_TRITON_AWQ=1 VLLM_ROCM_USE_AITER_MOE=1 AITER_ONLINE_TUNE=1

MODEL=Qwen/Qwen2.5-7B-Instruct
COMMON=(
    --tensor-parallel-size 1
    --gpu-memory-utilization 0.85
    --max-model-len 10240
    --max-num-batched-tokens 32768
    --max-num-seqs 128
    --no-enable-prefix-caching
    --trust-remote-code
    --kv-cache-dtype fp8
)

kv() {  # args: kv_role http_port handshake_port notify_port
    printf '{"kv_connector":"MoRIIOConnector","kv_role":"%s","kv_connector_extra_config":{"backend":"xgmi","proxy_ip":"127.0.0.1","proxy_ping_port":"36367","http_port":"%s","handshake_port":"%s","notify_port":"%s"}}' "$@"
}

python "$PROXY" --port 10001 > logs/proxy.log 2>&1 & PIDS+=($!)

HIP_VISIBLE_DEVICES=0 CUDA_VISIBLE_DEVICES=0 \
    vllm serve "$MODEL" "${COMMON[@]}" \
        --host 0.0.0.0 --port 8100 --kv-transfer-config "$(kv kv_producer 8100 6300 6100)" \
    > logs/prefill_0.log 2>&1 & PIDS+=($!)

for i in 0 1 2; do
    HIP_VISIBLE_DEVICES=$((i+1)) CUDA_VISIBLE_DEVICES=$((i+1)) \
        vllm serve "$MODEL" "${COMMON[@]}" \
            --host 0.0.0.0 --port $((8200+i)) \
            --kv-transfer-config "$(kv kv_consumer $((8200+i)) $((7300+i*10)) $((7500+i*10)))" \
        > logs/decode_${i}.log 2>&1 & PIDS+=($!)
done

echo "[run] launched ${#PIDS[@]} services — tailing logs (Ctrl-C to stop)"
tail -F logs/*.log

Repro scripts (1p1d_2tp/run.sh, homogeneous TP=2)

#!/usr/bin/env bash
# 1p1d homogeneous TP=2 (AMD MI3xx, MoRIIO/XGMI READ mode) — prefill TP=2 + decode TP=2.
set -o pipefail

cd "$(dirname "${BASH_SOURCE[0]}")"
mkdir -p logs && rm -f logs/*.log
touch logs/proxy.log logs/prefill_0.log logs/decode_0.log

PIDS=()
trap 'echo; echo "[run] stopping..."; kill "${PIDS[@]:-}" 2>/dev/null; pkill -P $$ 2>/dev/null; wait 2>/dev/null; exit' INT TERM

PROXY=$(find /vllm-workspace /app /workspace /opt /usr/local /code /root -maxdepth 8 \
    -name 'moriio_toy_proxy_server.py' -print -quit 2>/dev/null || true)
[ -f "$PROXY" ] || { echo "ERROR: moriio_toy_proxy_server.py not found." >&2; exit 1; }

export VLLM_ROCM_USE_AITER=1 MORI_IO_ENABLE_NOTIFICATION=0 VLLM_MORIIO_CONNECTOR_READ_MODE=1
export VLLM_USE_TRITON_AWQ=1 VLLM_ROCM_USE_AITER_MOE=1 AITER_ONLINE_TUNE=1

MODEL=Qwen/Qwen2.5-7B-Instruct
COMMON=(
    --tensor-parallel-size 2
    --gpu-memory-utilization 0.85
    --max-model-len 10240
    --max-num-batched-tokens 32768
    --max-num-seqs 128
    --no-enable-prefix-caching
    --trust-remote-code
    --kv-cache-dtype fp8
)

kv() {
    printf '{"kv_connector":"MoRIIOConnector","kv_role":"%s","kv_connector_extra_config":{"backend":"xgmi","proxy_ip":"127.0.0.1","proxy_ping_port":"36367","http_port":"%s","handshake_port":"%s","notify_port":"%s"}}' "$@"
}

python "$PROXY" --port 10001 > logs/proxy.log 2>&1 & PIDS+=($!)

