Replacing circular queue by single buffer in CPU Profiler.

src/cpu-profiler.cc

Index: src/cpu-profiler.cc
diff --git a/src/cpu-profiler.cc b/src/cpu-profiler.cc
index ff470e231a959f063ccf6422be5976a3a2d52aeb..787bf1875644f2e53292f74c7178df46dc7f19e7 100644
--- a/src/cpu-profiler.cc
+++ b/src/cpu-profiler.cc
@@ -39,9 +39,6 @@
 namespace v8 {
 namespace internal {
 
-static const int kEventsBufferSize = 256 * KB;
-static const int kTickSamplesBufferChunkSize = 64 * KB;
-static const int kTickSamplesBufferChunksCount = 16;
 static const int kProfilerStackSize = 64 * KB;
 
 
@@ -51,9 +48,7 @@ ProfilerEventsProcessor::ProfilerEventsProcessor(ProfileGenerator* generator, Sa
       sampler_(sampler),
       running_(true),
       interval_in_useconds_(interval_in_useconds),
-      ticks_buffer_(sizeof(TickSampleEventRecord),
-                    kTickSamplesBufferChunkSize,
-                    kTickSamplesBufferChunksCount),
+      ticks_buffer_is_empty_(true),

[Jakob Kummerow, 2012/09/04 11:25:18]

You should still initialize ticks_buffer_(NULL) too (C++ doesn't do that
automatically).

[rogulenko, 2012/09/04 13:14:55]

Did you mean that you would like ticks_buffer_ to be a pointer?

[Jakob Kummerow, 2012/09/04 13:36:22]

Ah, sorry, somehow I thought it was one already. It's fine then.

       enqueue_order_(0) {
 }
 
@@ -208,8 +203,8 @@ bool ProfilerEventsProcessor::ProcessCodeEvent(unsigned* dequeue_order) {
 }
 
 
-bool ProfilerEventsProcessor::ProcessTicks(int64_t stop_time, unsigned dequeue_order) {
-  while (stop_time == -1 || OS::Ticks() < stop_time) {
+bool ProfilerEventsProcessor::ProcessTicks(unsigned dequeue_order) {
+  while (true) {
     if (!ticks_from_vm_buffer_.IsEmpty()
         && ticks_from_vm_buffer_.Peek()->order == dequeue_order) {
       TickSampleEventRecord record;
@@ -217,35 +212,26 @@ bool ProfilerEventsProcessor::ProcessTicks(int64_t stop_time, unsigned dequeue_o
       generator_->RecordTickSample(record.sample);
     }
 
-    const TickSampleEventRecord* rec =
-        TickSampleEventRecord::cast(ticks_buffer_.StartDequeue());
-    if (rec == NULL) return !ticks_from_vm_buffer_.IsEmpty();
-    // Make a local copy of tick sample record to ensure that it won't
-    // be modified as we are processing it. This is possible as the
-    // sampler writes w/o any sync to the queue, so if the processor
-    // will get far behind, a record may be modified right under its
-    // feet.
-    TickSampleEventRecord record = *rec;
-    if (record.order == dequeue_order) {
+    if (ticks_buffer_is_empty_) return !ticks_from_vm_buffer_.IsEmpty();
+    if (ticks_buffer_.order == dequeue_order) {

[Jakob Kummerow, 2012/09/04 11:25:18]

Does it still make sense to have a dequeue_order specified and compared against
when there's no queue any more?

[rogulenko, 2012/09/04 13:14:55]

ProfilerEventsProcessor has two queues. One to keep stack samples (circular
queue, that is removed by this patch), another to keep code events. Code events
are used to keep up-to-date a map from pointers in JavaScript stack to code
lines. Actually dequeue_order for a stack sample is the number of code events
recorded before taking this stack sample. Global dequeue_order is the number of
processed code events. So inequality here means that we processed less code
events than we recorded before taking a stack sample => we should process
another code event.

       // A paranoid check to make sure that we don't get a memory overrun
       // in case of frames_count having a wild value.
-      if (record.sample.frames_count < 0
-          || record.sample.frames_count > TickSample::kMaxFramesCount)
-        record.sample.frames_count = 0;
-      generator_->RecordTickSample(record.sample);
-      ticks_buffer_.FinishDequeue();
+      if (ticks_buffer_.sample.frames_count < 0
+          || ticks_buffer_.sample.frames_count > TickSample::kMaxFramesCount)
+        ticks_buffer_.sample.frames_count = 0;

[Jakob Kummerow, 2012/09/04 11:25:18]

{} around the conditional block please

+      generator_->RecordTickSample(ticks_buffer_.sample);
+      ticks_buffer_is_empty_ = true;
     } else {
       return true;
     }
   }
-  return false;
 }
 
 
 void ProfilerEventsProcessor::ProcessEventsQueue(int64_t stop_time, unsigned* dequeue_order) {
   while (OS::Ticks() < stop_time) {
     // Process ticks until we have any.
-    if (ProcessTicks(stop_time, *dequeue_order)) {
+    if (ProcessTicks(*dequeue_order)) {
       // All ticks of the current dequeue_order are processed,
       // proceed to the next code event.
       ProcessCodeEvent(dequeue_order);
@@ -262,11 +248,6 @@ void ProfilerEventsProcessor::Run() {
     sampler_->DoSample();
     ProcessEventsQueue(stop_time, &dequeue_order);
   }
-
-  // Process remaining tick events.
-  ticks_buffer_.FlushResidualRecords();
-  // Perform processing until we have tick events, skip remaining code events.
-  while (ProcessTicks(-1, dequeue_order) && ProcessCodeEvent(&dequeue_order)) { }
 }
 
 
@@ -321,15 +302,22 @@ CpuProfile* CpuProfiler::FindProfile(Object* security_token, unsigned uid) {
 }
 
 
-TickSample* CpuProfiler::TickSampleEvent(Isolate* isolate) {
+TickSample* CpuProfiler::StartTickSampleEvent(Isolate* isolate) {
   if (CpuProfiler::is_profiling(isolate)) {
-    return isolate->cpu_profiler()->processor_->TickSampleEvent();
+    return isolate->cpu_profiler()->processor_->StartTickSampleEvent();
   } else {
     return NULL;
   }
 }
 
 
+void CpuProfiler::FinishTickSampleEvent(Isolate* isolate) {
+  if (CpuProfiler::is_profiling(isolate)) {
+    isolate->cpu_profiler()->processor_->FinishTickSampleEvent();
+  }
+}
+
+
 void CpuProfiler::DeleteAllProfiles() {
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate->cpu_profiler() != NULL);