bug#58558: 29.0.50; re-search-forward is slow in some buffers

[Lars Ingebrigtsen]

Ihor Radchenko <yantar92@posteo.net> writes:

> After 11 hours of Emacs uptime and some edits in the buffer (actually,
> just a few hours; mostly idle), running the benchmark-progn
> repetitively:
>
> ;; Elapsed time: 8.339753s
> ;; Elapsed time: 9.243140s
> ;; Elapsed time: 9.868761s
> ;; Elapsed time: 10.330362s
> ;; Elapsed time: 11.279218s
> ;; Elapsed time: 13.581893s
> ;; Elapsed time: 13.675609s
> ;; Elapsed time: 14.553157s
> ;; Elapsed time: 14.651782s
> ;; Elapsed time: 17.253983s
>
> The elapsed time gradually increases. It is definitely a clue, but very
> odd one.

The slowdowns are so dramatic that they should show up on a profiler --
which might give us a clue which parts of Emacs is slowing down.  I
briefly tried to use "perf" under Linux to connect to a running Emacs
and get some data out of it, but...  er...  I've never used it before,
and...

Does anybody have a recipe for how to do runtime function tracing for a
running process?