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 <p>
 Android runtime (ART) includes a just-in-time (JIT) compiler with code profiling
 that continually improves the performance of Android applications as they run.
 The JIT compiler complements ART's current ahead-of-time (AOT) compiler and
 improves runtime performance, saves storage space, and speeds application and
 system updates. It also improves upon the AOT compiler by avoiding system
 slowdown during automatic application updates or recompilation of applications
 during over-the-air (OTA) updates.
 </p>

 <p>
 Although JIT and AOT use the same compiler with a similar set of optimizations,
 the generated code might not be identical. JIT makes use of runtime type
 information, can do better inlining, and makes on stack replacement (OSR)
 compilation possible, all of which generates slightly different code.
 </p>

 <h2 id="architectural-overview">JIT architecture</h2>

 <img src="./images/jit-arch.png" alt="JIT architecture"/>
 <figcaption><strong>Figure 1.</strong> JIT architecture.</figcaption>

 <h2 id="flow">JIT compilation</h2>

 <p>JIT compilation involves the following activities:</p>
 <img src="./images/jit-profile-comp.png" alt="Profile-guided comp"/>
 <figcaption><strong>Figure 2.</strong> Profile-guided compilation.</figcaption>

 <ol>
 <li>The user runs the app, which then triggers ART to load the <code>.dex</code>
 file.
  <ul>
  <li>If the <code>.oat</code> file (the AOT binary for the <code>.dex</code>
  file) is available, ART uses it directly. Although <code>.oat</code> files are
  generated regularly, they don't always contain compiled code (AOT binary).</li>
  <li>If no <code>.oat</code> file is available, ART runs through JIT or an
  interpreter to execute the <code>.dex</code> file.</li>
  ART always uses the <code>.oat</code> files if available. Otherwise, it uses
  the APK and extracts it in memory to get to the <code>.dex</code>; this incurs
  a big memory overhead that is equal to the size of the dex files.</li>
 </ul>
 </li>
 <li>JIT is enabled for any application that is not compiled according to the
 <code>speed</code> compilation filter (which says "compile as much as you can
 from the app").</li>
 <li>The JIT profile data is dumped to a file in a system directory that only
 the application can access.</li>
 <li>The AOT compilation (<code>dex2oat</code>) daemon parses that file to drive
 its compilation.
 <br>
 <br>
 <img src="./images/jit-daemon.png" alt="JIT daemon"/>
 <figcaption><strong>Figure 3.</strong> JIT daemon activities.</figcaption>
 </li>
 </ol>

 <p>
 The Google Play service is an example used by other applications that behave
 similar to shared libraries.
 </p>

 <h2 id="jit-workflow">JIT workflow</h2>

 <img src="./images/jit-workflow.png" alt="JIT architecture"/>
 <figcaption><strong>Figure 4.</strong> JIT data flow.</figcaption>

 <ul>
 <li>Profiling information is stored in the code cache and subjected to garbage
 collection under memory pressure.
  <ul>
  <li>There is no guarantee a snapshot taken when the application was in the
  background will contain complete data (i.e., everything that was JITed).</li>
  <li>There is no attempt to ensure everything is recorded (as this can impact
  runtime performance).</li>
  </ul>
 </li>
 <li>Methods can be in three different states:
  <ul>
  <li>interpreted (dex code)</li>
  <li>JIT compiled</li>
  <li>AOT compiled</li>
  </ul>
  If both JIT and AOT code exists (e.g. due to repeated de-optimizations),
  the JITed code is preferred.
 </li>
 <li>The memory requirement to run JIT without impacting foreground app
 performance depends upon the app in question. Large apps require more memory
 than small apps. In general, large apps stabilize around 4 MB.</li>
 </ul>

 <h2 id="turn-on-jit-logging">Turning on JIT logging</h2>
 <p>To turn on JIT logging, run the following commands:</p>
 <pre class="devsite-click-to-copy">
 <code class="devsite-terminal">adb root</code>
 <code class="devsite-terminal">adb shell stop</code>
 <code class="devsite-terminal">adb shell setprop dalvik.vm.extra-opts -verbose:jit</code>
 <code class="devsite-terminal">adb shell start</code>
 </pre>

 <h2 id="disable-jit-and-run-applications-in-interpreter">Disabling JIT</h2>
 <p>To disable JIT, run the following commands:</p>
 <pre class="devsite-click-to-copy">
 <code class="devsite-terminal">adb root</code>
 <code class="devsite-terminal">adb shell stop</code>
 <code class="devsite-terminal">adb shell setprop dalvik.vm.usejit false</code>
 <code class="devsite-terminal">adb shell start</code>
 </pre>

 <h2 id="force-compilation-of-a-specific-package">Forcing compilation</h2>

 <p>To force compilation, run the following:</p>
 <pre class="devsite-terminal devsite-click-to-copy">
 adb shell cmd package compile
 </pre>

 <p>Common use cases for force compiling a specific package:</p>
 <ul>
 <li>Profile-based:
 <pre class="devsite-terminal devsite-click-to-copy">
 adb shell cmd package compile -m speed-profile -f my-package
 </pre>
 </li>
 <li>Full:
 <pre class="devsite-terminal devsite-click-to-copy">
 adb shell cmd package compile -m speed -f my-package
 </pre>
 </li>
 </ul>

 <p>Common use cases for force compiling all packages:</p>
 <ul>
 <li>Profile-based:
 <pre class="devsite-terminal devsite-click-to-copy">
 adb shell cmd package compile -m speed-profile -f -a
 </pre>
 </li>
 <li>Full:
 <pre class="devsite-terminal devsite-click-to-copy">
 adb shell cmd package compile -m speed -f -a
 </pre>
 </li>
 </ul>

 <h2 id="clear-profile-data-and-remove-compiled-code">Clearing profile data</h2>
 <p>To clear profile data and remove compiled code, run the following:</p>
 <ul>
 <li>For one package:
 <pre class="devsite-terminal devsite-click-to-copy">
 adb shell cmd package compile --reset my-package
 </pre>
 </li>
 <li>For all packages:
 <pre class="devsite-terminal devsite-click-to-copy">
 adb shell cmd package compile --reset -a
 </pre>
 </li>
 </ul>

   </body>
 </html>
	<html devsite>
	<head>
	<title>Implementing ART Just-In-Time (JIT) Compiler</title>
	<meta name="project_path" value="/_project.yaml" />
	<meta name="book_path" value="/_book.yaml" />
	</head>
	<body>
	<!--
	Copyright 2017 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.
	-->



	<p>
	Android runtime (ART) includes a just-in-time (JIT) compiler with code profiling
	that continually improves the performance of Android applications as they run.
	The JIT compiler complements ART's current ahead-of-time (AOT) compiler and
	improves runtime performance, saves storage space, and speeds application and
	system updates. It also improves upon the AOT compiler by avoiding system
	slowdown during automatic application updates or recompilation of applications
	during over-the-air (OTA) updates.
	</p>

	<p>
	Although JIT and AOT use the same compiler with a similar set of optimizations,
	the generated code might not be identical. JIT makes use of runtime type
	information, can do better inlining, and makes on stack replacement (OSR)
	compilation possible, all of which generates slightly different code.
	</p>

	<h2 id="architectural-overview">JIT architecture</h2>

	<img src="./images/jit-arch.png" alt="JIT architecture"/>
	<figcaption><strong>Figure 1.</strong> JIT architecture.</figcaption>

	<h2 id="flow">JIT compilation</h2>

	<p>JIT compilation involves the following activities:</p>
	<img src="./images/jit-profile-comp.png" alt="Profile-guided comp"/>
	<figcaption><strong>Figure 2.</strong> Profile-guided compilation.</figcaption>

	<ol>
	<li>The user runs the app, which then triggers ART to load the <code>.dex</code>
	file.
	<ul>
	<li>If the <code>.oat</code> file (the AOT binary for the <code>.dex</code>
	file) is available, ART uses it directly. Although <code>.oat</code> files are
	generated regularly, they don't always contain compiled code (AOT binary).</li>
	<li>If no <code>.oat</code> file is available, ART runs through JIT or an
	interpreter to execute the <code>.dex</code> file.</li>
	ART always uses the <code>.oat</code> files if available. Otherwise, it uses
	the APK and extracts it in memory to get to the <code>.dex</code>; this incurs
	a big memory overhead that is equal to the size of the dex files.</li>
	</ul>
	</li>
	<li>JIT is enabled for any application that is not compiled according to the
	<code>speed</code> compilation filter (which says "compile as much as you can
	from the app").</li>
	<li>The JIT profile data is dumped to a file in a system directory that only
	the application can access.</li>
	<li>The AOT compilation (<code>dex2oat</code>) daemon parses that file to drive
	its compilation.
	<br>
	<br>
	<img src="./images/jit-daemon.png" alt="JIT daemon"/>
	<figcaption><strong>Figure 3.</strong> JIT daemon activities.</figcaption>
	</li>
	</ol>

