Minor cleanup preparing for recording parent-child data

base/tracked_objects.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TRACKED_OBJECTS_H_
 #define BASE_TRACKED_OBJECTS_H_
 #pragma once
 
 #include <map>
 #include <stack>
@@ skipping 146 matching lines @@
 // TODO(jar): We can implement a Snapshot system that *tries* to grab the
 // snapshots on the source threads *when* they have MessageLoops available
 // (worker threads don't have message loops generally, and hence gathering from
 // them will continue to be asynchronous).  We had an implementation of this in
 // the past, but the difficulty is dealing with message loops being terminated.
 // We can *try* to spam the available threads via some message loop proxy to
 // achieve this feat, and it *might* be valuable when we are colecting data for
 // upload via UMA (where correctness of data may be more significant than for a
 // single screen of about:profiler).
 //
-// TODO(jar): We need to save a single sample in each DeathData instance of the
-// times recorded.  This sample should be selected in a uniformly random way.
-//
 // TODO(jar): We should support (optionally) the recording of parent-child
 // relationships for tasks.  This should be done by detecting what tasks are
 // Born during the running of a parent task.  The resulting data can be used by
 // a smarter profiler to aggregate the cost of a series of child tasks into
 // the ancestor task.  It can also be used to illuminate what child or parent is
 // related to each task.
 //
 // TODO(jar): We need to store DataCollections, and provide facilities for
 // taking the difference between two gathered DataCollections.  For now, we're
 // just adding a hack that Reset()s to zero all counts and stats.  This is also
@@ skipping 94 matching lines @@
   // assumes ownership of the returned instance.
   base::DictionaryValue* ToValue() const;
 
   // Reset the max values to zero.
   void ResetMax();
 
   // Reset all tallies to zero. This is used as a hack on realtime data.
   void Clear();
 
  private:
-  // Number of runs seen.
+  // Members are ordered from most regularly read and updated, to least
+  // frequently used.  This might help a bit with cache lines.
+  // Number of runs seen (divisor for calculating averages).
   int count_;
-  // Data about run time durations.
+  // Basic tallies, used to compute averages.
   DurationInt run_duration_sum_;
+  DurationInt queue_duration_sum_;
+  // Max values, used by local visualization routines.  These are often read,
+  // but rarely updated.
   DurationInt run_duration_max_;
+  DurationInt queue_duration_max_;
+  // Samples, used by by crowd sourcing gatherers.  These are almost never read,
+  // and rarely updated.
   DurationInt run_duration_sample_;
-  // Data about queueing times durations.
-  DurationInt queue_duration_sum_;
-  DurationInt queue_duration_max_;
   DurationInt queue_duration_sample_;
 };
 
 //------------------------------------------------------------------------------
 // A temporary collection of data that can be sorted and summarized.  It is
 // gathered (carefully) from many threads.  Instances are held in arrays and
 // processed, filtered, and rendered.
 // The source of this data was collected on many threads, and is asynchronously
 // changing.  The data in this instance is not asynchronously changing.
 
@@ skipping 368 matching lines @@
   }
 
  private:
 
   DISALLOW_COPY_AND_ASSIGN(AutoTracking);
 };
 
 }  // namespace tracked_objects
 
 #endif  // BASE_TRACKED_OBJECTS_H_