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[KV Offload] Avoid quadratic event polling - #55756
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Use ordered deques so transfer completion polling scales with completed prefixes instead of the total event backlog. Co-authored-by: OpenAI Codex <codex@openai.com> Signed-off-by: felix h <felix314159@users.noreply.github.com>
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Can someone add the 'ready-run-all-tests' or 'ready' label pls? |
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WalkthroughThe worker now uses deques for event and pending-index tracking. Copy backends accept deque-based event collections. New tests verify completed-prefix reporting, store-event metadata draining, and event query counts. ChangesEvent queue updates
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: ⚪ Minimal · up to The worker now drains transfer-completion events efficiently while preserving ordered load and store completion reporting. Current coverage supports the intended behavior change with no remaining merge-blocking risk. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches 💡 1🛠️ Fix failing CI checks 💡
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I checked this against main at 971378f466. The pop(0) and set scans are still there, it merges cleanly, and tests/v1/simple_kv_offload passes with it on CPU.
- This also fixes store completion order on a single worker. On main, stores that finish in the same poll come back in set order, e.g. events 7 and 8 as
[8, 7], andupdate_connector_outputthen emits the childBlockStoredbefore its parent. #63249 fixes the same thing for the OffloadingConnector. The new test also passes against main'sworker.py; could it use ids 7 and 8 and assertlist(worker_meta.completed_store_events) == [7, 8]? - With more than one worker,
aggregate()can still merge as[8, 7]when one rank reports a step later. Iteratingsorted(meta.completed_store_events.items())atvllm/v1/simple_kv_offload/manager.py:1082fixed both cases in my repro. That could go here or in a follow-up.
What changed
SimpleCPUOffloadWorkerpreviously drained completed transfer events withrepeated
list.pop(0)and scanned every pending event ID on every engine step.This made burst completion quadratic in the backlog and made a no-progress poll
linear in all pending transfers.
Use ordered deques for both event records and pending IDs. Scheduler event IDs
are monotonic, each backend queue is FIFO per transfer direction, and the worker
only consumes completed prefixes, so the queue order preserves the existing
completion semantics. A CPU-only test covers both load and store streams,
including stopping at the first incomplete event and reporting each completion
once.
Performance
My benchmarks used the original polling loop and the patched
worker method. Times are medians of nine runs for completed-event draining:
For 100 polls while the oldest event remained incomplete (11-run medians):
Validation
.venv/bin/python -m pytest tests/v1/simple_kv_offload/test_worker_events.py -q1 passed.venv/bin/pre-commit run --files <changed files>and CUDA API validation
Model evaluation was not run because this changes host-side event bookkeeping
only and does not change model execution, token generation, or numerical output.