Minor cleanup preparing for recording parent-child data

I removed the branch-free macro.  I really need to 
use a profiler to see if such changes are valuable.

I cleaned up the placement of slots, putting the
rare-to-use values together (so they'll probably get
better handled by cache lines.

r=rtenneti
Review URL: http://codereview.chromium.org/8888004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113749 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 21 insertions, 23 deletions

diff --git a/base/tracked_objects.cc b/base/tracked_objects.cc
index ffb083b..614c17a 100644
--- a/base/tracked_objects.cc
+++ b/base/tracked_objects.cc
@@ -43,7 +43,7 @@ DeathData::DeathData(int count) {
   count_ = count;
 }
 
-// TODO(jar): I need to see if this macro to optimize branching is worth it.
+// TODO(jar): I need to see if this macro to optimize branching is worth using.
 //
 // This macro has no branching, so it is surely fast, and is equivalent to:
 //             if (assign_it)
@@ -56,28 +56,24 @@ DeathData::DeathData(int count) {
 void DeathData::RecordDeath(const DurationInt queue_duration,
                             const DurationInt run_duration,
                             int32 random_number) {
+  ++count_;
   queue_duration_sum_ += queue_duration;
   run_duration_sum_ += run_duration;
-  ++count_;
+
+  if (queue_duration_max_ < queue_duration)
+    queue_duration_max_ = queue_duration;
+  if (run_duration_max_ < run_duration)
+    run_duration_max_ = run_duration;
 
   // Take a uniformly distributed sample over all durations ever supplied.
   // The probability that we (instead) use this new sample is 1/count_.  This
   // results in a completely uniform selection of the sample.
   // We ignore the fact that we correlated our selection of a sample of run
   // and queue times.
-  bool take_sample = 0 == (random_number % count_);
-  CONDITIONAL_ASSIGN(take_sample, queue_duration_sample_, queue_duration);
-  CONDITIONAL_ASSIGN(take_sample, run_duration_sample_, run_duration);
-
-  CONDITIONAL_ASSIGN(queue_duration_max_ < queue_duration, queue_duration_max_,
-                     queue_duration);
-  CONDITIONAL_ASSIGN(run_duration_max_ < run_duration, run_duration_max_,
-                     run_duration);
-  // Ensure we got the macros right.
-  DCHECK_GE(queue_duration_max_, queue_duration);
-  DCHECK_GE(run_duration_max_, run_duration);
-  DCHECK(!take_sample || run_duration_sample_ == run_duration);
-  DCHECK(!take_sample || queue_duration_sample_ == queue_duration);
+  if (0 == (random_number % count_)) {
+    queue_duration_sample_ = queue_duration;
+    run_duration_sample_ = run_duration;
+  }
 }
 
 int DeathData::count() const { return count_; }
diff --git a/base/tracked_objects.h b/base/tracked_objects.h
index 1eca68b..404306c 100644
--- a/base/tracked_objects.h
+++ b/base/tracked_objects.h
@@ -164,9 +164,6 @@
 // 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
@@ -281,15 +278,20 @@ class BASE_EXPORT DeathData {
   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 run_duration_max_;
-  DurationInt run_duration_sample_;
-  // Data about queueing times durations.
   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_;
   DurationInt queue_duration_sample_;
 };