Re: Accessibility of man pages

[Dirk Gouders <dirk@gouders.net>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Dirk Gouders <dirk@gouders.net>
>> Cc: Colin Watson <cjwatson@debian.org>, Eli Zaretskii <eliz@gnu.org>,
>>         linux-man@vger.kernel.org, help-texinfo@gnu.org,
>>         nabijaczleweli@nabijaczleweli.xyz, g.branden.robinson@gmail.com,
>>         groff@gnu.org
>> Date: Sat, 08 Apr 2023 21:48:13 +0200
>> 
>> $ find /usr/share/man -type f -exec bzgrep -l RLIMIT_NOFILE {} \;
>> /usr/share/man/man1/runuser.1.bz2
>> /usr/share/man/man1/su.1.bz2
>> /usr/share/man/man1/nghttpx.1.bz2
>> /usr/share/man/man3/getdtablesize.3.bz2
>> /usr/share/man/man3/mq_open.3.bz2
>> /usr/share/man/man3/errno.3.bz2
>> /usr/share/man/man3/sysconf.3.bz2
>> /usr/share/man/man3p/getrlimit.3p.bz2
>> /usr/share/man/man3p/sysconf.3p.bz2
>> /usr/share/man/man3p/posix_spawn_file_actions_addclose.3p.bz2
>> /usr/share/man/man0p/sys_resource.h.0p.bz2
>> /usr/share/man/man2/pidfd_open.2.bz2
>> /usr/share/man/man2/poll.2.bz2
>> /usr/share/man/man2/getrlimit.2.bz2
>> /usr/share/man/man2/open.2.bz2
>> /usr/share/man/man2/select.2.bz2
>> /usr/share/man/man2/fcntl.2.bz2
>> /usr/share/man/man2/seccomp_unotify.2.bz2
>> /usr/share/man/man2/dup.2.bz2
>> /usr/share/man/man2/pidfd_getfd.2.bz2
>> /usr/share/man/man7/fanotify.7.bz2
>> /usr/share/man/man7/capabilities.7.bz2
>> /usr/share/man/man7/unix.7.bz2
>> /usr/share/man/man5/proc.5.bz2
>> 
>> Yes, it's very slow but close to `man -K`:
>> 
>> find...             man -K...
>> 
>> real 107.45         real 96.34
>> user 117.06         user 70.11
>> sys 14.43           sys 26.86
>> 
>> [a thought later]
>> 
>> Oh, I found something much faster:
>> 
>> $ time -p find /usr/share/man -type f | xargs bzgrep -l RLIMIT_NOFILE
>> [snip]
>> 
>> real 24.30
>> user 32.34
>> sys 6.84
>> 
>> Hmm, perhaps, someone has an explanation for this?
>
> Multiprocessing, obviously.  Your CPU has more than one execution
> unit, so the pipe via xargs runs 'find' and 'bzgrep' in parallel on
> two different execution units.  By contrast, "find -exec" runs them
> sequentially, in a single thread.

Yes, that must be it, thanks.  I noticed `man -K...` uses up to four
CPUs in parallel and therefore was unsure.

With your explanation, we can get even faster:

$ time -p find /usr/share/man -type f | xargs -P 6 bzgrep -l RLIMIT_NOFILE
[snip]

real 7.56
user 32.97
sys 7.02

Dirk

PS: Colin, too late, I noticed a Mail-Followup-To Header in your mail.
    For the future: Is it correct that in such a case one should use
    that recipient list (without your address) -- even if he replies to
    something you wrote?  In that case: I'm sorry I did that wrong.