Add StartProfiling to filter out v8 warm up

src/profiler/cpu-profiler.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/profiler/cpu-profiler.h"
 
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
 #include "src/frames-inl.h"
 #include "src/locked-queue-inl.h"
@@ skipping 282 matching lines @@
 }
 
 void CpuProfiler::CollectSample() {
   if (processor_) {
     processor_->AddCurrentStack(isolate_);
   }
 }
 
 void CpuProfiler::StartProfiling(const char* title, bool record_samples) {
   if (profiles_->StartProfiling(title, record_samples)) {
+    TRACE_EVENT0("v8", "CpuProfiler::StartProfiling");
     StartProcessorIfNotStarted();
   }
 }
 
 
 void CpuProfiler::StartProfiling(String* title, bool record_samples) {
   StartProfiling(profiles_->GetName(title), record_samples);
   isolate_->debug()->feature_tracker()->Track(DebugFeatureTracker::kProfiler);
 }
 
@@ skipping 17 matching lines @@
   is_profiling_ = true;
   isolate_->set_is_profiling(true);
   // Enumerate stuff we already have in the heap.
   DCHECK(isolate_->heap()->HasBeenSetUp());
   if (!FLAG_prof_browser_mode) {
     logger->LogCodeObjects();
   }
   logger->LogCompiledFunctions();
   logger->LogAccessorCallbacks();
   LogBuiltins();
   // Enable stack sampling.

[alph, 2017/06/19 18:39:47]

I suggest to move the event injection point to here, as most of the warmup time
is usually spent in LogCompiledFunctions & co.

[bgirard, 2017/06/19 19:04:32]

TRACE_EVENT0 will time all the work happening while it's on the stack which
would include the entire runtime of StartProcessorIfNotStarted including the
total time of LogCompiledFunctions.

Perhaps you're thinking of TRACE_EVENT_INSTANT0 which would let me insert a
marker when the execution has been completed? I would prefer to have an event
for the entire duration.

[alph, 2017/06/19 20:10:03]

That makes sense. I thought you wanted to mark a moment when the sampling is
really started. lgtm

   processor_->AddCurrentStack(isolate_);
   processor_->StartSynchronously();
 }
 
 CpuProfile* CpuProfiler::StopProfiling(const char* title) {
   if (!is_profiling_) return nullptr;
   StopProcessorIfLastProfile(title);
   return profiles_->StopProfiling(title);
 }
 
@@ skipping 28 matching lines @@
     ReportBuiltinEventRecord* rec = &evt_rec.ReportBuiltinEventRecord_;
     Builtins::Name id = static_cast<Builtins::Name>(i);
     rec->start = builtins->builtin(id)->address();
     rec->builtin_id = id;
     processor_->Enqueue(evt_rec);
   }
 }
 
 }  // namespace internal
 }  // namespace v8