Add JIT

Currently disabled by default unless -Xjit is passed in.

The proposed JIT is a method JIT which works by utilizing interpreter
instrumentation to request compilation of hot methods async during
runtime.

JIT options:
-Xjit / -Xnojit
-Xjitcodecachesize:N
-Xjitthreshold:integervalue

The JIT has a shared copy of a compiler driver which is accessed
by worker threads to compile individual methods.

Added JIT code cache and data cache, currently sized at 2 MB
capacity by default. Most apps will only fill a small fraction of
this cache however.

Added support to the compiler for compiling interpreter quickened
byte codes.

Added test target ART_TEST_JIT=TRUE and --jit for run-test.

TODO:
Clean up code cache.
Delete compiled methods after they are added to code cache.
Add more optimizations related to runtime checks e.g. direct pointers
for invokes.
Add method recompilation.
Move instrumentation to DexFile to improve performance and reduce
memory usage.

Bug: 17950037

Change-Id: Ifa5b2684a2d5059ec5a5210733900aafa3c51bca

6 files changed, 725 insertions, 0 deletions

diff --git a/runtime/jit/jit.cc b/runtime/jit/jit.cc
new file mode 100644
index 0000000000..539c181952
--- /dev/null
+++ b/runtime/jit/jit.cc
@@ -0,0 +1,160 @@
+/*
+ * Copyright 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "jit.h"
+
+#include <dlfcn.h>
+
+#include "entrypoints/runtime_asm_entrypoints.h"
+#include "interpreter/interpreter.h"
+#include "jit_code_cache.h"
+#include "jit_instrumentation.h"
+#include "mirror/art_method-inl.h"
+#include "runtime.h"
+#include "runtime_options.h"
+#include "thread_list.h"
+#include "utils.h"
+
+namespace art {
+namespace jit {
+
+JitOptions* JitOptions::CreateFromRuntimeArguments(const RuntimeArgumentMap& options) {
+  if (!options.GetOrDefault(RuntimeArgumentMap::UseJIT)) {
+    return nullptr;
+  }
+  auto* jit_options = new JitOptions;
+  jit_options->code_cache_capacity_ =
+      options.GetOrDefault(RuntimeArgumentMap::JITCodeCacheCapacity);
+  jit_options->compile_threshold_ =
+      options.GetOrDefault(RuntimeArgumentMap::JITCompileThreshold);
+  return jit_options;
+}
+
+Jit::Jit()
+    : jit_library_handle_(nullptr), jit_compiler_handle_(nullptr), jit_load_(nullptr),
+      jit_compile_method_(nullptr) {
+}
+
+Jit* Jit::Create(JitOptions* options, std::string* error_msg) {
+  std::unique_ptr<Jit> jit(new Jit);
+  if (!jit->LoadCompiler(error_msg)) {
+    return nullptr;
+  }
+  jit->code_cache_.reset(JitCodeCache::Create(options->GetCodeCacheCapacity(), error_msg));
+  if (jit->GetCodeCache() == nullptr) {
+    return nullptr;
+  }
+  LOG(INFO) << "JIT created with code_cache_capacity="
+      << PrettySize(options->GetCodeCacheCapacity())
+      << " compile_threshold=" << options->GetCompileThreshold();
+  return jit.release();
+}
+
+bool Jit::LoadCompiler(std::string* error_msg) {
