Re: Is it just me, or did 21.3.50 get a whole lot slower?

[Richard Stallman]

    First I noticed the nifty new color schemes, and fading modelines.
    However, I also saw that it was WAY WAY slower than 21.2.  'M-x' took
    0.2 seconds to show a prompt; there was a lag on inserting characters;
    RET at the end of a line waiting up to 2 full seconds at time.

Chances are this is due to some rather simple change, and we could
easily fix it if only we knew what.  If it does not happen to most
people, maybe it is due to a change in some package or feature that
you use.  Could you see if it is equally slow if you do `emacs -q'?

Is there any chance you can stop Emacs during those 2 seconds?  If you
can start Emacs under GDB, then during that time if you move the mouse
into the window where GDB is running and type C-c, it might stop
Emacs in time to get a backtrace.  If you do that a few times,
it might show you where the time is being spent.

    What I did notice is lots and lots of screen flicker.  It seems that
    refreshes were happening very often (maybe once every few seconds),
    which is very different from 21.2, where flicker just never happens.

You can set breakpoints in various parts of redisplay, such as
try_window and try_window_id, and set commands on them to continue
automatically.  That way, they will print out in the GDB window but
won't actually stop Emacs.  By comparing the slow version and a faster
version, you might see a difference in pattern which would tell us
something.