bug#44674: 28.0.50; Adding current-cpu-time for performance tests

[Eli Zaretskii <eliz@gnu.org>]

On November 16, 2020 9:58:40 AM GMT+02:00, Eli Zaretskii <eliz@gnu.org> wrote:
> On November 16, 2020 3:07:35 AM GMT+02:00, Stefan Monnier
> <monnier@iro.umontreal.ca> wrote:
> > Package: Emacs
> > Version: 28.0.50
> > 
> > 
> > I tried to write a test for the performance problem seen in
> bug#41029,
> > but found it very difficult to make it work half-reliably because we
> > only have access to wall-clock time from Elisp.
> > 
> > So I suggest we add a new primitive `current-cpu-time` with which
> > those
> > tests seem to be at least somewhat doable.
> > 
> > See my current patch below which includes a test for that
> > performance bug.  It clearly requires adding w32 support (or
> > fetching more clock functionality from gnulib) but I don't know how
> to
> > do that.
> 
> AFAIU, using 'clock' here is not the best idea, as there are caveats
> wrt to calling 'system', and the origin of the returned value is not
> well defined to be portable.
> 
> I suggest to use 'times' instead.  For w32, we could easily implement
> it, as we already have that functionality for 'getloadavg'.

Btw, once this goes in, how about making benchmark-run use it?