[Python-Dev] [ python-Patches-876206 ] scary frame speed hacks (original) (raw)

Dennis Allison allison at sumeru.stanford.EDU
Tue Mar 2 10:58:52 EST 2004

I would be cautious about anything that slows recursive functions becasue almost any interesting data structure traversal is recursive.

On Mon, 1 Mar 2004, Armin Rigo wrote:

Hello,

We are about to apply a patch that both speeds up frame allocation and make it simpler by removing the frame freelist (patch #876206). The drawback is that recursive functions would be slower now. The two alternatives that we have are thus:

(1) Ignore the recursive function problem and apply the patch. def f(n, m): if n > 0 and m > 0: return f(n-1, m) + f(n, m-1) else: return 1 f(11, 11) Takes 3.26s instead of just 2.64s. This is a major speed hit (20%). On the other hand, recursive functions are not so common in Python, and the patch simplifies the C source interestingly. (2) Don't remove the frame freelist but combine it with the new patch. This would give the best of both worlds performance-wise, but the frame allocation code becomes convoluted. It would amount to add a third way to allocate a frame, and all three ways give a frame with different guaranteed invariants (i.e. different sets of fields that we know to be already correct and thus don't have to initialize). The question is whether (1) or (2) is better. Armin

Python-Dev mailing list Python-Dev at python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/allison%40sumeru.stanford.edu

More information about the Python-Dev mailing list