Subject: bug#18522: 24.4.50; mapcar is very slow

From: Eli Zaretskii <[email-masked]>
Date: Sun, 21 Feb 2016 22:45:34 +0200

> From: Peter Münster <[email-masked]>
> Cc: [email-masked],  [email-masked],  [email-masked]
> Date: Sun, 21 Feb 2016 19:03:49 +0100
> 
> On Sun, Feb 21 2016, Eli Zaretskii wrote:
> 
> > Does this happen only with this particular symbol, or binding any
> > symbol slows down?
> 
> It depends on the symbol:
> 
> case-fold-search:     slow
> fill-column:          slow
> just-a-symbol:        fast
> custom-file:          fast
> 
> Can you reproduce it?

I see a 5-fold slow-down with case-fold-search, not a 30-fold as you
reported.

It sounds like the difference is between buffer-local variables and
global variables.  Setting the former will potentially loop over all
the buffers and set the value for every buffer that doesn't have a
local value.  See data.c around line 1517.  How many buffers do you
have in the "slow" version?  I have 230.