Simplify sampling rate calculation

src/profile-generator.cc

Index: src/profile-generator.cc
diff --git a/src/profile-generator.cc b/src/profile-generator.cc
index 8428303afe6da9daf82dddcb43aa0d827a8d4be6..4e2e38988a34a29b7f3331bd18532cf01c9bb131 100644
--- a/src/profile-generator.cc
+++ b/src/profile-generator.cc
@@ -372,19 +372,30 @@ void ProfileTree::ShortPrint() {
 }
 
 
+CpuProfile::CpuProfile(const char* title, unsigned uid, bool record_samples)
+    : title_(title),
+      uid_(uid),
+      record_samples_(record_samples),
+      start_time_ms_(OS::TimeCurrentMillis()),

[loislo, 2013/07/29 18:01:27]

Can we do that on the first sample?

[yurys, 2013/07/29 18:13:21]

Doing it here should be more fair. With the sampling being done on the
processing thread it will make no difference. The only problem might be the
delay we observed on some windows machines but I think we should find a way to
reduce that delay instead of cheating with the start time.

+      end_time_ms_(0) {
+}
+
+
 void CpuProfile::AddPath(const Vector<CodeEntry*>& path) {
   ProfileNode* top_frame_node = top_down_.AddPathFromEnd(path);
   if (record_samples_) samples_.Add(top_frame_node);
 }
 
 
-void CpuProfile::CalculateTotalTicks() {
+void CpuProfile::CalculateTotalTicksAndSamplingRate() {
+  end_time_ms_ = OS::TimeCurrentMillis();
   top_down_.CalculateTotalTicks();
-}
-
 
-void CpuProfile::SetActualSamplingRate(double actual_sampling_rate) {
-  top_down_.SetTickRatePerMs(actual_sampling_rate);
+  double duration = end_time_ms_ - start_time_ms_;
+  if (duration < 1) duration = 1;
+  unsigned ticks = top_down_.root()->total_ticks();
+  double rate = ticks / duration;
+  top_down_.SetTickRatePerMs(rate);
 }
 
 
@@ -529,8 +540,7 @@ bool CpuProfilesCollection::StartProfiling(const char* title, unsigned uid,
 }
 
 
-CpuProfile* CpuProfilesCollection::StopProfiling(const char* title,
-                                                 double actual_sampling_rate) {
+CpuProfile* CpuProfilesCollection::StopProfiling(const char* title) {
   const int title_len = StrLength(title);
   CpuProfile* profile = NULL;
   current_profiles_semaphore_->Wait();
@@ -543,8 +553,7 @@ CpuProfile* CpuProfilesCollection::StopProfiling(const char* title,
   current_profiles_semaphore_->Signal();
 
   if (profile == NULL) return NULL;
-  profile->CalculateTotalTicks();
-  profile->SetActualSamplingRate(actual_sampling_rate);
+  profile->CalculateTotalTicksAndSamplingRate();
   finished_profiles_.Add(profile);
   return profile;
 }
@@ -601,29 +610,6 @@ CodeEntry* CpuProfilesCollection::NewCodeEntry(
 }
 
 
-void SampleRateCalculator::Tick() {
-  if (--wall_time_query_countdown_ == 0)
-    UpdateMeasurements(OS::TimeCurrentMillis());
-}
-
-
-void SampleRateCalculator::UpdateMeasurements(double current_time) {
-  if (measurements_count_++ != 0) {
-    const double measured_ticks_per_ms =
-        (kWallTimeQueryIntervalMs * ticks_per_ms_) /
-        (current_time - last_wall_time_);
-    // Update the average value.
-    ticks_per_ms_ +=
-        (measured_ticks_per_ms - ticks_per_ms_) / measurements_count_;
-    // Update the externally accessible result.
-    result_ = static_cast<AtomicWord>(ticks_per_ms_ * kResultScale);
-  }
-  last_wall_time_ = current_time;
-  wall_time_query_countdown_ =
-      static_cast<unsigned>(kWallTimeQueryIntervalMs * ticks_per_ms_);
-}
-
-
 const char* const ProfileGenerator::kAnonymousFunctionName =
     "(anonymous function)";
 const char* const ProfileGenerator::kProgramEntryName =