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

From: Philipp Stephani <[email-masked]>
Date: Mon, 16 Nov 2020 11:48:42 +0100

Am Mo., 16. Nov. 2020 um 11:40 Uhr schrieb Eli Zaretskii <[email-masked]>:
>
> On November 16, 2020 12:11:34 PM GMT+02:00, "Mattias Engdegård" <[email-masked]> 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.