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<!DOCTYPE html>
<html lang="en-US">
<head>
<meta name="msapplication-config" content="/browserconfig.xml"/>
<meta name="viewport" content="width=device-width, initial-scale=1"/>
<meta charset="utf-8"/>
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<link rel="shortcut icon" type="image/png" href="/favicon.png"/>
<title>Drake: Running Profiling Tools</title>
<meta
name="description"
content="Drake ("dragon" in Middle English) is a C++ toolbox started by the Robot
Locomotion Group at the MIT Computer Science and Artificial Intelligence
Lab (CSAIL). The development team has now grown significantly, with core
development led by the Toyota Research Institute. It is a collection of
tools for analyzing the dynamics of our robots and building control
systems for them, with a heavy emphasis on optimization-based design/
analysis.
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<h1>Running Profiling Tools</h1>
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<article class="markdown-body">
<p>This page contains tips and tricks for capturing and understanding profiling
reports.</p>
<p>Some other good references are:</p>
<ul>
<li><a href="https://valgrind.org/docs/manual/cl-manual.html">Callgrid documentation</a></li>
<li><a href="https://kcachegrind.github.io/html/Home.html">Kcachegrind documentation</a></li>
<li><a href="https://baptiste-wicht.com/posts/2011/09/profile-c-application-with-callgrind-kcachegrind.html">Blog post</a></li>
</ul>
<h1 id="installation">Installation</h1>
<p>Install <code class="language-plaintext highlighter-rouge">valgrind</code>, <code class="language-plaintext highlighter-rouge">kcachegrind</code>, and <code class="language-plaintext highlighter-rouge">graphviz</code>. For example on Ubuntu:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sudo apt-get install valgrind kcachegrind graphviz
</code></pre></div></div>
<h1 id="compiling-your-example-program">Compiling your example program</h1>
<p>When profiling, you should use a representative example program.</p>
<p>Compile your example program with debug symbols (line numbers) enabled, but
still in optimized mode (<code class="language-plaintext highlighter-rouge">-O2</code>). That will allow you to drill down into
line-by-line performance costs, while maintainaing representative
performance. These builds are usually termed as “release with debug info”.
This is different than “debug builds” which typically have compiler
optimizations disabled (<code class="language-plaintext highlighter-rouge">-O0</code>).</p>
<p>In Bazel, build like this:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>bazel build -c opt --copt=-g //foo/bar:example
</code></pre></div></div>
<p>In CMake, configure like this:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo
</code></pre></div></div>
<h1 id="capturing-a-trace">Capturing a trace</h1>
<p>Run <code class="language-plaintext highlighter-rouge">valgrind</code> with <code class="language-plaintext highlighter-rouge">callgrind</code> to get profiling data. For example:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>valgrind --tool=callgrind bazel-bin/foo/bar/example
</code></pre></div></div>
<p>Each time this is run, it will create an output file file named
<code class="language-plaintext highlighter-rouge">callgrind.out.${PID}</code>. Typically you’d capture just one trace and inspect it
on its own, but in advanced uses you can combine multiple traces.</p>
<p>Oftentimes the call patterns in Drake will be difficult to view under the
default instrumentation settings, so we recommend running with extra flags.
These flags will slow down data collection, but are usually worth it:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>valgrind --tool=callgrind \
--separate-callers=10 \
bazel-bin/foo/bar/example
</code></pre></div></div>
<p>If you’re trying to micro-optimize a function, use <code class="language-plaintext highlighter-rouge">--dump-instr=yes</code> to see
per-instruction costs in the object code disassembly.</p>
<h1 id="viewing-the-trace">Viewing the trace</h1>
<p>Run <code class="language-plaintext highlighter-rouge">kcachegrind</code> to analyze profiling data. For example:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>kcachegrind callgrind.out.19482
</code></pre></div></div>
<h1 id="profiling-google-benchmark-executables">Profiling Google Benchmark executables</h1>
<p><a href="https://github.com/google/benchmark">Google Benchmark</a> throttles the number of
iterations it runs on each benchmark, which will skew the performance metrics
you see in the profiler. <a href="https://stackoverflow.com/questions/61843343/how-to-special-case-the-number-of-iterations-in-google-benchmark">You may want to manually specify the number of
iterations to run on each
benchmark</a>.</p>
</article>
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