[pypy-commit] pypy.org extradoc: write a draft of performance dissemination

[fijal]

Author: Maciej Fijalkowski <fijall at gmail.com>
Branch: extradoc
Changeset: r314:d0cf8619db86
Date: 2012-02-11 18:55 +0200
http://bitbucket.org/pypy/pypy.org/changeset/d0cf8619db86/

Log:	write a draft of performance dissemination

diff --git a/source/performance.txt b/source/performance.txt
new file mode 100644
--- /dev/null
+++ b/source/performance.txt
@@ -0,0 +1,43 @@
+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
+on it):
+
+* **Long integers**
+
+* **Building very large dicts**
+
+XXX
+
+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
+