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

[Philipp Stephani]

Am Mo., 16. Nov. 2020 um 11:40 Uhr schrieb Eli Zaretskii <eliz@gnu.org>:
>
> On November 16, 2020 12:11:34 PM GMT+02:00, "Mattias Engdegård" 
> <mattiase@acm.org> wrote:
> > > +The return value is a pair (CPU-TICKS . TICKS-PER-SEC).
> >
> > Perhaps not ideal to cons in a timing primitive where low overhead is
> > called for.
> > What about just returning an integer and have a different way to get
> > at TICKS-PER-SEC?
> > After all, the timer frequency is not specific to each measurement.
> >
> > Ideally the returned value should be a fixnum to minimise overhead,
> > but it may restrict the range on 32-bit platforms.
> >
> > I also agree with Phillipp's comment about clock_gettime.
>
> AFAUI, CLOCK_PROCESS_CPUTIME_ID accounts for all the threads, so might not be 
> what we want even if it is supported, since other threads might be involved 
> which we aren't interested in (e.g., GTK threads).

clock (on GNU/Linux) is a thin wrapper around
CLOCK_PROCESS_CPUTIME_ID, see
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/clock.c;hb=aac0f62c47beee5b546bacc330acc2dd21cda0dc.