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

From: Eli Zaretskii <[email-masked]>
Date: Mon, 16 Nov 2020 19:28:24 +0200

> From: Stefan Monnier <[email-masked]>
> Cc: Eli Zaretskii <[email-masked]>,  [email-masked],  Philipp Stephani
>  <[email-masked]>
> Date: Mon, 16 Nov 2020 10:27:29 -0500
> 
> > 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.
> 
> What do you mean by "origin" and by "calling 'system'"?

Quoting https://pubs.opengroup.org/onlinepubs/9699919799/:

          The clock() function shall return the implementation's best
          approximation to the processor time used by the process
          since the beginning of an implementation-defined era
	  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
	  related only to the process invocation.

How do you write portable Lisp code that returns consistent results
based on such shaky foundations?