bug#45248: 28.0.50; Emacs freezes with big C functions

[Ravine Var <ravine.var@gmail.com>]

Alan Mackenzie <acm@muc.de> writes:
> Let's be clear about the situation: CC Mode does just too much
> processing in refontification for current hardware to be able to scroll
> smoothly through a buffer at normal auto-repeat speeds.  Setting
> fast-but-imprecise-scrolling to non-nil is a handy workaround, but it
> isn't good enough to make the scrolling appear to be smooth when one
> holds down C-v.  I think (and hope) this is what you mean by
> "stuttering".

Yes, that's what I meant. These are my keyboard settings:

$ xset q | grep "repeat rate"
  auto repeat delay:  200    repeat rate:  30

> The bug which I'm hoping to have fixed was that in the large struct in
> Wireshark's function proto_register_rrc, the scrolling got slower and
> slower as one got further into the struct.  On my machine, 80% of the
> way through that struct, scrolling a single screen (62 lines) was taking
> between four and five seconds, which was unacceptably slow.  With the
> bug fix, this scrolling takes about 75 milliseconds, regardless of the
> position in the struct.  This is apart from the first screen drawing in
> the neighbourhood, which takes a little time to fill the new cache
> entry.
>
> Could you please confirm that you see the same uniformity in scrolling
> speed anywhere inside a large struct, and that the speed is acceptably
> close to instantaneous for a single scrolling operation.  Or do you see
> something different?  Thanks!

I still see the behavior that you have described. With the patch,
scrolling becomes slower and slower rapidly and the screen locks up
(using emacs -Q). I tested with a single C file containing just
the function proto_register_rrc().