+  jit_library_handle_ = dlopen(
+      kIsDebugBuild ? "libartd-compiler.so" : "libart-compiler.so", RTLD_NOW);
+  if (jit_library_handle_ == nullptr) {
+    std::ostringstream oss;
+    oss << "JIT could not load libart-compiler.so: " << dlerror();
+    *error_msg = oss.str();
+    return false;
+  }
+  jit_load_ = reinterpret_cast<void* (*)(CompilerCallbacks**)>(
+      dlsym(jit_library_handle_, "jit_load"));
+  if (jit_load_ == nullptr) {
+    dlclose(jit_library_handle_);
+    *error_msg = "JIT couldn't find jit_load entry point";
+    return false;
+  }
+  jit_unload_ = reinterpret_cast<void (*)(void*)>(
+      dlsym(jit_library_handle_, "jit_unload"));
+  if (jit_unload_ == nullptr) {
+    dlclose(jit_library_handle_);
+    *error_msg = "JIT couldn't find jit_unload entry point";
+    return false;
+  }
+  jit_compile_method_ = reinterpret_cast<bool (*)(void*, mirror::ArtMethod*, Thread*)>(
+      dlsym(jit_library_handle_, "jit_compile_method"));
+  if (jit_compile_method_ == nullptr) {
+    dlclose(jit_library_handle_);
+    *error_msg = "JIT couldn't find jit_compile_method entry point";
+    return false;
+  }
+  CompilerCallbacks* callbacks = nullptr;
+  VLOG(jit) << "Calling JitLoad interpreter_only="
+      << Runtime::Current()->GetInstrumentation()->InterpretOnly();
+  jit_compiler_handle_ = (jit_load_)(&callbacks);
+  if (jit_compiler_handle_ == nullptr) {
+    dlclose(jit_library_handle_);
+    *error_msg = "JIT couldn't load compiler";
+    return false;
+  }
+  if (callbacks == nullptr) {
+    dlclose(jit_library_handle_);
+    *error_msg = "JIT compiler callbacks were not set";
+    jit_compiler_handle_ = nullptr;
+    return false;
+  }
+  compiler_callbacks_ = callbacks;
+  return true;
+}
+
+bool Jit::CompileMethod(mirror::ArtMethod* method, Thread* self) {
+  DCHECK(!method->IsRuntimeMethod());
+  const bool result = jit_compile_method_(jit_compiler_handle_, method, self);
+  if (result) {
+    method->SetEntryPointFromInterpreter(artInterpreterToCompiledCodeBridge);
+  }
+  return result;
+}
+
+void Jit::CreateThreadPool() {
+  CHECK(instrumentation_cache_.get() != nullptr);
+  instrumentation_cache_->CreateThreadPool();
+}
+
+void Jit::DeleteThreadPool() {
+  if (instrumentation_cache_.get() != nullptr) {
+    instrumentation_cache_->DeleteThreadPool();
+  }
+}
+
+Jit::~Jit() {
+  DeleteThreadPool();
+  if (jit_compiler_handle_ != nullptr) {
+    jit_unload_(jit_compiler_handle_);
+  }
+  if (jit_library_handle_ != nullptr) {
+    dlclose(jit_library_handle_);
+  }
+}
+
+void Jit::CreateInstrumentationCache(size_t compile_threshold) {
+  CHECK_GT(compile_threshold, 0U);
+  Runtime* const runtime = Runtime::Current();
+  runtime->GetThreadList()->SuspendAll();
+  // Add Jit interpreter instrumentation, tells the interpreter when to notify the jit to compile
+  // something.
+  instrumentation_cache_.reset(new jit::JitInstrumentationCache(compile_threshold));
+  runtime->GetInstrumentation()->AddListener(
+      new jit::JitInstrumentationListener(instrumentation_cache_.get()),
+      instrumentation::Instrumentation::kMethodEntered |
+      instrumentation::Instrumentation::kBackwardBranch);
+  runtime->GetThreadList()->ResumeAll();
+}
+
+}  // namespace jit
+}  // namespace art
diff --git a/runtime/jit/jit.h b/runtime/jit/jit.h
new file mode 100644
index 0000000000..b80015feca
--- /dev/null
+++ b/runtime/jit/jit.h
@@ -0,0 +1,102 @@
+/*
+ * Copyright 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_RUNTIME_JIT_JIT_H_
+#define ART_RUNTIME_JIT_JIT_H_
+
+#include <unordered_map>
+
+#include "instrumentation.h"
+
+#include "atomic.h"
+#include "base/macros.h"
+#include "base/mutex.h"
+#include "gc_root.h"
+#include "jni.h"
+#include "object_callbacks.h"
+#include "thread_pool.h"
+
+namespace art {
+
+class CompilerCallbacks;
+struct RuntimeArgumentMap;
+
+namespace jit {
+
+class JitCodeCache;
+class JitInstrumentationCache;
+class JitOptions;
+
+class Jit {
+ public:
+  static constexpr bool kStressMode = kIsDebugBuild;
+  static constexpr size_t kDefaultCompileThreshold = kStressMode ? 1 : 1000;
+
+  virtual ~Jit();
+  static Jit* Create(JitOptions* options, std::string* error_msg);
+  bool CompileMethod(mirror::ArtMethod* method, Thread* self)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void CreateInstrumentationCache(size_t compile_threshold);
+  void CreateThreadPool();
+  CompilerCallbacks* GetCompilerCallbacks() {
+    return compiler_callbacks_;
+  }
+  const JitCodeCache* GetCodeCache() const {
+    return code_cache_.get();
+  }
+  JitCodeCache* GetCodeCache() {
+    return code_cache_.get();
+  }
+  void DeleteThreadPool();
+
+ private:
+  Jit();
+  bool LoadCompiler(std::string* error_msg);
+
+  // JIT compiler
+  void* jit_library_handle_;
+  void* jit_compiler_handle_;
+  void* (*jit_load_)(CompilerCallbacks**);
+  void (*jit_unload_)(void*);
+  bool (*jit_compile_method_)(void*, mirror::ArtMethod*, Thread*);
+
+  std::unique_ptr<jit::JitInstrumentationCache> instrumentation_cache_;
+  std::unique_ptr<jit::JitCodeCache> code_cache_;
+  CompilerCallbacks* compiler_callbacks_;  // Owned by the jit compiler.
+};
+
+class JitOptions {
+ public:
+  static JitOptions* CreateFromRuntimeArguments(const RuntimeArgumentMap& options);
+  size_t GetCompileThreshold() const {
+    return compile_threshold_;
+  }
+  size_t GetCodeCacheCapacity() const {
+    return code_cache_capacity_;
+  }
+
+ private:
+  size_t code_cache_capacity_;
+  size_t compile_threshold_;
+
+  JitOptions() : code_cache_capacity_(0), compile_threshold_(0) {
+  }
+};
+
+}  // namespace jit
+}  // namespace art
+
+#endif  // ART_RUNTIME_JIT_JIT_H_
diff --git a/runtime/jit/jit_code_cache.cc b/runtime/jit/jit_code_cache.cc
new file mode 100644
index 0000000000..8d4965e70f
--- /dev/null
+++ b/runtime/jit/jit_code_cache.cc
@@ -0,0 +1,121 @@
+/*
+ * Copyright 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "jit_code_cache.h"
+
+#include <sstream>
+
+#include "mem_map.h"
+#include "mirror/art_method-inl.h"
+#include "oat_file-inl.h"
+
+namespace art {
+namespace jit {
+
+JitCodeCache* JitCodeCache::Create(size_t capacity, std::string* error_msg) {
+  CHECK_GT(capacity, 0U);
+  CHECK_LT(capacity, kMaxCapacity);
+  std::string error_str;
+  // Map name specific for android_os_Debug.cpp accounting.
+  MemMap* map = MemMap::MapAnonymous("jit-code-cache", nullptr, capacity,
+                                     PROT_READ | PROT_WRITE | PROT_EXEC, false, &error_str);
+  if (map == nullptr) {
+    std::ostringstream oss;
+    oss << "Failed to create read write execute cache: " << error_str << " size=" << capacity;
+    *error_msg = oss.str();
+    return nullptr;
+  }
+  return new JitCodeCache(map);
+}
+
+JitCodeCache::JitCodeCache(MemMap* mem_map)
+    : lock_("Jit code cache", kJitCodeCacheLock), num_methods_(0) {
+  VLOG(jit) << "Created jit code cache size=" << PrettySize(mem_map->Size());
+  mem_map_.reset(mem_map);
+  uint8_t* divider = mem_map->Begin() + RoundUp(mem_map->Size() / 4, kPageSize);
+  // Data cache is 1 / 4 of the map. TODO: Make this variable?
