Re: Gap buffer problem?

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Gerd Möllmann <gerd.moellmann@gmail.com>
>> Cc: Óscar Fuentes <ofv@wanadoo.es>,  Pip Cet
>>  <pipcet@protonmail.com>
>> Date: Wed, 11 Dec 2024 06:27:43 +0100
>> 
>> Pip Cet via "Emacs development discussions." <emacs-devel@gnu.org>
>> writes:
>> 
>> > To be fair, part of that may be the gap buffer problem rather than GC.
>> 
>> Could you please tell more about the gap buffer problem?
>> 
>> I've read a little about the tradeoffs between gap buffers, piece
>> tables, ropes, but I'm wondering if there is something concrete already
>> known for sure that is a performance problem in Emacs. Maybe a bug that
>> has been analyzed or something.
>> 
>> (I'm asking because I just recently encountered a performance problem
>> when adding something to xdisp.c:27339 (with cc-mode, Eglot, Corfu), and
>> editing there was so slow that it was absolutely no fun, and that on a
>> an M1 pro. Haven't investigated the reason.)
>
> Unless you have a huge (and I mean a HUGE) buffer, and some Lisp that
> moves point, then inserts a small number of characters, then moves
> point far away and again inserts a small number of characters, etc.,
> I'd be very surprised if the gap buffer caused significant performance
> problems on a modern CPU.
>
> Can you profile that case and post the expanded profile?  I'm always
> happy to be wrong about performance bottlenecks, and profiles are good
> at proving me wrong.

Maybe I'll try to investigate that further at some point. Such things
always tend to be so time consuming...