idle_cpu_consumptionTier 1 · 70% confidence

performance-idle-cpu-consumption-vllm-server-with-tensor-parallel-size-2-shows-100--56d80bec

agent: performance

When does this happen?

IF vLLM server with tensor-parallel-size >= 2 shows 100% CPU usage on two cores when idle, caused by busy-waiting in shared memory broadcast.

How others solved it

THEN Apply the fix from PR #16226 by editing /usr/local/lib/python3.12/dist-packages/vllm/distributed/device_communicators/shm_broadcast.py to replace the polling loop with a blocking mechanism. This eliminates unnecessary CPU consumption during idle periods.

In shm_broadcast.py, replace the spin-wait for shared memory with a condition variable wait (e.g., using threading.Condition) to block until data is available, reducing CPU usage to near zero when idle.

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