Don't blame old-space GC time against a new-space GC that triggered it.

runtime/vm/heap.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/heap.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
@@ skipping 395 matching lines @@
     class_table->ResetCountersOld();
   }
 }
 #endif
 
 void Heap::EvacuateNewSpace(Thread* thread, GCReason reason) {
   ASSERT(reason == kFull);
   if (BeginNewSpaceGC(thread)) {
     RecordBeforeGC(kNew, kFull);
     VMTagScope tagScope(thread, VMTag::kGCNewSpaceTagId);
     TIMELINE_FUNCTION_GC_DURATION(thread, "EvacuateNewGeneration");

[danunez, 2017/08/22 17:01:26]

I think you'll need to do the same for the Evacuate call here.

[rmacnak, 2017/08/22 17:10:51]

There's no trailing old-space GC here to exclude.

     NOT_IN_PRODUCT(UpdateClassHeapStatsBeforeGC(kNew));
     new_space_.Evacuate();
     NOT_IN_PRODUCT(isolate()->class_table()->UpdatePromoted());
     RecordAfterGC(kNew);
     PrintStats();
     NOT_IN_PRODUCT(PrintStatsToTimeline(&tds));
     EndNewSpaceGC();
   }
 }
 
 void Heap::CollectNewSpaceGarbage(Thread* thread,
                                   ApiCallbacks api_callbacks,
                                   GCReason reason) {
   ASSERT((reason == kNewSpace) || (reason == kFull));
   if (BeginNewSpaceGC(thread)) {
     bool invoke_api_callbacks = (api_callbacks == kInvokeApiCallbacks);
     RecordBeforeGC(kNew, reason);
-    VMTagScope tagScope(thread, VMTag::kGCNewSpaceTagId);
-    TIMELINE_FUNCTION_GC_DURATION(thread, "CollectNewGeneration");
-    NOT_IN_PRODUCT(UpdateClassHeapStatsBeforeGC(kNew));
-    new_space_.Scavenge(invoke_api_callbacks);
-    NOT_IN_PRODUCT(isolate()->class_table()->UpdatePromoted());
-    RecordAfterGC(kNew);
-    PrintStats();
-    NOT_IN_PRODUCT(PrintStatsToTimeline(&tds));
-    EndNewSpaceGC();
+    {
+      VMTagScope tagScope(thread, VMTag::kGCNewSpaceTagId);
+      TIMELINE_FUNCTION_GC_DURATION(thread, "CollectNewGeneration");
+      NOT_IN_PRODUCT(UpdateClassHeapStatsBeforeGC(kNew));
+      new_space_.Scavenge(invoke_api_callbacks);
+      NOT_IN_PRODUCT(isolate()->class_table()->UpdatePromoted());
+      RecordAfterGC(kNew);
+      PrintStats();
+      NOT_IN_PRODUCT(PrintStatsToTimeline(&tds));
+      EndNewSpaceGC();
+    }
     if ((reason == kNewSpace) && old_space_.NeedsGarbageCollection()) {
       // Old collections should call the API callbacks.
       CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kPromotion);
     }
   }
 }
 
 void Heap::CollectOldSpaceGarbage(Thread* thread,
                                   ApiCallbacks api_callbacks,
                                   GCReason reason) {
@@ skipping 446 matching lines @@
     : StackResource(thread) {
   Dart::vm_isolate()->heap()->WriteProtect(false);
 }
 
 WritableVMIsolateScope::~WritableVMIsolateScope() {
   ASSERT(Dart::vm_isolate()->heap()->UsedInWords(Heap::kNew) == 0);
   Dart::vm_isolate()->heap()->WriteProtect(true);
 }
 
 }  // namespace dart