Re: 64 bit official Windows builds

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Thu, 11 Feb 2016 08:58:45 -0500
> 
> >> Could I ask, what is the benefit of 64 bits compared to 32 bits for 
> >> windows ?
> > It will run roughly twice faster.
> [...]
> > slower, because running a 32-bit executable on a 64-bit Windows
> > requires expensive thunking for every call to any Windows API,
> 
> Holy crap?  Really?  It's hard to believe that 64-bit Windows's
> emulation of the 32-bit API is so inefficient that it causes a "rough
> slowdown" by a factor 2 in an application like Emacs.
> 
> Do you see such a factor-of-2 difference when doing "rm lisp/**/*.elc;
> make"?  Or in which kind of circumstance have you seen such a slowdown?

I measured that by running GNU Find compiled from the same sources on
a large and deep directory tree on the same Windows 7 box.

That thunking is the culprit is my theory, not a fact; however, I
cannot find any other explanation.  If someone does, I'm all ears.