HIP_VISIBLE_DEVICES=0,1 CUDA_VISIBLE_DEVICES=0,1 \
    vllm serve "$MODEL" "${COMMON[@]}" \
        --host 0.0.0.0 --port 8100 --kv-transfer-config "$(kv kv_producer 8100 6300 6100)" \
    > logs/prefill_0.log 2>&1 & PIDS+=($!)

HIP_VISIBLE_DEVICES=2,3 CUDA_VISIBLE_DEVICES=2,3 \
    vllm serve "$MODEL" "${COMMON[@]}" \
        --host 0.0.0.0 --port 8200 --kv-transfer-config "$(kv kv_consumer 8200 7300 7500)" \
    > logs/decode_0.log 2>&1 & PIDS+=($!)

echo "[run] launched ${#PIDS[@]} services — tailing logs (Ctrl-C to stop)"
tail -F logs/*.log

Benchmark client (profiles.py)

import argparse
import concurrent.futures
import json
import pathlib
import random
import statistics
import time

import requests


DEFAULT_PROMPTS = str(pathlib.Path(__file__).resolve().parent / "model_outputs.json")
DEFAULT_MODEL = "Qwen/Qwen2.5-7B-Instruct"


def percentile(xs, q):
    s = sorted(xs)
    return s[max(0, min(int(len(s) * q / 100), len(s) - 1))]


def load_prompts(path, n):
    with open(path) as f:
        rows = [json.loads(line) for line in f if line.strip()]
    return [r.get("model_input", "") for r in rows[:n]]


def build_body(text, model, input_tokens, output_tokens, best_of_n, shuffle):
    if shuffle:
        words = text.split(" ")
        random.shuffle(words)
        text = " ".join(words)
    body = {"model": model, "prompt": text}
    if output_tokens:
        body["max_tokens"] = output_tokens + random.randint(-10, 10)
    if input_tokens:
        body["truncate_prompt_tokens"] = input_tokens + random.randint(-100, 100)
    if best_of_n:
        body["n"] = best_of_n
    return body


def send_one(host, model, prompt, input_tokens, output_tokens, best_of_n, shuffle):
    body = build_body(prompt, model, input_tokens, output_tokens, best_of_n, shuffle)
    start = time.time()
    try:
        r = requests.post(f"{host}/v1/completions", json=body, timeout=600)
        r.raise_for_status()
        usage = r.json().get("usage") or {}
        cached = (usage.get("prompt_tokens_details") or {}).get("cached_tokens", 0)
        return {
            "latency": time.time() - start,
            "error": False,
            "in_tokens": usage.get("prompt_tokens"),
            "out_tokens": usage.get("completion_tokens", 0),
            "cached": cached,
        }
    except Exception:
        return {"latency": time.time() - start, "error": True}


def run_batch(host, model, prompts, batch_size, **kw):
    start = time.time()
    with concurrent.futures.ThreadPoolExecutor(max_workers=batch_size) as ex:
        futures = [ex.submit(send_one, host, model, p, **kw) for p in prompts]
        results = [f.result() for f in concurrent.futures.as_completed(futures)]
    return time.time() - start, results


def summarise(bs, duration, results):
    times = [r["latency"] for r in results]
    errors = sum(1 for r in results if r["error"])
    ok = [r for r in results if not r["error"]]
    print(f"\n### batch_size={bs} ###")
    print(f"  requests:           {len(results)}")
    print(f"  duration (s):       {duration:.2f}")
    print(f"  errors:             {errors}")
    print(f"  throughput (req/s): {len(results) / duration:.2f}")
    print(f"  avg latency (s):    {statistics.fmean(times):.2f}")
    for q in (50, 75, 90, 95):
        print(f"  p{q} latency (s):     {percentile(times, q):.2f}")
    if not ok:
        return
    ins = [r["in_tokens"] for r in ok if r["in_tokens"]]
    outs = [r["out_tokens"] for r in ok]
    if ins:
        print(f"  mean input tokens:  {statistics.fmean(ins):.1f}")
        print(f"  mean output tokens: {statistics.fmean(outs):.1f}")
        total_in = sum(ins)
        total_cached = sum(r["cached"] for r in ok)
        print(f"  cache hit rate:     {100 * total_cached / total_in:.1f}%")


