[pypy-dev] Possible student project on PyPy

[Paolo Giarrusso]

Hi, for a student project, we are evaluating the possibility to
experiment with some ideas on PyPy.

Even if it is a student project, we have high expectations (our aim is
to really improve PyPy's speed, if possible). But we are still trying
to choose which features to implement (we started with some nice
ideas, but part of them is already implemented).

We will work for something like 2 months on a separate branch - maybe
we can give readonly access to the source code repository, but write
access would be a problem for our exam, for obvious reasons.

Do you have any possibility to host a development branch for this project?

To let you know who we are, I'll present us:

- I, Paolo 'Blaisorblade' Giarrusso, am a past Linux kernel hacker, I
worked also with Java, C++, and a bit of Python, and I am currently a
graduate student at Aarhus University, Denmark;
- Sigurd is a PhD candidate at Aarhus University, Denmark, currently
working, among other things, on a cryptography research project in
Python (viff.dk).

- our professor is Lars Bak, the lead architect of the Google V8
Javascript engine, on which we implemented various optimizations in
the previous months.

We are obviously open to suggestions, and we have been looking at the
status blog and at various blogs.

It seems that there is still space for improvement in the space of
garbage collectors, as mentioned here:
- http://codespeak.net/pypy/extradoc/talk/osdc2008/paper.txt
working on that could be interesting.

The main idea we wanted to apply to Python, based on a suggestion from
Lars, is the main peculiar V8 idea, the one of hidden classes with
transitions. That allows avoiding dictionary lookups for property
accesses on objects, using instead a Java-like data representation in
memory, without any visible effects on the Python semantics.

While revising this email, we saw that this is already partially
implemented: for what the blog says, the memory savings where done but
not the memory speedups. Also, the blog does not mention whether and
how class transitions are used. Some of the initial ideas below may
already have been implemented, so point out what is there and what can
be interesting.
I've also read the discussion about the JIT, which will be missing in
the next release.

Obviously, this would require partial reworking the core object model of PyPy.

Still, we think that specialization will especially benefit from this,
even because this allows to specialize better also on class types, not
only on primitive types. It is not clear to me how do you handle
changes (like addition of a property) to a single object - is it
possible to specialize the code on the (anonymous) type of this new
object? Can you give me pointers inside the documentation, if this is
already explained? I've read the EU reports about this and partial
compilation, but it is still unclear to us how things work.

Btw, the first thing to do is studying the object model and reflection
capability of Python. Since Lars said that the target of a VM designer
is to allow programmers work in the most pleasant way and use advanced
features without incurring any cost, our development plan should try
to optimize also reflective features as much as possible.

Just to make an example, in Python you can register an handler for
unknown method calls on an object (I don't remember how, but I'm
pretty sure something like this exists). This idea means that our
design should be able to do inline caching by storing a call to this
handler (maybe we'll defer the implementation, but the initial design
should allow doing that IMHO).

Any comments?
--
Paolo Giarrusso