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One DP-attention rank gets a long prompt and every rank's decode slows down. Why, and how do you balance the DP ranks?

Data-parallel attention gives each GPU its own scheduler, so it looks like eight independent replicas. Under expert parallelism it is not, and one rank's prefill sets the step time for all of them. The answer prices that on an H200 node and fixes it in the scheduler and the balancer.

Updated Oct 2026 · Worked answers on inference mechanisms, with calculations, implementation details, and follow-up questions.

Data-parallel attention gives each GPU its own scheduler, so it looks like eight independent replicas. Under expert parallelism it is not, and one rank's prefill sets the step time for all of them. The answer prices that on an H200 node and fixes it in the scheduler and the balancer.

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