[Python-Dev] int/float freelists vs pymalloc

[Neal Norwitz]

On Feb 8, 2008 10:54 AM, Christian Heimes <lists at cheimes.de> wrote:
> Andrew MacIntyre wrote:
> > However, my tests do show that something is funny with the current
> > freelist implementation for floats on at least 2 platforms, and that
> > doing without that sort of optimisation for float objects would likely
> > not be a hardship with PyMalloc.
>
> float objects are slightly larger than int objects. On a 32bit OS both
> have ob_type pointer of size 4, a ref counter of size 4. But an int
> object has a value of type long with 4 bytes and a float stores its
> value in a double with size 8.
>
> I assume that the difference in size leads to a different allocation timing.

It's not just size.  Architectures may require data aligned on 4, 8,
or 16 addresses for optimal performance depending on data type.  IIRC,
malloc aligns by 8 (not sure if that was a particular arch or very
common).  I don't know if pymalloc handles alignment.

n