[Python-Dev] Tagged integers (original) (raw)

Michael Hudson mwh at python.net
Thu Jul 15 11:15:23 CEST 2004

James Y Knight <foom at fuhm.net> writes:

Investigating the pybench some more, it seems that speedup for many of the tests is because of the shortcut for tagged types in PyINCREF and PyDECREF. E.g. with the pybench TupleSlicing test, as written, the speed diff is -39.13%. However, changing the tuple to contain strings instead of integers causes the change to be +0.03%.

This makes me think that perhaps using an inline tagged representation for things like True, False, and single character strings < 256 might be a win as well, even though they don't ever cause memory allocation -- just because of the refcounting. Well, I tried making booleans a tagged types as well: pybench then runs 11% faster than standard python (vs the 7% with just tagged integers).

Interesting!

P.S.: I have also previously experimented with removing refcounting from Python completely, and using the Boehm GC, because I theorized that refcounting could very well be slower than a full conservative GC. It mostly worked (I did not finish, so it did not support destructors or weakrefs), but was not a win, because it was no longer possible to use large block allocation and free list tricks for integers, and thus integer allocation caused a huge slowdown. I might revisit that now. I do realize using Boehm GC has pretty much a negative probability of making it into standard python, though. :)

The last time I mentioned that the Boehm GC didn't help Python much (on comp.lang.lisp) Hans Boehm showed up and claimed that it was because we weren't using it properly :-) Let us know how it goes...

Cheers, mwh

-- A difference which makes no difference is no difference at all. -- William James (I think. Reference anyone?)

More information about the Python-Dev mailing list