def main():
    p = argparse.ArgumentParser()
    p.add_argument("--host", default="localhost:10001")
    p.add_argument("--prompts", default=DEFAULT_PROMPTS)
    p.add_argument("--model", default=DEFAULT_MODEL)
    p.add_argument("--samples", type=int, default=200)
    p.add_argument("--batches", default=",".join(map(str, range(3, 100))))
    p.add_argument("--input_tokens", type=int)
    p.add_argument("--output_tokens", type=int)
    p.add_argument("--best_of_n", type=int)
    p.add_argument("--max_latency", type=float, default=5.0)
    p.add_argument("--no_shuffle_input", dest="shuffle_input", action="store_false")
    args = p.parse_args()

    host = args.host if args.host.startswith("http") else f"http://{args.host}"
    prompts = load_prompts(args.prompts, args.samples)
    kw = dict(
        input_tokens=args.input_tokens,
        output_tokens=args.output_tokens,
        best_of_n=args.best_of_n,
        shuffle=args.shuffle_input,
    )
    for bs in [int(b) for b in args.batches.split(",")]:
        duration, results = run_batch(host, args.model, prompts, bs, **kw)
        summarise(bs, duration, results)
        times = [r["latency"] for r in results]
        if (
            statistics.fmean(times) > args.max_latency
            and percentile(times, 50) > args.max_latency
        ):
            print(f"break: latency exceeds max ({args.max_latency}s)")
            break


if __name__ == "__main__":
    main()

# terminal 1 — bring up the topology (pick one)
./1p3d/run.sh             # 1 prefill + 3 decode (TP=1)
# or
./1p1d_2tp/run.sh         # 1 prefill TP=2 + 1 decode TP=2

# terminal 2 — drive load
python3 profiles.py --host localhost:10001 --best_of_n 8 --input_tokens 2048 --output_tokens 80 --max_latency 5

Test Result

With both fixes applied on the 1p3d and 1p1d_2tp setups (AMD MI3xx, MoRIIO XGMI READ, Qwen2.5-7B fp8, best_of_n=8):

• No engine crashes (no AssertionError from _update_from_kv_xfer_finished, no EngineDeadError).
• All decode TP ranks actively reading and generating tokens; no silent rank.
• All requests succeed; no errors or tracebacks on prefill or decode.

Checks

Local pre-commit run on the changed files:

SKIP=pip-compile,pip-compile-rocm,pip-compile-xpu,pip-compile-docs,\
update-dockerfile-graph,validate-docker-versions,format-torch-nightly-test \
  pre-commit run --files \
    vllm/distributed/kv_transfer/kv_connector/v1/moriio/moriio_connector.py \
    tests/v1/kv_connector/unit/test_moriio_connector.py

All pass: ruff-check, ruff-format, typos, SPDX headers, root lazy imports, forbidden imports, torch.cuda call check, mypy-3.10, attention backend docs, boolean-ops-in-with-statements. DCO signoff present on both commits.

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Code Review

This pull request updates the MoRIIO connector to support 'best-of-n' scenarios by transitioning the mapping between transfer IDs and request IDs from 1:1 to 1:many. Key changes include updating the scheduler to manage sibling request IDs, implementing gated release logic in the worker to ensure siblings are only freed after vLLM marks them as finished, and ensuring notifications use the shared transfer ID. Comprehensive unit tests were added to cover these new behaviors. Feedback highlights the need to update type hints to reflect the new 1:many mapping and identifies a potential memory leak where untracked request IDs could accumulate in the _read_finished_seen set.

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @crazyguitar.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork