58 lines
2.3 KiB
JavaScript
58 lines
2.3 KiB
JavaScript
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/**
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* Metric helpers shared by the idle and streaming profilers.
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*
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* Both commands read the same `Performance.getMetrics` counters and need the
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* same derivations, so the maths lives here and each entry point only decides
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* which numbers to report.
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*/
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export const round = (value, digits = 2) => Number(Number(value ?? 0).toFixed(digits))
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export const metricMap = (metrics = []) => Object.fromEntries(metrics.map(({ name, value }) => [name, value]))
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/**
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* Least-squares slope of a sampled series, in units per second. A slope
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* separates a genuine upward trend from the sawtooth that garbage collection
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* produces, which start/end deltas alone cannot distinguish.
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*/
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export const growthPerSecond = (samples, key) => {
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if (samples.length < 2) return 0
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const meanTime = samples.reduce((total, sample) => total + sample.elapsedSeconds, 0) / samples.length
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const meanValue = samples.reduce((total, sample) => total + (sample[key] ?? 0), 0) / samples.length
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let covariance = 0
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let variance = 0
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for (const sample of samples) {
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const timeDelta = sample.elapsedSeconds - meanTime
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covariance += timeDelta * ((sample[key] ?? 0) - meanValue)
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variance += timeDelta * timeDelta
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}
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return variance === 0 ? 0 : Number((covariance / variance).toFixed(3))
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}
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/** Percentile of an unsorted numeric series, using nearest-rank. */
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export const percentile = (values, fraction) => {
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if (values.length === 0) return 0
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const sorted = [...values].sort((left, right) => left - right)
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const rank = Math.min(sorted.length - 1, Math.max(0, Math.ceil(fraction * sorted.length) - 1))
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return round(sorted[rank])
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}
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/**
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* Long tasks block input and animation, so a streaming capture is judged by
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* its task-duration distribution rather than by an average frame rate.
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*/
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export const summarizeLongTasks = (traceEvents, thresholdMs = 50) => {
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const durations = traceEvents
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.filter((event) => event.name === "RunTask" && Number(event.dur) > 0)
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.map((event) => Number(event.dur) / 1000)
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const long = durations.filter((duration) => duration >= thresholdMs)
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return {
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taskCount: durations.length,
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longTaskCount: long.length,
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longTaskTotalMs: round(long.reduce((total, duration) => total + duration, 0)),
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longestTaskMs: round(Math.max(0, ...durations)),
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taskP95Ms: percentile(durations, 0.95),
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taskP99Ms: percentile(durations, 0.99),
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}
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}
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