Make CPU profiler do not hog 100% of CPU.

src/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/v8.h"
 
 #include "src/cpu-profiler-inl.h"
 
 #include "src/compiler.h"
 #include "src/deoptimizer.h"
@@ skipping 102 matching lines @@
     return FoundSampleForNextCodeEvent;
   }
   generator_->RecordTickSample(record->sample);
   ticks_buffer_.Remove();
   return OneSampleProcessed;
 }
 
 
 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();
   }
 
   // Process remaining tick events.
   do {
     SampleProcessingResult result;
     do {
       result = ProcessOneSample();
@@ skipping 379 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 v8::internal