New approach to Crankshaft decision-making

src/platform-linux.cc

Index: src/platform-linux.cc
diff --git a/src/platform-linux.cc b/src/platform-linux.cc
index e72d095b0aded82a47a8e71a399544971336cc51..1ea7f5783a82a0671159c33fd114f9b1c8f5857e 100644
--- a/src/platform-linux.cc
+++ b/src/platform-linux.cc
@@ -1038,7 +1038,8 @@ class SignalSender : public Thread {
   explicit SignalSender(int interval)
       : Thread("SignalSender"),
         vm_tgid_(getpid()),
-        interval_(interval) {}
+        interval_(interval),
+        tick_count_(0) {}
 
   static void InstallSignalHandler() {
     struct sigaction sa;
@@ -1065,7 +1066,11 @@ class SignalSender : public Thread {
       instance_ = new SignalSender(sampler->interval());
       instance_->Start();
     } else {
+#if defined(V8_TARGET_ARCH_ARM) || defined(V8_TARGET_ARCH_MIPS)
+      // Flexible interval, assertion doesn't make sense.
+#else
       ASSERT(instance_->interval_ == sampler->interval());
+#endif
     }
   }
 
@@ -1080,6 +1085,14 @@ class SignalSender : public Thread {
     }
   }
 
+  static void ResetInterval(int interval) {
+    ScopedLock lock(mutex_);
+    if (instance_ != NULL) {
+      instance_->interval_ = interval;
+      instance_->tick_count_ = 0;
+    }
+  }
+
   // Implement Thread::Run().
   virtual void Run() {
     SamplerRegistry::State state;
@@ -1098,6 +1111,19 @@ class SignalSender : public Thread {
       if (!cpu_profiling_enabled) {
         if (rate_limiter_.SuspendIfNecessary()) continue;
       }
+#if defined(V8_TARGET_ARCH_ARM) || defined(V8_TARGET_ARCH_MIPS)
+      // ARM and MIPS CPUs are typically slower than IA32/X64, so for them
+      // the tick interval is increased to let them perform a more significant
+      // amount of work between subsequent ticks.
+
+      static const int kNumberOfFastTicks = 5;
+      static const int kSlowTickIntervalMs = 5;
+
+      if (tick_count_ == kNumberOfFastTicks) {
+        interval_ = kSlowTickIntervalMs;
+      }
+      tick_count_++;
+#endif
       if (cpu_profiling_enabled && runtime_profiler_enabled) {
         if (!SamplerRegistry::IterateActiveSamplers(&DoCpuProfile, this)) {
           return;
@@ -1165,7 +1191,8 @@ class SignalSender : public Thread {
   }
 
   const int vm_tgid_;
-  const int interval_;
+  int interval_;
+  int tick_count_;
   RuntimeProfilerRateLimiter rate_limiter_;
 
   // Protects the process wide state below.
@@ -1214,4 +1241,9 @@ void Sampler::Stop() {
 }
 
 
+void Sampler::ResetInterval(int interval) {
+  SignalSender::ResetInterval(interval);
+}
+
+
 } }  // namespace v8::internal