Thanks, running the "init_speedup" branch resolved the issue.

Now running (detached-init) with 250 sessions:
  (0.17904190499999997 1 0.02780058099999999)

Niklas Eklund <niklas.eklund@posteo.net> writes:

> Great that you provide these steps and benchmark results. I don't manage
> to reproduce it locally today. But I did notice some slower
> initialization the other day, not sure why I didn't today.

the slowdown happens for the first evaluation of (detached-init), after
that running (detached-init) runs quickly. so to reproduce it you need to
remove (detached-init) from the init file, and running it independently,
and exiting emacs every time. and rerun it again

> I have created a branch named init_speedup. Could you try that one out
> and see if it improves the situation on your end.

Latest changes in handling initialization of sessions are slowing down emacs startup.

to reproduce:
  - running emacs with (detached-init) in init.el
  - running multiple commands with detached.el
  - exiting emacs
  - running emacs again

evaluating "(benchmark-run 1 (detached-init))":
 with 30 sessions  -> (1.160732093 1 0.025991540000000007)
 with 300 sessions -> (10.819843602 30 0.8100858790000001)

running the profiler: