fix(predictive-perf): split CPU and Layout task multipliers

lighthouse-core/gather/computed/dependency-graph/estimator/estimator.js

@@ -10,10 +10,18 @@ const TcpConnection = require('./tcp-connection');
 
 // see https://cs.chromium.org/search/?q=kDefaultMaxNumDelayableRequestsPerClient&sq=package:chromium&type=cs
 const DEFAULT_MAXIMUM_CONCURRENT_REQUESTS = 10;
+
+// Fast 3G emulation target from DevTools, WPT 3G - Fast setting
 const DEFAULT_RESPONSE_TIME = 30;
 const DEFAULT_RTT = 150;
 const DEFAULT_THROUGHPUT = 1600 * 1024; // 1.6 Mbps
-const DEFAULT_CPU_MULTIPLIER = 5;
+
+// same multiplier as Lighthouse uses for CPU emulation
+const DEFAULT_CPU_TASK_MULTIPLIER = 4;
+// layout tasks tend to be less CPU-bound and do not experience the same increase in duration
+const DEFAULT_LAYOUT_TASK_MULTIPLIER = 2;
+// if a task takes more than 10 seconds it's usually a sign it isn't actually CPU bound and we're over estimating
+const DEFAULT_MAXIMUM_CPU_TASK_DURATION = 10000;
 
 function groupBy(items, keyFunc) {
   const grouped = new Map();
@@ -41,7 +49,8 @@ class Estimator {
         throughput: DEFAULT_THROUGHPUT,
         defaultResponseTime: DEFAULT_RESPONSE_TIME,
         maximumConcurrentRequests: DEFAULT_MAXIMUM_CONCURRENT_REQUESTS,
-        cpuMultiplier: DEFAULT_CPU_MULTIPLIER,
+        cpuTaskMultiplier: DEFAULT_CPU_TASK_MULTIPLIER,
+        layoutTaskMultiplier: DEFAULT_LAYOUT_TASK_MULTIPLIER,
       },
       options
     );
@@ -53,7 +62,8 @@ class Estimator {
       TcpConnection.maximumSaturatedConnections(this._rtt, this._throughput),
       this._options.maximumConcurrentRequests
     );
-    this._cpuMultiplier = this._options.cpuMultiplier;
+    this._cpuTaskMultiplier = this._options.cpuTaskMultiplier;
+    this._layoutTaskMultiplier = this._options.layoutTaskMultiplier;
   }
 
   /**
@@ -227,7 +237,13 @@ class Estimator {
   _estimateTimeRemaining(node) {
     if (node.type === Node.TYPES.CPU) {
       const auxData = this._nodeAuxiliaryData.get(node);
-      const totalDuration = Math.round(node.event.dur / 1000 * this._cpuMultiplier);
+      const multiplier = node.didPerformLayout()
+        ? this._layoutTaskMultiplier
+        : this._cpuTaskMultiplier;
+      const totalDuration = Math.min(
+        Math.round(node.event.dur / 1000 * multiplier),
+        DEFAULT_MAXIMUM_CPU_TASK_DURATION
+      );
       const estimatedTimeElapsed = totalDuration - auxData.timeElapsed;
       this._setAuxData(node, {estimatedTimeElapsed});
       return estimatedTimeElapsed;

lighthouse-core/gather/computed/page-dependency-graph.js

@@ -11,7 +11,10 @@ const CPUNode = require('./dependency-graph/cpu-node');
 const GraphEstimator = require('./dependency-graph/estimator/estimator');
 const TracingProcessor = require('../../lib/traces/tracing-processor');
 
-const MINIMUM_TASK_DURATION = 10 * 1000;
+// tasks shorter than 10 ms are unlikely have a significant impact
+const MINIMUM_TASK_DURATION = 10000;
+// video files tend to be enormous and throw off all graph traversals
+const IGNORED_MIME_TYPES_REGEX = /^video/;
 
 class PageDependencyGraphArtifact extends ComputedArtifact {
   get name() {
@@ -47,6 +50,7 @@ class PageDependencyGraphArtifact extends ComputedArtifact {
     const urlToNodeMap = new Map();
 
     networkRecords.forEach(record => {
+      if (IGNORED_MIME_TYPES_REGEX.test(record.mimeType)) return;
       const node = new NetworkNode(record);
       nodes.push(node);
       idToNodeMap.set(record.requestId, node);

lighthouse-core/test/audits/predictive-perf-test.js

@@ -25,15 +25,15 @@ describe('Performance: predictive performance audit', () => {
     }, Runner.instantiateComputedArtifacts());
 
     return PredictivePerf.audit(artifacts).then(output => {
-      assert.equal(output.score, 96);
-      assert.equal(Math.round(output.rawValue), 2453);
-      assert.equal(output.displayValue, '2,450\xa0ms');
+      assert.equal(output.score, 99);
+      assert.equal(Math.round(output.rawValue), 1696);
+      assert.equal(output.displayValue, '1,700\xa0ms');
 
       const valueOf = name => Math.round(output.extendedInfo.value[name]);
       assert.equal(valueOf('optimisticFMP'), 754);
-      assert.equal(valueOf('pessimisticFMP'), 2070);
-      assert.equal(valueOf('optimisticTTCI'), 3340);
-      assert.equal(valueOf('pessimisticTTCI'), 3649);
+      assert.equal(valueOf('pessimisticFMP'), 1191);
+      assert.equal(valueOf('optimisticTTCI'), 2438);
+      assert.equal(valueOf('pessimisticTTCI'), 2399);
     });
   });
 });

lighthouse-core/test/gather/computed/dependency-graph/estimator/estimator-test.js

@@ -51,7 +51,10 @@ describe('DependencyGraph/Estimator', () => {
       const cpuNode = new CpuNode(cpuTask({duration: 200}));
       cpuNode.addDependency(rootNode);
 
-      const estimator = new Estimator(rootNode, {defaultResponseTime: 500});
+      const estimator = new Estimator(rootNode, {
+        defaultResponseTime: 500,
+        cpuTaskMultiplier: 5,
+      });
       const result = estimator.estimate();
       // should be 2 RTTs and 500ms for the server response time + 200 CPU
       assert.equal(result, 300 + 500 + 200);
@@ -83,7 +86,10 @@ describe('DependencyGraph/Estimator', () => {
       nodeA.addDependent(nodeC);
       nodeA.addDependent(nodeD);
 
-      const estimator = new Estimator(nodeA, {defaultResponseTime: 500});
+      const estimator = new Estimator(nodeA, {
+        defaultResponseTime: 500,
+        cpuTaskMultiplier: 5,
+      });
       const result = estimator.estimate();
       // should be 800ms A, then 1000 ms total for B, C, D in serial
       assert.equal(result, 1800);
@@ -103,7 +109,10 @@ describe('DependencyGraph/Estimator', () => {
       nodeC.addDependent(nodeD);
       nodeC.addDependent(nodeF); // finishes 400 ms after D
 
-      const estimator = new Estimator(nodeA, {defaultResponseTime: 500});
+      const estimator = new Estimator(nodeA, {
+        defaultResponseTime: 500,
+        cpuTaskMultiplier: 5,
+      });
       const result = estimator.estimate();
       // should be 800ms each for A, B, C, D, with F finishing 400 ms after D
       assert.equal(result, 3600);