[pypy-commit] pypy.org extradoc: Regen and clarify. Add a missing file

fijal noreply at buildbot.pypy.org
Sun Feb 12 21:57:42 CET 2012

Author: Maciej Fijalkowski <fijall at gmail.com>
Branch: extradoc
Changeset: r321:a4458e04b049
Date: 2012-02-12 22:57 +0200

Log:	Regen and clarify. Add a missing file

diff --git a/performance.html b/performance.html
new file mode 100644
--- /dev/null
+++ b/performance.html
@@ -0,0 +1,117 @@
+<!DOCTYPE html>
+	<title>PyPy :: PyPy</title>
+	<meta http-equiv="content-language" content="en" />
+	<meta http-equiv="content-type" content="text/html; charset=utf-8" />
+	<meta name="author" content="PyPy Team" />
+	<meta name="description" content="PyPy" />
+	<meta name="copyright" content="MIT" />
+	<meta name="document-rating" content="general" />
+	<link rel="stylesheet" type="text/css" media="screen" title="default" href="css/site.css" />
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+<script type="text/javascript">
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+<div id="body-outer"><div id="body-inner"><div id="body" class="clearfix">
+<div id="header">
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+	<div id="logo"><a href="http://pypy.org"><img src="image/pypy-logo.png" alt="PyPy" height="110px" /></a></div>
+	<hr class="clear-left" />
+	<div id="menu-sub"><a href="index.html">Home</a><span class="menu-sub-sep"> | </span><a href="features.html">Features</a><span class="menu-sub-sep"> | </span><a href="download.html">Download</a><span class="menu-sub-sep"> | </span><a href="compat.html">Compatibility</a><span class="menu-sub-sep"> | </span><a href="performance.html">Performance</a><span class="menu-sub-sep"> | </span><a href="http://doc.pypy.org">Dev Documentation</a><span class="menu-sub-sep"> | </span><a href="http://morepypy.blogspot.com">Blog</a><span class="menu-sub-sep"> | </span><a href="people.html">People</a><span class="menu-sub-sep"> | </span><a href="contact.html">Contact</a><span class="menu-sub-sep"> | </span><a href="py3donate.html">Py3k donations</a><span class="menu-sub-sep"> | </span><a href="numpydonate.html">NumPy donations</a></div>
+	<hr class="clear" />
+<div id="content">
+<div id="main">
+<h1 class="title">PyPy</h1>
+<p>One of the goals of the PyPy project is to provide a fast and compliant
+python interpreter. Some of the ways we achieve this are by providing a
+high-performance garbage collector (GC) and a high-performance
+Just-in-Time compiler (JIT).  Results of comparing PyPy and CPython can
+be found on the <a class="reference external" href="http://speed.pypy.org">speed website</a>. Those benchmarks are not a random
+collection: they are a combination of real-world Python programs &ndash;
+benchmarks originally included with the (now dead) Unladen Swallow
+project &ndash; and benchmarks for which we found PyPy to be slow (and improved).
+Consult the descriptions of each for details.</p>
+<p>The JIT, however, is not a magic bullet. There are several characteristics
+that might surprise people who are not used to JITs in
+general or to the PyPy JIT in particular.  The JIT is generally good at
+speeding up straight-forward Python code that spends a lot of time in the
+bytecode dispatch loop, i.e., running actual Python code &ndash; as opposed
+to running things that only are invoked by Python code.  Good
+examples include numeric calculations or any kind of heavily
+object-oriented program.  Bad examples include doing computations with
+large longs &ndash; which is performed by unoptimizable support code.  When the
+JIT cannot help, PyPy is generally slower than CPython.</p>
+<p>More specifically, the JIT is known not to work on:</p>
+<ul class="simple">
+<li><strong>Tests</strong>: The ideal unit tests execute each piece of tested code
+once.  This leaves no time for the JIT to warm up.</li>
+<li><strong>Really short-running scripts</strong>: A rule of thumb is if something runs below
+0.2s the JIT has no chance, but it depends a lot on the program in question.
+In general, make sure you warm up your program before running benchmarks, if
+you're measuring something long-running like a server.  The time required
+to warm up the JIT varies; give it at least a couple of seconds.  (PyPy's
+JIT takes an especially long time to warm up.)</li>
+<li><strong>Long-running runtime functions</strong>: These are the functions provided
+by the runtime of PyPy that do a significant amount of work.
+PyPy's runtime is generally not as optimized as CPython's and we expect those
+functions to take somewhere between the same time as CPython to twice as long.
+This includes, for example, computing with longs, or sorting large lists.
+A counterexample is regular expressions: although they take time, they
+come with their own JIT.</li>
+<p>Unrelated things that we know PyPy to be slow at (note that we're probably
+working on it):</p>
+<ul class="simple">
+<li><strong>Building very large dicts</strong>: At present, this is an issue with our GCs.
+Building large lists works much better; the random order of
+dictionary elements is what hurts performance right now.</li>
+<li><strong>CPython C extension modules</strong>: Any C extension module recompiled
+with PyPy takes a very large hit in performance.  PyPy supports C
+extension modules solely to provide basic functionality.
+If the extension module is for speedup purposes only, then it
+makes no sense to use it with PyPy at the moment.  Instead, remove it
+and use a native Python implementation, which also allows opportunities
+for JIT optimization.  If the extension module is
+both performance-critical and an interface to some C library, then it
+might be worthwhile to consider rewriting it as a pure Python version
+that uses something like <tt class="docutils literal">ctypes</tt> for the interface.</li>
+<li><strong>Missing RPython modules</strong>: A few modules of the standard library
+(like <tt class="docutils literal">csv</tt> and <tt class="docutils literal">cPickle</tt>) are in C in CPython, but in pure Python
+in PyPy.  Sometimes the JIT is able to do a relatively good job, and
+sometimes not. In most cases (like <tt class="docutils literal">csv</tt> and <tt class="docutils literal">cPickle</tt>), we're slower
+than cPython, with the notable exception of <tt class="docutils literal">json</tt>.</li>
+<p>We generally consider things that are slower on PyPy than CPython to be bugs
+of PyPy.  If you find some issue that is not documented here,
+please report it to our <a class="reference external" href="http://bugs.pypy.org">bug tracker</a> for investigation.</p>
+<div id="sidebar">
\ No newline at end of file
diff --git a/source/performance.txt b/source/performance.txt
--- a/source/performance.txt
+++ b/source/performance.txt
@@ -65,7 +65,8 @@
 * **Missing RPython modules**: A few modules of the standard library
   (like ``csv`` and ``cPickle``) are in C in CPython, but in pure Python
   in PyPy.  Sometimes the JIT is able to do a relatively good job, and
-  sometimes not.
+  sometimes not. In most cases (like ``csv`` and ``cPickle``), we're slower
+  than cPython, with the notable exception of ``json``.
 We generally consider things that are slower on PyPy than CPython to be bugs
 of PyPy.  If you find some issue that is not documented here,

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