2 files changed, 10 insertions, 34 deletions
diff --git a/toolkit/components/perfmonitoring/nsPerformanceStats.cpp b/toolkit/components/perfmonitoring/nsPerformanceStats.cpp
index 33aeaf7c2..59d84ced1 100644
--- a/toolkit/components/perfmonitoring/nsPerformanceStats.cpp
+++ b/toolkit/components/perfmonitoring/nsPerformanceStats.cpp
@@ -662,9 +662,6 @@ nsPerformanceStatsService::nsPerformanceStatsService()
                                        nsPerformanceGroup::GroupScope::RUNTIME // scope
                                      ))
   , mIsHandlingUserInput(false)
-  , mProcessStayed(0)
-  , mProcessMoved(0)
-  , mProcessUpdateCounter(0)
   , mIsMonitoringPerCompartment(false)
   , mJankAlertThreshold(mozilla::MaxValue<uint64_t>::value) // By default, no alerts
   , mJankAlertBufferingDelay(1000 /* ms */)
@@ -953,13 +950,6 @@ nsPerformanceStatsService::SetJankAlertBufferingDelay(uint32_t value) {
   return NS_OK;
 }
 
-nsresult
-nsPerformanceStatsService::UpdateTelemetry()
-{
-  /* STUB */
-  return NS_OK;
-}
-
 
 /* static */ nsIPerformanceStats*
 nsPerformanceStatsService::GetStatsForGroup(const js::PerformanceGroup* group)
@@ -992,12 +982,6 @@ nsPerformanceStatsService::GetSnapshot(JSContext* cx, nsIPerformanceSnapshot * *
     }
   }
 
-  js::GetPerfMonitoringTestCpuRescheduling(cx, &mProcessStayed, &mProcessMoved);
-
-  if (++mProcessUpdateCounter % 10 == 0) {
-    mozilla::Unused << UpdateTelemetry();
-  }
-
   snapshot.forget(aSnapshot);
 
   return NS_OK;
@@ -1098,6 +1082,9 @@ nsPerformanceStatsService::GetPerformanceGroups(JSContext* cx,
     return false;
   }
 
+  // Returning a vector that is too large would cause allocations all over the
+  // place in the JS engine. We want to be sure that all data is stored inline.
+  MOZ_ASSERT(out.length() <= out.sMaxInlineStorage);
   return true;
 }
 
@@ -1326,8 +1313,12 @@ nsPerformanceStatsService::GetResources(uint64_t* userTime,
 
 void
 nsPerformanceStatsService::NotifyJankObservers(const mozilla::Vector<uint64_t>& aPreviousJankLevels) {
-  GroupVector alerts;
-  mPendingAlerts.swap(alerts);
+
+  // The move operation is generally constant time, unless
+  // `mPendingAlerts.length()` is very small, in which case it's fast anyway.
+  GroupVector alerts(Move(mPendingAlerts));
+  mPendingAlerts = GroupVector(); // Reconstruct after `Move`.
+
   if (!mPendingAlertsCollector) {
     // We are shutting down.
     return;
diff --git a/toolkit/components/perfmonitoring/nsPerformanceStats.h b/toolkit/components/perfmonitoring/nsPerformanceStats.h
index c82a3e92c..661a78a1a 100644
--- a/toolkit/components/perfmonitoring/nsPerformanceStats.h
+++ b/toolkit/components/perfmonitoring/nsPerformanceStats.h
@@ -19,7 +19,7 @@
 class nsPerformanceGroup;
 class nsPerformanceGroupDetails;
 
-typedef mozilla::Vector<RefPtr<nsPerformanceGroup>> GroupVector;
+typedef mozilla::Vector<RefPtr<nsPerformanceGroup>, 8> GroupVector;
 
 /**
  * A data structure for registering observers interested in
@@ -363,21 +363,6 @@ protected:
                    nsPerformanceGroup* group);
 
 
-
-
-  /**********************************************************
-   *
-   * To check whether our algorithm makes sense, we keep count of the
-   * number of times the process has been rescheduled to another CPU
-   * while we were monitoring the performance of a group and we upload
-   * this data through Telemetry.
-   */
-  nsresult UpdateTelemetry();
-
-  uint64_t mProcessStayed;
-  uint64_t mProcessMoved;
-  uint32_t mProcessUpdateCounter;
-
   /**********************************************************
    *
    * Options controlling measurements.