Simplify sampling rate calculation

src/profile-generator.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 354 matching lines @@
 }
 
 
 void ProfileTree::ShortPrint() {
   OS::Print("root: %u %u %.2fms %.2fms\n",
             root_->total_ticks(), root_->self_ticks(),
             root_->GetTotalMillis(), root_->GetSelfMillis());
 }
 
 
+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();
+
+  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);
 }
 
 
-void CpuProfile::SetActualSamplingRate(double actual_sampling_rate) {
-  top_down_.SetTickRatePerMs(actual_sampling_rate);
-}
-
-
 void CpuProfile::ShortPrint() {
   OS::Print("top down ");
   top_down_.ShortPrint();
 }
 
 
 void CpuProfile::Print() {
   OS::Print("[Top down]:\n");
   top_down_.Print();
 }
@@ skipping 121 matching lines @@
       current_profiles_semaphore_->Signal();
       return false;
     }
   }
   current_profiles_.Add(new CpuProfile(title, uid, record_samples));
   current_profiles_semaphore_->Signal();
   return true;
 }
 
 
-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();
   for (int i = current_profiles_.length() - 1; i >= 0; --i) {
     if (title_len == 0 || strcmp(current_profiles_[i]->title(), title) == 0) {
       profile = current_profiles_.Remove(i);
       break;
     }
   }
   current_profiles_semaphore_->Signal();
 
   if (profile == NULL) return NULL;
-  profile->CalculateTotalTicks();
-  profile->SetActualSamplingRate(actual_sampling_rate);
+  profile->CalculateTotalTicksAndSamplingRate();
   finished_profiles_.Add(profile);
   return profile;
 }
 
 
 bool CpuProfilesCollection::IsLastProfile(const char* title) {
   // Called from VM thread, and only it can mutate the list,
   // so no locking is needed here.
   if (current_profiles_.length() != 1) return false;
   return StrLength(title) == 0
@@ skipping 36 matching lines @@
   CodeEntry* code_entry = new CodeEntry(tag,
                                         name,
                                         name_prefix,
                                         resource_name,
                                         line_number);
   code_entries_.Add(code_entry);
   return code_entry;
 }
 
 
-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 =
     "(program)";
 const char* const ProfileGenerator::kGarbageCollectorEntryName =
     "(garbage collector)";
 const char* const ProfileGenerator::kUnresolvedFunctionName =
     "(unresolved function)";
 
 
@@ skipping 80 matching lines @@
     if (no_symbolized_entries) {
       *entry++ = EntryForVMState(sample.state);
     }
   }
 
   profiles_->AddPathToCurrentProfiles(entries);
 }
 
 
 } }  // namespace v8::internal