+  // Put data at the start.
+  data_cache_ptr_ = mem_map->Begin();
+  data_cache_end_ = divider;
+  data_cache_begin_ = data_cache_ptr_;
+  mprotect(data_cache_ptr_, data_cache_end_ - data_cache_begin_, PROT_READ | PROT_WRITE);
+  // Code cache after.
+  code_cache_begin_ = divider;
+  code_cache_ptr_ = divider;
+  code_cache_end_ = mem_map->End();
+}
+
+bool JitCodeCache::ContainsMethod(mirror::ArtMethod* method) const {
+  return ContainsCodePtr(method->GetEntryPointFromQuickCompiledCode());
+}
+
+bool JitCodeCache::ContainsCodePtr(const void* ptr) const {
+  return ptr >= code_cache_begin_ && ptr < code_cache_end_;
+}
+
+void JitCodeCache::FlushInstructionCache() {
+  UNIMPLEMENTED(FATAL);
+  // TODO: Investigate if we need to do this.
+  // __clear_cache(reinterpret_cast<char*>(code_cache_begin_), static_cast<int>(CodeCacheSize()));
+}
+
+uint8_t* JitCodeCache::ReserveCode(Thread* self, size_t size) {
+  MutexLock mu(self, lock_);
+  if (size > CodeCacheRemain()) {
+    return nullptr;
+  }
+  code_cache_ptr_ += size;
+  return code_cache_ptr_ - size;
+}
+
+uint8_t* JitCodeCache::AddDataArray(Thread* self, const uint8_t* begin, const uint8_t* end) {
+  MutexLock mu(self, lock_);
+  const size_t size = end - begin;
+  if (size > DataCacheRemain()) {
+    return nullptr;  // Out of space in the data cache.
+  }
+  std::copy(begin, end, data_cache_ptr_);
+  data_cache_ptr_ += size;
+  return data_cache_ptr_ - size;
+}
+
+const void* JitCodeCache::GetCodeFor(mirror::ArtMethod* method) {
+  const void* code = method->GetEntryPointFromQuickCompiledCode();
+  if (ContainsCodePtr(code)) {
+    return code;
+  }
+  MutexLock mu(Thread::Current(), lock_);
+  auto it = method_code_map_.find(method);
+  if (it != method_code_map_.end()) {
+    return it->second;
+  }
+  return nullptr;
+}
+
+void JitCodeCache::SaveCompiledCode(mirror::ArtMethod* method, const void* old_code_ptr) {
+  DCHECK_EQ(method->GetEntryPointFromQuickCompiledCode(), old_code_ptr);
+  DCHECK(ContainsCodePtr(old_code_ptr)) << PrettyMethod(method) << " old_code_ptr="
+      << old_code_ptr;
+  MutexLock mu(Thread::Current(), lock_);
+  auto it = method_code_map_.find(method);
+  if (it != method_code_map_.end()) {
+    return;
+  }
+  method_code_map_.Put(method, old_code_ptr);
+}
+
+}  // namespace jit
+}  // namespace art
diff --git a/runtime/jit/jit_code_cache.h b/runtime/jit/jit_code_cache.h
new file mode 100644
index 0000000000..aa8c7173a5
--- /dev/null
+++ b/runtime/jit/jit_code_cache.h
@@ -0,0 +1,118 @@
+/*
+ * Copyright 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_RUNTIME_JIT_JIT_CODE_CACHE_H_
+#define ART_RUNTIME_JIT_JIT_CODE_CACHE_H_
+
+#include "instrumentation.h"
+
+#include "atomic.h"
+#include "base/macros.h"
