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From: Philipp Stephani
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Subject: bug#44674: 28.0.50; Adding current-cpu-time for performance tests
Date: Mon, 16 Nov 2020 19:39:35 +0100
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To: Stefan Monnier
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Am Mo., 16. Nov. 2020 um 16:27 Uhr schrieb Stefan Monnier
:
>
> Philipp wrote:
> > It might be beneficial to use the higher-resolution clock_gettime with
> > CLOCK_PROCESS_CPUTIME_ID if available and only fall back to clock()
> > otherwise.
> >
> > While there, consider also implementing a function to read the
> > CLOCK_MONOTONIC clock =E2=80=93 that should be preferred over the realt=
ime
> > clock for stopwatch-style measurements.
>
> Given that we've lived without any of it for so many years, I'm not sure
> it's worth the trouble.
It's definitely not a pressing concern, but the current approach does
give wrong results if a leap second happens or on other occasions. See
e.g. https://go.googlesource.com/proposal/+/master/design/12914-monotonic.m=
d
for why Go introduced monotonic clock measurements. Other languages
had the distinction between wall clocks and monotonic clocks for a
long time as well (e.g. Java System.nanoTime).
> Also since I'm not familiar with any of those
> interfaces, I'd welcome it if someone else could do that if
> they're interested.
I wouldn't mind doing it, if there's general agreement that it's worth havi=
ng.
But it would really just be:
1. clock_gettime(CLOCK_MONOTONIC_ID)
2. check for errors
3. make_lisp_time