bug#18522: 24.4.50; mapcar is very slow

[Eli Zaretskii]

> From: Peter Münster <pmlists@free.fr>
> Cc: rudalics@gmx.at,  larsi@gnus.org,  18522@debbugs.gnu.org
> Date: Mon, 22 Feb 2016 08:37:29 +0100
> 
> On Sun, Feb 21 2016, Eli Zaretskii wrote:
> 
> > How many buffers do you have in the "slow" version? I have 230.
> 
> 12. (Because regularly I kill unused buffers...)

Curiouser and curiouser...

I just tried this in another, larger session (with more than 500
buffers), and got a 10-fold slowdown there.  So this is definitely
correlated to some measure of the session's size, although perhaps
not the number of the buffers.  Plus, it sounds like symbols that can
be buffer-local share this problem.  Can you try several more
buffer-local and not buffer-local symbols, to see if indeed the
conclusion is valid?

> What happens, if you kill 90% of your buffers?

Sorry, I can't: this is my main session where I do everything.  And
chances are killing them won't change the results, judging by your
measurements.

I think the next step is to profile the code below "let".  Can you try
using 'perf' for that purpose?