Make CPU profiler do not hog 100% of CPU.

src/cpu-profiler.cc

Index: src/cpu-profiler.cc
diff --git a/src/cpu-profiler.cc b/src/cpu-profiler.cc
index a8a57d1d67c6679eb61233db32a3a2903fd33810..5d021ec5358f3991e085873d156252ad1d1120fa 100644
--- a/src/cpu-profiler.cc
+++ b/src/cpu-profiler.cc
@@ -120,16 +120,32 @@ ProfilerEventsProcessor::SampleProcessingResult
 
 void ProfilerEventsProcessor::Run() {
   while (!!base::NoBarrier_Load(&running_)) {
-    base::ElapsedTimer timer;
-    timer.Start();
-    // Keep processing existing events until we need to do next sample.
+    base::TimeTicks nextSampleTime =
+        base::TimeTicks::HighResolutionNow() + period_;
+    base::TimeTicks now;
+    SampleProcessingResult result;
+    // Keep processing existing events until we need to do next sample
+    // or the ticks buffer is empty.
     do {
-      if (FoundSampleForNextCodeEvent == ProcessOneSample()) {
+      result = ProcessOneSample();
+      if (result == FoundSampleForNextCodeEvent) {
         // All ticks of the current last_processed_code_event_id_ are
         // processed, proceed to the next code event.
         ProcessCodeEvent();
       }
-    } while (!timer.HasExpired(period_));
+      now = base::TimeTicks::HighResolutionNow();
+    } while (result != NoSamplesInQueue && now < nextSampleTime);
+
+    if (nextSampleTime > now) {
+#if V8_OS_WIN

[Benedikt Meurer, 2015/04/30 05:06:01]

I don't really like this special casing for Windows here. Is there no
alternative to Sleep on Windows which would work for our purpose?

[yurys, 2015/04/30 08:10:02]

Would "Multimedia Timers" work here?

[alph, 2015/04/30 10:13:34]

I'm not aware of such method. I appreciate if you can suggest something.
AFAIK this is a fundamental windows thread scheduler property. There's a
possibility to decrease scheduler time slice down to 1ms, but this is still too
much for our purposes.

[alph, 2015/04/30 10:13:34]

They have 1ms resolution at best which is still not enough for us.

+      // Do not use Sleep on Windows as it is very imprecise.
+      // Could be up to 16ms jitter, which is unacceptable for the purpose.
+      while (base::TimeTicks::HighResolutionNow() < nextSampleTime) {
+      }
+#else
+      base::OS::Sleep(nextSampleTime - now);
+#endif
+    }
 
     // Schedule next sample. sampler_ is NULL in tests.
     if (sampler_) sampler_->DoSample();