bug#18522: 24.4.50; mapcar is very slow

[Eli Zaretskii]

> From: Peter Münster <pmlists@free.fr>
> Date: Thu, 25 Sep 2014 23:36:36 +0200
> Cc: 18522@debbugs.gnu.org
> 
> Please find attached 2 files with profiler-reports when entering a Gnus
> group:
> - profiler-slow.txt: entering a group is slow, and emacs was uptime since
>   about 3 days
> - profiler-fast.txt: entering the same group after a fresh restart of emacs

Is that for the same input?  How come command-execute was called 2464
times in the first profile, and only 303 times in the second?  This
alone can explain an 8-fold slowdown.

Sorry if this is a silly question: I don't use Gnus.  But to compare 2
profiles, you need to create each one of them when Emacs does the same
job in each time.  Otherwise, there's a factor at work that we cannot
glean from the profile alone.

Anyway, looks like gnus-summary-read-group-1 takes a lot of CPU in
both cases, which is above the mapcar part.  Below mapcar, the most
expensive part is parse-time-string, which doesn't really surprise me.