[pypy-commit] pypy.org extradoc: write a draft of performance dissemination
noreply at buildbot.pypy.org
Sat Feb 11 17:55:29 CET 2012
Author: Maciej Fijalkowski <fijall at gmail.com>
Date: 2012-02-11 18:55 +0200
Log: write a draft of performance dissemination
diff --git a/source/performance.txt b/source/performance.txt
new file mode 100644
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+One of the goals of the PyPy project is to provide a fast and compliant python
+interpreter. Part of the way we achieve this is to provide a high-performance
+garbage collector and a high performance JIT. Results of comparing PyPy and
+CPython can be found on the `speed website`_. Those benchmarks are not a random
+collection. They're a combination of real-world Python programs, benchmarks
+originally included and benchmarks we found PyPy to be slow on. Consult
+descriptions of each for details.
+JIT is however not a magic bullet. There are several characteristics that might
+be surprising for people having first encounter with it. JIT is generally good
+at speeding up straightforward python code that spends a lot of time in
+the bytecode dispatch loop, numerics, heave oo etc. When JIT does not help,
+PyPy is generally slower than CPython, those things include:
+* **Tests**: Ideal unit tests would execute each piece of tested code which
+ leaves no time for the JIT to warm up.
+* **Really short-running scripts**: A rule of thumb is if something runs below
+ 0.2s 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.
+* **Functions in runtime**: Functions that take significant time in runtime.
+ PyPy's runtime is generally not as optimized as CPython's and expect those
+ functions to take somewhere between same time as CPython to 2x longer.
+ XXX explain exactly what runtime is
+Unrelated things that we know PyPy is slow at (note that we're probably working
+* **Long integers**
+* **Building very large dicts**
+We generally consider things that are slower on PyPy than CPython PyPy's bugs.
+In case you find a thing that's not documented here, report it to our
+`bug tracker`_ for investigation
+.. _`bug tracker`: http://bugs.pypy.org
+.. _`speed website`: http://speed.pypy.org
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