+#include "base/mutex.h"
+#include "gc_root.h"
+#include "jni.h"
+#include "oat_file.h"
+#include "object_callbacks.h"
+#include "safe_map.h"
+#include "thread_pool.h"
+
+namespace art {
+
+class CompiledMethod;
+class CompilerCallbacks;
+
+namespace mirror {
+class ArtMethod;
+}  // namespcae mirror
+
+namespace jit {
+
+class JitInstrumentationCache;
+
+class JitCodeCache {
+ public:
+  static constexpr size_t kMaxCapacity = 1 * GB;
+  static constexpr size_t kDefaultCapacity = 2 * MB;
+
+  static JitCodeCache* Create(size_t capacity, std::string* error_msg);
+
+  const uint8_t* CodeCachePtr() const {
+    return code_cache_ptr_;
+  }
+  size_t CodeCacheSize() const {
+    return code_cache_ptr_ - code_cache_begin_;
+  }
+  size_t CodeCacheRemain() const {
+    return code_cache_end_ - code_cache_ptr_;
+  }
+  size_t DataCacheSize() const {
+    return data_cache_ptr_ - data_cache_begin_;
+  }
+  size_t DataCacheRemain() const {
+    return data_cache_end_ - data_cache_ptr_;
+  }
+  size_t NumMethods() const {
+    return num_methods_;
+  }
+
+  bool ContainsMethod(mirror::ArtMethod* method) const
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  bool ContainsCodePtr(const void* ptr) const;
+
+  uint8_t* ReserveCode(Thread* self, size_t size) LOCKS_EXCLUDED(lock_);
+
+  uint8_t* AddDataArray(Thread* self, const uint8_t* begin, const uint8_t* end)
+      LOCKS_EXCLUDED(lock_);
+
+  // Get code for a method, returns null if it is not in the jit cache.
+  const void* GetCodeFor(mirror::ArtMethod* method)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) LOCKS_EXCLUDED(lock_);
+
+  void SaveCompiledCode(mirror::ArtMethod* method, const void* old_code_ptr)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) LOCKS_EXCLUDED(lock_);
+
+ private:
+  // Takes ownership of code_mem_map.
+  explicit JitCodeCache(MemMap* code_mem_map);
+  void FlushInstructionCache();
+
+  Mutex lock_;
+  // Mem map which holds code and data. We do this since we need to have 32 bit offsets from method
+  // headers in code cache which point to things in the data cache. If the maps are more than 4GB
+  // apart, having multiple maps wouldn't work.
+  std::unique_ptr<MemMap> mem_map_;
+  // Code cache section.
+  uint8_t* code_cache_ptr_;
+  const uint8_t* code_cache_begin_;
+  const uint8_t* code_cache_end_;
+  // Data cache section.
+  uint8_t* data_cache_ptr_;
+  const uint8_t* data_cache_begin_;
+  const uint8_t* data_cache_end_;
+  size_t num_methods_;
+  // TODO: This relies on methods not moving.
+  // This map holds code for methods if they were deoptimized by the instrumentation stubs. This is
+  // required since we have to implement ClassLinker::GetQuickOatCodeFor for walking stacks.
