Re: What makes set-window-buffer slow?

[Eli Zaretskii]

> From: Clément Pit--Claudel <address@hidden>
> Date: Thu, 23 Jun 2016 14:30:02 -0400
> Cc: Andreas Schwab <address@hidden>, Emacs developers <address@hidden>
> 
> > On Thu, Jun 23, 2016 at 01:45:56PM -0400, Clément Pit--Claudel wrote:
> >> Thanks for this suggestion! I probably have to investigate why
> >> redisplay is slow, then; that's bound to be rather tricky :/
> > 
> > Redisplay is NOT slow.  It's written in C and is heavily optimised.
> 
> Thanks for the clarification! Do you know what else might make 
> set-window-buffer slow?
> 
> >> Is there a reason for set-window-buffer to trigger redisplay if the window 
> >> was already displaying that same buffer?
> > 
> > I can't answer your exact question, but should redisplay get triggered
> > in these circumstances, its optimisations would ensure that the reusable
> > part of the display would, in fact, get reused.
> 
> Nifty. Thanks!

Instead of hypothesizing, I suggest to profile your code with
profiler.el.  If indeed redisplay is taking the time, you should see
that in the profile.