	<p>
	The Google Play service is an example used by other applications that behave
	similar to shared libraries.
	</p>

	<h2 id="jit-workflow">JIT workflow</h2>

	<img src="./images/jit-workflow.png" alt="JIT architecture"/>
	<figcaption><strong>Figure 4.</strong> JIT data flow.</figcaption>

	<ul>
	<li>Profiling information is stored in the code cache and subjected to garbage
	collection under memory pressure.
	<ul>
	<li>There is no guarantee a snapshot taken when the application was in the
	background will contain complete data (i.e., everything that was JITed).</li>
	<li>There is no attempt to ensure everything is recorded (as this can impact
	runtime performance).</li>
	</ul>
	</li>
	<li>Methods can be in three different states:
	<ul>
	<li>interpreted (dex code)</li>
	<li>JIT compiled</li>
	<li>AOT compiled</li>
	</ul>
	If both JIT and AOT code exists (e.g. due to repeated de-optimizations),
	the JITed code is preferred.
	</li>
	<li>The memory requirement to run JIT without impacting foreground app
	performance depends upon the app in question. Large apps require more memory
	than small apps. In general, large apps stabilize around 4 MB.</li>
	</ul>

	<h2 id="turn-on-jit-logging">Turning on JIT logging</h2>
	<p>To turn on JIT logging, run the following commands:</p>
	<pre class="devsite-click-to-copy">
	<code class="devsite-terminal">adb root</code>
	<code class="devsite-terminal">adb shell stop</code>
	<code class="devsite-terminal">adb shell setprop dalvik.vm.extra-opts -verbose:jit</code>
	<code class="devsite-terminal">adb shell start</code>
	</pre>

	<h2 id="disable-jit-and-run-applications-in-interpreter">Disabling JIT</h2>
	<p>To disable JIT, run the following commands:</p>
	<pre class="devsite-click-to-copy">
	<code class="devsite-terminal">adb root</code>
	<code class="devsite-terminal">adb shell stop</code>
	<code class="devsite-terminal">adb shell setprop dalvik.vm.usejit false</code>
	<code class="devsite-terminal">adb shell start</code>
	</pre>

	<h2 id="force-compilation-of-a-specific-package">Forcing compilation</h2>

	<p>To force compilation, run the following:</p>
	<pre class="devsite-terminal devsite-click-to-copy">
	adb shell cmd package compile
	</pre>

	<p>Common use cases for force compiling a specific package:</p>
	<ul>
	<li>Profile-based:
	<pre class="devsite-terminal devsite-click-to-copy">
	adb shell cmd package compile -m speed-profile -f my-package
	</pre>
	</li>
	<li>Full:
	<pre class="devsite-terminal devsite-click-to-copy">
	adb shell cmd package compile -m speed -f my-package
	</pre>
	</li>
	</ul>

	<p>Common use cases for force compiling all packages:</p>
	<ul>
	<li>Profile-based:
	<pre class="devsite-terminal devsite-click-to-copy">
	adb shell cmd package compile -m speed-profile -f -a
	</pre>
	</li>
	<li>Full:
	<pre class="devsite-terminal devsite-click-to-copy">
	adb shell cmd package compile -m speed -f -a
	</pre>
	</li>
	</ul>

	<h2 id="clear-profile-data-and-remove-compiled-code">Clearing profile data</h2>
	<p>To clear profile data and remove compiled code, run the following:</p>
	<ul>
	<li>For one package:
	<pre class="devsite-terminal devsite-click-to-copy">
	adb shell cmd package compile --reset my-package
	</pre>
	</li>
	<li>For all packages:
	<pre class="devsite-terminal devsite-click-to-copy">
	adb shell cmd package compile --reset -a
	</pre>
	</li>
	</ul>

	</body>
	</html>