New approach to Crankshaft decision-making

src/platform-linux.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1020 matching lines @@
 class SignalSender : public Thread {
  public:
   enum SleepInterval {
     HALF_INTERVAL,
     FULL_INTERVAL
   };
 
   explicit SignalSender(int interval)
       : Thread("SignalSender"),
         vm_tgid_(getpid()),
-        interval_(interval) {}
+        interval_(interval),
+        tick_count_(0) {}
 
   static void InstallSignalHandler() {
     struct sigaction sa;
     sa.sa_sigaction = ProfilerSignalHandler;
     sigemptyset(&sa.sa_mask);
     sa.sa_flags = SA_RESTART | SA_SIGINFO;
     signal_handler_installed_ =
         (sigaction(SIGPROF, &sa, &old_signal_handler_) == 0);
   }
 
   static void RestoreSignalHandler() {
     if (signal_handler_installed_) {
       sigaction(SIGPROF, &old_signal_handler_, 0);
       signal_handler_installed_ = false;
     }
   }
 
   static void AddActiveSampler(Sampler* sampler) {
     ScopedLock lock(mutex_);
     SamplerRegistry::AddActiveSampler(sampler);
     if (instance_ == NULL) {
       // Start a thread that will send SIGPROF signal to VM threads,
       // when CPU profiling will be enabled.
       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
     }
   }
 
   static void RemoveActiveSampler(Sampler* sampler) {
     ScopedLock lock(mutex_);
     SamplerRegistry::RemoveActiveSampler(sampler);
     if (SamplerRegistry::GetState() == SamplerRegistry::HAS_NO_SAMPLERS) {
       RuntimeProfiler::StopRuntimeProfilerThreadBeforeShutdown(instance_);
       delete instance_;
       instance_ = NULL;
       RestoreSignalHandler();
     }
   }
 
+  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;
     while ((state = SamplerRegistry::GetState()) !=
            SamplerRegistry::HAS_NO_SAMPLERS) {
       bool cpu_profiling_enabled =
           (state == SamplerRegistry::HAS_CPU_PROFILING_SAMPLERS);
       bool runtime_profiler_enabled = RuntimeProfiler::IsEnabled();
       if (cpu_profiling_enabled && !signal_handler_installed_) {
         InstallSignalHandler();
       } else if (!cpu_profiling_enabled && signal_handler_installed_) {
         RestoreSignalHandler();
       }
       // When CPU profiling is enabled both JavaScript and C++ code is
       // profiled. We must not suspend.
       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;
         }
         Sleep(HALF_INTERVAL);
         if (!SamplerRegistry::IterateActiveSamplers(&DoRuntimeProfile, NULL)) {
           return;
         }
         Sleep(HALF_INTERVAL);
       } else {
@@ skipping 47 matching lines @@
               "SignalSender usleep error; interval = %u, errno = %d\n",
               interval,
               errno);
       ASSERT(result == 0 || errno == EINTR);
     }
 #endif
     USE(result);
   }
 
   const int vm_tgid_;
-  const int interval_;
+  int interval_;
+  int tick_count_;
   RuntimeProfilerRateLimiter rate_limiter_;
 
   // Protects the process wide state below.
   static Mutex* mutex_;
   static SignalSender* instance_;
   static bool signal_handler_installed_;
   static struct sigaction old_signal_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(SignalSender);
 };
@@ skipping 28 matching lines @@
 }
 
 
 void Sampler::Stop() {
   ASSERT(IsActive());
   SignalSender::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 
+void Sampler::ResetInterval(int interval) {
+  SignalSender::ResetInterval(interval);
+}
+
+
 } }  // namespace v8::internal