Improve how we compute the power consumption numbers from the Firefox Profiler output

lib/firefox/geckoProfiler.js

@@ -8,26 +8,69 @@ import { BrowserError } from '../support/errors.js';
 const delay = ms => new Promise(res => setTimeout(res, ms));
 const log = intel.getLogger('browsertime.firefox');
 
-// Return power usage in Wh
-function computePowerSum(counter) {
+// Return power usage in Wh for a single counter.
+function computeCounterPowerSum(counter) {
   let sum = 0;
   // Older Firefoxes see https://github.com/sitespeedio/sitespeed.io/issues/3944#issuecomment-1871090793
   if (counter.sample_groups) {
     for (const groups of counter.sample_groups) {
       const countIndex = groups.samples.schema.count;
-      for (const sample of groups.samples.data) {
-        sum += sample[countIndex];
+      // NOTE: We intentionally ignore the first index of the counters as they
+      // might contain incorrect values.
+      for (
+        let sampleIndex = 1;
+        sampleIndex < groups.samples.data.length;
+        sampleIndex++
+      ) {
+        sum += groups.samples.data[sampleIndex][countIndex];
       }
     }
   } else {
     const countIndex = counter.samples.schema.count;
-    for (const sample of counter.samples.data) {
-      sum += sample[countIndex];
+    // NOTE: We intentionally ignore the first index of the counters as they
+    // might contain incorrect values.
+    for (
+      let sampleIndex = 1;
+      sampleIndex < counter.samples.data.length;
+      sampleIndex++
+    ) {
+      sum += counter.samples.data[sampleIndex][countIndex];
     }
   }
+
   return sum * 1e-12;
 }
 
+// Return the power usage by the whole profile including the sub processes.
+// The return value is in Wh value.
+function computeFullProfilePower(profile) {
+  let power = 0;
+  for (const counter of profile.counters) {
+    if (
+      counter.category === 'power' &&
+      // If power counters starts with "Power:", it means that there are several
+      // individual components that Firefox records. For Linux and Windows,
+      // intel CPUs might produce 'CPU package' to show the whole power
+      // consumption of the CPU. But on top of that it also shows some individual
+      // components like, DRAM, iGPU, individual CPU cores etc. We don't want
+      // to include them as it might produce double the power values it normally consumes.
+      //
+      // Linux track names: https://searchfox.org/mozilla-central/rev/5ad94327fc03d0e5bc6aa81c0d7d113c2dccf947/tools/profiler/core/PowerCounters-linux.cpp#48-70
+      // Windows track names: https://searchfox.org/mozilla-central/rev/5ad94327fc03d0e5bc6aa81c0d7d113c2dccf947/tools/profiler/core/PowerCounters-win.cpp#32-55
+      (!counter.name.startsWith('Power:') ||
+        counter.name === 'Power: CPU package')
+    ) {
+      power += computeCounterPowerSum(counter);
+    }
+  }
+
+  for (const subprocessProfile of profile.processes) {
+    power += computeFullProfilePower(subprocessProfile);
+  }
+
+  return power;
+}
+
 /**
  * Timeout a promise after ms. Use promise.race to compete
  * about the timeout and the promise.
@@ -213,20 +256,15 @@ export class GeckoProfiler {
           geckoProfilerDefaults.features
         );
         if (chosenFeatures.includes('power')) {
-          log.info('Collecting CPU power consumtion');
+          log.info('Collecting CPU power consumption');
           const profile = JSON.parse(
             await storageManager.readData(
               `geckoProfile-${index}.json`,
               path.join(pathToFolder(url, options))
             )
           );
-          let power = 0;
-          for (const counter of profile.counters) {
-            if (counter.category === 'power') {
-              power += computePowerSum(counter);
-            }
-          }
-          result.powerConsumption = Number(power);
+
+          result.powerConsumption = computeFullProfilePower(profile);
         } else {
           log.warning(
             'Missing power setting in geckoProfilerParams.features so power will not be collected'