Bug 1929640 - Add a mode to CCGCScheduler where it can collect faster in case lots of garbage is created and there isn't too much idle time to run the slices, r=mccr8,sfink

Differential Revision: https://phabricator.services.mozilla.com/D228215

dom/base/CCGCScheduler.cpp

@@ -241,6 +241,10 @@ void CCGCScheduler::NoteCCEnd(const CycleCollectorResults& aResults,
   mIsCollectingCycles = false;
   mLastCCEndTime = aWhen;
   mNeedsFullCC = CCReason::NO_REASON;
+  mPreferFasterCollection =
+      mCurrentCollectionHasSeenNonIdle &&
+      (aResults.mFreedGCed > 10000 || aResults.mFreedRefCounted > 10000);
+  mCurrentCollectionHasSeenNonIdle = false;
 }
 
 void CCGCScheduler::NoteWontGC() {
@@ -255,6 +259,14 @@ void CCGCScheduler::NoteWontGC() {
 bool CCGCScheduler::GCRunnerFired(TimeStamp aDeadline) {
   MOZ_ASSERT(!mDidShutdown, "GCRunner still alive during shutdown");
 
+  if (!aDeadline) {
+    mCurrentCollectionHasSeenNonIdle = true;
+  } else if (mPreferFasterCollection) {
+    // We found some idle time, try to utilize that a bit more given that
+    // we're in a mode where idle time is rare.
+    aDeadline = aDeadline + TimeDuration::FromMilliseconds(5.0);
+  }
+
   GCRunnerStep step = GetNextGCRunnerAction(aDeadline);
   switch (step.mAction) {
     case GCRunnerAction::None:
@@ -544,15 +556,24 @@ void CCGCScheduler::EnsureOrResetGCRunner() {
       StaticPrefs::javascript_options_gc_delay_interslice()));
 }
 
+TimeDuration CCGCScheduler::ComputeMinimumBudgetForRunner(
+    TimeDuration aBaseValue) {
+  // If the main thread was too busy to find idle for the whole last collection,
+  // allow a very short budget this time.
+  return mPreferFasterCollection ? TimeDuration::FromMilliseconds(1.0)
+                                 : TimeDuration::FromMilliseconds(std::max(
+                                       nsRefreshDriver::HighRateMultiplier() *
+                                           aBaseValue.ToMilliseconds(),
+                                       1.0));
+}
+
 void CCGCScheduler::EnsureGCRunner(TimeDuration aDelay) {
   if (mGCRunner) {
     return;
   }
 
-  TimeDuration minimumBudget = TimeDuration::FromMilliseconds(
-      std::max(nsRefreshDriver::HighRateMultiplier() *
-                   mActiveIntersliceGCBudget.ToMilliseconds(),
-               1.0));
+  TimeDuration minimumBudget =
+      ComputeMinimumBudgetForRunner(mActiveIntersliceGCBudget);
 
   // Wait at most the interslice GC delay before forcing a run.
   mGCRunner = IdleTaskRunner::Create(
@@ -615,13 +636,13 @@ void CCGCScheduler::KillGCRunner() {
 void CCGCScheduler::EnsureCCRunner(TimeDuration aDelay, TimeDuration aBudget) {
   MOZ_ASSERT(!mDidShutdown);
 
-  TimeDuration minimumBudget = TimeDuration::FromMilliseconds(std::max(
-      nsRefreshDriver::HighRateMultiplier() * aBudget.ToMilliseconds(), 1.0));
+  TimeDuration minimumBudget = ComputeMinimumBudgetForRunner(aBudget);
 
   if (!mCCRunner) {
     mCCRunner = IdleTaskRunner::Create(
-        CCRunnerFired, "EnsureCCRunner::CCRunnerFired", 0, aDelay,
-        minimumBudget, true, [this] { return mDidShutdown; });
+        [this](TimeStamp aDeadline) { return CCRunnerFired(aDeadline); },
+        "EnsureCCRunner::CCRunnerFired", 0, aDelay, minimumBudget, true,
+        [this] { return mDidShutdown; });
   } else {
     mCCRunner->SetMinimumUsefulBudget(minimumBudget.ToMilliseconds());
     nsIEventTarget* target = mozilla::GetCurrentSerialEventTarget();

dom/base/CCGCScheduler.h

@@ -132,7 +132,7 @@ class CCGCScheduler {
         mReadyForMajorGC(!mAskParentBeforeMajorGC),
         mInterruptRequested(false) {}
 
-  static bool CCRunnerFired(TimeStamp aDeadline);
+  bool CCRunnerFired(TimeStamp aDeadline);
 
   // Parameter setting
 
@@ -178,7 +178,9 @@ class CCGCScheduler {
   JS::SliceBudget CreateGCSliceBudget(mozilla::TimeDuration aDuration,
                                       bool isIdle, bool isExtended) {
     mInterruptRequested = false;
-    auto budget = JS::SliceBudget(aDuration, &mInterruptRequested);
+    // Don't try to interrupt if we are in a mode where idle time is rare.
+    auto budget = JS::SliceBudget(
+        aDuration, mPreferFasterCollection ? nullptr : &mInterruptRequested);
     budget.idle = isIdle;
     budget.extended = isExtended;
     return budget;
@@ -350,6 +352,8 @@ class CCGCScheduler {
   JS::SliceBudget ComputeInterSliceGCBudget(TimeStamp aDeadline,
                                             TimeStamp aNow);
 
+  TimeDuration ComputeMinimumBudgetForRunner(TimeDuration aBaseValue);
+
   bool ShouldForgetSkippable(uint32_t aSuspectedCCObjects) const {
     // Only do a forget skippable if there are more than a few new objects
     // or we're doing the initial forget skippables.
@@ -451,6 +455,8 @@ class CCGCScheduler {
   JS::SliceBudget ComputeForgetSkippableBudget(TimeStamp aStartTimeStamp,
                                                TimeStamp aDeadline);
 
+  bool PreferFasterCollection() const { return mPreferFasterCollection; }
+
  private:
   // State
 
@@ -523,6 +529,9 @@ class CCGCScheduler {
   bool mIsCollectingCycles = false;
   bool mUserIsActive = true;
 
+  bool mCurrentCollectionHasSeenNonIdle = false;
+  bool mPreferFasterCollection = false;
+
  public:
   uint32_t mCCollectedWaitingForGC = 0;
   uint32_t mCCollectedZonesWaitingForGC = 0;

dom/base/nsJSEnvironment.cpp

@@ -55,6 +55,7 @@
 #include "mozilla/AutoRestore.h"
 #include "mozilla/BasePrincipal.h"
 #include "mozilla/CycleCollectorStats.h"
+#include "mozilla/MainThreadIdlePeriod.h"
 #include "mozilla/PresShell.h"
 #include "mozilla/SchedulerGroup.h"
 #include "mozilla/StaticPrefs_dom.h"
@@ -1246,7 +1247,7 @@ void nsJSContext::EndCycleCollectionCallback(
         "A max duration ICC shouldn't reduce GC delay to 0");
 
     TimeDuration delay;
-    if (aResults.mFreedGCed > 10000 && aResults.mFreedRefCounted > 10000) {
+    if (sScheduler->PreferFasterCollection()) {
       // If we collected lots of objects, trigger the next GC sooner so that
       // GC can cut JS-to-native edges and native objects can be then deleted.
       delay = TimeDuration::FromMilliseconds(
@@ -1268,10 +1269,17 @@ void nsJSContext::EndCycleCollectionCallback(
 #endif
 }
 
-/* static */
 bool CCGCScheduler::CCRunnerFired(TimeStamp aDeadline) {
   AUTO_PROFILER_LABEL_RELEVANT_FOR_JS("Incremental CC", GCCC);
 
+  if (!aDeadline) {
+    mCurrentCollectionHasSeenNonIdle = true;
+  } else if (mPreferFasterCollection) {
+    // We found some idle time, try to utilize that a bit more given that
+    // we're in a mode where idle time is rare.
+    aDeadline = aDeadline + TimeDuration::FromMilliseconds(5.0);
+  }
+
   bool didDoWork = false;
 
   // The CC/GC scheduler (sScheduler) decides what action(s) to take during