clock(3) man page: precision vs accuracy

clock(3) man page: precision vs accuracy

[Vincent Lefevre]

http://man7.org/linux/man-pages/man3/clock.3.html contains:

       In glibc 2.17 and earlier, clock() was implemented on top of
       times(2).  For improved precision, since glibc 2.18, it is
                      ^^^^^^^^^^^^^^^^^^
       implemented on top of clock_gettime(2) (using the
       CLOCK_PROCESS_CPUTIME_ID clock).

This looks strange. The user doesn't seek improved precision, but
improved accuracy: if one gets more digits but the value itself is
less accurate (i.e. the error against the ideal value is larger),
this is bad. Perhaps changing "precision" to "accuracy" would be
correct (I assume that the real goal of the change was not just
improved precision, but more importantly the resulting improved
accuracy). I've reported a bug about the glibc documentation:

  https://sourceware.org/bugzilla/show_bug.cgi?id=17383

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Re: clock(3) man page: precision vs accuracy

[Michael Kerrisk (man-pages)]

On 09/12/2014 05:08 AM, Vincent Lefevre wrote:
> http://man7.org/linux/man-pages/man3/clock.3.html contains:
> 
>        In glibc 2.17 and earlier, clock() was implemented on top of
>        times(2).  For improved precision, since glibc 2.18, it is
>                       ^^^^^^^^^^^^^^^^^^
>        implemented on top of clock_gettime(2) (using the
>        CLOCK_PROCESS_CPUTIME_ID clock).
> 
> This looks strange. The user doesn't seek improved precision, but
> improved accuracy: if one gets more digits but the value itself is
> less accurate (i.e. the error against the ideal value is larger),
> this is bad. Perhaps changing "precision" to "accuracy" would be
> correct (I assume that the real goal of the change was not just
> improved precision, but more importantly the resulting improved
> accuracy). I've reported a bug about the glibc documentation:
> 
>   https://sourceware.org/bugzilla/show_bug.cgi?id=17383

It looks to me like your supposition is correct, Vincent.
I have changed "precision" to "accuracy".

Cheers,

Michael

-- 
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Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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