+  SafeMap<mirror::ArtMethod*, const void*> method_code_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(JitCodeCache);
+};
+
+
+}  // namespace jit
+}  // namespace art
+
+#endif  // ART_RUNTIME_JIT_JIT_CODE_CACHE_H_
diff --git a/runtime/jit/jit_instrumentation.cc b/runtime/jit/jit_instrumentation.cc
new file mode 100644
index 0000000000..160e6789be
--- /dev/null
+++ b/runtime/jit/jit_instrumentation.cc
@@ -0,0 +1,117 @@
+/*
+ * Copyright 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "jit_instrumentation.h"
+
+#include "jit.h"
+#include "jit_code_cache.h"
+#include "mirror/art_method-inl.h"
+#include "scoped_thread_state_change.h"
+
+namespace art {
+namespace jit {
+
+class JitCompileTask : public Task {
+ public:
+  explicit JitCompileTask(mirror::ArtMethod* method, JitInstrumentationCache* cache)
+      : method_(method), cache_(cache) {
+  }
+
+  virtual void Run(Thread* self) OVERRIDE {
+    ScopedObjectAccess soa(self);
+    VLOG(jit) << "JitCompileTask compiling method " << PrettyMethod(method_);
+    if (Runtime::Current()->GetJit()->CompileMethod(method_, self)) {
+      cache_->SignalCompiled(self, method_);
+    } else {
+      VLOG(jit) << "Failed to compile method " << PrettyMethod(method_);
+    }
+  }
+
+  virtual void Finalize() OVERRIDE {
+    delete this;
+  }
+
+ private:
+  mirror::ArtMethod* const method_;
+  JitInstrumentationCache* const cache_;
+};
+
+JitInstrumentationCache::JitInstrumentationCache(size_t hot_method_threshold)
+    : lock_("jit instrumentation lock"), hot_method_threshold_(hot_method_threshold) {
+}
+
+void JitInstrumentationCache::CreateThreadPool() {
+  thread_pool_.reset(new ThreadPool("Jit thread pool", 1));
+}
+
+void JitInstrumentationCache::DeleteThreadPool() {
+  thread_pool_.reset();
+}
+
+void JitInstrumentationCache::SignalCompiled(Thread* self, mirror::ArtMethod* method) {
+  ScopedObjectAccessUnchecked soa(self);
+  jmethodID method_id = soa.EncodeMethod(method);
+  MutexLock mu(self, lock_);
+  auto it = samples_.find(method_id);
+  if (it != samples_.end()) {
+    samples_.erase(it);
+  }
+}
+
+void JitInstrumentationCache::AddSamples(Thread* self, mirror::ArtMethod* method, size_t count) {
+  ScopedObjectAccessUnchecked soa(self);
+  // Since we don't have on-stack replacement, some methods can remain in the interpreter longer
+  // than we want resulting in samples even after the method is compiled.
+  if (method->IsClassInitializer() ||
+      Runtime::Current()->GetJit()->GetCodeCache()->ContainsMethod(method)) {
+    return;
+  }
+  jmethodID method_id = soa.EncodeMethod(method);
+  bool is_hot = false;
+  {
+    MutexLock mu(self, lock_);
+    size_t sample_count = 0;
+    auto it = samples_.find(method_id);
+    if (it != samples_.end()) {
+      it->second += count;
+      sample_count = it->second;
+    } else {
+      sample_count = count;
+      samples_.insert(std::make_pair(method_id, count));
+    }
+    // If we have enough samples, mark as hot and request Jit compilation.
+    if (sample_count >= hot_method_threshold_ && sample_count - count < hot_method_threshold_) {
+      is_hot = true;
+    }
+  }
+  if (is_hot) {
+    if (thread_pool_.get() != nullptr) {
+      thread_pool_->AddTask(self, new JitCompileTask(method->GetInterfaceMethodIfProxy(), this));
+      thread_pool_->StartWorkers(self);
+    } else {
+      VLOG(jit) << "Compiling hot method " << PrettyMethod(method);
+      Runtime::Current()->GetJit()->CompileMethod(method->GetInterfaceMethodIfProxy(), self);
+    }
+  }
+}
+
+JitInstrumentationListener::JitInstrumentationListener(JitInstrumentationCache* cache)
+    : instrumentation_cache_(cache) {
+  CHECK(instrumentation_cache_ != nullptr);
+}
+
+}  // namespace jit
+}  // namespace art
diff --git a/runtime/jit/jit_instrumentation.h b/runtime/jit/jit_instrumentation.h
new file mode 100644
index 0000000000..9576f4b341
--- /dev/null
+++ b/runtime/jit/jit_instrumentation.h
@@ -0,0 +1,107 @@
+/*
+ * Copyright 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_RUNTIME_JIT_JIT_INSTRUMENTATION_H_
+#define ART_RUNTIME_JIT_JIT_INSTRUMENTATION_H_
+
+#include <unordered_map>
+
+#include "instrumentation.h"
+
+#include "atomic.h"
+#include "base/macros.h"
+#include "base/mutex.h"
+#include "gc_root.h"
+#include "jni.h"
+#include "object_callbacks.h"
+#include "thread_pool.h"
+
+namespace art {
+namespace mirror {
+  class ArtField;
+  class ArtMethod;
+  class Class;
+  class Object;
+  class Throwable;
+}  // namespace mirror
+union JValue;
+class Thread;
+class ThrowLocation;
+
+namespace jit {
+
+// Keeps track of which methods are hot.
