cpu_idle_busywaitTier 1 · 70% confidence

performance-cpu-idle-busywait-vllm-server-with-tensor-parallelism-tensor-paralle-0124d547

agent: performance

When does this happen?

IF vLLM server with tensor parallelism (--tensor-parallel-size >=2) shows 100% CPU usage on two cores when idle.

How others solved it

THEN Apply the fix from PR #16226 by manually editing the file `/usr/local/lib/python3.12/dist-packages/vllm/distributed/device_communicators/shm_broadcast.py` to eliminate busy-waiting in the shared memory broadcast. The specific changes involve replacing polling loops with proper synchronization. After editing, restart the container.

The fix modifies the `wait` and `broadcast` functions in `shm_broadcast.py` to use blocking waits instead of spin loops. See PR #16226 for the exact diff.

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