Re: Redisplay slower in Emacs 28 than Emacs 27

[Lars Ingebrigtsen]

I'm doing some benchmarking here, and my test case is to insert 200
big-ish images in a buffer, and then scrolling through the buffer.

:data image, current sxhash, equal_lists: 6.3s.
:data image, NOOP sxhash, equal_lists: 3.4s.

:file image, current sxhash, equal_lists: 3.4s.
:file image, NOOP sxhash, equal_lists: 3.4s.

:data image, current sxhash, Fequal: 6.4s.
:data image, NOOP sxhash, Fequal: 3.4s.

So -- the Fequal/equal_list doesn't make any difference.  As suspected,
the sxhash is the major opportunity to speed things up in this area.

Now, if we want to retain Fequal-ity (which is what Emacs 27 does), we
can't make sxhash more efficient here.

However, if we continue using equal_lists (which compares list members
with EQ), we can write a new hash function for image.c that just uses
identity/number values of the elements, and we'd get a nice speed-up.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no