+class JitInstrumentationCache {
+ public:
+  explicit JitInstrumentationCache(size_t hot_method_threshold);
+  void AddSamples(Thread* self, mirror::ArtMethod* method, size_t samples)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void SignalCompiled(Thread* self, mirror::ArtMethod* method)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  void CreateThreadPool();
+  void DeleteThreadPool();
+
+ private:
+  Mutex lock_;
+  std::unordered_map<jmethodID, size_t> samples_;
+  size_t hot_method_threshold_;
+  std::unique_ptr<ThreadPool> thread_pool_;
+};
+
+class JitInstrumentationListener : public instrumentation::InstrumentationListener {
+ public:
+  explicit JitInstrumentationListener(JitInstrumentationCache* cache);
+
+  virtual void MethodEntered(Thread* thread, mirror::Object* /*this_object*/,
+                             mirror::ArtMethod* method, uint32_t /*dex_pc*/)
+      OVERRIDE SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
+    instrumentation_cache_->AddSamples(thread, method, 1);
+  }
+  virtual void MethodExited(Thread* /*thread*/, mirror::Object* /*this_object*/,
+                            mirror::ArtMethod* /*method*/, uint32_t /*dex_pc*/,
+                            const JValue& /*return_value*/)
+      OVERRIDE { }
+  virtual void MethodUnwind(Thread* /*thread*/, mirror::Object* /*this_object*/,
+                            mirror::ArtMethod* /*method*/, uint32_t /*dex_pc*/) OVERRIDE { }
+  virtual void FieldRead(Thread* /*thread*/, mirror::Object* /*this_object*/,
+                         mirror::ArtMethod* /*method*/, uint32_t /*dex_pc*/,
+                         mirror::ArtField* /*field*/) OVERRIDE { }
+  virtual void FieldWritten(Thread* /*thread*/, mirror::Object* /*this_object*/,
+                            mirror::ArtMethod* /*method*/, uint32_t /*dex_pc*/,
+                            mirror::ArtField* /*field*/, const JValue& /*field_value*/)
+      OVERRIDE { }
+  virtual void ExceptionCaught(Thread* /*thread*/, const ThrowLocation& /*throw_location*/,
+                               mirror::ArtMethod* /*catch_method*/, uint32_t /*catch_dex_pc*/,
+                               mirror::Throwable* /*exception_object*/) OVERRIDE { }
+
+  virtual void DexPcMoved(Thread* /*self*/, mirror::Object* /*this_object*/,
+                          mirror::ArtMethod* /*method*/, uint32_t /*new_dex_pc*/) OVERRIDE { }
+
+  // We only care about how many dex instructions were executed in the Jit.
+  virtual void BackwardBranch(Thread* thread, mirror::ArtMethod* method, int32_t dex_pc_offset)
+      OVERRIDE SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
+    CHECK_LE(dex_pc_offset, 0);
+    instrumentation_cache_->AddSamples(thread, method, 1);
+  }
+
+ private:
+  JitInstrumentationCache* const instrumentation_cache_;
+};
+
+}  // namespace jit
+}  // namespace art
+
+#endif  // ART_RUNTIME_JIT_JIT_INSTRUMENTATION_H_