[Python-Dev] Alignment assumptions
Thu, 28 Feb 2002 22:34:05 +0100
On donderdag, februari 28, 2002, at 07:57 , Tim Peters wrote:
> [David Abrahams]
>> A quick grep-find through the Python-2.2 sources reveals the
>> Include/dictobject.h:49: long aligner;
> This is in
> #ifdef USE_CACHE_ALIGNED
> long aligner;
> and AFAIK nobody ever defines the symbol. It's a cache-line
> gimmick, but is effectively a nop (except to waste memory) on
> "almost all"
> machines. IIRC, the author never measured any improvement by
> using it (not
> surprising, since I believe almost all mallocs at least 8-byte
> align now).
> I vote we delete it.
MacPython uses it. At the time it was put in it caused a 15%
increase in Pystones because dictionary entries were aligned in
cache lines. But: this was in the PPC 601 and 604 era, I must
say that I've never tested whether it made any difference on G3
Put in a bug report in my name, and one day I'll get around to
testing whether it still makes a difference on current hardware
and rip it out if it doesn't.
- Jack Jansen <Jack.Jansen@oratrix.com>
- If I can't dance I don't want to be part of your revolution --
Emma Goldman -