Why there are negative response time?

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in page https://dubbo.apache.org/en/docs/v2.7/user/perf-test/, why `Response time avg value` has negative values?


Start with the performance-test documentation page linked in the issue and inspect the explanation of the “Response time avg value.” Determine why the displayed values can be negative, then update the page to clarify the cause and verify that the revised explanation matches the shown example.

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