chrome-devtools-frontend/front_end/models/trace/lantern/metrics/MaxPotentialFID.ts

Chrome DevTools UI

// Copyright 2024 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import * as Core from '../core/core.js';
import * as Graph from '../graph/graph.js';
import type * as Simulation from '../simulation/simulation.js';

import {
  type Extras,
  Metric,
  type MetricCoefficients,
  type MetricComputationDataInput,
  type MetricResult,
} from './Metric.js';

class MaxPotentialFID extends Metric {
  static override get coefficients(): MetricCoefficients {
    return {
      intercept: 0,
      optimistic: 0.5,
      pessimistic: 0.5,
    };
  }

  static override getOptimisticGraph(dependencyGraph: Graph.Node): Graph.Node {
    return dependencyGraph;
  }

  static override getPessimisticGraph(dependencyGraph: Graph.Node): Graph.Node {
    return dependencyGraph;
  }

  static override getEstimateFromSimulation(simulation: Simulation.Result, extras: Extras): Simulation.Result {
    if (!extras.fcpResult) {
      throw new Core.LanternError('missing fcpResult');
    }

    // Intentionally use the opposite FCP estimate, a more pessimistic FCP means that more tasks
    // are excluded from the FID computation, so a higher FCP means lower FID for same work.
    const fcpTimeInMs = extras.optimistic ? extras.fcpResult.pessimisticEstimate.timeInMs :
                                            extras.fcpResult.optimisticEstimate.timeInMs;

    const timings = MaxPotentialFID.getTimingsAfterFCP(
        simulation.nodeTimings,
        fcpTimeInMs,
    );

    return {
      timeInMs: Math.max(...timings.map(timing => timing.duration), 16),
      nodeTimings: simulation.nodeTimings,
    };
  }

  static override compute(data: MetricComputationDataInput, extras?: Omit<Extras, 'optimistic'>): MetricResult {
    const fcpResult = extras?.fcpResult;
    if (!fcpResult) {
      throw new Core.LanternError('FCP is required to calculate the Max Potential FID metric');
    }

    return super.compute(data, extras);
  }

  static getTimingsAfterFCP(nodeTimings: Simulation.Result['nodeTimings'], fcpTimeInMs: number):
      Array<{duration: number}> {
    return Array.from(nodeTimings.entries())
        .filter(([node, timing]) => node.type === Graph.BaseNode.types.CPU && timing.endTime > fcpTimeInMs)
        .map(([_, timing]) => timing);
  }
}

export {MaxPotentialFID};