Track how much time the compiler thread spends doing useful work.

src/optimizing-compiler-thread.cc

Index: src/optimizing-compiler-thread.cc
diff --git a/src/optimizing-compiler-thread.cc b/src/optimizing-compiler-thread.cc
index ec302badab116162f0865159e534cc995364a9ef..d0cc167041931939a787912f7c3b884994e6d4a0 100644
--- a/src/optimizing-compiler-thread.cc
+++ b/src/optimizing-compiler-thread.cc
@@ -43,13 +43,22 @@ void OptimizingCompilerThread::Run() {
 #endif
   Isolate::SetIsolateThreadLocals(isolate_, NULL);
 
+  int64_t epoch = 0;
+  if (FLAG_trace_parallel_recompilation) epoch = OS::Ticks();
+
   while (true) {
     input_queue_semaphore_->Wait();
     if (Acquire_Load(&stop_thread_)) {
       stop_semaphore_->Signal();
+      if (FLAG_trace_parallel_recompilation) {
+        time_spent_total_ = OS::Ticks() - epoch;
+      }
       return;
     }
 
+    int64_t compiling_start = 0;
+    if (FLAG_trace_parallel_recompilation) compiling_start = OS::Ticks();
+
     Heap::RelocationLock relocation_lock(isolate_->heap());
     OptimizingCompiler* optimizing_compiler = NULL;
     input_queue_.Dequeue(&optimizing_compiler);
@@ -64,6 +73,10 @@ void OptimizingCompilerThread::Run() {
 
     output_queue_.Enqueue(optimizing_compiler);
     isolate_->stack_guard()->RequestCodeReadyEvent();
+
+    if (FLAG_trace_parallel_recompilation) {
+      time_spent_compiling_ += OS::Ticks() - compiling_start;
+    }
   }
 }
 
@@ -72,6 +85,13 @@ void OptimizingCompilerThread::Stop() {
   Release_Store(&stop_thread_, static_cast<AtomicWord>(true));
   input_queue_semaphore_->Signal();
   stop_semaphore_->Wait();
+
+  if (FLAG_trace_parallel_recompilation) {
+    double compile_time = static_cast<double>(time_spent_compiling_);
+    double total_time = static_cast<double>(time_spent_total_);
+    double percentage = (compile_time * 100) / total_time;
+    PrintF("  ** Compiler thread did %.2f%% useful work\n", percentage);
+  }
 }