[Python-Dev] Tunable parameters in dictobject.c (was dictnotes.txt out of date?)

[Antoine Pitrou]

On Mon, 18 Jun 2012 21:31:27 +0200
Maciej Fijalkowski <fijall at gmail.com> wrote:
> On Mon, Jun 18, 2012 at 5:04 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> 
> > On Mon, 18 Jun 2012 15:28:24 +0100
> > Mark Shannon <mark at hotpy.org> wrote:
> > >
> > > But do they? The results of benchmarking would seem to suggest (at least
> > > on my test machine) that overly-sparse dicts are slower.
> > > Possibly due to increased cache misses.
> >
> > Or, at least, they are not faster. See the synthetic experiments in
> > http://bugs.python.org/issue10408
> >
> > That said, Raymond might have witnessed different results at the time.
> > Hardware evolves quickly and the parameters change (memory latency
> > today is at least 50+ CPU cycles, which is quite a lot of wasted work on
> > a pipelined superscalar CPU).
> >
> > Regards
> >
> > Antoine.
> >
> >
> More like 200-500 CPU cycles on modern CPUs.

You are right. I was thinking 50 nanoseconds (which for a - relatively
high-end - 3GHz CPU puts us at 150 cycles).

Regards

Antoine.