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<h2>Performance</h2>

<h3>Overview</h3>

<p>Performance is a top priority for WebKit.  We adhere to a simple directive for all work we do on WebKit.</p>

<p><i>The way to make a program faster is to never let it get slower.</i></p>

<p>We have a zero-tolerance policy for performance regressions.
If a patch lands that regresses performance according to our benchmarks,
then the person responsible must either back the patch out of the tree or drop everything immediately and fix the regression.</p>

<p>Common excuses people give when they regress performance are, "But the new way is cleaner!" or "The new
way is more correct." We don't care. No performance regressions are allowed, regardless of the reason. There is no justification
for regressing performance. None.</p>

<p>We have a number of benchmarks that we use to measure performance.</p>

<ol>
<li>The i-Bench test suite is the most well-known cross-browser benchmark.
The HTML Load Speed and JavaScript tests are the most important sub-tests in the suite.
No check-in can regress the benchmark scores for these tests.
As of this writing, you can get the i-Bench test suite from
<a href="http://www.lionbridge.com/lionbridge/en-US/services/outsourced-testing/benchmark-software.htm">this page</a> on the Lionbridge website.
After accepting the license agreement you'll be able to download the suite from an FTP site at pcmag.com.</li>
<li>The <a href="http://www.24fun.com/downloadcenter/benchjs/benchjs.html">24Fun test</a> has become a popular site for people testing JavaScript
and DHTML performance. The scores on this test must also not regress.</li>
<li>Our internal page load test suite (called the PLT for short) must also not regress.
The PLT contains pages that are representative of sites that are encountered in
the real world. The harness itself is built into Safari and is accessible from the <i>Debug</i> menu.
You can actually make Safari run the PLT on any set of test pages.
Unfortunately, the pages we use internally at Apple contain copyrighted material and therefore cannot be open source at this time.
We hope that in the future sites will be willing to donate snapshots of their front pages so that an open source cross-browser
test suite can be developed with content that is not as homogenous as the i-Bench pages.</li>
</ol>

<h3>Get Involved!</h3>

<p>How can you help improve WebKit's performance?</p>

<dl>
<dt>Test for Regressions</dt>
<dd>If you have your own performance tests, run WebKit through them daily. Make sure that the performance of the sites you care about
does not regress. Test the above benchmarks on your hardware to help double-check that there have not been any regressions. Remember, the best
way to stay fast is to never let your code become slower.

<dt>Open Source Benchmark</dt>
<dd>We have discussed with Mozilla and Opera the idea of an open-source cross-browser benchmark. The stumbling block to the construction of such
a test suite is that we need to get buy-in from high profile sites like <a href="http://www.google.com">Google</a>, <a href="http://www.amazon.com">Amazon</a>
or <a href="http://www.yahoo.com">Yahoo</a> to use snapshots of their front pages in the benchmark. The benefits of having your site in such a benchmark
are obvious, since browser vendors will make your sites faster as they optimize for the content of the benchmark.

<p>If you work for one of these high profile sites we encourage you to <a href="../../contact.html">contact us</a> if you are interested in having your
company contribute content
to such a benchmark.</p>

<dt>Profile with Shark</dt>
<dd>OS X now has an excellent profiling tool called Shark. If you find operations that are slow in WebKit, we encourage you to use Shark to isolate
performance problems and file bugs with that information. <a href="http://developer.apple.com/tools/shark_optimize.html">Here is a link</a> to get you
started using Shark.

</dl>
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